HOMOGENEOUS CATALYSIS BY HETEROPOLY ACIDS - A REDOX TRANSFORMATION OFH-4[SIMO12O40] IN ELECTROPHILIC REACTIONS

The transformation of the silico-molybdic acid (H-4[SiMo12O40]) used a s catalyst in the dehydration of 1,4-butanediol was studied by IR, UV- VIS and ESR spectroscopies. During the reaction, the color of the cata lyst changed gradually with the concomitant appearance of a broad new doubler in the 600-900 nm region in the electron spectra. At the begin ning, ESR data indicate valence-state change of the molybdenum in the heteropoly acid (Mo(VI)-->Mo(V)). After longer reaction times the reac tion mixture became diamagnetic. The phenomenon was rooted in the form ation of aldehydes and other fragments, which can provide suitable ele ctron transfer linkage for the formation of diamagnetic bridges betwee n molybdenum(V)-containing heteropoly blue species.