Synthesis and thermal properties of two novel P-N compounds

Article abstract of DOI:10.14233/ajchem.2015.17956

Two novel P-N compounds were synthesized through a two-step reaction including the synthesis of 2-chloro-5,5-dimethyl-1,3,2-dioxaphosphorinane-2-oxide (M) and its reaction with 2,2,6,6-tetramethylpiperidine-4-amine and N-butyl-2,2,6,6-tetramethylpiperidin-4-amine. The structures were confirmed by NMR (1H, ¹³C, ³¹P), FT-IR and MS. Their thermal properties were also evaluated by thermogravimetric analysis (TGA). The TG curves showed that the two compounds have residues of 4.9 and 1.1 wt % at 600 °C and the temperature of maximum weight loss rate (T_max) was 292 and 255 °C, respectively.

Full text of DOI:10.14233/ajchem.2015.17956

Asian Journal of Chemistry; Vol. 27, No. 7 (2015), 2505-2507
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2015.17956
Synthesis and Thermal Properties of Two Novel P-N Compounds
*
SHANSHAN WEI, LIGONG CHEN and YANG LI
School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, P.R. China
*Corresponding author: Tel/Fax: +86 22 27406314; E-mail: liyang777@tju.edu.cn
Received: 6 May 2014;
Accepted: 22 July 2014;
Published online: 30 March 2015;
AJC-17067
Two novel P-N compounds were synthesized through a two-step reaction including the synthesis of 2-chloro-5,5-dimethyl-1,3,2-
dioxaphosphorinane-2-oxide (M) and its reaction with 2,2,6,6-tetramethylpiperidine-4-amine and N-butyl-2,2,6,6-tetramethylpiperidin-
4-amine. The structures were confirmed by NMR (1H, 13C, 31P), FT-IR and MS. Their thermal properties were also evaluated by
thermogravimetric analysis (TGA). The TG curves showed that the two compounds have residues of 4.9 and 1.1 wt % at 600 ºC and the
temperature of maximum weight loss rate (Tmax) was 292 and 255 ºC, respectively.
Keywords: Synthesis, P-N compounds, Flame retardants, Thermal properties, Tmax
.
were few reports about connecting the two parts in one mole-
cule. Therefore, we designed two novel P-N compounds i.e.,
5,5-dimethyl-2-[(2,2,6,6-tetramethylpiperidin-4-yl)amino]-
1,3,2-dioxaphosphinane-2-oxide (A) and 2-[butyl(2,2,6,6-
tetramethylpiperidin-4-yl)amino]-5,5-dimethyl-1,3,2-dioxa-
phosphinane-2-oxide (B) (Fig. 1).
INTRODUCTION
As well known, polymers have been widely employed in
the daily life of human beings because of their advantages
such as enough strength, corrosion resistance and good insu-
lation. However, the flammable, aging characters limit their
uses in many areas.
Intensive studies have been done to improve the properties
of polymers1-4. Fortunately, various additives doped in these
polymers are successfully developed.
O
O
O
O
O
H
P
N
P
N
NH
NH
O
Flame retardants (FRs) and light stabilizers (LSs) are two
important classes of polymer additives which are very helpful
in retarding the degradation processes5,6. The mono intume-
scent flame retardant (IFR) containing P-N in the molecular
was the new generation of the flame retardants as the low smoke
emission and toxic gases produced during burning, anti-
dripping property and the synergistic effect between P and N7.
It is usually composed of three parts: the carbon agent,
the acid agent and the blowing agent8-10. Some intumescent
flame retardants were synthesized though 2-chloro-5,5-
dimethyl-1,3,2-dioxaphosphorinane-2-oxide (M)11-13. It pro-
vided both carbon agent and acid agent for the flame retardants.
2,2,6,6-Tetramethylpiperidine -4-amine and its deriverates
consist of a class of efficient hindered amine light stabilizers
(HALSs) due to their ability to remain an active participant in
the Denisov cycle, forming and reforming the nitroxyl radical
intermediate14-16. It was reported that the hindered amines could
perform as the flame retardants17,18. 2,2,6,6-Tetramethylpiperi-
dine-amine has an unhindered nitrogen atom which could serve
as the blowing agent of the flame retardant. However, there
A
B
Fig. 1. Structure of compound A and B
The aim of this work was to synthesize the designed
compounds which contained the 2-chloro-5,5-dimethyl-1,3,2-
dioxaphosphorinane-2-oxide (M) and 2,2,6,6-tetramethylpiperi-
dineamine or its deriverates in the same molecule. Their thermal
properties were studied using the thermogravimetric analysis.
Further studies on the dual-function additives are in progress.
EXPERIMENTAL
Reagents and solvents were obtained from commercial
suppliers. 2,2,6,6-Tetramethyl-piperidine-4-amine and N-
butyl-2,2,6,6-tetramethylpiperidin-4-amine were kindly
supplied from Tiangang Specialty Chemicals Co., Beijing,
China. Anhydrous dichloromethane and acetonitrile were

