Preparation of aldehydes and ketones

We know that the creation of organic molecules (ketones and aldehydes) can be done on a laboratory and industrial scale. Furthermore, did you know that the formation of ketone and aldehyde occurs spontaneously in many living organisms? For example, one of the phases of photosynthesis is ketone creation in the type of ribulose-1, 5-bisphosphate, which aids in the creation of essential organic molecules.

Ketones are sugars that are found in the body. It’s also found as ketone bodies in most vertebrates, including humans. In this article, we’ll look at how different chemical reactions can be used to make aldehydes and ketones.

Ketones and aldehydes

Simple organic molecules with a carbonyl group are known as aldehydes and ketones. A carbon-oxygen double bond exists in the carbonyl group. So, because the carbonyl group does not contain any reactive functional groups like OH and Cl, these organic molecules are essential.

Aldehydes

A carbonyl group with an alkyl group on one end with hydrogen on another is known as an aldehyde. The R and Ar, respectively, denote alkyl and aryl members. The aldehyde is written as –CHO in the abbreviated form.

Ketones

Ketone is a carbonyl group member with an alkyl and aryl group on both ends. RC(=O)R’ seems to be the chemical formula. Both the carbon-containing substituents R and R’ are unique in this situation.

Preparation methods of aldehydes and ketones

There is a variety of ways to make aldehydes and ketones. Let us look at some of the preparation methods.

• Formation of alcohols by oxidation

Preparation of aldehydes and ketones by oxidation of alcohols and the use of essential oxidising agents such as K2Cr2O7, KMnO4, and CrO3 allows for oxidation. The oxidation of the alcohol to aldehyde and then into a carboxylic acid is facilitated by strong oxidising agents.

Low molecular weight primary alcohols can be oxidised to produce aldehydes. However, suppose the reaction temperature modulates, so the boiling temperature of the aldehyde is lesser than that of the boiling point of the alcohol. In that case, the reaction mixture can prevent further oxidation upon aldehyde formation, which aids in distilling aldehyde from the reaction mixture shortly after its appearance. As a result, it’s critical to keep the reaction conditions slightly over 349K. 

Aldehydes or ketones can be synthesised by oxidising primary and secondary alcohol using agents like Collins reagent, PCC, and Cu at 573 K.

• Dehydrogenation of alcohol

The preparation of aldehydes and ketones by oxidation of alcohols helps convert volatile types of alcohol to aldehydes. It is helpful in industrial settings. In this method, alcohol vapours are transported via heavy metal catalysts, including Cu or Ag. Aldehyde is produced by primary alcohol, while ketones are produced by secondary alcohol. 

If primary or secondary alcohol vapours flow over copper gauze at such a temperature of 573 K, for example, dehydrogenation occurs. In the dehydrogenation process, n-propyl drinking leads to the synthesis of propionaldehyde. 

During the dehydrogenation of alcohol, several metal catalysts, including copper or silver, can be used under heating conditions. On the other hand, this method is ideal for converting precious alcohols into aldehydes. It’s also suitable for industrial applications.

Furthermore, since aldehydes cannot be further oxidised, it is one of the better general methods of preparation of aldehydes and ketones. As a result, there is also no danger of aldehydes converting to carboxylic acids.

• Oxidation of primary and secondary alcohols

• Friedel-crafts acylation

• Glycol cleavage

Preparation of aldehydes and ketones from hydrocarbons

This approach is further broken down into two parts. They are:

• Alkenes undergo ozonolysis

Ozonolysis of alkenes can lead to the formation of aldehyde or ketone. Ozonolysis is indeed a reaction wherein ozone atoms, or O3 is added to an alkene chemical, resulting in the creation of ozonide. The tiny molecules are formed by reducing the ozonide compound using zinc dust and water, which in this case are the respective aldehydes as well as ketones. Here, based on the substitution arrangement of an alkene molecule, the reaction creates aldehydes, ketones, and both compounds in rare circumstances. 

• Alkynes hydration

Insufficient catalyst, alkynes follow Markovnikov’s rule to generate ketones. In the combination of HgSO4 and H2SO4, all alkynes react with water to create ketones. Furthermore, when ethyne combines with water due to a catalyst (HgSO4 or H2SO4), acetaldehyde is formed. It is the only case where an alkyne creates acetaldehyde after being hydrated. Ketones are produced when all the alkynes are hydrated.

Conclusion

The information mentioned above will clear all your doubts regarding the general preparation method of aldehydes and ketones. Methanoyl or formyl is a term used to describe aldehydes and ketones. This group’s carbon atom contains two leftover bonds that can be filled by aryl, alkyl, as well as other substituents. A compound is a ketone if none of the substituents is hydrogen. An aldehyde is a chemical that has at least one hydrogen atom.