130 PRACTICAL ORGANIC CHEMISTRY zwitter-ion, NH 3-CH 2 COO: consequently although the ammonium salt of glycine may De initially formed in the above reaction, it readily dissociates during the subsequent concentration of the solution to give the free glycine). The glycine so formed has to be separated from the ammonium chloride, and the salt-like nature of the zwitterion precludes "NH 1-CHiCOO^ the use of most organic solvents for this purpose. \^ / The mixture can be treated with copper hydroxide \ / (cf. p. 382) and the glycine precipitated as the Cu insoluble non-ionic cupric complex (annexed / \ formula): the latter can then be filtered off, washed and decomposed in aqueous suspension by hydro-gen sulphide. The following more convenient method is based on the fact that glycine is much less soluble than ammonium chloride in methanol. Note that the amino-acids, because of their salt-like nature, usually decompose on heating, and therefore seldom have sharp melting-points. Furthermore, all
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