Tetrahydrothiophene is a five-membered, fully saturated, sulfur heterocycle comprised of four sp3-hybridized carbon atoms and a sulfur atom. It is also known as thiolane or thiophane. The bond angle C2-S-C5 = 93 degrees is smaller than its oxygen counterpart THF (106.4 degrees) because of its larger atomic size. The C-C bond length is normal in size (1.54 ?). The C-S bond length has been lengthened because of the greater atomic radius of sulfur.

Physical Properties 

Tetrahydrothiophene is a colorless, volatile, unpleasant-smelling liquid, soluble in most of the organic solvents, with a bp of 119°C, an mp of ?96°C, and a density of 0.997 g/mL at 20°C. The ring is nonplanar and flexible in nature.

Synthesis

Tetrahydrothiophene has been prepared by the reaction of hydrogen sulfide and furan in the vapor phase at 400°C in the presence Al2O3 as catalyst. 

It has also been prepared by the reaction of 1,4-dihalobutane with sodium sulfide at 80°C in DMF using NaH as a strong base in good yields. 

A reaction of 1,4-dihydroxybutane with H2S in the presence of Al2O3 as a catalyst at 400°C afforded parent tetrahydrothiophene.

Chemical Reactivity

The reactivity of tetrahydrothiophene closely resembles dialkyl sulfide and readily reacts with alkyl halide in the presence of Br?nsted acid affording sulfonium salt. It may be used as an alkylating agent. The sulfonium salts on reaction with carbanion generated in situ from reactive methylene compounds such as malononitrile, dimethylmalonate, etc. undergo ring fission, which after methylation and treatment with sodium methoxide afforded dimethyl cyclopentane-1,1-dicarboxylate.

Acid-catalyzed reaction of tetrahydrothiophene with alcohol in the presence of H2SO4 forms sulfonium salts, which on reaction with phenol and thiophenol gave respective ether and thioethers.