Pyrazole
Title: Pyrazole
CAS Registry Number: 288-13-1
Additional Names: 1,2-Diazole
Molecular Formula: C3H4N2
Molecular Weight: 68.08
Percent Composition: C 52.93%, H 5.92%, N 41.15%
Literature References: Prepn from acetylene and diazomethane: H. v. Pechmann, Ber. 31, 2950 (1898). Two tautomeric forms. 1H-NMR: J. F. K. Wilshire, Aust. J. Chem. 19, 1935 (1966); 13C-NMR: W. M. Litchman, J. Am. Chem. Soc. 101, 545 (1979); 15N-NMR: I. I. Schuster et al., J. Org. Chem. 44, 1765 (1979). Spectral studies: D. Dumanovic et al., Talanta 22, 819 (1975). Inhibition of alcohol dehydrogenase: W. K. Lelbach, Experientia 25, 816 (1969). Induction of thyroid necrosis: S. Szabo et al., Science 199, 1209 (1979). Toxicity: G. Magnussen et al., Experientia 28, 1198 (1972).
Properties: Needles or prisms from petr ether; pyridine-like odor, bitter taste. mp 69.5-70°. bp757.9 186-188°. pK (25°) 11.52. uv max (12M H2SO4): 215 nm (log e 3.76); at pH 6.1: 310 nm (log e 3.61). Sol in water, alcohol, ether, benzene. LD50 (24 hr) in rats, mice (mmol/kg): 19, 21 i.v.; 21, 22 orally (Magnussen).
Melting point: mp 69.5-70°
Boiling point: bp757.9 186-188°
pKa: pK (25°) 11.52
Absorption maximum: uv max (12M H2SO4): 215 nm (log e 3.76); at pH 6.1: 310 nm (log e 3.61)
Toxicity data: LD50 (24 hr) in rats, mice (mmol/kg): 19, 21 i.v.; 21, 22 orally (Magnussen)
Use: Chelating agent; in organic synthesis.

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