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 language | English |
|---|---|
| Pages (from-to) | 875-882 |
| Number of pages | 8 |
| Journal | Chemistry - A European Journal |
| Volume | 6 |
| Issue number | 5 |
| Publication status | Published - Mar 3 2000 |
Fingerprint
Keywords
- Active carbon
- Oxidations
- Oxygen
- Polyoxometalates
- Quinones
ASJC Scopus subject areas
- Chemistry(all)
Cite this
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. / Neumann, Ronny; Khenkin, Alexander M.; Vigdergauz, Inga.
In: Chemistry - A European Journal, Vol. 6, No. 5, 03.03.2000, p. 875-882.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Quinones as co-catalysts and models for the surface of active carbon in the phosphovanadomolybdate-catalyzed aerobic oxidation of benzylic and allylic alcohols
T2 - Synthetic, kinetic, and mechanistic aspects
AU - Neumann, Ronny
AU - Khenkin, Alexander M.
AU - Vigdergauz, Inga
PY - 2000/3/3
Y1 - 2000/3/3
N2 - 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.
AB - 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.
KW - Active carbon
KW - Oxidations
KW - Oxygen
KW - Polyoxometalates
KW - Quinones
UR - http://www.scopus.com/inward/record.url?scp=0034599005&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0034599005&partnerID=8YFLogxK
M3 - Article
VL - 6
SP - 875
EP - 882
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
SN - 0947-6539
IS - 5
ER -