Synthesis of novel liquid crystalline and fire retardant molecules based on six-armed cyclotriphosphazene core containing Schiff base and amide linking units

RSC Advances

View Article Online

View Journal | View Issue

PAPER

Synthesis of novel liquid crystalline and ﬁre

retardant molecules based on six-armed

cyclotriphosphazene core containing Schiﬀ base

and amide linking units†

Cite this: RSC Adv., 2020, 10, 28918

Zuhair Jamain, *^a^bMelati Khairuddean* and Tay Guan-Seng^c

b

Nucleophilic substitution reaction between 4-hydroxybenzaldehyde and hexachlorocyclotriphosphazene,

HCCP formed hexakis(4-formlyphenoxy)cyclotriphosphazene, 1. Intermediates 2a–e was formed from the

alkylation reaction of methyl 4-hydroxybenzoate with alkyl bromide which further reduced to form benzoic

acid intermediates. Further reaction of 2a–e and other substituted benzoic acid formed 3a–h, which then

reduced to give subsequent amines, 4a–h. Other similar reaction was used to synthesis 4i. Condensation

reaction between 1 and 4a–i yielded hexasubstituted cyclotriphosphazene compounds, 5a–i having

Schiﬀ base and amide linking units, and these compounds consist of diﬀerent terminal substituents such

as heptyl, nonyl, decyl, dodecyl, tetradecyl, hydroxy, carboxy, chloro, and nitro groups, respectively.

Compound 5j with amino substituent at terminal end was formed from the reduction of 5i. All the

intermediates and compounds were characterized using Fourier Transform Infrared (FT-IR), Nuclear

Magnetic Resonance (NMR) and CHN elemental analysis. Mesophase texture of these compounds were

determined using Polarized Optical Microscope (POM) and their mesophase transition were further

conﬁrmed using Diﬀerential Scanning Calorimetry (DSC). Only compounds 5a–e with alkoxy chains

exhibited smectic A phase while other intermediates (1, 2a–e, 3a–h, and 4a–i) and ﬁnal compounds (5f–

j) are found to be non-mesogenic with no liquid crystal behaviour. The conﬁrmation of the identity of

the SmA phase was determined using XRD analysis. The study on the structure–properties relationship

was conducted in order to determine the eﬀect of the terminal group, length of the chains and linking

units to the mesophase behaviour of the compounds. Moreover, the ﬁre retardant properties of these

compounds were determined using Limiting Oxygen Index (LOI) testing. Polyester resin with LOI value of

2.53% was used as matrix for moulding in the study. The LOI value increased to 24.71% when this

polyester resin incorporated with 1 wt% of HCCP. Generally, all the ﬁnal compounds showed a positive

results with LOI value above 27% and the highest LOI value was belonged to compound 5i with 28.53%.

The high thermal stability of the Schiﬀ base molecules and the electron withdrawing group of the amide

bonds and nitro group enhanced the ﬁre retardant properties of this compound.

2

Received 28th April 2020

Accepted 23rd July 2020

DOI: 10.1039/d0ra03812a

rsc.li/rsc-advances

nitrogen atoms, whereby six chlorine atoms can be substituted

with any selected nucleophiles. Due to the high reactivity of the

1

. Introduction

In the early years, Allcock and his co-workers started the P–Cl bond, the corresponding substitution method allows the

research work on phosphazene compounds which was then structure–activity studies in the side arm and their multiarmed

3

developed into the investigation of phosphazene liquid crys- rigid ring allows the exploration of the discotic structures. It

1,2

talline materials.

Hexachlorocyclotriphosphazene, HCCP was reported that compounds with the cyclotriphosphazene

N P Cl ) is a ring consisting of alternating phosphorus and core (N ) attached to diﬀerent substrates exhibited diﬀerent

(

3 3

P

3

6

4

physical and chemical properties. They have been used in

many elds such as liquid crystal and re retardant applications

due to their fascinating properties.

a

Faculty of Science and Natural Resources, Universiti Malaysia Sabah (UMS), 88400

Kota Kinabalu, Sabah, Malaysia. E-mail: zuhairjamain@ums.edu.my

5,6

b

Liquid crystal (LC) is an anisotropic material with owing

School of Chemical Sciences, Universiti Sains Malaysia (USM), 11800 Penang,

properties (liquid) as well as ordered (solid) and optical prop-

School of Industrial Technology, Universiti Sains Malaysia (USM), 11800 Penang, erties. Since it has the features of both uid and solid, it

Malaysia. E-mail: melati@usm.my

c

7

Malaysia

Electronic supplementary information (ESI) available: Fig. 1–5: DSC

thermogram of compounds 5a–e, respectively. See DOI: 10.1039/d0ra03812a

became an important intermediate phase or mesomorphic

phase. LC of organic compounds is divided into two categories

†

8

28918 | RSC Adv., 2020, 10, 28918–28934

This journal is © The Royal Society of Chemistry 2020

View Article Online

Paper

RSC Advances

which are lyotropic and thermotropic LC. Thermotropic LC are resulted in the molecules that favoured a lamellar arrangement

17

inuenced by the change in temperature while lyotropic LC in the smectic layer. The correlation between the molecular

which are composed mainly of the amphiphilic bilayer are structure such as core system, linking units and terminal

9,10

concentration and temperature dependant.

The inuence of diﬀerent elements and the extended

groups are the most important aspect in liquid crystal eld.

Jim ´e nez et al. (2011) reported the synthesis of hexasub-

chemical subunits on the molecules allows the construction of stituted cyclotriphosphazene derivatives attached to the side

the targeted liquid crystal compounds. The molecular shape arms with an ester linking unit but diﬀerent terminal chains.

and the terminal chain length are the key variables in designing The formation of the mesophase depended on the balance

new liquid crystal compounds with specic types of molecular between the rigid core and the exible terminal chains while the

11–13

organization in a particular range of temperature.

Linking type and stability of the mesophase were determined by the

units are normally structural units that connect one core to space lling and nanosegregation. The combination of these

another, which maintain the linearity of the core while being factors along with tailoring of the interface curvature by the

compatible with the rest of the structure. A linking unit between space requirements of the incompatible molecular blocks will

ring systems is to increase the length of the molecules and to determines the diﬀerence mesophase morphologies of these

14

18

alter the polarisability and exibility of the molecules. Schiﬀ cyclotriphosphazene molecules. Moreover, He et al. (2013)

base is one the interesting linking unit that provide a stepped have synthesized the room temperature columnar mesogens of

core structure which can maintain the linearity of the molecules hexasubstituted cyclotriphosphazenes compounds with Schiﬀ

to provide high stability. This enables the mesophase formation base and ether linking units. They found out that increasing the

whereby the phase transition temperature and the physical chain length increased the melting point and decreased the

1

9

properties changes are usually contributed by the linking clearing point.

group. On the other hand, the formation of an amide linking

15

On the other side, HCCP also known to be used as a molecule

unit led to higher rigidity due to the presence of the partial to have high re retardancy. Fire retardant materials play an

double bond character of the C–N bond which resulted in important role in protecting property from damage. Fire retar-

16

higher transition and clearing temperatures of the mesogens.

dation occurred due to the removal of heat from the materials

The partial double bond in C–N bond reduces the coplanarity of that can burn and the formation of char during the re which

20

the molecule and the broadening of the rigid core, which will interrupt the contact from combustion. Generally,

Scheme 1 Formation of intermediates (1, 2a–e, 3a–h, and 4a–i) and hexasubstituted cyclotriphosphazene compounds, 5a–i.

This journal is © The Royal Society of Chemistry 2020

RSC Adv., 2020, 10, 28918–28934 | 28919

View Article Online

RSC Advances

Paper



ndings showed that the modication of cyclotriphosphazene

core system able to induce the thermal stability, which

24,25

enhances the re resistance of the compounds.

Therefore, the interest of the research is to gain a better

insight of the structure–properties relationship of these types of

compounds. Addition of HCCP into a compound is to increase

the resistance of the material towards ignition. Both liquid

crystal and re retardant properties were studied. Thus, this

research focused on the preparation of a series of hexasub-

stituted cyclotriphosphazene derivatives with Schiﬀ base and

amide linking units that bore a diﬀerent terminal end. In this

work, polyester resin will be used as a medium for moulding in

order to study the re retardant of the compounds. Only 1 wt%

is added in this resin in order to achieve highest re retardancy

with less additive usage. Polyester resin is chosen due to good

mechanical properties, fast curing, low cost and more sensitive

to elevated temperatures.

Scheme 2 Reduction of compound 5i to 5j.

materials with limiting oxygen index (LOI) value above 26% are

2

. Results and discussion

considered re retardant and self-extinguishing behaviour can

21,22

be observed.

Zhang et al. (2012) have synthesized and In this work, HCCP has been used as a core system to prepare

studied the re retardant properties of hexakis(4-nitrophenoxy) hexasubstituted cyclotriphosphazene compounds consist of

cyclotriphosphazene on poly(ethylene terephthalate). The LOI Schiﬀ base and amide linking units. Intermediate 1 was

value of poly(ethylene terephthalate) increased from 26.8% to synthesized from the reaction of HCCP with 4-hydrox-

23

3

5.1% when 10 wt% of this compound was added. Moreover, ybenzaldehyde. Methyl 4-hydroxybenzoate with diﬀerent alkyl

Rong et al. have conducted two independent studies on the bromide (heptyl, nonyl, decyl, dodecyl, and tetradecyl) were

cyclotriphosphazene core system in 2015 and 2017. Their used to form methyl 4-(alkoxy)benzoates. Without isolation,

Fig. 1 FTIR spectra overlay of compounds 5a–j.

28920 | RSC Adv., 2020, 10, 28918–28934

This journal is © The Royal Society of Chemistry 2020

View Article Online

Paper

RSC Advances

H stretching) in the IR spectra of the latter. Intermediate 4i

which was synthesized using other method also showed similar

ꢀ1

bands at 3207 and 3408 cm (N–H stretching). Other bands at

ꢀ

1

690 (C]O), 1590 (C]C), 1250 (C–O), and 1175 cm (C–N)

stretching were observed in both intermediates 3a–h and 4a–i.

ꢀ1

The diagnostic bands at 3200 and 825 cm were attributable to

the O–H stretching and C–Cl bending, respectively in 3f–g and

Fig. 2 Structure of compound 5c with complete atomic numbering.

4f–g.

The overlay IR spectra of compounds 5a–j with Schiﬀ base

and amide linking units are shown in Fig. 1. The reaction

between hexasubstituted cyclotriphosphazene benzaldehyde, 1

and intermediates 4a–i gave 5a–i. The appearance of the ex-

these methyl 4-(alkoxy)benzoates were further reduced to form

subsequent benzoic acid intermediates, 2a–e. Intermediates 3a–

h with amide linking unit were aﬀorded from the reaction of 2a–

e and some para substituted benzoic acid such as hydroxy,

carboxy, and chloro, respectively. These intermediates were

then reduced to form 4a–h. Intermediate 4i was prepared using

diﬀerent synthetic route. Finally, condensation reaction of 1

with 4a–i yielded nal compounds 5a–i with Schiﬀ base and

amide linking units. Further reduction of 5i formed compound

ꢀ

1

pected absorption band at 1644 cm

for C]N stretching

conrmed the successful condensation reaction of intermedi-

ates 4a–i. Further reduction of compound 5i produced

compound 5j with the appearance of two-spike at 3207 and

ꢀ

1

3416 cm

(N–H stretching). Besides, all the compounds

showed the absorption band for the N–H stretching of the

ꢀ

1

amide linkage at 3365 cm

.

5j with amino group at the terminal end. The structures of these

On the other hand, compounds 5f and 5g showed the over-

lapping of the absorption bands for hydroxy (–OH) and N–H

stretching of the amide groups because peak broadening of the

O–H stretching. Other absorptions bands were observed at

intermediates and nal compounds were conrmed using

FTIR, NMR and CHN elemental analysis. The overall synthesis

pathway for intermediates and hexasubstituted cyclo-

triphosphazene compounds for this series are described in

Schemes 1 and 2.

