SYNTHESIS OF MYRISTIC ACID (Tetradecanoic acid)

Method A

• Dissolve 23.2g (0. 184 mol) of redistilled hexanoic acid, b.p. 204.5-205.5 °C/7 60 mmHg, and 21.6g (0.1 mol) of methyl hydrogen sebacate in 200 ml of absolute methanol to which 0.13g of sodium has been added. 

• Electrolyse at 2.0 amps, while maintaining the temperature  between 30 and 40 °C, until the pH is about 8.0 (c. 6 hours). 

• Neutralise the contents of the electrolysis cell with a little acetic acid and distil off the methanol on a water bath. 

• Dissolve the residue in 200 ml of ether, wash with three 50 ml portions of saturated sodium hydrogen carbonate solution, once with water, dry with magnesium sulphate, and distil through an efficient fractionating column. 

• Collect the decane at 60°C/10mmHg (3.0g), the methyl myristate at 158-160 °C/10mmHg (12.5 g, 52%) and dimethyl octadecanedioate at 215-230 °C/7mmHg (1.5g).

• Reflux a mixture of 7.3g of methyl myristate with a solution of 4.8g of sodium hydroxide in 200 ml of 90 per cent methanol for 2 hours, distil off the methanol on a water bath, dissolve the residue in 400 ml of hot water, add 15 ml of concentrated hydrochloric acid to the solution at 50 °C in order to precipitate the organic acid, and cool. 

• Collect the acid by suction filtration, wash it with a little water and dry in a vacuum desiccator. The yield of myristic acid (tetradecanoic acid), m.p. 57-58 °C, is 5.9g (87%).

Method B

• Dissolve 55.2g (0.32 mol) of pure decanoic acid, m.p. 31-32 °C, and 25.6 g (0. 1 6 mol) of methyl hydrogen adipate in 200 ml of absolute methanol to which 0.25 g of sodium has been added. 

• Electrolyse at 2.0 amps at 25-35 °C until the pH of the electrolyte is 8.2 (c. 9 hours). 

• Neutralise the contents of the electrolytic cell with acetic acid, distil off the methanol on a water bath, dissolve the residue in about 200 ml of ether, wash with three 50 ml portions of saturated sodium hydrogen carbonate solution and remove the ether on a water bath. 

• Treat the residue with a solution of 8.0 g of sodium hydroxide in 200 ml of 80 per cent methanol, reflux for 2 hours and distil off the methanol on a water bath. 

• Add about 600 ml of water to the residue to dissolve the mixture of sodium salts: extract the hydrocarbon with four 50 ml portions of ether, and dry the combined ethereal extracts with magnesium sulphate. 

• After removal of the ether, 23.1g of almost pure octadecane, m.p. 23-24 °C, remains. 

• Acidify the aqueous solution with concentrated hydrochloric acid (c. 25 ml), cool to °C, filter off the mixture of acids, wash well with cold water and dry in a vacuum desiccator. The yield of the mixture of sebacic and myristic acids, m.p. 52-67 °C, is 26 g. 

• Separate the mixture by extraction with six 50 ml portions of almost boiling light petroleum, b.p. 40-60 °C. The residue (5.2 g), m.p. 132°C, is sebacic acid. 

• Evaporation of the solvent gives 20g (55%) of myristic acid, m.p. 52-53 °C; the m.p. is raised slightly upon recrystallisation from methanol.

Cognate preparations: Sebacic acid (decanedioic acid)

• Dissolve 40g (0.25 mol) of methyl hydrogen adipate in 100 ml of absolute methanol to which 0.1g of sodium has been added. 

• Pass a current of about 2.0 amps until the pH of the solution is about 8 (c.5 hours); test with narrow-range indicator paper. 

• Transfer the contents of the electrolysis cell to a 500-ml round-bottomed flask, render neutral with a little acetic acid and distil off the methanol on a water bath. 

• Dissolve the residue in 150 ml of ether, wash with three 50 ml portions of saturated sodium hydrogen carbonate solution, then with water, dry over magnesium sulphate and distil under reduced pressure. 

• Collect the dimethyl sebacate at 155°C/8mmHg; it melts at 26 °C and the yield is 14.6-16.0 g (51-56%). 

• Reflux 14.6g (0.064 mol) of the ester with a solution of 10 g of sodium hydroxide in 125 ml of 80 per cent methanol for 2 hours on a water bath. 

• Add 200 ml of water to dissolve the solid which separates, extract with two 30 ml portions of ether and warm the aqueous solution on a water bath to remove dissolved ether. 

• Acidify the ice-cold aqueous solution to litmus by the addition of concentrated hydrochloric acid. 

• Collect the precipitated acid by suction filtration, wash it with a little cold water and dry at 100 °C. The yield of sebacic acid, m.p. 133 °C, is 11.5g (89%).

Octadecanedioic acid

• Dissolve 31.5g (0.145 mol) of methyl hydrogen sebacate in 140 ml of absolute methanol to which 0.4g 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 111-113°C/20mmHg (4.6g), followed by dimethyl octadecanedioate at 212-219°C/4mmHg (mainly at 214-215 °C/4mmHg), m.p. 56°C(16.5g, 66%). 

• Reflux 6.8g of the dimethyl ester with a solution of 3.2g 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 5.3g (84%). 

• Recrystallisation from absolute methanol raises the m.p.to 124.5 °C.