Microwave-assisted synthesis of 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane

Article abstract of DOI:10.14233/ajchem.2016.19413

1,3-Bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane was synthesized under microwave irradiation. The structure of the compound was analyzed by infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy and gas chromatography. The optimal reaction condition was obtained by the single factor method. Under the optimal condition, the overall yield could reach 83.9 % and the purity of 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane was 99.1 %. It is found that under microwave radiation the reactions are very rapid with good yield, better quality and less time is required for the completion of the reaction.

Full text of DOI:10.14233/ajchem.2016.19413

Asian Journal of Chemistry; Vol. 28, No. 3 (2016), 567-571
A
SIAN
J
OURNAL OF HEMISTRY
C
http://dx.doi.org/10.14233/ajchem.2016.19413
Microwave-Assisted Synthesis of 1,3-Bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane
1,*
2
2
2
2
XITAO CHENG1,2,*, WENHONG LI , CUNSHE ZHANG , FANGFANG HUANG , QIANJIN WANG and KUI ZHOU
1School of Chemical Engineering, Northwest University, Xi'an 710069, Shaanxi Province, P.R. China
2Shaanxi Provincial Research and Design Institute of Petroleum and Chemical Industry, Xi'an 710054, Shaanxi Province, P.R. China
*Corresponding author: Tel: +86 29 88305825; E-mail: Liwenhong@nwu.edu.cn
Received: 15 June 2015;
Accepted: 13 August 2015;
Published online: 5 December 2015;
AJC-17652
1,3-Bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane was synthesized under microwave irradiation. The structure of the compound
was analyzed by infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy and gas chromatography. The optimal reaction
condition was obtained by the single factor method. Under the optimal condition, the overall yield could reach 83.9 % and the purity of
1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane was 99.1 %. It is found that under microwave radiation the reactions are very
rapid with good yield, better quality and less time is required for the completion of the reaction.
Keywords: Microwave synthesis, Hydroxypropyl polysiloxane, Hydrosilylation, Allyloxytrimethylsilane.
industrial production for using the Grignard reagent which
was prepared in harsh conditions [1].
INTRODUCTION
Hydroxyalkyl silicone is a carbon-containing functional
group polysiloxane. Due to the high reactivity of hydroxyalkyl,
it can make polysiloxane link with organic polymers through
Si-C bond by react with -OH, -Br, -COOH and -NCO, etc. to
achieve the purpose of the silicone-modified organic polymer,
thereby greatly improving the releasability gloss, lubricity, heat
resistance, cold resistance, weather resistance and hydrolysis
resistance, etc. [1,2]. Therefore, the introduction of the hydro-
xyalkyl chain polysiloxane segment, is an effective way to
make activated carbon having a reactive silicone functional
group. The most commonly used is 1,3-bis(3-hydroxypropyl)-
1,1,3,3-tetramethyldisiloxane (BHTS).
Because of larger difficulty of BHTS preparation, the
preparation method is seldom reported. Predecessors have
conducted some research on preparation methods, Knoth used
dimethyldichlorosilane, 3-chloropropyl alcohol and sodium
to synthesis BHTS [3], for the Si-Cl bond easily hydrolyzed,
the total yield was only l3 %. Fang et al. [4] increased the total
yield to 45.2 % with dimethyl dimethoxy silane instead of
dimethyldichlorosilane. Speier prepared BHTS by hydro-
silylation of allyl acetate and 1,1,3,3-tetramethyl-disiloxane
[5], the yield was just 29 % although the synthetic method
was simple. Jiang Hongqin et al. used 1,3-bis(3-chloropropyl)-
1,3-dimethoxy-1,3-dimethyl siloxane as a raw material, after
the Grignard, ester substituted and alcoholysis reaction the
total yield could reach 75 %, but it was not appropriate for
Recently microwave technology is used more widely in
various fields of chemistry. Introduce microwave radiation in
organic synthesis may accelerate the reaction rate and improve
product yield [6-8]. In this paper, BHTS was synthesized under
microwave irradiation with temperature-controlled non-pulsed
microwave reactor.
