Reaction of Acetoxysilanes with Hydroxy Compounds

Article abstract of DOI:10.1023/A:1014244427477

Tetraacetoxysilane reacts with hexanol, cyclohexanol, and phenol to give products of complete or partial replacement of the acetoxy groups. The rate of hydrolysis of the SiOR group in alkoxy(phenoxy)-silanes and alkoxy(phenoxy)acetoxysilanes in homogeneous (THF) and heterogeneous media (on cellulose surface) increases in the series c=Si-OC6H5 > =Si-OC6H13 > =Si-OC6H11.

Full text of DOI:10.1023/A:1014244427477

Russian Journal of General Chemistry, Vol. 71, No. 12, 2001, pp. 1924 1928. Translated from Zhurnal Obshchei Khimii, Vol. 71, No. 12, 2001,
pp. 2031 2035.
Original Russian Text Copyright
2001 by Kopylov, Kireev, Ivanov, Astaf’ev, Kozlov.
Reaction of Acetoxysilanes with Hydroxy Compounds
V. M. Kopylov, V. V. Kireev, V. V. Ivanov, G. Yu. Astaf’ev, and Yu. V. Kozlov
Chemistry and Technology of Organoelement Compounds
State Research Center of the Russian Federation, Moscow, Russia
Received April 24, 2001
Abstract Tetraacetoxysilane reacts with hexanol, cyclohexanol, and phenol to give products of complete
or partial replacement of the acetoxy groups. The rate of hydrolysis of the SiOR group in alkoxy(phenoxy)-
silanes and alkoxy(phenoxy)acetoxysilanes in homogeneous (THF) and heterogeneous media (on cellulose
surface) increases in the series Si OC6H5 > Si OC6H13
>
Si OC6H11.
Reactions of acetoxysilanes with organic com-
pounds having a hydroxy group are important for
synthesis of monomers and polymers. Such reactions
could take two pathways. The first of these is trans-
esterification leading to formation of ester and
hydroxysilane, and the second is substitution reaction,
resulting in formation of alkoxy(aroxy)acetoxysilanes.
Si(OOCCH3)2(OR)2 + ROH
+ CH3COOH,
Si(OOCCH3)(OR)3
Si(OOCCH3)(OR)3 + ROH
Si(OR)4 + CH3COOH
Compounds with a desired degree of substitution
of the acetoxy groups can be synthesized by varying
the reactant ratio. The reactions of tetraacetoxysilane
with hexanol and cyclohexanol were exothermic: on
mixing the reactants at a molar ratio of 1:4 the
mixture spontaneously warmed up to 40 and 28 C,
respectively. It was difficult to reveal heat effect in
the reaction of tetraacetoxysilane with phenol, for
the latter is solid at room temperature; therefore, the
mixture was heated to 50 C. On gradually raising the
temperature to 120 C, in all cases the conversion was
92 96% with respect to acetoxy groups. No hexanol,
cyclohexanol, or phenol was found among the prod-
ucts by GLC.
The esterification process is utilized in the synthesis
of organic polysiloxanes [1 3] and silica gel [4].
According to [1 3], the reaction is catalyzed by traces
of strong or Lewis acids. The substitution pathway
was studied comsiderably more poorly. The formation
of alkoxysilanes and mixed alkoxyacetoxysilanes was
reported in [5 8]. It should be noted that only limited
published data are available on the effect of various
factors on the formation of alkoxysilanes and mixed
alkoxyacetoxysilanes by reaction of acetoxysilanes
with organic hydroxy compounds. On the other hand,
alkoxy(aroxy)silanes derived therefrom, especially
from biologically active compounds, attract interest
from the viewpoint of practice. Due to slow hydrol-
ysis, such alkoxy(aroxy)silanes are characterized by
more prolonged action, as compared to the initial
compound. The absence of a catalyst makes it possible
to use the products without special purification, for
the only by-product is acetic acid.
