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Organic Lab Reactions 175

Organic Lab Reactions 175 - 170 THE FORMATION OF CYCLIC...

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170 THE FORMATION OF CYCLIC KETONES Phosphorus Pentoxide. The direct dehydration of arylbutyric and arylpropionic acids has been accomplished in some instances with phos- phorus pentoxide in organic solvents such as benzene or toluene (Table XII). The procedure involves treating the solution of the acid with 1 to 10 parts of powdered phosphorus pentoxide and boiling the suspension for one to three hours with mechanical stirring. The addition of a portion of Filter-Cel equal in weight to the amount of acid being cyclized may improve the reaction by holding in suspension the phosphoric anhydride, which otherwise tends to form a sticky coagulum. 192 After the reaction is terminated, the excess phosphorus pentoxide usually is decomposed with dilute alkali and the product purified in the customary manner. The method appears fairly general and has the advantage over sulfuric acid in that no substitution reactions comparable to sulfonation can take place.
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