In the Cannizzaro reaction given below:
`2Ph-CHO overset(overset(Θ)OH)rarrPh-CH_(2)OH+PhCO_(2)^(-)` the slowest step is:

Options

A. The attack of `OH^(-)` at the carbonyl group
B. The transfer of hydride to the carbonyl group
C. The abstraction of proton from the carboxylic group
D. The deprotonation of `PhCH_(2)OH`

Answer

To determine the slowest step in the Cannizzaro reaction, let's break down the process step by step.

### Step 1: Understanding the Cannizzaro Reaction
The Cannizzaro reaction involves the disproportionation of aldehydes in the presence of a strong base. In this reaction, two molecules of an aldehyde (in this case, benzaldehyde) react to produce an alcohol and a carboxylate ion.

**Hint:** Recall that disproportionation reactions involve the simultaneous oxidation and reduction of the same species.

### Step 2: Mechanism Overview
In the Cannizzaro reaction, one molecule of benzaldehyde is oxidized to form a carboxylate ion (benzoate), while the other molecule is reduced to form an alcohol (benzyl alcohol). The reaction requires a strong base, which facilitates the transfer of hydride ions.

**Hint:** Focus on how the aldehyde molecules interact with the base and each other during the reaction.

### Step 3: Formation of the Anionic Intermediate
The reaction begins with the nucleophilic attack of hydroxide ion (OH⁻) on the carbonyl carbon of benzaldehyde. This forms an anionic intermediate where the oxygen carries a negative charge.

**Hint:** Identify the role of the hydroxide ion in initiating the reaction.

### Step 4: Hydride Ion Transfer
The anionic intermediate formed can act as a reducing agent. It transfers a hydride ion (H⁻) to another molecule of benzaldehyde. This step is crucial, as it involves the transfer of a hydride ion to the electrophilic carbon of the second aldehyde molecule.

**Hint:** This is a key step where the reduction occurs; think about why this step might be slow.

### Step 5: Rate Determining Step
The transfer of the hydride ion is the slowest step in the reaction mechanism and is known as the rate-determining step. This step controls the overall rate of the reaction, as it involves the breaking and forming of bonds.

**Hint:** Consider how the complexity of transferring a hydride ion affects the speed of the reaction.

### Conclusion
In summary, the slowest step in the Cannizzaro reaction is the transfer of the hydride ion from the anionic intermediate to the carbonyl carbon of another benzaldehyde molecule. This step is critical as it determines the kinetics of the entire reaction.

**Final Answer:** The slowest step in the Cannizzaro reaction is the hydride ion transfer from the anionic intermediate to the carbonyl carbon of another aldehyde.