Carboxylic acids

The homologous series of carboxylic acids is represented by the general formula:

$C_nH_{2n+1}COOH$

where n represents the number of carbon atoms.

1. Replace the suffix "-ane" from the alkane with "-oic acid".
2. The longest carbon chain must include the carboxyl group.
3. If substituents are present, their positions are indicated, starting the numbering from the carboxyl group.

Examples:

1. CH₃CH₂COOH → Propanoic acid
2. CH₃CH₂CH₂CH₂COOH → Pentanoic acid
3. (CH₃)₂C(COOH)CH₃ → 3,3-Dimethylbutanoic acid

Physical properties

1. State: Lower members (e.g., formic and acetic acids) are liquids; higher members are solids.
2. Solubility: Soluble in water due to hydrogen bonding. Solubility decreases with chain length.
3. Odor: Characteristic sharp or sour smell (e.g., vinegar).

Chemical properties

Carboxylic acids exhibit acidic behavior and undergo a variety of reactions.

Reaction with bases (neutralization)

Carboxylic acids react with bases to form salts and water.

$CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O$

Reaction with metals

They react with reactive metals to form salts and hydrogen gas.

$2CH_3COOH + 2Na \rightarrow 2CH_3COONa + H_2\uparrow$

Esterification

Carboxylic acids react with alcohols to form esters in the presence of concentrated sulfuric acid.

$CH_3COOH + C_2H_5OH \rightarrow CH_3COOC_2H_5 + H_2O$

Reaction with phosphorus halides

Carboxylic acids react with phosphorus halides to form acyl halides.

$CH_3COOH + PCl_5 \rightarrow CH_3COCl + POCl_3 + HCl$

Reduction

Carboxylic acids can be reduced to primary alcohols using reducing agents such as lithium aluminum hydride (LiAlH₄).

1. Food Industry: Acetic acid is used in vinegar as a preservative.
2. Pharmaceuticals: Used to produce drugs like aspirin.
3. Soap Production (Saponification): Carboxylic acids react with bases to form soaps

Saponification is the reaction of an ester with a strong base to produce soap and glycerol.

$Ester + NaOH \rightarrow Soap + Glycerol$

1. Overexposure can cause irritation to the skin and eyes.
2. Methanoic acid is toxic and can cause burns or damage to the respiratory system if inhaled.