Synthesis, crystal structure, and flame retardance of 2-(3-silatranyl- propylamino)-4-(2,4-dichlorophenyl)-5,5-dimethyl-1,3,2-dioxaphosphinane-2- sulfide

Article abstract of DOI:10.1080/10426507.2012.657311

2-(3-Silatranylpropylamino)-4-(2,4-dichlorophenyl)-5,5-dimethyl-1,3,2-dioxa phosphinane-2-sulfide 4 was synthesized by a nucleophilic substitution reaction of 2-chloro-1,3,2-dioxaphosphinane-2-sulfide 2 with -aminopropylsilatrane 3, which was prepared by the cyclization reaction of triethanolamine and -aminopropyltriethoxysilane. The structure of the title compound was confirmed by IR, ¹H NMR, ³¹P NMR, EI-MS, and elemental analysis as well as by single crystal X-ray diffraction and its thermal properties were studied by thermogravimetry (TG) and differential scanning calorimetry (DSC). Thermal analysis and preliminary fire retardance testing suggest that compound 4 should function as a good flame retardant.

Full text of DOI:10.1080/10426507.2012.657311

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Phosphorus, Sulfur, and Silicon and the
Related Elements
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Synthesis, Crystal Structure,
and Flame Retardance of 2-(3-
Silatranyl-Propylamino)-4-(2,4-
Dichlorophenyl)-5,5-Dimethyl-1,3,2-
Dioxaphosphinane-2-Sulfide
De-Jian Wang a , Qiong-Lin Mou a , Shi-Guan Wan b , Xin-Jian Song a
& Da-Ting Tian a
a Key Laboratory of Biological Resources Protection and Utilization
of Hubei Province, School of Chemical and Environmental
Engineering , Hubei University for Nationalities , Enshi , Hubei ,
People's Republic of China
b Guangdong Tyen Chemicals Co., Ltd. , Foshan , Guangdong ,
People's Republic of China
Accepted author version posted online: 23 Jan 2012.Published
online: 07 Jun 2012.
To cite this article: De-Jian Wang , Qiong-Lin Mou , Shi-Guan Wan , Xin-Jian Song & Da-Ting Tian
(2012) Synthesis, Crystal Structure, and Flame Retardance of 2-(3-Silatranyl-Propylamino)-4-(2,4-
Dichlorophenyl)-5,5-Dimethyl-1,3,2-Dioxaphosphinane-2-Sulfide, Phosphorus, Sulfur, and Silicon and
the Related Elements, 187:8, 944-951, DOI: 10.1080/10426507.2012.657311
To link to this article: http://dx.doi.org/10.1080/10426507.2012.657311
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Phosphorus, Sulfur, and Silicon, 187:944–951, 2012
Copyright ꢀC Taylor & Francis Group, LLC
ISSN: 1042-6507 print / 1563-5325 online
DOI: 10.1080/10426507.2012.657311
SYNTHESIS, CRYSTAL STRUCTURE, AND FLAME
RETARDANCE OF 2-(3-SILATRANYL-PROPYLAMINO)-4-
(2,4-DICHLOROPHENYL)-5,5-DIMETHYL-1,3,2-
DIOXAPHOSPHINANE-2-SULFIDE
De-Jian Wang,1 Qiong-Lin Mou,1 Shi-Guan Wan,2
Xin-Jian Song,1 and Da-Ting Tian1
1Key Laboratory of Biological Resources Protection and Utilization of Hubei
Province, School of Chemical and Environmental Engineering, Hubei University
for Nationalities, Enshi, Hubei, People’s Republic of China
2Guangdong Tyen Chemicals Co., Ltd., Foshan, Guangdong, People’s Republic
of China
GRAPHICAL ABSTRACT
Abstract
2-(3-Silatranylpropylamino)-4-(2,4-dichlorophenyl)-5,5-dimethyl-1,3,2-dioxa
phosphinane-2-sulfide 4 was synthesized by a nucleophilic substitution reaction of 2-chloro-
1,3,2-dioxaphosphinane-2-sulfide 2 with γ -aminopropylsilatrane 3, which was prepared by
the cyclization reaction of triethanolamine and γ -aminopropyltriethoxysilane. The structure
of the title compound was confirmed by IR, 1H NMR, 31P NMR, EI-MS, and elemental analysis
as well as by single crystal X-ray diffraction and its thermal properties were studied by
thermogravimetry (TG) and differential scanning calorimetry (DSC). Thermal analysis and
preliminary fire retardance testing suggest that compound 4 should function as a good flame
retardant.
Keywords Crystal structure; flame retardance; (sulfur substituted)phosphonoaminopropyl
silatrane; thermal property
Received 6 November 2011; accepted 10 January 2012.
The authors are thankfully acknowledge grants received from the National Nature Science Foundation of
Hubei Province (No. 2011CDB087), the Key Project of Hubei Provincial Education Department (No. Q20111904),
and the Project of Team Research for Excellent Mid-Aged & Young Teachers of Higher Education of Hubei
Province, China (No. T201006).
Address correspondence to Xin-Jian Song, Key Laboratory of Biological Resources Protection and Utiliza-
tion of Hubei Province, School of Chemical and Environmental Engineering, Hubei University for Nationalities,
Enshi, Hubei 445000, P. R. China. E-mail: whxjsong@yahoo.com.cn
944

