Practical investigations
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I'm doing the bromine clock reaction for my individual investigation and can't find a reaction mechanism for either the reaction between bromide, bromate(V) and hydrogen ions or the reaction between bromine and phenol. Could you please recommend any promising sources?
Igloo writes ...
A suitable article for you to read is on the web at:
http://jbcs.sbq.org.br/jbcs/2001/vol12_n6/13.pdf
Although it starts in Spanish, this introduction is in fact a quote for the subsequent article in English!
The short answer to your question is that the reaction is first order wrt to bromide ions, first order wrt bromate(V) ions and second order wrt hydrogen ions, and a simplified version of the mechanism which has been proposed for this reaction is:
H+ + Br - ---> HBr (fast)
H+ + BrO3- ---> HBrO3 (fast)
HBr + HBrO3 ---> HBrO + HBrO2 (slow)
HBrO2 + HBr ---> 2HBrO (fast)
HBrO + HBr ---> H2 O + Br2 (fast)
Read the article for a more detailed account.
As for the reaction between bromine and phenol, this is well documented on the web and also appears in many A-level textbooks. Bromine undergoes a substitution reaction on the aromatic ring, similar to, but much more easily than, that with benzene itself. Enter “mechanism bromine phenol” into Google and find an article which suits.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
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updated: 13 January 2007
