Hydrolysis shellac

Composition. Shellac is primarily a mixture of aUphatic polyhydroxy acids in the form of lactones and esters. It has an acid number of ca 70, a saponification number of ca 230, a hydroxyl number of ca 260, and an iodine number of ca 15. Its average molecular weight is ca 1000. Shellac is a complex mixture, but some of its constituents have been identified. Aleuritic acid, an optically inactive 9,10,16-trihydroxypalmitic acid, has been isolated by saponification. Related carboxyflc acids such as 16-hydroxy- and 9,10-dihydroxypalmitic acids, also have been identified after saponification. These acids may not be primary products of hydrolysis, but may have been produced by the treatment. Studies show that shellac contains carboxyflc acids with long methylene chains, unsaturated esters, probably an aliphatic aldehyde, a saturated aliphatic ester, a primary alcohol, and isolated or unconjugated double bonds. 

Shellac [124,125] is a natural resin used in very old times for varnishes and moulding compounds. The resin secreted by the lac insect, Kerriar paca, is collected by scraping the shellac-encrusted trees found in southern parts of Asia. It consists of a complex mixture of cross-linked polyesters derived from hydroxy acids, principally aleuritic acid (9,10,16-trihydroxyhexadecanoic acid). From a structural point of view, it appears that this material can be used as a crosslinking agent and/or as a monomer for developing dentrite-like polymers. The question is whether it is possible to produce this material from shellac by controlled hydrolysis. 

Limmatrapirat S, Limmatrapirat C, Luangtana-Anan M, et al. Modification of physicochemical and mechanical properties of shellac by partial hydrolysis. Int J Pharm 2004 278(1) 41-49. 

Aleuritic acid n. Ci5H28(OH)3COOH, dl-erythro-9,10,6-trihydroxy-hexadecanoic acid. Acid obtained from the major constituent of the hard lac portion of shellac. It is present as an interester acid, of mono-carboxylic type, which on hydrolysis with caustic soda yields a mixture of two sodium salts, sodium aleuritate and sodium lacollate. 

Studies of the products of alkaline hydrolysis of shellac, the resinous material used as enteric coating for pills and tablets in pharmaceutics, would perhaps suggest the presence of cedrane-type sesquiterpenoids in insect defensive secretions. Thus shellac, which is formed by heat treatment of the protective... 

Shellac is a varnish of animal origin, and its composition is quite different from that of plant resins. It is secreted by the female lac bug in India and Thailand and has been used as a stain, a varnish, and in artifacts such as 78 rpm record discs. While it has been replaced by man-made polymers for most uses, it is still used in French polishing of furniture and on musical instruments. Hydrolysis gives a mixture of hydroxy acids such as aleuritic acid, R-6-hydroxyhexadecanoic acid, jalaric acid, and the colorant laccaic acids (Figure 21.30). The material is composed of low molecular weight, cross-linked polyesters. 

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