Synthesis of novel 1,2-diol containing azo dyes for polymeric substrates

Article abstract of DOI:10.4067/S0717-97072017000200014

Two novel 1,2-diol containing azo dyes have been synthesized for application on polymeric textile substrates. We used multistep synthesis scheme which involved selectively bonding azo chromophore with glycerol moiety such that only one alcohol out of the three gets bonded to the chromophore while rest two remain unchanged. The 1,2-diol moiety, common in both dyes, is responsible for forming hydrogen bonds with polar sites on a polymeric substrate. The molecular structure of the final molecule and synthesized intermediates were elucidated by UV/Vis, FT-IR, MS (EI, ESI, and CI) and ¹H-NMR spectroscopic techniques. Dyes were applied to polyester and nylon 66 fabrics as disperse dyes by exhaust dyeing method and furnished good to excellent fastness properties on both of them.

Full text of DOI:10.4067/S0717-97072017000200014

J. Chil. Chem. Soc., 62, Nº 2 (2017)
SYNTHESIS OF NOVEL 1,2-DIOL CONTAINING AZO DYES FOR POLYMERIC SUBSTRATES
HAMDULLAH KHADIM SHEIKH*, MEHDI HASSAN KAZMI
Department of Applied Chemistry & Chemical technology, University of Karachi. KU Circular Road, Karachi 75270, Pakistan.
ABSTRACT
Two novel 1,2-diol containing azo dyes have been synthesized for application on polymeric textile substrates. We used multistep synthesis scheme which
involved selectively bonding azo chromophore with glycerol moiety such that only one alcohol out of the three gets bonded to the chromophore while rest two
remain unchanged. The 1,2-diol moiety, common in both dyes, is responsible for forming hydrogen bonds with polar sites on a polymeric substrate. The molecular
1
structure of the final molecule and synthesized intermediates were elucidated by UV/Vis, FT-IR, MS (EI, ESI, and CI) and H-NMR spectroscopic techniques.
Dyes were applied to polyester and nylon 66 fabrics as disperse dyes by exhaust dyeing method and furnished good to excellent fastness properties on both of them.
Keywords: Azo chromophore, Glycerol, Hydrogen bond, Polyester, Nylon 66
mass spectrometer. EI-MS was recorded on Varian MAT 312 spectrometer.
CI-MS was recorded on JOEL JM S-600H mass spectrometer. All reactions
and purity were monitored by thin layer chromatography (TLC), performed
on Merck pre-coated silica gel 60 F254 20 x 20 cm aluminum sheets and spots
seen under UV light at 254 and 366 nm. Dyeing was carried out on Roaches
Model-S multi bath dyeing machine. Imerol X nonionic detergent, Laval RDN
dispersing agent, PES and nylon 66 fabrics were acquired from Archroma
Pakistan limited.
INTRODUCTION
Other than ionic or covalent bonding, hydrogen bonding along with dipole-
dipole interaction and dispersion forces are the major modes of intermolecular
interaction between dye molecule and substrates specifically in textile synthetic
fiber dyeing1,2. Recently, there has been a lot of interest in synthesis of new
disperse dyes3,4,5,6. Almost all these newly developed dyes are small planar
molecules that can easily penetrate in between the polymeric chains of fiber.
Usually, they contain protic or aprotic polar groups that are capable of forming
hydrogen bonds with polar sites (mostly hydrogen bond acceptor groups) of
the polymeric substrates. Higher number of polar sites in the dye molecule
results in more dyeing affinity and better fastness properties because of
intermolecular interaction between these sites within fiber and dye molecule7.
Our work is aimed at exploring the potential utility of polyhydric alcohols in
combination with azo chromophore to form a disperse dye with superior dye-
fiber interaction capacity. The designed glycerol azo dyes E and F are small
and planar molecules that can easily enter the space between polymeric chains
of the substrate while on the edge of the molecule they wield two vicinal OH
sites that are capable of interacting with polar sites on the substrate (Figure 1).
This results in better fixation and fastness properties. Selection of polyhydric
alcohols was based upon that fact that OH group forms stronger hydrogen
bonds compared to other protic moieties like amines because of larger
electronegativity difference between O and H 8.
