Method of preparing glycol esters of organosilanes

The present invention relates to a method of preparing dimeric or polymeric organosilane esters whose ester component is at least one glycol moiety and whose silicon atoms are linked together by a glycol moiety. These compounds are known and are used as hydraulic fluids whose preparation involves considerable difficulty. The present invention avoids these difficulties by setting out from organosilane diglycol esters or triglycol esters and transposing them with diglycols or polyglycols. In this transposition the glycol ether corresponding to the glycols is formed and is removed by distillation. The degree of condensation of the organosilane ester products depends on the weight-ratio of the organosilane glycol ester to the diglycols or polyglycols.

BACKGROUND OF THE INVENTION 
The subject matter of the present invention is a method for the preparation 
of glycol esters of organosilanes, in which at least two organosilicon 
groupings are linked together by a glycol or polyglycol moiety in the 
manner of an ester. The compounds are suitable as hydraulic fluids, heat 
carrier oils or system intermediates. 
It is known, for example, from German Offenlegungsschrift No. 2,445,552 
that a number of organosilane esters of mono- or polyfunctional organic 
hydroxy compounds in hydraulic oil formulations are a good guarantee of 
reliability and safety in hydraulically operated mechanical systems 
against very often life-threatening failures. This is due mostly to their 
water-binding properties, their compatibility with rubber and their 
heat-stability. They therefore constitute a considerable advance over the 
prior art. 
The desire to employ these substances practically, however, has hitherto 
been thwarted by the fact that the production of these compounds on a 
large technical scale presents serious problems. 
The above-mentioned compounds are essentially those of the formula 
##STR1## 
wherein R is a glycol substituent of the general formula 
##STR2## 
R'=RO-- or a substituent from the group R"; R"=alkyl (C.sub.1 -C.sub.20), 
branched if desired, alkenyl, cycloalkyl or aryl; 
R'"=H or CH.sub.3 ; 
n=1-12 
p=0-10 (average degree of condensation), 
and in some cases their branching products if R'=RO--. 
For lack of any more practical method of procedure, the preparation of 
these very much sought-after products had to be performed in accordance 
with the above-mentioned patents, by partially esterifying a chlorosilane 
of the formula 
##STR3## 
wherein X represents either chlorine or R' of the meaning given above, and 
R" has the same meaning as above, in the presence of an amine (pyridine, 
for example) intercepting hydrogen chloride, with a glycol of the formula 
##STR4## 
wherein R'" and n have the meaning given above, and then continuing and 
completing the esterification, also in the presence of an amine, with a 
glycol ether of the formula 
##STR5## 
wherein R'", R"" and q have the meaning given above. In some cases the two 
glycols could be used in reverse order. Towards the end of the reaction, 
the large and unusable amount of amine hydrochloride which necessarily had 
to form as a by-product had to be separated, and the large amount of 
solvent that had to be used on account of the great production of salt had 
to be removed by evaporation. 
Lastly, then, the surplus of salt still dissolved in the product had to be 
removed by a complex refinement because it cannot be tolerated in 
hydraulic applications. The yields of this burdensome method of 
preparation in no case exceeded 70%. The disadvantages of this method of 
preparation--the only one available heretofore--are obvious. 
To avoid the difficulties involved in the process described above, attempts 
have also been made to arrive at the desired products by the catalyzed or 
uncatalyzed transesterification of organosilane esters of the general 
formula 
##STR6## 
wherein Y represents a substituent R' in the meaning given above, or a 
substituent --OR"", and R"" also has the meaning given above, with glycols 
or glycol monoethers. These reactions, however, were very slow and 
incomplete. But it was regularly found that these processes of 
transesterification do not lead to the desired products but instead yield 
products of different composition. Especially the low alkoxy group is 
quite stubbornly retained, making the products unsuitable for hydraulic 
applications because their excessively low Gilpin vapor lock temperature 
impairs their ability to perform. These discouraging results suggested the 
conclusion that the transesterification approach is not promising, on 
account of the above-described disadvantages. 
The problem therefore existed of finding a method of preparing the 
above-named glycol esters which does not have the burdensome disadvantages 
described above.

