The decomposition of triphenylimidazole-para-acetate follows specific base catalysis and can be conveniently followed by fluorescence

Author(s)

Reis, Roberta Albino ^[1] ; Boaro, Andreia ^[1] ; Orfao, Ronaldo Barros ^[1] ; Melo, Diego Ulysses ^[1] ; Bartoloni, Fernando Heering ^[1]

Affiliation

^[1] Univ Fed ABC, Ctr Ciencias Nat & Humanas, BR-09210580 Santo Andre, SP - Brazil

• Document type: Journal article
• Source: LUMINESCENCE; v. 34, n. 2, p. 234-242, MAR 2019.
• Web of Science Citations: 0

Abstract

The kinetics of the decomposition reaction of 4-(4,5-diphenyl-1H-imidazol-2-yl)phenyl acetate (1) in basic alcoholic media was investigated, using a simple fluorescence (FL) spectrophotometric procedure. The process was conveniently studied using FL, since the triphenylimidazole-derived ester 1 and its reaction products (the corresponding phenol 2 and phenolate 2(-)) are all highly fluorescent (phi(FL) > 37%). By carefully selecting excitation and emission wavelengths, observed rate constants k(1) in the order of 10(-3) to 10(-2) s(-1) were obtained from either reactant consumption (lambda(ex) = 300 nm, lambda(em) = 400 nm) or product formation (lambda(ex) = 350 nm, lambda(em) = 475 nm); these were shown to be kinetically equivalent. Intensity-decay time profiles also gave a residual FL intensity parameter, shown to be associated to the distribution of produced species 2 and 2(-), according to the basicity of the medium. Studying the reaction in both methanol (MeOH) and isopropanol (iPrOH), upon addition of HO-, provided evidence that the solvent's conjugate base is the active nucleophilic species. When different bases were used (tBuO(-), HO-, DBU and TEA), bimolecular rate constants k(bim) ranging from 4.5 to 6.5 L mol(-1) s(-1) were obtained, which proved to be non-dependent on the base pK(aH), suggesting specific base catalysis for the decomposition of 1 in alcoholic media. (AU)

• FAPESP's process: 12/13807-7 - New tools for the study of electron transfer reactions in PS II model systems
• Grantee: Fernando Heering Bartoloni
• Support Opportunities: Regular Research Grants
• FAPESP's process: 14/05813-2 - Use of fluorophores containing phenolic and nitrogenated groups on metal detection by light emission
• Grantee: Ronaldo Barros Orfão Junior
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 16/10585-4 - Mechanistic aspects regarding the induced decomposition of hydroperoxides and silylperoxides derived from lophine
• Grantee: Andréia Boaro
• Support Opportunities: Scholarships in Brazil - Doctorate