Table of Contents
Ketone-preparation
In organic chemistry, ketones are a class of compounds containing a carbonyl group (C=O) bonded to two carbon atoms. The general formula for a ketone is R-CO-R’, where R and R’ can be any alkyl or aryl group. Ketones are a subcategory of aldehydes, which also contain a carbonyl group but only one carbon atom.
The most common way to prepare ketones is by the reaction of an aldehyde with an organolithium reagent, such as n-butyllithium, in the presence of a base. The organolithium reagent abstracts a hydrogen atom from the aldehyde, creating a carbon-carbon double bond and a ketone. For example, the reaction of acetaldehyde with n-butyllithium in the presence of a base produces methyl ketone:
This reaction can also be used to prepare ketones from esters. For example, the reaction of methyl acetate with n-butyllithium in the presence of a base produces methyl ketone:
Ketones can also be prepared by the oxidation of alkenes using a variety of oxidizing agents, such as potassium permanganate or chromic acid. For example, the oxidation of propene with potassium permanganate produces propionaldehyde:
Structure of Ketones
Ketones are organic molecules that contain a carbonyl group. This group is made up of a carbon atom double-bonded to an oxygen atom. The simplest ketone is acetone, which is found in nail polish remover and other solvents.
Ketone Reactions
There are three primary types of ketone reactions: reduction, oxidation, and hydrolysis.
Reduction reactions involve the addition of electrons to a ketone, while oxidation reactions involve the removal of electrons from a ketone. Hydrolysis reactions involve the breaking of the carbon-oxygen bond in a ketone molecule by the addition of water.
Identifying Ketones
When ketones are present in the urine, this is a sign that the body is breaking down fatty acids for energy. This occurs when the body is unable to use glucose for energy, which can be a sign of diabetes or another condition that affects glucose metabolism. Ketones are also present in the blood and can be used to diagnose ketoacidosis, a serious condition that occurs when the body produces too many ketones and blood pH falls below 7.35.
Preparation of Ketones
The ketones can be prepared by the reaction of a carboxylic acid with an alcohol in the presence of a strong base, such as sodium hydride. In this reaction, the carboxylic acid is converted to the corresponding ketone.
The ketones can also be prepared by the reaction of an aldehyde with a ketone in the presence of a base, such as sodium hydride. In this reaction, the aldehyde is converted to the corresponding ketone.
Preparation of Ketones From Nitriles
A ketone can be prepared from a nitrile by reduction with a strong reducing agent, such as lithium aluminum hydride (LiAlH4), followed by acidification of the resulting alcohol.
Preparation of Ketones by Dehydrogenation of Alcohols
Ketones are prepared by dehydrogenation of alcohols in the presence of an acid catalyst. The acid converts the alcohol to aldehyde, which is then dehydrogenated to ketone.
The mechanism for the dehydrogenation of an alcohol to a ketone is shown below.
In the first step, the alcohol is converted to an aldehyde. The aldehyde is then dehydrogenated to form the ketone.
Preparation of Ketones from Acyl Chlorides
The ketones can be prepared from the acyl chlorides using potassium or sodium ethoxide in ethanol. The reaction proceeds through the formation of an enolate, which is then protonated to give the ketone.
The reaction can also be performed using sodium or potassium hydroxide in methanol.
Ketones Preparation From Benzene and Substituted Benzenes to Form Aromatic Ketones
Aromatic ketones are prepared by the oxidation of benzene and substituted benzenes. The oxidation is conducted in the presence of a catalyst, such as chromic acid or manganese dioxide. The products are the corresponding aromatic ketones.