Synthesis:
(2,2-Dimethyl-1,3-dioxolan-4-yl)methanol (A):
Glycerol (0.246 mol) and acetone (0.738 mol) were heated to reflux in
the presence of p-toluenesulfonic acid (0.68 gm) for 10 hours. Reaction vessel
was then brought to room temperature and cold Na2CO3 solution (0.035 M)
was added to it. Organic product layer was extracted with dichloromethane
(DCM), dried over sodium sulfate. Evaporation of the solvent gave the pure 1,
2 isopropylidene glycerol (solketal) A.
Colorless liquid; yield: 71 %; b.p. 189 oC; UV-Vis (13.5 M in Ethyl
acetate) [λmax, nm (εmax,L mol-1 cm-1)] 271.0 (0.29); IR (KBr) νmax (cm-1): 3416.7
(O-H alcohol), 2935.5 (C-H aliphatic), 1120.0 (C-O ether), 1051.1 (C-O 1o
alcohol); 1H-NMR (CDCl3, 300 MHz, 25 °C, TMS) δ (ppm): 1.33 (3H,s, C H3),
1.40 (3H, s, C H3), 3.58 (1H, m, -C4H -O-), 3.67 (1H, m, -C4H -O-), 3.77 1(1H,
m, -C6H2-O-),24.02 (1H, m, -C6H2-O-)2, 4.21 (1H,m, -C5H-O-); 2EI-MS m/z (rel.
int.): 132 [M]+(1.02), 117 (28.68) [M-CH3]+, 101 (50.29) [M- CH3O] +, 73
(42.13) [M-C3H7O]+, 57 (100) [M-C3H72O]+.
Synthesis route (Scheme 1) involved bonding the partially protected form
of glycerol A with 4-(dimethylamino)benzoic acid to form C (Couplar I). For
the synthesis of F, C was directly coupled with diazonium compound. For
the synthesis of E, C was deprotected in acidic conditions to reform the diol
moiety. The resultant molecule D (Couplar II) served as a coupling component
that coupled with a diazonium compound to form azo chromophore E. D
(Couplar II) with its two vicinal OH groups, provides the opportunity to further
modify the structure of coupling component before chromophore formation.
(2,2-Dimethyl-1,3-dioxolan-4-yl)methyl 4-(dimethylamino)benzoate (C):
4-(dimethylamino)benzoic acid (5 x 10-3mol) and carbonyldiimidazole (5
x 10-3mol) were dissolved in THF (30 ml). After 2 hours of stirring, solketal
A (0.0125 mol) was added into the vessel along with triethylamine base (0.52
ml). Reaction mixture was left stirring for 48 hours after which solvent was
dried off. Solid reaction mixture was poured into 0.05 M solution of Na2CO3.
The obtained precipitate of the product was filtered, washed again with water,
extracted with dichloromethane and was dried over sodium sulfate. Evaporation
of solvent gave the ester product C.
We selected azo chromophore to play the role of color imparting part in
our intended molecule. Azo dyes represent by far the most significant class
of commercial organic dyes. They account for 60-70 % of the dye used in
traditional textile application9. Azo chromophore synthesis also provides the
margin to tune up the intended molecular properties as per requirement.
EXPERIMENTAL
o
White solid; yield: 40 %; m.p. 89 C; UV-Vis (3.58 x 10-5 M in Ethyl
acetate) [λmax, nm (εmax, L mol-1 cm-1)] 310.0 (57725.1); IR (KBr) νmax (cm-
1): 2934.53 (C-H aliphatic), 1692.74 (C=O ester), 1614.41 (C=C aromatic),
1277.52 (C-O ester), 1205.94 (C-N amine), 1105.42 (C-O ether) cm-1; 1H-NMR
(CDCl3, 400 MHz, 25 °C, TMS) δ (ppm): 1.37 (3H, s, C1H3), 1.43 (3H, s, C2H3),
3.04 (6H, s, C H3, C15H3), 3.86 (1H, m, -C4H -O-), 4.13 (1H, m, -C4H -O-),
4.34 (2H, m, -1C4 6H2-O), 4.43 (1H, m, -C5H-O-)2, 6.84 (2H, d, J= 8.8 Hz, 2C10H,
C12H), 7.96 (2H, d, J = 8.8 Hz, C9H, C13H); (+)ESI-MS m/z: 280.1 [M+H]+),
222.1 [M-C3H5O4]+, 148.1 [M- C3H11O3]+, 122.6 [M- C7H9O4]+.
