Process for the simultaneous and continuous preparation of acyloxysilanes and carboxylic acid chlorides

Acyloxysilanes and carboxylic acid chlorides can be prepared simultaneously and continuously from organochlorosilanes and monocarboxylic acid anhydrides. Catalytically active amounts of organic bases soluble in the reaction mixture, their salts or organic acid amides are employed here.

FIELD OF THE INVENTION 
The present invention relates to a process for the simultaneous and 
continuous preparation of acyloxysilanes and carboxylic acid chlorides by 
reaction of organochlorosilanes with monocarboxylic acid anhydrides. 
BACKGROUND OF THE INVENTION 
Acyloxysilanes have found various uses in the chemical industry. They are 
suitable, for example, as crosslinking silicon compounds in the 
preparation of compositions which can be stored in the absence of water 
and can be hardened to elastomers at room temperature in the presence of 
moisture. Such compositions are obtained by mixing diorganopolysiloxanes 
containing end groups which can undergo condensation and crosslinking 
silicon compounds. Examples of acyloxysilanes which are suitable for this 
purpose are vinyl-, methyl- and ethyltriacetoxysilanes. Carboxylic acid 
chlorides are important and, in some cases, valuable raw materials for the 
synthesis of organic compounds. 
It is known that alkanoyloxysilanes can be prepared continuously by 
reaction of organochlorosilanes with alkanoic acids at elevated 
temperature in a column (DE-PS 28 01 780). The alkanoic acid is passed in 
vaporized form from the bottom upwards in countercurrent with the 
organochlorosilane and reacts to form alkanoyloxysilane and hydrogen 
chloride. 
A disadvantage of this procedure is that the hydrogen chloride formed is in 
contact with the alkanoic acids employed for relatively long periods of 
time under conditions under which the formation of water and alkanoyl 
chlorides takes place. This results in additional siloxane formation and 
requires expensive low-temperature cooling at the top of the column so 
that the substances entrained in the stream of hydrogen chloride according 
to their vapor pressure are deposited and the hydrogen chloride is 
rendered usable for purposes for which particular purity requirements are 
imposed. Another disadvantage of this procedure is that metering of the 
alkanoic acids introduced into the column must be regulated by an 
expensive device which is controlled by a temperature measurement point in 
the lower part of the column. 
It is also a further disadvantage of the procedure of DE-PS 28 01 780 that 
the reaction, which is associated with the release of large amounts of 
gas, must be carried out in vacuo, which necessitates particular pressure 
stabilization equipment. 
Because of the deficiencies associated with the procedure according to 
DE-PS 28 01 780, ethyltriacetoxysilane is obtained in the distillation 
column with an ethyltriacetoxysilane content of only 94%, coupled with a 
content of 2% of acetic acid and evidently 4% of siloxanes, as well as a 
content of hydrolyzable chlorine of about 50 ppm. 
Only a slight improvement to this situation is achieved if in this known 
procedure the addition of the alkanoic acid together with the 
organochlorosilane is carried out in the lower part of the column and 
additional alkanoic acid is introduced in the upper part of the column 
(DE-PS 32 21 702). 
It is also known that the reaction of organochlorosilanes can be carried 
out with anhydrides corresponding to the alkanoic acids; however, only a 
discontinuous procedure has been described for this reaction. 
There was therefore the problem of discovering a continuous process, which 
can be used on a large industrial scale, for the preparation of 
acyloxysilanes which does not have the deficiencies of the procedures 
according to the prior art described herein, and in which a high-quality 
by-product in the form of carboxylic acid chloride is obtained instead of 
the relatively useless by-product hydrogen chloride. 
SUMMARY OF THE INVENTION 
These problems were solved by developing a process for the simultaneous and 
continuous preparation of an acyloxysilane and a carboxylic acid chloride 
by reacting an organochlorosilane with excess monocarboxylic acid 
anhydride at elevated temperatures, separating off the carboxylic acid 
chloride after the reaction has ended and subsequently collecting the 
acyloxysilane, wherein said process is characterized in that the starting 
components are passed through one or more reactors at temperatures of 
25.degree. to 100.degree. C. with the addition of organic bases which are 
soluble in the reaction mixture, their salts or organic acid amides. The 
carboxylic acid chloride formed is then removed in vacuo in a distillation 
reactor and the reaction mixture which remains after the carboxylic acid 
chloride has been separated off is transferred to the central intake of a 
column. Excess carboxylic acid anhydride is distilled off at the top of 
the column in vacuo and the acyloxysilane is removed from the bottom of 
the distillation column. 
