Studies on Azo Compounds: Part VII-Protonation Constants and Kinetics of Some Thiazole Azo and Azomethine Dyes

Abstract

143-147<span style="font-size:11.0pt;line-height:115%; font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;mso-fareast-font-family:="" "times="" new="" roman";mso-fareast-theme-font:minor-fareast;mso-hansi-theme-font:="" minor-latin;mso-bidi-font-family:"times="" roman";mso-ansi-language:en-us;="" mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">The protonation (pkp) and ionization (pka) constants of some thiazole azo and azomethine dyes were determined in aqueous universal buffer solutions of varying pH values at 25<span style="font-size:11.0pt; line-height:115%;font-family:" calibri","sans-serif";mso-ascii-theme-font:minor-latin;="" mso-fareast-font-family:"times="" new="" roman";mso-fareast-theme-font:minor-fareast;="" mso-hansi-theme-font:minor-latin;mso-bidi-font-family:arial;mso-ansi-language:="" en-us;mso-fareast-language:en-us;mso-bidi-language:ar-sa"="">±0.1oC and at ion strength of 0.1 using the spectrophotometric method. Protonation occurs on the imino nitrogen atom of the thiazole nucleus and it is affected by the nature of the substituents. The rate of protonation of azomethine dyes is slower than that of thiazole azo dyes; therefore, the rate constants of azomethine dyes were evaluated. The order of protonation is 1.5.</span