What is Knoevenagel reaction explain its mechanism?

The Knoevenagel reaction is a modified Aldol Condensation with a nucleophilic addition between an aldehyde or ketone, and an active hydrogen compound in the presence of a basic catalyst, resulting in C–C bond formation. The active hydrogen compound contains a C–H bond which can be deprotonated by the basic catalyst.

What is the Knoevenagel condensation catalyzed by?

The Knoevenagel condensation reaction of acetylacetone with benzaldehyde catalyzed by piperidine in methanol solvent takes place via carbinolamine, iminium, and enolate intermediates.

What is the starting reactant in Knoevenagel reaction?

The Knoevenagel-Doebner reaction starts with the chain extension promoted by the catalyst piperidine. This condensation reaction is followed by a subsequent decarboxylation of the formed di-acid promoted by the solvent pyridine (32.

What is the product of Knoevenagel condensation reaction?

Knoevenagel condensation is a nucleophilic addition of an active hydrogen containing compound to a carbonyl group. This is followed by a dehydration reaction in which a molecule of water is eliminated. The product formed is α, β – conjugated enone.

What is Stobbe condensation reaction?

Stobbe condensation involves reaction of aldehyde or ketone with succinic ester in the presence of basic catalyst like sodium hydroxide or potassium tertiary butoxide to form alkylidene succinic acid. • This reaction limited to α – ω diester ester group at 1st carbon and last carbon.

What is condensation mechanism?

Condensation reactions in organic are when two molecules join together to make a combined/bigger molecule. The process also splits out a small molecule such as water during the process.

What is benzoin condensation give an example?

Product obtained is a conjugated enone. Complete answer: 1) Benzoin condensation. An example of this reaction is when benzaldehyde is refluxed with aqueous alcoholic potassium cyanide then we obtain an α− hydroxy ketone called benzoin as the product.

What is the product of Knoevenagel reaction?

The Knoevenagel reaction is based on nucleophilic addition, in which active hydrogen compound added to the carbonyl compound followed by the removal of water. The product obtain is α,β-unsaturated ketone.

Why is the Knoevenagel reaction important?

The Knoevenagel condensation is one of the most important methodologies for carbon–carbon double bond formation in synthetic organic chemistry and allows the production of various α,β-unsaturated acids, commonly referred to as cinnamic acids (1. Emil Knoevenagel and the Roots of Aminocatalysis.

Which base is used in Knoevenagel reaction?

Knoevenagel condensation (Scheme 1) is a widely used reaction in research and industry and has been of importance for several pharmaceutical products. Generally this reaction is catalyzed by organo-bases, such as pyridine or piperidine.

What is the mechanism of Doebner reaction?

The Doebner reaction is the chemical reaction of an aniline with an aldehyde and pyruvic acid to form quinoline -4- carboxylic acids. The reaction serves as an alternative to the Pfitzinger reaction. The reaction mechanism is not exactly known, two proposals are presented here.

Why does the Doebner reaction fail with 2-chloro-5-aminopyridine?

It is reported in the literature that the Doebner reaction fails in case of 2-chloro-5-aminopyridine. In this case the cyclization would take place at the amino group instead of the benzene ring and lead to a pyrrolidine derivative.

What type of reaction is Doebner Miller reaction?

The Doebner–Miller reaction is an acidic condensation between primary aromatic amines (e.g., anilines) and α,β-unsaturated carbonyl compounds (mostly α,β-unsaturated aldehydes) to give 2,3-disubstituted quinolines.

What is the reaction mechanism of aniline and aldehyde?

An alternative mechanism is based on the aniline and the aldehyde forming at first the Schiff base upon water elimination. The subsequent reaction with the enol form of pyruvic acid ( 1) leads to the formation of the above-mentioned aniline derivative ( 3) followed by the above-described reaction mechanism: