The Reaction of Alkyl Halides with Mercuric Thiocyanate in Tetrahydrofuran. The Solvent Incorporation and the Intermediacy of O-Alkyltetrahydrofuranram Ions.

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Abstract The reaction of alkyl halides with mercuric thiocyanate in tetrahydrofuran (THF) affords mainly the THF-incorporated products, R[O(CH2)4]nNCS and R[O(CH2)4]nSCN (mostly n=1 and 2), where the isomer ratios (N/S ratios) are nearly 1. The reaction of EtO(CH2)mBr (m=2–5) with mercuric thiocyanate in THF or n-Bu2O proceeds rapidly only in the case of m=4 to give EtO(CH2)4NCS and EtO(CH2)4SCN, the N/S ratio being also nearly 1, and gives EtNCS and EtSCN when m=5, while the reaction with potassium thiocyanate in DMF affords a good yield of EtO(CH2)mSCN (m=2–5) as nearly the only product. It is suggested that the titled reaction involves the initial formation of a five-membered oxonium ion, O-alkyltetrahydrofuranium ion, and a subsequent attack by XHg(SCN)2−.