Relative Basicity of Amines and Other Compounds

The relative acidity of different compounds can be compared using their pAT values. The relative basicity of different compounds (such as amines) can be compared using the p a values of their conjugate acids. 

Problem 25.23 Which amine in each pair is the stronger base The pK values given are for the conjugate acid of each amine. 

To compare the basicity of two compounds, keep in mind the following  

The relative basicity of 1 , 2°, and 3° amines depends on additional factors, and will not be considered in this text. 

One electron-donor group makes the amine more basic. 

Primary (1 °), 2°, and 3° alkylamines are more basic than NH3 because of the electron-donating inductive effect of the R groups. 

Problem 25.23 Which compound in each pair is more basic (a) (CH3)2NH and NH3 (b) CH3CH2NH2 and CICH2CH2NH2  

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Relative Basicity of Amines and Other Compounds Piperidine Pyridine... 

EC oxidation is commonly employed in the analysis of some basic drugs, especially morphine and related opioids (Chapter 6, Section 1). Even if a compound is not amenable to EC oxidation, its metabolites may be. Phase I metabolism of aromatic xenobiotics often proceeds with aromatic hydroxylation. Hydrolysis of phenolic esters, reduction of diazo double bonds to primary amines and other reactions also occur. EC detection is not widely used to measure acidic or neutral compounds, such as salicylate or paracetamol after overdosage, since these compounds, although easily oxidised, are normally present at relatively high concentrations and UV detection is adequate. However, EC methods may be useful in measuring the plasma concentrations of these compounds attained after a single oral dose. ... 

Basicity of aniline Aniline, like all other amines, is a basic compound ( Tb = 4.2 X 10 °). Anilinium ion has a = 4.63, whereas methylammo-nium ion has a pK = 10.66. Arylamines, e.g. aniline, are less basic than alkylamines, because the nitrogen lone pair electrons are delocalized by interaction with the aromatic ring tt electron system and are less available for bonding to H+. Arylamines are stabilized relative to alkylamines because of the five resonance structures as shown below. Resonance stabilization is lost on protonation, because only two resonance structures are possible for the arylammonium ion. 

It is also appropriate to mention the modern mechanistic work on the very first type of reaction in the chemistry of aliphatic diazo compounds, namely deamination (1-1). In contrast to the 1,3-dipolar cycloadditions deaminations of aliphatic amines are relatively seldom applied for synthetic purposes (see Sect. 7.7), because they lead in most cases to a mixture of nucleophilic substitution products as well as elimination and rearrangement products. It has been clear, at least since the work of Young and Andrews (1944), Ingold s group (Brewster et al., 1950) and others, that, basically, these reactions belong to the class of nucleophilic aliphatic substitutions in spite of a bewildering number of complicating factors (see Chapt. 7). 

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