SYNTHESIS, CRYSTAL STRUCTURE, AND FLAME RETARDANCE
945
INTRODUCTION
Flame retardants have been extensively used for polymer materials. There is a grow-
ing demand for new, environmental friendly flame retardants in modern society. Although
halogenated flame retardants have been widely applied because of their excellent flame re-
tarding effect, they are currently being phased out due to perceived environmental concerns
such as the emission of toxic gases and corrosive smoke emission upon combustion.1,2 Thus,
more and more attention has been paid to such halogen-free flame retardants as intumescent
flame retardants (IFR), especially nitrogen-phosphorus intumescent flame retardants owing
to their high efficiency and low toxicity.3–6 Silicon-containing compounds can significantly
enhance the flame retardance of a polymer through both char formation in the condensed
phase and the trapping of active radicals in the vapor phase.7–9 In addition, sulfur is an
important antiflaming element.10–13 The inclusion of sulfur within the chemical structure
may play a role in cooperativity with the elements of phosphorus, nitrogen, and silicon in
the same flame retardant. However, there have been no reports on flame retardants simul-
taneously containing phosphorus, nitrogen, sulfur, and silicon. In view of these, and as a
continuation of our search for good flame retardants and research on the stereochemistry
of (sulfur substituted)phosphonoaminopropylsilatrane, 2-(3-silatranylpropylamino)-4-(2,4-
dichlorophenyl)-5,5-dimethyl-1,3,2-dioxaphosphinane-2-sulfide was investigated, focused
on its preparation, crystal structure together with thermal stability, and flame retardance.
The synthetic route of the title compound 4 is outlined in Scheme 1.
Cl
Cl
Cl
Cl
Cl
S
P
PSCl3
O
OH
KOH
CHO
+
CHO
Cl
Cl
EtOH
O
OH
2
1
OCH2CH2
OCH2CH3
N(CH2CH2OH)3
NH2CH2CH2CH2 Si OCH2CH3
OCH2CH3
Si
N
NH2CH2CH2CH2
OCH2CH2
OCH2CH2
reflux
3
Cl
Cl
Cl
Cl
S
O
S
O
O
O
P
Cl
O
N
P
2
Si
N
O
H
O
4
Scheme 1 An outline of the synthetic route of the title compound 4.