ꢀ

1

691 cm for the carbonyl (C]O) stretching, and also at 1592,

ꢀ

1

1254, and 1178 cm

for C]C, C–O, and C–N stretching,

respectively. As usual, the diagnostic bands at 2851 and

2.1. FTIR spectral data discussion

ꢀ1

3

2919 cm which corresponding to the Csp –H symmetrical and

Intermediate 1 was successfully synthesized with the disap-

asymmetrical stretching of alkoxy chains can be observed in

ꢀ

1

ꢀ

1

pearance absorption band at 3250 cm for O–H stretching. The

other absorption bands were observed at 2730 ðH ꢀ C ꢁOÞ(H–

compounds 5a–e. In addition, the bending at 819 cm was

assigned to the C–Cl bending in compound 5h. The absorption

bands from the cyclotriphosphazene ring, P]N stretching

ꢀ

1

C]O), 1700 (C]O), 1595 (C]C), and 1205 cm (C–O). The IR

ꢀ1

data of intermediates 2a–e showed the absorption bands at

appeared at 1197 cm , while P–O–C bending was located at

77 cm.

3

(

250 (O–H stretching), 2852 and 2921 (Csp –H stretching), 1680

9

ꢀ

1

C]O stretching), 1605 (C]C stretching), and 1250 cm (C–O

stretching). Intermediates 3a–h were successfully synthesized

as evident from the appearance of a new band at 3300 cm (N–

ꢀ

1

2.2. NMR spectral data discussion

1

H stretching) of the amide linkage. Further reduction of inter- The absent of the hydroxyl signal in the H-NMR spectrum of

mediates 3a–h gave rise to intermediates 4a–h with the intermediate 1 conrmed the nucleophilic substitution of the 4-

ꢀ

1

appearance of two absorption bands at 3200 and 3400 cm (N– hydroxybenzaldehyde. The singlet at d 9.90 ppm was assigned to

1

Fig. 3 H NMR spectrum of compound 5c.

This journal is © The Royal Society of Chemistry 2020

RSC Adv., 2020, 10, 28918–28934 | 28921

View Article Online

RSC Advances

Paper

the aldehydic proton and two doublets at d 7.78 and 7.16 ppm NMR data of 2a–e showed the carbon signals for aromatic

were assigned for two diﬀerent aromatic protons in the ring and aliphatic chains. The signal for the aliphatic carbons

1

3

compound. The C-NMR data of 1 showed the signal for alde- displayed similar pattern but only diﬀered in the intensity,

hydic carbon at d 191.69 ppm and four aromatic signals at which due to the diﬀerent length in the carbon chains. The

3

1

d 153.59, 133.55, 131.46, and 121.03 ppm. The P NMR showed carboxy carbon for 2a–e showed a signal at the most downeld

a singlet at d 7.60 ppm, indicated that all the benzaldehyde was region at d 168.78, 169.36, 168.78, 167.95, and 169.18 ppm,

successfully attached to the phosphorus atom in the cyclo- respectively. No signal for the methyl observed in both spectra

triphosphazene ring.

indicating that the reduction reaction was a success.

1

The H-NMR data of 2a–e revealed similar pattern with two

Meanwhile, the H-NMR data of intermediates 3a–h showed

doublets assigned for two aromatic protons, while all the peaks a similar pattern with a singlet corresponded to the amide

in the upeld region were assigned to the aliphatic protons of proton (N–H) in the most downeld region at d 10.61, 10.22,

1

3

heptyl, nonyl, decyl, dodecyl, and tetradecyl chains. The C- 10.33, 10.25, 10.25, 9.72, 11.06, and 9.90 ppm, respectively. Both

13

Fig. 4 (a) C NMR, (b) DEPT 90 and (c) DEPT 135 spectra of compound 5c.

28922 | RSC Adv., 2020, 10, 28918–28934

This journal is © The Royal Society of Chemistry 2020

View Article Online

Paper

RSC Advances

1

13

the H and C-NMR data showed the presence of four doublets quaternary, six aromatics, one oxymethylene, seven methylene,

of protons and eight carbons signal for the aromatic ring. The and one methyl carbons. DEPT 90 (Fig. 4b) and DEPT 135

reduction of intermediates 3a–h to 4a–h showed the appearance (Fig. 4c) experiments were conducted to distinguish the types of

1

of N–H signals of the amine group at d 5.00 ppm in the H-NMR carbons. In the DEPT 90 spectrum, the azomethine carbon, C5

spectra. For nal compound, 5c was used to represent the was observed at d 158.09 ppm while the aromatic carbons

structure conrmation in the series. The structure of compound resonated at d 130.47 (C3), 129.94 (C13), 129.28 (C8), 121.75

5

c with complete atomic numbering is illustrated in Fig. 2.

In the H NMR spectrum of compound 5c (Fig. 3), two

(C7), 121.69 (C14), and 114.81 ppm (C2).

1

13

For others homologues, the H and C NMR spectra of

singlets in the downeld region at d 9.82 (H5) and d 8.65 ppm compounds 5a, 5b, 5d, and 5e appeared a similar splitting

H10) were assigned to the amide and azomethine protons, patterns and chemical shis as shown in compound 5c but only

(

respectively. Five distinguishable doublets located within diﬀered in term of the number of protons and carbons in the

d 7.02–7.96 ppm were assigned to the aromatic protons. One of alkyl chains. Compounds 5f–j attached with small substituents

these signals with integrating to four protons were overlapped such as hydroxy, carboxy, chloro, nitro, and amino at the

and appeared as a triplet (H3 and H13).

However, the eﬀect of the amide group as an electron with- for aromatic protons in the H NMR spectra.

drawing group which caused the electron density of the mole-

terminal end showed a singlet of amide signal and six doublets

1

13

Both H and C NMR spectra of these compounds showed

cule to decrease, forced H8 to experience more deshielding a slight diﬀerence in the chemical shi values, which due to the

eﬀect compared to H7 and H14, which was more deshielded chemical environment, electronegativity eﬀect, and bond

than H2. An oxymethylene proton, H16 appeared as a triplet at angles. Meanwhile, compounds 5f and 5g displayed an addi-

1

d 4.08 ppm and all the methylene protons (H17–H24) were tional signal for hydroxyl and carboxyl proton peaks in the H

assigned in the region of d 1.27–1.78 ppm. A triplet in the most NMR spectra. Moreover, all the compounds in this series

3

1

upeld region was assigned to H25 at d 0.88 ppm.

showed a singlet in the P NMR spectrum due to hexa-

1

3

The C NMR spectrum of compound 5c (Fig. 4a) showed 23 substituted in the arms (Fig. 5).

carbon signals comprising of one azomethine, seven

31

Fig. 5

P NMR spectrum of compound 5c.

This journal is © The Royal Society of Chemistry 2020

RSC Adv., 2020, 10, 28918–28934 | 28923

View Article Online

RSC Advances

.3. Determination of liquid crystal behaviour using POM

Paper

2

found to be mesogenic. These compounds showed Smectic A

(

SmA) phase of focal-conic fans in both heating and cooling

The POM optical photomicrograph was obtained using the

Olympus system model bx53 linksys32. In this study, only

compounds 5a–e with Schiﬀ base and amide linking unit

attached to diﬀerent chain length at the terminal end were

cycles (Fig. 6). However, other intermediates and compounds

did not show any liquid crystal texture, therefore these

compounds are known as non-mesogenic. Observation under

POM for compounds 5f–j only showed the phase transition of

ꢂ

Fig. 6 The optical photomicrographs of compounds 5a–e in the cooling cycle showing the SmA phase, (a) 270.55 C for compound 5a, (b)

ꢂ

2

68.77 C for compound 5b, (c) 268.50 C for compound 5c, (d) 255.43 C for compound 5d, and (e) 247.78 C for compound 5e (magniﬁcation

scale: 20 ꢃ 0.25).

28924 | RSC Adv., 2020, 10, 28918–28934

This journal is © The Royal Society of Chemistry 2020

View Article Online

Paper

RSC Advances

ꢀ

1

Table 1 Phase transitional properties of compounds 5a–e upon thermogram. The thermal enthalpy, DH (kJ mol ) of each

a

heating and cooling cycles

phase transition of compounds 5a–e are summarized in Table 1.

The DSC thermograms of compounds 5a–e showed two

curves for the transition of crystal to SmA and to isotropic phase

in both cycles. All compounds showed high melting and

clearing temperature in the heating cycle. From the DSC data,

ꢂ

Transition temperature ( C), enthalpy, DH (kJ

mol )

ꢀ1

Compound Mode

5

a

b

c

Heating Cr 188.02, 186.54 SmA 286.83, 48.13

Cooling

280.47, ꢀ58.43 SmA 170.05, ꢀ212.30 Cr

Heating Cr 177.09, 173.10 SmA 287.87, 68.64

Cooling

282.57, ꢀ73.98 SmA 161.53, ꢀ207.61 Cr

Heating Cr 174.44, 156.52 SmA 286.15, 70.96

Cooling

Heating Cr 171.44, 191.73 SmA 281.61, 83.37

Cooling

275.76, ꢀ88.98 SmA 155.73, ꢀ211.63 Cr

Heating Cr 168.58, 125.75 SmA 276.25, 76.22

Cooling

267.13, ꢀ76.78 SmA 149.00, ꢀ182.89 Cr

I

the melting temperature was observed at 188.02, 177.09, 174.44,

I

ꢂ

1

71.44, and 168.58 C, which corresponded to compounds 5a–e,

I

respectively. The DSC thermogram of compound 5c was illus-

I

278.75, ꢀ77.83 SmA 158.16, ꢀ204.07 Cr trated in Fig. 7. The melting and clearing temperature of the

d

e

I

compounds showed similar pattern whereby the temperature

decreased as the number of alkyl chains increased. As reported

by Moriya et al. (2006), the melting and clearing temperature

I

26

decreased with an increased number of alkyl chains. More-

over, all the compounds have high enthalpy changes at the

clearing temperature. This behaviour was related to the high

molecular weight of hexasubstituted cyclotriphosphazene

a

Cr ¼ crystal, SmA ¼ smectic A, I ¼ isotropic.

crystal to isotropic in the heating cycle. Similar phase transi-

tions were also observed in the reversed order of the cooling

cycle.

Table 2 The XRD data of compounds 5c

XRD data analysis

Value

2.4. Determination of thermal transitions using POM

The DSC experiment was conducted to conrm the phase 2 theta

1.93

45.74

41.23

1.11

d-Layer spacing

transition observed under POM. Only compounds with liquid

crystal were further sent for DSC measurement. The transition

temperatures and enthalpy change involved during the transi-

tion in the heating and cooling cycles were recorded in the DSC

Molecular length (L)

Calculated d/L

Arrangement of SmA

Monolayer

Fig. 7 DSC thermogram of compound 5c.

This journal is © The Royal Society of Chemistry 2020

RSC Adv., 2020, 10, 28918–28934 | 28925

View Article Online

RSC Advances

Paper

The main criteria for a molecule to adopt liquid crystal

behaviour include the molecular shape which should be rela-

tively thin or at within rigid molecular frameworks, which

31

usually based on benzene rings. In general, terminal group

which extends the molecular long axis without increasing the

molecular width increase the thermal stability of the meso-

phase. The nature of the terminal substituents or end groups in

the molecule of the mesogen has profound inuence on the

liquid crystal properties of the compound. There are varieties of

terminal groups being employed in the liquid crystal molecules

and the common groups vary from a small polar substituent

32

(

e.g. chloro or nitro) to a long chain (e.g. alkyl or alkoxy). The

choice of a terminal group is very important to generate the

expected liquid crystal mesophase in a molecule.

Fig. 8 XRD diﬀractogram of compound 5c.

Most of the molecules consist of one terminal alkyl chain

showed liquid crystal behaviour. This was proven when all the



nal compounds (5a–e) with the alkoxy chains at the terminal

compounds, which eﬀected by their p-energy, hydrogen- end exhibited the smectic A phase in both cooling and heating

27

bonding and van der Waals forces.

cycles. The length of the alkoxy side chain showed strong

inuence on the mesophase formation. Longer alkoxy chains

33

induced the liquid crystal behaviour with broader temperature

2

.5. Determination of liquid crystal using XRD analysis

34

ranges as well as decreased melting temperatures, T

m

.

In

The conrmation of the SmA phase observed in these series

were carried out using XRD analysis. The XRD data of

compounds 5c is summarized in Table 2. Compound 5c was

used as representative for further discussion. The XRD dif-

fractogram of compound 5c is shown in Fig. 8. The XRD dif-

fractogram of compound 5c showed a single sharp peak at 2q ¼

addition, the number of alkoxy side chains greatly aﬀect

35

molecular self-assembly. Besides, the long alkyl chains add



exibility to the rigid core and stabilize the molecular interac-

34

tions needed for the formation of liquid crystal mesophase.