EXPERIMENTAL
Allyl alcohol, hexamethyldisilazane (HMDS), 1,1,3,3-
tetramethyldisiloxane (HMM), platinum tetrachloride were
commercial product. Isopropyl alcohol (A.R.), p-toluene-
sulfonic acid (A.R.), imidazole (A.R.), pyridine (A.R.), sodium
hydroxide (A.R.), phenolphthalein (A.R.), o-phthalic anhydride
(A.R.) were all commercial reagents. Potassium biphthalate
was standard reagent.
The reactions were conducted in a MAS-II Microwave
Workstation with a maximum power output of 1000W, equipped
with a magnetic stirrer. The product was analyzed byVECTOR-
22 infrared spectrometer with resolution of 4.0 cm-1 and the
average data of ten times test. 1H NMR spectra were measured
on a Varian INOVA-400 NMR spectrometer (1H, 300 MHz).
Content Analysis were performed using a Agilen GC 7890A
gas chromatograph, with PH-1 capillary columns (30.0 m ×
320 µm, film thickness 0.25 µm), the column temperature were
200 °C, injection port temperature were 270 °C, FID detector
temperature were 270 °C, the carrier gas: high purity nitrogen,

568 Cheng et al.
Asian J. Chem.
the column flow: 1 mL/min, the split ratio: 100:1, sample were
injected in split mode, the sample were dissolved in methanol.
Synthesis procedure of BHTS: The general procedure
of preparing BHTS is presented in Fig. 1.
20 min, then stirred high speed for 10 min. After that open
microwave reactor, set the reaction temperature, when the
temperature reached, cautiously added, dropwise, 1,1,3,3-
tetramethyl-disiloxane in 1h, holding the temperature for a
certain time. Then distilled the mixture to collect 129-131 °C
fraction by vacuum distillation (pressure: 0.0998 MPa), which
was TPMS, a colourless transparent liquid.
O
Hydrosilylation
HMM
Hydroxyl protection
HMDS
OH
Si
Preparation of BHTS: This kind of reaction often use
acetic acid as catalysis, siloxane containing substitution get
reaction with excess of methanol, the alcoholysis reaction usually
need more than 8 h. In this paper, self-made TPMS was used
as raw materiel, double hydroxypropyl polysiloxane were get
under microwave irradiation condition. It was more efficient
and higher function-price ratio.
Hydrolyzation
Si
O
(CH2)3
Si
O
Si
(CH2)3O Si
p–Toluenesulfonic acid
0.1 mol TPMS, a given mass of water and p-methyl-
benzene sulfonic acid catalyst were added into four-neck
round-bottom flask which was equipped with thermometer,
stirrer and condenser pipe, set up the microwave irritation time,
temperature, started stir and heat to certain temperature,
holding the temperature for a certain time. After the reaction,
the 66-68 °C fraction of the mixture was collected by vacuum
distillation (pressure: 0.0984 MPa) to collect BHTS.
HO
(CH2)3
Si
O
Si
(CH2)3
O
Fig. 1. Synthesis route of 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyl-
disiloxane
Preparation of allyloxytrimethylsilane (ATMS): In the
presence of platinum tetrachloride, allyl alcohol can react with
1,1,3,3-tetramethyldisiloxane reacted to get Si-O-CH2, which
lead to the yield of the main product reduced greatly. So the
alcoholic hydroxyl groups need to be protected to avoid the
side effects. Trimethylchlorosilane was often used as hydroxyl
protection reagent in literature [9], but this method can produce
HCl, which may corrode the equipment and that the reaction
condition was strict. In this paper the synthetic process was
studied using hexamethyldisilazane as hydroxyl protection
reagent.
