1-(3-Chlorophenyl)ethanone → (2E)-4-(3-chlorophenyl)-4-oxobut-2-enoic acid

A stirred mixture of 3'-Chloroacetophenone (15 mL, 97 mmol) and glyoxylic acid monohydrate (9 g, 97 mmol) was heated at 130° C. under reduced pressure (1,5 mmHg), over 8 hours. During this time the reduced pressure was maintained in order to remove the water formed during the reaction. After cooling, the crude reaction product was taken up in aqueous 10% potassium carbonate solution (100 mL) and the resulting solution was washed with diethyl ether (3×30 mL), the alkaline aqueous layer was cooled at 0° C. and then cautiously acidified with 6N HCl. The resulting suspension was extracted with ethyl acetate (3×50 mL), the collected organic extracts were washed with brine and dried (Na2SO4). Concentration of the solvent in vacuo afforded a yellow solid (8 g) which was chromatographed (SiO2 ;CH2Cl2 /MeOH 98:2) to provide the pure acid (6 g, 30%), lightly yellow solid melting at 158-59° C. (diisopropyl ether).