#Chalcone
Like the Grignard reaction, the Aldol Condensation is an extremely useful carbon-carbon bond-forming reaction in organic chemistry. Under the reaction conditions in the experiment, two equivalents of aldehyde will react. The aldol condensation is a reaction that is named based on the type of product formed when two aldehydes (or ketones), in the presence of dilute base, yields a molecule having both alcohol and aldehyde functional groups. An example of the type of base-catalyzed aldol condensation that you will perform is shown below The acidity of the alpha-carbon makes beta-dehydration of aldols an easy reaction. (This is of course quite different than the chemistry of normal alcohols.) This conjugated enone synthesis is catalyzed by both acids and bases. This shows the mechanism of the experiment performed. The reaction proceeds by an aldol
condensation. First, an acid-base reaction. Hydroxide functions as a base and removes the acidic
α-hydrogen giving the reactive enolate.The nucleophilic enolate attacks the aldehyde at the electrophilic carbonyl C in a nucleophilic addition type process giving an intermediate alkoxide.
An acid-base reaction. The alkoxide deprotonates a water molecule creating
hydroxide and the β−hydroxyaldehydes or aldol product. Dibenzalacetone is a common ingredient in sunscreen. This is because dibenzalacetone absorbs UV light and
helps to protect the skin from the sun’s damaging rays. The properties that are most valuable in a compound that is used in sunscreen are the compound’s abilities to absorb, reflect, or even scatter the harmful UV rays. Another importance is for the compound to not cause an allergic reaction on a person’s skin. This experiment was being performed so that dibenzalacetone could be synthesized from benzaldehyde and acetone. This experiment was performed to show how a ketone and an aldehyde could be added together through the aldol condensation. The aldol condensation is extremely important because it can form a β-hydroxy aldehyde or ketone from two
carbonyl compounds. This type of reaction proceeds through the creation of a resonance-stabilized enolate ion from one of the carbonyl groups. The enolate ion can then act as a strong nucleophile and add to another carbonyl group. It is extremely important that one of the carbonyl groups has an acidic alpha hydrogen (one adjacent to a carbonyl group) so that the enolate ion can be formed. Aldol products can be formed through either acidic or basic conditions and since they are usually exothermic the reaction will be driven to completion. In this experiment, you will run an aldol condensation between an aldehyde and a ketone and then the product of the reaction precipitates out of solution and can be collected by filtration. The crude product is normally purified by recrystallization. Weigh your product and determine percent yield. What reactant is your percent
yield based on? Determine the melting point and compare to the literature value. Aldol condensation occurs in aldehydes having α-hydrogen with a dilute base to give β-hydroxy aldehydes called aldols. This reaction is most commonly known as aldol condensation. If the condensation reaction occurs between two different carbonyl compounds it is called crossed aldol condensation.
Aldol Condensation can be defined as an organic reaction in which enolate ion reacts with a carbonyl compound to form β-hydroxy ketone or β-hydroxy aldehyde, followed by dehydration to give a conjugated enone. Aldol Condensation plays a vital role in organic synthesis, creating a path to form carbon-carbon bonds. Crossed Aldol Condensation. The condensation reaction between two different molecules of an aldehyde or ketone in a protic solvent such as water or alcohol constitutes the crossed aldol reaction. When condensation is between two different carbonyl compounds, it is called crossed aldol condensation. When both aldehydes have alpha hydrogens, both can form carbanions and can also act as carbanion acceptors. Hence a mixture of four products is formed which has little synthetic value. If one of the aldehydes has no alpha hydrogen then it can act only as a carbanion acceptor. In such a case, only two products are formed. A common substrate for the crossed aldol reaction is an aromatic aldehyde, which has no alpha position. Furthermore, dehydration of the initial condensation product is rapid which leads to the formation of the α, β – unsaturated ketone and prevents the retro-aldol reaction from taking place.
The general reaction of aldol condensation is Types of Condensation It is important to differentiate aldol condensation from various reactions of carbonyl compounds.In a case of Perkin reaction, enolate generated by anhydride is aromatic.A Claisen condensation contains two ester compounds.
A Henry reaction contains an aliphatic nitro compound and an aldehyde.Dieckmann condensation contains 2 ester groups present in the same molecule, which produces cyclic molecule.