It is provided a process for the preparation of a compound of formula (I)wherein R1 is selected from the group consisting of H, -OM, -CH3, -COOM, -CH2OH, -CH(CH3)(OH), and -NH2；R2 is selected from the group consisting of -H, -OM, -COOM, -NH2, -CH3CH(NH2)(CH2)3OH, -NH2(CH2)mCOOM, -CONH2, -NHC(NH2)2, -SH, -SCH3, -CH(CH3)2, -CH(CH3)(OH), -CH(CH3)(CHCH2CH3), -PhOH, -Ph,and-NH2(CH2)mOM, wherein m is 1 or 2；R3, R4, R5, and R6 are independently selected from the group consisting of -H, -OM, -COOM, -NH2, -SO3M, (C1-C4)alkyl, and halogen；wherein M is independently selected from the group consisting of H, an alkali metal and NH4+, and n is 0 to 1,the process comprising reacting a compound of formula (II)wherein R3, R4, R5, and R6 are as defined above,with a compound of formula (III)wherein R1, R2 and n are as defined above,and glyoxylic acid or a salt thereof in the presence of a base, without the addition of an organic solvent, and in the presence of an amount of water from 1 to 13.3 mol for each mol of glyoxylic acid.
