Mechanism of the acidcatalyzed dehydration of an alcohol to yield an alkene. The process is an E1 reaction and involves a carbocation intermediate
Two electrons from the oxygen atom bond to H+, yielding a protonated alcohol intermediate
The carbon-oxygen bond breaks, and the two electrone from the bond stay with oxygen, leaving a carbocation intermediate.
Two. electrons from a neighboring carbon- hydrohen bond form the alkene bond, and H+(a proton) is eliminated.
To circumvent the need for strong acid and allow the dehydration of secondary alcohols in a gentler way, reagents have been developed that are effective under mild, basic conditions. One such reagent, phosphorus oxychloride (POCl3) in the basic amine solvent pyridine, is often abole to effect the dehydration of secondary and tertiaryalcohols at 0'C.