Benzil's Multistep Synthesis Through The Oxidation Of Benzoin

Benzil is produced in the first step of this experiment’s multistep synthesis through the oxidation of benzoin. In order to produce the desired o-diketone, the alcohol on benzoin must be oxidized. Nitric acid was the oxidizing agent used in this experiment. As a result, the alcohol group on benzoin acted as the nucleophile and attacked the electrophilic nitrogen of nitric acid. As this step forms oxonium, excess water in the system deprotonated the oxonium to restore the neutral charge on oxygen. However, the organic nitrate was unstable due to its positively charged nitrogen. To stabilize the compound, the formation of a ketone occurred through the elimination of nitric dioxide. With this elimination, the desired o-diketone was synthesized.
The theoretical mass of 301 mg and an experimental mass of 253 mg created an 84.05% yield of product. The crude benzil product had a melting point of 80.3°C-87.5°C with an overall melting range of 7.2°C. According to Merck Millipore, pure benzil has a melting point of 93°C-97°C. Therefore, the crude product contained impurities as the melting point was lower than expected and had a wide melting range. Possible impurities could have been water due to inadequate drying or unreacted benzoin. Consequently, the crude benzil was purified by recrystallization. This recrystallization produced soft crystal lumps that were small and a very pale yellow. The theoretical mass of 301 mg and an experimental mass of 161 mg created a percent yield of 53.49%. Benzil could have been lost due to error, which would explain the decrease in yield. However, as the benzil was purified, impurities were removed. Therefore, the lowered percent yield is mostly a result of the removal of undesired impurities in the product. The pure benzil product had a melting point of 93.3°C-94.7°C with an overall melting range of 1.4°C. The melting point of the purified benzil was within the melting point of pure benzil established by Merck Millipore and had a small melting range. Therefore, the purification step was successful in removing unwanted impurities. The second step conversion from benzil to benzilic acid produced sharp flaky
Each intermediate product formed with crystallization experiences a minimum loss of about 10%. This estimate is for multi-step synthesis that follows a linear pathway. To minimize this product loss estimate, a convergent pathway would be a better multi-step synthesis to follow. Generally, in multi-step synthesis loss of product can be due to errors in transferring. The product is lost as it is impossible to scrape out all of the crystals out when transferring to the Buchner funnel. Loss also occurs when transferring the crystals from the Buchner funnel to the watch glass. Consequently, percent yield will be lower. Additionally, as water was a possible impurity, increasing the vacuum time of the crystals will provide for sufficient removal of water. The synthesis of benzil in the first step of this reaction creates a crude product that must be purified. Consequently, purity of the product and percent yield is inversely related. A really pure product will have a low percent yield and a product with a high percent yield will contain impurities. Although percent yield will decrease regardless, increasing the amount of starting material will maximize the overall end product. With more product overall, more purification steps can be taken at each intermediate step to optimize purity, and enough product will be produced to obtain a more accurate melting