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2. Dehydrohalogenation of Alkyl Halides (KOH in ethanol is required)

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-During the synthesis of complex molecules, a functional group in a molecule may interfere with an intended reaction on another functional group in the same molecule.
- An example is that a Grignard reagent can't be prepared from a halo alcohol
-This problem is solved by 'protecting' the interfering functional group.
It involves 3 steps:
1)introducing a protecting group
2)carrying out the desired reaction
3)removing the protecting group
An example is the formation of Grignard reagent:

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Reduction of Aldehydes and Ketones
-Catalytic Hydrogenation:
1.C=O bond is broken down in both Aldehyde and Ketone.
2.Alkoxide ion intermediate is formed.
3.Protonated by addition of H3O+ to give the final product.

Aldehydes give 1° alcohol.

Ketones give 2° alcohol.

-Grignard synthesis:

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1. Substitution of Alkyl Halides (A strong base such as NaOH, KOH is required.)

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-Alcohols are a special class of compounds where it can be prepared from and converted to other kinds of organic compounds.

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-A bimolecular dehydration reaction that happens when a primary alcohol is insufficiently heated.
-Only symmetrical ethers are formed

It occurs by the Sn2 reaction(nucleophilic substitution), where:

1. The oxygen atom of another alcohol displaces water from the protonated alcohol

2. A protonated ether and a water molecule are formed instead.

The figure below shows the entire reaction:

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-Elimination of H20 from molecule through an acid-catalysed reaction.
-Different classes of alcohols require different conditions

-Required Temperature for different classes of alcohols decreases with increasing substitution of the carbon bonded to the hydroxyl group:

1° alcohols: 170° - 180°C

2° alcohols: 100°– 140 °C

3° alcohols: 25°– 80°C

-Product formed is an alkene if sufficiently heated.

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Dehydration general reaction to alkenes drawing

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E1 Process For Secondary and Tertiary alcohols.

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E1 Process For Secondary and Tertiary alcohols.

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Main points:

1. O in the alcohol is protonated.

2.Unimolecular loss of H2O to generate a carbocation intermediate.

3. A proton is lost from the neighbouring C atom to complete the process.

-It follows Zaitsev's rule.

The figure below illustrates the mechanism:

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Main Steps:
1. The hydroxyl oxygen donates two electrons to a proton from sulfuric acid, forming an alkyloxonium ion.
2. The conjugate base, HSO4-,  reacts with one of the adjacent hydrogen atoms
3. At the same time, the alkyloxonium ion leaves, forming a double bond.

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McMurry, J., 2019. Organic chemistry 9th ed., United States, CA: Cengage Learning.

Vollhart, K. Peter C. and Neil Schore. Organic Chemistry, Structure and Function. 5th Ed. W. H. Freeman and Company, 2007

Anon, 2021. Types of Alcohols - Primary, Secondary & Tertiary Alcohols. BYJUS. Available at: https://byjus.com/chemistry/types-of-alcohols/ [Accessed July 24, 2021].

Anon, 2020. Dehydration Reactions of Alcohols. Available at: https://chem.libretexts.org/@go/page/45250 [Accessed July 25, 2021].

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- Alcohols are a class of organic compounds where an Alkyl Chain is bonded to a hydroxyl(-OH) group.
- Due to -OH group, Alcohols have certain physical properties:

Polar Compounds

High boiling Points(compared to other organic compounds)

Both weakly acidic and weakly basic

- There are three classes of alcohols: primary, secondary and tertiary: