(a) How is propanone prepared from i) 2, 2 dichloro propane ii) isopropyl alcohol iii) propyne. Give the suitable chemical reaction for the conversion of ethanoic acid into i) methane ii) methyl…

(a) Preparation of Propanone and Conversion of Ethanoic Acid

i) Preparation of Propanone from 2,2-Dichloropropane

2,2-Dichloropropane can be converted into propanone by hydrolysis followed by dehydrohalogenation (elimination of HCl). The reaction proceeds as follows:

CCl₃CH₃alc. KOHHeatacetoneacetone+2HCl

1. Hydrolysis with aqueous NaOH (or KOH) replaces the chlorine atoms with hydroxyl groups, forming 2,2-dihydroxypropane (a gem-diol, which is unstable and decomposes to propanone).
2. The gem-diol loses water to form propanone (acetone).

{"type":"reaction","reactants":[{"formula":"C3H6Cl2"},{"formula":"NaOH","coef":2}],"products":[{"name":"propanone"},{"formula":"NaCl","coef":2},{"formula":"H2O"}],"conditions":"aqueous","reversible":true}

Chemical Equation: $$\mathrm{C}{}_3\mathrm{H}{}_6\mathrm{Cl}{}_2+2\mathrm{NaOH}\to (\mathrm{CH}{}_3){}_2\mathrm{C}(\mathrm{OH}){}_2+2\mathrm{NaCl}\to (\mathrm{CH}{}_3){}_2\mathrm{C}=\mathrm{O}+\mathrm{H}{}_2\mathrm{O}$$

---

ii) Preparation of Propanone from Isopropyl Alcohol (Propan-2-ol)

Isopropyl alcohol (propan-2-ol) can be oxidized to propanone using a mild oxidizing agent such as acidified potassium dichromate (K₂Cr₂O₇/H₂SO₄) or potassium permanganate (KMnO₄). The reaction involves the oxidation of the secondary alcohol to a ketone.

propan-2-olpropan-2-olconc. H₂SO₄Heatacetoneacetone+H₂O

{"type":"reaction","reactants":[{"name":"propan-2-ol"},{"formula":"K2Cr2O7"},{"formula":"H2SO4"}],"products":[{"name":"propanone"},{"formula":"Cr2O3"},{"formula":"K2SO4"},{"formula":"H2O"}],"conditions":"heat"}

Chemical Equation: $$3(\mathrm{CH}{}_3){}_2\mathrm{CHOH}+\mathrm{K}{}_2\mathrm{Cr}{}_2\mathrm{O}{}_7+4\mathrm{H}{}_2\mathrm{SO}{}_4\to 3(\mathrm{CH}{}_3){}_2\mathrm{C}=\mathrm{O}+\mathrm{Cr}{}_2\mathrm{O}{}_3+\mathrm{K}{}_2\mathrm{SO}{}_4+4\mathrm{H}{}_2\mathrm{O}$$

---

iii) Preparation of Propanone from Propyne

Propyne (prop-1-yne) can be converted into propanone by hydration in the presence of mercuric sulfate (HgSO₄) and sulfuric acid (H₂SO₄). This follows Markovnikov’s rule, where water adds across the triple bond to form an enol, which tautomerizes to the ketone.

propynepropyneH₂O/HgSO₄Hydrationacetoneacetone

{"type":"reaction","reactants":[{"name":"propyne"},{"formula":"H2O"}],"products":[{"name":"propanone"}],"conditions":"HgSO4/H2SO4"}

Chemical Equation: $$\mathrm{CH}{}_3-\mathrm{C}\equiv \mathrm{CH}+\mathrm{H}{}_2\mathrm{O}\to (\mathrm{CH}{}_3){}_2\mathrm{C}=\mathrm{O}$$

---

Conversion of Ethanoic Acid

i) Conversion of Ethanoic Acid into Methane

Ethanoic acid can be converted into methane by decarboxylation using sodium hydroxide (NaOH) followed by reduction with sodium amalgam (Na/Hg). The process involves:

1. Decarboxylation of ethanoic acid to form methane via the sodium salt of ethanoate.
2. Reduction of the sodium salt with sodium amalgam (a mild reducing agent).

