C.
2,2-Difluorosuccinic acid. In a
3-l. three-necked flask fitted with stirrer,
thermometer, and dropping funnel,
80 g. (2 moles) of sodium hydroxide is dissolved in 2 l. of water and
158 g. (1 mole) of potassium permanganate is then added. The mixture is cooled to 15–20° with an
ice-salt bath, and
107 g. (0.75 mole) of 1-chloro-2,3,3-trifluorocyclobutene is added through the dropping funnel during 1 hour while the permanganate solution is stirred and maintained at 15–20°. After the solution has been stirred for 2 hours more at this temperature, the
manganese dioxide is removed by filtration and rinsed with three 300-ml. portions of water. The combined filtrate and washings are concentrated to a volume of 500 ml. by evaporation on a
steam bath (Note
3). The solution is then cooled and
85 ml. of concentrated sulfuric acid is added slowly with stirring. The cold solution is extracted with four
250-ml. portions of ether (Note
4). Drying of the
ether extract is accomplished by agitating it for 5 minutes with
30 g. of anhydrous magnesium sulfate. When the drying agent has been removed by filtration and rinsed with
ether, the filtrate and the
ether washings are combined and concentrated to give
91–97 g. (
79–84%) of
2,2-difluorosuccinic acid. The acid is recrystallized by dissolving it in hot
nitromethane (1.25 ml. per g.), filtering the solution through a layer of filter aid if necessary, and cooling the solution to 3°. The crystals are collected by suction filtration and rinsed with
30 ml. of cold nitromethane. After drying, this gives
85–92 g. (
74–80%) of
2,2-difluorosuccinic acid, m.p.
144–146°.