Water → 5-Oxoheptanoic acid

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A modification of the procedure of Ijima et al. Chem. Pharm. Bull. 19, 1053-5 (1971) was used. A solution of 2-methyl-1,3-cyclohexanedione (40 g, 0.317 mole, Aldrich) and Ba(OH)2.8H2O (360 g) in water (840 mL) was heated at reflux for 48 h. After standing overnight at room temperature and cooling to 0° C., the precipitated barium hydroxide was removed by suction filtration. CO2 gas (generated from Dry Ice) was bubbled through the filtrate to precipitate any remaining barium hydroxide as barium carbonate. The precipitate was removed by suction filtration, and water was removed in vacuum until crystallization started. The resulting mixture was acidified to pH 1 (conc. HCl) and extracted with OEt2 (3×300 mL). The extract was dried (Na2SO4) and stripped of solvent in vacuum giving 5-oxoheptanoic acid (Compound XXI) as a white solid (43.3-45.1 g, 95-99%, lit.112 69%): mp 48°-49.5° C. (lit.182 50° C.); IR (KBr pellet) cm-1 3000 (very br), 1725, 1710, 1690, 1460, 1435, 1420, 1380, 1340, 1280, 1210, 1120, 1085, 985, 910, 770, 685; 1H NMR (200 MHz, CDCl3) δ 10.2 (br, 1H), 2.51 (t, 7.1 Hz, 2H), 2.43 (q, 7.3 Hz, 2H), 2.40 (t, 7.1 Hz, 2H), 1.91 (rough pentet, 2H), 1.06 (t, 7.3 Hz, 3H); 13C NMR (22.5 MHz, CDCl3) δ 211.5, 178.6, 41.0, 36.0, 33.1, 18.7, 7.8; mass spectrum (16 eV) m/e (% base) 144 (M+, 4.1), 126 (61.3), 115 (88.8), 98 (40.0), 87 (40.1), 70 (21.3), 57 (100); TLC (OEt2, I2) Rf=0.37.

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