SYNTHESIS OF DODECANEDIOIC ACID

SebacoyI chloride:

• Convert 20 g (0. 1 mol) of sebacic acid into the corresponding acid chloride by heating it on a water bath in a flask fitted with a reflux condenser (protected with a calcium chloride tube) with 20 ml of thionyl chloride; the apparatus should be assembled in a fume cupboard. 

• Purify the product by distillation under reduced pressure (use appropriate traps to protect the pump from the fumes of hydrogen chloride and sulphur dioxide). 

• Collect the sebacoyl chloride as a fraction of b.p. 140-143 °C/2mmHg; the yield is 18 g (77%).

1,8-Bis-diazoacetyloctane

• Dissolve 7.4 g (0.033 mol) of the resulting sebacoyl chloride in anhydrous ether and add the solution slowly to an ethereal solution containing about 6.8 g of diazomethane, i.e. two portions of the ethereal solution. 

• Allow the mixture to stand overnight and remove any excess reagent together with some of the ether by distillation from a warm-water bath. 

• To ensure that no undue hazard results from the possible presence of undecomposed excess diazomethane use a distillation assembly as described for the distillation of diazomethane-ethereal solutions. 

• When the distillate is colourless, change the receivers, and complete the removal of solvent by distillation under reduced pressure (water pump). 

• After recrystallisation from benzene the resulting 1,8-bis-diazoacetyloctane has m.p. 91 °C; the yield is 6.4 g (83%).

Dodecanedioic acid

• Add, with stirring, a solution of 5 g (0.02 mol) of the bis-diazoketone in 100 ml of warm dioxane to a suspension of 6.0 g of freshly precipitated silver oxide (2) in 250 ml of water containing 8 g of sodium thiosulphate maintained at 75 °C. 

• A brisk evolution of nitrogen occurs; after 1.5 hours at 75 °C, filter the liquid from the black silver residue. 

• Acidify the almost colourless filtrate with nitric acid and extract the gelatinous precipitate with ether. 

• Evaporate the dried ethereal extract: the residue of crude dodecanedioic acid weighs 3.3 g (72%), and has m.p. 116-1 17 °C. 

• Recrystallisation from 20 per cent aqueous acetic acid raises the m.p. to 127-1 28 °C.

• Alternatively, treat 3.9 g (0.01 56 mol) of the bis-diazoketone in 50 ml of warm dioxane with 15 ml of 20 per cent aqueous ammonia and 3 ml of a 10 per cent aqueous silver nitrate solution under reflux in a 250- or 500-ml flask on a water bath. 

• Nitrogen is evolved for a few minutes, followed by a violent reaction and the production of a dark brown opaque mixture. 

• Continue heating for 30 minutes on the water bath and filter hot; the diamide of dodecane-dioic acid is deposited on cooling. 

• Filter the product and air dry; the yield is 3.1g (87%), m.p. 182-1 84 °C, raised to 184-185 °C after recrystallisation from 20 per cent aqueous acetic acid. Hydrolyse the diamide by refluxing for 2-5 hours with a four molar excess of 3m potassium hydroxide solution. 

• Acidify and recrystallise the precipitated acid from 20 per cent acetic acid. The yield of dodecanedioic acid, m.p. 127-128 °C, is almost quantitative.

Notes to keep in mind:

1.  Precautions in the use of diazomethane are fully described in Section 4.2.25, p. 430, and should be carefully noted; the operations should be carried out in a fume cupboard.

2.  Prepare the silver oxide by adding dilute sodium hydroxide solution gradually to a stirred 10 per cent aqueous silver nitrate solution - until precipitation is just complete. Wash the product thoroughly with distilled water.