946
D.-J. WANG ET AL.
RESULTS AND DISCUSSION
Synthesis
The synthesis was initiated by allowing easily accessible 2,4-dichlorobenzaldehyde
to react with isobutyraldehyde in the presence of potassium hydroxide to form diol 1 which
readily reacted with phosphorus thiochloride to afford 2-chloro-1,3,2-dioxaphosphinane-
2-sulfide 2.14 Nucleophilic substitution reaction of 2 with γ -aminopropylsilatrane 3 gave
the target compound 4. In this step, triethylamine needed to be added as an acid binding
agent which resulted in a shorter reaction time and higher isolated yield. The structure of
the title compound 4 was characterized by IR, 1H NMR, 31P NMR, EI-MS, and elemental
analysis. These spectroscopic data are in good agreement with the assumed structure.
Crystal Structure Analysis
The selected bond lengths and angles are listed in Table 1 and the X-ray data are
summarized in Table 2. The molecular structure, the packing diagram, and hydrogen-bond
dimer of 4 are depicted in Figure 1, and Figures S 1 and S 2, respectively. Significant
hydrogen bonding is demonstrated by the data presented in Table S 1. (Figures S 1 and S 2,
and Table S 1 are included in the Supplemental Materials, available online.)
The crystal structure of 4 (Figure 1) reveals that the cyclic dioxaphosphinane ring
in the molecule adopts a thermodynamically stable cis conformation, while the silatrane
fragment forms a cage-like structure in which there exists an intramolecular Si←N donor-
acceptor bond [Si1 N2 = 2.146(2) Å; see Table 1], which is remarkably longer than
an usual Si N bond (1.7–1.8 Å). In the crystal structure, centrosymmetrically related
Table 1 Selected bond lengths (Å) and bond angles (◦) for compound 4
Bond
Dist.
Bond
Dist.
S(1) P(1)
P(1) O(1)
P(1) O(2)
P(1) N(1)
Si(1) O(3)
Si(1) O(4)
Si(1) O(5)
N(2) Si(1)
O(1) C(7)
1.9298(9)
1.5987(15)
1.5810(17)
1.601(2)
1.6538(19)
1.6618(16)
1.6656(17)
2.146(2)
O(2) C(9)
O(3) C(15)
O(4) C(17)
O(5) C(19)
N(1) C(12)
N(2) C(18)
N(2) C(20)
N(2) C(16)
1.448(3)
1.408(4)
1.416(3)
1.426(3)
1.460(3)
1.464(3)
1.468(3)
1.471(3)
1.461(2)
Angle
(◦)
Angle
(◦)
O(2) P(1) O(1)
O(2) P(1) N(1)
O(1) P(1) N(1)
O(2) P(1) S(1)
O(1) P(1) S(1)
N(1) P(1) S(1)
O(3) Si(1) O(4)
O(3) Si(1) O(5)
O(4) Si(1) O(5)
O(3) Si(1) C(14)
O(4) Si(1) C(14)
101.62(9)
104.14(10)
106.49(9)
114.73(7)
113.39(6)
115.12(8)
117.66(10)
119.43(11)
117.48(9)
97.22(13)
98.84(10)
O(5) Si(1) C(14)
C(7) O(1) P(1)
C(9) O(2) P(1)
C(15) O(3) Si(1)
C(17) O(4) Si(1)
C(19) O(5) Si(1)
C(12) N(1) P(1)
C(18) N(2) C(20)
C(18) N(2) C(16)
C(20) N(2) C(16)
97.35(10)
115.41(12)
116.23(16)
122.55(17)
122.66(15)
121.60(15)
126.34(19)
113.5(2)
114.5(2)
113.6(2)

