Acid chlorides

Acid chlorides which are also known as acyl chlorides are organic compounds that contain a carbonyl group (C=O) bonded to a chlorine atom. They are derived from carboxylic acids by replacing the hydroxyl group (-OH) with a chlorine atom. Acid chlorides are highly reactive and serve as important intermediates in organic synthesis.

1.0General Structure and Nomenclature of Acid Chloride

The general formula for acid chlorides is RCOCl, where:

• R is an alkyl or aryl group.
• CO represents the carbonyl group (C=O).
• Cl is the chlorine atom attached to the carbonyl carbon.

Nomenclature and Common names of Acid Chlorides

• The IUPAC name for acid chlorides is derived from the corresponding carboxylic acid by replacing the suffix "-ic acid" or "-oic acid" with "-yl chloride".
• Example: Ethanoyl chloride is named after ethanoic acid (acetic acid), and benzoyl chloride is derived from benzoic acid.

Common Names:

• Acid chlorides are often named based on their parent carboxylic acid.
• • CH₃COCl is acetyl chloride (from acetic acid).
  • C₆H₅COCl is benzoyl chloride (from benzoic acid).

2.0General Properties of Acid Chloride

Physical Properties of Acid Chlorides:

Chemical Properties of Acid Chloride

1. Hydrolysis:

• Acid chlorides react vigorously with water to form carboxylic acids and hydrochloric acid (HCl). The nucleophilic water molecule attacks the electrophilic carbonyl carbon, leading to the release of HCl.
• RCOCl + H₂O → RCOOH + HCl

2. Reaction with Alcohols (Formation of Esters):

• Acid chlorides react with alcohols in the presence of a base like pyridine to form esters.
• RCOCl + R′OH → RCOOR′ + HCl
• Example: Acetyl chloride reacts with ethanol to form ethyl acetate.

3. Reaction with Ammonia and Amines (Formation of Amides):

• Acid chlorides react with ammonia or amines to form primary, secondary, or tertiary amides.
• RCOCl + NH₃ → RCONH₂ + HCl
• Example: Benzoyl chloride reacts with ammonia to form benzamide.

4. Friedel-Crafts Acylation

• Reaction: Acid chlorides react with aromatic compounds in the presence of a Lewis acid catalyst like aluminum chloride (AlCl₃) to form aryl ketones.
• $\text{RCOCl}+C_6{H}_6\stackrel{{\text{AlCl}}_3}{\to }{\text{RCOC}}_6{H}_5+\text{HCl}$
• Example: Acetyl chloride reacts with benzene to form acetophenone.

5. Reaction with Grignard Reagents (Formation of Ketones or Tertiary Alcohols):

• Acid chlorides react with Grignard reagents to form ketones or tertiary alcohols depending on the amount of Grignard reagent used.
• RCOCl + RMgX → RCOOR′
• Example: Acetyl chloride reacts with methylmagnesium bromide to form acetone.

6. Reduction to Aldehydes and Alcohols

• Acid chlorides can be reduced to aldehydes using lithium tri-tert-butoxyaluminum hydride or to alcohols using lithium aluminium hydride (LiAlH₄).
• RCOCl + 2[H] → RCHO + HCl
• RCOCl + 4[H] → RCH₂OH + HCl

7. Reaction with Lithium Dialkyl Cuprates (Gilman Reagent)

• Acid chlorides react with lithium dialkyl cuprates to form ketones.
• RCOCl + (R′)₂CuLi  → RCOR′ + R′Cu + LiCl

Here is a summary of the Chemical Reactions of Acid chlorides

3.0Preparation of Acid Chlorides

1. From Carboxylic Acids:

• Acid chlorides are commonly prepared by reacting a carboxylic acid with thionyl chloride (SOCl₂), phosphorus trichloride (PCl₃), or phosphorus pentachloride (PCl₅). 
• RCOOH + SOCl₂ → RCOCl + SO₂ + HCl

2. From Esters: Acid chlorides can be synthesized by treating esters with phosphorus pentachloride (PCl₅).