Science of Synthesis

Margaretha, P., Science of Synthesis, (2007) 35, 81.

Although the reactions of alcohols with the triphenylphosphine/tetrachloromethane reagent combination usually occur with high efficiency, under mild and neutral conditions, there has been a (parallel) continuous search for new reagents and improved preparative procedures that allow the efficient conversion of alcohols into chlorides. Thus, a mixture of triphenylphosphine and 2,3-dichloro-5,6-dicyanobenzo-1,4-quinone in dichloromethane affords a charge-transfer complex, which reacts further with tetrahexylammonium chloride to form an oxyphosphonium chloride ‌37‌. This intermediate then reacts with the alcohol to generate the alkyl chloride, triphenylphosphine oxide, and the ammonium salt of the hydroquinone (‌Scheme 28‌) (the optimal molar ratio R1OH/Ph3P/DDQ/R24NCl is 1:1.4:1.4:1.4). It is important that the alcohol is added to a mixture of the three other components (i.e., before the addition of the ammonium chloride), otherwise mono- and dialkyl ethers of 2,3-dichloro-5,6-dicyano-1,4-dihydroxybenzene are produced. The conversion of a primary alcohol occurs readily, at room temperature. As illustrative examples, 1-chlorobutane, 1-chloro-2-phenylethane, (E)-1-chlorohexadec-8-ene, and 2-(2-chloroethyl)thiophene can be synthesized by this procedure in yields ranging from 70–85%.[‌78‌]

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