i. Oxidation

a) Oxidation of Alcohol: Alcohols can be oxidized using strong oxidizing agents like or KMnO4 to produce carboxylic acids. The oxidation of ethanol ($C_2H_5OH$) to acetic acid ($CH_3COOH$) is an example:

$C_2H_5OH + \rightarrow CH_3COOH$

b) Oxidation of Carbonyl Compounds: Aldehydes are easily oxidized to carboxylic acids, whereas ketones resist oxidation but can form carboxylic acids under drastic conditions. For example, oxidation of acetaldehyde ($CH_3CHO$) to acetic acid ($CH_3COOH$):

$CH_3CHO + \rightarrow CH_3COOH$

Note: Methanoic acid cannot be prepared through oxidation as it can further be oxidized to carbon dioxide.

ii. Hydrolysis

Acyl compounds can be hydrolyzed to give carboxylic acids. For example, hydrolysis of an ester (ethyl acetate) gives acetic acid:

$CH_3COOCH_2CH_3 + H_2O \rightarrow CH_3COOH + CH_3CH_2OH$

iii. Formation via Grignard Reagent

Carbon dioxide reacts with a Grignard reagent (e.g., methylmagnesium bromide) followed by acidic hydrolysis to form carboxylic acids:

$CH_3MgBr + CO_2 \rightarrow CH_3COOH \text{ (after hydrolysis)}$

Carboxylic acids have the highest boiling points compared to alcohols, phenols, and other carbonyl compounds due to strong hydrogen bonding between their molecules. They also undergo dimerization in non-polar solvents due to these interactions:

$2RCOOH \rightleftharpoons (RCOOH)_2$

Acidic behavior of carboxylic acids

Carboxylic acids are stronger acids than alcohols and phenols. The acidic strength depends on the length of the carbon chain and the type of substituents present in the carboxyl group. For example, acetic acid ($CH_3COOH$) dissociates as follows:

$CH_3COOH \rightleftharpoons CH_3COO^- + H^+$

When a strong electronegative substituent like halogens is present, the acidic strength increases due to the negative inductive effect that stabilizes the carboxylate ion:

$CH_3COOH + X^- \rightarrow CH_3COO^- + HX$

i. Reaction with sodium bicarbonate

Carboxylic acids react with sodium bicarbonate to release carbon dioxide gas, which turns lime water milky. The general reaction is:

$RCOOH + NaHCO_3 \rightarrow RCOONa + CO_2 + H_2O$

ii. Reaction with alkali

Carboxylic acids react with alkali to form salts and water. For example, acetic acid reacting with sodium hydroxide:

$CH_3COOH + NaOH \rightarrow CH_3COONa + H_2O$

iii. Reaction with strong metals

Carboxylic acids react with strong metals to produce carboxylate salts and hydrogen gas. For example, reaction with sodium:

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

a. Halogenation

Carboxylic acids react with halogenating agents like $PX_5$, $PX_3$, and $SOX_2$ to form acyl halides. For example, the reaction of acetic acid with phosphorus trichloride ($PCl_3$):

$CH_3COOH + PCl_3 \rightarrow CH_3COCl + POCl_2 + HCl$

b. Reaction with alcohol (ester formation)

Carboxylic acids react with alcohols in the presence of sulfuric acid to form esters. For example, the reaction of acetic acid with ethanol:

$CH_3COOH + C_2H_5OH \rightarrow CH_3COOC_2H_5 + H_2O$

i. Reaction with alcohol

Carboxylic acids react with alcohols in the presence of an acid to form esters, which helps distinguish them from phenols, which do not react with alcohols.

ii. Reaction with sodium bicarbonate

Carboxylic acids react with sodium bicarbonate to produce effervescence of carbon dioxide gas, which turns lime water milky.

iii. Ferric chloride test

Carboxylic acids react with ferric chloride to form an iron (III) carboxylate, which appears as a buff-colored compound. This reaction is used to distinguish carboxylic acids from alcohols and phenols. For example, reaction with ferric chloride ($FeCl_3$):

$RCOOH + FeCl_3 \rightarrow Fe(RCOO)_3 + 3HCl$

iv. Formation of ester

Acyl chloride reacts with phenol in the presence of a catalyst to form esters. For example:

$CH_3COCl + C_6H_5OH \rightarrow C_6H_5COOCH_3 + HCl$