Abstract: A mixture comprising one or more compounds of the general formula (II) where R6 is H, C1 to C20 alkyl, where C1 to C20 alkyl comprises straight-chain or branched C1 to C20 alkyl groups or cyclic C3 to C20 alkyl groups, alkanoyl having C1 to C8 alkyl, where C1 to C8 alkyl comprises straight-chain or branched C1 to C8 alkyl groups or cyclic C3 to C8 alkyl groups, cyanophenyl, 2-chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, 2,4-dichlorophenyl, 3,4-dichlorophenyl, 2-bromophenyl, 3-bromophenyl, 4-bromophenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, dimethylphenyl, such as 3,4-dimethylphenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 2-ethylphenyl, 3-ethylphenyl, 4-ethylphenyl, 2-ethoxyphenyl, 3-ethoxyphenyl, 4-ethoxyphenyl, 4-isopropylphenyl, benzyl, 2-pyridyl, 3-pyridyl, 4-pyridyl, (carboxymethyl)phenyl, in which the carboxyl group may also be esterified with C1 to C6 alkyl, where C1 to C6 alkyl comprises straight-chain or branched C1 to C6 alkyl groups or cyclic C3 to C6 alkyl groups, (N,N