Ketenes, preparation from acyl halides

For acyl halides or anhydrides which do not afford ketenes in the presence of base (such as perfiuoroacyi halides), however, the a-acylmethylenephosphoranes can be prepared directly in one step from the phosphonium salts by using two equivalents of base by the present procedure (Table I).2 Both tetrahydrofuran and methylene chloride have been used as solvents and in the case of the title compound, tetrahydrofuran provides the best results. Good yields of the phosphoranes are generally obtained when is an electron-withdrawing group such as ester or nitrile. The yields of phosphoranes obtained for the thiomethyl or phenyl cases can be... 

Dimers of other ketenes also can be prepared from the monomers, but frequently it is more convenient to prepare the dimers directly by extending the reaction time or increasing the reaction temperature. The most convenient preparation of higher aldoketene dimers is that of dehydro-halogenation of acyl halides with tertiary aliphatic amines." ... 

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