Question

Which property is used to study the kinetics of the inversion of cane sugar? How is the property helpful in determining the order of the reaction?

Answer 1

A first-order reaction occurs when cane sugar (sucrose) is hydrolysed with a diluted mineral acid (such as HCl). This is how the reaction happens.

\[\ce{\underset{Sucrose}{C12H22O11} + H2O ->[H+] \underset{D-Glucose}{C6H12O6} + \underset{Fructose}{C6H12O6}}\]

\[\ce{\underset{Dextrorotatory}{[\alpha]_D} = +66.5^\circ}\]

\[\ce{\underset{Laevorotatory}{[\alpha]_D = +52.5^\circ [\alpha]_D = -92.3}}\]

This is a pseudo-unimolecular reaction and proceeds with an inversion in the optical nature of the reaction mixture. Sucrose solution has a specific rotation of [α]_D = +66.5° and is dextrorotatory. It is hydrolysed to produce D-glucose and D-fructose. Whereas D-fructose is laevorotatory with [α]_D = −92.3%, D-glucose is dextrorotatory with [α]_D = +52.5°. The entire solution turns laevorotatory, and the optical properties of the initial reaction mixture are reversed because D-fructose has a higher specific rotation than D-glucose. For this reason, the reaction is known as "inversion of cane sugar".