Azocoupling products.V~1.Electronic spectroscopy study of two azocoupling products of l-(4-hydroxy-6-methyl-pyrimidin-2-yl)-3-methyl-pyrazolin-5-one

摘要

A systematic study of the effect of solvent,sample concentration,time and acid or alkali addition,respectively of pH',upon the electronic absorption spectra of two dyes 7 and 8,as well as the pK_a' determination of these dyes was carried out.In C_6H_6,CHCl_3,DMSO,and acidic media (AcOH,acidified EtOH) these dyes that theoretically may be involved in azo-hydrazone tautomerism have been detected only as hydrazone tautomers 7e and 8c.In exchange,in neutral and alkalized EtOH,respectively in DMF,in concentration range 10~(-4)-10~(-6) mol L~(-1) these tautomers are in equilibrium with monodeprotonated (9,10) and twice deprotonated (13,14) species.By increase of pH,or by dilution,the equilibrium shifts increasingly towards the deprotonated species.The monodeprotonated species,correspond also to a hydrazone structure 9,10,whilst the doubly deprotonated species represent a common dianion that should be predominantly azo in character (13,14).