Conjugation within the Schiﬀ base moiety led to possible of

controlling the alignment and orientation of their molecules to

ꢂ

1

.19 and a broad peak with wide angle at 2q ¼ 15–21 , indi-

36

generate liquid crystal properties. Schiﬀ base linking unit

cating that the molecules favour the smectic layered arrange-

provide a stepped core structure which can maintain the

28

ment. Generally, compound exhibited the lamellar structure

for smectic liquid crystalline phase showed the sharp and

strong peak at low angle (1 < 2q < 4 ), and a broad peak asso-

ciated with lateral packing at 2q z 20 in the XRD curve. The

sharp peak indicated the regular arrangement in spaced layer,

while a broad peak for the disordered packing of alkyl chains.

According to the XRD data, the d-layer spacing and molecular

length (L) obtained from the molecular calculation of

compound 5c was found to be 45.74 A and 41.23 A, respectively.

The calculated d/L was 1.11 (d z L), which approximately to 1.

This phenomenon showing that the SmA phase observed under

POM is monolayer arrangement. This suggested that the side

arms which connected to the phosphorus atoms of the cyclo-

triphosphazene ring were arranged three up and three down.

The behaviour of homeotropic alignment caused these side

arms aligns perpendicular to the cyclotriphosphazene ring as

32

molecular linearity. This linearity provides high stability and

enabling mesophase formation. However, all compounds (5f–j)

with small substituent such as hydroxy, carboxy, chloro, nitro,

and amino groups at the terminal end were found to be non-

mesogenic. Kelker and Hatz reported the behaviour of the

small substituent at the terminal end do not always form liquid

ꢂ

29

30

33,35

crystal phases.

The lone pair of electrons or p bonds in

compounds 5f and 5g tend to resonate onto the aromatic ring

ꢀ

which resulted in the cancellation of dipole moments of the

36,37

molecules.

As a result, the formation of the mesophase in

the molecules cannot be induced.

Even though compound 5h and 5i attached with polar

substituent, which possesses strong dipole moment, the pres-

ence of the amide linking unit resulted in high melting

16

temperature and the mesophase cannot be observed.

Compound 5j did not exhibited any liquid crystal character due

to the properties of the NH as an electron donating group,

30

this shape is suitable for the smectic arrangement. The

proposed molecular shape and the possible smectic arrange-

ment of compound 5c are shown in Fig. 9.

2

which maximise the repulsive interactions between adjacent

aromatic rings and caused the tendency for formation of the

38

mesophase was reduced. The POM observation of compounds

2.6. Structure–properties relationship

5a–j are summarized in Table 3.

The skeleton structures of a molecule inuence the liquid

crystal properties. A compound must possess certain require-

ment in order to exhibit liquid crystal mesophase. The physical

properties of even the simplest liquid crystal compound are

2

.7. Determination of re retardant properties using LOI

testing

truly remarkable due to the self-assembly of molecules in an In this research, polyester resin has been used as a matrix for

ordered, yet uid, and liquid crystal mesophase.

moulding. Polyester resins are unsaturated synthetic resin and

28926 | RSC Adv., 2020, 10, 28918–28934

This journal is © The Royal Society of Chemistry 2020

View Article Online

Paper

RSC Advances

Fig. 9 (a) The proposed molecular shape and (b) the possible smectic arrangement of compound 5c.

Table 3 POM observation of compounds 5a–j

Compound Terminal substituent

can be considered as a combustible material. This resin

produces a lot of heat during combustion due to low thermal

stability and becomes a potential to re risk. Thus, the modi-

POM observation



cation of polyester resin by mixing with hexasubstituted

5

a

b

c

d

e

f

g

h

i

Heptyloxy

Nonyloxy

Decyloxy

Dodecyloxy

Tetradecyl

Hydroxy

Carboxy

Chloro

(–OC

(–OC10

(–OC12

(–OC14

(–OH)

(–COOH)

(–Cl)

(–NO

7

H

15

)

Smectic A

cyclotriphosphazene compounds having re retardant proper-

ties are needed to overcome this problem.

9

19

21

25

29

)

The sample was prepared by mixing 1 wt% of the nal

compound with polyester resin. About 1 wt% of methyl ethyl

ketone peroxide (MEKP) curing agent was added to the mixture

and stirred until the sample is homogeneous and then poured

into the moulds. The samples were cured for 5 hours in an oven

Smectic A

Non-mesogenic

Nitro

Amino

2

)

j

(–NH

2

)

ꢂ

at 60 C and le overnight at room temperature before it was

burned using LOI testing. The LOI test was performed using an

This journal is © The Royal Society of Chemistry 2020

RSC Adv., 2020, 10, 28918–28934 | 28927

View Article Online

RSC Advances

Paper

Table 4 LOI test results

3

1

.2. Syntheses

Synthesis of hexakis(4-formlyphenoxy)cyclotriphosphazene,

. Intermediate 1 was synthesized according to the method re-

Material

LOI value (%)

Pure polyester resin

Polyester resin + 1 wt% of HCCP

Compound 5a

Compound 5b

Compound 5c

Compound 5d

Compound 5e

Compound 5f

Compound 5g

22.53 (ꢄ0.00)

24.71 (ꢄ0.00)

27.90 (ꢄ0.00)

27.71 (ꢄ0.00)

24

ported by Rong et al. (2015) with some modications. 4-

Hydroxybenzaldehyde (9.77 g, 0.08 mol) and triethylamine

(10.12 g, 0.1 mol) were dissolved in 150 mL acetone and the

ꢂ

mixture was cooled to 0 C in an ice bath. The mixture was

27.55 (ꢄ0.00) stirred for 30 minutes. Then,

a

solution of hexa-

27.53 (ꢄ0.00)

28.37 (ꢄ0.00)

27.93 (ꢄ0.04)

28.42 (ꢄ0.00)

28.53 (ꢄ0.00)

chlorocyclotriphosphazene (3.48 g, 0.01 mol) in 50 mL acetone

was added dropwise to the mixture. A white salt began to

ꢂ

precipitate within few minutes. Aer 2 hours at 0 C, the reac-

tion was allowed to attain at room temperature and was

Compound 5h

Compound 5i

Compound 5j

27.90 (ꢄ0.00) continued to stir for an additional 94 hours. The reaction was

monitored using TLC. Upon completion, the mixture was

poured into 250 mL of cold water and le overnight in the

FTT oxygen index, according to BS 2782: Part 1: Method 141 and fridge. The precipitate formed was then ltered, washed with

ISO 4589 with the dimension of 120 mm ꢃ 10 mm ꢃ 4 mm.

water and dried. The precipitate was recrystallised from meth-

ꢂ

According to LOI data in Table 4, pure polyester resin has the anol. Yield: 8.11 g (94.19%), mp: 200.8–204.2 C, white powder.

ꢀ

1

LOI value of 22.53%. The LOI value of polyester resin was FTIR (cm ): 2730 ðH ꢀ C ꢁOÞ; 1699 (C]O stretching), 1595

increased to 24.71% when incorporated with 1 wt% of HCCP. (C]C stretching), 1205 (C–O stretching), 1151 (P]N stretch-

1

Schiﬀ base linking units was found to enhance the properties of ing), 944 (P–O–C stretching). H-NMR (500 MHz, DMSO-d

6

)



re-retardant. This phenomenon was attributed to the high d, ppm: 9.90 (s, 1H), 7.78 (d, J ¼ 10.0 Hz, 2H), 7.16 (d, J ¼

13

thermal stability of the Schiﬀ base molecules, which promoted 10.0 Hz, 2H). C-NMR (125 MHz, DMSO-d

6

) d, ppm: 191.69,

153.59, 133.55, 131.46, 121.03. P-NMR (500 MHz, DMSO-d

Interestingly, when Schiﬀ base unit was combined with an d, ppm: 7.60 (s, 1P). CHN elemental analysis: calculated for

amide unit, the LOI values showed a slight increase. This

: C: 58.55%, H: 3.51%, N: 4.88%; found: C:

positive result was attributed to the properties of the electron 58.28%, H: 3.48%, N: 4.83%.

withdrawing group of the amide bond which enhanced the

Synthesis of 4-(alkoxy)benzoic acid, 2a–e

4-(Heptyloxy)benzoic acid, 2a. Intermediate 2a was synthe-

the compounds have high LOI value, indicating these sized according to the method reported by Chun-Chieh et al.

3

1

39

the formation of char on the surface in the condensed phase.

)

6

C H N O P

42 30 3 12 3

40,41



ammability properties of the compounds.

As a result, all

43

compounds have high thermal stability and re retardancy. (2016) with some modications. Methyl-4-hydroxybenzoate

Compound 5i showed the highest LOI value compared to other (15.20 g, 0.10 mol) and 1-bromoheptane (17.89 g, 0.10 mol)

compounds due to the eﬀect of electron withdrawing of nitro dissolved in 20 mL DMF separately, were mixed in a 100 mL

42

group which enhance the synergistic eﬀect of P–N bonds. This round bottom ask. Potassium carbonate (20.73 g, 0.15 mol)

behaviour caused the compounds exhibited both condensed and potassium iodide (1.66 g, 0.01 mol) were added to the

and gas phase action and thus, prevents the sample from mixture and was reuxed for 12 hours. Upon completion, the

further burning. Hence, these compounds possessed highest mixture was poured into 300 mL cold water and the precipitate

LOI value.

formed was ltered. The precipitate was mixed with potassium

hydroxide, KOH (11.22 g, 0.20 mol) in 150 mL ethanol. The

mixture was reuxed for 3 hours. All the reaction progress was

monitored by TLC. The mixture was then poured into 300 mL

water and a clear solution was formed. HCl was added to the

solution and the mixture was stirred slowly until the precipitate

was formed. The precipitate was ltered, washed with water and

dried overnight to obtain a white powder. The same method was

used to synthesis 2b–e. Yield: 20.23 g (85.72%), mp: 105.2–

3. Experimental

3.1. Chemicals

The chemicals and solvents used in this work are phosphoni-

trilic chloride trimer, 1-bromoheptane, 1-bromononane, 1-bro-

modecane,

hydroxybenzaldehyde, 4-hydroxybenzoic acid, 4-chlorobenzoic

acid, 4-nitrobenzoic acid, terephthalic acid, 1,4-phenylenedi-

amine, 4-nitroaniline, sodium sulphide hydrate, potassium

carbonate, potassium iodide, potassium hydroxide, sodium

hydroxide, glacial acetic acid, thionyl chloride, methanol,

ethanol, acetone, dichloromethane, tetrahydrofuran, N,N-

1-bromododecane,

1-bromotetradecane,

4-

ꢂ

ꢀ1

1

2

1

06.5 C, white powder. FTIR (cm ): 3250 (O–H stretching),

3

919 and 2850 (Csp –H stretching), 1684 (C]O stretching),

1

607 (aromatic C]C stretching), 1252 (C–O stretching). H-

NMR (500 MHz, CDCl ) d, ppm: 7.78 (d, J ¼ 5.0 Hz, 2H), 6.73

3

(

1

d, J ¼ 10.0 Hz, 2H), 3.96 (t, J ¼ 7.5 Hz, 2H), 1.68–1.74 (m, 2H),

.40–1.46 (m, 2H), 1.27–1.38 (m, 6H), 0.89 (t, J ¼ 7.5 Hz, 3H).

dimethylformamide, n-hexane, ethyl acetate, and triethylamine. 13

C-NMR (125 MHz, CDCl

3

) d, ppm: 168.78, 158.91, 135.20,

All the chemicals and solvents were used as received without

further purication and purchased from Merck, Qr ¨e c (Asia),

Sigma-Aldrich, Acros Organics, Fluka, and BDH (British Drug

Houses).

130.31, 112.80, 67.73, 31.09, 28.83, 28.28, 25.44, 21.82, 13.60.

20 3

CHN elemental analysis: calculated for C14H O : C: 71.16%, H:

8.53%; found: C: 71.01%, H: 8.57%.

