Dimethyl octadecanedioate

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

Simple anodic coupling by electrolysis in anhydrous methanolic solution (containing a little sodium methoxide) of methyl hydrogen adipate (Expt 5.147) gives dimethyl sebacate methyl hydrogen sebacate (Expt 5.147) in turn yields dimethyl octadecanedioate (Expt 5.131, cognate preparations). 

Two alternative syntheses of methyl myristate, and thence myristic acid, are described (Expt 5.131). In Method A hexanoic acid (2mol) is coupled with methyl hydrogen sebacate (1 mol), the products being methyl myristate, decane and dimethyl octadecanedioate. 

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%). 

The present procedure offers an alternative electrochemical setup to accomplish the Kolbe electrolysis of half esters to that reported earlier for the preparation of dimethyl octadecanedioate.17 In the present case the apparatus offers general versatility and electrode coating is prevented by an additive (pyridine). In the earlier case periodic current reversal was necessary. 

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