Hydrocarbons · Question 2

In the following reaction sequence, the major product Q is L-Glucose [ii) Cr2O3, 775 K, 10-20 atm]i) HI, P [UV]Cl2 (excess) Q

1. [figure]
2. [figure]
3. [figure]
4. [figure]

Answer

(4) [figure]

Solution

L-Glucose (open chain) [figure] [ ]HI [figure]

HI/ removes every –OH and reduces –CHO; the unbranched C₆ chain becomes n-hexane.

[figure] [ 10-20 atm]Cr2O3, 775 K [figure] (P)

Aromatisation (cyclisation + dehydrogenation) of n-hexane gives benzene, P.

[figure] [UV]Cl2 (excess) [figure] (Q)

In UV light benzene adds three Cl2 by a free-radical path (addition, not substitution): Q = 1,2,3,4,5,6-hexachlorocyclohexane (BHC).

Answer: (D)