28928 | RSC Adv., 2020, 10, 28918–28934

This journal is © The Royal Society of Chemistry 2020

View Article Online

Paper

RSC Advances

4

-(Nonyloxy)benzoic acid, 2b. 1-Bromononane (20.69 g, 0.10 acid, 2a (7.08 g, 0.03 mol) and thionyl chloride (3.57 g, 0.03 mol)

mol) was used in the reaction. Yield: 22.31 g (84.51%), mp: in 40 mL DCM was mixed in 100 mL round bottom ask to form

ꢂ

ꢀ1

1

04.8–105.7 C, white powder. FTIR (cm ): 3250 (O–H an acid chloride. The mixture was stirred at room temperature

3

stretching), 2919 and 2849 (Csp –H stretching), 1694 (C]O for 2 hours to form a clear solution. A solution of 4-nitroaniline

stretching), 1606 (aromatic C]C stretching), 1252 (C–O (4.14 g, 0.03 mol) in 20 mL THF was added dropwise to the

1

stretching). H-NMR (500 MHz, CDCl ) d, ppm: 7.80 (d, J ¼ mixture and a white precipitate began to form. Triethylamine,

3

1

0.0 Hz, 2H), 6.74 (d, J ¼ 5.0 Hz, 2H), 3.97 (t, J ¼ 5.0 Hz, 2H), Et

3

N (1.52 g, 0.015 mol) was nally added and the mixture was

1

.69–1.74 (m, 2H), 1.41–1.47 (m, 2H), 1.27–1.39 (m, 10H), 0.88 (t, stirred for 8 hours. All the reactions progress are monitored by

1

3

J ¼ 5.0 Hz, 3H). C-NMR (125 MHz, CDCl

) d, ppm: 169.36, TLC. The precipitate formed was ltered and the ltrate was

59.16, 134.83, 130.37, 113.02, 67.95, 31.10, 28.84, 28.76, 28.62, collected. Aer it was dried, the product formed was recrystal-

8.39, 25.46, 21.80, 13.48. CHN elemental analysis: calculated lised from methanol. The same method was used to synthesis

3

1

2

ꢂ

for C16

H

24

O

3

: C: 72.69%, H: 9.15%; found: C: 71.95%, H: 9.15%. 3b–h. Yield: 7.56 g (70.79%), mp: 137.1–139.8 C, yellow powder.

ꢀ

1

3

4

-(Decyloxy)benzoic acid, 2c. 1-Bromodecane (22.09 g, 0.10 FTIR (cm ): 3357 (N–H stretching), 2932 and 2854 (Csp –H

mol) was used in the reaction. Yield: 23.68 g (85.18%), mp: stretching), 1660 (C]O stretching), 1598 (aromatic C]C

04.1–105.3 C, white powder. FTIR (cm ): 3253 (O–H stretching), 1248 (C–O stretching), 1176 (C–N stretching). H-

ꢂ

ꢀ1

1

3

stretching), 2920 and 2849 (Csp –H stretching), 1694 (C]O NMR (500 MHz, CDCl

3

) d, ppm: 10.61 (s, 1H), 8.23 (d, J ¼

stretching), 1606 (aromatic C]C stretching), 1251 (C–O 5.0 Hz, 2H), 8.03 (d, J ¼ 5.0 Hz, 2H), 7.95 (d, J ¼ 10.0 Hz, 2H),

1

stretching). H-NMR (500 MHz, CDCl

3

) d, ppm: 7.78 (d, J ¼ 7.04 (d, J ¼ 10.0 Hz, 2H), 4.03 (t, J ¼ 7.5 Hz, 2H), 1.68–1.74 (m,

0.0 Hz, 2H), 6.73 (d, J ¼ 10.0 Hz, 2H), 3.96 (t, J ¼ 5.0 Hz, 2H), 2H), 1.36–1.42 (m, 2H), 1.23–1.33 (m, 6H), 0.85 (t, J ¼ 7.5 Hz,

.68–1.73 (m, 2H), 1.40–1.46 (m, 2H), 1.26–1.36 (m, 12H), 0.87 (t, 3H). C-NMR (125 MHz, CDCl ) d, ppm: 166.15, 162.59, 146.09,

) d, ppm: 168.78, 143.42, 130.26, 126.95, 124.78, 120.56, 115.03, 68.82, 31.51,

59.00, 134.78, 130.36, 112.83, 67.73, 31.13, 28.82, 28.80, 28.77, 29.08, 28.66, 25.81, 22.22, 13.94. CHN elemental analysis:

8.63, 28.47, 25.45, 21.85, 13.60. CHN elemental analysis: calculated for C20 : C: 67.40%, H: 6.79%, N: 7.86%;

1

3

1

3

J ¼ 7.5 Hz, 3H). C-NMR (125 MHz, CDCl

3

1

2

24 2 4

H N O

calculated for C H O : C: 73.35%, H: 9.41%; found: C: 73.14%, found: C: 66.81%, H: 6.84%, N: 7.77%.

1

7

26 3

H: 9.35%.

-(Dodecyloxy)benzoic acid, 2d. 1-Bromododecane (24.89 g, (7.92 g, 0.03 mol) was used in the reaction. Yield: 7.90 g

4-(Nonyloxy)-N-(4-nitrophenyl)benzamide, 3b. Intermediate 2b

4

ꢂ

ꢀ1

0

1

.10 mol) was used in the reaction. Yield: 26.88 g (87.84%), mp: (68.58%), mp: 136.3–138.2 C, yellow powder. FTIR (cm ): 3349

04.2–105.6 C, white powder. FTIR (cm ): 3250 (O–H (N–H stretching), 2921 and 2851 (Csp –H stretching), 1660 (C]

stretching), 2920 and 2850 (Csp –H stretching), 1702 (C]O O stretching), 1601 (aromatic C]C stretching), 1248 (C–O

3

stretching), 1603 (aromatic C]C stretching), 1250 (C–O stretching), 1176 (C–N stretching). H-NMR (500 MHz, CDCl )

ꢂ

ꢀ1

3

1

stretching). H-NMR (500 MHz, CDCl ) d, ppm: 7.83 (d, J ¼ d, ppm: 10.22 (s, 1H), 8.18 (d, J ¼ 10.0 Hz, 2H), 8.00 (d, J ¼

3

5

1

.0 Hz, 2H), 6.84 (d, J ¼ 10.0 Hz, 2H), 4.00 (t, J ¼ 7.5 Hz, 2H), 10.0 Hz, 2H), 7.96 (d, J ¼ 10.0 Hz, 2H), 7.03 (d, J ¼ 10.0 Hz, 2H),

.69–1.75 (m, 2H), 1.40–1.44 (m, 2H), 1.26–1.35 (m, 16H), 0.87 (t, 4.09 (t, J ¼ 5.0 Hz, 2H), 1.73–1.78 (m, 2H), 1.42–1.48 (m, 2H),

1

3

13

J ¼ 5.0 Hz, 3H). C-NMR (125 MHz, CDCl

3

) d, ppm: 167.95, 1.25–1.39 (m, 10H), 0.87 (t, J ¼ 7.5 Hz, 3H). C-NMR (125 MHz,

1

2

60.55, 134.78, 130.75, 113.53, 67.88, 31.13, 28.83, 28.81, 28.79, CDCl ) d, ppm: 166.26, 162.50, 145.95, 143.26, 130.27, 126.65,

3

8.78, 28.67, 28.58, 28.47, 25.39, 21.85, 13.59. CHN elemental 124.87, 120.56, 114.93, 68.66, 31.54, 29.17, 29.00, 28.95, 28.83,

analysis: calculated for C19

C: 73.74%, H: 9.98%.

H

30

O

3

: C: 74.47%, H: 9.87%; found: 25.77, 22.29, 14.04. CHN elemental analysis: calculated for

: C: 68.73%, H: 7.34%, N: 7.29%; found: C: 68.03%,

22 28 2 4

C H N O

4

-(Tetradecyloxy)benzoic acid, 2e. 1-Bromotetradecane H: 7.39%, N: 7.27%.

27.73 g, 0.10 mol) was used in the reaction. Yield: 28.12 g

4-(Decyloxy)-N-(4-nitrophenyl)benzamide, 3c. Intermediate 2c

84.19%), mp: 103.8–104.7 C, white powder. FTIR (cm ): 3251 (8.24 g, 0.03 mol) was used in the reaction. Yield: 8.66 g

(

ꢂ

ꢀ1

3

ꢂ

ꢀ1

O–H stretching), 2919 and 2850 (Csp –H stretching), 1701 (C] (72.53%), mp: 135.5–137.1 C, yellow powder. FTIR (cm ): 3346

3

O stretching), 1607 (aromatic C]C stretching), 1252 (C–O (N–H stretching), 2919 and 2851 (Csp –H stretching), 1657 (C]

1

stretching). H-NMR (500 MHz, CDCl

5

3

) d, ppm: 7.80 (d, J ¼ O stretching), 1598 (aromatic C]C stretching), 1246 (C–O

1

.0 Hz, 2H), 6.74 (d, J ¼ 10.0 Hz, 2H), 3.97 (t, J ¼ 5.0 Hz, 2H), stretching), 1176 (C–N stretching). H-NMR (500 MHz, CDCl

3

)

1

.68–1.74 (m, 2H), 1.40–1.46 (m, 2H), 1.20–1.36 (m, 20H), 0.87 (t, d, ppm: 10.33 (s, 1H), 8.19 (d, J ¼ 10.0 Hz, 2H), 8.00 (d, J ¼

1

3

J ¼ 7.5 Hz, 3H). C-NMR (125 MHz, CDCl ) d, ppm: 169.18, 5.0 Hz, 2H), 7.95 (d, J ¼ 5.0 Hz, 2H), 7.03 (d, J ¼ 10.0 Hz, 2H),

3

1

2

59.27, 134.27, 130.42, 113.02, 67.91, 31.11, 28.83, 28.82, 28.81, 4.07 (t, J ¼ 7.5 Hz, 2H), 1.70–1.76 (m, 2H), 1.39–1.45 (m, 2H),

13

8.80, 28.79, 28.77, 28.76, 28.59, 28.44, 25.44, 21.80, 13.49. CHN 1.22–1.36 (m, 12H), 0.85 (t, J ¼ 7.5 Hz, 3H). C-NMR (125 MHz,

: C: 75.41%, H: CDCl ) d, ppm: 166.18, 162.51, 146.05, 143.24, 130.29, 126.72,

124.89, 120.52, 114.93, 68.66, 31.59, 29.24, 29.20, 29.02, 28.99,

Synthesis of 4-(substituted)-N-(4-nitrophenyl)benzamide, 28.92, 25.80, 22.32, 14.07. CHN elemental analysis: calculated

a–h

for C23 : C: 69.32%, H: 7.59%, N: 7.03%; found: C:

-(Heptyloxy)-N-(4-nitrophenyl)benzamide, 3a. Intermediate 3a 69.12%, H: 7.59%, N: 6.99%.

was synthesized according to the method reported by Davidson

4-(Dodecyloxy)-N-(4-nitrophenyl)benzamide, 3d. Intermediate

et al. (2006) with some modications. 4-Heptyloxybenzoic 2d (9.18 g, 0.03 mol) was used in the reaction. Yield: 9.15 g

elemental analysis: calculated for C21

H

34

O

3

1

0.25%; found: C: 74.51%, H: 10.15%.

3

30 2 4

H N O

4

44

ꢂ

ꢀ1

(

71.60%), mp: 133.4–135.8 C, yellow powder. FTIR (cm ): 3344

This journal is © The Royal Society of Chemistry 2020

RSC Adv., 2020, 10, 28918–28934 | 28929

View Article Online

RSC Advances

Paper

3

(

N–H stretching), 2916 and 2849 (Csp –H stretching), 1657 (C] 8.02 (d, J ¼ 10.0 Hz, 2H), 7.83 (d, J ¼ 10.0 Hz, 2H), 7.55 (d, J ¼

1

3

O stretching), 1598 (aromatic C]C stretching), 1248 (C–O 5.0 Hz, 2H), 6.87 (d, J ¼ 5.0 Hz, 2H). C-NMR (125 MHz, CDCl )

3

1

stretching), 1176 (C–N stretching). H-NMR (500 MHz, CDCl ) d, ppm: 166.58, 162.51, 146.91, 143.21, 130.69, 125.84, 124.57,

3

d, ppm: 10.25 (s, 1H), 8.16 (d, J ¼ 10.0 Hz, 2H), 7.96 (d, J ¼ 121.22, 117.10. CHN elemental analysis: calculated for

5

4

1

.0 Hz, 2H), 7.92 (d, J ¼ 10.0 Hz, 2H), 7.00 (d, J ¼ 10.0 Hz, 2H),

13 9 2 3

C H ClN O : C: 56.44%, H: 3.28%, N: 12.81%; found: C:

.05 (t, J ¼ 5.0 Hz, 2H), 1.68–1.74 (m, 2H), 1.37–1.43 (m, 2H), 56.27%, H: 3.25%, N: 12.76%.

