Pyridinium chloro chromate (PCC) oxidises an alcohol group selectively in the presence of carbon-carbon double bond.

Pent-3-en-2-ol to Pent-3-in-2-one Conversion

To convert pent-3-en-2-ol into pent-3-in-2-one, the best reagent is Pyridinium chloro-chromate (PCC). PCC is a mild oxidizing agent that selectively oxidizes alcohols to aldehydes or ketones without further oxidation to carboxylic acids. It is commonly used in organic synthesis for this purpose.

Reaction Mechanism:
The conversion of pent-3-en-2-ol to pent-3-in-2-one involves an oxidation reaction. The double bond in the alcohol is oxidized to a ketone, resulting in the formation of pent-3-in-2-one.

The reaction mechanism can be summarized as follows:
1. The PCC reagent reacts with the alcohol to form a chromate ester intermediate.
2. The chromate ester intermediate undergoes a rearrangement, resulting in the formation of a ketone.
3. The chromate ester is reduced back to PCC, completing the catalytic cycle.

Advantages of PCC:
PCC is preferred for this conversion due to several advantages:
1. Mild oxidizing agent: PCC is a mild oxidizing agent, which ensures selective oxidation of the alcohol without over-oxidation to a carboxylic acid.
2. High selectivity: PCC selectively converts alcohols to aldehydes or ketones, making it suitable for this specific transformation.
3. Compatible with other functional groups: PCC is compatible with a wide range of functional groups, making it useful in complex organic synthesis.
4. Ease of use: PCC is commercially available and easy to handle, making it a convenient reagent for organic chemists.

Alternative Reagents:
While PCC is the best reagent for this specific transformation, other reagents can also be used to convert pent-3-en-2-ol to pent-3-in-2-one, including:
- Chromic anhydride in glacial acetic acid: This reagent combination can also oxidize alcohols to aldehydes or ketones, but it is more aggressive and can lead to over-oxidation in some cases.
- Acidic dichromate: Acidic dichromate can oxidize alcohols to aldehydes or ketones, but it is less selective and can result in further oxidation to carboxylic acids.
- Acidic permanganate: Acidic permanganate is a strong oxidizing agent that can convert alcohols to carboxylic acids. However, it is not suitable for selectively converting alcohols to ketones.

In conclusion, Pyridinium chloro-chromate (PCC) is the best reagent to convert pent-3-en-2-ol into pent-3-in-2-one due to its mild and selective oxidation properties.

As we know that,in this question option b is the correct answer. Because other reagent will affect the c=c bond so chromic anhydride in glacial acetic acid is the best reagent