Sulphinic acid derivatives, method for producing them, and their use

A sulfinic acid compound of the formula (I)

• and the salt thereof, wherein
• M is a hydrogen atom, an ammonium ion, a monovalent metal ion or an equivalent of a divalent metal ion of the groups Ia, IIa, IIb, IVa or VIIIb of the Periodic Table of the Elements;
• R1 is OH;
• R2 is H or an alkyl, alkenyl, cycloalkyl or aryl group, wherein the alkyl, alkenyl, cycloalkyl, and aryl group are unsubstituted or substituted with 1, 2 or 3 substituents which are chosen independently of one another from C1-C6-alkyl, OH, O-C1-C6-alkyl, halogen and CF3;
• and
• R3 is COOM or COOR4;
• and
• R4 and R5 independently of one another are H or C1-C6 alkyl.