2506 Wei et al.
Asian J. Chem.
distilled from calcium hydride and phosphorus pentoxide,
respectively. Melting points were measured on aYRT-3 Melting
Point Tester without correction. The IR spectra were recorded
with KBr pellets on a Bruker-Tensor 27 spectrometer. The NMR
spectra (1H, 13C and 31P ) were recorded on a Bruker-400 MHz
NMR spectrometer. Compounds were dissolved in CDCl3 or
MeOD and chemical shifts were referenced to TMS (1H and
13C NMR) and 85 % H3PO4 (31P NMR). MS were recorded on
an LCQ Advanced MAX mass spectrometer. The thermal
properties were measured with a STA 409 PC thermogravi-
metric (TG) analyzer at a scanning rate of 10 ºC/min under
high purity N2, from room temperature to 600 ºC. The weights
of the samples were kept within 9-12 mg.
Synthesis of 2-chloro-5,5-dimethyl[1,3,2]dioxaphos-
phorinane 2-oxide (M)11,21: A solution of phosphorus oxy-
chloride (1.53 g, 0.01 mol) in 20 mL of dichloromethane was
added dropwise over a period of 20 min from a dropping funnel
to a stirred solution of 2,2-dimethyl-1,3-propanediol (0.52 g,
5 mmol) in 50 mL of dichloromethane at reflux. Continuous
dry nitrogen purge under mild suction was used to remove the
hydrogen chloride evolved in the reaction. After the addition,
the reaction mixture was stirred at refluxing for 4 h. The progress
of the reaction was monitored by TLC. The residue was washed
with petroleum ether (60-90 ºC, 3 mL × 100 mL) and then
dried under vacuum at 0.1 MPa for 4 h at 70 ºC to give a white
solid (1.82 g). Yield: 98.6 %, m.p. 99.1-100 ºC (lit.: 94-96
ºC11). IR (KBr, νmax, cm-1): 2976, 2947, 1473, 1304, 1053, 1005,
983, 922, 786, 54811,12. 1H NMR (400 MHz, CDCl3) δ (ppm):
0.94 (3H, s), 1.35 (1H, s), 3.98-4.08 (2H, dd, J = 12 Hz, J = 28
Hz), 4.25-4.28 (2H, d, J = 12 Hz). 31P NMR (125 MHz, CDCl3)
δ (ppm): -2.6611.
Synthesis of 5,5-dimethyl-2-[(2,2,6,6-tetramethyl-
piperidin-4-yl)amino][1,3,2]dioxaphosphinane-2-oxide (A):
A mixture of 2,2,6,6-tetramethylpiperidine-4-amine (1.71 g,
0.011 mol) and triethylamine (1.30 g, 0.012 mol) dissolved in
acetonitrile (100 mL) under dry N2 were placed into a four-
necked 250 mL flask equipped with a magnet stirrer, a thermo-
meter, a reflux condenser and a dropping funnel. The inter-
mediate M (1.85 g, 0.01 mol) in acetonitrile (50 mL) was added
dropwise over a period of 1.5 h when the mixture was heated
to reflux. After the addition, the reaction mixture was kept
refluxing for 7 h, monitored by TLC. The filtrate obtained from
filtering was evaporated under reduced pressure (0.1 MPa).
The residue was dissolved in dichloromethane and washed
with distilled water to give the crude product. The solid was
further purified by recrystallization from methanol and water.
After dried under vacuum at 0.1 MPa at room temperature for
overnight, the white solid (A) was obtained (2.41 g). Yield:
79.2 %, m.p. 129.2-130.1 ºC. IR (KBr, νmax, cm-1): 3532, 3237,
2967, 1588, 1462, 1391, 1231, 1059, 1013, 827, 630, 486. 1H
NMR (400 MHz, MeOD) δ (ppm): 1.02 (3H, s), 1.16 (3H, s),
1.49 (6H, s), 1.51 (6H, s), 1.55-1.61 (2H, t, J =12 Hz), 2.07-
2.12 (2H, dd, J = 4 Hz, J = 12 Hz), 3.58-3.62 (1H, m), 3.96-
4.03 (2H, dd, J = 12 Hz, J = 16 Hz), 4.15-4.19(2H, m). 13C
NMR (100 MHz, MeOD) δ (ppm): 76.6, 76.5, 57.4, 43.3, 43.2,
42.2, 31.6, 31.5, 29.2, 23.8, 20.2, 19.7. 31P NMR (125 MHz,
MeOD) δ (ppm): 5.0. MS (ESI) m/z: calcd. for C14H29N2O3P
305.19 (positive ion), found 305.20 (positive ion).
2-[Butyl-(2,2,6,6-tetramethylpiperidin-4-yl)amino]-
5,5-dimethyl[1,3,2]dioxaphosphinane-2-oxide (B): White
solid.Yield: 81.7 %, m.p. 130.5-131.1 ºC. IR (KBr, νmax, cm-1):
3293, 2960, 1470, 1375, 1361, 1251, 1230, 1208, 1053, 1008,
817,627, 509, 487. 1H NMR (400 MHz, MeOD) δ (ppm): 0.89
(3H, s), 0.93-0.97 (3H, t, J = 8 Hz), 1.18 (6H, s), 1.24 (6H, s),
1.29-1.35 (2H, m ), 1.31 (3H, s), 1.45-1.51 (2H, m), 1.53-
1.61 (2H, m), 1.63-1.67 (2H, dd, J = 4 Hz, J = 12 Hz), 2.99-
3.07 (2H, m), 3.77-3.94 (3H, m), 4.29-4.32(2H, d, J = 12 Hz).
13C NMR (100 MHz, MeOD) δ (ppm): 77.4, 76.8, 76.0, 75.9,
51.5, 49.8, 44.1, 42.9, 42.8, 35.0, 34.4, 31.8, 31.7, 28.4, 22.4,
20.8, 20.2, 13.8. 31P NMR (125 MHz, MeOD) δ (ppm): -8.9.
MS (ESI) m/z: calcd. for C18H37N2O3P 361.25 (positive ion),
found 361.26 (positive ion).
RESULTS AND DISCUSSION
The designed compounds were synthesized through a two-
steps reaction. The synthetic route was shown in Scheme-I.
HN
NH
R
N
R
O
OH
OH
O
O
O
O
O
POCl3
P
NH
P
Cl
TEA
A
B
R=H
R=CH3(CH2)
M
–
3
Scheme-I: Synthetic rout of compound A and B
The intermediate M was prepared by the cyclization of
phosphorus oxychloride and 2,2-dimethyl-1,3-propanediol at
a high yield (98.6 %) and then reacted with 2,2,6,6-tetramethyl-
piperidine-amine and N-butyl-2,2,6,6-tetramethylpiperidin-4-
amine in acetonitrile using triethylamine as the acid binding
agent. The target compounds were obtained in yields of 79.2
and 81.7 %, respectively.
The recorded TG curves of compounds A and B were
presented in Fig. 2. The analysis showed that the initial
degradation of A was at about 200 ºC and it had a residual
mass of about 5 % at 600 ºC. The temperature of maximum
weight loss rate (Tmax) was 292 ºC with the rate of 1.36 wt %/
ºC. Between 200 and 327 ºC, a rapid degradation was observed
which might be related to the chain breakage of the P-O-C13.
During this temperature range, about 56 % mass loss was noted.
There was a major mass loss peak (272 ºC) and a minor one
(306 ºC). Between 327 and 416 ºC, a multistep decomposition
was found with the 24 % weight loss which might be associated
with the char formation13,19
.
Compared with A, the compound B showed a one-step
degradation. The highest mass-loss rate was 1.95 wt %/ºC at
254.8 ºC (Tmax of B) and the residue at 600 ºC was 1.1 wt %.
The important data of the TGA was shown in Table-1. It
was clear that both A and B met the condition that the initial
decomposition temperature of additives lower than that of the
polymers19,20. At the same time, both A and B had low residues
at high temperature (600 ºC). Therefore, further studies were
necessary on improving the char-forming efficiency of
compounds A and B.
Conclusion
Two P-N compounds were synthesized successfully with
yields of 79.2 and 81.7 %, respectively. Their chemical structures

