Carbon Dioxide → 7-methoxy-2H-phthalazin-1-one

Participants

Reaction Steps

A hot solution of potassium permanganate (570 g, 3.6 mole) in water (1520 ml) was added in portions to a vigorously stirred mixture of 2-methyl-4-methoxyacetophenone (152 g, 0.93 mole) and potassium carbonate (76 g, 0.55 mole) in water (5700 ml) at 100°. The colour was allowed to discharge between additions, and the mixture was heated for a further 30 minutes after completion of the addition. The cold filtered solution was re-heated to 90° and the pH adjusted to 8.0. Hydrazine hydrate (51 g, 1.04 mole) was added and the volume of the solution was reduced to 3000 ml by evaporation. The filtered solution was made strongly acidic with hydrochloric acid and the resultant precipitate collected and washed with water. The solid was digested several times with methanol to leave a residue of 4-carboxy-7-methoxy-1(2H)-phthalazinone (51 g, 25%, m.p. 239°-240° (decomposition). The carboxylic acid was heated in an oil bath at 260° until evolution of carbon dioxide ceased (about 5 minutes), then immediately cooled. Soxhlet extraction of the product with water gave 7-methoxy-1(2H)-phthalazinone (41.3 g, 25%) m.p. 228°-229°).

Provenance & Evidence