Chloromethyl methylether

The chloromethylation of thiophene has come somewhat into discredit, partly because of the lachrymatory nature of 2-thenyl chloride, partly because this reaction is highly dependent on the conditions used. Formalin in concentrated hydrochloric acid has been used for chloromethylation, as has the anhydrous system, formaldehyde and hydrogen chloride." The use of a-chloromethyl methylether has also been recommended. The sensitivity of chloromethylation to the experimental conditions is illustrated by the fact that addition of zinc chloride gives di-(2-thienyl)methane as the main product and... 

The situation is somewhat different in the case of chloromethylation of the same type of low cross-linked polymer in its shrunken state (nonsolvated) in n-hexane. This solvent coats but does not solvate the polymer beads. When the reactive complex of chloromethyl methyl ether/stannic tetrachloride is added, the macromolecules on the surface zone of the polymer pellets are immediately solvated due to much higher concentration of reactants at reactive phenyl moities, in contrast to the highly diluted state of the Friedel-Crafts alkylation in the first example. On the other hand, the relatively small amount of chloro-methyl-methylether/SnCl4 added in n-hexane is only sufficient to solvate and functionalize most exposed outer parts of the macromolecular thread in the shell zone of the polymer, depending on the accidental distribution of cross-links in that area of the macromolecule. 

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