Taking into account the quantitative yield of acetic
acid, the lack of ester impurities therein (GLC), and
intensities of signals from acetoxy and alkoxy (or
1
phenoxy) groups in the H NMR spectra, we can
conclude that the process involves only replacement
of acetoxy groups in tetraacetoxysilane. According to
1
the H NMR data, alkoxy(phenoxy)acetoxysilanes are
In the present communication were report on the
results of our study of the reaction of tetraacetoxy-
silane with hexanol, cyclohexanol, and phenol. All
these reagents contain six carbon atoms but have
different structures. Their reactions with tetraacetoxy-
silane occur in four stages, according to the following
scheme:
mixtures of compounds with different degrees of
substitution, whose ratio is determined by the struc-
ture of the hydroxy compound and reactant ratio
(Table 1). The concentration of each product was
determined from the signal intensity ratio of OCH2
protons in hexyl derivatives, OCH proton in cyclo-
hexyl derivatives, and CH3 protons of the acetoxy
groups in phenoxy derivatives. As the number of
alkoxy substituents decreases in going from Si(OAlk)4
to Si(OCOCH3)3OAlk, the OCH2 and OCH signals
shift downfield. The difference between the chemical
Si(OOCCH3)4 + ROH Si(OOCCH3)3(OR) + CH3COOH,
Si(OOCCH3)3(OR) + ROH
Si(OOCCH3)2(OR)2
+ CH3COOH,
1070-3632/01/7112-1924$25.00 2001 MAIK Nauka/Interperiodica

REACTION OF ACETOXYSILANES WITH HYDROXY COMPOUNDS
1925
Table 1. Product composition in the reactions of tetraacetoxysilane with hydroxy compounds (1H NMR data)
Fraction, %
Sample
Si[Hex]4
Si[Ac][Hex]3
Si[Ac]2[Hex]2
Si[Ac]3[Hex]
Si[OC6H13]4
100
35
1
Si[OCOCH3][OC6H13]3
Si[OCOCH3]2[OC6H13]2
Si[OCOCH3]3[OC6H13]
58
35
17
7
58
19
6
64
Si[cyclo-HexO]4 Si[Ac][cyclo-HexO]3 Si[AcO]2[cyclo-HexO]2 Si[AcO]3[cyclo-HexO]
Si[OC6H11]4
100
Si[OCOCH3][OC6H11]3
Si[OCOCH3]2[OC6H11]2
Si[OCOCH3]3[OC6H11]
33
57
26
15
10
62
35
10
50
Si[PhO]4
100
Si[AcO][PhO]3
Si[AcO]2[PhO]2
Si[AcO]3[PhO]
Si[OC6H5]4
Si[OCOCH3][OC6H5]3
Si[OCOCH3]2[OC6H5]2
Si[OCOCH3]3[OC6H5]
46
25
12
40
44
29
14
31
59
shifts of OCH2 and CH3 (n-hexanol), as well as
between the chemical shifts of OCH and one of the
CH2 groups (cyclohexanol) depends on the number
of alkoxy groups. Table 1 summarizes the data on
the product compositions. The occurrence of side
esterification process was judged by the presence or
absence of acetic acid esters. As noted above, no ester
formation was observed in the reactions of tetra-
acetoxysilane with hexanol, cyclohexanol, and phenol.
We also carried out the reaction in the presence of
3 wt % of KU-23 cation exchanger containing
3.8 mg-equiv of SO3H groups per g. In this case,
the process was accompanied by esterification and
formation of the corresponding esters. The contribu-
tion of esterification was minimized by carrying out
the reaction under reduced pressure with simultaneous
Table 2. Yields of phenyl and alkyl acetates, depending
on the reaction conditions
Yield, %
Reaction
reduced
pressure
atmospheric
pressure
Si(OCOCH3)4 + 4C6H5OH
Si(OCOCH3)4 + 2C6H5OH
Si(OCOCH3)4 + 4C6H11OH
Si(OCOCH3)4 + 2C6H11OH
13.82
9.75
7.80
2.02
20.80
44.60
9.06
number of acetoxy group rises. These findings may
be explained by catalytic effect of acetic acid on the
removal of liberated acetic acid from the reaction hydrolysis of Si OR groups and by fast formation
zone (Table 2).
of hydroxy groups on the silicon atom, which can also
participate in the hydrolysis process through inter-
action with Si OR groups. The catalytic effect of
acetic acid is confirmed by acceleration of the
hydrolysis of tetraalkoxysilanes on addition of
an equimolar amount of acetic acid (1 mol of acetic
acid per mole of tetraalkoxysilane).
