Brief acid hydrolysis of 1,2:5,6-di-O-isopropylidene-3,4-di-O-methylsulfonyl-D-mannitol (1a), removes the isopropylidene groups giving the disulfonated hexitol, 2a. Upon continued acid hydrolysis of 2a, one sulfonate group is lost with formation of a sulfonated monoanhydro hexitol, 5a, then the second ester group is lost to give 1,4:3,6-dianhydro-D-iditol (D-isoidide, 3a). If the disulfonate, 2a, is treated with base, an isomeric dianhydro hexitol, the bisoxirane 4, is formed. Under similar basic conditions, the monoanhydro hexitol, 5a, is stable. On acid hydrolysis, the bisoxirane, 4, gives hexitols and only 20% of D-isoidide, which indicates that 4 cannot be an intermediate in the conversion of 2a to 3a. These results indicate that, in 2a at least, five-membered anhydro rings are formed preferentially in acid hydrolyses and three-membered rings in saponification.The stage and course of hydrolysis of 2a are readily monitored by observing the τ 4–6 region in the n.m.r. spectra of D2O samples of the hydrolysate.