Multistep Synthesis of Benzilic Acid

2109 Words Nov 10th, 2012 9 Pages
Multi-Step Synthesis of Benzilic Acid from Benzoin

The main purpose of this experiment was to convert a secondary alcohol to a ketone, utilizing a mild and selective oxidizing agent. In addition, this converted alpha diketone was then subjected to rearrangement to a carboxylate salt, then acidification, to produce an alpha-hydroxyacid. In this experiment, benzoin was used and converted into benzil, which was then used to synthesize benzillic acid.
The yields were not ideal: .081g of benzil- a 27.5% yield; .038g of benzilic acid- a 34.97% yield. The matching melting points and IR readings, however, confirmed a high degree of purity for each compound: 95.6°C for benzil, and 104.5°C for benzilic acid, meager .632% and .333%
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Once the final solid product was obtained in both reactions the melting point procedure was used to determine the level of remaining impurity of the final product, comparing the experimental and expected values found in literature. In conjunction with the melting point procedure, infrared spectroscopy was used to reveal the different functional groups of the products. In other words, the IR machine indicates whether our final product matches up with the desired one, matching carbonyl and alcohol absorption peaks (or the lack thereof) to their theoretical presence (either benzil or benzillic acid).
1.5ml of nitric acid was added to .30g of benzoin in a conical vial with a stir vane. The mixture was then heated in a 70 degree Celsius water bath, while stirred, for one hour. The mixture in the conical vial was then cooled to room temperature and, using a pipette, the solution was transferred to a beaker containing 4ml of ice water. The mixture slowly crystallized in the beaker and the crystallized product was filtered on a hirsch funnel with vacuum. 5 ml of cold water was used to wash the product and then the product was allowed to dry.
The solid product was then collected from the funnel and added to a hot 95% ethanol solution in an Erlenmeyer flask and completely dissolved. Once the solid was dissolved completely, the solution was allowed to cool to room temperature. Once yellow crystals formed, the solution was placed into