DETAILED DESCRIPTION OF THE INVENTION 
The chlorosilanes which can be employed as starting substances in the 
process according to the invention correspond to the general formula 
EQU R.sup.1.sub.a R.sup.2.sub.b SiCl.sub.4-a-b, 
wherein a can have the value 3, 2 or 1 and b can have the value 1 or 0. 
Preferably, a=1 and b=0. 
R.sup.1 and R.sup.2 represent hydrogen or identical or different saturated 
hydrocarbon radicals of 1 to 10 carbon atoms or unsaturated hydrocarbon 
radicals of 2 to 10 carbon atoms, which can optionally contain functional 
groups, for example halogen, which do not undergo a reaction under the 
reaction conditions described. 
The following compounds can thus be employed, for example, as 
silicon-containing starting substances: 
vinyltrichlorosilane, 
ethyltrichlorosilane, 
methyltrichlorosilane, 
trichlorosilane, 
propyltrichlorosilane and 
2-chloroethyl-methyldichlorosilane. 
The carboxylic acid anhydrides employed according to the invention are 
mainly derived from monobasic aliphatic acids, preferably from those 
having 2 to 4 carbon atoms. The hydrocarbon radicals of the acid may be 
saturated or unsaturated. Examples of such anhydrides are ethanoic 
anhydride, propanoic anhydride and butanoic anhydride. However, compounds 
in which a hydrogen atom of the aliphatic radical is replaced by a phenyl 
radical, such as phenylmethanoic anhydride, can also be employed. 
The reactor system used in the process according to the invention is a 
system which, in the simplest case, consists of two reaction vessels 
connected in series, through which the starting substances flow and in 
which their residence time can be adjusted to suit the product-specific 
reaction requirements by an appropriate vessel design. The reactors are 
advantageously connected such that the reaction mixture formed is removed 
from the preceding reactor at the top and fed into the subsequent reactor 
at the bottom. The second reactor is called a distillation reactor and is 
provided with a column top which is fitted with a reflux divider and 
condenser and via which the carboxylic acid chlorides formed in the 
preceding reactor, and still forming in the distillation reactor in the 
course of removal of the carboxylic acid chlorides by distillation, are 
removed under a pressure of 5 to 300 mbar. Any desired number of reactors 
in which the reaction and establishment of the reaction equilibrium take 
place can be chosen. One reactor is usually sufficient to ensure complete 
reaction of the starting component used in less than the equivalent amount 
and that therefore the reaction mixture which leaves the distillation 
reactor and is passed into the central intake of a column no longer 
contains the component used in less than the equivalent amount. Preferred 
reactors in the context of the present invention are tube reactors. 
The reactors can be heated, for example, via double-walled jacket systems. 
It should be made certain here that the reactors can be exposed to various 
temperature ranges so that the most favorable reaction temperatures for 
achieving optimum rates of reaction can be established for the particular 
starting substances. Agitation of the reaction mixture can be established 
effectively in the distillation reactor, for example by using stirrer 
systems having an intense action, so that as complete as removal as 
possible of the carboxylic acid chloride formed, according to the starting 
components employed, is achieved. If possible, the residual chlorine 
content in the reaction mixture, which emerges from the distillation 
reactor and enters the central intake of the distillation column 
downstream, should not exceed 8,000 ppm. However, chlorine contents 
slightly in excess of this do not present problems. As a result of a mode 
of operation adapted to suit these contents of the column downstream of 
the distillation reactor, it is possible for chlorine contents in the 
intake which are too high, to be compensated without the slightest 
reductions being found in the quality of the products leaving the bottom 
of the distillation column. 
It has been found that in order to achieve economical space-time yields, 
the temperatures used in the reactors should not fall below 25.degree. C. 
The space-time yield is also reduced if the temperature used in the 
reactors is in a temperature range in which intermolecular condensation of 
the acyloxysilanes to give siloxanes is initiated to an increased degree. 
