What are Ketones and Aldehydes?

Aldehydes and ketones are organic compounds with the structural formulas -CHO and RC(=O)R’, where R and R’ are carbon-containing substituents.

What Are Aldehydes?
What Are Ketones?
Occurrence Of Ketones And Aldehydes
Preparation Of Ketones And Aldehydes
Uses Of Aldehydes And Ketones
FAQs

What are Aldehydes?

The carbonyl group in aldehydes has one hydrogen atom attached to it, along with either a second hydrogen atom or a hydrogen group that can be alkyl or contain a benzene ring.

Example:

One can see that every single one of these molecules has the exact same end. The complexity of the other attached group is the only distinction.

What are Ketones?

The carbonyl group in ketones is attached to two hydrocarbon groups. These can be those with benzene rings or those with alkyl groups. Ketone has no hydrogen atom attached to its carbonyl group.

Example:

Propane is generally written as CH3COCH3. The carbonyl group in pentanone can be in the middle or near the end of the chain, resulting in pentan-3-one or pentan-2-one.

The methanoyl or formyl group refers to aldehydes and ketones. This group’s carbon atom has two remaining bonds that could be filled with aryl, alkyl, or substituents. The compound is a ketone if neither of these substituents is hydrogen. An Aldehyde is a compound that contains at least one hydrogen atom.

Occurrence of Ketones and Aldehydes

In nature, aldehydes and ketones can be found, often in combination with other functional groups. Examples of such compounds found primarily in microorganisms or plants include cinnamon aldehyde, vanillin, Citra, helminthosporal, carvone, and camphor. Muscone, testosterone, progesterone, and cortisol, on the other hand, are examples of compounds derived from animals and humans.

Preparation of Ketones and Aldehydes

Aldehydes and Ketones can be synthesized through various reactions. Some of these reactions include:

Stay tuned with Valour Education to learn more about different types of aldehydes and ketones, their physical and chemical properties.

Uses of Aldehydes and Ketones

Formaldehyde is the most basic form of aldehyde, while acetone is the smallest type of ketone. Many aldehydes and ketones have practical uses due to their chemical properties. Here are some examples of how aldehydes and ketones are used:

Uses of Aldehydes

Formaldehyde is a gas, but it can be dissolved in water to form a 40% solution called formalin. Formalin is used for preserving biological specimens. Formaldehyde is also used in embalming, tanning, preparing glues and polymeric products, as germicides, insecticides, and fungicides for plants. It has applications in drug testing and photography.
When formaldehyde is reacted with phenol, it forms Bakelite, which is used in plastics, coatings, and adhesives.
Acetaldehyde is mainly used in the production of acetic acid and pyridine derivatives.
Benzaldehyde is used in perfumes, cosmetic products, and dyes. It is also used to provide almond flavor to food products and as a bee repellent.

Uses of Ketones

The most widely used ketone is acetone, which is an effective solvent for numerous plastics and synthetic fibers.
Acetone is commonly used at home as a nail polish remover and paint thinner.
In medicine, it is utilized for chemical peels and acne treatments.
Methyl ethyl ketone (MEK), also known as butanone, is a prevalent solvent used in the production of textiles, varnishes, plastics, paint removers, paraffin wax, etc.
MEK is also utilized as a welding agent for plastics due to its dissolving properties.
Cyclohexanone is another essential ketone that is primarily utilized in the production of nylon.

Distinguishing Test between Aldehyde and Ketone

Acetaldehyde and Acetone can be distinguished by

Tollens’ reagent is a solution of ammoniacal silver nitrate AgNO3 that is used to distinguish between acetaldehyde and acetone. It reacts with acetaldehyde, oxidizing it to acetic acid and causing the silver ions in the reagent to be reduced to silver metal, resulting in the formation of a silver mirror. This reaction does not occur with acetone, allowing for differentiation between the two compounds. Molisch, Schiff’s, and iodoform tests react similarly with both aldehydes and ketones, but only Tollens’ reagent gives a silver mirror with aldehydes and not with ketones.

Frequently Asked Questions

Here are the answers to some frequently asked questions about aldehydes and ketones:

Q1: How are Aldehydes and Ketones Different?

A: Aldehydes have a hydrogen atom attached to the carbonyl carbon, while ketones have two alkyl or aryl groups attached. Aldehydes are easily oxidizable due to the presence of a C-H bond, which makes them strong reducing agents.

Q2: Why are Aldehydes more Reactive towards Nucleophilic Substitutions than Ketones?

A: Aldehydes are more reactive towards nucleophilic substitutions because the hydrogen atom in aldehydes offers little steric hindrance, while the two alkyl/aryl groups in ketones offer more steric hindrance. The partially positive charge on the carbonyl carbon is also more stabilized by the two R groups in ketones.

Q3: Why are the Boiling Points of Ketones Higher than those of Aldehydes?

A: Ketones have higher boiling points than aldehydes because of the presence of two electron-donating R groups, which make them more polar. This increased polarity leads to higher dipole moments and thus higher boiling points.

Q4: What are the uses of Ketones?

A: Ketones are used as excellent solvents in industries such as medicine, textiles, varnishes, plastics, and paint remover. Acetone, the most common ketone, is also used as a nail paint remover and paint thinner.

Q5: What are the uses of aldehydes?

A: Formaldehyde, the simplest aldehyde, is used to preserve biological specimens, in embalming, tanning, and preparing glues and polymeric products, as well as germicides, insecticides, fungicides for plants, drug testing, and photography. Acetaldehyde is used in the production of acetic acid and pyridine derivatives, while benzaldehyde is used in perfumes, cosmetic products, and dyes. It is also added to provide almond flavor to food products and used as a bee repellent.