Hexamethyldisilazane was added into four-neck round-
bottom flask, which was equipped with thermometer, stirrer
and constant pressure funnel and condenser pipe, then setting
the microwave reaction parameters, when thermometer reached
75 °C. After that cautiously added dropwise allyl alcohol in
1 h, after that, set reaction temperature to start reaction, then
distilled the mixture at atmospheric to collect 100-102 °C
fraction, which was ATMS.
Preparation of 1,3-bis(3-trimethylsiloxypropyl)-
tetramethyl disiloxane (TPMS): Hydrosilylation is occurred
between compound with silicon hydrogen bond and olefin/
alkyne, which can form corresponding silicon-carbon comp-
ounds. By this means, many organic silicon-carbon compounds
can be synthesized. It often use hyperoxide, platinum compound,
etc., one of the most commonly used is platinum compounds/
complexes, such as Speier platinum catalyst.
Most of the hydrosilylation use chloroplatinic acid as
catalyst, the common dosage was 60-100 mg/kg in platinum
(hereinafter the same) [5,10]. For the expensive price of chloro-
platinic acid compare to platinum tetrachloride, the platinum
tetrachloride was chosen as catalyst under microwave radiation.
It was expected to reduce the amount of catalyst to improving
the relationship of performance to cost.
RESULTS AND DISCUSSION
Optimization of process of ATMS: Allyloxytrimethyl-
silane was synthesized with microwave irradiation. The effect
of feed ratios (HMDS/allyl alcohol), reaction temperature and
reaction time were investigated and the results are shown in
Fig. 2.
Fig. 2a showed that the dosage of hydroxyl protection
reagent HMDS greatly affected the yield of ATMS. The allyl
alcohol reaction incompletely when the dosage of hydroxyl
protection reagent HMDS is small. The more HMDS added
the higher yield of ATMS is. Whereas more HMDS not only
waste raw material but also cause the difficulty of after treat-
ment. The experiment shows that the advisable weight ratio
of HMDS:allyl alcohol is 0.7 :1.
As shown in Fig. 2b, at low temperature the reaction speed
is slow, so the yield is low. With the increase of temperature,
the reaction speed rise, the yield of ATMS correspondingly
increased. At 120 °C, the reaction is basically finished. At high
temperature unsaturated group self-condensed seriously, which
made the yield reduced. In conclusion, the optimal reaction
temperature is 120 °C
As show in Fig. 2c, other reaction condition is fixed, the
longer reaction time is the higher yield of ATMS. But after
4 h, the yield decreased a little, then it maintained, so the
optimal reaction time was 4 h.
Through the above experiment, the optimal reaction
condition is as follows: in microwave irradiation, the weight
ratio of HMDS:allyl alcohol equal to 0.7:1, reaction temperature
is 120 °C, reaction time is 4 h. The yield of ATMS is 95.5 %.
The product is clear and purity.
A given mass of ATMS and four platinum chloride/
isopropyl alcohol catalysts was added into four-neck round-
bottom flask, which was equipped with thermometer, stirrer
and nitrogen catheter and condenser pipe with calcium chloride
anhydrous dry pipe. Bubbling nitrogen to expel oxygen for
Optimization process ofTPMS: 1,3-Bis(3-trimethylsiloxy
propyl)tetramethyl disiloxane was synthesized with microwave
irradiation. The effect of feed ratios (HMDS/allyl alcohol),
reaction time, reaction temperature and catalyst dosage were
investigated and the results are shown in Table-1.