The temperature range in which intermolecular condensation of the 
acyloxysilanes starts depends both on the chlorosilane employed and on the 
acyloxy group which replaces the chlorine in the chlorosilane, so that the 
optimum reaction temperature must be determined from case to case in 
preliminary experiments. When the synthesis of most acyloxysilanes is used 
in practice, there are no differences in respect to the space-time yield 
if the reaction temperature used in each case in the individual reaction 
units of the reactor system is kept in the temperature range of 50.degree. 
to 90.degree. C. 
The procedure described thus far for reacting the starting substances of 
organochlorosilane and monocarboxylic acid anhydride in the reaction units 
of the reactor system can be carried out with economically acceptable 
space-time yields only if, in accordance with the present invention, the 
reaction of the starting substances fed in is carried out in the presence 
of additives having a catalytic action. 
Organic bases, salts thereof and acid amides have proved to be particularly 
suitable substances having a catalytic action for carrying out the 
procedure according to the invention. 
Primary, secondary and tertiary amines can thus be employed as organic 
bases. Examples which may be mentioned are the compounds phenylamine, 
cyclohexylamine, propylamine, isopropylamine, morpholine, piperidine, 
dicyclohexylamine, triethylamine, triethanolamine, pyridine, 
benzothiazole, and methylpyrrolidone. 
It has been found that secondary and tertiary amines containing different 
groups in the molecule, for example, methylethylamine and 
dimethylethylamine, are also active in the context of the present 
invention. Mixtures of the amines mentioned likewise show a corresponding 
activity, without positive or negative synergistic effects having been 
found. 
No differences have been found in using salts compared with using the bases 
themselves in respect to activity in carrying out the reactions according 
to the invention. The salt form which is preferably employed is 
hydrochloride. However, hydrobromides and the salts formed with organic 
acids, such as the propionates, can also be employed without limiting the 
activity. The salts of the organic bases employed are preferably added to 
the reaction starting substances in dissolved form, ethanol, for example, 
being a suitable solvent. 
Organic acid amides have proved to be equally effective as the organic 
bases and salts thereof in accelerating the course of the reaction 
according to the invention. Examples which may be mentioned are the 
compounds acetamide, N-methylacetamide, N,N-methylethylpropionamide, 
benzamide and thiourea. 
The acid amides are added in liquid or also in dissolved form. Mixtures of 
the above acid amides also show a corresponding activity, without 
synergistic effects being observed here. 
The amount of additives to be used can be varied within wide limits. To 
achieve optimum results the amounts of active substance to be added to the 
mixture of the starting substances can be 5 to 1,000 ppm. The preferred 
range is 10 to 100 ppm, based on the particular mixture of the reactants 
intended for reaction. The use of larger amounts provides no further 
advantages. 
The reaction mixture which has essentially been freed from the 
corresponding carboxylic acid chlorides passes from the distillation 
reactor into the central intake of a column used as a distillation column 
in a manner which is known per se. The column can be operated either under 
normal pressure or under reduced pressure. The mode of operation of the 
column is adapted to suit the particular heat stability of the 
acyloxysilanes prepared. The carboxylic acid chloride is preferably 
removed from the distillation reactor under a pressure of 5 to 300 mbar. 
The particularly preferred made of operation comprises operating the 
column under a pressure of 5 to 25 mbar. With this mode of operation, the 
boiling range of the carboxylic acid anhydride employed corresponding to 
the particular column internal pressure is established as the temperature 
at the top of the column. 
As already mentioned, the mode of operation of the column is adapted to 
suit the heat stability of the acyloxysilanes formed in each case. In 
other words the operating pressure in the column is chosen so that at the 
bottom of the distillation column a temperature prevails which is below 
the temperature at which intermolecular condensation of the acyloxysilane 
present is detectable. 
1.05 to 1.2 mol of carboxylic acid anhydride are preferably employed per 
gram-atom of silicon-bonded chlorine.

The invention is explained below with the aid of the drawing and the 
examples. 
