A Short Note on Ketones

Inorganic compounds such as ketones belong to a class known as heterocyclic compounds. 

On their surface is a carbonyl group, which is a double bond formed by the elements carbon and oxygen (-C=O). The absence of any other reactive groups in their structure, such as –OH or –Cl, distinguishes them from more complicated compounds. In the case of aldehydes and ketones, the presence of the carbonyl group has a significant impact on the chemistry of compounds.

What Are Ketones? 

Ketones are a class of organic compounds that are characterised by the presence of the carbonyl group wherein the carbon atom forms a double bond with the oxygen atom. They do not share their bond with the hydrogen atoms in the carbonyl group. Ketones are widely used as solvents for textiles and paints, and are commonly used as chemical intermediaries. 

Properties of Ketones

• They have high boiling points.
• They have dipole characteristics.
• They are less soluble in water.
• They form bisulfite addition products when added to sodium bisulfite.

Occurrence of Ketones and Aldehydes 

When combined with other functional groups, ketones and aldehyde are found widespread in nature. Citra (lemongrass), camphor (camphor trees), cinnamaldehyde (cinnamon bark), helminthosporal (a fungal toxin), and carvone (spearmint and caraway) are all compounds that are found chiefly in plants. However, hormones such as progesterone (female sex organ), testosterone (male sex organ), cortisone (adrenal hormone), and muscone (musk deer) have both animal and human origins.

Uses of Ketones 

Ketones play a crucial role in the products used by us every day. They are widely used for formulating ink applications, wood coatings, and adhesives. 

• The most commonly used type of ketone is acetic acid. It is used in the formation of nail paint removers and paint thinner. 
• Acting as a great solvent for some types of synthetic fibres and plastics, ketones are of great utility. 
• Acetophenone, an aromatic ketone, is used in scents such as cherry, strawberry, honeysuckle, and jasmine. 
• Cyclohexanone, a cyclic ketone, is an important component in the production of nylon. 
• Some essential functions of humans and other organisms are also performed by ketones. Hormones such as progesterone, testosterone, cortisone, and aldosterone are all ketones. 
• Butanone, also known as methyl ethyl ketone, is a common solvent used in manufacturing plastics, paint thinners, varnishes, textiles, etc. 
• Ketone is widely used in the cosmetic industry and also for the treatment of acne.
• Ketones are necessary for the production of many organic compounds. 

Physical Properties of Ketones

• Physical State

Methane is a noxious gas, but ethanol is a volatile liquid that boils at around 21oC. Colourless liquids are aldehydes and ketones with 11 carbon atoms or more. 

• Bonding

This functional group is carbon double-bonded to oxygen. Since oxygen is more electronegative than carbon, it draws electrons in a carbon-oxygen bond towards itself. There are diffuse positive and negative charges from the carbon and oxygen atoms, respectively. It becomes highly polarised. A nucleophile can attack the slightly positive carbon atom, while electrophiles attack the slightly negative oxygen atom.

The carbon-oxygen double bond is broken in carbonyl compound reactions. Each has a carbonyl group.

• Solubility

All aldehydes and ketones are miscible in water. For example, ethane, methane, and propanone are all miscible with water. Aldehydes and ketones can establish hydrogen bonds with water molecules but not with each other. An aldehyde or ketone atom’s oxygen attracts one of the lone pairs on its hydrogen atom to establish a hydrogen bond. Aldehydes and ketones are water-soluble due to a hydrogen connection between the polar carbonyl group and water molecules.

• Hydrogen Bonding

Aldehydes and ketones have dipoles that limit their usefulness as hydrogen bond acceptors. Not because there is a hydrogen atom on the carbonyl oxygen atom; this is because these chemicals easily form H-bonds with polar molecules like water.

Since aldehydes and ketones lack hydrogen atoms that are directly attached to the carbonyl oxygen atom, intermolecular hydrogen bonding is absent. They can establish hydrogen bonds with water molecules because the carbonyl oxygen acts as a hydrogen bond acceptor. Their boiling points are higher than alkanes and ethers because of hydrogen bonding. Aldehydes and ketones are water-soluble due to hydrogen bonding.

• Smell

Aldehydes and ketones, except lower carbon number aldehydes, are generally pleasant to the nose. Aldehyde and ketone molecules grow less pungent and more aromatic as the molecule’s size increases.

• Boiling Point

Because of the polarity of the carbonyl (>C=O) group, the boiling temperatures of aldehydes and ketones are greater than those of their non-polar counterparts with comparable molecular masses. Their boiling point, on the other hand, is lower than that of their equivalent alcohols or carboxylic acids. 

Conclusion 

The carbonyl group (>C=O) is present in ketone. The nature of the carbonyl group has a significant impact on the physical properties of ketones. 

This article provides an overview of the physical properties of ketones, with a focus on the solubility and boiling points of these organic substances. The boiling point of these compounds is higher than that of their hydrocarbon equivalents. We have also learned why alcohols and carboxylic acids have greater boiling temperatures than their comparable aldehyde and ketone acid counterparts.