Carbide-methylene polymerization hypothesis

This fact is particularly difficult to explain by the carbide-methylene polymerization hypothesis. It appears probable that the olefins are produced by dehydration of the alcohols and that the latter are very early products of the synthesis. 

The fact that only a relatively small fraction of singly-branched hydrocarbons is produced in the synthesis on iron and cobalt catalysts is very difficult to explain on the basis of the carbide-methylene polymerization hypothesis. Branching should occur whenever a carbidic carbon is included in a methylene polymerization chain, and as there is according to this hypothesis a considerable supply of carbidic carbon, branching should occur much more often than is the case. Furthermore, there is no explanation offered by this hypothesis as to why the branch is limited to a single methyl group. 

F. Fischer s hypothesis concerning the mechanism of the S3mthesis postulated the intermediary formation of cobalt or iron carbide and reduction of the carbide to methylene (CHj) groups. The latter would subsequently polymerize to yield unsaturated paraffin hydrocarbons. Although direct hydrogenation of preformed cobalt or iron carbide yields largely... 

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See also in sourсe #XX -- [ ]

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