Oxidation of Benzoin and Rearrangement of Benzil to Produce Benzilic Acid Essay

The objective of the lab was to produce benzilic acerbic from benzoin. Benzoin was successfully oxidized with nitric harshulous to body benzil. The percent ease off of benzil was 59.26% and the melting mention range was 94.1-95.5C. The literature melting point of smooth benzil is 95C, which shews the correct ware was stimulateed. Benzil was then rearranged using potassium hydroxide to form benzilic unpleasant. The percent yield of benzilic acid was 57.94% and the melting point range was 147.9-149.8C. The literature melting point of uncontaminated benzilic acid is one hundred fiftyC this also indicates that the correct product was isolated. Crude products were formed through cryst allization and then recrystallized to obtain pure products. Melting points were taken of each product to prove its identity.Introduction The purpose of the experiment was to force benzilic acid from benzoin. This reaction would occur in a two-step process of oxidation of a -hydroxyketone to f orm the -diketone, benzil. Then, a rearrangement would occur to form the -hydroxyacid, benzilic acid. Benzoin is an organic compound consisting of an ethylene bridge bound to phenyl groups and with hydroxyl radical and ketone functional groups. The nitric acid would readily oxidize benzoin to benzil, a diketone, itself would reduced to nitrous acid, which would disrupt to oxides of nitrogen and water. Additional water was added after the initial reaction to act as a bestial and facilitate removal of the hydrogen on the carbon that initially held the hydroxyl functional group. This indicated the removal of NO2, and generated the carbonylic to complete the oxidation.The conversion of benzil, an -diketone, into the salt of -hydroxyacid by means of base treatment is generally referred to as the benzilic acid rearrangement. As potassium hydroxide was added to benzil, the stable salt, potassium benzilate, was formed. The salt was acidified by the addition of hydrochloric acid until the pH of the solution became acidic and solid benzilic acid precipitated.The ability to be able to produce benzilic acid is vital. Benzilic acid is used in organic synthesis as a base point for preparation of glycolate pharmaceuticals. aft(prenominal) the oxidation of benzoin, the melting point characteristic of the product would prove that the benzil was produced. If the melting point range were narrow, it would indicate that few impurities existed in the benzil product. Again, after the rearrangement of benzil, a melting point would be taken to prove that benzilic acid was produced and how pure the final product was. Crystallization through folderol lav is important in this process, so that the solid crystal product could be obtained as a precipitate from the reaction solution. After the crystals are obtained, it is important to recrystallize to remove impurities.This allows the most accurate and precise melting point to be taken of the product and also gives the most accurate per cent yield of the product, without impurity creation weighed into the final product. To avoid errors, it would be best to make sure the benzil produced in the first step had a narrow melting point range. If the benzil contained many impurities, it would most likely produce inaccuracies in the next step of the process when benzil was rearranged to benzilic acid. Procedure0.30 grams benzoin, 1.5 mL of concentrated nitric acid, and a spin vane were placed into a 5-mL conelike vial with an link up tenor condenser. The mixture was heated in a 70C water bath for close to 90 minutes, while being stirred, until the red nitrogen oxide gases were no longer present in the air condenser. Afterwards, the mixture was removed from heat and transferred into a beaker that contained 4 mL of ice-cold water. The mixture was cooled in an ice bath and then crystals were gathered by vacuum filtration using a Hirsch funnel and rinsed with cold nitric acid. The dried crystals were then recrystallized u sing 95% ethanol.The pure benzil product was weighed and a melting point was taken. Then, 0.100 grams of pure benzil, 0.30 mL of 95% ethanol, and a spin vane was placed into a 3-mL conical vial with an accustomed air condenser. The mixture was heated with an aluminum block at 100C, while being stirred, until all the benzil had dissolved. Using a pipet, 0.25 mL of an aqueous potassium hydroxide solution was added drop wise into the conical vial through the air condenser. The mixture was boiled at 110C while being stirred for approximately 15 minutes and the reaction mixture changed from deep blue-black to brown in color.The vial was removed from heat and allowed to cool to room temperature. The mixture was crystallized in an ice bath and the crystals were collected over a Hirsch funnel using vacuum filtration and rinsed with ice-cold 95% ethanol. The solid crystals were transferred to a 10-mL Erlenmeyer flask that contained 3 mL of 70C water. The flask was swirled while 0.50 mL of 1 M hydrochloric acid was added to the flask. With each drop added a white precipitate formed immediately. The solution was checked to confound a pH of 2, if it was not, more acid was added to the flask. The mixture was cooled to room temperature and then cooled in an ice bath. The crystals were collected by vacuum filtration using a Hirsch funnel and rinsed with ice-cold water. The pure benzilic acid crystals were weighed and a melting point was obtained.