Lab H: Aldol Condensation Flashcards
What are some real life applications for dibenzylideneacetone?
It is a component of some sunscreens and is also an ingredient in many industrially important transition metal catalysts. The conjugation in dibenzylideneacetone allows fro absorption of sunlight.
What does the general aldol condensation reaction consist of?
Enolate formation, nucleophilic attack of the enolate on an electrophilic carbonyl compound(aldol reaction) , and elimination of water to given an a,b-unsaturated carbonyl compound
In this experiment, we will be doing a crossed-aldol condensation which means that
the enolate is derived from a different carbonyl compound other than the electrophile
The crossed-aldol reaction is often a difficult reaction to control because
both of the carbonyl compounds can act as the enolate and both can also act as the electrophile which can result in a mixture of four different products
How can you control the distribution of products in this experiment?
You can control the distribution of products by careful choice of the base used for the enolate formation or by controlling the molar proportions of the two carbonyl compounds. In this lab, the crossed aldol condensation will be controlled by using one carbonyl compound without any a-hydrogens, benzaldehyde. Because of the lack of a-hydrogens, benzaldehyde cannot form an enolate and therefore can only react as the electrophile in the reaction.
Describe the general procedure for this reaction.
- Obtain the following in this specific order: ethanol, benzaldehyde, KOH
- Stir
- Add acetone
- Stir
- rinse with ice cold ethanol
- Vacuum
What are the health hazards associated with potassium hydroxide? What about acetone?
KOH - extremely corrosive
Acetone - Flammable
Give an overview of the aldol reaction.
two molecules of an aldehyde or ketone react with each other in the presence of a bee to form a beta-hydroxy carbonyl compound.
In the aldol reaction, the formation of a new C-C bon happens at the
alpha carbon
Where does the name aldol come form?
Many aldol products contain an aldehyde and alcohol.
How do enolates form?
Enolates are formed when a strong base removes a proton on the alpha carbon.
Why is a C-H bond on the alpha carbon more acidic?
Because the resulting enolate is resonance stabilized
Compare the pKa of the a-H in an aldheyde/ketone, alkane, and the O-H bond in alcohol and acids
a-H in an aldehyde/keton = 20
C-H bonds in alkanes = 50
OH bonds in alcohols = 17
acids = 4
Review the ranking list from orgo exam 3 prep
Draw out the basic aldol reaction
Refer to notes
Draw out the formation of an enolate.
Refer to ntoes
What are the two types of aldol reactions?
- Symmetrical aldol reactions: An aldol reaction that occurs between two identical aldehydes or two identical
ketones as the starting components - Crossed/mixed aldol reactions: Aldol reactions
that can occur between two different carbonyl compounds.
Draw out a crossed aldol reaction between acetaldehyde and propanal.
Refer to notes
Why are crossed aldol reactions not synthetically useful?
A mixture of four possible aldol products can be formed
When are crossed aldol reactions most successful?
One carbonyl compound has no a-H’s and therefore cannot form an enclave anion - this leads to the formation of only one product.
Give an example of an aldehyde with no a-H.
Refer to notes
Draw out the crossed aldol reaction between benzaldehyde and acetaldehyde. Draw out the reactants too.
Refer to notes
Draw out the crossed aldol reaction between benzaldehyde and acetone. Draw out the reactants too.
Refer to notes
Draw out the aldol reaction in this experiment. The order of incorporating chemicals is important. List the order of the reactants, solvent, and base.
Refer to notes
Order of chemicals
- Solvent (95% ethanol) first
- Benzaldehyde then KOH
- Acetone added last to prevent it from reacting with itself.
