Alcohols can suffer dehydration reactions as well as oxidation. However, an important difference is that ALL classes of alcohols, including tertairy, can be deydrated, although of course tertiary ones cannot be oxidised.
The reagent is concentrated sulphuric acid, but the conditions become milder as the classification moves from primary to secondary to tertiary. For example, ethanol is dehydrated with 95% sulphuric acid at 170 deg. to give ethene; butan-2-ol with 60% sulphuric acid at 100 deg and methylpropan-2-ol with 20% sulphuric acid at 85-90 deg.
Remember that in each case the product will be an alkene, but with some alcohols different isomeric alkenes are possible. For simplicity's sake consider the -OH group being removed together with a hydrogen atom from a neighbouring carbon atom, to make water. This can give the unsaturation either side of the original alcohol group, with geometric isomerism also a possibility, depending on the structure of the original alcohol. Do watch out for this!
Posted by dcox at October 12, 2009 08:31 AM