Hydrogen Bromide → 2,2,4-Trimethyl-1,2-dihydro-6-quinolinol

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6-Ethoxy-2,2,4-trimethyl-3,4-dihydroquinoline [Ethoxyquin, Tokyo Kasai] (70 g, 0.32 mole), was added to 250 mL of 48% HBr, and the mixture was heated to reflux for about 1 hour. The solution was cooled and poured into water. The aqueous suspension was made basic (pH=14) by the addition of 50% aqueous NaOH. Concentrated HCl was added to adjust the pH to about 4, then the mixture was made slightly basic by the addition of saturated sodium bicarbonate solution. The mixture was extracted with EtOAc and the organic layers were dried (brine, MgSO4) and concentrated in vacuo. The thick dark oil was triturated with toluene and the insoluble residue was filtered. The crude solid was recrystallized from toluene to give 6-hydroxy-1,2-dihydro-2,2,4-trimethylquinoline as a light brown solid (mp 182°-184°, 34 g, 0.18 mole, 56%). An analytical sample was prepared by another recrystallization from toluene to provide light brown crystals, mp 182°-184°: IR (KBr) 3302, 2972, 2934, 1586, 1495, 1344, 1244, 1154, 880, 814 cm-1 ; 1H NMR (D-6 DMSO) δ1.12 (s, 6H), 1.33 (s, 3H), 3.34 (s, 1H), 5.17 (br s, 1H), 5.26 (s, 1H), 6.28-6.42 (m, 3H); MS m/e 190 (MH+).

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