Essay on Multistep Synthesis of Benzilic Acid

2070 WordsApr 20, 20129 Pages
Abstract: The objective of the experiment was to prepare Benzilic acid by multistep synthesis starting with benzaldehyde. In this setup however, product of the first step, Benzoin, is provided thereby omitting the first step involving the conversion of benzaldehyde. For this experiment, the microscale techniques of reflux, crystallization, and melting-point determination were used. Utilizing these techniques a product yield of 93% for benzil and 57% for Benzilic acid was obtained, as well as a melting point range of 94.8 – 95.4oC for benzil and 152.0 – 153.9oC for Benzilic acid. With the literature melting-point value of benzil being 95oC ( Pavia, 2012), the product was deemed of pure enough quality to be used in the preparation of…show more content…
Procedure To prepare Benzil, .30g of Benzoin was placed in a 5-mL conical vial with 1.5mL of concentrated nitric acid. With the addition of a spin vane and attachment of an air condenser, the mixture was heated and stirred for an hour in a hot water bath at 70oC. The red nitrogen oxide gases were allowed to evolve completely before the air condenser was detached and the mixture was transferred to a beaker containing 4mL ice-cold water then cooled via ice bath. The crude product was then collected and washed with 5mL cold water through vacuum filtration. The weighed product was then transferred and dissolved with hot 95% ethanol in another flask over light heat. Once dissolved completely, the flask was removed from heat, seeded, and then allowed to cool first at room temperature, than in an ice-bath. Following crystallization, the product was collected and rinsed with 95% ethanol vacuum filtration for 5 minutes. After air-drying, the dry benzil was weighed and a melting point was taken. To rearrange into Benzilic acid, .100g of benzil and 95% ethanol was mixed into a 3mL conical vial. Following the addition of a spin vane and attachment of an air condenser, the mixture was heated with an aluminum block at 95oC. After dissolving completely, .25mL of aqueous potassium hydroxide was added and gently boiled at 110oC with stirring for 15 minutes. The brown mixture was transferred to a beaker,

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