1

3

.19–1.34 (m, 16H), 0.82 (t, J ¼ 5.0 Hz, 3H). C-NMR (125 MHz,

Reduction of intermediates 3a–h to aﬀord 4a–h

CDCl

3

) d, ppm: 166.31, 162.52, 146.90, 143.32, 130.24, 126.65,

N-(4-Aminophenyl)-4-(heptyloxy)benzamide, 4a. Intermediate

1

2

24.86, 120.61, 114.97, 68.69, 31.54, 29.23, 29.22, 29.18, 29.16, 4a was synthesized according to the method reported by Shaoyu

9.15, 28.93, 28.88, 25.74, 22.27, 13.99. CHN elemental analysis: and Jiangbing (2012) with some modications. A solution of

45

calculated for C H N O : C: 70.40%, H: 8.03%, N: 6.57%; intermediate 3a (5.00 g, 0.014 mmol) in 40 mL ethanol and

2

5

34 2 4

found: C: 70.06%, H: 8.03%, N: 6.50%.

a solution of sodium sulphide hydrate, Na S$9H O (0.89 g, 0.01

2 2

4-(Tetradecyloxy)-N-(4-nitrophenyl)benzamide, 3e. Interme- mol) in 20 mL ethanol and 20 mL water were mixed in 250 mL

diate 2e (10.02 g, 0.03 mol) was used in the reaction. Yield: round bottom ask. The mixture was reuxed for 12 hours. The

ꢂ

9

(

.68 g (71.07%), mp: 131.7–133.6 C, yellow powder. FTIR reaction progress was monitored by TLC. Upon completion, the

ꢀ1

3

cm ): 3343 (N–H stretching), 2916 and 2851 (Csp –H stretch- mixture was cooled in an ice bath. The precipitate formed was

ing), 1657 (C]O stretching), 1606 (aromatic C]C stretching), ltered, washed with cold ethanol and dried to form a white

1

254 (C–O stretching), 1178 (C–N stretching). H-NMR (500 precipitate. The same method was used to synthesis 4b–h.

ꢂ

MHz, CDCl ) d, ppm: 10.25 (s, 1H), 8.17 (d, J ¼ 5.0 Hz, 2H), 7.96 Yield: 3.55 g (77.53%), mp: 155.3–157.1 C, white powder. FTIR

3

ꢀ1

(

2

d, J ¼ 5.0 Hz, 2H), 7.92 (d, J ¼ 10.0 Hz, 2H), 7.01 (d, J ¼ 5.0 Hz, (cm ): 3330 (N–H amide stretching), 3403 and 3204 (N–H

3

H), 4.05 (t, J ¼ 5.0 Hz, 2H), 1.69–1.74 (m, 2H), 1.37–1.43 (m, amine stretching), 2921 and 2854 (Csp –H stretching), 1696

13

H), 1.17–1.36 (m, 20H), 0.82 (t, J ¼ 5.0 Hz, 3H). C-NMR (125 (C]O stretching), 1609 (aromatic C]C stretching), 1254 (C–O

1

MHz, CDCl

1

2

3

) d, ppm: 166.32, 162.53, 146.91, 143.33, 130.25, stretching), 1173 (C–N stretching). H-NMR (500 MHz, CDCl

26.66, 124.86, 120.61, 114.98, 68.70, 31.55, 29.25, 29.23, 29.22, d, ppm: 9.69 (s, 1H), 7.89 (d, J ¼ 5.0 Hz, 2H), 7.34 (d, J ¼ 5.0 Hz,

9.19, 29.18, 29.16, 29.15, 28.94, 28.89, 25.75, 22.28, 14.00. CHN 2H), 7.00 (d, J ¼ 5.0 Hz, 2H), 6.53 (d, J ¼ 10.0 Hz, 2H), 4.87 (s,

3

)

elemental analysis: calculated for C H N O : C: 71.34%, H: 2H), 4.02 (t, J ¼ 5.0 Hz, 2H), 1.69–1.75 (m, 2H), 1.38–1.44 (m,

2

7

38 2 4

1

3

8

.43%, N: 6.16%; found: C: 70.68%, H: 8.38%, N: 6.12%.

2H), 1.25–1.36 (m, 6H), 0.86 (t, J ¼ 7.5 Hz, 3H). C-NMR (125

4

-(Hydroxy)-N-(4-nitrophenyl)benzamide, 3f. 4-Hydroxybenzoic MHz, CDCl ) d, ppm: 164.64, 161.46, 145.46, 129.72, 128.76,

3

acid (4.14 g, 0.03 mol) was used in the reaction. Yield: 5.66 g 127.64, 122.74, 114.38, 114.17, 68.15, 31.68, 29.05, 28.87, 25.90,

ꢂ

ꢀ1

(

73.13%), mp: 163.6–165.2 C, yellow powder. FTIR (cm ): 3340 22.50, 14.40. CHN elemental analysis: calculated for

N–H stretching), 3201 (O–H stretching), 1698 (C]O stretch- : C: 73.59%, H: 8.03%, N: 8.58%; found: C: 73.26%,

20 26 2 2

C H N O

ing), 1600 (aromatic C]C stretching), 1252 (C–O stretching), H: 8.08%, N: 8.51%.

1

175 (C–N stretching). H-NMR (500 MHz, CDCl

3

) d, ppm: 9.72

N-(4-Aminophenyl)-4-(nonyloxy)benzamide, 4b. Intermediate

(

s, 1H), 8.04 (d, J ¼ 5.0 Hz, 2H), 7.71 (d, J ¼ 10.0 Hz, 2H), 6.90 (d, 3b (5.00 g, 0.013 mol) was used in the reaction. Yield: 3.60 g

13

ꢂ

ꢀ1

J ¼ 5.0 Hz, 2H), 6.88 (d, J ¼ 10.0 Hz, 2H). C-NMR (125 MHz, (78.09%), mp: 153.7–154.9 C, white powder. FTIR (cm ): 3340

CDCl ) d, ppm: 166.77, 162.55, 146.89, 143.12, 130.75, 125.80, (N–H amide stretching), 3410 and 3201 (N–H amine stretching),

3

1

24.47, 120.50, 113.96. CHN elemental analysis: calculated for 2919 and 2851 (Csp –H stretching), 1698 (C]O stretching),

13 10 2 4

C H N O : C: 60.47%, H: 3.90%, N: 10.85%; found: C: 60.10%, 1609 (aromatic C]C stretching), 1254 (C–O stretching), 1178

1

H: 3.88%, N: 10.79%.

4

(

(C–N stretching). H-NMR (500 MHz, CDCl

-(Carboxy)-N-(4-nitrophenyl)benzamide, 3g. Terephthalic acid 1H), 7.88 (d, J ¼ 10.0 Hz, 2H), 7.33 (d, J ¼ 10.0 Hz, 2H), 6.99 (d, J

4.98 g, 0.03 mol) was used in the reaction. Yield: 5.12 g ¼ 10.0 Hz, 2H), 6.53 (d, J ¼ 10.0 Hz, 2H), 4.87 (s, 2H), 4.02 (t, J ¼

3

) d, ppm: 9.69 (s,

ꢂ

ꢀ1

59.67%), mp: 168.7–170.8 C, light brown powder. FTIR (cm ): 5.0 Hz, 2H), 1.69–1.74 (m, 2H), 1.38–1.43 (m, 2H), 1.22–1.35 (m,

1

3

341 (N–H stretching), 3100–3270 (O–H stretching), 1700 (C]O 10H), 0.85 (t, J ¼ 5.0 Hz, 3H). C-NMR (125 MHz, CDCl₃)

stretching), 1606 (aromatic C]C stretching), 1248 (C–O d, ppm: 164.64, 161.46, 145.46, 129.72, 128.75, 127.63, 122.75,

1

stretching), 1177 (C–N stretching). H-NMR (500 MHz, CDCl

3

)

114.38, 114.18, 68.15, 31.72, 29.40, 29.21, 29.09, 29.04, 25.92,

d, ppm: 11.06 (s, 1H), 10.07 (s, 1H), 8.10 (d, J ¼ 10.0 Hz, 2H), 8.08 22.55, 14.41. CHN elemental analysis: calculated for

(

2

1

d, J ¼ 5.0 Hz, 2H), 7.98 (d, J ¼ 10.0 Hz, 2H), 6.90 (d, J ¼ 10.0 Hz,

C

22

H

30

N

2

O

2

: C: 74.54%, H: 8.53%, N: 7.90%; found: C: 74.31%,

) d, ppm: 167.03, 164.33, 140.06, H: 8.54%, N: 7.88%.

39.29, 136.08, 130.55, 130.34, 129.94, 126.57, 116.19. CHN N-(4-Aminophenyl)-4-(decyloxy)benzamide, 4c. Intermediate 3c

1

3

H). C-NMR (125 MHz, CDCl

3

elemental analysis: calculated for C H N O : C: 58.75%, H: (5.00 g, 0.013 mol) was used in the reaction. Yield: 3.58 g

1

4

10 2 5

ꢂ

ꢀ1

3

.52%, N: 9.79%; found: C: 58.43%, H: 3.50%, N: 9.80%.

(77.44%), mp: 153.4–154.1 C, white powder. FTIR (cm ): 3340

4

-(Chloro)-N-(4-nitrophenyl)benzamide, 3h. 4-Chlorobenzoic (N–H amide stretching), 3404 and 3213 (N–H amine stretching),

3

acid (4.69 g, 0.03 mol) was used in the reaction. Yield: 6.11 g 2919 and 2851 (Csp –H stretching), 1700 (C]O stretching),

73.67%), mp: 155.1–157.4 C, yellow powder. FTIR (cm ): 3342 1606 (aromatic C]C stretching), 1254 (C–O stretching), 1176

N–H stretching), 1691 (C]O stretching), 1602 (aromatic C]C (C–N stretching). H-NMR (500 MHz, CDCl ) d, ppm: 9.68 (s,

3

ꢂ

ꢀ1

(

1

stretching), 1250 (C–O stretching), 1170 (C–N stretching), 827 1H), 7.89 (d, J ¼ 10.0 Hz, 2H), 7.34 (d, J ¼ 10.0 Hz, 2H), 7.00 (d, J

1

(

C–Cl bending). H-NMR (500 MHz, CDCl

3

) d, ppm: 9.90 (s, 1H), ¼ 10.0 Hz, 2H), 6.53 (d, J ¼ 10.0 Hz, 2H), 4.87 (s, 2H), 4.03 (t, J ¼

28930 | RSC Adv., 2020, 10, 28918–28934

This journal is © The Royal Society of Chemistry 2020

View Article Online

Paper

RSC Advances

7

1

.5 Hz, 2H), 1.69–1.75 (m, 2H), 1.38–1.44 (m, 2H), 1.22–1.35 (m, C]C stretching), 1254 (C–O stretching), 1178 (C–N stretching).

1

3

1

2H), 0.86 (t, J ¼ 7.5 Hz, 3H). C-NMR (125 MHz, CDCl₃)

H-NMR (500 MHz, CDCl ) d, ppm: 10.06 (s, 1H), 8.10 (d, J ¼

3

d, ppm: 164.57, 161.45, 145.48, 129.72, 128.77, 127.69, 122.73, 10.0 Hz, 2H), 7.98 (d, J ¼ 5.0 Hz, 2H), 7.92 (d, J ¼ 10.0 Hz, 2H),

1

3

1

2

14.38, 114.15, 68.15, 31.75, 29.45, 29.40, 29.21, 29.15, 29.05, 6.67 (s, 2H), 6.60 (d, J ¼ 10.0 Hz, 2H). C-NMR (125 MHz,

5.93, 22.55, 14.42. CHN elemental analysis: calculated for CDCl ) d, ppm: 167.07, 156.08, 139.27, 136.17, 136.11, 130.34,

: C: 74.96%, H: 8.75%, N: 7.60%; found: C: 74.65%, 129.94, 126.81, 112.86. CHN elemental analysis: calculated for

H: 8.75%, N: 7.57%. : C: 65.62%, H: 4.72%, N: 10.93%; found: C: 65.28%,

N-(4-Aminophenyl)-4-(dodecyloxy)benzamide, 4d. Intermediate H: 4.70%, N: 10.85%.

d (5.00 g, 0.012 mol) was used in the reaction. Yield: 3.61 g N-(4-Aminophenyl)-4-(chloro)benzamide, 4h. Intermediate 3h

78.32%), mp: 151.8–153.4 C, yellow powder. FTIR (cm ): 3352 (5.00 g, 0.018 mol) was used in the reaction. Yield: 3.05 g

3

23 32 2 2

C H N O

14 12 2 3

C H N O

3

ꢂ

ꢀ1

(

ꢂ

ꢀ1

N–H amide stretching), 3402 and 3206 (N–H amine stretching), (68.43%), mp: 170.4–172.1 C, white powder. FTIR (cm ): 3344

