Q.How do you convert the following : (Any three)

(a) Phenol → Picric acid

Concept: Electrophilic aromatic substitution (nitration).

Phenol undergoes nitration with concentrated $\ce{HNO3/H2SO4}$ at room temperature. The —OH group strongly activates the ring, directing nitro groups to ortho and para positions. Under strong conditions, all three positions get nitrated, yielding 2,4,6-trinitrophenol (picric acid). …

Let's tackle each conversion one by one. The key is to think about what functional group change is happening and which reaction class accomplishes it.

(a) Phenol to picric acid

Concept: Picric acid is 2,4,6-trinitrophenol. We are adding three nitro groups to the benzene ring of phenol. Phenol is highly activated towards electrophilic substitution because the -OH group donates electrons. However, direct nitration with concentrated nitric acid would oxidise the phenol. We need a controlled nitration.

Step 1: Protect the ring from oxidation. We first treat phenol with concentrated sulphuric acid. This sulphonates the ring at the para position (and some ortho), giving phenol-4-sulphonic acid. The -SO₃H group is a bulky, deactivating group that slows down further reaction and prevents oxidation.

Step 2: Nitrate the remaining positions. We then treat this with concentrated nitric acid. The -SO₃H group is displaced by the incoming nitro group at the para position, while the two ortho positions get nitrated directly. This gives 2,4,6-trinitrophenol.

Step 3: (Implicit) The -SO₃H group is lost during nitration, so no separate hydrolysis step is needed.

(b) Propanone to 2-Methylpropan-2-ol

Concept: We are converting a ketone (propanone, also called acetone) into a tertiary alcohol (2-methylpropan-2-ol, also called tert-butyl alcohol). The carbon skeleton is increasing by one carbon atom. This is a classic case of a Grignard reaction.

Step 1: Identify the Grignard reagent. The target alcohol has the structure (CH₃)₃COH. Compared to propanone (CH₃COCH₃), we need to add one methyl group to the carbonyl carbon. So the Grignard reagent must be methyl magnesium halide, CH₃MgX (usually CH₃MgBr).

Step 2: Perform the Grignard addition. React propanone with methyl magnesium bromide in dry ether (anhydrous conditions). The Grignard reagent acts as a nucleophile, attacking the electrophilic carbonyl carbon. The oxygen gets a negative charge.

Step 3: Hydrolyse the alkoxide. After the addition, we add dilute acid (like dil. H₂SO₄ or NH₄Cl solution). This protonates the alkoxide ion to give the tertiary alcohol.

(c) Phenol to anisole

Concept: Anisole is methoxybenzene, C₆H₅OCH₃. We are converting the -OH group of phenol into an -OCH₃ group. This is an ether formation. The classic method is the Williamson ether synthesis.

Step 1: Generate the phenoxide ion. Phenol is weakly acidic. Treat it with a strong base like aqueous sodium hydroxide (NaOH). This deprotonates the phenol to form sodium phenoxide, C₆H₅ONa. The phenoxide ion is a much better nucleophile than phenol itself.

Step 2: Perform an Sₙ2 reaction. React the sodium phenoxide with methyl iodide (CH₃I) or dimethyl sulphate [(CH₃)₂SO₄]. The phenoxide ion attacks the electrophilic carbon of methyl iodide, displacing iodide. This gives anisole and sodium iodide. …