Question

If 2 -butanol was treated with dichromate, what reaction would occur? (A) Reduction, resulting in the formation of butene (B) Oxidation, resulting in the formation of butanoic acid (C) Oxidation, resulting in the formation of butanone (D) No reaction would occur.

Short answer

The reaction is an oxidation, resulting in the formation of butanone. Correct answer: (C).

Step-by-step solution

Identify the nature of the reactant

2-butanol is a secondary alcohol. Secondary alcohols have the hydroxyl group (-OH) attached to a carbon atom that is connected to two other carbon atoms.

Recall the properties of dichromate

Dichromate is a common oxidizing agent. It is known to oxidize secondary alcohols to ketones.

Determine the product of oxidation

When a secondary alcohol like 2-butanol undergoes oxidation, it typically forms a ketone. In this case, the product would be butanone (methyl ethyl ketone).

Choose the correct answer

Based on the reaction of a secondary alcohol with dichromate, the correct answer is (C) Oxidation, resulting in the formation of butanone.

Key concepts

Oxidation of Alcohols

Oxidation is a fundamental reaction in organic chemistry where a molecule loses electrons. When it comes to alcohols, the oxidation process involves converting the alcohol into a different type of compound. There are three main types of alcohols: primary, secondary, and tertiary. Each type of alcohol behaves differently during oxidation.

For primary alcohols, oxidation can proceed in two stages: first to an aldehyde, and then to a carboxylic acid. Secondary alcohols are oxidized to ketones, while tertiary alcohols do not oxidize easily because they lack a hydrogen atom bonded to the carbon with the -OH group. This difference in behavior is crucial when predicting the outcome of an oxidation reaction involving alcohols.

The oxidizing agents play a significant role in these reactions. Common oxidizing agents include potassium permanganate (KMnO4) and dichromate (Cr2O7^2−). Understanding which oxidizing agent is being used can help determine the final product of the oxidation process.

Secondary Alcohols

Secondary alcohols are defined by their structure. In a secondary alcohol, the carbon atom holding the hydroxyl group (-OH) is connected to two other carbon atoms. Because of this unique bonding, secondary alcohols behave distinctly during chemical reactions compared to primary and tertiary alcohols.

When secondary alcohols undergo oxidation, they lose hydrogen atoms and form ketones. This is a key characteristic: secondary alcohols always convert into ketones upon oxidation, unlike primary alcohols, which can transform into aldehydes or carboxylic acids.

A great example is 2-butanol. In 2-butanol, the hydroxyl group is attached to the second carbon of a four-carbon chain. This carbon is connected to two other carbons, classifying it as a secondary alcohol. Understanding this classification helps predict and explain the results of reactions involving 2-butanol.

Dichromate Reactions

Dichromate ions (Cr2O7^2−) are powerful oxidizing agents frequently used in organic chemistry to oxidize alcohols. When alcohols react with dichromate, it typically causes the alcohol to lose electrons and hydrogen atoms, leading to a new type of compound.

For secondary alcohols like 2-butanol, dichromate will oxidize them into ketones. This happens because dichromate helps break bonds in the alcohol, resulting in the formation of a double-bonded oxygen atom, transforming the molecule into a ketone.

The process is straightforward: 2-butanol reacts with dichromate to form butanone (methyl ethyl ketone). This reaction is a controlled process where dichromate specifically targets the -OH group in the secondary alcohol, ensuring the desired ketone is formed. Recognizing this reaction helps understand how powerful and specific oxidizing agents like dichromate can be in organic synthesis.