SIDE REACTIONS FROM THE REDUCTION OF AZO DYES WITH DITHIONITE

The recently introduced amendment to the Consumer Goods Act in Germany concerns itself with the prohibition of the manufacture, marketing an d import of consumer goods dyed with those azo dyes, which by cleavage of the azo bond(s) can liberate certain toxic listed aromatic amines. In many laboratory analytical methods the reduction of the azo bond i s accomplished by treatment with sodium dithionite. However, using thi s strong reducing agent more than just the azo groups can be cleaved a s specified in the German Act. In some cases even new amines can be ge nerated which are neither part of the dye structure nor involved in th e synthesis of the dye. These additional amines are formed by a side r eaction due to the analytical procedure used and can thus lead to inco rrect analytical results. The example reported here relates to the for mation of 4-aminodiphenyl, when the diazo component is aniline.