Untitled document - The purpose of this lab is to synthesize benzhydrol by reducing the benzophenone PDF

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The purpose of this lab is to synthesize benzhydrol by reducing the benzophenone with sodium borohydride, and characterize it when you find the melting point....

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Synthesis of benzhydrol Objective The purpose of this lab is to synthesize benzhydrol by reducing the benzophenone with sodium borohydride, and characterize it when you find the melting point.

Experimental log There are two parts of our synthesis. Part one starting with the reaction weigh out 4.5 grams of benzophenone, and crush it up making it easier to dissolve in the methanol. Now in a 150ml beaker measure out 30 ml methanol and dissolve the benzophenone. In a smaller beaker prepare a solution of 1.0 grams of sodium borohydride in 15 ml cold water and stir(be careful because the solid is flammable). Now slowly and in small portions add the sodium borohydride into the solution (carefully watching the solution so that the temperature does not exceed 45 C) it is recommended to add 1-2 ml borohydride every 1-2 minutes. The reaction is exothermic and the addition should not be rapid. After all the sodium borohydride is added continue to stir the mixture for approximately 15 more minutes. When some precipitate has formed place the beaker in an ice bath and continue to stir, a heavy slurry if crystals should begin to form. Now for part 2 of the lab the work up, start this part by preparing an ice bath by filling a 400ml beaker about halfway with crushed ice and water, carefully add 10 ml of hcl to the bath. We will decompose the excess sodium borohydride by slowly stirring the crystalline slurry into the ice/water/hcl solution in the 400ml beaker. Collect the benzhydrol by vacuum filtration and wash the solid twice with 50 ml portions of water. Now while the benzhydrol is drying, determine the melting point of the benzophenone(include this measurement for comparison with the melting point of the recovered product. For next lab period collect and let the product dry, determine mass and melting point and include this measurements in your lab report and record your optimelt parameters. Mass benzophenone used

4.5 grams

Moles benzophenone

.0246g/MM

Theoretical yield

1.52G

% yield

296.4%

Experimental melting point

benzophenone

Benzhydrol 65.6-66.9 C

Our experimental melting point of benzhydrol was at a range of 65.6 TO 66.9 compared to the literature value of 69 C. with our being about 3 degrees lower we can conclude that there was still some impurities, maybe from the unitesls, or from gloves and pre existing impurities in our glassware. The melting point of pure benzhydrol is 15-20 C higher than pure benzophenone and

this could be accounted to the hydroxyl group making the sp2 carbon to an sp3 bond. The result of this is making a tighter hydrogen bond making it harder to break and raising the melting point of the compound....