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

Options

A. tge 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 of benzaldehyde, we can break down the process step by step.

### Step 1: Understand the Cannizzaro Reaction
The Cannizzaro reaction occurs with aldehydes that do not have alpha hydrogens. In this case, benzaldehyde (Ph-CHO) undergoes a reaction in the presence of hydroxide ions (OH⁻) to produce benzyl alcohol (Ph-CH₂OH) and benzoate ion (PhCO₂⁻).

**Hint:** Identify the key characteristics of the Cannizzaro reaction, specifically the absence of alpha hydrogens in the aldehyde.

### Step 2: Nucleophilic Attack
In the first step, the hydroxide ion acts as a nucleophile and attacks the electrophilic carbon of the carbonyl group (C=O) in benzaldehyde. This leads to the formation of a tetrahedral intermediate.

**Hint:** Remember that nucleophiles attack electrophiles, and the carbonyl carbon is electrophilic due to the partial positive charge.

### Step 3: Formation of Tetrahedral Intermediate
The nucleophilic attack results in a tetrahedral intermediate. This intermediate can either revert back to the starting materials or proceed to the next step.

**Hint:** Consider the stability of the tetrahedral intermediate and what factors might influence its conversion to products.

### Step 4: Hydride Transfer
The next step involves the transfer of a hydride ion (H⁻) from the tetrahedral intermediate to another molecule of benzaldehyde. This step is crucial because it involves bond breaking and formation, making it energetically demanding.

**Hint:** Focus on the significance of the hydride transfer and why it might be a slow step in the reaction mechanism.

### Step 5: Proton Transfer and Product Formation
After the hydride transfer, the tetrahedral intermediate collapses, leading to the formation of benzyl alcohol and benzoate ion. The proton from the hydroxyl group of the intermediate is transferred to complete the reaction.

**Hint:** Recognize that proton transfers are generally fast compared to bond-breaking steps.

### Conclusion: Identify the Slowest Step
Among the steps outlined, the hydride transfer is the slowest step in the Cannizzaro reaction. This is because it involves the breaking of a C-H bond and the formation of a new bond, which requires more energy and is less favorable than the other steps.

**Final Answer:** The slowest step in the Cannizzaro reaction is the transfer of hydride to the carbonyl group.