Addition of water to ethylenic bonds

Electrophilic addition of water to olefins, yielding alcohols, occurs readily under catalysis by acids, sulfuric acid being that generally used  

Addition of water follows Markovnikov s rule in principle, but mixtures are formed rather than the single homogeneous adduct expected according to the rule.57 Some olefins are hydrated in the presence of dilute sulfuric acid (isobutene), but others require concentrated acids (propene, 1- and 2-butene). Negative substituents on the doubly bonded atoms reduce the reactivity (as for cinnamic acid and dichloroethylene), whereas alkyl groups increase it. In all cases reaction should be at as low a temperature as possible when sulfuric acid is used. Too great a concentration of sulfuric acid often causes polymeri- 

The preparation of tert-pentyl alcohol from 2-methyl-2-butene will be described as an example 58 

A mixture of ice (500 g) and concentrated sulfuric acid (500 g) is cooled to 0° and 2-methyl-2-butene (500 ml) is added to it with vigorous stirring. The mixture is stirred for a further hour, then the aqueous layer is separated from the unchanged olefin, poured on ice(ca. 2 kg), neutralized cautiously with a concentrated solution of sodium hydroxide (720 g), and distilled until addition of potassium carbonate to a portion of the distillate no longer separates pentyl alcohol. Addition of potassium carbonate to the distillate causes separation of the tert-pentyl alcohol, which is dried with the same reagent and distilled, affording ca. 90% of the pure alcohol, b.p. 103°. 

Reviews of the hydration of olefins are given by Asinger59 and Seka,60 and of the use of boron trifluoride for that purpose by Topchiev et al.61 

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