S-(4-biphenyl)-thiosulphuric acids and their salts, method for producing the same and method for producing 4-mercaptobiphenyls

A process for preparing S-(4-biphenyl)-thiosulfuric acids and corresponding to the formula (I)

• in which
• A represents hydrogen, an equivalent of a metal atom or optionally substituted ammonium and
• R and R′ independently of one another each represent hydrogen, a C1-C6-alkyl group, a C1-C6-alkoxy group or a halogen, the process comprising reacting
• A) S-(4-biphenyl)-sulfinic acids or salts thereof of the formula (II)
• with
• B) an aqueous bisulfite solution at a pH in the range from 2 to 7.

A process for preparing 4-mercaptobiphenyls of the formula (III)

• in which R and R′ are independently of one another each represent hydrogen, a C1-C6-alkyl group, a C1-C6-alkoxy group or a halogen;
• the comprising the steps of heating
• A) S-(4-biphenyl)-thiosulfuric acids and salts corresponding to the formula (I)
• in which
• A represents hydrogen, an equivalent of a metal atom or optionally substituted ammonium and
• R and R′ independently of one another each represent hydrogen, a C1-C6-alkyl group, a C1-C6-alkoxy group or a halogen, with
• B) an aqueous bisulfite solution at a pH of from 2 to 7 in the presence of a strong aqueous acid and
• C) reducing the resulting bisdiphenyl disulfide of the formula (IV)
• wherein the compounds of formula (I) are prepared with a process that comprises the steps of (1) reacting S-(4-biphenyl)-sulfinic acids or salts thereof of the formula (II)
• with (2) an aqueous bisulfite solution at a pH in the range from 2 to 7.