We also determined the relative rates of hydrolysis
of the resulting acetoxyalkoxysilanes in homogeneous
medium (THF) containing a specified amount of
water. Figure 1 shows that the rate of hydrolysis at
the Si OR group in alkoxy(phenoxy)silanes and
alkoxy(phenoxy)acetoxysilanes increases in the series
Si OC6H5 > Si OC6H13 > Si OC6H11. This series
conforms to increase in the electron-acceptor power
of the organic radical in ROH molecule and decrease
in steric hindrance; therefore, the highest rate of
hydrolysis is observed for tetraphenoxysilane. The
rate of hydrolysis of alkoxy(phenoxy) groups in
alkoxy(phenoxy)acetoxysilanes is higher than in tetra-
alkoxy(phenoxy)silanes, and it increases as the
We also examined the hydrolysis of esterification
products with atmospheric moisture on the surface
of cellulose (paper napkin). Here, two processes are
possible: hydrolysis with atmospheric moisture (by
analogy with the hydrolysis in solution) and grafting
on the cellulose surface. Taking into account the high
reactivity of acetoxy groups toward surface hydroxy
groups and water, alkoxy(phenoxy)acetoxysilanes
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 12 2001

1926
KOPYLOV et al.
1
3
1
100
2
100
2
3
4
5
6
80
60
4
5
80
60
40
7 8
9
10
11
40
12
20
0
6
20
0
7
13
10 15 20
0
50
100 150 200
250
Time, h
0
5
25 30
Time, days
Fig. 2. Hydrolysis of acetoxyalkoxy(phenoxy)silanes on
the cellulose surface: (1) Si[AcO] [PhO] , (2) Si[AcO]
2
2
3
Fig. 1. Hydrolysis of acetoxyalkoxy(phenoxy)silanes in
THF (20 C, c = 0.2 M, c = 1 mol per functio-
[PhO], (3) Si[AcO] [C H O], (4) Si[AcO][PhO] ,
3
6
11
3
(5) Si[AcO] [HexO], (6) Si[PhO] , (7) Si[AcO]
silane
H2O
3
4
2
nal group): (1) Si[PhO] , (2) Si[AcO] [HexO] ,
[HexO] , (8) Si[AcO][HexO] , (9) Si[AcO][HexO] ,
4
2
2
2 3 3
(3)
Si[AcO] [C H O] ,
(4)
Si[AcO][HexO] ,
(10) Si[AcO] [C H O] , (11) Si[AcO][C H O] ,
2 6 11 2 6 11 3
2
6
11
2
3
(5) Si[AcO][C H O] , (6) Si[HexO] , (7) Si[C H O] .
(12) Si[HexO] , (13) Si[C H O] .
6
11
3
4
6
11
4
6
11
4
4
should readily be immobilized on the cellulose
surface. The relative rates of hydrolysis were deter-
mined by measuring the weight of a sample at definite
time intervals. The liberated acetic acid and alcohol
were removed from the surface by heating to 85 C.
was added, a white solid (tetraacetoxysilane) began to
separate. After the addition was complete, the mixture
was stirred for 2 h, and excess acetic anhydride and
acetryl chloride formed during the reaction were
removed on a rotary evaporator at a bath temperature
The results are presented in Fig. 2. It is seen that the of 70 80 C, the pressure being gradually reduced to
hydrolysis in solution is faster by a factor of 20 30
(depending on the substrate structure), but the rela-
tions between the reaction rate and the substituent
nature and the degree of substitutions are the same as
in the hydrolysis on the cellulose surface.
6 mm. The residue was tetraacetoxysilane, a colorless
crystalline substance. Yield 440 g (94%), mp 110 C.
Reaction of tetraacetoxysilane with alcohols and
phenol. All reactions were carried out in a flask
equipped with a stirrer, dropping funnel, thermometer,
and reflux condenser capped with a drying tube.
Tetraacetoxysilane was mixed with n-hexanol, cyclo-
hexanol, or phenol at a molar ratio of 1:1 to 1:4,
and the mixture was stirred for 2 3 h at 90 100 C.
