Possible impurities are trimethylacetic acid and C9 and C13 acids. Dissolve 15g of acid in CCl₄ (300mL) and shake with 110 mL of 15N aqueous NH₃ and the ammonium salt separates and is collected. Acid impurities form soluble ammonium salts. The salt is washed with cold Me₂CO (20mL) and suspended in H₂O (250mL). This is treated with 12N HCl and extracted with CHCl₃ (100mL). The dried (Na₂SO₄) is evaporated and the residue recrystd from a mixture of MeOH (30mL) and H₂O (ca 10mL) to give the pure acid (10-11g). Also recrystd from absolute EtOH and dried under vacuum at 100 °C.

Alternatively, the 1- carboxylic acid (CAS NO. ) (5g) is refluxed for 2h with 15mL of MeOH and 2mL of 98 % H₂SO₄ (cool when mixing this soln). Pour into 10 volumes of H₂O and extract with the minimum volume of CHCl₃ to give clear separation of phases. The extract is washed with H₂O and dried (CaCl₂) and distd. The is collected at 77-79 °C/lmm, m 38-39 °C. The ester is hydrolysed with the calculated amount of N KOH and refluxed until clear. Acidification with HCl provides the pure acid with 90% recovery. The amide crysts from cyclohexane, m 189 °C.