Glutaric acid from, trimethylene dicyanide

In a 2-litre round-bottomed flask, equipped with a double surface condenser, place 60 g. of trimetliylene dicyanide (Section 111,114) and 900 g. of 50 per cent, sulphuric acid (by weight). Reflux the mixture for 10 hours and allow to cool. Saturate the solution with ammonium sulphate and extract with four 150 ml. portions of ether dry the ethereal extracts with anhydrous sodium or magnesium sulphate. Distil off the ether on a water bath the residual glutaric acid (69 g.) crystallises on cooling and has m.p. 97-97-5°. Upon recrystallisation from chloroform, or benzene, or benzene mixed with 10 per cent, by weight of ether, the m.p. is 97 -5-98°. 

Suberic acid. Prepare hexamethylene dibromide from hexamethy-lene glycol (Section 111,15) according to the procedure described in Section 111,35). Convert the 1 6-dibromohexane, b.p. 114-115°/12 mm., into hexamethylene dicyanide, b.p. 178-180°/15 mm., by refluxing it with a 20-25 per cent, excess of aqueous - alcoholic sodium cyanide solution (compare Section 111,114), distilling off the liquid under diminished 

Heat a mixture of hexamethylene dicyanide with 15 times its weight of 50 per cent, sulphuric acid by weight under reflux for 10 hours. The acid crystallises out on cooling. Filter off the suberic acid upon a sintered glass funnel, and recrystallise it from acetone m.p. 141-142°. The yield is 90 per cent, of the theoretical. 

Pimelic acid. This may be prepared from 1 5-pentanediol or tetra-hydropyran, through the dibromide (Sections 111,35 and 111,37) and dinitrile exactly as described for Suberic Acid. An alternative method for the preparation of 1 5-dibromopentane, together with full details of the subsequent steps, is given in the following Section. 

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