Chloromethane acidic catalyst

Zinc chloride is also a catalyst for a liquid-phase process using concentrated hydrochloric acid at 100-150°C. Hydrochloric acid may be generated in situ by reacting sodium chloride with sulfuric acid. As mentioned earlier, methyl chloride may also be produced directly from methane with other chloromethanes. However, methyl chloride from methanol may be further chlorinated to produce dichloromethane, chloroform, and carbon tetrachloride. 

Hydrostannation of carbonyl compounds with tributyltin hydride is promoted by radical initiation and Lewis or protic acid catalysis.The activation of the carbonyl group by the acidic species allows the weakly nucleophilic tin hydride to react via a polar mechanism. Silica gel was a suitable catalyst allowing chemoselective reduction of carbonyl groups under conditions that left many functional groups unchanged. Tributyltin triflate generated in situ from the tin hydride and triflic acid was a particularly efficient catalyst for the reduction of aldehydes and ketones with tributyltin hydride in benzene or 1,2-di-chloromethane at room temperature. Esters and ketals were not affected under these conditions and certain aldehydes were reduced selectively in preference to ketones. 

It is now possible to polymerize isobutylene to butyl rubber in toluene instead of the usual chloromethane.215 A new titanium sandwich catalyst does the trick. European manufacturers are phasing out some chloroparaffin lubricants.216 In Japan, rubber is being chlorinated in water instead of carbon tetrachloride.217 This still involves chlorine, but does get rid of the solvent. 1,2-Dimethoxyethane is being used as an alternative to chlorinated solvents for the Schmidt Reaction for conversion of an ester to an amine through an acid azide and a carbamate (3.6).218 This eliminated accidents from polyazides made in situ from methylene chloride or chloroform. 

The Ci5-phosphonium salt for astaxanthin is obtained by addition of a lithium acetylide (with n-butyllithium [63]) to the ketal-protected ketone, followed by the cleavage of the alcohol protecting groups, and crystallisation from diisopropyl ether. The triple bond is reduced with zinc and acetic acid in di-chloromethane or with hydrogen on a Lindlar catalyst. The alcohol is converted into the corresponding bromide in a biphasic system of HBr in dichlo-romethane, and finally reacted with triphenylphosphane to give the phospho-nium salt. 

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