BRIEF SUMMARY OF THE INVENTION 
As the solution to this problem, a method has been found which is 
characterized in that silicon esters of the general formula 
##STR7## 
wherein R, R' and R" have the same meanings as above, are mixed with 
glycols of General Formula III in a ratio determined by the degree of 
condensation desired (p), at temperatures of 20.degree. to 220.degree. C., 
and then the glycol monoalkyl ethers of General Formula IV are removed by 
fractional distillation. The procedure of the invention is performed with 
surprising ease, without catalyst, and rapidly and completely yields the 
sought-after compounds of General Formula I, while the glycol ethers of 
General Formula IV which are displaced by the incorporation of the glycols 
of General Formula III are recovered by distillation. The ratio of 
compounds VI and III to one another is what determines the average degree 
of condensation p that is achieved in the Compound I prepared in 
accordance with the invention. 
The molar ratio of the glycol ester VI to the alkylene glycol III is to 
amount to no more than 2:1. The greater the desired degree of condensation 
p is, the less is the amount of glycol ester VI that is required. 
The yields of the method of the invention are virtually quantitative, and 
the products are usable directly and without further purification, and yet 
they will comply with the very high quality requirements of hydraulic oil 
formulations. Even when combined with the other conditioners used in these 
formulations, such as stabilizers for example, the products prepared by 
the method of the invention are compatible and present no problems. 
Examples of substances prepared by the method of the invention are monomers 
and condensation products of: 
##STR8## 
Suitable starting substances in accordance with General Formula VI are, for 
example, 9,9-dimethyl-2,5,8,10,13,16-hexaoxa-9-silaheptadecane, 
15,15-dimethyl-2,5,8,11,14,16,19,22,25,28-decaoxa-15-silanonacosane, and 
ethyltris(2-ethoxypropoxy)-silane. These starting substances can be 
prepared simply in accordance with U.S. Pat. No. 4,228,092 from the 
corresponding chlorosilanes by direct esterification with the 
corresponding glycol monoethers, with the removal of hydrogen chloride. 
Suitable condensation substances in accordance with General Formula II are, 
for example, ethylene glycol, triethylene glycol, polyethylene glycol 500, 
1,2-propylene glycol, di-1,2-propylene glycol, tri-1,2-propylene glycol 
etc. It is desirable for the alkylene glycol (III) to have a boiling point 
that is higher than the boiling point of the glycol monoalkyl ether (IV) 
which is removed from the reaction mixture by distillation. 
The preparation of the compounds of General Formula I by the method of the 
invention in a simple and effective manner is best accomplished by mixing 
the two starting substances III and VI in the ratio determined by the 
desired degree of condensation p, and the mixture is placed in the body of 
a good vacuum distillation column. There it is allowed to react at 
temperatures of up to 220.degree. C., until the glycol has reacted with 
the silane esters (VI) to such an extent that at least a partial release 
of the glycol monoalkyl ether IV that forms in the reaction has taken 
place. The length of time will depend both on the temperature and on the 
compounds used. It is between approximately 50 minutes and 12 hours. 
Preferably the temperature is adjusted so that the distillation can begin 
after 2 to 4 hours have elapsed. The preferred temperatures are below the 
boiling points of the components involved, preferably between 90.degree. 
and 160.degree. C. Then the glycol monoalkyl ether of General Formula IV 
that has been displaced is fractionally distilled in such a manner that 
any remainder incompletely incorporated glycol of General Formula III do 
not pass over. This distillation can also be performed in vacuo. 
For this method of distillation in accordance with the invention, 
high-vacuum stills of three and more theoretical trays have proven 
especially valuable. In a column of this kind, at the optimum vacuum, the 
product can be freed of any still volatile substances, to such an extent 
that it satisfies all quality requirements of the hydraulic fluid art. If 
desired, the quality can be further improved by additional concentration 
in a short-cut distillation or in a falling film or thin layer evaporator. 
Glycol organosilane esters of General Formula I synthesized in this elegant 
manner by the method of the invention are suitable not only as hydraulic 
oil, in combination, if desired, with conditioners such as stabilizers and 
anticorrosive additives, but also as an improving additive in other 
hydraulic formulations. Furthermore, on account of their relatively high 
heat capacity, they are also suitable as agents for the transfer of heat. 
Due to their extraordinary thermal stability, they have a considerable 
life in closed heat transfer circuits, even at working temperatures around 
340.degree. C. Their very good compatibility with conditioners also make 
them suitable for use as aids in combining substances which are not 
miscible with one another; for example, chloroparaffins are miscible with 
silicone oils in the presence of the substances prepared in accordance 
with the invention. 
Example 
The two cubic meter boiler of a Sulzer column of approximately eight 
theoretical plates was charged with 330 kg (2.2 kmol) of triethylene 
glycol and 1538 kg (4 kmol) of 
12,12-dimethyl-2,5,8,11,13,16,19,22-octaoxa-12-silatricosane (BP.sub.0.1 
184.degree. C.; D.sub.4.sup.20 1.0396) and heated for 3 hours at 
128.degree. C. Then, at a reflux ratio of 5, and the boiler temperature 
rising slowly to 202.degree. C., at a vacuum of 0.6 mbar and 88.degree. C. 
top temperature, 716 kg of triethylene glycol monomethyl ether of a 
reusable, high purity, was distilled off over a period of approximate 5 
hours. Then the vacuum was lowered over a period of about 15 minutes to 
0.02 mbar, whereupon an additional 22 kg of distillate was obtained, which 
contained a small amount of starting ester plus additional ethylene glycol 
monomethyl ether. Finally the vacuum was relieved with dry nitrogen. 1130 
kg of a clear, colorless product (yield, about 99 %) of the structure: 
##STR9## 
with the value of p between 1.2 and 1.6 was withdrawn from the body of the 
column. 
The product has a silicon content of 9.86%. The density amounts to 
D.sub.4.sup.20 =1.057. 
The viscosities measured were: 
3.65 mPa.sec (95.degree. C.) 
11.75 mPa.sec (38.degree. C.) and 
990.44 mPa.sec (-40.degree. C.). 
The boiling point at standard pressure was 377.degree. C. The flash point 
was at 223.degree. C. 
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.