Replacement of the Diazonium Group by –OH

The diazonium group of benzenediazonium ions can be replaced by –OH to yield phenols by addition of the arenediazonium salt to hot aqueous acid:

Replacement of the Diazonium Group by –H

The diazonium group of benzenediazonium ions can be replaced by –H to yield arenes by reduction of the arenediazonium salt with hypophosphorous acid:

 

Coupling Reactions of Benzenediazonium Ions

Benzenediazonium ions react with highly reactive aromatic compounds in an alkaline medium to give azo compounds

Example:

• Benzenediazonium ions react with highly reactive aromatic compounds in an alkaline medium to give azo compounds

• Diazonium coupling reactions are typical electrophilic aromatic substitutions in which the positively charged diazonium ion is the electrophile that reacts with the electron-rich ring of a phenol or arylamine.

• Reaction usually occurs at the para position, although orto attack can take place if the para position is blocked

Example:

• This reaction is used to identify 1° aromatic amines

• Azo compounds are usually intensely coloured – N = N – link brings the two aromatic rings into conjugation, and the p electrons are delocalized over the entire structure

• Azo compounds are used as dyes due to intense colours

 

Uses of Amines and their Derivatives

• Azo compounds are highly coloured and can be synthesized from relatively inexpensive compounds
Þ widely used in dyeing industry

Examples:

1. Methyl orange (an orange dye for fabrics)

2. Sunset Yellow FCF (an orange-yellow dye for food products)

3. Direct Brown 138 (a brown dye for fabrics)

4. Ponceau (a red dye for food products)

As Drugs

Amine derivatives are commonly used as drugs such as painkillers (analgesics), transquillizers and antihistamines

1. Acetaminophen (also known as paracetamol)

• used to relieve pains

• less harmful to the stomach compared with aspirin

2. Chlorpheniramine

• helps to relieve allergic disorders caused by cold, insect bites and stings

• present in some over the counter drugs such as Coricidin, Coltaline, Piriton and Dristan

3. Chlorpromazine

• sedative effect without inducing sleep

• used to relieve anxiety, excitement, restlessness and even metal disorders

Контрольні питання до лекції 7.

1. Напишіть структурні формули сполук. Розташуйте сполуки за збільшенням їх основності. Дайте пояснення. П -хлоранілін, 2-бром-4-хлоранілін, о -толуїдин

2. Вкажіть правильну схему синтезу трет-бутанолу з ізобутилену. Напишіть реакції. А) ; В) ; С) ; D) .

3. Встановити будову сполуки за брутто-формулою та продуктами хімічного перетворення: С₇Н₉N, з соляною кислотою утворює сіль, після послідовної взаємодії з нітритною кислотою і нітритом калію в присутності міді утворює п-нітротолуол. Напишіть реакції.

4. Запропонуйте схему синтезу м -метилфенолу з хлорбензолу

5. Запропонуйте схему синтезу барвника з азо- і діазокомпоненти. Назвіть сполуки.