Micmicroscale Reduction of a Ketone to Alcohol

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Micro – scale Reduction of a Ketone to an Alcohol: Benzophenone to Diphenylmethanol with Sodium Borohydride Abstract: Purpose of experiment 2.1 was to perform reduction reaction of benzophenone to diphenylmethanol with sodium borohydride as a reducing agent. The reducing agent was used in excess to ensure complete reduction of the carbonyl group. The product was isolated as a solid by filtration and its purity was checked using Thin Layer Chromatography with different ratios of mixture of polar and non – polar solvents and by checking its melting point, which was 520C - 620C. Infra – Red spectroscopy was not performed, however previously printed graphs were compared and analysed based on tables in Chemistry Laboratory Manual. Purpose of the Experiment: To produce diphenylmethanol from the reduction of benzophenone by using sodium borohydride as a reducing agent. To check purity of a product by using thin layer chromatography (TLC) and by performing a melting point. Introduction: The key step in the reduction of a carbonyl compound by either lithium aluminium hydride or sodium borohydride is the transfer of a hydride ion from the metal to the carbonyl carbon. In this transfer the hydride ion acts as nucleophile. The mechanism for the reduction of a ketone by sodium borohydride: (1) Method (Based on Chemistry Laboratory Manual): 1. 0.4510g of benzophenone was dissolved in 5 cm3 of ethanol in boiling tube containing a magnetic stirrer bar. 2. O.1249g of sodium borohydride was added and left for 30 minutes. 3. The mixture was poured into a beaker containing 25cm3 of ice – water and 2.5cm3 of concentrated HCl. Reaction mixture was left in ice – bath for 10 min. 4. Precipitated product was recovered by vacuum filtration and washed with two portions of 5 cm3 of ice – cold water. 5. Precipitated product was placed in pre – weighted beaker and dried

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