Q.4. What will formed when ethylchloride is treated with KOH(aq)?
(a) Methanol (b) Ethanol (c) Methanol (d) Ethanal.
Answers
Answer:
(a) The Lucas reagent is an aqueous solution of strong acid (HCl) and zinc chloride (ZnCl
2
). Primary alcohols such as ethanol react with Lucas reagent very slowly on heating to give alkyl halide i.e., chloro-ethane.
Ethanol
CH
3
CH
2
OH
+
Conc.
HCl
→
AnhydrousZnCl
2
Chloroethane
CH
3
CH
2
Cl
+H
2
O.
(b) Ethanol when refluxed with PCl
5
forms ethyl chloride.
Ethanol
CH
3
CH
2
OH
+
pentachloride
Phosphorus
PCl
5
→
Ethylchloride
CH
3
CH
2
Cl
+HCl+
oxychloride
Phosphorus
POCl
3
(c) Alkyl bromides are prepared by the action of bromine in presence of red phosphorus on alcohols in situ. In this reaction phosphorus tribromide is formed as an intermediate which in turn reacts with ethanol and forms corresponding alkyl bromide, i.e., ethyl bromide.
2P+3Br
2
→
tribromide
Phosphorus
2PBr
3
Ethanol
3CH
3
CH
2
OH
+PBr
3
→
Ethylbromide
3CH
3
CH
2
Br
+H
3
PO
3
(d) Ethanol on reaction with acidified potassium dichromate gets oxidised to corresponding aldehyde which on further oxidation gives carboxylic acid.
Ethanol
CH
3
CH
2
OH
dil.H
2
SO4
→
K
2
Cr
2
O
7
Ethanal
CH
3
C
∣∣
O
−H
→
[O]
Ethanoicacid
CH
3
COOH
.