Organic Lab Reactions 169

Organic Lab Reactions 169 - (1 part is added gradually with...

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164 THE FORMATION OF CYCLIC KETONES ene group. The possibility of interfering ketone condensations of the type discussed above is therefore eliminated. Being a structural feature this is true regardless of the method of cyclization. It may be presumed, therefore, that the conditions for cyclizing ^-substituted acids by any method are in general less critical than for acids retaining both a- hydrogen atoms. For the sulfuric acid method of cyclization there is no single procedure which is entirely general, because the concentration of the acid, and the reaction time and temperature, may be critical. The method of R. D. Haworth 1W has been used in the ring closure of a large number of acids, but the description serves only to indicate the form of procedure. In order to obtain optimum yields, it may be necessary to alter the condi- tions and concentrations. Procedure V. Ring Closure with Sulfuric Acid. 193 For the conversion of 7-arylbutyric acids into cyclic ketones, the finely powdered acid
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Unformatted text preview: (1 part) is added gradually with stirring to a mixture of concentrated sulfuric acid (3 volumes) and water (1 volume). After one hour's heat-ing on the water bath the colored solution is cooled, diluted with water by pouring onto ice, and extracted with ether. The extract is washed with water, which removes traces of colored sulfonation product, then with dilute aqueous ammonia, and dried over anhydrous potassium carbonate; the solvent is removed, the residue distilled under reduced pressure, and the distillate crystallized from a suitable solvent. An interesting application of sulfuric acid cyclization was reported m in which 0-benzylglutaric acid (LXXXIII) was cyclized to the keto acid LXXXIV by the action of concentrated sulfuric acid at room tem-perature. The yield of crude material was 88%. This seems to be a CO 2 H CH 2 LXXXIII P 2 X CHCH< CH 2 CH 2 CO 2 H LXXXV 1M Stevenson and Thorpe, J. Chem. Soc, 1922, 1717....
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