SYNTHESIS, CRYSTAL STRUCTURE, AND FLAME RETARDANCE
947
Table 2 Crystallographic data and parameters for compound 4
Empirical formula
Formula weight
CCDC deposit no.
Crystal system
Space group
a (Å)
C20H31Cl2N2O5PSSi
541.49
848545
Orthorhombic
Pbcn
13.3238(7)
18.9520(10)
20.3489(11)
90
90
90
5138.4(5)
8
1.400
b (Å)
c (Å)
α (◦)
β (◦)
γ (◦)
Volume (Å3)
Z
Density (calcd.) (Mg·m−3
)
Absorption coefficient (mm−1
F(000)
)
0.476
2272
1.87 to 28.00
θ range for data collection (◦)
Index ranges
−13 ≤ h ≤ 17, −24 ≤ k ≤ 24, −24 ≤ l ≤ 26
Reflections collected
Independent reflections
Absorption Correction
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ (I)]
R indices (all data)
Large diff. peak and hole (e·Å−3
30151
6131 [Rint = 0.0367]
None
Full-matrix least-squares on F2
6131/0/292
1.046
R1 = 0.0488, wR2 = 0.1315
R1 = 0.0715, wR2 = 0.1477
0.643 and −0.269
)
molecules are linked by pairs of N H···S hydrogen bonds into dimers, generating rings
2
with graph-set motif R2 (8) (Figure S 2 and Table S 1).
Thermal Properties
From the TG-DSC thermograms (Figure 2), it appeared that the decomposition of
the sample begins at 28◦0 ◦C and occurs in two stages. The first decomposition step occurs
between 280 and 350 C and is accompanied by a loss of 57.3% of the initial sample
mass. The second step of decomposition occurs between 350 and 600 ◦C. When reaching
◦
500 C, 32.05% char residue could be observed, illustrating a good char-formation abil-
ity and thermal stability of this fire retardant. From the corresponding DSC profile, one
endothermic peak in the first decomposition stage are noted, as is very beneficial in intu-
mescent flame retardant system according to the condensed phase flame-retardant process,
because the endothermic decomposition of flame retardant removes heat and cools the
polymer materials.
Flame Retardance
The flame retardance in epoxy E-44 of compound 4 was preliminarily evaluated
employing horizontal burning test.15 The samples (110 mm × 6 mm × 3.5 mm) were
prepared by mixing the fire retardant, epoxy resin (E-44) and curing agent (polyamide resin

948
D.-J. WANG ET AL.
Figure 1 Molecular structure of compound 4 with the atomic labeling.
Figure 2 TG-DSC thermograms of compound 4.

SYNTHESIS, CRYSTAL STRUCTURE, AND FLAME RETARDANCE
949
Table 3 Results of horizontal burning test of compound 4 (GB2408-80)
Reach the first line
Reach the second line
Burning
Compd.
(25 mm away from ignition)
(100 mm away from ignition)
length (mm)
blank
4
yes
no
yes
no
burn out
12
650) in a 1:5:4 w/w ratio. Two marked lines were drawn on each sample at a distance of
25 mm and 100 mm from the end to be ignited. The horizontal burning test was conducted
according to GB2408-80 horizontal standard. Five specimens were tested for repeatability.
The results are outlined in Table 3. Besides, the samples foam and expand when burning
without melting and dropping and with low smoking. It is evident from the results that the
title compound has good flame resistance.
CONCLUSION
In summary, the present article describes the synthesis, crystal structure, thermal sta-
bility as well as flame retardance of 2-(3-silatranylpropylamino)-4-(2,4-dichlorophenyl)-
5,5-dimethyl-1,3,2-dioxaphosphinane-2-sulfide as the first example of intumescent flame
retardants simultaneously incorporating phosphorus, nitrogen, sulfur, and silicon. Thermal
analysis and preliminary fire retardance testing in epoxy E-44 suggest that the title com-
pound should function as a good flame retardant, as may be attributed to the synergetic
effect of phosphorus, sulfur, silicon, and nitrogen elements. In spite of only a single example
and the preliminary results of fire testing presented by this work, we believe that such a
type of novel flame-retardant additives show the potential of application in epoxy resin and
other polymer materials, ready to be further investigated.
EXPERIMENTAL
Melting points were measured with an X-4 digital melting-point apparatus and un-
corrected. 1H NMR spectra were obtained using a Varian Mercury Plus-400 Spectrometer
with TMS as internal standard and DMSO-d6 as the solvent. IR spectra were recorded using
a Nicolet NEXUS 470 FT-IR spectrophotometer with KBr pellets in the range of 4000–
400 cm−1. MS spectra were performed by a Finnigan Trace MS 2000 organic mass spec-
trometer using the electron ionization (EI) method. Elemental analysis was measured by a
Perkin-Elmer CHN 2400 elemental analyzer. X-ray diffraction data were collected using a
Bruker Smart APEX-CCD diffractometer equipped with a graphite-monochromatized Mo
Kα (λ = 0.71073 Å) radiation. DSC experiments were carried out with a CDR-1 thermal
analyzer at a heating rate of 10 K/min under a nitrogen flow. 1-(2,4-Dichlorophenyl)-2,2-
dimethylpropane-1,3-diol 1 was prepared according to a previously reported method.16,17
Synthesis of the Title Compound 4
To a stirred solution of 1 (10 mmol, 1.75 g) and phosphorus thiochloride (10 mmol)
in dry tetrahydrofuran (8 mL), a solution of triethylamine (11 mmol) in dry tetrahydrofuran
(8 mL) was dropwise added over 1 h at ice-bath temperature, then at room temperture with
stirring for 14 h. After filtration, the solvent was removed under reduced pressure, and

