Microwave-assisted synthesis of naphthalenetetracarboxylic acid and o-phenylenediamine

The main method to produce vat red 14，a kind of vat dye，is through the reaction of naphthalenetetracarboxylic acid and o-phenylenediamine with the presence of catalyst. There exist two isomers of vat red 14，the trans-structure is named orange 7 and the cis-structure is named vat red 15. The investigations of microwave heating in the synthesis of vat red 14 were carried out，and the effects of different temperatures（130—160 ℃），reaction times （5—40 min），and heating rates were discussed. It was found that temperature，reaction time and heating rate were the key factors determining the reaction products. Cis-product decreased with increasing temperature，and long reaction time favored trans-product. Trans-product could reach as high as 61% at temperature of 160 ℃ and reaction time of 40 min. It was also found that pre-synthesis at 60—100 ℃ favored the formation of the trans-product.