Question

How would you synthesize alcohol from appropriate alkenes?

Answer 1

Hint: An alcohol is an organic functional group with at least one hydroxyl functional group (-OH) attached to a saturated carbon atom. An alkene is a hydrocarbon that has a double bond between two adjacent carbon atoms.

Complete answer:
-For alkenes to convert to alcohol, there must be the net addition of water across the double bond.

-By hydration of appropriate alkenes, alcohols can be synthesized. The hydrations of alkenes are too slow to behave any significance, hence acid-catalyzed hydration can fasten the synthesis of alcohol.

-The hydration of alkenes can give us an alcohol compound.

-The breaking of the pi bond in the alkene with an OH bond in water and the formation of a C-H bond and a C-OH bond results in yielding an alcohol product.
-This reaction is an exothermic reaction which yields $10-15kcal/mo{{l}^{-1}}$ energy.
-The mechanism of acid-catalyzed hydration involves the following steps-
Step1- The electrophilic addition of the proton (or acid) to the double bond forming a carbocation intermediate.

Step 2- - An addition of water afterward which results in the formation of an oxonium ion.

Step 3- Oxonium ion on deprotonation by any base as a catalyst or by another alkene molecule gives the alcohol.

-Another way of synthesis of an alcohol from alkenes can be by oxymercuration or demercuration. According to Markovnikov’s rule, the reaction of alkenes with mercuric acetate followed by the reduction gives alcohol.
$C{{H}_{2}}C{{H}_{2}}\xrightarrow[{{H}_{2}}O/NaB{{H}_{4}}]{(C{{H}_{3}}COO)Hg}C{{H}_{3}}C{{H}_{2}}OH$
-According to anti-Markovnikov’s rule, alkenes on hydroboration-oxidation in the presence of diborane and hydrogen peroxide give alcohol.
\[C{{H}_{3}}CHC{{H}_{2}}\xrightarrow[{{H}_{2}}{{O}_{2}}]{{{B}_{2}}{{H}_{6}}}C{{H}_{3}}C{{H}_{2}}C{{H}_{2}}OH\]

Note:
Protonation of the alkene gives a carbocation. The order of stability of the alkyl cations is
$3{}^\circ >2{}^\circ >1{}^\circ $.Therefore protonation occurring at less substituted carbon will create the more substituted carbocation where the water adds. The addition of a proton at the less substituted carbon and the –OH to the more substituted carbon is known as Markovnikov’s rule.