3

2

1

919 and 2851 (Csp –H stretching), 1698 (C]O stretching), (N–H amide stretching), 3473 and 3207 (N–H amine stretching),

606 (aromatic C]C stretching), 1254 (C–O stretching), 1178 1641 (C]O stretching), 1701 (aromatic C]C stretching), 1252

1

(C–N stretching). H-NMR (500 MHz, CDCl

3

) d, ppm: 9.69 (s, (C–O stretching), 1189 (C–N stretching), 825 (C–Cl bending). H-

) d, ppm: 10.08 (s, 1H), 8.33 (d, J ¼ 5.0 Hz,

5.0 Hz, 2H), 6.53 (d, J ¼ 10.0 Hz, 2H), 4.87 (s, 2H), 4.02 (t, J ¼ 2H), 8.09 (d, J ¼ 10.0 Hz, 2H), 7.88 (d, J ¼ 10.0 Hz, 2H), 6.61 (s,

1

H), 7.89 (d, J ¼ 10.0 Hz, 2H), 7.34 (d, J ¼ 10.0 Hz, 2H), 7.00 (d, J NMR (500 MHz, CDCl

3

¼

1

3

7

.5 Hz, 2H), 1.69–1.75 (m, 2H), 1.38–1.44 (m, 2H), 1.22–1.34 (m, 2H), 6.58 (d, J ¼ 10.0 Hz, 2H). C-NMR (125 MHz, CDCl

3

)

1

3

16H), 0.85 (t, J ¼ 5.0 Hz, 3H). C-NMR (125 MHz, CDCl₃) d, ppm: 166.87, 163.80, 150.45, 136.76, 132.60, 131.29, 128.90,

d, ppm: 164.62, 161.45, 145.47, 129.72, 128.77, 127.65, 122.74, 124.33, 118.11. CHN elemental analysis: calculated for

1

2

14.37, 114.16, 68.14, 31.75, 29.48, 29.46, 29.44, 29.43, 29.19, C H ClN O: C: 63.29%, H: 4.49%, N: 14.37%; found: C:

13 11 2

9.16, 29.04, 25.92, 22.55, 14.41. CHN elemental analysis: 63.12%, H: 4.50%, N: 14.26%.

calculated for C25

found: C: 75.56%, H: 9.13%, N: 7.01%.

H

36

N

2

O

2

: C: 75.72%, H: 9.15%, N: 7.06%;

Synthesis of N-(4-aminophenyl)-4-(nitro)benzamide, 4i.

Intermediate 4i was synthesized according to the method re-

N-(4-Aminophenyl)-4-(tetradecyloxy)benzamide, 4e. Interme- ported by Avdeenko and Marchenko (2001) with some modi-

46

diate 3e (5.00 g, 0.011 mol) was used in the reaction. Yield: cations. A mixture of 4-nitrobenzoic acid (6.21 g, 0.03 mol) and

ꢂ

3

(

.66 g (78.38%), mp: 150.6–152.8 C, yellow powder. FTIR thionyl chloride (3.57 g, 0.03 mol) was dissolved in 20 mL DCM

ꢀ1

cm ): 3345 (N–H amide stretching), 3411 and 3203 (N–H in a 100 mL round bottom ask. The mixture was stirred at

amine stretching), 2921 and 2851 (Csp –H stretching), 1698 room temperature for 2 hours. Upon completion, the corre-

C]O stretching), 1606 (aromatic C]C stretching), 1256 (C–O sponding acid chloride which was not isolated was reacted with

3

(

1

stretching), 1176 (C–N stretching). H-NMR (500 MHz, CDCl

3

)

1,4-phenylenediamine (6.48 g, 0.06 mol) in 10 mL THF. Then,

d, ppm: 9.31 (s, 1H), 7.88 (d, J ¼ 10.0 Hz, 2H), 7.34 (d, J ¼ triethylamine (1.52 g, 0.015 mol) was added dropwise to the

1

4

1

0.0 Hz, 2H), 6.98 (d, J ¼ 5.0 Hz, 2H), 6.59 (d, J ¼ 5.0 Hz, 2H), mixture and it was le to stir at room temperature for 8 hours.

.06 (t, J ¼ 7.5 Hz, 2H), 1.73–1.77 (m, 2H), 1.41–1.46 (m, 2H), The reaction progress was monitored by TLC. The precipitate

1

3

.25–1.38 (m, 20H), 0.87 (t, J ¼ 7.5 Hz, 3H). C-NMR (125 MHz, formed was ltered and the ltrate was collected. The ltrate

CDCl ) d, ppm: 164.94, 161.69, 145.25, 131.67, 129.63, 129.39, was evaporated, dried and puried using column chromatog-

3

ꢂ

1

2

22.94, 114.74, 114.60, 68.65, 31.62, 29.34, 29.33, 29.31, 29.27, raphy. Yield: 4.23 g (54.86%), mp: 187.7–189.3 C, yellow

ꢀ

1

9.26, 29.24, 29.12, 29.06, 28.96, 25.86, 22.31, 14.02. CHN powder. FTIR (cm ): 3341 (N–H amide stretching), 3408 and

: C: 76.37%, H: 3207 (N–H amine stretching), 1690 (C]O stretching), 1595

.50%, N: 6.60%; found: C: 76.18%, H: 9.47%, N: 6.62%. (aromatic C]C stretching), 1248 (C–O stretching), 1146 (C–N

N-(4-Aminophenyl)-4-(hydroxy)benzamide, 4f. Intermediate 3f stretching). H-NMR (500 MHz, CDCl

40 2 2

elemental analysis: calculated for C27H N O

9

1

3

) d, ppm: 9.93 (s, 1H), 7.90

(

5.00 g, 0.019 mol) was used in the reaction. Yield: 3.22 g (d, J ¼ 10.0 Hz, 2H), 7.87 (d, J ¼ 5.0 Hz, 2H), 7.59 (d, J ¼ 6.0 Hz,

ꢂ

ꢀ

1

3

72.87%), mp: 211.1–213.6 C, white powder. FTIR (cm ): 3340 2H), 6.63 (s, 2H), 6.59 (d, J ¼ 10.0 Hz, 2H). C-NMR (125 MHz,

N–H amide stretching), 3405 and 3211 (N–H amine stretching), CDCl ) d, ppm: 166.59, 162.98, 150.10, 136.44, 132.37, 131.10,

3

3200 (O–H stretching), 1691 (C]O stretching), 1609 (aromatic 128.51, 123.89, 114.70. CHN elemental analysis: calculated for

C]C stretching), 1254 (C–O stretching), 1178 (C–N stretching). : C: 65.62%, H: 4.72%, N: 10.93%; found: C: 65.34%,

14 12 2 3

C H N O

1

H-NMR (500 MHz, CDCl

3

) d, ppm: 9.73 (s, 1H), 8.24 (d, J ¼ H: 4.69%, N: 10.82%.

5

6

1

6

1

.0 Hz, 2H), 8.10 (d, J ¼ 10.0 Hz, 2H), 7.71 (d, J ¼ 10.0 Hz, 2H),

Synthesis of hexakis{((4-(substituted)benzamide)meth-

1

3

.89 (d, J ¼ 10.0 Hz, 2H). C-NMR (125 MHz, CDCl

3

) d, ppm: aneylylidene)azaneylylidene}triazaphosphazene, 5a–i

Hexakis{((4-(heptyloxy)benzamide)methaneyllidene)azaneylyli-

16.26. CHN elemental analysis: calculated for C H N O : C: dene}triazaphosphazene, 5a. Compound 5a was synthesized

66.28, 163.72, 150.37, 136.75, 132.54, 131.07, 128.83, 124.02,

1

3

12 2 2

8.41%, H: 5.30%, N: 12.27%; found: C: 68.17%, H: 5.27%, N: according to the method reported by Jamain et al. (2019) and

32,47

2.19%.

N-(4-Aminophenyl)-4-(carboxy)benzamide, 4g. Intermediate 3g intermediate 1 (0.70 g, 0.81 mmol) and intermediate 4a (1.86 g,

4.50 g, 0.016 mol) was used in the reaction. Yield: 3.10 g 5.69 mmol) in 50 mL methanol was mixed in a 100 mL round

Fareed et al. (2013) with some modications.

A mixture of

(

ꢂ

ꢀ1

76.96%), mp: 232.6–233.9 C, white powder. FTIR (cm ): 3351 bottom ask. A few drops of glacial acetic acid were added to the

N–H amide stretching), 3401 and 3202 (N–H amine stretching), solution. The mixture was reuxed for 18 hours. The reaction

3203 (O–H stretching), 1692 (C]O stretching), 1608 (aromatic progress was monitored by TLC. Upon completion, the

RSC Adv., 2020, 10, 28918–28934 | 28931

View Article Online

RSC Advances

Paper

precipitate formed was ltered and dried overnight. The

Hexakis{((4-(dodecyloxy)benzamide)methaneyllidene)azaneyly-

product was recrystallised from ethanol. The same method was lidene}triazaphosphazene, 5d. Intermediate 4d (2.25 g, 5.69

used to synthesis 5b–h. Yield: 1.47 g (66.74%), mp: 183.6– mmol) was used in the reaction. Yield: 1.66 g (65.25%), mp:

ꢂ

ꢀ1

ꢂ

ꢀ1

1

2

1

85.1 C, yellow powder. FTIR (cm ): 3365 (N–H stretching), 171.3–173.8 C, yellow powder. FTIR (cm ): 3363 (N–H

3

921 and 2854 (Csp –H stretching), 1691 (C]O stretching), stretching), 2916 and 2851 (Csp –H stretching), 1695 (C]O

644 (C]N stretching), 1592 (aromatic C]C stretching), 1254 stretching), 1644 (C]N stretching), 1592 (aromatic C]C

(

C–O stretching), 1197 (P]N stretching), 1178 (C–N stretching), stretching), 1255 (C–O stretching), 1197 (P]N stretching), 1178

77 (P–O–C stretching). H-NMR (500 MHz, DMSO-d ) d, ppm: (C–N stretching), 978 (P–O–C stretching). H-NMR (500 MHz,

6

1

9

5

7

5

6

.83 (s, 1H), 8.65 (s, 1H), 7.95 (d, J ¼ 5.0 Hz, 2H), 7.94 (d, J ¼ DMSO-d ) d, ppm: 9.82 (s, 1H), 8.65 (s, 1H), 7.95 (d, J ¼ 10.0 Hz,

6

.0 Hz, 2H), 7.80 (d, J ¼ 10.0 Hz, 2H), 7.55 (d, J ¼ 5.0 Hz, 2H), 2H), 7.94 (d, J ¼ 5.0 Hz, 2H), 7.80 (d, J ¼ 10.0 Hz, 2H), 7.54 (d, J ¼

.29 (d, J ¼ 10.0 Hz, 2H), 7.02 (d, J ¼ 10.0 Hz, 2H), 4.08 (t, J ¼ 10.0 Hz, 2H), 7.29 (d, J ¼ 10.0 Hz, 2H), 7.02 (d, J ¼ 10.0 Hz, 2H),

.0 Hz, 2H), 1.73–1.79 (m, 2H), 1.42–1.48 (m, 2H), 1.28–1.40 (m, 4.07 (t, J ¼ 7.5 Hz, 2H), 1.72–1.78 (m, 2H), 1.42–1.48 (m, 2H),

1

3

13

H), 0.89 (t, J ¼ 5.0 Hz, 3H). C-NMR (125 MHz, DMSO-d

6

)

1.24–1.37 (m, 16H), 0.87 (t, J ¼ 7.5 Hz, 3H). C-NMR (125 MHz,

d, ppm: 165.46, 162.05, 158.11, 146.97, 138.44, 136.35, 135.82, DMSO-d ) d, ppm: 165.46, 162.04, 158.07, 146.96, 138.42,

6

1

30.48, 129.94, 129.29, 127.70, 121.74, 121.69, 114.82, 68.65, 136.36, 135.80, 130.46, 129.93, 129.27, 127.68, 121.75, 121.68,

3

1

31.56, 29.11, 28.71, 25.85, 22.29, 14.06. P-NMR (500 MHz, 114.80, 68.63, 31.63, 29.35, 29.32, 29.29, 29.09, 29.08, 28.98,

3

1

6

DMSO-d ) d, ppm: 8.49 (s, 1P). CHN elemental analysis: calcu- 25.87, 22.34, 14.06. P-NMR (500 MHz, DMSO-d ) d, ppm: 8.50

lated for C₁₆₂H₁₇₄N O P : C: 71.74%, H: 6.47%, N: 7.75%; (s,

1P).

