Abstract:

The development and implementation of a new methodology “Achieving academic goals through problem solving, by means of individual and team work” increases the efficiency, effectiveness and relevance of teaching-learning process of the experimental work of students. The previously mentioned matter was studied in the Organic Chemistry II Course, Curriculum 2005 of bachelor’s degree in Chemistry from UNAM, using as a model for implementing the Williamson’s ethers’ synthesis. This methodology has incorporated the foundations of Combinatorial Chemistry as well as the integration of knowledge form other areas in order to resolve problems that led to the achievement of academic goals. In this work we used the reaction in order to obtain Williamson’s ethers using different phenols with different substituents within an alkaline environment (NaOA 33%) and cloroacetic acid in presence and absence of Kl. Academic goals were: a) investigate how the present substituents in the phenol modify the reactivity of phenolate as the nucleophile, b) Since the leaving group (chloride) of chloroacetic acid, being a derived primary halogenated and into a molecular nucleophilic reaction substitution it is not very efficient to transform it in situ into the corresponding iodinated compound, yields should be better, since the iodide is a better leaving group. The following phenols were reacted: phenol, p-methoxyphenol, thymol, b, naphthol, o-cresol, m-methoxypheno, p-chlorophenol, p-hydroxybenzoic acid, m-methylphenol with NaOH at 33% and chloroacetic acid. Seven of the above phenols were reacted with NaOH at 33% NaOH and chloroacetic acid in the presence of Kl. Each student synthesized a phenoxyacetic acid in the absence and presence of Kl, using the different phenols at the end of the session was held a seminar with the participation of all students to review the result. The most sensitive phenols to the presence of Kl were: 2.4-dinitrophenol with an increase in the yield of 22.27%, p-cresol with 32.68%, to thymol with 20.10% and o-cresol with 37.20%. Conclusions: 1) By working individually and by teams to synthesize different phenoxyacetic acids students got to clearly determine that the nature of the substituents present on the ring affect the efficiency of the reaction. The experiments allowed observing that the presence of Kl as a modifier of the reactivity of primary chlorine does not affect in the same way to the reactions of chloroacetic acid with different phenols in basic medium. 2) It was shown that educational goals can be achieved through problem solving, 3) through individual and team work the foregoing was achieved through combinatorial chemistry synthesis in parallel mode, 4) synthesis of the phenoxyacetic acids was performed in semimicro scale because the process of separation and purification of the product is developed to take place in micro scale. 5) Students used their previous knowledge of Organic Chemistry, Analytical Chemistry and they performed the treatment of hazardous wastes obtained during the experiments, and knowing that phenol gives the best results were incorporated the concept in the generation of waste and care health and the environment.

Keywords:

New pedagogical strategy, Experimental Organic Chemistry, Williamson Synthesis.