Fluoroacetate barium

Fluoroacetyl chloride, CH2FCOCl, was prepared by the action of phosphorus pentachloride on the free fluoroacetic acid (p. 121).1 It is extremely useful as fluoroacetylating agent in synthetic work. Because of its importance we have recently reinvestigated other methods of preparation.2 These may be summarized as follows (1) direct from fluoroacetamide (p. 125) by the action of phosphorus oxychloride and water (2) the action of phosphorus oxychloride on either sodium fluoroacetate (p. 121) or on barium fluoroacetate (p. 121). Good yields are obtained in both (1) and (2), and in each case the starting materials are more easily available than fluoroacetic acid itself. 

Fluoroacetic acid.1 A few drops of phenolphthalein solution are added to a mixture of methyl fluoroacetate (46-0 g., 0-5 mol.) and water (100 c.c.) and then powdered barium hydroxide octahydrate (78-9 g., 0-25 mol.) is added in small portions, the mixture being mechanically stirred after each addition until the alkaline reaction has disappeared. The resultant liquid is then made acid, if necessary by the addition of a few drops of methyl fluoroacetate, filtered and the filtrate concentrated to about 100 c.c. on a water-bath. The liquid is cooled and methylated spirit (500 c.c.) added in order to precipitate the barium fluoroacetate, which is filtered off, drained and dried, but not recrystallized yield 69-0 g. (95-0 per cent). 

Dry barium fluoroacetate (58 g., 0-2 mol.) is slowly added to 100 per cent sulphuric acid (122-5 g., 1 25 mol.). On distillation under reduced pressure, using a wide air-condenser, the fluoroacetic acid comes over between 83 and 100°/17 mm., and crystallizes immediately. It can be redistilled at atmospheric pressure and comes over at 167-168-5° yield 29-5 g. (94-2 per cent) colourless needles, m.p. 31-32°. (Found F, 24-3. Calc, for C2H302F F, 24-4 per cent.) These yields are considerably higher than those obtainable by Swarts s original method. 

The preparation of free fluoroacetic acid from methyl fluoroacetate via the barium salt is described on p. 121. An alternative and convenient method1 for preparing the free acid consists in treating fluoroacetamide with nitrous fumes, the pure acid being produced in 90 per cent yield. The two methods may be summarized thus ... 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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