Phenylamine and azo compounds
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Outline the three-step process for preparing phenylamine from benzene.
1. Nitration of benzene using concentrated HNO₃ and H₂SO₄ to form nitrobenzene. 2. Reduction of nitrobenzene with hot Sn/concentrated HCl. 3. Neutralization with NaOH(aq) to release phenylamine.
Describe the reaction of phenylamine with bromine water (Br₂(aq)).
Phenylamine reacts rapidly with Br₂(aq) at room temperature to form a white precipitate of 2,4,6-tribromophenylamine. This occurs because the lone pair of electrons on the nitrogen atom in phenylamine is delocalized into the benzene ring, activating it towards electrophilic substitution.
Outline the reaction of phenylamine with HNO₂ (or NaNO₂ and dilute acid) at temperatures below 10 °C.
Phenylamine reacts with nitrous acid (HNO₂, generated in situ from NaNO₂ and dilute HCl) at <10°C to form a diazonium salt (benzenediazonium chloride). This reaction requires low temperatures to prevent decomposition of the diazonium salt.
What product is formed when benzenediazonium chloride is warmed with H₂O?
Warming benzenediazonium chloride with water leads to the formation of phenol, nitrogen gas (N₂), and HCl. The diazonium group is replaced by a hydroxyl group (-OH).
Explain the relative basicities of aqueous ammonia, ethylamine, and phenylamine.
Ethylamine > Ammonia > Phenylamine. Ethylamine is the strongest base due to the electron-donating ethyl group increasing electron density on the nitrogen. Phenylamine is the weakest base, as the lone pair on nitrogen is delocalized into the benzene ring, making it less available for protonation.
What is an azo compound and how are they formed?
Azo compounds contain the functional group R-N=N-R', where R and R' are aryl groups. They are typically formed by the diazo coupling reaction, where a diazonium salt reacts with an activated aromatic compound (
Describe the reaction to create an azo dye, including the reagents and conditions.
Azo dyes are formed by reacting a diazonium salt with a coupling agent such as phenol or phenylamine under alkaline conditions (typically pH 9-10) and low temperature (0-5°C). This electrophilic substitution reaction forms the -N=N- bond that characterizes azo dyes.
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