The drawing shows, schematically, an embodiment of a plant for carrying out 
the process according to the invention. The starting substances of 
organochlorosilane and carboxylic acid anhydride together with additives 
which act as catalysts are fed from storage tanks 1 and 2 via metering 
pumps 3 and 4 into reactor 5 continuously in a fixed ratio of amounts, and 
are brought to the reaction temperature in this reactor. The reaction 
mixture passes from reactor 5 into reactor 6, from which it is passed, 
metered via rotameter 7, into distillation reactor 9, which is connected 
to a vacuum system 8. The carboxylic acid chloride formed is removed from 
the reaction mixture in this reactor, and after passing through vacuum 
pump 8 collects in cooling reservoir 14. The product which remains, which 
may still contain small amounts of carboxylic acid chloride and unreacted 
starting substances, is fed via flowmeter 10 into the central intake of 
the column 11, filled with saddle packing, of a distillation column 
connected to a vacuum system 15. Excess carboxylic acid anhydride is 
removed in the upper part of the column and fed continuously to cooled 
reservoir 12. The acyloxysilane is removed continuously from the bottom 13 
of the distillation column. 
EXAMPLE 1 (COMISON EXAMPLE) 
Preparation of ethyl-tris(ethanoyloxy)silane and ethanoyl chloride 
Ethyltrichlorosilane is introduced into reservoir tank 1 and ethanoic 
anhydride into reservoir 2. 125 g (0.765 mol) of ethyltrichlorosilane per 
hour and 281 g (2.76 mols) of ethanoic anhydride per hour are fed by means 
of metering pumps 3 and 4 into the lower part of reactor 5 (volume=1 
liter), in which the starting substances are heated to 60.degree. C. After 
passing through reactor 5, the reaction mixture enters, via condenser 16, 
reactor 6 (volume=1 liter), in which it is kept at 60.degree. C. and from 
which it is then fed, via rotameter 7, into distillation reactor 9 
(volume=1 liter) in an amount of about 406 g per hour. The reaction 
mixture is heated to 90.degree. C. in this reactor, and the ethanoyl 
chloride formed so far and still forming is distilled off from the 
reaction mixture under a pressure of 50 to 60 mbar (vacuum pump 8) and 
taken via condenser 18 to cooled reservoir 14. The amount of ethanoyl 
chloride collected per hour in reservoir 14 is about 172 g (2.2 mols) 
The product removed in the upper part of distillation reactor 9 is 
introduced via rotameter 10 into the central intake of distillation column 
11, which consists of a 1.60 m long glass tube of 5 cm diameter and is 
filled with saddle packing of 6 mm diameter. Condenser 19 at the top of 
the column and distillate reservoir 12 are charged with a cooling liquid 
(- 27.degree. C.) A 4 liter double-walled flask 13 heated by a thermostat 
(circulation temperature about 125.degree. C.) forms the bottom end of the 
column. The crude product fed in is worked up in the distillation column 
under an internal column pressure of 5 to 7 mbar at a temperature of about 
110.degree. C. at the bottom of the column. Ethyl-tris(ethanoyloxy)silane 
is constantly removed from the double-walled flask 13, which is 
half-filled with liquid, at a rate such that the level of liquid in flask 
13 remains unchanged. Excess ethanoic anhydride is distilled off in the 
upper part of the column, and is collected in distillate reservoir 12. The 
residual ethanoyl chloride is distilled off at the top of the column via 
condenser 19 and vacuum pump 15 into reservoir 14 provided with condenser 
17. 
The product removed from the double-walled flask 13 consists of 
______________________________________ 
ethyl-tris(ethanoyloxy)- 
about 95.8% by weight 
silane 
ethyl-di(ethanoyloxy)- 
about 0.37% by weight 
chlorosilane 
ethyl-ethanoyloxy- about 0.06% by weight 
dichlorosilane 
siloxanes about 1.9% by weight 
ethanoic anhydride about 1.8% by weight 
chlorine, hydrolyzable 
about 800 ppm. 
Yield: 97.5% 
______________________________________ 
EXAMPLE 2 (COMISON EXAMPLE) 
Preparation of methyl-tris(propanoyloxy)silane and propanoyl chloride 
The procedure described in Example 1 is repeated, with the following 
changes being made: 
Instead of ethyltrichlorosilane and ethanoic anhydride, 
methyltrichlorosilane and propanoic anhydride are reacted. 
