Quinones as co-catalysts and models for the surface of active carbon in the phosphovanadomolybdate-catalyzed aerobic oxidation of benzylic and allylic alcohols: Synthetic, kinetic, and mechanistic aspects

Ronny Neumann, Alexander M. Khenkin, Inga Vigdergauz

Research output: Contribution to journalArticle

53 Citations (Scopus)

Abstract

Quinones have been considered as reactive compounds present on the surface of active carbon. Thus, the co-catalytic use of quinones combined with the phosphovanadomolybdate polyoxometalate, PV2Mo10O40 5-, has been studied as an analogue of the known PV2Mo10O40 5-/C catalyst in oxidative dehydrogenation reactions. From the synthetic point of view both biphasic the quinone (org)-Na5PV2Mo10O40-(aq) and monophasic quinone (org)-4Q5PV2Mo10O40-(org) [4Q = (nC4H9)4-N+] systems are effective for the selective oxidation of benzylic and allylic alcohols to their corresponding aldehydes. Kinetic measurements carried out on the model oxidative dehydrogenation of 4-methylbenzyl alcohol in the presence of p-chloranil, 4Q5PV2Mo10O40, and molecular oxygen showed that the reaction was non-elementary, although the 4-methylbenzyl alcohol oxydehydrogenation was the rate-determining step. ESR measurements showed the presence of the semiquinone of p-chloranil, probably as a complex with the polyoxometalate. This proposed complex was shown to be a more potent oxidant than p-chloranil. Thus, for the oxidation of 4-methoxytoluene the semiquinone complex was active, whereas p-chloranil alone was inactive. Beyond the importance of understanding quinone-phosphovanadomolybdate polyoxometalate-catalyzed reactions, insight gained from the formation of semiquinone active species can be applied for heterogeneous and aerobic oxidative transformations catalyzed by PV2Mo10O40 5- with carbon matrices as active supports.

Original languageEnglish
Pages (from-to)875-882
Number of pages8
JournalChemistry - A European Journal
Volume6
Issue number5
Publication statusPublished - Mar 3 2000

    Fingerprint

Keywords

  • Active carbon
  • Oxidations
  • Oxygen
  • Polyoxometalates
  • Quinones

ASJC Scopus subject areas

  • Chemistry(all)

Cite this