Diazonium Salts — Reactions (Sandmeyer, coupling)
Nitrogen Compounds
8
JEE Qs
8%
Hard
60
min
Master the specific reagents and reaction conditions for each type of diazonium salt transformation, paying close attention to the mechanisms and product formation in coupling reactions for azo dye synthesis.
🧮 Key Formulas
✅ Key Points for JEE
- 1Diazonium salts are highly versatile intermediates for converting an aryl amine's amino group (-NH2) into a wide array of functional groups like -Cl, -Br, -I, -F, -CN, -OH, or even -H, all while retaining the aromatic ring structure.
- 2The Sandmeyer reaction (using CuX/HX) generally provides higher yields for preparing aryl chlorides, bromides, and cyanides compared to the Gattermann reaction (using Cu powder/HX).
- 3The Balz-Schiemann reaction is the preferred method for preparing fluorobenzene (Ar-F) from diazonium salts, involving treatment with HBF4 followed by heating.
- 4Coupling reactions are electrophilic aromatic substitution reactions where the diazonium ion acts as a weak electrophile, attacking electron-rich aromatic compounds (like phenols and anilines) to form intensely colored azo dyes.
- 5The pH conditions are crucial for coupling reactions: slightly acidic (pH 4-5) for aniline/amine coupling and slightly basic (pH 9-10) for phenol coupling to ensure sufficient concentration of the nucleophilic species and the diazonium ion.
⚠️ Common Mistakes
- ✕Confusing the specific reagents and conditions for different replacement reactions, especially distinguishing Sandmeyer (CuX/HX) from Gattermann (Cu/HX) and the unique methods for Ar-F (HBF4) and Ar-I (KI).
- ✕Incorrectly applying diazonium salt reactions to aliphatic amines; aliphatic diazonium salts are highly unstable and immediately decompose via carbocation formation, leading to rearrangement or elimination products.
- ✕Failing to recognize the electrophilic nature of the diazonium ion in coupling reactions and predicting incorrect positions of attack on substituted aromatic rings (e.g., ortho/para to activating groups).
📝 Practice Questions
See allQ56.Given below are two statements : Consider the following reaction (1) Both Statement I and Statement II are false (2) Statement I is true but Statement II is false (3) Statement I is false but Statement II is true (4) Both Statement I and Statement II are true
Q56.Identify correct statements : (A) Primary amines do not give diazonium salts when treated with NaNO2 in acidic condition. (B) Aliphatic and aromatic primary amines on heating with CHCl3 and ethanolic KOH form 2025 (28 Jan Shift 2) JEE Main Previous Year Paper carbylamines. (C) Secondary and tertiary amines also give carbylamine test. (D) Benzenesulfonyl chloride is known as Hinsberg's reagent. (E) Tertiary amines reacts with benzenesulfonyl chloride very easily. Choose the correct answer from the options given below : (1) (A) and (B) only (2) (D) and (E) only (3) (B) and (D) only (4) (B) and (C) only
Q68.Match the Compounds (List - I) with the appropriate Catalyst/Reagents (List - II) for their reduction into corresponding amines. Choose the correct answer from the options given below : (1) (A)-(II), (B)-(I), (C)-(III), (D)-(IV) (2) (A)-(III), (B)-(II), (C)-(IV), (D)-(I) (3) (A)-(II), (B)-(IV), (C)-(III), (D)-(I) (4) (A)-(III), (B)-(IV), (C)-(II), (D)-(I)
Q58.The correct set of ions (aqueous solution) with same colour from the following is: 2025 (23 Jan Shift 1) JEE Main Previous Year Paper (1) Sc3+, Ti3+, Cr2+ (2) V2+, Cr3+, Mn3+ (3) Ti4+, V4+, Mn2+ (4) Zn2+, V3+, Fe3+
Q66. For reaction The correct order of set of reagents for the above conversion is : (1) Br2 ∣FeBr3, H2O(Δ), NaOH (2) H2SO4, Ac2O, Br2, H2O(Δ), NaOH (3) Ac2O, Br2, H2O(Δ), NaOH (4) Ac2O, H2SO4, Br2, NaOH
Q55.Total number of nucleophiles from the following is : ⊖ NH3, PhSH, (H3C)2 S, H2C = CH2, O H, H3O⊕, (CH3)2CO, ⇌NCH3 (1) 7 (2) 4 (3) 6 (4) 5
NCERT Chapters
- Class 12 Chemistry Ch 13: Amines