Acid Chloride

What is Acid Chloride?

Acid chloride (or acyl chloride) is an organic compound with the functional group -COCl in organic chemistry. Their typical formula is RCOCl, where R is a side chain. They are reactive carboxylic acid derivatives. Specifically, acetyl chloride, CH3COCl, is an acyl chloride. The most important subset of acyl halides is acyl chlorides.

Acid Chloride Structure

General Structure of Acid Chloride

Formation of Acid Chlorides

Laboratory procedure

The formation of acid chlorides occurs when carboxylic acids react with thionyl chloride (SOCl2). During the reaction, the hydroxyl group of the carboxylic acid is transformed to a chlorosulfite intermediate, making it a superior leaving group. The chloride anion produced by the process functions as a nucleophile.

Industrial Process

• In an industrial procedure, acetic anhydride is reacted with hydrogen chloride to form acetyl chloride.

(CH₃CO)₂O + HCl → CH₃COCl + CH₃CO₂H

• Certain phosphorus chloride reagents, including phosphorus trichloride and phosphorus pentachloride, can also be employed to create acyl chlorides:

RCOOH + PCl₅ → RCOCl + POCl₃ + HCl

Naming Acid Chlorides

Acyl chlorides are termed by swapping -yl chloride for -ic acid, where the acyl chloride substituent takes precedence. Thus:

Carboxylic acid name	Acyl chloride name	Acyl chloride formula
acetic acid	Acetyl chloride	CH3COCl
propanoic acid	propanoyl chloride	CH3CH2COCl
butanoic acid	butanoyl chloride	CH3CH2CH2COCl

When other functional groups are predominant, acyl chlorides are designated by the prefix chlorocarbonyl.

• ClOCCH2COOH, for example, is known as (chlorocarbonyl)acetic acid

Physical Properties

1. Appearance – Lower acyl chlorides are odorous, colorless liquids.
2. Solubility: They can be dissolved in organic solvents like alcohol, ether, and chloroform.
3. Boiling and melting points- Due to their inability to form hydrogen bonds, the boiling and melting values of acyl chlorides are lower than those of the equivalent acids.

Chemical Properties and Reactions

As a result of their high reactivity, acid halides can be readily transformed into other acyl compounds by nucleophilic acyl substitution.

1. They are the most reactive derivatives of carboxylic acids.
2. Acid chlorides react with carboxylic acids to produce anhydrides via nucleophilic acyl substitution.

3. The hydrolysis of acyl chlorides by water produces the corresponding carboxylic acids.

4. When acid chlorides combine with alcohol nucleophiles, esters are produced. This is the preferred method of ester production. Frequently, pyridine is added to the reaction mixture to eliminate the HCl.

5. By reducing acyl chlorides with lithium aluminum hydride and di-isobutyl aluminum hydride, primary alcohols are generated.

6. In the presence of palladium, hydrogen, and BaSO4 convert them to an aldehyde. The Rosenmund Phenomenon describes this reaction.

7. Ammonia, 1° amines, and 2° amines react with acid chlorides to produce 1°, 2°, and 3° amides, in that order.

8. With the use of Grignard reagents, acid halides are transformed to 3° alcohols. The Grignard reagent contributes to the carbonyl carbon twice throughout this reaction.

9. An excellent yield of ketone product is produced when an acid chloride reacts with a diorgano cuprate (Gillman) reagent (R2CuLi).

Hazards

Due to the reactivity of acyl chlorides, they are often poisonous and should be handled with extreme care. They are lachrymatory compounds because they can react with water on the surface of the eye to produce unpleasant hydrochloric and organic acids. Vapors of acyl chloride can create similar difficulties when inhaled.

Uses of Acid chlorides

Naturally reactive chemical species, acid chlorides are essential building blocks for a vast array of downstream uses. Among its uses are the following:

• Reagents used in chemistry
• Pharmaceutical manufacturing
• The creation of organic compounds
• Origin of organic peroxides
• Manufacturing of agrochemicals
• Plastics and pigments

Frequently Asked Questions FAQs on Acid Chloride