The present invention relates to a compound of the general formula (I) where: X═S, SO or SO2； and one of the radicals R1 and R2 is a hydrogen atom and the other is a radical: a C1 to C18 linear or branched alkyl, optionally substituted by one or more halogen atom(s)； a C2 to C18 linear or branched alkenyl, optionally substituted by one or more halogen atom(s)； an aralkyl, optionally substituted by one or more C1 to C6alkoxy group(s)； or a COR3 or CONHR3, but not simultaneously, where R3 is a radical: a C1 to C18 linear or branched alkyl, optionally substituted by one or more halogen atom(s)； a C2 to C18 linear or branched alkenyl, optionally substituted by one or more halogen atom(s)； an aralkyl, optionally substituted by one or more C1 to C6alkoxy group(s)； an aralkenyl, optionally substituted by one or more C1 to C6 alkoxy groups and/or one or more OH group(s)； or an aryl radical, optionally substituted by one or more C1 to C6 alkoxy group(s).
