Multi-Step Synthesis, Step 1: Benzil by Oxidation of Benzoin with Nitric Acid Purpose The purpose of the lab report was gaining familiarity with multiple step synthesis, this experiment being the first in a series of 2 steps. It involves the oxidation of an Alphahydroxyketone to a diketone. Reaction and Mechanism Procedure Place 0.30 g of benzoin into a 10 mL round bottom flask and add a magnetic spin vane. Using a 10 mL graduated cylinder, add 1.5 mL of concentrated nitric acid to the round bottom flask. Attach an air condenser. Clamp both round bottom flask and air condenser. In a hood, set up a hot water bath with a thermometer. Keep the water bath boiling for 1 hour with moderate stirring. If after one-hour gases are still being evolved, continue heating for 15 additional minutes. Cool the mixture for a few minutes by removing the hot bath and detach the air condenser. With a Pasteur pipette, transfer the reaction mixture to a small beaker containing 4 mL of ice-cold water. Rinse the round bottom flask and spin vane with a small amount of water. Cool the mixture in an ice bath until crystals have formed. If the material oils out rather than crystallize, scratch the oil vigorously with a glass rod until crystallization starts. Collect the crude product on a Buchner funnel under vacuum. Wash product well with about 5 mL cold water to remove the nitric acid. Weigh the solid, calculate percent yield of crude product and determine its melting point. Purify the crude product by dissolving it in hot 95% ethanol in a small Erlenmeyer flask (about 5 mL per 0.5 g of product) using a hot plate. Remove the flask from the hot plate and allow the solution to cool slowly. As the solution cools, yellow crystals are formed. Continue cooling the mixture in an ice bath to complete the crystallization. Collect the purified product on a Buchner funnel under vacuum. Rinse the flask with small amounts (about 1 mL total) of ice-cold 95% ethanol to complete the transfer of product to the Buchner funnel. Continue vacuuming the crystals on the Buchner funnel for about 15 minutes. Weigh crystals and calculate percent yield of pure product. Determine the melting point and compare it with that of pure benzil (95°C). Save the product in a labeled vial and hand it to your instructor to be used as starting material for the next experiment, benzilic acid. Experimental Set-up Experiment observations Brown fumes started to evolves almost immediately (N O2). NO2 continued to evolve for entire duration of reaction time. Product was observed during reaction time formed as an oily compound. Upon cooling and addition of H 2 O , product precipitated out of solution as bright yellow solid, looked amorphous. Note that purification was not performed (step 8). Results and Calculations Mass of crude product gotten was 0.258g Theoretical yield = % yield = = 0.3 g benzoin x 210.23g/mol = 0.297g 212.24 g /mol mass of product 0.258 g x 100 = = x 100 = 87% theoretical yield 0.297 g Melting point (crude product) =72.0℃ -78.2℃ . Compared to literature value of 94.8℃ (from EPA DSSTOX). This is lower than literature value due to incomplete drying of product. Questions - What other oxidants can be used? Other oxidants may be ammonium nitrate, copper nitrate. - Is there a concern regarding the decomposition of product? There is no concern regarding the decomposition of the product. Discussion 4ml of ice-cold water is added in procedure because water is needed to wash away the remaining acid that is still in the solid product, it is ice cold because addition of water is an exothermic reaction and nitric acid with water will generate heat so ice cold water will help keep it in control. Improvement to this may be increasing reaction time would have given a better result, drying the product over a longer period of time, while transferring solid to the funnel by make sure to wash the funnel. Compared to literature value of 94.8℃ , the results obtained was 72.0℃ -78.2℃ . Benzil is used as a pharmaceutical intermediate, insecticide and curing agent. They are also used in the free radical curing of polymer networks. Benzil mechanism is formed from Benzoin oxidation with molecular weight of 212.24g/mol to form benzil and oxidation of a secondary alcohol with ketone. Conclusion Benzil was synthesized from the oxidation of Benzoin with Nitric Acid. The crude product was purified via recrystallization. The product was obtained as a pale yellow crystalline solid, in high yield. Spectrum and melting point data showed close correspondence with literature values, ascertaining the formation and purity of the product. Experiment was successful, Benzil was synthesized in high yield by the procedure described in this experiment. The product was successfully characterized using the melting point and IR data, sharp range of melting point displayed its purity.