Abstract:

Combinatorial Chemistry is used to synthesize a large number of molecules which can be used to determine structure-reactivity correlations or physical or physicochemical proprieties on the reactivity of certain groups. In this research, and using the previous tools, the oxidation of a primary alcohol (cinnamyl alcohol) was carried out using different oxidants described in the literature as adequate to perform the preferential oxidation towards the corresponding aldehyde and obtaining small amounts of the acid. During classes in Organic Chemical theory, at undergraduate level, students are taught different oxidants for alcohols, doing emphasis that in the case of primary alcohols is very difficult to stop the oxidation during the pass of aldehyde, however is different to use them experimentally. In a work session each student performed the oxidation with a reagent and final results were analyzed by all students and they have deduced by themselves which one is adequate. The oxidation where carried out at micro and/or semimicro scales analyzing the obtained products by Gas Chromatography. In this study the obtained results are presented with the following oxidants: NaOCI at 6%, NaOCl at 12%, MnO2, PS-CrO3, PCC and Collin’s reagent, it is noted that Collin’s reagent produced the best yield of aldehyde (96.6%) while NaOCl at 12% had the worst yield (2.9%); regarding to the carboxylic acid production NaOCl produced the greatest amount of acid with 0.6%. We emphasize that each system of experiments was challenge for students because there was a protocol for isolating the products.
Conclusions: 1) Through individual and team work students reached the clear conclusion that the nature of the used oxidant modified both the yield of cinnamaldehyde as well as the cinnamic acid and by instance the recovery of raw material; 2) Desired academic goal was achieved by teachers, to experimentally determine which of the oxidants studied in theory class is rally efficient; 3) It was demonstrated that Combinatorial Chemistry in the form of parallel synthesis can be effective adapted for teaching purposes; 4) It was observed that the oxidation on cinnamyl alcohol-micro scale is more efficient in order to obtain reliable quantitative results that allow discrimination of an oxidant from another; and 5) Students in order to solve the problem of “what oxidant is more effective to obtain aldehydes” used their prior knowledge of organic chemistry, analytical chemistry, also they used different separation processes and they made the treatment of hazardous wastes obtained during the experiments, incorporating health care and protecting the environment through the minimization and proper management of hazardous waste generated in teaching laboratories.

Keywords:

New pedagogical strategy, achieving academic goals for problem solving, oxidation alcohols.