SYNTHESIS OF HEPTANE-2,5-DIONE

CAUTION: All operations should be conducted in an efficient fume cupboard owing to the toxicity of aliphatic nitro compounds and of alkyl vinyl ketones.

• 1-Nitropropane (1 7.8 g 0.2 mol) and diisopropylamine (10 ml) in 200 ml of chloroform are stirred at 60 °C under a nitrogen atmosphere. 

• Methyl vinyl ketone (CAUTION) (7g, 0.1 mol) is added dropwise to this solution. 

• After 3 hours another portion of methyl vinyl ketone (7g, 0.1 mol) is added and the solution stirred for 24 hours. 

• The solution is washed sequentially with water, 10 per cent aqueous hydrochloric acid, 5 per cent sodium hydrogen carbonate, and saturated brine; the organic solution is dried over anhydrous sodium sulphate, concentrated and distilled to yield the nitroketone. 

• The yield is 17 g (55%), b.p. 120°C/10mmHg; p.m.r. spectrum (CC1 4 , TMS) 50.97 (t, 3H), 2.7-2.5 (m, 6H), 2.13 (s, 3H) and 4.38 (m, 1H).

Reduction of nitroketones with titanium(m) chloride at pH 1. 

• The foregoing nitroketone may be converted into the diketone by means of the following general procedure. 

• The nitroketone in solution in tetrahydrofuran (0.2 m) is treated with 4 equivalents of titanium(in) chloride (1) (20% aqueous hydrochloric acid solution) and stirred under nitrogen at room temperature for 24 hours. 

• The reaction mixture is then poured into ether and the phases separated. 

• The aqueous phase is extracted several times with ether; the organic extracts are combined, washed with 5 per cent sodium hydrogen carbonate and with brine, and then dried over anhydrous sodium sulphate, concentrated and distilled. 

• The yield of heptane-2,5-dione is 66 per cent; p.m.r. spectrum (CC1 4 , TMS) S 1.00 (t, 3H), 2.10 (s, 3H), 2.60 (s, 4H) and 3.41 (q, 2H).

Notes to keep in mind:

1.  A 20 per cent titanium(m) chloride solution in aqueous hydrochloric acid is available commercially. Solid titanium(m) chloride reagent is a flammable solid and should be handled only under an inert atmosphere, and if used in this reaction should be taken from a fresh bottle.