Experiment # 6 Ans:
The above reduction of benzyl gives two major products, viz., (+)-benzoin & hydrobenzoin, The hydrobenzoin exists in (+) & meso forms. After recrystallization we will get the pure Hydrobenzoin and the supernatant liquid will have the impurities including the benzoin. The reaction products are given below:
The recrystallized material will not be 100 % pure, and can have impurities of benzil (unreacted), the benzoin and all the isomers of hydrobenzoin. This due to the fact that they also have some solubility in the water.
Yield Calculation: The reduction yields the product w.r.t. starting material in 1:1 molar ration, if no other products are considered to be formed. Assuming this, we will calculate the yields, theoretical from the product molar masses and % experimental yield from the weight of the crystals obtained. The steps are as follows:
It is given that:
Weight of benzil taken = 0.584 g
Wight of the crystals = watch glass net wt. – watch glass tare wt.
Product weight obtained = 97.989 – 97.656 = 0.333 g (practical yield)
Now, since, 210.2 g/mol of benzil yields 214.3 g/mol of the hydrobenzoin
So, the 0.584 g benzil will give = [(214.3 / 210.2) * 0.584] g of hydrobenzoin
Theoretical yield = 0.595 g of hydrobenzoin
Percent yield = (product wt. obtained in g/ theoretical yield in g) * 100
= (0.333 / 0.595) * 100
= 55.97 %
Percent yield = = 55.97 % Hydrobenzoin
Comment on GC-MS spectra:
The second peak having very nearly identical mass is due to the benzoin impurity in the extract, whose molecular weight is just 1 amu less than the hydrobenzoin.
Experiment . the reduction of bencil (March 2020) Your name Sodium borohydride is a convert recent...
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