CHN

elemental

analysis:

calculated

for

15

18 3

found: C: 71.57%, H: 6.40%, N: 7.71%.

C₁₉₂H₂₃₄N O P : C: 73.61%, H: 7.53%, N: 6.71%; found: C:

15

18 3

Hexakis{((4-(nonyloxy)benzamide)methaneyllidene)azaneylyli-

dene}triazaphosphazene, 5b. Intermediate 4b (2.02 g, 5.69 mmol)

73.23%, H: 7.48%, N: 6.65%.

Hexakis{((4-(tetradecyloxy)benzamide)methaneyllidene)azaney-

was used in the reaction. Yield: 1.53 g (65.41%), mp: 178.1– lylidene}triazaphosphazene, 5e. Intermediate 4e (2.41 g, 5.69

ꢂ

ꢀ1

1

2

1

80.5 C, yellow powder. FTIR (cm ): 3365 (N–H stretching), mmol) was used in the reaction. Yield: 1.84 g (68.64%), mp:

3

ꢂ

ꢀ1

919 and 2849 (Csp –H stretching), 1691 (C]O stretching), 168.5–170.5 C, yellow powder. FTIR (cm ): 3317 (N–H

646 (C]N stretching), 1593 (aromatic C]C stretching), 1256 stretching), 2921 and 2849 (Csp –H stretching), 1691 (C]O

3

(

C–O stretching), 1197 (P]N stretching), 1178 (C–N stretching), stretching), 1641 (C]N stretching), 1599 (aromatic C]C

1

9

1

7

1

74 (P–O–C stretching). H-NMR (500 MHz, DMSO-d ) d, ppm: stretching), 1259 (C–O stretching), 1189 (P]N stretching), 1178

6

1

.82 (s, 1H), 8.65 (s, 1H), 7.96 (d, J ¼ 10.0 Hz, 2H), 7.94 (d, J ¼ (C–N stretching), 977 (P–O–C stretching). H-NMR (500 MHz,

0.0 Hz, 2H), 7.81 (d, J ¼ 10.0 Hz, 2H), 7.54 (d, J ¼ 10.0 Hz, 2H), DMSO-d ) d, ppm: 9.82 (s, 1H), 8.64 (s, 1H), 7.95 (d, J ¼ 10.0 Hz,

6

.29 (d, J ¼ 10.0 Hz, 2H), 7.02 (d, J ¼ 10.0 Hz, 2H), 4.08 (t, J ¼ 2H), 7.94 (d, J ¼ 5.0 Hz, 2H), 7.81 (d, J ¼ 5.0 Hz, 2H), 7.54 (d, J ¼

.5 Hz, 2H), 1.73–1.79 (m, 2H), 1.42–1.48 (m, 2H), 1.24–1.39 (m, 5.0 Hz, 2H), 7.29 (d, J ¼ 10.0 Hz, 2H), 7.02 (d, J ¼ 5.0 Hz, 2H),

1

3

0H), 0.88 (t, J ¼ 5.0 Hz, 3H). C-NMR (125 MHz, DMSO-d

6

)

4.07 (t, J ¼ 7.5 Hz, 2H), 1.72–1.78 (m, 2H), 1.42–1.47 (m, 2H),

13

d, ppm: 165.44, 162.05, 158.04, 146.95, 138.46, 136.36, 135.82, 1.22–1.38 (m, 20H), 0.87 (t, J ¼ 7.5 Hz, 3H). C-NMR (125 MHz,

1

3

30.46, 129.94, 129.27, 127.71, 121.74, 121.69, 114.80, 68.64, DMSO-d ) d, ppm: 165.44, 162.04, 158.04, 146.95, 138.44,

6

3

1

1.63, 29.28, 29.11, 28.93, 25.89, 22.36, 14.08. P-NMR (500 136.36, 135.81, 130.45, 129.93, 129.27, 127.69, 121.74, 121.67,

MHz, DMSO-d ) d, ppm: 8.51 (s, 1P). CHN elemental analysis: 114.79, 68.63, 31.64, 29.37, 29.36, 29.35, 29.34, 29.29, 29.11,

6

3

1

calculated for C174

.29%; found: C: 72.04%, H: 6.88%, N: 7.22%.

Hexakis{((4-(decyloxy)benzamide)methaneyllidene)azaneylyli-

198 15 18 3

H N O P : C: 72.55%, H: 6.93%, N: 29.09, 28.97, 25.87, 22.34, 14.05. P-NMR (500 MHz, DMSO-d₆)

7

d, ppm: 8.47 (s, 1P). CHN elemental analysis: calculated for

C₂₀₄H₂₅₈N O P : C: 74.22%, H: 7.88%, N: 6.36%; found: C:

15

18 3

dene}triazaphosphazene, 5c. Intermediate 4c (2.09 g, 5.69 mmol) 73.89%, H: 7.80%, N: 6.31%.

was used in the reaction. Yield: 1.55 g (64.39%), mp: 175.7–

Hexakis{((4-(hydroxy)benzamide)methaneyllidene)azaneylyli-

ꢂ

ꢀ1

1

2

1

77.6 C, yellow powder. FTIR (cm ): 3363 (N–H stretching), dene}triazaphosphazene, 5f. Intermediate 4f (1.30 g, 5.69 mmol)

3

919 and 2851 (Csp –H stretching), 1690 (C]O stretching), was used in the reaction. Yield: 1.23 g (71.33%), mp: 282.7–

644 (C]N stretching), 1593 (aromatic C]C stretching), 1259 285.1 C, yellow powder. FTIR (cm ): 3356 (N–H stretching),

ꢂ

ꢀ1

(

C–O stretching), 1197 (P]N stretching), 1181 (C–N stretching), 3260 (O–H stretching), 1697 (C]O stretching), 1640 (C]N

77 (P–O–C stretching). H-NMR (500 MHz, DMSO-d ) d, ppm: stretching), 1590 (aromatic C]C stretching), 1253 (C–O

6

1

9

5

7

1

.82 (s, 1H), 8.65 (s, 1H), 7.96 (d, J ¼ 10.0 Hz, 2H), 7.94 (d, J ¼ stretching), 1190 (P]N stretching), 1152 (C–N stretching), 980

1

.0 Hz, 2H), 7.80 (d, J ¼ 10.0 Hz, 2H), 7.55 (d, J ¼ 5.0 Hz, 2H), (P–O–C stretching). H-NMR (500 MHz, DMSO-d ) d, ppm: 8.42

6

.29 (d, J ¼ 10.0 Hz, 2H), 7.03 (d, J ¼ 5.0 Hz, 2H), 4.08 (t, J ¼ (s, 1H), 7.94 (d, J ¼ 5.0 Hz, 2H), 7.73 (d, J ¼ 10.0 Hz, 2H), 7.50 (d,

.5 Hz, 2H), 1.73–1.78 (m, 2H), 1.42–1.48 (m, 2H), 1.24–1.38 (m, J ¼ 10.0 Hz, 2H), 7.12 (d, J ¼ 10.0 Hz, 2H), 6.88 (d, J ¼ 10.0 Hz,

1

3

13

2H), 0.88 (t, J ¼ 7.5 Hz, 3H). C-NMR (125 MHz, DMSO-d₆) 2H), 6.80 (d, J ¼ 10.0 Hz, 2H). C-NMR (125 MHz, DMSO-d )

6

d, ppm: 165.46, 162.05, 158.10, 146.96, 138.43, 136.36, 135.81, d, ppm: 167.05, 160.60, 157.36, 156.14, 143.65, 138.25, 131.57,

1

3

1

30.47, 129.94, 129.28, 127.69, 121.75, 121.69, 114.81, 68.64, 130.67, 130.23, 129.09, 128.33, 122.59, 116.17, 116.07. P-NMR

3

1

1.63, 29.30, 29.26, 29.09, 28.97, 25.87, 22.34, 14.07. P-NMR (500 MHz, DMSO-d ) d, ppm: 8.52 (s, 1P). CHN elemental

6

(500 MHz, DMSO-d

6

90 15 18 3

) d, ppm: 8.48 (s, 1P). CHN elemental analysis: calculated for C₁₂₀H N O P : C: 67.89%, H:

analysis: calculated for C180

H

210

N

15

O

18

P

3

: C: 72.92%, H: 4.27%, N: 9.90%; found: C: 67.70%, H: 4.23%, N: 9.86%.

7.14%, N: 7.09%; found: C: 72.76%, H: 7.11%, N: 7.02%.

28932 | RSC Adv., 2020, 10, 28918–28934

View Article Online

Paper

Hexakis{((4-(carboxy)benzamide)methaneyllidene)azaneylyli-

RSC Advances

progress was monitored using TLC. Upon completion, the

dene}triazaphosphazene, 5g. Intermediate 4g (1.46 g, 5.69 mmol) mixture was cooled in an ice bath and the precipitate formed

was used in the reaction. Yield: 1.31 g (70.39%), mp: 296.1– was ltered, washed with cold ethanol and dried overnight.

ꢂ

ꢀ1

ꢂ

2

3

98.5 C, orange powder. FTIR (cm ): 3336 (N–H stretching), Yield: 0.71 g (64.20%), mp: 296.4–298.7 C, light brown powder.

ꢀ

1

290 (O–H stretching), 1699 (C]O stretching), 1642 (C]N FTIR (cm ): 3360 (N–H amide stretching), 3416 and 3207 (N–H

stretching), 1601 (aromatic C]C stretching), 1254 (C–O amine stretching), 1690 (C]O stretching), 1645 (C]N stretch-

stretching), 1190 (P]N stretching), 1174 (C–N stretching), 978 ing), 1591 (aromatic C]C stretching), 1254 (C–O stretching),

1

(

P–O–C stretching). H-NMR (500 MHz, DMSO-d ) d, ppm: 8.61 1196 (P]N stretching), 1172 (C–N stretching), 1013 (P–O–C

6

1

(

s, 1H), 8.21 (d, J ¼ 10.0 Hz, 2H), 8.10 (d, J ¼ 5.0 Hz, 2H), 8.01 (d, stretching). H-NMR (500 MHz, DMSO-d

6

) d, ppm: 8.68 (s, 1H),

J ¼ 10.0 Hz, 2H), 7.94 (d, J ¼ 5.0 Hz, 2H), 7.22 (d, J ¼ 10.0 Hz, 8.25 (d, J ¼ 5.0 Hz, 2H), 8.06 (d, J ¼ 5.0 Hz, 2H), 7.27 (d, J ¼

1

3

2

H), 6.82 (d, J ¼ 5.0 Hz, 2H). C-NMR (125 MHz, DMSO-d

6

)

10.0 Hz, 2H), 6.99 (d, J ¼ 5.0 Hz, 2H), 6.84 (d, J ¼ 5.0 Hz, 2H),

13

d, ppm: 167.47, 166.28, 157.21, 156.28, 150.29, 142.55, 140.52, 6.56 (d, J ¼ 10.0 Hz, 2H), 5.16 (s, 2H). C-NMR (125 MHz,

3

1

36.92, 131.02, 130.09, 128.60, 123.95, 123.19, 116.24. P-NMR DMSO-d

6

) d, ppm: 157.67, 155.00, 148.73, 147.96, 142.47,

(

500 MHz, DMSO-d ) d, ppm: 8.57 (s, 1P). CHN elemental 142.07, 129.64, 129.47, 128.94, 124.29, 123.56, 119.45, 116.32,

6

3

1

analysis: calculated for C₁₂₆H N O P : C: 66.05%, H: 115.76. P-NMR (500 MHz, DMSO-d

6

) d, ppm: 8.55 (s, 1P). CHN

elemental analysis: calculated for C120 : C: 68.08%,

H: 4.57%, N: 13.89%; found: C: 67.77%, H: 4.59%, N: 13.79%.

90

15 24 3

3.96%, N: 9.17%; found: C: 65.81%, H: 3.94%, N: 9.09%.

96 21 12 3

H N O P

Hexakis{((4-(chloro)benzamide)methaneyllidene)azaneylyli-

dene}triazaphosphazene, 5h. Intermediate 4h (1.40 g, 5.69 mmol)

was used in the reaction. Yield: 1.25 g (68.89%), mp: 272.5–

4

. Conclusion

ꢂ

ꢀ1

275.8 C, orange powder. FTIR (cm ): 3360 (N–H stretching),

695 (C]O stretching), 1644 (C]N stretching), 1601 (aromatic All the intermediates and hexasubstituted cyclotriphosphazene

1

C]C stretching), 1254 (C–O stretching), 1189 (P]N stretching), compounds were successfully synthesized and characterized.

