GB458839A - Chitin compounds - Google Patents

Abstract

Substantially undegraded, at least partially deacetylated chitin is prepared by treating chitin, preferably with limited access of air with 5--55 per cent aqueous caustic alkali at a temperature not exceeding 150 DEG C. until the product is soluble in dilute aqueous acetic acid to give solutions which, at a concentration of 2,5 parts of product per 100 parts of acid, have a viscosity greater than 1 poise at 25 DEG C. The raw material for treatment according to this invention is obtained for example from the shells of crustacae such as shrimps, crabs and lobsters (canning industry waste), together with insects such as beetles, grass-hoppers, locusts and the like, also fungi such as aspergillus niger and mushrooms. The raw chitin is preferably subjected to a preliminary cleaning process to free it from meat, lime and other foreign matter. The cleaning process varies with the source of the chitin used, but generally a mild alkali treatment such as with soda ash or dilute alkali is used followed by a treatment with dilute acid. In place of soda ash, trisodium phosphate, sodium sulphide, sodium sulphite, sodium bisulphite, calcium bisulphite, potassium or sodium bicarbonate or carbonate, calcium hydroxide, copper ammonium solution, sodium silicate, or certain putrificative bacteria may be used. The acid treatment which usually follows the alkali treatment serves to remove lime and other inorganic salts. In the special case of the use of fungi, where it is necessary to free chitin from cellulose, treatment with copper-ammonium, or sodium thiocyanate solutions or xanthation is necessary. After the preliminary purification the chitin may be bleached by treatment with a dilute solution of potassium permanganate, sodium hypochlorite, sulphur dioxide or sodium bisulphite. In general, however, bleaching is not necessary. The viscosity of the deacetylated chitin may be regulated by the time, temperature, and concentration of alkali during the deacetylation. Another method for reducing the viscosity of the deacetylated product is to treat the deacetylated chitin in dilute acetic acid solution with oxidizing agents such as chlorine, bromine, hypochlorous acid, perborates, permanganates, bichromates, oxygen or air. The viscosity of the deacetylated chitin may be raised by first heating the chitin itself in the dry state before treatment. Tables are given to show the effects of various oxidizing agents, under various conditions. Chitin being essentially a highly polymeric free primary amine, forms salts with acids. A list is given of salts of chitin which have been prepared, together with their properties. The solutions of chitin prepared according to the present invention find numerous uses such as those disclosed in Specifications 458,813; 458,814, 458,815, [both in Group III]; 458,816; 458,817, [Group III]; 458,818, [Group V], and 458,819. In examples: (1) shrimps' "heads and hulls" are subjected to a preliminary cleaning with a mixture of soda ash and the sodium salts of the sulphate esters of higher fatty alcohols at 100 DEG C. After washing with water the shells are soaked overnight in dilute hydrochloric acid, washed, and then deacetylated with 40 per cent sodium hydroxide at 115 DEG C. for 6 hours; (2) chitin cleaned as described in example (1) is deacetylated at 100 DEG C. for one hour with 50 per cent sodium hydroxide. The viscosity of the product may be modified by treatment with dilute hydrogen peroxide solution for 4 hours; (3) completely deacetylated chitin is prepared by heating chitin purified as described in example (1) with 50 per cent sodium hydroxide at 100 DEG C. for 48 hours. In this case exclusion of air is essential to prevent degradation. The Specification as open to inspection under Sect. 91 comprises also additional examples of methods of pre-treating chitin before deacetylation. Such examples are: (1) shrimp, lobster or crab shells are boiled with soda ash solution, washed, and then treated with 5 per cent hydrochloric acid; (2) crab shells are boiled with trisodium phosphate, hymolal salts and pine oil; (3) dry shrimp meal is treated with dilute hydrochloric acid, followed by soda ash and soap; (4) shrimp meal is treated first with gaseous sulphur dioxide under pressure and then with an aqueous solution of sulphur dioxide under pressure for 6 hours. The formation of the benzoic acid salt of deacetylated chitin is also described. This subject-matter does not appear in the Specification as accepted.