Induction period
![A sigmoid curve of an autocatalytic reaction. When t = 0 to 50, the rate of reaction is low. Thereafter, the reaction accelerates, until almost all reactants have been consumed. At that point, the reaction rate tapers off.](/Images/godic/202501/20/Sigmoid_curve_for_an_autocatalytical_reaction1333.jpg")
![Wilkinson's catalyst requires activation before it can participate in the catalytic cycle](/Images/godic/202501/20/RevisedCatCycle1333.png")
An induction period in chemical kinetics is an initial slow stage of a chemical reaction; after the induction period, the reaction accelerates. Ignoring induction periods can lead to runaway reactions.
In some catalytic reactions, a pre-catalyst needs to undergo a transformation to form the active catalyst, before the catalyst can take effect. Time is required for this transformation, hence the induction period. For example, with Wilkinson's catalyst, one triphenylphosphine ligand must dissociate to give the coordinatively unsaturated 14-electron species which can participate in the catalytic cycle: