Chemistry A2 · Nitrogen compounds. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Phenylamine, C6H5NH2, is made in two stages. Benzene is nitrated to nitrobenzene, which is then reduced with hot tin and concentrated HCl. This gives the salt C6H5NH3+, so NaOH(aq) is added to release the amine.
The lone pair on nitrogen is delocalised into the benzene ring. This makes the ring more reactive, so bromine water reacts at room temperature. It also makes the lone pair less available to accept H+, so phenylamine is a weaker base than ammonia.
With nitrous acid below 10 °C, phenylamine forms a diazonium salt. The cold salt couples with phenol in NaOH(aq) to give an azo compound, which contains –N=N– and is used as a dye.
Students let the diazonium salt warm up before coupling. Above 10 °C it reacts with water to give phenol and nitrogen gas, so no dye forms. Keep it in ice for the coupling step.
Answer: 7.44 g of phenylamine
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