Question

A better reagent to oxidize primary alcohols into aldehyde is :

• A. PCC
• B. Alkaline KMnO₄
• C. Acidified K₂Cr₂O₇
• D. CrO₃

Answer 1

The Correct Option is A

The oxidation of primary alcohols to aldehydes requires a reagent that selectively oxidizes the alcohol without further oxidizing the aldehyde to a carboxylic acid.

PCC (Pyridinium chlorochromate) is a better reagent for this purpose because it efficiently oxidizes primary alcohols to aldehydes without over-oxidation to carboxylic acids. This makes PCC particularly useful in synthetic organic chemistry.

Other oxidizing agents, such as potassium permanganate (KMnO₄) or chromic acid (H₂CrO₄), tend to further oxidize aldehydes to carboxylic acids. Therefore, PCC is preferred for selective oxidation of primary alcohols to aldehydes.

Conclusion: The better reagent to oxidize primary alcohols to aldehydes is PCC (Pyridinium chlorochromate).

Answer 2

Primary alcohols are typically oxidized to aldehydes. However, the challenge is to prevent further oxidation of the aldehyde to a carboxylic acid. Let's examine each reagent:

PCC (Pyridinium chlorochromate):
 PCC is a mild oxidizing agent that is highly selective for the oxidation of primary alcohols to aldehydes. The advantage of PCC over other reagents is that it does not over-oxidize the aldehyde to a carboxylic acid, as it functions under milder conditions. It is typically used in non-aqueous solvents such as dichloromethane, and its use results in the selective formation of aldehydes from primary alcohols.

Alkaline KMnO$_4$ (Potassium permanganate): 
 Alkaline KMnO$_4$ is a very strong oxidizing agent that can oxidize a variety of organic compounds, including alcohols, alkenes, and aromatic compounds. While it can oxidize primary alcohols to aldehydes, it is highly reactive and will continue to oxidize the aldehyde to a carboxylic acid. Therefore, it is not selective for aldehyde formation and would not be preferred for this purpose.

Acidified K$_2$Cr$_2$O$_7$ (Potassium dichromate):  
 Acidified K$_2$Cr$_2$O$_7$ is another strong oxidizing agent that can oxidize primary alcohols to carboxylic acids. While it can oxidize primary alcohols to aldehydes, it does so through a very strong oxidation process that will often result in further oxidation of the aldehyde to a carboxylic acid. Thus, it is not suitable for selective oxidation to aldehydes.

CrO$_3$ (Chromium trioxide):  
 Chromium trioxide, or Jones reagent, is another strong oxidizing agent that can oxidize primary alcohols to aldehydes but also continues oxidizing the aldehyde to a carboxylic acid. Like acidified K$_2$Cr$_2$O$_7$, it is not selective for aldehyde formation and will cause over-oxidation.

Thus, PCC is the best reagent for selectively oxidizing primary alcohols to aldehydes without further oxidation to carboxylic acids.

The key advantage of PCC is its ability to oxidize primary alcohols to aldehydes without over-oxidizing them to carboxylic acids, making it the reagent of choice for this reaction.