Methane photochlorination

Figure 7. Temperature dependence of quantum yield of chlorine consumption in reaction of methane photochlorination in structurally nonequilibrium glassy mixes of reactants (1) structurally nonequilibrium mix of reactants prepared by rapid spraying at 22 K (2) same mix after thermal annealing at 30-40 K (3) same mix after ultrasonic treatment at 22 K.

Chlorination of Alkanes. The most direct and economical method for the manufacture of chloromethanes is the thermal free-radical chlorination of methane.176 177 Whereas in the 1940s and 1950s photochlorination was practiced in some plants, thermal chlorination is the principal industrial process today. The product chloromethanes are important solvents and intermediates. Commercial operations perform thermal chlorination at about 400-450°C. Vapor-phase photochemical chlorination of methane may be accomplished at 50-60°C. Fast and effective removal of heat associated with thermally induced free-radical substitution is a crucial point. Inadequate heat control may lead to explosion attributed to the uncontrollable pyrolysis liberating free carbon and much heat ... 

After having considered a specific example, namely the photochlorination of methane, we will now consider the general pathway for such reactions. A free radical reaction need only have an initiation step and a termination step. However, this would be most unusual, because normally one or more propagation steps interpose. The reason is because, as radicals are very... 

Chain reaction A reaction that is self-perpetuating, e.g. the photochlorination of methane. The product quantum yield is greater than one, which means that more molecules of product are formed than quanta of light are absorbed by the reagent. There is typically an initiation step, followed by a large number of propagation steps, ending with a series of termination steps. 

Methanesulfonic acid is primarily manufactured by the batch or continuous oxidation of the methyl mercaptan or dimethyl disulfide with chlorine in saturated aqueous hydrochloric acidJ This chemistry is also the basis for much of the worldwide production of MSC, with photochlorination of methane (vide infra) being the most significant commercial alternative. Other alkanesulfonyl chlorides and sulfonic acids have also been produced in lesser quantities by the CI2/H2O oxidation. Reaction yields are typically 92-100%. The HCl by-product separates as vapor from the saturated reaction mixture. It is absorbed into water to afford a... 

PROBLEM 11.46 In Problem 11.25, we examine the photochlorination of ethane to give ethyl chloride. As was the case in the photochlorination of methane (p. 490), products containing more than one chlorine are also isolated in the photochlorination of ethane. What is the structure of the major dichloroethane produced in this reaction Rationahze your prediction with an analysis of the mechanism of the reaction. 

There is certainly strong experimental evidence for the existence of radical-solvent complexes. For instance, Russell and co-workers collected experimental evidence for radical-complex formation in studies of the photochlorination of 2,3-dimethylbutane in various solvents. In this work, different products were obtained in aliphatic and aromatic solvents, and this was attributed to formation of a tt-complex between the Cl atom and the aromatic solvent. Complex formation was confirmed by flash photolysis. Complex formation was also proposed to explain experimental results for the addition of trichloro-methane radical to 3-phenylpropene and to 4-phenyl-1-butene and for hydrogen abstraction of the t-butoxy radical from 2,3-dimethylbutane. " Complexes between nitroxide radicals and a large number of aromatic solvents have been detected. Evidence for complexes between polymer radicals and solvent molecules was collected by Hatada et al.f in an analysis of initiator fragments from the polymerization of MMA-d with AIBN and BPO initiators. They discovered that the ratio of disproportionation is combination depended on the solvent, and interpreted this as evidence for the formation of a polymer radical-solvent complex that suppresses the disproportionation reaction. 

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