Questions: Arenediazonium Salts and the Sandmeyer Reaction
4 questions to test your understanding
Score: 0 / 4
Question 1 Multiple Choice
Which reagent converts benzenediazonium chloride into benzonitrile, C₆H₅CN?
AKCN alone at room temperature
BCuCN
CH₃PO₂
DHBF₄ then heat
Copper(I) cyanide replaces the diazonium group with CN in a Sandmeyer reaction. H₃PO₂ replaces it with H, and HBF₄ followed by heat gives the aryl fluoride.
Question 2 Multiple Choice
Which sequence converts aniline into 1,3,5-tribromobenzene?
ABr₂/FeBr₃ on benzene three times
BBr₂ (excess), then NaNO₂/HCl at 0 °C, then H₃PO₂
CNaNO₂/HCl, then CuBr three times
DH₃PO₂, then Br₂ (excess)
The strongly activating NH₂ group directs three bromines to its ortho and para positions, which are meta to each other. Diazotization and treatment with H₃PO₂ then remove the nitrogen, leaving three bromines in a 1,3,5 pattern.
Question 3 True / False
Aliphatic diazonium salts are about as stable as arenediazonium salts and are equally useful in synthesis.
TTrue
FFalse
Answer: False
An alkyl diazonium ion loses N₂ very rapidly to give a carbocation, which leads to mixtures of products. The aromatic ring stabilizes ArN₂⁺ enough to use it in cold solution.
Question 4 Short Answer
What is azo coupling, and why does it require an activated aromatic ring?
Think about your answer, then reveal below.
Model answer: Azo coupling is electrophilic aromatic substitution in which an arenediazonium ion attacks an electron-rich arene, usually a phenol or aromatic amine, to form an Ar–N=N–Ar′ azo compound. The diazonium ion is a weak electrophile, so it reacts only with strongly activated rings.
The extended conjugation through the N=N link makes azo compounds absorb visible light, which is why many dyes and indicators, such as methyl orange, are azo compounds.