Aniline, basicity ionization

Trichloroacetic acid decomposes in water, alcohol and aniline and other basic solvents but it does not decompose in non-basic solvents such as benzene, carbon tetrachloride, sulfuric and acetic acid. Furthermore, the ethyl ester of trichloroacetic acid dissolves in alcohol but it does not decompose. It is known that this ester does not ionize in alcohol. Trichloroacetic acid, the sodium salt, the barium salt, and the anilinium salt all decompose in water at the same rate and all give beautiful first order constants throughout the whole course of the reaction. It is known that all these salts... 

Phenols are more acidic than alcohols because one of the non-bonding electron pairs on oxygen is drawn into the benzene ring by resonance. This stabilizes the phenoxide ion that is formed upon ionization and thus the acidity of phenol is enhanced by the phenomenon. This same withdrawal of electrons by the benzene ring stabilizes aniline and decreases the availability of the nonbonding electron pair on nitrogen. Both effects decrease the basicity of aniline relative to alkyl amines. 

It is apparent from the above definition that a substance cannot act as an acid unless a base is present to accept the protons. Thus, acids will undergo complete or partial ionization in basic solvents such as water, liquid ammonia, or ethanol, depending on the basicity of the solvent and the strength of the acid. But in neutral or inert solvents, ionization is insignificant. However, ionization in the solvent is not a prerequisite for an acid-base reaction, as in the last example in the table, where picric acid reacts with aniline. 

Workentin et al. have recently reported the results of an extensive laser flash photolysis investigation of the reactions of the cation radicals of 9-phenyl- and 9,10-diphenylanthracene (PA and DPA, respectively) with amines. Primary amines react with both cation radicals via nucleophilic addition with rate constants which reflect both the amine basicity and a steric requirement for bond formation. Steric effects are more pronounced for addition of DPA " vs. PA ", presumably due to the presence of substituents at both the 9- and 10-position. Tertiary amines and anilines react with PA " and DPA " via electron transfer with rate constants which correlate with amine ionization potentials. Rate constants for nucleophilic addition of primary amines are faster in acetonitrile than in acetonitrile/water solution. The rate-retarding effect of water is attributed to an equilibrium between the fiee amine (reactive) and hydrated amine (unreactive). The beneficial effect of water on preparative ET-sen itized photoamination may reflect its role as a catalyst for the proton transfer processes which follow C-N bond formation (Scheme 2). Hydration of the amine also should render it less reactive in primary and secondary electron transfer processes which can compete with the formation of the arene cation radical. 

Here, and Xq (with values between 0 and 1) represent possible correction factors that depend on sample composition. For example, if bases are absent from the sample, the term Xq 0, because values of C mainly affect the retention of ionized basic solutes. For similar reasons, if carboxylic acids are absent from the sample, x = 0. Note that if and Xq are assumed to be equal to one (equivalent to setting Fj = Fj), maximum values of F result, with a decrease in the nttmber of possible replacement columns with F < 3. When a basic compound is partly ionized, there is a reduced contribution of C to the separation. As a rough rule, weak bases such as anilines or pyridines have 01 for a mobile phase with pH < 6 and 0 for pH > 6. Similarly, strong bases (aminoalkyl derivatives) have = 0.1 for pH > 7 and Xq 1 for pH < 6. See Ref [18] for details. 

The measured proton exchange is that of the N—H proton in the anilinium acetate salt, BH OAc , with the carboxyl proton of the solvent. This rate is relevant to the present discussion because Bfr OAc" is the ionized form of the given aniline in acetic acid. It turns out that the rate constant for proton exchange is correlated with the basicity of the aniline, decreasing as the basicity increases. This suggests a two-step reaction mechanism, i.e. equations 29 and 30. 

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