Structures of the pyrazolones formed by oxidative coupling of phenols with 4-aminoantipyrine

The structures of reaction products between 4-amino-2,3-dimethyl-1-phenyl-3-pyrazolin-5-one and o-cresol, p-cresol, and p-ethylphenol are reported. The reaction of the former compound with phenols is used to estimate the concentration of phenol in potable water supplies. The reaction products are 2,3-dimethyl-4-[4-oxo-2,5-cyclohexadien-1-ylidene)amino]-1-phenyl-3-pyrazolin-5-one (monoclinic, P2 1 /c, red, Z = 4, a = 7.092(1), b = 26.616(2), c = 8.644(2) Å, β = 79.17(3)°, 1432 reflections, R = 0.083, R w  = 0.040), 1,9a-dihydro-1,6,9a-trimethyl-2-phenylpyrazolo[3,4-b][1,4]benzoxazin-3(2H)-one (orthorhombic, Pbca, yellow, Z = 8, a = 18.943(3), b = 12.749(5), c = 13.223(2) Å, 2122 reflections, R = 0.067, R w  = 0.038), and 6-ethyl-1,9a-dihydro-1,9a-dimethyl-2-phenylpyrazolo[3,4-b|[1,4]benzoxazin-3(2H)-one (orthorhombic, Pbca, yellow, a = 18.895(11), b = 12.737(5), c = 14.041(6) Å, Z = 8, 1126 reflections, R = 0.068, R w  = 0.061), respectively. The latter two compounds rearrange to form 1,2,4,10-tetrahydro-1,6-dimethyl-2-phenyl-3H-pyrazolo[3,4-c][1,5]benzoxazepin-3-one (monoclinic, P2 1 /c, white, Z = 8, a = 15.072(4), b = 14.491(4), c = 15.505(3) Å, β = 111.15(1)°, 3416 reflections, R = 0.101, R w  = 0.046) and 6-ethyl-1,2,4,10-tetrahydro-1-methyl-2-phenyl-3H-pyrazolo[3,4-c][1,5]benzoxazepin-3-one (monoclinic, C2/c, white, Z = 8, a = 33.768(3), b = 6.678(1), c = 15.836(2) Å, β = 115.41(1), 2805 reflections, R = 0.076, R w  = 0.043), respectively. The rearrangement is consistent with the observation that the pyrazolone rings of benzoxazinones are strained, as manifested by enlarged perimeters.