concentrated in vacuo and the residue dissolved in ethyl acetate the ethyl acetate solution is thoroughly extracted with dilute hydrochloric acid the combined extracts are made basic with 1n aqueous sodium hydroxide and this is thoroughly extracted with ether the combined extracts are dried and concentrated in vacuo to give 2 hexylamino carbonyl pyrrolidine the oily residue is dissolved in a minimum amount of ether and is mixed with a warm alcoholic solution of one equivalent of oxalic acid the crystalline oxalate precipitates upon cooling m p 128 u00b0 129 u00b0 by substituting a warm alcoholic solution of maleic acid a crystalline maleic acid addition salt separates on cooling m p 61 u00b0 64 u00b0 when n carbobenzoxy l proline is used as starting material the l oxalate is obtained m p 150 u00b0 151 u00b0 a 4 oxododecanoic acid a takeda et al j org chem 31 616 1966 is converted into its methyl ester by the method of r o clinton and s c laskowski j am chem soc 70 3135 1948 b a solution of 6 84 g 0 030 mol of methyl 4 oxododecanoate 15 0 g 0 150 mol of ammonium bromide and 3 80 g 0 060 mol of sodium cyanoborohydride is stirred at room temperature for 5 days method of r f borch et al.