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The decomposition of triphenylimidazole‐ para ‐acetate follows specific base catalysis and can be conveniently followed by fluorescence
Author(s) -
Reis Roberta Albino,
Boaro Andreia,
Orfão Ronaldo Barros,
Melo Diêgo Ulysses,
Bartoloni Fernando Heering
Publication year - 2019
Publication title -
luminescence
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.428
H-Index - 45
eISSN - 1522-7243
pISSN - 1522-7235
DOI - 10.1002/bio.3600
Subject(s) - chemistry , catalysis , methanol , fluorescence , base (topology) , decomposition , reaction rate constant , phenol , nucleophile , solvent , photochemistry , kinetics , organic chemistry , mathematical analysis , physics , mathematics , quantum mechanics
The kinetics of the decomposition reaction of 4‐(4,5‐diphenyl‐1 H ‐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 (Φ 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 ( λ ex = 300 nm, λ em = 400 nm) or product formation ( λ ex = 350 nm, λ 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 ( i PrOH), upon addition of HO − , provided evidence that the solvent's conjugate base is the active nucleophilic species. When different bases were used ( t BuO − , 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 p K aH , suggesting specific base catalysis for the decomposition of 1 in alcoholic media.