Primary and secondary alcohols are dehydrogenated by copper at 573 K to aldehydes and ketones respectively. In contrast tertiary alcohols are dehydrated to alkenes by heating with copper at 573 K. Similarly, primary alcohols are easily oxidised to form first an aldehyde and then a carboxylic acid while secondary alcohols are oxidised to ketones which are further oxidised to form a mixture of acids. Tertiary alcohols are oxidised with difficulty and with strong oxidising agents in acidic medium. They form first ketones and then acids. In the case of alcohols containing carbon-carbon double bond, some oxidising agents oxidise both double bond and OH group while other reagents donot affect C-Chond.
The reagent which oxidises `1^(@)` alcohol to aldehyde without affecting C=C double bond is

Options

A. `CrO_(3)` aqueous acetone solution
B. aqueous `K_(2)Cr_(2)O_(7)`
C. alkaline `KMnO_(4)`
D. none of these

Answer

To solve the question regarding the reagent that oxidizes a primary alcohol to an aldehyde without affecting the carbon-carbon double bond, we can follow these steps:

### Step 1: Understand the Reaction
We need to identify a reagent that can selectively oxidize a primary alcohol (1° alcohol) to an aldehyde. The reagent must be mild enough not to oxidize the carbon-carbon double bond present in the molecule.

### Step 2: Identify Suitable Reagents
Common oxidizing agents include:
- Potassium dichromate (K2Cr2O7)
- Permanganate (KMnO4)
- Jones reagent (CrO3 in aqueous acetone)

Among these, we need to determine which one is mild enough to perform the desired oxidation without affecting the C=C double bond.

### Step 3: Analyze the Reagents
1. **Jones Reagent (CrO3 in aqueous acetone)**: This is a mild oxidizing agent that can oxidize primary alcohols to aldehydes without affecting the C=C double bond.
2. **Potassium Dichromate (K2Cr2O7)**: This is a strong oxidizing agent that can oxidize both the alcohol and the double bond.
3. **Permanganate (KMnO4)**: This is also a strong oxidizing agent that can oxidize both the alcohol and the double bond.

### Step 4: Conclusion
Since Jones reagent is the only one that can oxidize a primary alcohol to an aldehyde without affecting the carbon-carbon double bond, we conclude that:

**The reagent which oxidizes 1° alcohol to aldehyde without affecting C=C double bond is Jones reagent (CrO3 in aqueous acetone).**

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