Step 1: Cinnamaldehyde + Cyclopentanone (Mix for 1 min).
Step 2: Add 10% NaOH + Water to the mixture above (Mix for 3 min).
Step 3: Add Ethanol to the mixture above (Mix for 3 min). Precipitate will form.
Step 4: Collect precipitate by suction filtration and wash it with Glacial Acetic Acid + Water (Continue suction for 5 to 10 min).
Step 5: Transfer the crude product known as BPC (or (2E,5E)-2,5-bis((E)-3-phenylallylidene)cyclopentan-1-one)) into beaker with Ethanol and heat it up until it boils (or also known as "recrystallization").
Step 6: Collect the pure BPC (crystals) by suction filtration and wash it with Ice-Cold Ethanol (Continue suction for 5 min).
Overall Reaction:
a) There are 9 geometric isomers (i.e. âcisâ and âtransâ or âEâ and âZâ isomers) of BPC; however in this reaction, the product mixture is composed of one major geometric isomer of BPC. Clearly draw the major geometric isomer of BPC; then draw any two of the other 8 geometric isomers. Briefly describe why the formation of one geometric isomer predominates over the formation of the other 8 geometric isomers.
b) Ketones with α-hydrogens can undergo a process called, "keto-enol tautomerism". Please answer the following sub-parts regarding this process.
I) Draw the keto-enol tautomers of cyclopentanone.
II) Which of the two tautomers is more stable? Why is it more stable?
III) Please show the mechanism for the formation of keto-enol tautomers of cyclopentanone in the presence of an acid.
c) The last step of the formation of BPC involves dehydration of the aldol by elimination of a hydroxide ion; which is generally considered a poor leaving group. Please justify why the elimination of OHâ occurs in this reaction.
In this experiment, (2,SE)-2,5-bis(lE)-3-phenylallylidene)cyclopentan-1-one example of a crossed aldol condensation. (BPC) is synthesized in an Initially, ë°ë¬ë°3-phenylalylidene)cyclopentan-1-one (PC) is formed dil. NaOH(aq) cinnamaldehyde cyclopentanone However, in the presence of excess cinnamaldehyde, PC rapidly undergoes a second condensation to form BPC: dil. NaOH(aq) cinnamaldehyde PC BPC OH OH- cinnamaldehyde H. H cinnamaldehyde OH Oh The first step involves the acid-base reaction between a strong base such as hydroxide ion and a hydrogen located a carbon alpha to a carbonyl group. In the subsequent step (see Step 2), the enolate attacks the carbonyl group of aldehyde and followed by the loss of OH- as a leaving group to give an enal, which has the alkene and the ketone functional groups
Why is it important that all of the solids dissolve during the reflux period for you to obtain a good yield of product?
A. Because everything needs to be in solution for the reaction to happen to the fullest extent.
B. Because the product will be impure if the intermediate doesn't dissolve completely.
C. Because the ethanol will evaporate off if it's not dissolved.
D. All of the above
What is the gas that is evolved during neutralization?
A. O2
B. CO2
C. SO2
D. CO3
Why is it necessary to neutralize the reaction mixture to work up the product?
A. Because it is dangerous to work with an acidic solution.
B. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as ammonia and must be protonated so that it becomes insoluble and collectable.
C. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as a soluble carboxylic acid and must be neutralized so that it becomes insoluble and collectable.
D. Because after the addition of ethanol and sulfuric acid, the benzocaine exists as a soluble ammonium salt and must be neutralized so that it becomes insoluble and collectable.
If you end up adding 1.5 mL of concentrated sulfuric acid (18 M), how many mL of 10% aqueous sodium carbonate would be required to neutralize the reaction mixture?
