Aryloxyacetic acids, from phenols

To a mixture of 10 g. of the compound and 3-5 ml. of 33 per cent, sodium hydroxide solution in a test-tube, add 2-5 ml. of 50 per cent, chloroacetic acid solution. If necessary, add a little water to dissolve the sodium salt of the phenol. Stopper the test-tube loosely and heat on agently-boiling water bath for an hour. After cooling, dilute with 10 ml. of water, acidify to Congo red with dilute hydrochloric acid, and extract with 30 ml. of ether. Wash the ethereal extract with 10 ml, of water, and extract the aryloxyacetic acid b shaking with 25 ml. of 5 per cent, sodium carbonate solution. Acidify the sodium carbonate extract (to Congo red) with dilute hydrochloric acid, collect the aryloxyacetic acid which separates, and recrystallise it from hot water. 

The derivative selected in any particular instance should be one which clearly singles out one compound from among all the possibilities and thus enables an unequivocal choice to be made. The melting points of the derivatives to be compared should differ by at least 5-10°. Whenever possible, a derivative should be selected which has a neutralisation equivalent as well as a melting point (e.g., an aryloxyacetic acid derivative of a phenol. Section IV,114,4, or a hydrogen S nitrophthalate of an alcohol. Section 111,25,5). 

Problem 24.17 Phenols are often identified as their aryloxyacetic acids, ArOCH2COOH. Suggest a reagent and a procedure for the preparation of these derivatives. (Hint See Sec. 24.8.) Aside from melting point, what other property of the aryloxyacetic acids would be useful in identifying phenols (Hint See Sec. 18.21.)... 

Add 1 g of the phenol to 1 5 g of chloracetic acid and 5 ml of 30% sodium hydroxide solution. Addition of a little water may be necessary to dissolve the sodium salt of the phenol. Boil for 30 minutes (60 minutes may be required in some cases). Cool, acidify to Congo Red with 2N hydrochloric add, and extract with ether. Wash the ethereal solution with water, then with dilute sodium carbonate solution into which the aryloxyacetic acid passes. (The naphthoxyacetic adds may be predpitated at this stage as their sodium salts. The precipitate should be removed and addified to liberate the derivative.) Addify the alkaline extract and recrystallize the predpitated product from water. As a further check, the equivalent weight of the derivative may be determined (as for carboxylic acids, page 123). 

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See also in sourсe #XX -- [ ]

See also in sourсe #XX -- [ ]

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