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Properties of substance:

pentafluorobenzoic acid

Group of substances:

organic

Empirical formula (Hill's system for organic substances):

C7HF5O2

Structural formula as text:

C6F5COOH

Melting point (°C):

103.3

Boiling point (°C):

220

Synthesis 1:

Reference: McBee, E. T., Rapkin, E. Pentafluorobenzoic Acid / Journal of the American Chemical Society. - 1951. - Vol. 73, No. 3 pp. 1366 [doi: 10.1021/ja01147a520]


C6F5CF3 + 2H2O → C6F5COOH + 3HF

A mixture of 10 g. (0.042 mole) of perfluorotoluene and 30 g. of concentrated sulfuric acid was stirred vigorously at reflux temperature for one week. During this period the lower acid layer became black while the unreacted fluorocarbon layer remained colorless. Hydrogen fluoride evolution was extremely slow.

When the fluorocarbon layer had completely disappeared the black acid solution was poured on ice, diluted with water to a volume of 250 ml., and boiled with Norite for several minutes. After filtration, the resulting colorless solution was ether extracted and the extract dried with Drierite. Evaporation of the ether gave white crystals of pentafluorobenzoic acid. While the material can be recrystallized from water, a mixture of petroleum ether (90–100°) diluted with some toluene proved more satisfactory. From this solvent pair 2.2 g. (25% yield) of large square plates of pentafluorobenzoic acid, m.p. 106–107°, was obtained.

Anal. Calcd. for C7HF5O2: C, 39.6; H, 0.47. Found: C, 39.4; H, 0.47.

References:

  1. CRC Handbook of Chemistry and Physics. - 95ed. - CRC Press, 2014. - pp. 3-436
  2. Синтезы фтороорганических соединений. - М.: Химия, 1977. - pp. 174-175 [Russian]

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    © Collected Ruslan Anatolievich Kiper, burewestnik@mail.ru