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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 °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 13C-labeled dimethyl ether, gives methylethyloxonium ion thus providing the crucial first C-C bond. No intramolecular Steven's-type rearrangement takes place, and methyl ethyl ether is not a significant intermediate as also shown in experiments comparing the products formed from reacting CD3OCH2CH3 under similar conditions. The ethyloxonium ion readily undergoes ß-elimination forming ethylene. Initialy formed ethylene subsequently can undergo further reaction with the ylide giving via cyclopropane propylene or it can undergo more complex alkylation/oligomerization/cracking reactions giving a mixture of alkenes, alkanes and via cyclization-dehydrogenation aromatics. The complexity of these processes was shown by reacting ethylene itself, as well as 13CH3OH and ethylene, under conditions of the condensation reaction. It is also necessary to differentiate initially formed ethylene via direct C¡ -* C2 conversion from that formed in secondary processes together with higher condensation products. The conversion of methyl mercaptan (dimethyl sulfide), methyl halides, and methylamines to ethylene follows similar onium ylide pathways.

The catalytic monohalogenation (chlorination and bromination ) of methane was achieved over either supported solid acid (such as FeO,Clr/Al2O3, TaOF3/A1203, NbOF3/A1203, ZrOF2/Ai203, SbOF3/Al2O3, SbFs/graphite , and Nafion-H/TaFs) or platinum metal (Pt/A1203 and Pd/BaSO4) catalysts. The reactions were carried out at temperatures between 180 and 250°C, with GHSV of 50-1400 giving 8-58% conversions with selectivity in methyl chloride (bromide) generally exceeding 90%. Limited methylene halide formation accompanies the reactions, but no formation of haloforms or carbon tetrahalides was observed. The mechanism of the halogenations is considered to involve insertion of a surface -coordinated electrophilic halogen species or electron-deficient metal site into a methane C-H bond involving five-coordinate intermediate carbonium ion formation, with subsequent cleavage-halogenolysis giving the monohalogenated methane. Catalytic hydrolysis of methyl halides was also studied over y-alumina-supported metal oxide /hydroxide catalysts , giving mixtures of methyl alcohol and dimethyl ether. Combining the selective monohalogenation of methane with subsequent hydrolysis and oxyhalogenative recycling of byproduct HX allows conversion of methane to methyl alcohol /dimethyl ether, a route which offers an alternative to the presently exclusively used preparation of methyl alcohol via syngas. The preparation of methyl halides and/or methyl alcohol/ dimethyl ether directly from methane also offers a way to convert methane via previously described bifunctional acid-base-catalyzed condensation into ethylene and subsequently into homogeneous lower olefins and/or higher hydrocarbons.Recently there has been a revival of interest in "C1 chemistry"2 from coal or natural gas) aiming at devising economical processes mostly utilizing syngas (i.e., mixtures of CO and H2 produced to manufacture hydrocarbons. An innovative new process for the 0002-7863 /85/1507 -7097 $01.50/0 0 1985 American Chemical Society Across Conventional Lines Downloaded from www.worldscientific.com by KAINAN UNIVERSITY on 02/05/15. For personal use only.

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reaction 8a ?=* 8b 5=* 8c -8d at 6 temperatures from 26 to 170 °C. In all cases, the position of equilibrium was approached from at least two initial mixtures of isomers with sufficiently different isomer compositions (for la ^lb, for example, pure la, pure lb, and a 1:1 mixture of these forms were used). The values of the thermodynamic parameters were evaluated by linear least-squares treatments of In K vs. T"1.