Introduction to Aldehydes

Aldehydes and ketones are the compounds that incorporate a carbonyl functional group, C=O. These are the organic compounds having the structures -CHO and RC(=O)R’, where R and R’ represent the carbon-containing substituents, respectively.

About Aldehydes

Chemists may use hundreds of individual aldehydes to synthesise other compounds on a daily basis, but they are much less important in industrial synthesis (i.e., the production of compounds on the scale of tons). According to the amount of tonnes of formaldehyde used per year, only one formaldehyde, the aldehyde, is used to a large extent in the industry worldwide.


Formaldehyde (which is made predominantly by the oxidation of methanol) is defined as a gas, but it is generally handled as a 37% solution in water, known as formalin. It can be used in the preservation, tanning, and embalming of plants and vegetables, as well as as a fungicide, germicide, and insecticide, but its most common use is in the manufacture of certain polymeric materials.

The plastic Bakelite can be prepared by a reaction between the phenol and formaldehyde. It is not a linear chain, but it has a three-dimensional structure. Similar three-dimensional polymers are made from formaldehyde and the compounds melamine and urea. These polymers are not only used as plastics but also, even more importantly, as coatings and adhesives. Plywood is made up of thin wood sheets that have been bonded together with one of these polymers. In addition to the Bakelite, the trade names Melmac and Formica can be used for a few of the polymers that are made from formaldehyde.

The figure given below represents that phenol-formaldehyde resins are both heat-resistant and waterproof, though somewhat brittle. They're made by reacting phenol with formaldehyde and then cross-linking polymer chains.

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Benzaldehyde Uses

Industrial Uses

Primarily, the industrial significance of aldehydes can be used as perfumes, solvents, and flavouring agents or as intermediates in the manufacture of dyes, plastics, and also pharmaceuticals. Certain aldehydes take place naturally in the flavouring agents. Among these is benzaldehyde that provides both the flavour and odour of fresh almonds; oil of cinnamon or cinnamaldehyde; and vanillin, which is the main flavouring agent of vanilla beans.

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In addition, certain aldehydes also perform important functions in humans, including other living organisms. Aldehyde examples are given as the carbohydrates (including starch, cellulose, and sugars), which are based on the compounds that possess a ketone or aldehyde group along with the hydroxyl groups; the steroid hormones, several of which, including testosterone, progesterone, aldosterone, and cortisone are ketones; and the retinal, which is an aldehyde, upon combining with a protein (or opsin) in the eye’s retina to form rhodopsin, is the primary compound involved in the vision process.

In the retinal portion, rhodopsin exposure to light initiates a cis-trans isomerization. The resulting change in the molecular geometry can be responsible for generating a nerve impulse, which is sent to the brain and then perceived as a visual signal.

Examples of Aldehydes and Ketones

Let us look at the example of aldehyde and ketone.

Example of the aldehyde group

Let us look at the example of aldehyde group, represented in the figure below:

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We can observe that all these hold the exact similar end to the molecule. The only difference is the complexity of the other attached group.

Example of the Ketone Group

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Generally, propane is chemically written as CH3COCH3. The carbonyl group in pentanone may be in the centre or near the end of the chain, resulting in pentane-2-one or pentane-3-one.

Uses of Aldehyde and Ketone

Let us look at some of the uses of aldehydes and ketones.

Uses of Aldehydes

Uses of aldehydes in medicine

Over the centuries, cinnamaldehyde has been used to treat the disorders such as a normal cold. Also, research has it that Cinnamaldehyde is given as a natural medicinal compound, which clears the common cold and also helps in the treatment of diarrhoea. Also, cinnamaldehyde helps in the treatment and prevention of cancer. And, aldehyde formalin can be used as a treatment for ovine footrot when the compound is diluted to 10%.

Other Miscellaneous Uses

  • Formaldehyde is given as a gas compound. It forms Formalin with 40 percent solution in water, which can be used in preserving the biological specimens.

  • Insecticides, germicides, and fungicides for plants can be used in formaldehyde, which is used in tanning, embalming, the preparation of polymeric materials, and glues. Also, it is used in photography and drug testing.

  • Formaldehyde forms Bakelite when reacted with phenol, which is used in coatings, adhesives, and plastics.

  • Acetaldehyde is largely used for the production of pyridine derivatives and acetic acid.

  • Benzaldehyde can be used in dyes, cosmetic products, and perfumes. It is also added to provide the almond flavour to food products and used as a bee repellent.

Uses of Ketones

  • Acetone is the most common ketone, which is an excellent solvent for a number of synthetic fibres and plastics.

  • Acetone is used in the household as a paint thinner and nail paint remover.

  • It can be used as medicine for acne treatments and in chemical peeling.

  • Methyl ethyl ketone (or MEK) is a chemical butanone and common solvent, which is used in the production of varnishes, textiles, paint remover, plastics, paraffin wax, and so on.

  • Also, due to its dissolving properties, MEK is used as a welding agent for plastics.

  • Cyclohexanone is the other essential ketone that is primarily used in nylon production.

FAQs (Frequently Asked Questions)

1. Give the Example of a Carbonyl Compound.

Ans. An example of carbonyl compound can be given as urea, carbamates, and also the derivatives of phosgene, carbonate esters, acyl chlorides chloroformates, thioesters, lactones, isocyanates, hydroxamates, and lactams.

2. Differentiate Aldehydes and Ketones.

Answer: In ketones, the other side of the carbon present in the carbonyl group is bonded to an R group (can be either the same or a different kind of a chain of carbon-hydrogen); in aldehydes, carbon’s other side in the carbonyl group is always bonded to the only Hydrogen.

3. What is Benzaldehyde?

Answer: The organic compound benzaldehyde (C6H5CHO) is made up of a benzene ring and a formyl substituent. It is given as the simplest aromatic aldehyde and also one of the most used compounds industrially.

4. What are Ketone Bodies?

Answer: Ketone bodies are small organic chemicals: Methyl-ethyl-ketone, acetone, and one other. The cells may burn them as fuel so that they have a caloric value. But they are not the volatile compounds, which evaporate through the skin, and hence, they get wasted.