Esters p-bromophenacyl

B) Phenacyl and p-Bromophenacyl esters. The sodium salt of an acid in aqueous-ethanolic solution will react with phenacyl bromide, CjHjCOCHgBr, and with p-bromophenacyl bromide, BrC,H4COCH2Br... 

C) Phenacyl and p-Bromophenacyl esters. Ammonium salts in aqueous-ethanolic solution do not however usually condense satisfactorily with phenacyl and />-bromophenacyl bromide. The aqueous solution of the ammonium salt should therefore be boiled with a slight excess of sodium hydroxide to remove ammonia, and the solution then cooled, treated with hydrochloric acid until just alkaline to phenol-phthalein, and then evaporated to dryness. The sodium salt is then treated as described (p. 349) to give the ester. Filter the ester, and wash with water to remove senium halide before recrystallisation. 

Use the procedure given under 2 for p-bromophenacyl esters. If the ester does not crystallise out on coofing, reheat the reaction mixture, and add small portions of hot water to the point of incipient cloudiness and allow to cool. 

Acidify the residue in the flask with dUute sulphuric acid and distil off 10-15 ml. of the solution. Test a smaU portion of the distillate for acidity, and also observe the odour. Neutralise the main portion with sodium hydroxide solution (add a drop of phenolphthalein to act as indicator), evaporate to smaU bulk, and convert the sodium salt into the p-bromophenacyl ester or into some other suitable derivative (Section 111,85) determine the m.p. of the derivative. 

Drop 1 g. of sodium into 10 ml. of ethyl alcohol in a small flask provided with a small water condenser heat the mixture until all the sodium has dissolved. Cool, and add 1 g. of the ester and 0-5 ml. of water. Frequently the sodium salt of the acid will be deposited either at once or after boiling for a few minutes. If this occurs, filter oflF the solid at once, wash it with a little absolute ethyl alcohol (or absolute methylated spirit), and convert it into the p-bromophenacyl ester, p-nitro-benzyl ester or S-benzyl-tso-thiuronium salt (for experimental details, see Section 111,85). If no solid separates, continue the boiling for 30-60 minutes, boil oflF the alcohol, allow to cool, render the product just neutral to phenolphthalein with dilute sulphuric or hydrochloric acid, convert the sodium salt present in solution into a crystalline derivative (Section 111,85), and determine its melting point. 

The excess of alkah is then neutralised with dilute hydrochloric acid (phenolphthalein) and the solution is evaporated to dryness on the water bath. The acid may then be characterised as the S-benzyl-tao-thiuronium salt or as the p-bromophenacyl ester (Section 111,85). In many instances the derivative may be prepared directly from the neutralised solution. 

When monocrotaline is hydrogenolysed the acid scission product is monocrotalic acid, CgHigOj, m.p. 181-2°, [a]p ° — 5-33° (HgO), which provides a methyl ester, m.p. 79-80°, [ ]d°° — 16-2° (EtOH), containing one active H atom and a p-bromophenacyl ester, m.p. 162-3°. It is a lactonic acid, which on boiling with sodium hydroxide solution loses carbon dioxide and produces a/3-dimethyllaevulic acid (monocrotic acid, II). 

Bromopentane, 279 p-Bromophenacyl bromide, 960, 961 p-Bromophenacyl esters, 362 o-Bromophenol, 666, 679 p-Bromophenol, 666, 679 Bromophenol blue, 989, 990... 

A general procedure is to hydrolyse the acid chloride (or anhydride) by warming with dilute alkali and acidifying the resulting solution with dilute hydrochloric acid to Congo red. If the acid is sparingly soluble, filter it off and characterise it in the usual way. If no precipitate of carboxylic acid is obtained, adjust the pH of the solution to neutrality to phenolphthalein and evaporate to dryness. Use the mixture of the sodium salt of the acid and sodium chloride thus obtained for the preparation of a suitable derivative (e.g. the p-bromophenacyl ester). 

A mixture of potassium fluoride (33.83 g, 0.582 mol), 2,4 -dibromoacetophenone (80.93 g, 0.291 mol), and DMF (350 ml) was stirred at room temperature for 5 min. A solution of 4 1 mixture of (cis trans) acids (45.0 g, 0.265 mol) in DMF (50 ml) was then added to the reaction mixture and the whole stirred at room temperature for 3 h, then at 100°C for 30 min. The reaction mixture was cooled to room temperature and diluted with H20 (200 ml). The aqueous solution was extracted with Et20 (4x400 ml). The combined ethereal extracts were washed with H20 (3x400 ml) and dried over sodium sulfate. After the solvent was partially removed in vacuo, a precipitate was formed. The slurry was the filtered to give 51.0 g (53%) of p-bromophenacyl ester of 6-ethyl-5-methyl-3,6-dihydro-2H-pyran-2-carboxylic acids as a white solid material, melting point 137°-138°C. 

To a solution of the p-bromophenacyl ester of 6-ethyl-5-methyl-3,6-dihydro-2H-pyran-2-carboxylic acids (46.0 g, 0.125 mol) in glacial AcOH (650 ml) was slowly added zinc (dust, 49.31 g, 0.754 mol) in a 60 min-period at room temperature. The reaction mixture was stirred at room temperature for 8 h, then filtered on Celite, and the zinc residue washed with AcOH (200 ml), then THF (200 ml). Most of the solvent was evaporated and the crude reaction mixture diluted with Et20 and washed with H20 (2x150 ml). The organic layer was treated with a diluted NaOH solution to pH 10. The aqueous phase was washed with Et20 several times, then acidified with a 1.0 N HCI solution to pH 4, and extracted with Et20. The combined organic extracts were... 

Higher carboxylic acids Capillary column Electron capture flame ionisation Carboxylic acids derivitivised to p-bromophenacyl esters [629]... 

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