- THE PHENYLCARBENE REARRANGEMENT REVISITED
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The evolution of mechanistic ideas about the phenylcarbene rearrangement has been reviewed, and three closely linked problems have been identified toward whose solution this research has been aimed: 1.Why do the ratios of the stable end products from the rearrangements of o-, m- and p-tolylmethylene differ when all three reactions have been thought to pass through a common intermediate? 2.Why does the rearrangement of 2-methylcycloheptatrienylidene lead to exclusive formation of styrene? 3.What is the mechanism of styrene formation from o-tolylmethylene? New mechanisms have been proposed in which m- and p-tolylmethylene can rearrange to styrene without necessarily being converted to o-tolylmethylene.The formation of a small amount of 2,6-dimethylstyrene from the rearrangement of 3,4,5-trimethylphenylmethylene is viewed as evidence for such a mechanism, and a set of interconverting norcaradienylidenes are believed to be the crucial intermediates.Other alternatives are considered and rejected on the basis of the rearrangement products of 3,5-dimethyl- and 3,4,5-trimethylphenylmethylene.
- Gaspar, Peter P.,Hsu, Jong-Pyng,Chari, Sarangan,Jones, Maitland Jr.
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p. 1479 - 1508
(2007/10/02)
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- Method for preparing C3 -C4 olefins and vinylaromatic compounds
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A method for preparing C3 -C4 olefins and vinylaromatic compounds, viz. styrene, vinyltoluenes or vinylxylenes which comprises alkylation of toluene or methyl derivatives thereof with a C2 -C3 olefin into the methyl group. The resulting alkylaromatic compounds are subjected to conversion to the desired products in the presence of ethylene on a catalyst consisting of chromium oxide, tungsten oxide and an oxide of an alkali or alkali-earth metal supported by a carrier. The method according to the present invention makes it possible to increase the yield of vinylaromatic compounds, obtain individual isomers of vinyltoluene or vinylxylene and efficiently utilize the part of the alkyl radical of the alkylaromatic compound lost in the prior art method.
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