Multistep Synthesis of Benzilic Acid

2052 words 9 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…

The product was then transferred into a flask containing 3mL of water at 70oC and then stirred. While swirling the flask .50mL of 1M hydrochloric acid was added. Following a period of cooling, the product was then ice-bathed. The product then collected and washed with 3-4mL ice cold water through vacuum filtration. After air-drying for a few minutes, the weight was recorded followed with melting point characterization.

Results and Calculations
Benzoin .304g
Crude Benzil .28g
Purified Benzil .10g
Starting Benzil .11g
Benzilic Acid .07g
Table 1: Raw data for Experiment 36

Percent Yield of Crude Benzil 93%
Recovery Yield of Purified Benzil 35%
Melting Point Range of Purified Benzil 94.8 – 95.4oC
Recovery Yield of Benzilic Acid 57%
Melting Point Range of Benzilic Acid (#1) 155.4 – 156.5oC
Melting Point Range of Benzilic Acid (#2) 152.0 – 153.9oC
Table 2: Results for Experiment 36

Calculating Limiting Reactant 36b
.304g Benzoin x _1 mol Benzoin__ = .00143 mol Benzoin 212.24g Benzoin

Density of Nitric Acid = 1.5129
Mass = ?
Volume = 1.5mL

Density = Mass/Volume  Mass = (Density)* (Volume)

(1.5129)*(1.5) = 2.27g Nitric Acid

2.27g Nitric Acid x _1 mol Nitric Acid__ = .03601 mol Nitric Acid 63.01g Nitric Acid
The limiting reactant is Benzoin, and since Benzoin is equal in moles to Benzil, exactly .00432 mol of Benzil should be theoretically produced.