The hydrolysis of sucrose in presence of a mineral acid takes place according to the equation.
An important characteristic of the reaction is that sucrose is dextro – rotatory whereas the products – glucose and fructose are dextro rotatory and laevo-rotatory respectively. Further the laevo –rotation of fructose is more (being – 92o) than the dextro – rotation of glucose (being – 52.5o) so that the mixture as a whole is laevo – rotatory. Thus on hydrolysis, the dextro – rotator sucrose gradually changes into the laevo-rotatory mixture. It is for this reason that the reaction is called ‘Inversion of Sucrose.’
The kinetics of the above reaction is studied by noting the angle of Rotation at different intervals of time with the help of a polarimeter.
Reading of the polarimeter at zero time = r0
Reading of the polarimeter at any time t = rt
Reading of the polarimeter at infinite time =r∞
(I.e. after 24 hours or more)
It is evident that the reading at zero time will be positive and would decrease with the passage of time, pass through zero and ultimately become negative. A little careful consideration shows that Angle of rotation at any instant of time
Substituting the value of a and (a – x) from equations (ii) and (iii) in the first order equation,
The applicability of this equation for the inversion of sucrose was first shown by Wilhelm (1850). It should be noted that the actual value of k, of course, depends upon the concentration of the H+ ions.
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