Functional action of Keggin-type mono-vanadium(V)-substituted heteropolymolybdate as a single species on catalytic hydroxylation of benzene in the presence of hydrogen peroxide

✍ Scribed by Kenji Nomiya; Kazunori Yagishita; Yukihiro Nemoto; Tada-aki Kamataki

• Publisher: Elsevier Science
• Year: 1997
• Tongue: English
• Weight: 988 KB
• Volume: 126
• Category: Article
• ISSN: 1381-1169
• DOI: 10.1016/s1381-1169(97)00096-4

✦ Synopsis

Benzene hydroxylation in the presence of hydrogen peroxide has been studied using tetrabutylammonium salts of three types of mono-vanadium(V)-substituted heteropolyanions (HPA) as catalyst precursors: (i) [PMo, ,V0,,14-(PMo, , V, l), which has been first prepared herein and identified as a single species, (ii) '[PMo, ,VO,,]"-' ('PMo, , V', 41, which has been obtained traditionally by the so-called ether-extraction method and known as a mixed species only with an averaged composition P:Mo:V = 1: I I : 1 and (iii) [PW, ,V0,]4-(PW, ,V, 2), which has been prepared as a single species. The PMo, , V, 1, catalytically oxidized benzene to phenol under the conditions: 0.1 mmol catalyst, 10 ml (113 mmol) benzene, 5 or IO ml of CH,CN and 2 ml of 30% aqueous H,O,. The catalytic turnover by 1 for phenol production was dependent on the amount of CH,CN: it was I .3 after 120 h reaction with 10 ml CH,CN and 1.7 after 192 h reaction with 5 ml CH,CN. On the other hand, the PW,, V, 2, did not show catalytic activity even after 240 h reaction under the same conditions. In comparison, it was also confirmed there was no catalytic effect by [PMo,,O,,]~-(PMo,,, 3) without a vanadium(V) center. The 'PMo,,V', 4, has apparently shown a more enhanced effect, e.g. with catalytic turnover of 7.5 after 144 h reaction with IO ml CH,CN. These observations significantly suggest that the catalysis by 1 for benzene hydroxylation is due to cooperative action of the molybdenum framework with one vanadium(V) center. Such action of the polyoxoanion framework has not been observed in the selectively site-substituted vanadium(V) heteropolytungstates such as [ a-I ,2-PW,,,V20,,I]'m and [ (Y-I,~,~-PW~V~O~~]~~, the catalyses by which were due to the dinuclear vanadium centers with corner-shared octahedra. Furthermore, the marked stability of the mono-vanadium(V)-substituted species 1 of several vanadium(V)-substituted heteropolymolybdates as catalyst precursors was clarified in the benzene hydroxylation. 0 1997 Elsevier Science B.V.