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Preparation of Alcohols and Phenols

Alcohols can be prepared by hydration of alkenes and reduction of aldehydes or ketones, while phenol is industrially prepared by the cumene process.

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Student-friendly explanation

In acid-catalysed hydration, water adds across a carbon-carbon double bond to form an alcohol, usually following Markovnikov orientation for unsymmetrical alkenes. Aldehydes reduce to primary alcohols and ketones reduce to secondary alcohols using reducing agents such as sodium borohydride or lithium aluminium hydride. In the cumene process, benzene is converted into cumene, which forms cumene hydroperoxide on oxidation and gives phenol along with acetone on acidic cleavage.

How to write this in exams

  1. 1

    Start with the exact idea

    Alcohols can be prepared by hydration of alkenes and reduction of aldehydes or ketones, while phenol is industrially prepared by the cumene process.

  2. 2

    Then show how to use it

    Look for the functional group in the reactant, choose addition or reduction, apply orientation if an unsymmetrical alkene is present, then check whether the product class matches the starting material.

  3. 3

    Add one concrete example

    Ethene gives ethanol on acid-catalysed hydration. Propanone gives propan-2-ol on reduction.

  4. 4

    Avoid this incomplete answer

    Writing propan-1-ol from normal acid hydration of propene is usually wrong because Markovnikov addition gives propan-2-ol.

Definition

Alcohols can be prepared by hydration of alkenes and reduction of aldehydes or ketones, while phenol is industrially prepared by the cumene process.

Example

Ethene gives ethanol on acid-catalysed hydration. Propanone gives propan-2-ol on reduction.

Rule to remember

Reaction patterns: alkene + H2O/H+ gives alcohol; RCHO + reducing agent gives RCH2OH; R2CO + reducing agent gives R2CHOH; cumene oxidation followed by acid cleavage gives phenol and acetone.

Memory hook

Alkene adds water; carbonyl gains hydrogen; cumene gives phenol.

Examples and method

Worked example

Prepare propan-2-ol from propene. Use acid-catalysed hydration; H and OH add across the double bond, and OH attaches to the more substituted carbon, giving CH3CHOHCH3.

Method to apply

Look for the functional group in the reactant, choose addition or reduction, apply orientation if an unsymmetrical alkene is present, then check whether the product class matches the starting material.

Diagram support

A reaction-flow diagram for the cumene process can help connect cumene, cumene hydroperoxide, phenol and acetone.

How CBSE asks it

It is commonly asked as product prediction, conversion, reagent selection, or a short note on the cumene process.

Avoid common mistakes

Common confusion

A frequent error is writing a tertiary alcohol as the product of ketone reduction; simple ketones reduce to secondary alcohols.

Common wrong answer

Writing propan-1-ol from normal acid hydration of propene is usually wrong because Markovnikov addition gives propan-2-ol.

Exam tip

In preparation questions, identify the starting functional group first: alkene suggests addition of water, aldehyde or ketone suggests reduction, and cumene points to phenol.

Quick check

What alcohol is obtained by reduction of ethanal?

Ethanol, because aldehydes reduce to primary alcohols.

Answer writing and exam use

1-mark answer

Alcohols can be prepared by hydration of alkenes and reduction of aldehydes or ketones, while phenol is industrially prepared by the cumene process.

2-mark answer

Alcohols can be prepared by hydration of alkenes and reduction of aldehydes or ketones, while phenol is industrially prepared by the cumene process. Reaction patterns: alkene + H2O/H+ gives alcohol; RCHO + reducing agent gives RCH2OH; R2CO + reducing agent gives R2CHOH; cumene oxidation followed by acid cleavage gives phenol and acetone. Ethene gives ethanol on acid-catalysed hydration. Propanone gives propan-2-ol on reduction.

3-mark answer

In acid-catalysed hydration, water adds across a carbon-carbon double bond to form an alcohol, usually following Markovnikov orientation for unsymmetrical alkenes. Aldehydes reduce to primary alcohols and ketones reduce to secondary alcohols using reducing agents such as sodium borohydride or lithium aluminium hydride. In the cumene process, benzene is converted into cumene, which forms cumene hydroperoxide on oxidation and gives phenol along with acetone on acidic cleavage. Reaction patterns: alkene + H2O/H+ gives alcohol; RCHO + reducing agent gives RCH2OH; R2CO + reducing agent gives R2CHOH; cumene oxidation followed by acid cleavage gives phenol and acetone. Prepare propan-2-ol from propene. Use acid-catalysed hydration; H and OH add across the double bond, and OH attaches to the more substituted carbon, giving CH3CHOHCH3. It is commonly asked as product prediction, conversion, reagent selection, or a short note on the cumene process. Writing propan-1-ol from normal acid hydration of propene is usually wrong because Markovnikov addition gives propan-2-ol.
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