Don’t let the acetone spoil your reaction

Organic reactions are sometimes very mysterious, the supposed course of reaction and reaction results are often different, sometimes even to find a side reaction, and that side reaction is more valuable than the original reaction; However, most of the time life is not good, either the side effects are mixed, or the side effects do not know what

Solvent, as one of the important factors affecting the reaction effect, can sometimes determine the success or failure of a reaction. So it’s important for us to know a little bit about the reactivity of the solvent, so that we don’t let the solvent spoil our reaction. Knowing the reactivity of the solvent can lead to a better explanation of the reaction results, even if it makes sense to discover that the solvent is involved in the reaction. In this issue we will introduce some of the organic reactions that acetone is involved in.

Acetone is the simplest saturated ketone, is a colorless transparent liquid, soluble in water, methanol, ethanol, ether, dichloromethane, chloroform, pyridine and other organic solvents. Flammable, volatile, chemical properties are more active, so the organic reaction with acetone as a solvent is less, acetone is generally used as a cleaning solvent in the laboratory. Industrial production of acetone is generally isopropyl benzene method, isopropyl benzene oxidation can obtain phenol and acetone at the same time, which is an important industrial preparation of bisphenol A raw materials. Acetone in the industry is mainly used as a solvent for explosives, plastics, rubber, fiber, dyeing and finishing, painting and other industries, but also the synthesis of ketene, acetic anhydride, iodoform, polyisoprene rubber, methyl methacrylate, chloroform, epoxy resin and other compounds of the important raw materials.

Acetone reactivity

After all, acetone is a kind of ketone, with the common properties of ketone compounds. The overall reactivity of acetone can be summarized into two aspects: 

(1) nucleophile attack on the carbonyl group; 

(2) The reaction of α-position of carbonyl group (electrophilic + free radical).

Aldol condensation

Aldol condensation reaction catalyzed by Br? Nsted acid was found as early as the 1840s. Aldol condensation reaction catalyzed by Br? Nsted acid was one of the most basic methods to construct C-C bond. The α-C-H bond of acetone carbonyl group has a certain acidity, which can attack the compounds containing carbonyl group in the form of enol or enol anion under the catalysis of acid and base. Therefore, acetone is generally not used as the solvent for substrates with carbonyl structure.

Claisen–Schmidt response

If hydrogen atoms exist on the hydroxyl β carbon, it is easy to eliminate a molecule of water to get α, β-unsaturated ketone compounds under the action of acid and base. This is the Claisen — Schmidt reaction.

In addition, primary alcohol can react similarly with acetone in the presence of an oxidant.

Mannich reaction

Mannich reaction, also known as amine methylation reaction, is a three-component reaction of aldehyde, ketone, formaldehyde and amine containing α-hydrogen.

Alpha halogenation of carbonyl group

The α-site of carbonyl group is active and can react with NBS, NCS, bromide water and so on

Summary: because acetone can react with electrophilic reagents, also can react with nucleophile reagents, so there are not many solvents in the organic reaction, but some reactions such as free radical reaction (even acetone can play the role of photosensitization to promote free radical initiation process), cyclic reaction using acetone as a solvent is particularly good.