Electrophilic methane conversion

Abstract

Conversion of methane into substituted derivatives and higher hydrocarbons is a most desirable goal. If we survey the literature and current textbooks of organic chemistry,' they report pyrolytic and free -radical reactions (such as combustion , hydrogenation, nitration, sulfochlorination).2 These reactions show little selectivity , characteristic of radical reactions . The chlorination of methane , for example , gives all four possible chloromethanes . Recently, catalytic oxidative condensation of methane to ethane with metal oxides3 gained significance . Conversion to ethylene and acetylene via high-temperature conversion with chlorine4 was also explored . It should be noted that the long-known high-temperature production of acetylene from methane is a related radical process . In many of these processes, however, a significant portion of methane is lost to further oxidation and soot formation. A new approach to the possible chemical conversion of methane involves organometallic insertion reactions.5 Pioneering work with iridium complexes and other transition-metal systems (rhodium , osmium , rhenium, etc.) was carried out. However , until now these were noncatalytic , stoichiometric reactions taking place in the coordination sphere of the metal complexes and therefore limited in their practical application. In the present Account an additional alternative, i.e., the-electrophilic conversion reactions of methane to condensed and substituted products , will be discussed, a field where the research interest of my group centered in recent years. Scheme I summarizes the presently existing alternative possibilities of methane conversion . Biological conversion of methane to higher hydrocarbons or to methyl alcohol may also be significant for the future.6