Process for preparing polysulfane silanes

A process for preparing polysulfane silanes of the formula I

• (R1O)3-mR2mSi—R3—Sx—R3—SiR2m(OR1)3-m I,
• wherein R1 are identical or different and are C1-C10 alkyl groups, phenyl groups or alkyl polyether groups —(R′—O)r—R″, where R′ are identical or different and are a branched or unbranched, saturated or unsaturated, aliphatic, aromatic or mixed aliphatic/aromatic divalent C1-C30 hydrocarbon group, r is an integer from 1 to 30, and R″ are unsubstituted or substituted, branched or unbranched monovalent alkyl, alkenyl, aryl or aralkyl group,
• R2 are identical or different and are C6-C20 aryl groups, C1-C10 alkyl groups, C2-C20 alkenyl groups, C7-C20 aralkyl groups or halogens,
• R3 are identical or different and are branched or unbranched, saturated or unsaturated, aliphatic, aromatic or mixed aliphatic/aromatic divalent C1-C30 hydrocarbon groups, and m are identical or different and are 0, 1, 2 or 3,
• x is 1-10,
• by reaction of silane of the formula II
• (R1O)3-mR2mSi—R3-Hal II
• where R1, R2, R3 and m are as defined above and Hal is a halogen,
• with one or more metal sulfides of the formula III
• M(SH)f and/or M3-fSx-y III
• where M is an element of main group 1 or 2,
• f=1 for M of main group 1 and f=2 for M of main group 2 and y has a value from 0 to x−1,
• optionally in the presence of one or more salts of monohydric or polyhydric acids,
• with the optional addition of y mol of sulfur,
• in aqueous R1—OH solvent, wherein R1 is as defined above,
• the water content of the aqueous R1—OH solution is 5% to 40% by weight, characterized in that
• a. the process stream from the reaction of silane of the formula II with one or more metal sulfides of the formula III, optionally in the presence of one or more salts and optionally with the addition of sulfur, in aqueous R1—OH solution, comprising polysulfane silanes of the formula I, solvent R1—OH, water and process salts, is combined with a wash solution from step d, comprising solvent R1—OH, water and polysulfane silanes of the formula I,
• b. the solvent R1—OH and water are removed by distillation,
• c. a remaining suspension comprising polysulfane silane of the formula I and process salt is subjected to a filtration or a sedimentation,
• d. the process salt from step c is washed with solvent R1—OH and then dried, and
• the wash solution comprising solvent R1—OH, water and polysulfane silane of the formula I is recycled to process step a.