Difference Between Acyl and Acetyl

Acyl vs Acetyl
 

There are several functional groups in molecules, which are used to characterize the molecules. Acyl is one such functional group, which can be seen in many classes of molecules.

Acyl

An acyl group has a formula of RCO. There is a double bond between C and O, and the other bond is with an R group. Acyl groups are found in esters, aldehydes, ketones, anhydrides, amides, acid chlorides, and carboxylic acids. Therefore, the other bond with the carbon atom can be of –OH, -NH₂, -X, -R, -H etc. Acyl group is a functional group, and most of the time, this term applies in organic chemistry but, in inorganic chemistry, also we can find this term. Inorganic acids like sulfonic acid and phosphonic acid contain an oxygen atom, which is double bonded to another atom. In these instances, also their functional group is said to be an acyl group. However, usually, acyl group is characterized by a carbon and oxygen atom, which is linked by a double bond. Identifying an acyl group is easy because of the C=O part. Especially in IR spectroscopy, C=O stretching band is one of the prominent and a strong band. C=O peak occurs at different frequencies for different acyl compounds like carboxylic acids, amides, esters, etc. Therefore, this helps in structure determination also. Other than spectroscopic methods, by simple chemical tests we can identify acyl compounds. Following are some of those, which we can do in the laboratory.

• Since carboxylic acids are weak acids, litmus paper test or pH paper test can be used to identify water-soluble carboxylic acids. Water insoluble carboxylic acids dissolve in aqueous sodium hydroxide.

•  Acyl chlorides hydrolyze in water and gives precipitates with aqueous silver nitrate.

• Acid anhydrides dissolve when heated briefly with aqueous sodium hydroxide.

• Amides can be distinguished from amines with dilute HCl.

• Esters and amides are hydrolyzed slowly when reacting with sodium hydroxide. From the hydrolyzed products, the acyl compound can be identified. Ester produces a carboxylate ion and an alcohol, whereas amide produces a carboxylate ion and an amine or ammonia.

Nucleophilic substitution reactions can take place at the acyl carbon because it has a slight positive charge. Many reactions of this type occur in living organisms, and they are known as acyl transfer reactions. From all the acyl compounds, acyl chlorides have the highest reactivity toward nucleophilic substitution and amides have the least reactivity.

Acetyl

Acetyl group is a common example for an organic acyl group. This is also known as ethanoyl group. It has the chemical formula of CH₃CO. Therefore, the R group in the acyl is replaced by a methyl group. Other bond in the carbon can be with a –OH, -NH₂, -X,-R,-H etc. For example, CH₃COOH is known as acetic acid. The introduction of an acetyl group into a molecule is called acetylation. This is a common reaction in biological systems and synthetic organic chemistry.

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