Methyltrichlorosilane is fed into the reactor system in an amount of 114 g 
(0.765 mol) per hour, and propanoic anhydride in an amount of 383 g (2.94 
mols) per hour. The amount of propanoyl chloride collected per hour in 
reservoir 14 is about 212 g (2.29 mols). The product removed from 
double-walled flask 13 of the distillation column has the following 
composition: 
______________________________________ 
methyl-tris(propanoyloxy)- 
about 96.1% by weight 
silane 
methyl-bis(propanoyloxy)- 
about 0.32% by weight 
chlorosilane 
methyl-propanoyloxydi- 
about 0.05% by weight 
chlorosilane 
siloxanes about 1.7% by weight 
propanoic anhydride 
about 1.8% by weight 
chlorine, hydrolyzable 
700 ppm. 
Yield: 96.9% 
______________________________________ 
EXAMPLE 3 (COMISON EXAMPLE) 
Preparation of methylpropyl-bis(ethanoyloxy)silane and ethanoyl chloride 
The procedure described in Example 1 is repeated, with the following 
changes being made: 
Instead of ethyltrichlorosilane, methylpropyldichlorosilane is reacted with 
ethanoic anhydride. Methylpropyldichlorosilane is fed into the reactor 
system in an amount of 120 g (0.765 mol) per hour, and ethanoic anhydride 
in an amount of 234 g (2.29 mols) per hour. 
The amount of ethanoyl chloride collected per hour in reservoir 14 is about 
120 g (1.53 mol). 
The product removed from double-walled flask 13 of the column has the 
following composition: 
______________________________________ 
methylpropyl-bis(ethanoyl- 
96.7% by weight 
oxy(silane) 
methylpropyl-ethanoyloxy- 
0.7% by weight 
chlorosilane 
siloxanes 1.5% by weight 
ethanoic anhydride 1.1% by weight 
chlorine, hydrolyzable 
about 1,180 ppm. 
Yield: 97.5% 
______________________________________ 
EXAMPLE 4 
Preparation of ethyl-tris(ethanoyloxy)silane and ethanoyl chloride 
The procedure described in Example 1 is repeated, with the following 
amendments being made: 
Instead of 125 g (0.765 mol) of ethyltrichlorosilane and 281 g (2.76 mols) 
of ethanoic anhydride, 156 g (0.96 mol) of ethyltrichlorosilane and 352 g 
(3.46 mols) of ethanoic anhydride, to which 51 mg of triethylamine have 
been added (corresponding to 100 ppm, based on the mixture of the 
reactants), are used per hour for the feed. 
The product removed from double-walled flask 13 consists of: 
______________________________________ 
ethyl-tris(ethanoyloxy)- 
97.2% by weight 
silane 
ethyl-di(ethanoyloxy)- 
-- 
chlorosilane 
ethyl-ethanoyloxy- -- 
dichlorosilane 
siloxanes 1.7% by weight 
ethanoic anhydride 1.1% by weight 
chlorine, hydrolyzable 
3 ppm. 
Yield: 97.8% 
______________________________________ 
EXAMPLE 5 
Preparation of ethyl-tris(ethanoyloxy)silane and ethanoyl chloride 
The procedure described in Example 4 is repeated. Instead of 51 mg of 
triethylamine, an amount of 5.1 mg of triethylamine (corresponding to 10 
ppm, based on the mixture of the reactants) is added to the ethanoic 
anhydride. 
The product removed from double-walled flask 13 consists of: 
______________________________________ 
ethyl-tris(ethanoyloxy)- 
97.2% by weight 
silane 
ethyl-di(ethanoyloxy)- 
-- 
chlorosilane 
ethyl-ethanoyloxy- -- 
dichlorosilane 
siloxanes 1.9% by weight 
ethanoic anhydride 0.9% by weight 
chlorine, hydrolyzable 
5 ppm. 
Yield: 97.6% 
______________________________________ 
EXAMPLES 6 TO 9 
Preparation of ethyl-tris(ethanoyloxy)silane and ethanoyl chloride 
The procedure described in Example 4 is repeated. Instead of 51 mg of 
triethylamine, an amount of 
25 mg of phenylamine or 
25 mg of cyclohexylamine or 
25 mg of n-propylamine or 
25 mg of isopropylamine 
(corresponding to 50 ppm, based on the mixture of the reactants) is added 
to the ethanoic anhydride. 
