The preparation of cyclohexene by acid catalyzed dehydration is a classic in the cannon of undergraduate laboratory instruction; this reaction is an example of a greener variation of the reaction.
In this exercise the focus is on the use of concentrated (85%) H3PO4 in place of the stronger - and more corrosive - H2SO4 as the catalyst. Students' attention is drawn to the fact that when a liquid alcohol is dehydrated there is no need for additional 'solvent', only the alcohol and catalytic quantities of strong acid are required. Consistent with the emphasis "green chemistry" puts on the atom economy (atom efficiency) of a reaction, this exercise illustrates that the formation of water that occurs not only reduces atom economy but also represents a 'by-product' (waste) that must be dealt with appropriately (freed of acid, and purified for reuse). Nonetheless, water is certainly the most benign of by-products. Similarly, the use of a drying agent represents another relatively benign disposal matter.
The link to the laboratory procedure includes pre- and post- lab questions.
Summary prepared July 2005 by Rita Hessley, Department of Chemical Technology at the University of Cincinnati.
Doxsee, K. M.; Hutchison, J. E. Green Organic Chemistry - Strategies, Tools, and Laboratory Experiments, Print 2004; pp 129-134.