Process for purifying acetoxysiloxanes
Processes are described for purifying acidic, preferably superacidic, in particular trifluoromethanesulfonic acid-acidified, end-equilibrated acetoxysiloxanes, wherein the acidic, preferably superacidic, in particular trifluoromethanesulfonic acid-acidified, acetic anhydride-containing and optionally acetic acid-containing equilibrated, preferably end-equilibrated acetoxysiloxane, which is optionally dissolved in an inert solvent, is contacted with a base, the precipitate is filtered off thereafter and then the filtrate obtained is optionally purified by distillation.
1. A process for purifying acidic equilibrated acetic anhydride-containing acetoxysiloxane, wherein
(a) the acidic acetic anhydride-containing equilibrated, acetoxysiloxane, which is optionally dissolved in an inert solvent, is contacted with a base, wherein the acetoxy siloxane contains acetic acid of from 0.4 to 3.5 per cent by weight, based on the acetoxysiloxane;
(b) a precipitate is filtered off; and
(c) the filtrate obtained is purified by distillation.
2. The process according to claim 1 , wherein in step (a) the base introduced is ammonia,
and thereafter the precipitate comprising ammonium triflate, ammonium acetate or acetamide, is filtered off, and then the filtrate obtained is subjected to distillation in order to remove siloxane cycles, D 4 /D 5 /D 6 , and also any inert solvent used,
wherein the contact of the siloxane with ammonia is conducted in the temperature range from 0° C. to 50° C., wherein an one- to 10-fold stoichiometric excess of ammonia, is used based on the cumulative amount of the acidic acetic anhydride-containing equilibrated acetoxysiloxane.
3. The process according to claim 1 , wherein in step (a) contact is made with a solid and/or liquid base, and thereafter the precipitate, is filtered off, and then the filtrate obtained is subjected to distillation, in order to remove acetic acid, acetic anhydride, siloxane cycles and also any inert solvent used,
wherein the solid and/or liquid base to be used comprises a hydrogen carbonate and/or carbonate of the alkali or alkaline earth metals, and/or an organic amine base, comprising primary and/or secondary amines and/or tertiary amines, hydroxyalkyl group-bearing amines selected from the group consisting of diisopropanolamine and triisopropanolamine,
wherein the contact of the siloxane with a solid and/or liquid base is conducted in the temperature range from 0° C. to 140° C., and
wherein a one- to 10-fold stoichiometric excess of solid and/or liquid base, is used based on the acid equivalent, to be neutralized.
4. The process according to claim 1 , wherein the acetoxy group-bearing siloxanes to be purified have been prepared from cyclic siloxanes D 4 /D 5 /D 6 , and/or from hydroxy group-bearing siloxanes and/or from mixtures of cyclic branched DT siloxanes using acid, as catalyst with acetic anhydride and with the addition of acetic acid or
in that a linear or branched, acetoxy function-bearing siloxanes to be purified have been prepared in a reaction system comprising
a) silanes and/or siloxanes bearing alkoxy groups, and/or
b) silanes and/or siloxanes bearing acetoxy groups, and/or
c) silanes and/or siloxanes bearing hydroxy groups, and/or
d) a reaction medium comprising acetic anhydride, perfluoroalkanesulfonic acid.
5. The process according to claim 1 , wherein the acetoxy group-bearing siloxanes to be purified contain acid in amounts of from 0.4 to 1.0 per cent by mass.
6. The process according to claim 1 , wherein the inert solvent is selected from the group consisting of alkanes, cycloalkanes, aromatics and alkylaromatics.
7. The process according to claim 1 , wherein the procedure is effected solventlessly.
8. The process according to claim 1 , wherein in step (a) contact is made with a solid and/or liquid base, and thereafter a precipitate comprising trifluoromethanesulfonate salts, is filtered off, and then the filtrate obtained is subjected to distillation, in order to remove acetic acid, the acetic anhydride, siloxane cycles and any inert solvent used,
wherein the solid and/or liquid base comprises a hydrogencarbonate and/or carbonate of the alkali or alkaline earth metals, and/or an organic amine base, comprising primary and/or secondary amines and/or tertiary amines, hydroxyalkyl group-bearing amines including diisopropanolamine, triisopropanolamine or an acetate salt,
wherein treatment of the siloxane with a solid and/or liquid base is conducted in the temperature range from 20° C. to 110° C.,
wherein a one- to 5-fold stoichiometric excess of solid and/or liquid base, is used based on a trifluoromethanesulfonic acid equivalent, to be neutralized.
9. The process according to claim 1 , wherein the acetoxy group-bearing siloxane to be purified contains acetic acid in amounts of from 0.8 to 1.8 per cent by weight, based on the acetoxy group-bearing siloxane to be purified.