Water → 2-Hydroxyxanthone
Reaktionsgleichung
C[O:2][C:3]1[CH:16]=[CH:15][C:14]2[O:13][C:12]3[C:7](=[CH:8][CH:9]=[CH:10][CH:11]=3)[CH2:6][C:5]=2[CH:4]=1.Cl.N1C=CC=CC=1.[OH2:24]>>[OH:2][C:3]1[CH:16]=[CH:15][C:14]2[O:13][C:12]3[C:7](=[CH:8][CH:9]=[CH:10][CH:11]=3)[C:6](=[O:24])[C:5]=2[CH:4]=1Komponenten
4
Versuchsvorschrift
A solid mixture of 2-methoxy-9H-xanthene 2 (3.09 g, 14.6 mmole) and pyridine hydrochloride (23.85 g, 206.4 mmole) was heated at 200-210° for 1.5 hrs. The resulting reaction mixture was cooled to about 80° and treated with water, while a white powder dropped out of solution. The suspended mixture was stirred at ambient temperature and then cooled to 0°. The solid was filtered on a Buchner funnel and washed with cold water. A large quantity of CH2Cl2 was needed to redissolve the crude product. The CH2Cl2 solution was washed with dilute HCl solution. The aqueous layer was extracted with CH2Cl2. The combined organic layers were dried over anhydrous Na2SO4. TLC showed a small by-product at the origin, but neither of the starting material nor the oxidation product, 2-hydroxy-9H-xanthene-9-one, was formed. The CH2Cl2 solution was filtered through a silica gel plug, the silica gel was flushed with 20% EtOAc-hexanes (100 ml). After concentration of the filtrate, the crude 2-hydroxy-9H-xanthene 3 (2.68 g, 93%) was collected as a slightly yellow powder: mp 137-139° C. 1H NMR (DMSO-d6): delta 9.18 (1H, s), 7.14-7.22 (2H, m), 6.97-7.03 (2H, m), 6.87 (1H, dd, J=7.3, 1.8 Hz), 6.57-6.62 (2H, m) and 3.94 (2H, s).