The products removed from double-walled flask 13 have the following 
composition range: 
______________________________________ 
ethyl-tris(ethanoyloxy)- 
97.2 to 97.4% by weight 
silane 
ethyl-di(ethanoyloxy)- 
-- 
chlorosilane 
ethyl-ethanoyloxy- -- 
dichlorosilane 
siloxanes 1.9 to 2.0% by weight 
ethanoic anhydride 0.6 to 0.9% by weight 
chlorine, hydrolyzable 
2 to 7 ppm. 
Yield: 97.2 to 97.4%. 
______________________________________ 
EXAMPLES 10 TO 12 
Preparation of ethyl-tris(ethanoyloxy)silane and ethanoyl chloride 
The procedure described in Example 4 is repeated. Instead of 51 mg of 
triethylamine, an amount of 
18 mg of diethylamine or 
18 mg of dicyclohexylamine or 
18 mg of piperidine 
(corresponding to 35 ppm, based on the mixture of the reactants) is added 
to the ethanoic anhydride. 
The products removed from double-walled flask 13 have the following 
composition range: 
______________________________________ 
ethyl-tris(ethanoyloxy)- 
97.0 to 97.3% by weight 
silane 
ethyl-di(ethanoyloxy)- 
-- 
chlorosilane 
ethyl-ethanoyloxy- -- 
dichlorosilane 
siloxanes 1.6 to 2.3% by weight 
ethanoic anhydride 0.7 to 1.1% by weight 
chlorine, hydrolyzable 
2 to 5 ppm. 
Yield: 97.1 to 97.9%. 
______________________________________ 
EXAMPLES 13 TO 15 
Preparation of ethyl-tris(ethanoyloxy)silane and ethanoyl chloride 
The procedure described in Example 4 is repeated. Instead of 51 mg of 
triethylamine, an amount of 
34 mg of pyridine or 
34 mg of benzothiazole or 
34 mg of methylpyrrolidone 
(corresponding to 65 ppm, based on the mixture of the reactants) is added 
to the ethanoic anhydride. 
The products removed from double-walled flask 13 have the following 
composition range: 
______________________________________ 
ethyl-tris(ethanoyloxy)- 
96.5 to 97.4% by weight 
silane 
ethyl-di(ethanoyloxy)- 
-- 
chlorosilane 
ethyl-ethanoyloxy- -- 
dichlorosilane 
siloxanes 2.1 to 2.4% by weight 
ethanoic anhydride 0.7 to 1.1% by weight 
chlorine, hydrolyzable 
3 to 7 ppm. 
Yield: 96.8 to 97.4%. 
______________________________________ 
EXAMPLE 16 
Preparation of ethyl-tris(ethanoyloxy)silane and ethanoyl chloride 
The procedure described in Example 4 is repeated Instead of 51 mg of 
triethylamine, an amount of 52 mg of triethylamine hydrochloride 
(dissolved in ethanol, corresponding to 50 ppm, based on the mixture of 
the reactants) is added to the ethanoic anhydride. 
The product removed from double-walled flask 13 has the following 
composition: 
______________________________________ 
ethyl-tris(ethanoyloxy)- 
97.6% by weight 
silane 
ethyl-di(ethanoyloxy)- 
-- 
chlorosilane 
ethyl-ethanoyloxy- -- 
dichlorosilane 
siloxanes 1.6% by weight 
ethanoic anhydride 0.8% by weight 
chlorine, hydrolyzable 
3 ppm. 
Yield: 97.9% 
______________________________________ 
EXAMPLES 17 TO 19 
Preparation of ethyl-tris(ethanoyloxy)silane and ethanoyl chloride 
The procedure described in Example 4 is repeated. Instead of 51 mg of 
triethylamine, an amount of 
50 mg of acetamide (dissolved in ethanol) or 
25 mg of N,N-methylethylacetamide or 
12 mg of thiourea (dissolved in ethanoic acid) 
(corresponding to 100 ppm or 50 ppm or 25 ppm, respectively, based on the 
mixture of the reactants) is added to the ethanoic anhydride. 
