Given below are two statements :
Statement I: D-glucose pentaacetate reacts with 2, 4-dinitrophenylhydrazine.
Statement II : Starch, on heating with concentrated sulfuric acid at and atmosphere pressure produces glucose.
In the light of the above statements, choose the correct answer from the options given below
Statement I: D-glucose pentaacetate reacts with 2, 4-dinitrophenylhydrazine.
Statement II : Starch, on heating with concentrated sulfuric acid at and atmosphere pressure produces glucose.
In the light of the above statements, choose the correct answer from the options given below
- (A)Both Statement I and Statement II are false
- (B)Statement I is false but Statement II is true✓ Correct
- (C)Statement I is true but Statement II is false
- (D)Both Statement I and Statement II are true
Answer: (B)
Solution
Glucose pentaacetate has every oxygen function, including the anomeric position, tied up as an acetate ester, so the molecule is locked in its cyclic form with no free carbonyl exposed. Carbonyl-specific reagents such as 2,4-dinitrophenylhydrazine therefore give no reaction with the pentaacetate — this is in fact the classical evidence that glucose exists as a cyclic hemiacetal rather than an open-chain aldehyde, so Statement I is false. Industrially, glucose is obtained by acid hydrolysis of starch carried out under heat (about 100°C) and moderate pressure (2–3 atm), which is what Statement II describes, and it is true. Statement I is false, Statement II is true.
JEE Main · 2025 · 28 Jan 2025 · Shift 1 · Single correct option