SYNTHESIS OF 1-PHENYLPENTANE-1,2-DIONE

• A 250-ml round-bottomed flask equipped with a reflux condenser is charged with dichloromethane (100ml), acetic acid (5ml) and 1-phenylpent-l-yne (2.0 g, 0.014 mol). 

• The solution is stirred magnetically and heated to reflux before finely powdered potassium permanganate (5.85 g, 0.037 mol) (1) and the phase transfer reagent, Adogen 464 (1.6 g) (2) are added. 

• After being vigorously stirred for 4 hours the precipitated manganese dioxide is filtered off and washed with two 50-ml portions of dichloromethane. 

• Residual manganese dioxide is reduced by addition to the combined filtrates of 20 per cent hydrochloric acid (40 ml) followed by small portions of sodium hydrogen sulphite until all brown colour has disappeared. 

• The organic phase is separated, washed with water and dried over magnesium sulphate. 

• Most of the solvent is removed on a rotary evaporator and the remaining oil distilled under vacuum to give a small forerun of starting material (0.14g) followed by 1-phenylpentane-l,2-dione. 

• The yield is 1.98 g (81%), b.p. 108-1 10 °C/ 5.5mmHg; i.r. spectrum 2990, 2950, 2965, 1710, 1680cm" 1 ; p.m.r. spectrum (CC1 4 , TMS) 5 0.99 (t, 3H), 1.67 (m, 2H), 2.81 (t, 2H), and 7.57 (m, 5H).

Notes to keep in mind:

1.  The finely powdered grade is available from Cams Chemical Company under the trade name Cairox M; this grade is also obtainable from other chemical manufacturers.

2.  Adogen 464 is a registered trademark of The Ashland Chemical Company and is obtainable commercially.