The objective of the experiment was to reduce Benzil, using sodium borohyride as the reducing agent. In a benzil reduction, there are five possible products than can occur, specifically a racemic mixture of benzoin, racemic mixture of hydrobenzoin, or meso-hydrobenzoin. Therefore, three different tests were conducted in determining the identity of the product: melting point, thin light chromatography, and infrared spectroscopy. (a) Mechanism and reaction equation of benzyl reduction
Stereochemistry plays a vital role in the five possible products of benzil reduction. The five possible products in the reduction of benzil are due to the two carbonyl groups in benzil. If the sodium borohydride reduced …show more content…
If the product was racemic, the melting points for the product mixed with the meso-hydrobenzoin standard would be broader and would have a significantly higher melting depression. However, the experimental melting point values convey a small degree of melting depression which indicates the presence of impurities. In this case, the high indoor humidity in the laboratory room from which the experiment was conducted may have attributed to impurities. It is very common for humidity especially during summer to affect the recrystallization process by introducing more water vapor in the air. As a result, the water molecules may have been mixed in the Erlenmeyer flask along with the mixture which accounts for the melting point depression. Even with impurities, the results still indicated that the product is a meso-hydrobenzoin.
Possible identity of product based on IR
-the IR indicates absence or presence of functional groups. Therefore, it shows how many carbonyl groups were reduced by indicating the number of OH peaks.
Possible identity of product based on TLC
Thin light chromatography helps identify unknown products using polarity. Since the silica gel is polar, the solute that is very polar will stick more to the plate than a solute that is not as polar which allows the developing solvent to carry it as it travels up the plate. In the plate containing the racemic standard, all three spots traveled different distances by which the spot that contained