Michael & Aldol Condensation Reaction
We are preparing an a,b-unsaturated ketone via Michael and aldol condensation reactions. The reactants are trans-chalcone and ethyl acetoacetate (in ethanol and NaOH). This creates 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone. What I'm wondering is:
Why is it possible to separate the product from sodium hydroxide using acetone?
Could you tell me what is the purpose of this reaction (Michael and aldol condensation reactions), and the stepwise mechanism of the reaction.
Also if we started with 1.2 grams of trans-chalcone , 0.75 grams of ethyl acetoacetate what would be the theoretical yield ?
well... from what I understand, the reason that the product separates from the NaOH is because the product is dissolvable in acetone while the inorganic by-products and such are not. Thus after centrifuging the mixture, all the supernatant (acetone) has the product.
I got 1.43g as percent yield
To answer your questions, let's first start with the purpose of the Michael and aldol condensation reactions and then move on to the mechanism of the reaction.
1. Purpose of Michael and Aldol Condensation Reactions:
The Michael and aldol condensation reactions are commonly used in organic synthesis to synthesize a wide range of compounds, including a,b-unsaturated ketones. These reactions are particularly useful for forming carbon-carbon bonds and creating molecules with complex structures. The reaction you mentioned aims to synthesize 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone, which is an example of an a,b-unsaturated ketone.
2. Stepwise Mechanism of the Reaction:
The reaction you described involves two steps: the Michael addition and the aldol condensation. Here's a stepwise breakdown of the reaction:
Step 1: Michael Addition
- The trans-chalcone (a substituted benzalacetophenone) acts as the Michael acceptor.
- Ethyl acetoacetate (a beta-dicarbonyl compound) acts as the Michael donor.
- In the presence of a base (sodium hydroxide in ethanol), the nucleophilic enolate of ethyl acetoacetate attacks the beta-carbon of the trans-chalcone, resulting in the formation of a C-C bond.
- This step forms an intermediate compound containing a new carbon-carbon bond.
Step 2: Aldol Condensation
- The intermediate compound undergoes an intramolecular aldol condensation, where the alpha-carbon of the ethyl acetoacetate reacts with the carbonyl group of the trans-chalcone.
- This reaction leads to the formation of a new six-membered ring, resulting in the final product, 6-ethoxycarbonyl-3,5-diphenyl-2-cyclohexenone.
Now, concerning your question about separating the product from sodium hydroxide using acetone:
3. Separation from Sodium Hydroxide:
The reason acetone is used in this context is due to differences in solubility. Acetone is a common organic solvent that is miscible with many organic compounds but not with water. Sodium hydroxide is soluble in water but not in acetone. Therefore, by adding acetone to the reaction mixture, you can effectively separate the organic product (which is soluble in acetone) from the sodium hydroxide solution. This separation is usually done by either filtration or extraction.
Lastly, let's calculate the theoretical yield:
4. Theoretical Yield:
To determine the theoretical yield, we need to compare the moles of the limiting reagent to the stoichiometric ratio of the product. In this case, we'll assume all starting materials are consumed and converted to the desired product.
- Calculate the moles of trans-chalcone:
Moles of trans-chalcone = mass of trans-chalcone / molar mass of trans-chalcone
- Calculate the moles of ethyl acetoacetate:
Moles of ethyl acetoacetate = mass of ethyl acetoacetate / molar mass of ethyl acetoacetate
- Determine the limiting reagent (the reactant with fewer moles) by comparing the moles of the two reactants.
- Use the stoichiometry of the balanced equation to relate the moles of the limiting reagent to the moles of the product.
- Multiply the moles of the product by the molar mass of the product to obtain the theoretical yield in grams.
Note: The molar masses and balanced equation are needed to perform the calculations accurately. Without these values, we cannot provide an exact theoretical yield.
I hope this explanation helps! Let me know if you have any further questions.