Materials:
All the reagents and solvents were obtained from Merck Millipore and
Sigma-Aldrich Chemical Company, USA. All the solvents were of analytical
grade and were dried using standard methods. Melting points were recorded
on Griffin MFB-590 melting point apparatus and are uncorrected. IR spectra
were registered on Jasco-320-A spectrophotometer using KBr discs. UV-
Vis spectra were recorded on Thermoscientific evolution-300 UV-Vis
spectrophotometer.1H-NMR spectra were recorded in CDCl3 with SiMe4 as the
internal standard at 300, 400 and 500 MHz on different types of Bruker Avance
AM spectrometers. ESI-MS were recorded on QSTAR XL Hybrid LC/MS/MS
2,3-Dihydroxypropyl 4-(dimethylamino)benzoate (D):
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e-mail: hamdullah.khadim.sheikh@gmail.com

J. Chil. Chem. Soc., 62, Nº 2 (2017)
Product C (3 x 10-3mol) and boric acid (0.032 mol) is dissolved in the 25
ml of diglyme and H O mixture (4:1). Temperature was raised to 100 0C and
reaction is continued 2for 3.5 hours. The reaction mass is then cooled down
to room temperature and solvent is evaporated under vacuum. Solid product
mass is dissolved in water and extracted with dichloromethane. Dissolved
product is dried over sodium sulfate. Evaporation of dichloromethane gave the
deprotected product D.
8.8 Hz, C15H, C17H), 8.01 (1H, s, C10H); (-)CI-MS m/z: 387.1 [M-H]-, 371.1
[M-OH]-, 266.1 [M-C H4NO2]-; Anal. Calc. for C H20N4O : C, 55.67; H, 5.19;
N, 14.43; O, 24.72 %.6Found: 55.64; H, 5.18; N,118 4.45; O6, 24.70 %.
2,3-Dihydroxypropyl 3-[(4-acetylphenyl)azo]-4-(dimethylamino)benzoate
(F):
Sodium nitrite (2.85 x 10-3mol) was dissolved in 10 ml of water and cooled
White solid; yield: 95 %; m.p. 90 °C; UV-Vis (4.18 x 10-5 M in Ethyl
acetate) [λmax, nm (ε , L mol-1 cm-1)] 310.0 (49450.2); IR (KBr) ν (cm-1):
3459.0 (O-H alcohoml)a,x 2934.0 (C-H aliphatic), 1693.0 (C=O ester)m, a1x 611.81
(C=C aromatic), 1277.52 (C-O ester), 1206.17 (C-N amine), 1038.32 (C-O
to 0 C. In a separate pre-chilled beaker at 0 C, 4-aminoacetophenone (2.85
x 10-3mol) was taken along with HCl (5.7 x 10-3mol). Sodium nitrite solution
was slowly added dropwise to the nitroaniline and HCl vessel. In another
o
o
vessel, C (2.85 x 10-3mol) was stirred in 100 ml ethanol and cooled to 0 C.
o
1
1o alcohol), 1105.06 (C-O 2o alcohol); H-NMR (CDCl3, 400 MHz, 25 °C,
Diazonium solution of 4-aminoacetophenone was slowly added to the vessel
containing coupling component C while maintaining pH with 2 % sodium
acetate solution. Reaction mixture is stirred at constant conditions for 4 hours
after which azo compound starts to precipitate out, which is filtered. Solid
product mass is then dissolved in water and extracted with dichloromethane,
dried over sodium sulfate. Evaporation of solvent gave the azo product F which
was further purified by column chromatography (ethyl acetate: hexane).
TMS) δ (ppm): 3.05 (6H,s, C11H , C12H3), 3.86 (1H, m, C1H -O-), 4.13 (1H,
m, C1H -O-), 4.34 (2H, m, C3H2-3O-), 4.43 (1H, m, C2H-O-), 26.92 (2H, d, J=
8.4 Hz,2C7H, C9H), 7.98 (2H, d, J = 8.8 Hz, C6H, C10H); (+)ESI-MS m/z: 240.1
[M+H]+, 207.1 [M- CH4O]+, 166 [M- C3H52O]+, 148 [M- C3H7O3]+.
