Hydration reactions
Hydration of an alkene
In the hydration of an alkene, acid and water are added to an alkene. In the mechanism, the pi bond of the alkene attacks H+ of the hydronium (H3O+). The two possible carbocations that can be formed are compared. The more stable one, which is usually the more substituted one, is lower energy and its path followed. This leads to more of the Markovnikov alcohol.
If the reaction is performed with concentrated H2SO4 or H3PO4, the reaction equilibrium is driven to the alkene starting material because H2SO4 or H3PO4 are dehydrating acids and absorb the water. If the acid is diluted with plenty of water, the reaction equilibrium is driven to the alcohol. One difficulty with this reaction is that alkenes are not usually very water soluble, so it is difficult to run this reaction. Also, rearrangements are possible since a carbocation is formed. For these reasons, there are better ways to make Markovnikov alcohols.
Markovnikov Hydrohalogenation of an Alkene
Hydrosulfonation
Hydrosulfonation could be a better way to make Markovnikov alcohols. Since alkenes do not dissolve very well in water, concentrated sulfuric acid (H2SO4) can be used. Normally, sulfuric acid drives the equilibrium to the alkene, but sulfuric acid does dissolve the alkene. If the reaction is run cold, it leads to the Markovnikov hydrogen sulfonate. At this point in the reaction mechanism, if plenty of water is added and the reaction is heated, the hydrogen sulfonate becomes a Markovnikov alcohol.
The problem with this reaction is concentrated sulfuric acid is used for the first part of the reaction. Sulfuric acid reacts with many functional groups. If there are any sensitive functional groups on the alkene, the sulfuric acid will chew them up. If a chemistry student spent six months of research making a large, beautiful, complicated molecule that contains an alkene and they want to make a Markovnikov alcohol out of it, they would not want to add concentrated sulfuric acid to it! Also, since a carbocation is formed, rearrangements are possible.
Oxymercuration/Demercuration -
with water -
A triangle reaction
A good, gentle way to make Markovnikov alcohols is oxymercuration in water followed by demercuration. But, before we get into this reaction, you should learn an important analogy that I call Triangle Reactions. I am the only one who teaches this analogy, but you should learn it!