Aniline, basicity Subject

Cyclophosph(V)azanes with five-coordinate phosphorus are mostly dimeric, four-membered ring derivatives, [X3PNR]2 (6). Several reviews cover the subject. A simple preparation of these compounds involves the reaction of PCI5 with primary amines (or their hydrochlorides), the so-called Kirsanov reaction. Weakly basic amines form monomeric Cl3P=NR, but with more basic amines (e.g. with R = alkyl), the products are the cyclic dimers. Various anilines give either a monomer or a cychc dimer, depending upon their basicity. ... 

It should also be noted that decarboxylation of / -oxo acids is subject to specific catalysis by primary amines as well as to general catalysis. For example, the very smooth decarboxylation of 2,2-dimethylacetoacetic acid in water is uninfluenced by addition of a secondary or tertiary amine but its rate is increased by a factor of 10 on addition of aniline. The explanation lies in the fact that primary amines can react to form / -imino acids, whose imino-nitro-gen atom, being considerably more strongly basic than the ketonic oxygen atom, causes almost complete transfer of the proton from the carboxyl group, and it is this transfer that initiates the decomposition. A further example is the violent decomposition to acetone and carbon dioxide that occurs when a small amount of aniline is added to acetonedicarboxylic acid. 

The basic assumption of the Hammett method is that the activity coefficient ratio /bh+//b is independent of the nature of B at any given solvent composition. This seems to be a reasonably good assumption for a closely related series of bases, such as the primary anilines, but may not be true for bases of different structural types. This has led to the proposal of many different types of acidity function, and to much controversy as to the meaning and usefulness of the Hammett and related acidity functions. This subject has been extensively reviewed elsewhere [16]. Although it now appears that the concept of the acidity function is perhaps not as generally useful as was originally believed, at the present time we do not have any more reliable method of assessing the acidities of superacid media. 

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