Methyl chloride ions, decomposition

The reaction of 39 with methyl 4,6-0-benzylidene-2-deoxy-2-iodo-a-D-altropyranoside (48) gave a complex mixture of products, from which methyl 4,6-0-benzylidene-2,3-dideoxy-a-D-eryf/iro-hex-2-eno-pyranoside (50) could be isolated. The formation of 50 was ex-plained83(b) by attack by chloride ion on the iodine atom in intermediate 49, followed by elimination of the substituent at C-3. Compound 50 itself reacts with reagent 39, and, therefore, prolonged reaction times led to extensive decomposition. 

As typified by the ethanolysis of (CH3)2Pd(PEt3)2, many solvolyses of metal-carbon bonds are found to be quite complex when studied in detail. Even the generalization that the C—M bond hydrolyzes to give alkane and metal ion is not universally valid. Schrauzer and Windgassen (23) found that a methylcobalt compound with dimethylglyoxime ligands gave methane and methyl chloride in a 3 1 ratio on treatment with hot concentrated hydrochloric acid. Traces of ethane also formed, apparently by thermal decomposition with formation of methyl radicals. Warm concentrated KOH solution decomposed this complex with formation of methane. 

A 1989 review of the literature by Clarke gave many examples which support the importance of copper-silicon rich phases near the surface during the MCS reaction. Clarke noted that CusSi (eta phase) forms above 880 °C but will form at 350 °C in the presence of chloride ion. Methyl chloride reacts with copper to form copper chloride which then serves as the chloride source needed for formation of the eta phase, thus explaining the shorter induction period obtained using copper chloride vs other copper catalysts. The mechanism of replacement of silicon from the surface is by diffusion of copper into the bulk silicon to reform a copper-silicon rich surface. Iron-silicon phases stabilize the eta phase and metal promoters catalyze chloride transfer, e.g. see equation 2. Silicon also reacts with ZnCl2 and AICI3. Excess zinc causes unproductive decomposition of MeCl to give methane. Finally, Clarke presented data that ruled out the importance of methyl radicals in the MCS reaction. 

Use of trimethylsilylmethyl triflate enables the effective formation of intermediate iminium salts in the reaction mixture because the counteranion, triflate ion, is nonnucleophilic both to carbon and silicon atoms. N-Silyl-methylation can also be performed with other alkylating agents, such as silymethyl chloride, bromide, and iodide. However, the resulting iminium salts desilylate immediately after they are formed by the attack of the halide counteranions, leading to a serious decomposition of the requisite iminium intermediates. The final step of desilylation generating azomethine ylides is effected by a fluoride anion which is selectively nucleophilic to a silicon atom. 

Methyl-dichloroamine, (W-dichloromethylamine) CH3NCI2, is prepared by treating methylamine with bleaching-powder. It is a liquid, insoluble in water, which possesses a characteristic, disagreeable odor. It boils without decomposition at 59°-60°. This fact is of interest as nitrogen chloride, NCI3, explodes violently when heated. The halogen is not converted into an ion when methyl-dichloramine is treated with water. 

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