Patent GB-588968-A (GB)
Title: Improvements in and relating to the polymerization of dextrose and maltose
IPC: A24B15/30
Filed: 1942-11-03
Abstract: Crystalline dextrose or maltose is polymerized by heating with a catalyst comprising a finely-divided non-alkaline boron compound containing boron trioxide at a temperature which does not reduce the material to a molten state.  The crystals may be superficially melted provided their shape is not substantially affected, the product resembling the original crystals and being suitable for use as a humectant, e.g. as a substitute for glycerine in the treatment of tobacco.  Commercial a -anhydro dextrose, substantially pure b -anhydro dextrose and dextrose or maltose hydrate, preliminarily heated to remove free or molecular water, may be treated.  Suitable boron compounds are boron trioxide and tetra-, ortho- and, preferably meta-boric acid, preferably pre-dried and pulverized to 170 mesh/inch or finer.  The materials may be mixed mechanically or a suspension of the sugar in a solution of the catalyst may be evaporated to coat the crystals. The materials may be heated at a polymerizing temperature below the melting point of the sugar, e.g. 133-145 DEG  C. in the case of dextrose and 100 DEG  C. for maltose, or above the melting point if a large amount of catalyst, e.g. 35 per cent by weight of the sugar, is present.  The amount and degree of polymerization are increased by heating to a temperature below, and then to a temperature, e.g. 25-30 DEG  C. above, the melting point.  Best results with minimum colour formation are obtained at a lower temperature by the use in addition of a secondary catalyst consisting of a mineral acid, acid salt or substantially neutral salt (pH 5-7), e.g. the materials may be treated with, or reacted in the presence of, sulphur dioxide or dry hydrochloric acid gas or mixed with 1 per cent by weight of barium, sodium or potassium perchlorate or sodium chloride.  The secondary catalyst, e.g. acidic gas or sodium chloride, may be effected on trays in an oven or a rotary heater, over or through which heated air is circulated to vaporize and discharge the water produced.  Boric acid may be recovered by suspending the product in methanol, removing the resultant methyl borate and excess methanol by distilling and decanting, treating the distillate with alkali, distilling off the methanol, treating the alkali borate with acid, crystallizing out the ortho boric acid and converting to meta boric acid in a hot air heater.  In examples: (1) pre-dried a -anhydro dextrose is heated (a) with 5 per cent by weight of meta boric acid at 135 DEG  C. for 5 hours and, preferably, further heated at 175 DEG  C. for 1-5 hours, or (b) with 35 per cent meta boric acid at 150 DEG  C. for 5 hours, or (c) after treatment to incorporate .005 per cent hydrochloric acid gas or a trace of sulphur dioxide or the addition of 1 per cent of sodium chloride or barium perchlorate, with 5 per cent meta boric acid at 140 DEG  C. for 5 hours, preferably after a preliminary heating at 120 DEG  C. for 5-20 hours; (2) equal parts of dextrose hydrate and boron trioxide or meta boric acid are heated at 100 DEG  C. for 3 hours to drive off hydrate water and then at 135 DEG  C. for 5 hours; (3) maltose hydrate is heated at 100 DEG  C. for 24 hours to remove water, mixed with 5 per cent meta boric acid and, preferably, .005 per cent hydrochloric acid gas incorporated, and then heated at 100 DEG  C. for 24 hours or at 135-140 DEG  C. for 5 hours.  The Specification as open to inspection under Sect. 91 comprises also the treatment of other crystalline sugars, except xylose and sucrose.  This subject-matter does not appear in the Specification as accepted.