OCTADECANEDIOIC ACID, DIMETHYL ESTER

DIMETHYL OCTADECANEDIOATE (Octadecanedioic acid, dimethyl ester)... 

Octadecanedioic acid. Dissolve 31.5 g (0.145 mol) of methyl hydrogen sebacate in 140 ml of absolute methanol to which 0.4 g of sodium has been added. Electrolyse at 2.0 amps until the pH of the electrolyte is 7.8-8.0 (3.5-4 hours). Work up as described for sebacic acid. Upon distillation, an unsaturated ester passes over at lll-113°C/20mmHg (4.6 g), followed by dimethyl octadecanedioate at 212-219°C/4mmHg (mainly at 214-215°C/4mmHg), m.p. 56 °C (16.5 g, 66%). 

Reflux 6.8 g of the dimethyl ester with a solution of 3.2 g of sodium hydroxide in 150 ml of 80 per cent methanol for 2 hours on a water bath. When cold, filter off the solid and wash it with a little cold methanol. Dissolve the solid in 350 ml of warm water, add concentrated hydrochloric acid to the solution at 60 °C until acidic to litmus, filter off the precipitated acid, wash with a little water and dry at 100 °C. The resulting octadecanedioic acid, m.p. 122°C, weighs 5.3 g (84%). Recrystallisation from absolute methanol raises the m.p. to 124.5 °C. 

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