Vol. 28, No. 3 (2016)
Microwave-Assisted Synthesis of 1,3-Bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane 569
100
TABLE-1
OPTIMIZATION PROCESS OF 1,3-BIS(3-TRIMETHYLSILOXY
PROPYL)TETRAMETHYL DISILOXANE
(a) Feed ratio
90
Parameter
Yield (%)
46.2
65.3
79.7
83.6
83.2
83.4
35.3
52.4
64.3
83.8
83.4
83.5
36.4
75.6
83.5
85.4
88.1
87.7
83.8
38.1
70.8
91.7
91.5
89.3
85.1
80
70
60
50
40
30
1.5:1
1.8:1
2.1:1
2.4:1
2.8:1
3.2:1
30
50
70
90
110
120
50
60
70
80
90
100
110
5
Molar ratio HMM:ATMS
[Catalyst: 60 mg/kg, temp.:
70 °C, time: 2 h]
Reaction time (min)
[Molar ratio: 2.4:1,
catalyst: 60 mg/kg,
temp.: 70 °C]
Reaction time = 4 h
Reaction temperature = 120 °C
0.3:1
0.5:1
0.6:1
0.7:1
1:1
Feed ratios
Reaction temperature (°C)
[Molar ratio: 2.4:1,
catalyst: 60 mg/kg,
time: 2 h]
100
90
80
70
60
50
(b) Temperature
10
20
30
40
Catalyst dosage (mg/kg)
[Molar ratio: 2.4:1,
temp.: 90 °C, time: 2 h]
50
much energy consumption. The experiment shows that the
reaction has been completed, when the molar ratio of HMM
to ATMS is 2.4:1 and low-cost.
Feed ratio = 0.7:1
Reaction time = 4 h
As shown in Table-1, the yield of the product were
increased rapidly as the microwave radiation time went on.
But when the time reach 90 min, the yield of the product tends
to be constant value, so the optimum reaction time is 90 min.
Table-1 revealed that the reaction were finished at 90 °C.
With rising temperature, the energy of the system increased
and it accelerate the reaction.At high temperature unsaturated
group self-condensed seriously, the catalyst chloroplatinic acid
separated out from isopropanol at high temperature. All these
made the yield of ATMS reduce. In conclusion, the optimal
reaction temperature is 90 °C.
Thus, the conversion rate increased rapidly with the increase
of catalyst dosage. After the dosage of catalyst surpassed 20
mg/kg, instead of increase, the yield of product decreased.
With more platinum, the unsaturated double bonds of ATSM
self-condensed or isomerized easily, it lower the yield of the
product. And platinum is precious metals, the dosage impact
on the cost of production greatly, therefore, the appropriate
dosage of catalyst is 20 mg/kg.
Optimization of process of BHTS: 1,3-Bis(3-hydroxy-
propyl)-1,1,3,3-tetramethyldisiloxane was synthesized with
microwave irradiation. The effect of the amount of water,
hydrolysis temperature, hydrolysis time and catalyst dosage
were investigated and the results are shown in Fig. 3.
It can be seen from Fig. 3a, the conversation rate increase
rapidly with the increase of water dosage. After the dosage of
water surpassed 4.68 g, the conversion rate of product began
to decrease. At beginning, the water is not enough to react
with TMPS by theory, so the conversation rate increases with
100
110
120
130
140
Reaction temperature (°C)
100
90
80
70
60
50
(c) Reaction time
Feed ratio = 0.7:1
Reaction temperature = 120 °C
0
1
2
3
4
5
6
7
8
Reaction time (h)
Fig. 2. Effect of process conditions on yield of allyloxytrimethylsilane
The essence of hydrosilylation is that the carbon-carbon
double bonds and silicon hydrogen bond take addition reaction
by certain molar ratio. But as shown in Table-1, the yield of
the product is increased, as the molar ratio of HMM to ATMS
from 1.5:1 to 2.4:1. When the molar ratio exceeds 2.4:1, the
yield of the product has no remarkable change which indicated
that the reaction has been completed. As the HMM increases,
the scale of the distillation becomes large, which will cause

570 Cheng et al.
Asian J. Chem.
