1. Oxidation of Primary Alcohols 1° ROH (or RCHO) + KMnO4/H+ (or K2Cr2O7/H+) → RCOOH. Strong oxidizing agents needed. Secondary alcohols give ketones, not carboxylic acids. Benzylic methyl groups are oxidized to –COOH by acidic KMnO4.
2. Grignard Carboxylation RMgX + CO2 (dry ether) → RCOOMgX → (H3O+) → RCOOH. Adds exactly one carbon as –COOH. Always requires anhydrous conditions (any proton source destroys RMgX). To find the Grignard reagent: remove –COOH from the target acid.
3. Nitrile Hydrolysis RCN + H3O+ (reflux) → RCOOH + NH4+. Alternatively, RCN + NaOH → RCOONa + NH3 (base). Retains the same carbon skeleton as the nitrile. Used to convert alkyl halide (RX → RCN via SN2 with NaCN) into carboxylic acid (chain extended by one C).
4. Saponification RCOOR' + NaOH (reflux) → RCOONa + R'OH. Irreversible. Product is the sodium carboxylate salt. Used industrially for soap making.
5. Kolbe Electrolysis Applications 2 RCOO– (anode) → R–R + 2 CO2. Used for synthesis of symmetrical alkanes. Mixed Kolbe (two different salts) gives three alkane products. Kolbe of sodium benzoate → biphenyl. Kolbe of sodium acetate → ethane.
6. Fischer Esterification Applications RCOOH + R'OH → RCOOR' (flavors, solvents, pharmaceuticals). Aspirin = acylation of salicylic acid's –OH by acetic acid/acetic anhydride. Ethyl acetate (solvent) = acetic acid + ethanol. Methyl benzoate = benzoic acid + methanol.
7. Decarboxylation Applications Soda lime decarboxylation used for chain shortening. Malonic ester synthesis uses easy thermal decarboxylation of malonic acid (6-membered cyclic TS). Amino acid decarboxylation relevant to biochemistry.
8. HVZ Product Applications Alpha-halocarboxylic acids from HVZ are synthetic intermediates. 2-Chloropropanoic acid → lactic acid (SN2 hydrolysis). 2-Bromopropionic acid → pharmaceutical intermediates (amino acid synthesis via nucleophilic substitution).
9. Acyl Chloride Applications RCOCl (from SOCl2 route) is the most reactive carboxylic acid derivative — used to make esters, amides, anhydrides faster than RCOOH.
10. Carbon Chain Relationships Grignard + CO2: n-carbon RX → (n+1)-carbon RCOOH. Nitrile route: n-carbon RX → (n+1)-carbon RCOOH. Soda lime: n-carbon RCOO– → (n–1)-carbon alkane. All three relationships are directly tested in NEET.