GB600870A - Improvements relating to the manufacture of the 1:4-3:6-dianhydrides of mannitol andsorbitol - Google Patents

Abstract

1 : 4 - 3 : 6 - Dianhydrides of mannitol and sorbitol are made by hydrogenating sucrose or invert sugar in an atmosphere of hydrogen at 75-100 atmos. and 110-120 DEG C. with a Raney nickel catalyst in the presence of sodium and calcium carbonates to give a mixture of mannitol and sorbitol, and treating the mixture with an acid. The mixture of dianhydrides may be fractionally distilled, and the fractions recrystallized to obtain the separate pure products. Alternatively, mannitol may be separated from the mixture with sorbitol and only the latter converted to the dianhydride. Suitable acids are hydrochloric, sulphuric, phosphoric, and benzene or p-toluene sulphonic. In examples: (1) sucrose is added to boiling 0.1 N-sulphuric acid, barium hydroxide added, the filtrate hydrogenated, the product filtered and evaporated to give the hexitols which are refluxed with concentrated hydrochloric acid, the solution evaporated, and the residue distilled under reduced pressure to give the dianhydrides which are then separated; (2) the mixture of hexitols of (1) is heated with concentrated sulphuric acid and xylene so that water is azeotropically removed, and product worked up to recover the anhydrides; (3) xylene and p-toluene sulphonic acid are used similarly to give the anhydrides which are recovered; (4) the mixture of hexitols of (1) is dissolved in aqueous alcohol, manitol removed by crystallization, and the mother liquors treated as in (2) to give dianhydro sorbitol.