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Alcohols: Synthesis and Chemical Reactions

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Alcohols: Synthesis and Chemical Reactions

Alcohols are a class of organic compounds characterized by the presence of a hydroxyl $(- OH)$ group attached to a carbon atom. This functional group imparts distinctive chemical and physical properties to alcohols, making them a versatile group of compounds with a wide range of applications.

Alcohols can be classified based on the number of carbon atoms attached to the carbon bearing the hydroxyl group. The simplest alcohol is methanol $({CH}_{3} OH)$ , followed by ethanol $(C_{2} H_{5} OH)$ , which is the type of alcohol found in alcoholic beverages. As the carbon chain lengthens, we encounter a variety of alcohols, each with unique properties and uses.

The general formula for simple acyclic alcohol is ‌ $C_{n} H_{2 n} OH$ , where ‌ $n = 1, 2, 3 .. .$ .

The saturated carbon chain is often designated by the symbol $R$ , so that $R - OH$ can represent alcohol in the homologous series.

Question:

Select the classification of alcohol based upon Hydroxyl Group.

Monohydric Alcohols Trihydric Alcohols Dihydric Alcohols

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Write the IUPAC name of the compounds from their structure:

The IUPAC Name is

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SYNTHESIS OF PREPARATION OF ALCOHOL: Grignard Reaction

Grignard Reaction:

The Grignard reaction is a powerful method for forming carbon-carbon bonds and is widely used in organic synthesis. It involves the reaction of an alkyl or aryl halide with magnesium to form an organomagnesium compound, commonly known as a Grignard reagent. This reagent can then react with a carbonyl compound (aldehyde or ketone) to produce an alcohol.

Here's a step-by-step explanation of the synthesis by Grignard reaction with mechanisms:

1. Formation of the Grignard Reagent

Reagents: Alkyl or aryl halide (e.g., $R - X$ where $X = Cl, Br, I$ ), magnesium ( $Mg$ ), and ether solvent (e.g., diethyl ether).

Mechanism:

Step a. Initiation: Magnesium undergoes a single electron transfer with the alkyl or aryl halide. This results in the formation of a radical intermediate and a magnesium cation.

$R - X + Mg \to R \cdot + MgX$

Question:

What is the purpose of using an ether solvent in the formation of a Grignard reagent

		It stabilizes the Grignard reagent
		It prevents the precipitation of insoluble salts
		It enhances the nucleophilicity of the Grignard reagent
		All of the above

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Step b. Propagation:

The radical reacts with another alkyl or aryl halide molecule, forming an organomagnesium compound (Grignard reagent) and regenerating the magnesium cation.

$R \cdot + R - X \to R - R + X \cdot$

$R - R + MgX + \to R - Mg - X$

Step c. Coordination with Ether:

Ether molecules coordinate with the magnesium cations, solvating them and preventing their precipitation as insoluble salts.

$Mg (X) + + 2 (ether) \to {[MgX {(ether)}_{2}]}^{+}$

Question:

During the initiation step, magnesium undergoes a single electron transfer with the alkyl or aryl halide, forming a intermediate and a magnesium cation.

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2. Reaction with Carbonyl Compound

Reagents: Carbonyl compound (aldehyde or ketone, denoted as $R_{2} C = O$ ).

Mechanism:

Step a. Nucleophilic Attack:

The Grignard reagent $(R - Mg - X)$ acts as a strong nucleophile, attacking the electrophilic carbon of the carbonyl group.

$RMgX + R_{2} C = O \to R_{3} COMgX$

Question:

The Grignard reagent acts as a nucleophile and attacks the electrophilic carbon of the carbonyl group.

		True
		False

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Step b. Acid-Base Reaction:

The resulting alkoxide ion $(R_{3} {CO}^{-})$ is protonated by water, which is present in the reaction mixture.

$R_{3} COMgX + H_{2} O \to R_{3} CH + MgXOH$

Question:

Match the following species with their corresponding roles in the reaction.

Grignard reagent

Alkoxide ion

Protonated product

1.		Result of acid-base reaction with water
2.		Formed after the nucleophilic attack on the carbonyl group
3.		Acts as a strong nucleophile

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3. Work-Up

The reaction mixture is usually quenched with a dilute acid, such as hydrochloric acid (HCl), to neutralize the alkoxide ion and protonate the product.

Question:

The reaction mixture is usually quenched with a base dilute acid HCL acid salt to neutralize the alkoxide ion and protonate the product.

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