Vol. 27, No. 7 (2015)
Synthesis and Thermal Properties of Two Novel P-N Compounds 2507
TG curves showed the residue at 600 ºC of compound A and
B was 5.0 and 1.1 wt %, respectively. The temperature of
maximum weight loss rate (Tmax) was 292 ºC with the rate of
1.36 wt%/ºC (A) and 254.8 ºC with the rate of 1.95 wt %/ºC
(B). The residues of both A and B at high temperature (600 ºC)
were low. Further researches on the properties and modifying
the compounds were required.
6
5
4
3
2
1
0
90
70
Compound
A
50
30
10
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6
5
4
3
2
1
0
90
Compound
B
70
50
30
10
-10
-30
20
120
220
320
420
520
Temperature (°C)
Fig. 2. TG curves of compounds A and B in N2 atmosphere
TABLE-1
TGA DATA OF COMPOUND A AND Ba
T-10 %
T-50 %
Tmax
Residue (wt %)
At 600 ºC
Sample
(ºC)b
(ºC)c
(ºC)d
257
200
311
244
292
255
5.0
1.1
A
B
aErrors 0.5 wt %, 1 ºC. T-10 % temperature at which the weight
b
loss of the sample was 10 %. cT-50 % temperature at which the weight
d
loss of the sample was 50 %. Tmax temperature of maximum weight
loss rate of the sample.
were characterized by 1H NMR, 13C NMR, 31P NMR, IR and
MS. The thermal properties were investigated by TGA. The