950
D.-J. WANG ET AL.
the residual mixture was recrystallized from cyclohexane to afford white crystals 2. mp:
122–123 ◦C; Yield: 65%.
Triethanolamine (10 mmol, 1.49 g) and aminopropyltriethoxysilane (10 mmol, 2.21 g)
were placed into a 100-mL, round-bottomed, three-necked flask fitted with a thermometer
and a reflux condenser. The mixture was stirred at reflux for 3 h. The ethanol produced
was removed by distillation at reduced pressure to afford γ -aminopropylsilatrane 3 in 83%
yield as white solid. mp: 87–88 ◦C (Lit.18 87.2–87.9 ◦C).
To a mixture of γ -aminopropylsilatrane 3 (5 mmol, 1.16 g), triethylamine
(6 mmol), and anhydrous 1,2-dichloroethane (15 mL), a solution of 2 (5 mmol, 1.73 g)
in anhydrous 1,2-dichloroethane (5 mL) was added dropwise. The reaction mixture was
stirred for 3 h at room temperature. The solvent was removed under reduced pressure
and the residue was washed twice with a little water and was recrystallized from
ethanol-water to give 2-(3-silatranylpropylamino)-4-(2,4-dichlorophenyl)-5,5-dimethyl-
◦
1,3,2-dioxaphosphinane-2-sulfide 4 in 76% yield as yellowish crystals. mp: 187–188 C;
1H NMR (DMSO-d6, 400 MHz): δ 7.45-7.70 (m, 3H, Ar-H), 6.06 (t, J = 10 Hz, 1H, NH),
5.80 (s, 1H, OCH), 3.33-3.94 (m, 8H, OCH2), 2.51-2.94 (m, 8H, NCH2), 1.49-1.55 (m,
2H, C-CH2), 1.48 (s, 3H, CH3), 1.02 (s, 3H, CH3), 0.16 (t, J = 8 Hz, 2H, SiCH2); 31P
NMR (DMSO-d6, 400 MHz): δ 70.1; IR (KBr, ν in cm−1): 3229 (N H), 1096 and 1005
(P O C), 1027 (Si O C), 751 (P S); EI-MS (%): m/z 329 (0.6), 299 (1.5), 270 (6.7),
174 (100), 129 (7.8), 91 (2.6). Anal. Calcd. for C20H31Cl2N2O5PSSi: C 44.36, H 5.77, P
5.72; Found: C 44.51, H 5.68, P 5.85.
Crystallographic Measurement
The colorless crystals of compound 4 were obtained by vapor diffusion of THF in
dimethylformamide at room temperature. A single crystal with dimensions of 0.24 × 0.24 ×
0.20 mm3 was selected and mounted on a BRUKER SMART APEX-CCD diffractometer.
The intensity data were collected by using a ψ-ω scan mode at 298(2) K. Absorption
correction was not applied. The structure was solved by direct methods with SHELXS-9719
and expanded using Fourier difference techniques. Structural refinement was carried out
by full-matrix least-squares techniques on F2 using the SHELXL-97 package.
SUPPLEMENTARY MATERIAL
Crystallographic data for compound 4 have been deposited in the Cambridge Crys-
tallographic Data Center (Deposition No. CCDC-848545). These data can be obtained free
of charge via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crystal-
lographic Data Centre, 12, Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033;
or deposit@ccdc.cam.ac.uk).
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