In a 25 mL Erlenmeyer flask, add benzoin (0.5 g) and ethanol (4 mL) and gently swirl the contents for several minutes at room temperature. Even if not all the benzoin dissolves, add sodium borohydride (0.1 g) using the microspatula in small increments over the span of five minutes. For 20 min, swirl the mixture at rt. In an ice water bath, cool the mixture. To the flask, add distilled water (5 mL) and HCl (.3 mL, 6 M). After 15 min in the ice bath, add more water (2.5 mL) to the mixture. To collect the product, vacuum filter the mixture using the Hirsch funnel and wash the solution with a small amount of ice-cold water. After the solution dries on the filter for 15 min, determine the crude mass and percent yield (0.544 g, 107.8%) of the product and save some of the crude product (~1-2m g) for thin layer chromatography analysis and melting point determination (134-135 °C). Using acetone (~2 mL), recrystallize the crude product in a 25 mL Erlenmeyer flask. Erlenmeyer flask is removed to the heat, add an equal portion of room temperature hexanes (~2 mL) to the solution. When the white crystals are dry are dry, determine the mass and percent yield (0.278 g, 55.1%) melting point of the pure product (136-137 °C). For thin layer chromatography (TLC) analysis, dissolve a small amount of benzoin (starting material), reserved crude product, and recrystallized pure product (~1-2 mg) in ethyl acetate (~2 mL). On one silica gel plate on a line 1 cm from the bottom of the plate, spot the starting material in lane 1, crude product in lane 2 and co-spot the starting material and crude product in lane 3. On the second plate one a line 1 cm from the bottom of the plate, spot the starting material in lane 1, in lane 2 spot the recrystallized product, and in the third lane co-spot both the starting material and recrystallized product. The solvent used to run the TLC of each plate is a 9:1 CH2Cl2 solution. To view the results of the TLC, view them under shortwave UV light.
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