Butanedioic acid, anhydride from

Exercise 23-24 Show how a mixture of amines prepared from 1-bromobutane and an excess of butanamine may be resolved into its components by reaction with the anhydride of 1,4-butanedioic acid, (CH2)2(CO)20, separation of the products through advantage of their solubility properties in acid or base, and regeneration of the corresponding amines (Section 18-10C). Write equations for the reactions involved. 

It is possible to make either the diester or the monoester of butanedioic acid (succinic acid) from the cyclic anhydride as shown. Why does the one method give the monoester and the other the diester ... 

Propose a mechanism for the thamal formation of butanedioic anhydride from the dioic acid. 

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