![[Halogenation of Propanone - Mechanism A]](../images/four1a.gif)
HALOGENATION OF PROPANONE
Review
| Overall Reaction | Pk + I2 → PI + H+ + I- |
| Proposed Mechanism | |
Since the reaction is known to be 0th Order with respect to halogen, the 0th order rate coefficient (and the Reaction Rate) would be equal to the negative of the slope of a plot of [I2] versus Time.
In the CH213 - Halogenation of Propanone experiment, a variety of reaction solutions are made up (with differing initial reactant concentrations), and the iodine concentration as a function of time is monitored.
Using these results, it is possible to determine an experimental rate law for the reaction, of the form:
Rate = kexpt[H+]O(A)[I2]O(I2)[I-]O(I-)[Pk]O(P)where the orders for acid, iodine, iodide and the keto form of propanone are O(A), O(I2), O(I-) and O(P) respectively.
Confirmation that Proposed Mechanism equates to the Overall Reaction
Before the experimental rate expression can be compared with the proposed mechanism (to see if they are consistent), an appropriate rate expression must be derived from the mechanism.
First, the proposed mechanism should be checked, to ensure that it gives the overall reaction.
Given that the overall reaction is
Pk + I2 → PI + H+ + I-
And that the proposed mechanism is
It can be stated that