PIONEER JUNIOR COLLEGE - ASKnLearn

26 2,4-D and MCPA are two common weed killers.
8
OCH 2 CH 2 OH
O
OCH 2 C
OH
Cl Cl
Cl
CH 3
2,4-D
MCPA
Which of the following reagents can be used to distinguish between them?
A
B
C
D
sodium metal
2,4-dinitrophenylhydrazine
aqueous sodium carbonate
hot acidified potassium manganate(VII)
27 Compound Y forms an orange precipitate with 2,4-dinitrophenylhydrazine. However,
it does not react with Fehling’s solution. The reaction of Y with HCN yields a product
which contains a chiral centre.
Which of the following could be compound Y?
A
B
C
D
diphenylketone
benzaldehyde
phenylmethanol
2-phenylethanal
28 A commercial use of chloroethanoic acid is in the manufacture of the herbicide
2,4,5–T which can be synthesised from 1,2,4,5-tetrachlorobenzene by the following
route.
Cl
Cl
excess NaOH
Cl
Cl
NaOH
Cl
Cl
ClCH 2
CO 2
H
Cl
Cl
Cl
Cl
high temp
I
Cl
OH
Cl
O - Na +
II
Cl
OCH 2 CO 2 H
1,2,4,5-tetrachlorobenzene
2,4,5-T
Which of the following statement about the compounds and their reactions is correct?
A
B
C
D
Reaction I involves electrophilic substitution.
Reaction II involves nucleophilic substitution.
2,4,5–T is readily hydrolysed by aqueous NaOH.
1,2,4,5-tetrachlorobenzene forms a white precipitate with hot aqueous silver
nitrate.