ONIUM YLIDE CHEMISTRY. 1. BIFUNCTIONAL ACID-BASE-CATALYZED CONVERSION OF HETEROSUBSTITUTED METHANES INTO ETHYLENE AND DERIVED HYDROCARBONS. THE ONIUM YLIDE MECHANISM OF THE C₁ yields C₂ CONVERSION.

The conversion of heterosubstituted methanes, such as methyl alcohol, dimethyl ether, methyl mercaptan, dimethyl sulfide, methylamines, and methyl halides, to ethylene and hydrocarbons derived thereof takes place over bifunctional acidic-basic-supported transition-metal oxide or oxyhalide catalysts, such as tungsten oxide supported on alumina, between 300 and 350 degree C. The conversion of methyl alcohol starts with bimolecular dehydration to dimethyl ether followed by acid-catalyzed transmethylation giving trimethyloxonium ion (or related catalyst-bound methyloxonium ion). The trimethyloxonium ion then undergoes base-induced deprotonation forming a catalyst surface-bound methylenedimethyloxonium ylide. Intermolecular methylation of the ylide, indicated by experiments using singly **1**3C-labeled dimethyl ether, gives methylethyloxonium ion thus providing the crucial first C-C bond.