`R - CH_(2) - CH_(2) OH` can be converted into `RCH_(2) CH_(2) COOH`. The correct sequence of the reagents is

Options

A. `PBr_(3), KCN, H_(3) O^(+)`
B. `PBr_(3) KCN, H_(2)`
C. `KCN, H_(3)O^(+)`
D. `HCN , PBr_(3) H_(3) O^(+)`

Answer

To convert the alcohol `R - CH₂ - CH₂ - OH` into the carboxylic acid `R - CH₂ - CH₂ - COOH`, we can follow a specific sequence of reactions. Here’s the step-by-step solution:

### Step 1: Convert the Alcohol to Alkyl Halide
- **Reagent**: PBr₃ (Phosphorus tribromide)
- **Reaction**: The hydroxyl group (-OH) of the alcohol is converted into a bromine atom (-Br) through a substitution reaction. This results in the formation of an alkyl bromide, `R - CH₂ - CH₂ - Br`.

### Step 2: Nucleophilic Substitution with Cyanide
- **Reagent**: KCN (Potassium cyanide)
- **Reaction**: The bromine atom in the alkyl bromide is a good leaving group, allowing the cyanide ion (CN⁻) to attack the carbon atom. This results in the formation of a nitrile, `R - CH₂ - CH₂ - C≡N`.

### Step 3: Hydrolysis of the Nitrile
- **Reagent**: Water (H₂O) in acidic or basic conditions
- **Reaction**: The nitrile undergoes hydrolysis, converting the -C≡N group into a carboxylic acid (-COOH). This results in the formation of the desired product, `R - CH₂ - CH₂ - COOH`.

### Final Answer
The correct sequence of reagents is:
1. PBr₃
2. KCN
3. H₂O (for hydrolysis)