STUDY OF THE REACTION OF MAGENTA WITH NITRITE IN ACIDIC MEDIUM

The reaction of magenta with nitrite in an acidic medium of H_2SO_4 or HCl has been used as a method for the determination of nitrite ion. By a thorough UV-spectrophotometric study, it was concluded that ① in a relatively strong acidic medium, one of the amino group in magenta morecule is diazotized with NO~-_2 ion, and finally hydrolyzed to form a hydroxy group. ② The for mation ratio of the reaction product of magenta and NO~-_2 was found to be 1 to 1, and its structure was deduced. ③ Explanation for the phenomenon of "red shift" of absorption maxina of the reaction product in the presence of excess amount of NO~-_2 was given. It was stated that elucidation of the mechanism mentioned above provides a theoratical basis for the optimization of reaction condition in the determination of nitrite by this reaction.