Acidity of amines

The reaction of diazo compounds with amines is similar to 10-15. The acidity of amines is not great enough for the reaction to proceed without a catalyst, but BF3, which converts the amine to the F3B-NHR2 complex, enables the reaction to take place. Cuprous cyanide can also be used as a catalyst. The most common substrate is diazomethane, in which case this is a method for the methylation of amines. Ammonia has been used as the amine but, as in the case of 10-44, mixtures of primary, secondary, and tertiary amines are obtained. Primary aliphatic amines give mixtures of secondary and tertiary amines. Secondary amines give successful alkylation. Primary aromatic amines also give the reaction, but diaryl or arylalkyl-amines react very poorly. 

The present information does not allow discrimination between these two routes. The high-pH path probably involves concerted attack of OH and Mn04 upon neutral amine because the possibility of attack of oxidant upon C6H5CH2NH or C6H5CHNH2 is too remote in view of known acidities of amines. 

P Chemical Shifts of (HI) and pKa Values of the Conjugate Acids of Amines... 

The gas-phase basicity and acidity of amines were in a chapter of the first updated volume of this series2, which provides extensive tables of values of aliphatic and aromatic... 

Acidities of amines in solution are less well known than those of alcohols. Streit-wieser and co-workers report that cyclohexylamine is somewhat less acidic than triphenylmethane,88 but there is little information available about the effects of structural variation on acidity. In the gas phase, Brauman and Blair found the order (most acidic to least acidic) (C2H5)2NH > (CH3)3CCH2NH2 (CH3)3... 

For dissociation of conjugate acid of amines. k Robinson and Stokes 46). 

Explain the observed difference in the pKg values of the conjugate acids of amines A and B. 

The acidity of amines is enhanced by more than 30 orders of magnitude when coordinated to Au(III) for example,... 

Comp>arison of the Basicity and Acidity of Amines and Amides... 

In the amine, the electron pair is mainly localized on the nitrogen. In the amide, the electron pair is delocalized to the carbonyl oxygen. The effect of this delocalization is seen in the low pKa values for the conjugate acids of amides, compared with those for the conjugate acids of amines, for example ... 

Solvents appear as important players in questions of stability. For example, both the conjugate bases of alcohols (alkoxides) and the conjugate acids of amines (ammonium ions) depend greatly on solvation for stabilization. In assessing basicity or acidity, one must take account of the solvent. 

Brauman and Blair have argued that the polarization stabilization effect of alkyl groups should be essentially the same for negative as for corresponding positive ions [27]. Qualitative results for acidities of amines and alcohols were compared with corresponding results for basicities of amines in support of their argument. 

Like the alcohols (Section 8-3), amines are both basic and acidic. Because nitrogen is less electronegative than oxygen, the acidity of amines is about 20 orders of magnitude less than that of comparable alcohols. Conversely, the lone pair is much more available for protonation, thereby causing amines to be better bases. 

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