2,3-Dihydroxypropyl 4-(dimethylamino)-3-(4-nitrophenyl)azo]benzoate
(E):
Rust colored powder; yield: 65 %; m.p. 130 oC; Rf: 0.40 (Ethyl
acetate:Hexane, 1:9); UV-Vis (7.27 x 10-5 M in DMF) [λmax, nm (εmax, L mol-1
cm-1) ]: 415.0 (41265.4); IR (KBr) νmax (cm-1): 3442.7 (O-H alcohol), 2923.9
(C-H aliphatic), 1693.4 (C=O ester), 1680.0 (C=O ketone), 1608.5 (C=C),
1519.8 (N=N azo), 1274.9 (C-O ester), 1188.1 (C-N amine), 1043.4 (C-O 1o
alcohol), 1105.1 (C-O 2o alcohol); 1H-NMR (CDCl3, 500 MHz, 25 °C, TMS) δ
(ppm): 2.59 (3H, s, C20H3), 3.05 (6H, s, C11H3, C H ), 3.86 (1H, m, C1H2-O-),
4.13 (1H, m, C1H2-O-), 4.34 (2H, m, C3H2-O-),124.344 (1H, m, C H-O-), 7.49
(1H, d, J= 8.5 Hz, C H), 7.97 (2H, d, J= 8.0 Hz, C H, C18H), 7.829 (1H, d, J=
9.0 Hz, C6H), 8.01(27H, d, J= 8.5 Hz, C15H, C17H), 184.02 (1H, s, C10H).); (-)CI-
MS m/z: 384.1 [M-H]-, 324.1 [M-C H O ]-, 266.1 [M-C8H7O]-; Anal. Calc. for
Nitroaniline (2.85 x 10-3mol) was taken in a beaker along with 5.7 x 10-
o
3mol of HCl. Mixture was cooled to 0 C. In another vessel sodium nitrite
(2.85 x 10-3mol) was dissolved in 10 ml of water and cooled to 0 oC. Sodium
nitrite solution was slowly added dropwise to the nitroaniline and HCl vessel.
In another vessel, 2.85 x 10-3mol of D was dissolved in 100 ml ethanol and
0
brought to 0 C. Diazonium solution of nitroaniline was slowly added to the
vessel containing D while maintaining the pH at 5.5 with 2 % sodium acetate
solution. Reaction mixture is stirred at constant conditions for 2.5 hours after
which azo compound starts to precipitate out, which is filtered. Solid product
mass is then dissolved in water and extracted with dichloromethane, dried over
sodium sulfate. Evaporation of dichloromethane gave the azo product E.
2
C H23N3O5: C, 62.33; H, 6.01; N, 10.950; 2O, 20.76 %. Found: C, 62.34; H, 6.00;
N2,010.88; O, 20.77 %.
Brightredpowder;yield:76%;m.p. 135oC;Rf:0.56(Ethylacetate:Hexane,
1:9); UV-Vis (5.15 x 10-5 M in DMF) [λmax, nm (εmax, L mol-1 cm-1)] 494.0
(60194.1); IR (KBr) ν (cm-1): 3442.7 (O-H alcohol), 2923.9 (C-H aliphatic),
1697.2 (C=O ester), 1m6a0x 8.5 (C=C aromatic), 1514.0 (N=N azo), 1371.3 (N-O
nitro), 1278.7 (C-O ester), 1118.1 (C-N amine), 1039.6 (C-O 1o alcohol),
Dyeing process:
Same dyeing procedure was used for both dyes E and F on polyester and
nylon fabrics separately with 1%, 2% and 3 % dye o.w.f (on weight of fabric).
Fabric (10 gm) was first prewashed in the liquor ratio of 1:20 with a nonionic
detergent imerol X (2 g/L) in presence of sodium carbonate (2 g/L) at 70 oC for
30 mins. Fabric was then allowed to dry.
1105.1 (C-O 2o alcohol); H-NMR (CDCl3, 400 MHz, 25 °C, TMS) δ (ppm):
1
3.03 (6H, s, C11H3, C12H ), 3.86 (1H, m, C H -O-), 4.13 (1H, m, -C1H2-O-), 4.34
(2H, m, C3H2-O-), 4.433(1H, m, C2H-O-)1, 62.86 (1H, d, J= 8.4 Hz, C7H), 7.54
(2H, d, J= 8.8 Hz, C14H, C18H), 7.69 (1H, d, J= 8.8 Hz, C6H), 7.93 (2H, d, J=
Figure 1.- 1,2- Diol moiety of dye molecule forming hydrogen bonds with adjacent polyester chains.
10 gm of prewashed fabric was immersed in an aqueous bath maintained at
60 oC with a liquor ratio of 1:20. pH at 5.5 was adjusted by acetic acid (10 %).
