Glucitol displacement reactions

Another study pertinent to the present discussion is that of the acid-catalyzed dehydration of tetratols, pentitols, and hexitols, all of which yield tetrahydrofuran derivatives as the primary products. These reactions are first order with respect to the alcohol and the acidity function Hq, and the direct relationship shown from plots of versus Hq implies that the reaction proceeds via a protonated intermediate.In all cases except one, the major cyclic product is derived from HO-5 displacement of water from C-1. The exception is D-mannitol (213), where HO-3 participation leads to a slight preference for formation of 2,5-anhydro-D-glucitol (214) over 1,4-anhydro-D-mannitol (215). Inversion at C-2 occurs with HO-5 participation during ring opening of the epoxide (214). 

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