In Cannizzaro's reaction
`2PhCHOoverset(OH^(-))toPhCH_(2)OH+PhCOO^(-)`
The rate determining step is

Options

A. Proton abstraction from carboxylic group
B. Attack of `OH^(-)` on carbonyl carbon
C. Transfer of hydride to carbonyl group
D. None of these

Answer

To determine the rate-determining step (RDS) in Cannizzaro's reaction, let's break down the process step by step.

### Step 1: Understanding the Reaction
Cannizzaro's reaction involves the disproportionation of aldehydes that do not have alpha hydrogens in the presence of a strong base (OH⁻). In this case, we are dealing with benzaldehyde (PhCHO).

### Step 2: Initial Attack by Hydroxide Ion
The hydroxide ion (OH⁻) acts as a nucleophile and attacks the carbonyl carbon of benzaldehyde. This leads to the formation of a tetrahedral intermediate. The oxygen atom of the carbonyl group becomes negatively charged, and the carbon atom becomes positively charged due to the nucleophilic attack.

### Step 3: Formation of the Tetrahedral Intermediate
The tetrahedral intermediate can be represented as:
- PhC(OH)(O⁻) (where O⁻ is the negatively charged oxygen from the hydroxide ion).

### Step 4: Hydride Transfer
The crucial step in Cannizzaro's reaction is the transfer of a hydride ion (H⁻) from the tetrahedral intermediate to another molecule of benzaldehyde. This step is slow and is considered the rate-determining step (RDS) of the reaction.

### Step 5: Formation of Products
After the hydride transfer, one molecule of benzaldehyde is reduced to benzyl alcohol (PhCH₂OH), while the other molecule is oxidized to benzoate ion (PhCOO⁻). The overall reaction can be summarized as:
\[ 2 \text{PhCHO} + \text{OH}^- \rightarrow \text{PhCH}_2\text{OH} + \text{PhCOO}^- \]

### Conclusion
The rate-determining step in Cannizzaro's reaction is the hydride transfer from the tetrahedral intermediate to another molecule of benzaldehyde.

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