Liberated acetic acid was distilled off under reduced
pressure (on a rotary evaporator). Table 3 contains
We can conclude that, with the goal of creating
fragrant compounds or drugs with prolonged action,
exhaustively substituted derivatives of tetraacetoxy-
silane should be used. When such compounds are pre-
sumed to be applied to cellulose surface, the presence
of an acetoxy group is desirable.
1
the yields, physical properties, and H NMR spectra
EXPERIMENTAL
of the products.
1
The H and 29Si NMR spectra were obtained on
Reaction of tetraacetoxysilane with alcohols in
the presence of acid catalyst. a. Without removal
of acetic acid. Tetraacetoxysilane, 0.057 mol, was
mixed with 0.227 mol of appropriate alcohol and
0.75 g of KU-23 cation exchanger. The mixture was
heated for 2 h at 100 C, cooled to room temperature,
and analyzed by GLC for the corresponding ester,
alkyl or phenyl acetate.
1
a Bruker AM-360 spectrometer (360.13 MHz for H).
The hydrolysis of alkoxy(phenoxy)silanes in THF was
monitored by GLC using toluene as internal standard;
LKhM-80 chromatograph, 2000 4-mm column,
stationary phase SE-30 on silanized Chromosorb-W,
carrier gas helium.
Tetraacetoxysilane. Acetic anhydride, 8.14 mol,
was added dropwise with stirring to 1.77 mol of
SiCl4. The mixture slowly warmed up to 35 40 C.
When 60% of the total amount of acetic anhydride
b. With removal of acetic acid. Tetraacetoxysilane,
0.057 mol, was mixed with 0.227 mol of appropriate
alcohol and 0.75 g of KU-23 cation exchanger. The
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 12 2001

REACTION OF ACETOXYSILANES WITH HYDROXY COMPOUNDS
Table 3. Yields, physical constants, and 1H NMR spectra of alkoxy(phenoxy)acetoxysilanes
Yield,
1927
Compound
d240
n2D0
1H NMR spectrum (CDCl3), , ppm
%
93
95
Si[OC6H13]4
0.8927 1.4415 0.87 t (3H, CH3), 1.28 1.35 m (6H, CH2), 1.51 1.58 m (2H, CH2),
3.74 t (2H, OCH2)
Si[OC6H11]4
1.15 1.49 m (6H, CH2), 1.68 1.71 m (2H, CH2), 1.81 1.84 m (2H,
CH2), 3.81 3.86 m (1H, OCH)
Si[OC6H5]4
Si[OCOCH3][OC6H13]3
95
94
7.07 7.12 m (3H, Ph), 7.28 7.33 m (2H, Ph)
a
0.9323 1.4239 0.85 t (3H, CH3), 1.26 1.35 m (6H, CH2), 1.49 1.58 m (2H, CH2),
2.07 s (3H, Ac), 2.09 s (3H, Ac), 3.70, 3.72, 3.80, 3.88 t (2H, OCH2)
0.9965 1.4183 0.83 t (3H, CH3), 1.24 1.31 m (6H, CH2), 1.51 1.56 m (2H, CH2),
2.06 s (3H, Ac), 2.08 s (3H, Ac), 2.10 s (3H, Ac), 3.78, 3.87, 3.95 t
(2H, OCH2)
a
Si[OCOCH ] [OC H
]
6 13 2
95
94
94
95
93
3 2
Si[OCOCH3]3[OC6H13]a
0.78 t (3H, CH3), 1.18 1.26 m (6H, CH2), 1.46 1.52 m (2H, CH2),
2.02 s (3H, Ac), 2.04 s (3H, Ac), 2.07 s (3H, Ac), 3.73, 3.81, 3.90 t
(2H, OCH2)
a
Si[OCOCH3][OC6H11]3
1.0543 1.4641 1.11 1.46 m (6H, CH2), 1.64 1.68 m (2H, CH2), 1.78 1.82 m (2H,
CH2), 2.05 s (3H, Ac), 2.07 s (3H, Ac), 3.78 3.83, 3.89 3.96, 3.98
4.07 m (1H, OCH)
1.1043 1.4461 1.11 1.44 m (6H, CH2), 1.63 1.67 m (2H, CH2), 1.76 1.80 m (2H,
CH2), 2.03 s (3H, Ac), 2.05 s (3H, Ac), 2.07 s (3H, Ac), 3.88 3.92,