2 g/L of dispersing agent lycol RDN was added to the bath. The sample was
allowed to run for about 15 mins then 0.5 g/L (1% dye o.w.f) dye was added
to the liquor. Temperature was increased from 60 to 100 oC at the rate of 2 oC/
min followed by further elevation from 100 oC to 120 oC at 1 oC/min. Dyeing
was allowed to carry on for 60 mins. Dyeing vessel was then cooled back to 75
oC at 3 oC /min. Sample was rinsed with cold water multiple times and divided
into pieces for fastness evaluation tests. Process was repeated for 2% and 3%
dye concentrations for both PES and nylon fabrics. Dyeing process is given in
Figure 2.
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J. Chil. Chem. Soc., 62, Nº 2 (2017)
Figure 2.- Dyeing process.
Color Fastness tests:
Dye’s fastness to light, sublimation, washing, rubbing and perspiration were evaluated in accordance with ISO standards ISO 105-B02,ISO 105-P01, ISO
105- C01-4, ISO 105-X12 and ISO105-E04 respectively. Grey scale was used for assessing the change in shades while blue scale was used for evaluation of light
fastness test result. The details of these tests are reported in literature10. Table 1 shows the obtained fastness results.
Table 1. Fastness evaluation.
1 % Dye o.w.f
2 % Dye o.w.f
3 % Dye o.w.f
Test
Dye E
Nylon
Dye F
Nylon 66
Dye E
Nylon
Dye F
Nylon
Dye E
Nylon
Dye F
Nylon 66
PES
PES
PES
PES
PES
PES
66
66
66
66
Light
5
5
4-5
4-5
5
5
4-5
4
5
5
4-5
4
Washing a
A
5
5
4
4
4-5
5
5
5
4-5
4-5
4
5
5
4
4
5
5
4
4
4-5
4-5
4-5
4
4-5
4-5
4
5
5
4
4
5
5
4
4
4-5
4-5
4-5
3-4
4-5
4-5
4
B
C
4
4-5
4
D
4
4
4
4
Perspiration
Acid
5
5
5
5
5
5
4-5
5
5
5
5
5
5
5
4-5
5
5
5
5
5
5
5
4-5
4-5
Alkaline
Rubbing
Dry
5
4
4
5
4
4
5
4
5
4
5
4
4
5
4
4
5
4
5
4
5
5
4
4
5
4
4
5
4
4
5
4
Wet
Sublimation
4-5
4-5
4-5
4-5
aA = ISO -105-C01, B = ISO -105-C02, C = ISO -105-C03, D = ISO -105-C04
2nd step involved esterification of an activated arene (aromatic ring
RESULTS AND DISCUSSION
with electron donating substituent) with 1,2-isopropylidene glycerol A. The
activated arene itself must have suitable electrophilic substituent group on it
that can bond with the lone 10 OH of 1,2-isopropylidene glycerol A. We chose
4-(dimethylamino)benzoic acid as shown in Figure 3. Selection of N(CH3)2
substituent on aromatic ring was based upon the fact that we needed an electron
We first partially protected the glycerol’s OH groups in such a way that
two of them get protected (1,2-isopropylidene glycerol or solketal A) and
one remains available for further reaction. Physical and spectral data showed
complete agreement to that reported in literature11.
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J. Chil. Chem. Soc., 62, Nº 2 (2017)
donating substituent on aromatic ring while it should not behave nucleophilic or basic in any way, otherwise it would interfere in the esterification step and may
end up attacking acyl imidazole of B.
Scheme 1
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J. Chil. Chem. Soc., 62, Nº 2 (2017)
substituent groups on aniline can result in different shades. Selection of
4-(dimethylamino)benzoic acid as activated arene with N(CH3)2 at para position
pays off in the azo coupling reaction, as it directs the incoming electrophile
towards its ortho position. The other substituent on the rings of C and D i.e.
C=O of ester, being a deactivating group, directs at its meta position, which
happens to be the ortho of N(CH3)2. Hence, both substituents are directing at
the same position as demonstrated by block arrows in Figure 3.
Since this research is focused on application of these compounds in the
textile wet processing industry, the water solubility of these compounds is
of high importance. Because of high alkyl content in targeted molecule and
resultant hydrophobic nature, it would be difficult to apply on the substrate
from an aqueous bath. Utilization of a dispersing agent enables the application
onto the substrates from aqueous baths. This mode of application puts this
Figure 3.- 4- (dimethylamino) benzoic acid.
For esterification, COOH of 4-(dimethylamino)benzoic acid was reacted
with 1, 1’-carbonyldimidazole12,13 that incorporated imidazole leaving group
in the carboxylic acid group to form B. A was then added to the reaction
media along with N(CH3)3 base to obtain the product C. Obtained spectral data
matched up completely with that reported in literature14.
molecule in the category of disperse dyes16,17
.
