A mixture of 13.3 grams of anhydrous aluminum chloride and 100 ml of
carbon disulfide is added to 19.4 grams of 2-propionyloxybenzoic acid
(prepared from the reaction of propionyl chloride and 2-hydroxybenzoic acid).
After an initial evolution of hydrogen chloride, the solvent is removed by
distillation and the mixture is heated at 150° to 160°C for 4 hours. The cooled
reaction mixture is treated with ice and hydrochloric acid and the product, 2-
hydroxy-3-carboxypropiophenone, is obtained from the oily residue by
distillation in vacuo.
A mixture of 1.9 grams of 2-hydroxy-3-carboxypropiophenone, 5.0 grams of
sodium benzoate and 20.0 grams of benzoic anhydride is heated at 180° to
190°C for 6 hours. A solution of 15.0 grams of potassium hydroxide in 50 ml
of ethanol and 20 ml of water is added and refluxed for 1 hour. The mixture is
evaporated and the residue after addition of water yields 3-methylflavone-8-
carboxylic acid.
To a suspension of 12.0 grams of 3-methylflavone-8-carboxylic acid in 200 ml
of anhydrous benzene is added 10.0 grams of thionyl chloride. The mixture is
refluxed for 2 hours during which the suspended solid goes into solution. The
solvent is completely removed by distillation, the residue extracted with
benzene and the extract evaporated to dryness. The product, 3-
methylflavone-8-carboxylic acid chloride, is recrystallized from ligroin to give
crystals melting at 155° to 156°C.
To 11.0 grams of 3-methylflavone-8-carboxylic acid chloride dissolved in 150
ml of anhydrous benzene is added at room temperature 4.8 grams of
piperidinoethanol and the mixture refluxed for 2 to 3 hours. The separated
solid is filtered, washed with benzene and dried. The product, piperidinoethyl
3-methylflavone-8-carboxylate hydrochloride is obtained as a colorless
crystalline solid, MP 232° to 234°C, (from US Patent 2,921,070).
