Richard Monson discovered that alcohols were dehydrated in refluxing HMPT(HexaMethylPhosphoricTriamide). Under his direction I started a research project to elucidate the mechanism of the reaction. At the time Monson thought that the rate limiting step in the reaction was the elimination step and an experiment was designed to monitor the reaction, a kinetic experiment. After much false starts the results obtained indicated to Monson that the rate limiting step was not the elimination step but the formation of a phosphate ester. Why and how he knew this was a mystery to me. What I had to show him was a rate profile that was sigmoidal in shape.



These results were quite puzzling to me. There was nothing in any of the classes I had taken that had prepared me for a result like this. Originally we thought that the reaction was second order. Since one of the reactants was the solvent for the reaction, HMPT, the solvent concentration overwhelms the concentration of the other reactant, the alcohol, and can be ignored. The system can thus then be considered pseudo first order, i.e. proportional only to the concentration of the alcohol. Such a system would be expected to produce a rate profile such as the following:   

Graph of a First Order Chemical Reaction

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