Patent GB-810306-A (GB)
Title: Acid esters of starch
IPC: C09K23/52
Filed: 1955-09-26
Abstract: The invention comprises a starch or amylose polyacylate containing 5 to 35 per cent by weight of a fatty acid radical containing 2 to 4 carbon atoms, from 10 to 50 per cent by weight of an aliphatic dicarboxylic acid radical containing 4 to 6 carbon atoms or the orthocarboxy-benzoyl radical, and a free carboxyl content of from 2 to 15 per cent by weight, or a water-soluble salt thereof.  The compounds are used in the enteric coating of tablets (see Group VI). They are prepared by partially acylating starch or amylose with an anhydride derived from a monocarboxylic acid containing 2 to 4 carbon atoms, in the presence of an organic base, separating the partially acylated product, reacting it with an anhydride of an aliphatic dicarboxylic acid containing 4 to 6 carbon atoms or phthalic anhydride in the presence of an organic base, controlling the reaction time to obtain the desired extent of acylation, treating with a stronger acid and separating the product containing free carboxyl groups.  In a modification of the process, the product of the first stage of the reaction is obtained by partial saponification of a high acyl value starch or amylose acylate. Specified dicarboxylic acids are succinic, glutaric, maleic and adipic acids. Specified organic bases are pyridine and quinoline. The compounds may form salts with organic or inorganic bases and sodium salts are specified.  Starch is made reactive for use in the process by slurrying with water, adding boiling water and heating to form a paste, passing the paste through a colloid mill, cooling the effluent from the mill and precipitating the starch with alcohol, running the resultant suspension through a pulverizing machine, decanting the supernatant liquid, dehydrating the starch with alcohol, filtering off the starch and drying in vacuo.  Amylose is made reactive by treating a butanol-amylose complex with absolute or denaturated ethanol or methanol, centrifuging, decanting off the supernatant liquid, drying to equilibrium with atmospheric moisture and grinding. In examples starch and amylose, activated as above, are partially acetylated using acetic anhydride and pyridine in formamide and the product phthalylated with phthalic anhydride and pyridine. Tables list the properties and solubilities of the products.  In further examples starch acetate is prepared by acetylating starch as above, the product is partially saponified with aqueous sodium hydroxide and then phthalylated.  Many similar products such as amylose acetate glutarate, starch propionate succinate, amylose propionate phthalate and starch butyrate maleate are specified.ALSO:Tablets are enterically coated by dissolving a starch or amylose polyacylate, containing from 5 to 35 per cent by weight of a fatty acid radical containing from 2 to 4 carbon atoms, from 10 to 50 per cent by weight of an aliphatic dicarboxylic acid radical containing from 4 to 6 carbon atoms or the ortho-carboxy-benzoyl radical, and a free carboxyl content of from 2 to 15 per cent by weight or a water-soluble salt thereof (see Group IV (a)), in a volatile organic solvent, coating the tablets with the solution thus prepared and drying to evaporate the solvent.  In examples, solutions of amylose acetate phthalate and starch acetate phthalate in a mixture of acetone, denatured alcohol, sorbitan monooleate and propylene glycol are spread on steel plates and heated to give films which are suitable for coating tablets and the solution of starch acetate phthalate is used to coat tablets which resist artificial gastric juice (pH 1.2) but disintegrate in artificial pancreatic fluid (pH 6.9).