CONCLUSION
The protected OH sites of C are then deprotected in acidic media. This
step gave coupling component D (Couplar II) with open OH sites formed
separately, prior to chromophore formation. D was subsequently azo coupled
with diazotized 4-nitroaniline to afford the targeted compound E. Care was
taken in the temperature control of deprotection step as stronger acidic
condition at high temperature might result in hydrolysis of ester bond between
glycerol moiety and benzoic acid.
We designed novel 1,2-diol containing azo dyes through multistep
synthesis scheme. Presence of diol on the edge of the molecule gives rise to
stronger interaction with polar sites of the polymeric textile substrate through
hydrogen bonding. Because of such interaction, dye molecules showed good
to excellent fastness properties. Series of molecules with different chromatic
properties can be synthesized on the same pattern.
ACKNOWLEDGMENTS
Deprotection was also attempted to be infused in the diazotization step. In
a separate reaction, 4-aminoacetophenone was diazotized with sodium nitrite
in acidic conditions and the resulting diazonium compound was reacted with
intermediate C to obtain the target compound F. Acidic conditions of azo
coupling reaction were found to be capable of hydrolyzing the ketal. This
approach resulted into F. Direct azo coupling of C cuts down the deprotection
step, but it doesn’t give a 1,2-diol functional coupling component intermediate
such as D, prior to chromophore formation. Thus the opportunity to further
manipulate the coupling components structure prior to chromophore formation
ceases to exist. Product mass of F was found to contain both protected and
deprotected forms of F and required further chromatographic purification.
We thank Archroma Pakistan ltd. for their support in this project. We are
also thankful to Dean Faculty of Science of University of Karachi, Pakistan for
all the assistance in this research work.
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gives back the O-H absorption band at 3442.6 cm-1 even though there was no
prior deprotection step carried out. Similarly, the emergence of a new absorption
band at 1519.8 cm-1 indicated azo bond formation. Usually, a new peak at 1450-
1600 cm-1 after azo coupling reactions, is a sign for N=N formation15. The C=O
band also showed dual peaks due to two different types of C=O present in the
molecule. In IR spectra of E, a new peak emerged at 1514.0 cm-1 showing
formation of N=N bond.
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(2014).
In 1H-NMR of F, a singlet of three protons appeared at δ 2.59 ppm,
indicating the CH (α to the C=O) of acetophenone. In spectra of both E and
F, two doublets o3f two protons each appeared at δ 7.93 and 7.54 ppm for E
and at 8.01 and 7.97 ppm for F. These two signals represent the four aromatic
protons on the second aromatic ring (diazonium ring) of azo chromophore. The
downfield signals at δ 8.01 ppm in F and 8.97 ppm in E were that of two protons
on C15 and C , ortho to the ketone and nitro substituents respectively. Three
signals appea1r7ed for three aromatic protons on the aromatic ring of coupling
component, now part of azo chromophore. Proton on C10, ortho to both N=N
and C=O of ester, appeared at δ 8.02 ppm in F and at 8.01 ppm in spectra for E.
This signal in both dyes, is the most downfield in all of the spectra. Other two
protons on C6 and C7 i.e. ortho and meta to C=O of ester showed up at δ 7.69
and 6.86 ppm in E and at 7.89 and 7.49 ppm in F. Glycerol’s alkyl skeleton
of three carbon atoms is retained in intermediates A, C, D and subsequently in
target compounds E and F. Two distereotopic protons on C1, two on C and the
lone proton on C2, gave five multiplets in the range of δ 3.86- 4.43 p3pm in E
and at δ 3.86-4.44 ppm in F. The splitting pattern was same as that of aliphatic
protons of A, C and D. Singlet of six equivalent protons on C and C12 showed
up at δ 3.03 and 3.05 for E and F respectively. Mass spectra11(CI-MS) of both
E and F showed a common peak of 266.1 m/z which is attributed to loss of
diazonium ring with its para position substituent.
17. K. Singh, S. Singh, A. Mahajan, J. Taylor, Color. Technol., 119, 198-204,
(2003).
We used 4-nitoaniline and 4-aminoacetophenone for azo coupling with
coupling components D and C respectively, but other aniline derivatives can
also be employed. This flexibility provides the opportunity to manipulate
the chromatic and many other properties of the intended molecule. Different
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