3,4,5,6-Tetra- O-benzoyl-d-glucose diethyl dithioacetal ( 2) reacts with ethanethiol under acidic conditions to afford 3,4,5,6-tetra- O-benzoyl-2- S-ethyl-2-thio-d-mannose ( 3), the stereochemistry at C-2 of which has been assigned by chemical conversions on its debenzoylated derivative, the crystalline 2- S-ethyl-2-thio-d-mannose diethyl dithioacetal ( 4). In the presence of mercuric chloride (1.1 molar equiv), 4 is converted into crystalline ethyl 2- S-ethyl-1,2-dithio-α-d-mannofuranoside ( 5). Complete demercaptalation of 4 affords syrupy 2- S-ethyl-2-thio-d-mannopyranose ( 6), which was characterized as its phenylhydrazone 7 and the crystalline α-pyranose tetraacetate 9. Extended treatment of 4 with mercuric chloride and aqueous sodium hydrogencarbonate resulted in isolation of 6, along with its crystalline 2-epimer, 2- S-ethyl-2-thio-β-d-glucopyranose ( 10). Remercaptalation of 6 affords the manno diethyl dithioacetal 4 as the major product, whereas similar treatment of 10 yields ethyl 2- S-ethyl-1,2-dithio-α-d-glucopyranoside ( 13). The mechanism of conversion of 2 into 3, as well as the unusually facile interconversion of 2- S-ethyl-2-thio-d-mannose ( 6) and its d- gluco epimer 10, has been investigated.