3.99 4.04, 4.11 4.15 m (1H, OCH)
a
Si[OCOCH3]2[OC6H11]2
Si[OCOCH3]3[OC6H11]a
1.12 1.45 m (6H, CH2), 1.64 1.68 m (2H, CH2), 1.79 1.82 m (2H,
CH2), 2.06 s (3H, Ac), 2.09 s (3H, Ac), 2.12 s (3H, Ac), 4.00 4.04,
4.12 4.15 m (1H, OCH)
a
Si[OCOCH3][OC6H5]3
94
93
94
1.1932 1.5398 2.18 s (3H, Ac), 2.22 s (3H, Ac), 2.24 s (3H, Ac), 7.11 7.20 m (3H,
Ph), 7.32 7.39 m (2H, Ph)
1.2109 1.5100 2.13 s (3H, Ac), 2.17 s (3H, Ac), 2.18 s (3H, Ac), 7.03 7,10 m (3H,
Ph), 7.24 7.32 m (2H, Ph)
1.2537 1.4820 2.10 s (3H, Ac), 2.14 s (3H, Ac), 2.16 s (3H, Ac), 6.99 7.08 m (3H,
Ph), 7.22 7.28 m (2H, Ph)
a
Si[OCOCH3]2[OC6H5]2
Si[OCOCH3]3[OC6H5]a
a
The given formulas correspond to the averaged product composition.
mixture was heated to 80 C, and acetic acid was dis- minarily weighed, impregnated with the prepared
tilled off overa period of 2 h under reduced pressure. solution, and kept for 1 h at room temperature. It
The mixture was cooled to room temperature and
analyzed by GLC for the corresponding alkyl (phenyl)
acetate.
was then dried in an oven for 5 h at 85 C, weighed,
and the weight loss was calculated. This procedure
was carried out at specified time intervals.
REFERENCES
Hydrolysis of acetoxyalkoxy(phenoxy)silanes in
THF. Acetoxyalkoxy(phenoxy)silane, 0.5 g, was dis-
solved in 5 ml of THF containing a required amount
of water [4 mol of H2O per mole of Si(OCOCH3)n-
(OR)4 n, where n = 0, 1, 2, 3) and 0.1 g of toluene
as internal reference. The concentration of alcohol in
the mixture was determined by GLC at specified time
intervals. The results are shown in Fig. 1.
1. Leznov, N.S., Sabun, L.A., and Andrianov, K.A.,
Zh. Obshch. Khim., 1959, vol. 29, no. 4, pp. 1276
1281.
2. Leznov, N.S., Sabun, L.A., and Andrianov, K.A.,
Zh. Obshch. Khim., 1959, vol. 29, no. 5, pp. 1518
1522.
3. Khananashvili, L.M., Khimiya i tekhnologiya elemento-
organicheskikh monomerov i polimerov (Chemistry
and Technology of Heteroelement-Containing Organic
Monomers and Polymers), Moscow: Khimiya, 1998,
pp. 323 327.
Hydrolysis of acetoxyalkoxy(phenoxy)silanes on
the surface of cellulose. A sample of acetoxyalkoxy-
(phenoxy)silane was dissolved in toluene to attain
a concentration of 40%. A paper napkin was preli-
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 12 2001

1928
KOPYLOV et al.
4. Brunet, F. and Cabane, B., J. Phys. Chem., 1991,
Zh. Obshch. Khim., 1957, vol. 27, no. 4, pp. 921 926.
7. Voronkov, M.G., Davydova, V.P., and Dolgov, B.N.,
Izv. Akad. Nauk SSSR, Ser. Khim., 1958, no. 6,
pp. 698 701.
8. Dolgov, B.N., Davydova, V.P., and Voronkov, M.G.,
Zh. Obshch. Khim., 1957, vol. 27, no. 6, pp. 1593
1599.
vol. 95, no. 2, pp. 211 225, 945 951.
5. Andrianov, K.A., Zhdanov, A.A., and Bogdano-
va, A.A., Dokl. Akad. Nauk SSSR, 1954, vol. 94,
no. 4, pp. 697 699.
6. Dolgov, B.N., Davydova, V.P., and Voronkov, M.G.,
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 71 No. 12 2001