Counterion Effects in the Nucleophilic Substitution Reaction of the Acetate Ion with Alkyl Bromides in the Synthesis of Esters

• Autores: Elizabeth M. Valentín, Ingrid Montes, Waldemar Adam
• Localización: Journal of chemical education, ISSN 0021-9584, Vol. 86, Nº 11 (November), 2009, págs. 1315-1318
• Idioma: inglés
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• Resumen

  • Esters are often employed as artificial flavorings in foods and drinks, since the more volatile ones possess distinctive odors characteristic of common fruits. The present laboratory experiment introduces students to the esterification method in which a nucleophilic substitution reaction (either SN2 or SN1) between an alkyl halide and metal carboxylate is employed. The students learn that the metal counterion plays an important role with regard to the efficiency of the reaction and that the ester yield depends on the type of mechanism, namely, whether an SN2 or SN1 process occurs. For this purpose, a simple ester is synthesized, its yield determined gravimetrically, its purity established by gas chromatography analysis, and its identity assessed by mass spectrometry. The results are explained in terms of Pearson's hard and soft acid–base principle (HSAB), an empirical concept rarely covered in introductory organic chemistry.