Which of the following is not the mechanism of Cannizzaro reaction when the concentration of base is very high ?
`2HCHO overset("High conc.")underset("of base")rarr HCOO^(Θ)+CH_(3)O^(Θ)`

Options

A. The attack of `overset(Θ)(OH)` at the `(C=O)` group.
B. Removal of `H^(o+)` ion by the `O^(Θ)H` ion form `(underset(OH)underset(|)CH_(2)-O^(Θ))`.
C. The transfer of `H^(Θ)` ion to the `(C=O)` group of another `HCHO`.
D. The abstraction of proton from the carboxylic acid.

Answer

To determine which of the following is not a mechanism of the Cannizzaro reaction when the concentration of base is very high, we first need to understand the Cannizzaro reaction itself. The Cannizzaro reaction occurs with aldehydes that do not have alpha hydrogens in the presence of a strong base. In this reaction, one molecule of the aldehyde is oxidized to a carboxylic acid, while another molecule is reduced to an alcohol.

### Step-by-Step Solution:

1. **Understanding the Cannizzaro Reaction**:
- The Cannizzaro reaction involves aldehydes without alpha hydrogens reacting in the presence of a strong base.
- In this case, we are considering formaldehyde (HCHO).

2. **Formation of the Intermediate**:
- When formaldehyde is treated with a strong base, the oxygen atom of the aldehyde can accept a proton from the hydroxide ion (OH⁻), leading to the formation of an alkoxide intermediate (HCOO⁻).

3. **Hydride Transfer**:
- In the Cannizzaro reaction, one molecule of the aldehyde gets oxidized while another gets reduced.
- The hydride ion (H⁻) from the alkoxide intermediate can transfer to another molecule of formaldehyde, resulting in the formation of methanol (CH₃OH) and formate ion (HCOO⁻).

4. **High Concentration of Base**:
- When the concentration of base is very high, the reaction mechanism is slightly altered.
- The high concentration of hydroxide ions leads to the removal of protons from the alkoxide intermediate, preventing the abstraction of protons from the carboxylic acid formed.

5. **Identifying the Incorrect Mechanism**:
- The options provided likely include various steps of the reaction mechanism.
- The statement that suggests the abstraction of a proton from the carboxylic acid is incorrect because, in high concentrations of base, the hydroxide ions have already removed the acidic protons, making it impossible to abstract further protons from the carboxylic acid.

### Conclusion:
The mechanism that is not part of the Cannizzaro reaction when the concentration of base is very high is the abstraction of a proton from the carboxylic acid.

### Final Answer:
The incorrect mechanism is **the abstraction of a proton from the carboxylic acid**.

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