The products removed from double-walled flask 13 have the following 
composition range: 
______________________________________ 
ethyl-tris(ethanoyloxy)- 
97.0 to 97.2% by weight 
silane 
ethyl-di(ethanoyloxy)- 
-- 
chlorosilane 
ethyl-ethanoyloxy- -- 
dichlorosilane 
siloxanes 1.6 to 2.1% by weight 
ethanoic anhydride 0.9 to 1.2% by weight 
chlorine, hydrolyzable 
5 ppm. 
Yield: 97.4 to 97.8%. 
______________________________________ 
EXAMPLES 20 TO 24 
Preparation of methylpropyl-bis(ethanoyloxy)silane and ethanoyl chloride 
The procedure described in Example 3 is repeated, the following changes 
being made: 
Instead of 120 g (0.765 mol) of methylpropyldichlorosilane and 234 g (2.29 
mols) of ethanoic anhydride, 150 g (0.96 mol) of methyl 
propyldichlorosilane and 230 g (2.25 mols) of ethanoic anhydride, to which 
an amount of 
30 mg of n-propylamine or 
30 mg of diethylamine or 
30 mg of benzothiazole or 
30 mg of triethylamine hydrochloride (dissolved in ethanol) or 
30 mg of acetamide 
is added (corresponding to 75 ppm, based on the mixture of the reactants), 
are fed into the reactor system per hour. The products removed from 
double-walled flask 13 have the following composition range: 
______________________________________ 
methylpropyl-bis(ethanoyl- 
97.1 to 97.4% by weight 
oxy)silane 
methylpropyl-ethanoyloxy- 
-- 
chlorosilane 
siloxanes 1.6 to 2.2% by weight 
ethanoic anhydride 0.7 to 1.0% by weight 
chlorine, hydrolyzable 
5 to 7 ppm. 
Yield: 97.0 to 97.9%. 
______________________________________ 
EXAMPLE 25 
Preparation of vinyl-tris(propanoyloxy)silane and propanoyl chloride 
The procedure described in Example 2 is repeated, the following changes 
being made: 
Instead of 114 g (0.765 mol) of methyltrichlorosilane and 383 g (2.94 mols) 
of propanoic anhydride, 156 g (0.956 mol) of vinyltrichlorosilane and 440 
g (3.38 mols) of propanoic anhydride, to which 30 mg of methylethylamine 
and 30 mg of ethylamine have been added, are fed into the reactor system 
per hour. 
The product removed from double-walled flask 13 has the following 
composition: 
______________________________________ 
vinyl-tris(propanoyloxy)- 
97.3% by weight 
silane 
vinyl-bis(propanoyloxy)- 
-- 
chlorosilane 
vinyl-propanoyloxy- -- 
dichlorosilane 
siloxanes 1.8% by weight 
propanoic anhydride 0.9% by weight 
chlorine, hydrolyzable 
9 ppm. 
Yield: 97.7%. 
______________________________________ 
EXAMPLE 26 
Preparation of 2-chloroethylmethyl-bis-(ethanoyloxy)silane and ethanoyl 
chloride 
The procedure described in Example 4 is repeated. Instead of 156 g (0.96 
mol) of ethyltrichlorosilane and 352 g (3.46 mols) of ethanoic anhydride, 
to which 51 mg of triethylamine have been added, 255 g (1.44 mols) of 
2-chloroethylmethyldichlorosilane and 346 g (3.40 mols) of ethanoic 
anhydride, to which 51 mg of triethylamine have been added, are used per 
hour for the feed into the reactors. The product removed from 
double-walled flask 13 has the following composition: 
______________________________________ 
2-chloroethylmethyl-bis- 
97.2% by weight 
(ethanoyloxy)silane 
2-chloroethylmethyl- -- 
ethanoyloxy-chlorosilane 
siloxanes 1.8% by weight 
ethanoic anhydride 1.0% by weight 
chlorine, hydrolyzable 
10 ppm. 
Yield: 97.6% 
______________________________________ 
It will be understood that the specification and examples are illustrative 
but not limitative of the present invention and that other embodiments 
within the spirit and scope of the invention will suggest themselves to 
those skilled in the art.