Alcohol, phenol & ether MCQs for NEET — Chemistry Questions with Answers

When symmetrical ethers react with HI, the C-O bond breaks, forming an alcohol and an alkyl iodide. If excess HI is present and heated, the alcohol can further react to form alkyl iodide. However, with limited HI, ethanol and iodoethane are the primary products. The provided example 7.7 (i) shows $CH_3CH_2 – O – CH_2CH_3$ reacting with HI to give $CH_3CH_2OH$ and $CH_3CH_2I$.

According to the NCERT text, 'Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide.' This is the correct initial step in the industrial preparation of phenol from cumene.

The NCERT states, 'Diazonium salts are hydrolysed to phenols by warming with water or by treating with dilute acids.' Hydrolysis is the reaction with water that breaks a bond.

The NCERT states, 'Chlorobenzene is fused with NaOH at 623K and 320 atmospheric pressure. Phenol is obtained by acidification of sodium phenoxide so produced.' These harsh conditions are characteristic of the Dow's process.

NCERT states 'From benzenesulphonic acid: Benzene is sulphonated with oleum and benzene sulphonic acid so formed is converted to sodium phenoxide on heating with molten sodium hydroxide. Acidification of the sodium salt gives phenol.'

In methods like the one from benzenesulphonic acid or haloarenes, sodium phenoxide is formed. Acidification (e.g., with dilute acid) is used to protonate the phenoxide ion ($C_6H_5O^-$) to regenerate the neutral phenol ($C_6H_5OH$). The NCERT states, 'Acidification of the sodium salt gives phenol.'

The NCERT text specifies, 'A diazonium salt is formed by treating an aromatic primary amine with nitrous acid ($NaNO_2 + HCl$) at 273-278 K.' This low temperature range (0-5 °C) is crucial for the stability of diazonium salts.

The NCERT clearly mentions, 'Most of the worldwide production of phenol is from cumene.'

The NCERT states, 'In the laboratory, phenols are prepared from benzene derivatives by any of the following methods' and then lists methods like from haloarenes, benzenesulphonic acid, and diazonium salts, all of which involve replacing existing groups on the benzene ring with a hydroxyl group either directly or indirectly.

The NCERT specifies, 'Cumene (isopropylbenzene) is oxidised in the presence of air to cumene hydroperoxide.'