Sodium hydroxide, “flake treatment with

Crude 2-nitrotoluene, containing some hydrochloric and acetic acids, was charged into a vacuum still with flake sodium hydroxide to effect neutralisation prior to distillation. An explosion occurred later. Similar treatments had been used uneventfully previously, using the weaker bases lime or sodium carbonate for neutralisation. It seems likely that the explosion involved formation and violent decomposition of the sodium salt of an aci-nitro species, possibly of quinonoid type. 

Conversion of chitin into chitosan involves the deacetylation process, which is a harsh treatment usually performed with concentrated sodium hydroxide solution. Chitin flakes are treated in suspension with aqueous 40-50% caustic solution at 80-120°C with constant stirring for 4-6 h and this treatment is repeated once or more than once for obtaining high-amino-content product. To avoid depolymerization due to oxidation, sodium borohydrate is added. Excess alkali is drained off and the mixture is washed with water several times until it is free from alkali. Most of the alkali is then used either in deproteinization or in deacetylation. Excess water is removed in screw press and the wet chitosan cake is either sun dries or in drier at 60°C. Chitosan thus obtained is in the form of flakes and can be pulverized to powder. The flowchart for the manufacture of chitosan from the starting material (crustacean shells) is shown in Fig. 19.5. 

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