Keith C. Brown

13C nuclear magnetic resonance study of π-polarization in 3- and 4-substituted benzamides and N-chlorobenzamides

The substituent effect on the carbonyl carbon [C(α)]13C chemical shift in 3- and 4-substituted benzamides and N-chlorobenzamides has been studied in (CD3)2SO. Chlorine shields the carbonyl carbon A cross correlation was carried out for C(α) and the carbonyl carbon in N-chlorobenzamides is less sensitive to substituents than in the benzamides. The dual substituent parameter method indicated a significant diminution in the π-polarization effect (ρI) in N-chlorobenzamides compared to benzamides. This is in contrast to other carbonyl systems where ρI has been found to be essentially independent of the substituent attached to the carbonyl carbon. It is concluded that π-polarization in benzamide and its derivatives is more sensitive to the substituent attached to the carbonyl carbon than in the other classes of aromatic carbonyl compounds studied to date.

Benzoquinone imines. Part 18. Kinetics and mechanism of oxidative coupling reactions involving N,N-bis-(2-hydroxyethyl)-p-phenylenediamine

A kinetic and mechanistic study of oxidative coupling reactions of N,N-bis-(2-hydroxyethyl)-p-phenylenediamine with m-phenylenediamines, phenols, and acetoacetanilide is described. The reactions involve the rapid establishment of an equilibrium between N,N-bis-(2-hydroxyethyl)-p-benzoquinone di-imine and a hydroxy-amine intermediate (3). Competition between direct coupling of N,N-bis-(2-hydroxyethyl)-p-benzoquinone di-imine and hydrolysis to p-benzoquinone monomine via(3) with subsequent coupling leads to a mixture of two dye products. The relative yields are dependent on pH and coupler concentration. Kinetic evidence for the formation of the intermediate (3) is presented.

Benzoquinone imines. Part 17. Kinetics and mechanism of the hydrolysis and cyclization of 2-aminoindophenols in aqueous solution

2-Aminoindophenols undergo hydrolysis at the azomethine bridge at pH 8. At intermediate pH, decomposition occurs to give products which have not been identified. Phenazine formation involves the indophenol anion and hydrolysis the monocation. The neutral species is relatively stable. The instability of the anion towards oxidizing agents, including hydrogen peroxide formed in the air oxidation of the dihydrophenazine, mitigates against the use of the reaction for preparative purposes.

Benzoquinone imines. Part 15. Kinetics and mechanism of the hydrolysis and cyclization of 2-amino-N-(p-hydroxyphenyl)-p-benzoquinone di-imines in aqueous solution

2-Amino-N′-(p-hydroxyphenyl)-p-benzoquinone di-imines undergo hydrolysis at the azomethine bridge at pH <4, intramolecular cyclization to 2-amino-8-hydroxyphenazines at pH 6–10, and hydrolysis at the terminal imino-group at higher pH. Acid hydrolysis involves reaction of the dication with water forming p-aminophenol and 2-amino-p-benzoquinone monoimine. Phenazine formation occurs by intramolecular coupling of the 2-aminonitrogen of the zwitterion to the 2′-carbon atom, followed by oxidation. Alkaline hydrolysis involves attack by hydroxide ion on the zwitterion to give the corresponding 2-aminoindophenol.