{"type":"reaction","reactants":[{"formula":"CH3COOH"},{"formula":"NaOH"}],"products":[{"formula":"CH3COONa"},{"formula":"H2O"}],"conditions":"heat"}

Step 1 (Decarboxylation): $$\mathrm{CH}{}_3\mathrm{COOH}+\mathrm{NaOH}\to \mathrm{CH}{}_3\mathrm{COONa}+\mathrm{H}{}_2\mathrm{O}$$ Step 2 (Reduction with Na/Hg): $$\mathrm{CH}{}_3\mathrm{COONa}+4[\mathrm{H}]\to \mathrm{CH}{}_4+\mathrm{NaOH}+\mathrm{CO}{}_2$$

---

ii) Conversion of Ethanoic Acid into Methyl Ethanoate

Ethanoic acid can be converted into methyl ethanoate by esterification with methanol (CH₃OH) in the presence of concentrated sulfuric acid (H₂SO₄) as a catalyst.

{"type":"reaction","reactants":[{"formula":"CH3COOH"},{"formula":"CH3OH"}],"products":[{"formula":"CH3COOCH3"},{"formula":"H2O"}],"conditions":"conc. H2SO4, heat"}

Chemical Equation: $$\mathrm{CH}{}_3\mathrm{COOH}+\mathrm{CH}{}_3\mathrm{OH}\rightleftharpoons \mathrm{CH}{}_3\mathrm{COOCH}{}_3+\mathrm{H}{}_2\mathrm{O}$$

---

(b) Structural Formulas of Primary, Secondary, and Tertiary Amines of $\mathrm{C}{}_3\mathrm{H}{}_9\mathrm{N}$ and Separation by Hoffmann’s Method

Structural Formulas of $\mathrm{C}{}_3\mathrm{H}{}_9\mathrm{N}$ Amines

The molecular formula $\mathrm{C}{}_3\mathrm{H}{}_9\mathrm{N}$ corresponds to three isomeric amines:

1. Primary amine (1°): Propylamine (1-aminopropane)
2. Secondary amine (2°): Isopropylamine (2-aminopropane) and Ethylmethylamine
3. Tertiary amine (3°): Trimethylamine

Secondary amine (2°): EthylmethylamineSecondary amine (2°): EthylmethylamineTertiary amine (3°): TrimethylamineTertiary amine (3°): Trimethylamine

---

Separation of Amines by Hoffmann’s Method

Hoffmann’s method involves fractional distillation after treating the mixture with nitrous acid (HNO₂). The reactions are as follows:

1. Primary amines (1°) react with $\mathrm{HNO}{}_2$ to form diazotized salts, which decompose to give alcohols (or alkenes if unstable) and nitrogen gas. $$\mathrm{RNH}{}_2+\mathrm{HNO}{}_2\to \mathrm{ROH}+\mathrm{N}{}_2+\mathrm{H}{}_2\mathrm{O}$$

   • Example: Propylamine forms propan-1-ol and nitrogen gas.

2. Secondary amines (2°) react with $\mathrm{HNO}{}_2$ to form nitrosamines, which are oily, yellow liquids that are insoluble in water and can be separated by extraction. $$\mathrm{R}{}_2\mathrm{NH}+\mathrm{HNO}{}_2\to \mathrm{R}{}_2\mathrm{N}-\mathrm{N}=\mathrm{O}+\mathrm{H}{}_2\mathrm{O}$$

   • Example: Ethylmethylamine forms N-ethyl-N-methylnitrosamine.

3. Tertiary amines (3°) do not react with $\mathrm{HNO}{}_2$ and remain unchanged. They can be separated by distillation since they have different boiling points.

Procedure for Separation:

1. Treat the mixture with sodium nitrite (NaNO₂) and hydrochloric acid (HCl) to generate $\mathrm{HNO}{}_2$ in situ.
2. Primary amines evolve nitrogen gas and form alcohols (or alkenes), which can be distilled off.
3. Secondary amines form nitrosamines, which are extracted with an organic solvent (e.g., ether).
4. Tertiary amines remain in the aqueous layer and are distilled separately.

Boiling Points (Approximate):

• Primary amine (Propylamine): ~48°C
• Secondary amine (Ethylmethylamine): ~37°C
• Tertiary amine (Trimethylamine): ~3°C

By controlling the temperature, each amine can be separated based on their distinct reactivity and boiling points.