Basicity constants pyrrole

The methods outlined, of course, are readily applicable to a wide variety of substituted heterocycles like the carboxyl, hydroxy and mercapto derivatives of pyridines, pyridine 1-oxides, pyrroles, etc. The application to amines and to diaza compounds such as pyrimidine, where the two centers are basic, is obvious except that now 23 takes the role of the neutral compound, 21 and 22 the roles of the tautomeric first conjugate bases, and 20 the role of the second conjugate base. Extensions to molecules with more than two acidic or basic centers, such as aminonicotinic acid, pyrimidinecarboxylic acids, etc., are obvious although they tend to become algebraically cumbersome, involving (for three centers) three measurable Kg s, four Ay s, and fifteen ideal dissociation constants (A ), a total of twenty-two constants of which seven are independent. 

In their studies of the effect of solvent upon the N—H stretching frequency in pyrrole, Fuson and Josien [1] have shown the distinction between the solvent-solute interaction which is a function of dielectric constant alone [2, 3] and that which is more specific, involving N—H hydrogen bonding. The most pronounced frequency shifts are those caused by pyridine [4] (K—M N bonding) and by acetone (N—H 0 bonding). The choice of pyrrole for these studies was presumably partly governed by convenience since the N—H band in pyrrole is considerably more intense than in the more basic secondary amines. We have attempted an extension of this work in two directions ... 

Ava-Henrfs Law Constant, Josien and Fuson have made extensive studies of solvent effects on IR frequencies (1055, 1059), contributing much interesting and accurate data on H bonding systems. They note a systematic correlation between Av for either methanol or pyrrole and the Henry s Law constant of HCl in a series of aromatic solvents (1060). As the basicity of the aromatic increases, the constant decreases-and Ava rises. The data they compile are shown in Table 3-IV. For... 

The alkylation of thiophenes with a glyoxylate imine to give an a-aminoester has been achieved using an iron(III) catalyst. The mechanism in the case of 2-ethylthiophene is thought to involve co-ordination of the catalyst to the imine, allowing reaction with the thiophene through the intermediate (63). The reaction of a ,/3-unsaturated iminium ions with pyrrole is slow when only weakly basic counterions are present. However, in the presence of potassium trifluoroacetate, rapid deprotonation of the intermediate, (64), allows the rate constant for rate-determining carbon-carbon bond formation to be measured. 

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