Introdução à físico-química orgânica utilizando um colorímetro artesanal – Uma prática interdisciplinar

Abstract

INTRODUCTION TO PHYSICAL ORGANIC CHEMISTRY USING A HOMEMADE COLORIMETER -AN INTERDISCIPLINARY EXPERIMENT. Herein, we propose an interdisciplinary experiment for undergraduate course that involves concepts of organic and physical chemistry. Firstly, we propose the synthesis of three nitrophenyl acetates, varying the substituent position. Afterwards, we describe the construction of a homemade colorimeter using inexpensive materials and LED as both emission and detection dispositives. Finally, the colorimeter is used to follow the nucleophilic acyl transfer reactions catalyzed by imidazole under pseudo-first order conditions for the reactions of p-nitrophenyl, o-nitrophenyl and m-nitrophenyl acetate with imidazole. The substituent effect is correlated to the reactivity of the acetates, one of the benchmarks of a physical organic chemical approach. The effect of imidazole concentration is also evaluated. The proposed experiment is interesting because the students can thoroughly understand how a spectrophotometer works and since each student can construct their own colorimeter, they don´t have to rely on any equipment infrastructure. Additionally they can correlate two important areas: organic and physical chemistry by using a kinetic study in the understanding of organic reactions. Indeed, physical organic chemistry is a field of increasing interest specially for elucidating mechanisms and introducing students to this interdisciplinary approach is interesting since several undergraduate concepts are covered.