172 (C–N stretching), 1014 (P–O–C stretching), 819 (C–Cl POM has been used to determine the mesophase behaviour of

1

bending). H-NMR (500 MHz, DMSO-d ) d, ppm: 8.44 (s, 1H), these compounds and the results showed that only compounds

6

7

5

6

1

.86 (d, J ¼ 10.0 Hz, 2H), 7.77 (d, J ¼ 10.0 Hz, 2H), 7.41 (d, J ¼ 5a–e with alkoxy chains have liquid crystal properties. However,

.0 Hz, 2H), 7.39 (d, J ¼ 10.0 Hz, 2H), 7.14 (d, J ¼ 10.0 Hz, 2H), other compounds 5f–j were found to be non-mesogenic with no

1

3

.79 (d, J ¼ 10.0 Hz, 2H). C-NMR (125 MHz, DMSO-d

) d, ppm: liquid crystal behaviour. The presence of the amide linking unit

6

67.36, 156.69, 156.48, 142.59, 138.31, 136.02, 135.30, 131.48, caused compounds 5f–j with small substituent such as hydroxy,

3

1

30.20, 130.05, 129.18, 129.00, 123.00, 116.27. P-NMR (500 carboxy, chloro, nitro, and amino have high melting tempera-

MHz, DMSO-d ) d, ppm: 8.53 (s, 1P). CHN elemental analysis: ture and liquid crystal behaviour cannot be induced although

6

calculated for C₁₂₀H Cl N O P : C: 64.53%, H: 3.79%, N: the Schiﬀ base provide linearity and thermal stability in the

84

6 15 12 3

9.42%; found: C: 64.13%, H: 3.77%, N: 9.38%.

molecules. The XRD data of compound 5c conrmed the

Hexakis{((4-(nitro)benzamide)methaneyllidene)azaneylylidene}

formation of SmA phase. The homeotropic alignment was

triazaphosphazene, 5i. Intermediate 1 (1.50 g, 1.74 mmol) and occurred and suggested that the side arms were aligned three

intermediate 4i (3.13 g, 0.012 mol) were used in the reaction. up and three down. Further study on the re retardancy of nal

ꢂ

Yield: 2.23 g (71.15%), mp: 280.1–283.3 C, yellow powder. FTIR compounds was done using LOI testing. All the compounds

ꢀ1

(

cm ): 3367 (N–H stretching), 1691 (C]O stretching), 1641 gave excellent results and compound 5i showed the highest LOI

C]N stretching), 1598 (aromatic C]C stretching), 1252 (C–O value with 28.53%. The eﬀect of electron withdrawing of nitro

(

stretching), 1187 (P]N stretching), 1173 (C–N stretching), 1019 group play an important role for the compound to have high re

1

(

P–O–C stretching). H-NMR (500 MHz, DMSO-d ) d, ppm: 9.81 retardant value as this nitro group can induced the P–N syner-

6

s, 1H), 8.66 (s, 1H), 8.23 (d, J ¼ 10.0 Hz, 2H), 8.04 (d, J ¼ 10.0 Hz, gistic eﬀect.

2

H), 7.26 (d, J ¼ 10.0 Hz, 2H), 6.82 (d, J ¼ 10.0 Hz, 2H), 6.51 (d, J

1

3

¼

10.0 Hz, 2H), 6.46 (d, J ¼ 10.0 Hz, 2H). C-NMR (125 MHz,

Conﬂicts of interest

DMSO-d

6

) d, ppm: 157.63, 155.02, 148.82, 148.71, 142.42,

1

42.05, 140.85, 129.47, 124.29, 123.79, 123.56, 116.32, 116.06, The authors declare no conict of interest.

3

1

16.01. P-NMR (500 MHz, DMSO-d ) d, ppm: 8.54 (s, 1P). CHN

6

elemental analysis: calculated for C₁₂₀H N O P : C: 62.75%,

84

21 24 3

Acknowledgements

H: 3.69%, N: 12.81%; found: C: 62.33%, H: 3.65%, N: 12.69%.

Synthesis of

hexakis{((4-(amino)benzamide)meth- The authors would like to thank the Universiti Malaysia Sabah

aneyllidene)azaneylylidene}triazaphosphazene, 5j. Compound (UMS) for Grant No. SGA0037-2019 and Universiti Sains

j was synthesized according to the method reported by Deyan Malaysia (USM) for RUI (USM) Grant No. 1001/PKIMIA/811332.

5

48

et al. (2015) with some modications. A solution of compound

i (1.20 g, 0.52 mmol) in 20 mL hot ethanol and a solution of

5

References

sodium sulphide hydrate, Na S$9H O (0.33 g, 4.18 mmol) in

2

1

0 mL ethanol and 10 mL water were mixed in a 100 mL round

1 H. R. Allcock and R. L. Kugel, J. Am. Chem. Soc., 1965, 87,

4216–4217.

bottom ask. The mixture was reuxed for 7 hours. The reaction

2

H. R. Allcock, Chem. Rev., 1972, 72, 315–356.

RSC Adv., 2020, 10, 28918–28934 | 28933

View Article Online

RSC Advances

Paper

3

4

5

6

7

8

9

K. Moriya, T. Suzuki, S. Yano and M. Kajiwara, Liq. Cryst., 26 K. Moriya, T. Masuda, T. Suzuki, S. Yano and M. Kajiwara,

995, 19, 711–713. Mol. Cryst. Liq. Cryst., 2006, 318, 267–277.

H. R. Allcock, Phosphorus, Sulfur Silicon Relat. Elem., 2004, 27 S. Ahuja and N. Jespersen, Modern Instrumental Analysis,

79, 661–671. Elsevier Science, 2006.

J. Barber ´a , J. Jim ´e nez, A. Laguna, L. Oriol, S. P ´e rez and 28 D. Pociecha, D. Kardas, E. Gorecka, J. Szydlowska,

1

J. L. Serrano, Chem. Mater., 2006, 18, 5437–5445.

J. M. Khurana, S. Chauhan and G. Bansal, Monatsh. Chem.,

J. Mieczkowski and D. Guillon, J. Mater. Chem., 2003, 13,

34–37.

2

004, 135, 83–87.

29 B. Y. Zhang, Y. G. Jia, D. S. Yao and X. W. Dong, Liq. Cryst.,

2004, 31, 339–345.

Z. Hussain, F. Qazi, M. I. Ahmed, A. Usman, A. Riaz and

A. D. Abbasi, Biosens. Bioelectron., 2016, 85, 110–127.

30 D. Davarci, CBU J. Sci., 2016, 12, 535–542.

S. Singh and D. Dunmur, Liquid crystals: Fundamentals, 31 M. Hird, J. W. Goodby, N. Gough and K. J. Toyne, J. Mater.

World Scientic, 2002, pp. 1–3. Chem., 2001, 11, 2732–2742.

P. J. Collings and M. Hird, Introduction to Liquid Crystal: 32 Z. Jamain, M. Khairuddean and S. A. Saidin, J. Mol. Struct.,

Chemistry and Physic, Taylor & Francis, MIT Press, London,

997.

0 P. J. Collings, Liquid Crystals: Nature's Delicate Phase of

2019, 1186, 293–302.

33 Z. Jamain, M. Khairuddean and T. Guan-Seng, Int. J. Mol.

Sci., 2020, 21, 4267.

1

Matter, Princeton Univ. Press, New Jersey, 2nd edn, 2002, 34 E. L. Heeley, D. J. Hughes, Y. El Aziz, I. Williamson,

p. 204.

P. G. Taylor and A. R. Bassindale, Phys. Chem. Chem. Phys.,

2013, 15, 5518–5529.

1

2

1 C. Kim and H. R. Allcock, Macromolecules, 1987, 20, 1726–

1

727.

35 H. Kelker and R. Hatz, Handbook of liquid crystals, Verlag

Chemie, Weinheim, Germany, Deereld Beach, Florida,

USA, 1980.

2 K. Moriya, H. Mizusaki, M. Kato, T. Suzuki, S. Yano,

M. Kajiwara and K. Tashiro, Chem. Mater., 1997, 9, 255–263.

3 K. Moriya, T. Suzuki, H. Mizusaki, S. Yano and M. Kajiwara, 36 Z. Jamain, M. Khairuddean and T. Guan-Seng, Molecules,

Chem. Lett., 1997, 26, 1001–1002. 2020, 25, 2122.

4 D. Frenkel and B. M. Mulder, Mol. Phys., 1985, 55, 1171– 37 J. A. Uhood, E. G. Tarik and H. R. Howraa, Molecules, 2010,

192. 15, 5620–5628.

1

5 Z. Jamain, M. Khairuddean, N. N. Zulbaharen and 38 Z. Galewski and H. J. Coles, J. Mol. Liq., 1999, 79, 77–87.

T. K. Chung, Malaysian Journal of Chemistry, 2019, 21, 73–85. 39 H. S. El-Wahab, Pigm. Resin Technol., 2015, 44, 101–110.

6 K. V ´a clav, H. Martin, S. Ji ˇr ´ı , N. Vladim ´ı ra and P. Damian, Liq. 40 S. Zahra, J. Nasrin and S. Shahla, Carbohydr. Polym., 2015,

Cryst., 2012, 39, 943–955.

118, 183–198.

7 G. W. Gray, Molecular structure and the properties of liquid 41 W. De-Yi, Novel Fire Retardant Polymers and Composite

crystals, Academic Press, London, 1962.

8 L. Jim ´e nez, A. Laguna, A. M. Molter, J. L. Serrano, J. Barbera

and L. Oriol, Chem.–Eur. J., 2011, 17, 1029–1039.

9 Q. He, H. Dai, X. Tan, X. Cheng, F. Liu and C. Tschierske, J.

Mater. Chem. C, 2013, 1, 7148–7154.

Materials, Woodhead Publishing Series in Composites Science

and Engineering: Number 73, 2017.

42 K. A. Salmeia, S. Gaan and G. Malucelli, Polymers, 2016, 8,

319–355.

43 H. Chun-Chieh, C. Yu-Chaing, C. San-Yuan and L. Hong-

Cheu, RSC Adv., 2016, 6, 32319–32327.

0 Y. Jae Shin, Y. Rok Ham, S. H. Kim, D. H. Lee, S. B. Kim,

C. S. Park, Y. M. Yoo, J. G. Kim, S. H. Kwon and J. S. Shin, 44 A. H. Davidson, S. J. Davies and D. F. C. Moﬀat, PCT Int.

J. Ind. Eng. Chem., 2010, 16, 364–367. Appl., 2006, 2006117552.

1 Y. L. Liu, Y. C. Chiu and T. Y. Chen, Polym. Int., 2003, 52, 45 Z. Shaoyu and X. Jiangbing, Faming Zhuanli Shenqing,

256–1261. CN102618062, 2012.

2 K. Faghihi and M. Hagibeygi, Turk. J. Chem., 2007, 31, 65–73. 46 A. P. Avdeenko and I. L. Marchenko, Russ. J. Org. Chem.,

2

1

2

3 X. Zhang, Y. Zhong and Z. Mao, Polym. Degrad. Stab., 2012,

7, 1504–1510.

4 Y. Rong, H. Wentian, X. Liang, S. Yan and L. Jinchun, Polym.

Degrad. Stab., 2015, 122, 102–109.

2001, 37, 822–829.

9

47 G. Fareed, M. A. Versiani, N. Afza, N. Fareed, M. A. Kalhoro,

S. Yasmeen and M. A. Anwar, J. Chem. Soc. Pak., 2013, 35,

427–431.

2

25 Y. Rong, W. Bo, H. Xiaofeng, M. Binbin and L. Jinchun, 48 Z. Deyan, W. Yangyang, J. Jiong, Y. Wenzhu, Q. Baofeng,

Polym. Degrad. Stab., 2017, 144, 62–69.

L. Xia and S. Xuan, ChemComm, 2015, 51, 10656–10659.

28934 | RSC Adv., 2020, 10, 28918–28934

Article Doi

Synthesis of novel liquid crystalline and fire retardant molecules based on six-armed cyclotriphosphazene core containing Schiff base and amide linking units

DOI: 10.1039/d0ra03812a

Source and publish data:

Authors:

Article abstract of DOI:10.1039/d0ra03812a

Full text of DOI:10.1039/d0ra03812a

Products guided by the article

R&D Labs maybe for 15872-42-1

Relevant to this article

Hot Product