This is the first step of a 3 part synthesis. In order to complete the final step you need to
have enough (at least 100mg) benzil (starting material). By assuming that you will get a
yield of 60% and 70% for the first and second reaction respectively, how much
benzaldehyde must be used for the first reaction. Clear working is needed including a
calculation.
- It is possible after the reaction is left for 2 days (until your next lab period, which is a week)
there are no crystal formation. Outline 3 possible steps, which could be taken to induce
crystallization. - The benzoin condensation reaction is an older reaction, which at first uses KCN/NaCN
instead of Thyamine HCl. Discuss the impact this change has on the environment in the
context of green chemistry.
O
H
O
2 x KOH
OH
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O
O
HNO3
OH
O OH
KOH, Heat
Benzaldehyde Benzoin
Benzil
Benzillic Acid
O
H
O
2 x KOH
OH
Benzaldehyde Benzoin
Part B: Preparation of Benzil via Oxidation of Benzoin
This is second step in a 3 part synthesis. When you were ready to carry out this procedure as
outlined into your lab manual, you realize that you are out of HNO3, but you have both 6%
Bleach solution freshly prepared and CrO3 / H2SO4 on hand. Both reagents are capable of
oxidizing benzoin to benzil - Design an experiment with one of the reagent above to prepare benzil from benzoin.
- Please include the following in your experimental design.
a. a list of chemicals and equipment needed
b. an apparatus set up
c. what safety precautions are necessary
d. waste disposal
e. a procedure
f. what results will be collected
g. how would these results confirmed the identity of the desired compound
h. provide a mechanism. - Provide a rational for your reagent choice.
Part C. Benzillic Rearrangement.
This is the final step of this 3 steps sequence. - What is the overall yield if a yield of 63%, 71%, and 57% were obtained in steps 1, 2, an
3 respectively. - Provide 4 IR peaks that would be used to confirm the identity of benzillic acid.
- Discuss the importance of multi-step synthesis to the pharmaceutical industry.