100
90
80
70
60
50
40
100
(a) Amount of water
(b) Temperature
95
90
85
80
75
70
65
Temperature = 95 °C
Time = 1 h
Catalyst = 0.1 g
Water = 4.68 g
Time = 1 h
Catalyst = 0.1g
60
80
100
120
3.0
3.5
4.0
4.5
5.0
5.5
6.0
Hydrolysis temperature (°C)
Amount of water (g)
100
90
80
70
60
50
100
90
80
70
60
50
40
(c) Hydrolysis time
(d) Dosage of catalyst
Water = 4.68 g
Temperature = 90 °C
Catalyst = 0.1 g
Water = 4.68 g
Temperature = 90 °C
Time = 1 h
0
1
2
3
0.0
0.1
0.2
0.3
0.4
0.5
Hydrolysis time (h)
Catalyst dosage (g)
Fig. 3. Effect of process conditions on yield of 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane
waters added. When the amount of water surpasses 4.68 g, the
extra water may react with the product by the acid catalyst, so
the conversion rate decreases. Therefore, the appropriate
dosage of water is 4.68 g.
acid are added in three-flask with stir, thermometer, reflux
condensing tube, set the microwave reaction temperature
90 °C, with stirring, keep the temperature for 1 h. The BHTS
yield can reach 95.8 %.
It can be see from Fig. 3b, the reaction temperature influe-
nces the yield of product remarkably. Under 90 °C, the yield
of product increases rapidly as temperature go on. When the
temperature surpass 90 °C, the yield of product decreases as
temperature increases.At higher temperature, some side effects
of the hydroxide radical may occur. Meanwhile the water volati-
lization lost greatly at higher temperature, would effect the
yield of product oppositely. So the optimal temperature is 90 °C.
It can be seen from Fig. 3c, at the beginning of the reaction,
the yield of the product increases rapidly as the hydrolysis
time increase. But after 1 h, the yield of the product changes
very small. Some side effects of the hydroxide radical may
occur at high temperature within long time. So the optimal
reaction time is 1 h.
Fig. 3d shows the yield of the product rise rapidly as the
dosage of p-methylbenzene sulfonic acid increase. As the
catalyst dosage surpass 0.15 g, the yield of the product changes
small. So the optimal dosage is 0.15 g.
The optimization of process of BHTS are as follows: 39.4
g (0.1 mol) TMPS, 4.68 g water and 0.15 g p-toluenesulfonic
The infrared spectra (Fig. 4) shows an absorption peak at
3328 cm-l which is attributed to the stretching vibration absorp-
tion of OH, absorption peak in 1178 cm-l which is attributed
to the bending vibration absorption of Si-(CH2)3- and absorp-
tion peak in 1051 cm-l which is caused by the stretching vibration
absorption of Si-O-Si in BHTS.
Nuclear magnetic resonance hydrogen spectroscopy:
It can be seen from Fig. 5 that there are 5 proton peaks. The
no. 1 proton’s chemical shift is in high field because it belongs
to the methyl which is connected with the silicon proton. The
methylene which the no. 2 proton belongs to is connected with
another methylene except for silicon proton, so its chemical
shift is to the lower field. The carbon which the no. 4 proton
belongs to is connected with hydroxyl, therefore its chemical
shift is to the lowest field, in 3.469 ppm. The methylene which
the no. 3 proton belongs to is connected with alkyl and its
chemical shift is in 1.531 ppm. The chemical shift which is in
3.728 ppm belongs to hydroxyl hydrogen. From the data all
above, it can be seen that the synthesized product has the
desired structure.

Vol. 28, No. 3 (2016)
Microwave-Assisted Synthesis of 1,3-Bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane 571
Conclusion
Microwave radiation is applied to synthesize BHTS from
allyl alcohol and HMM. Product structure is analyzed and
identified by IR, 1H NMR and GC spectrometry. It is found
that under microwave radiation the reaction is rapid with good
yield, better quality and less time is required for the completion
of the reaction [3-5,10].
ACKNOWLEDGEMENTS
The support of this research by the Key Project ofTechnology
Department of Shannxi Province of China (No. 2012K08-13)
is gratefully acknowledged.
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Fig. 5. H NMR of 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyldisiloxane
Gas chromatography: The content of BHTS is 99.1 %
calculated by the area normalization method (Fig. 6).
0
5
10
15
20
Time (min)
Fig. 6. Gas chromatography of 1,3-bis(3-hydroxypropyl)-1,1,3,3-tetramethyl-
disiloxane