Give the decreasing order of ease of decarboxylation of the following acids when reacted with soda lime.
(I) `Cl_3 C - COOH`
(II) `Br_3 C-COOH`
(III) `CH_3 COOH`
(IV) `PhCOOH`.

Options

A. `(I) gt (II) gt (III) gt (IV)`
B. `(I) gt (II) gt (IV) gt (III)`
C. `(IV) gt (III) gt (II) gt (I)`
D. `(III) gt (IV) gt (II) gt (I)`]

Answer

To determine the decreasing order of ease of decarboxylation of the given acids when reacted with soda lime, we need to analyze the effects of substituents on the carboxylic acids. The key points to consider are the electron-withdrawing effects (−I effect) and the stability of the carbanion formed during decarboxylation.

### Step-by-step Solution:

1. **Identify the Compounds**:
- (I) `Cl3C-COOH` (Trichloroacetic acid)
- (II) `Br3C-COOH` (Tribromoacetic acid)
- (III) `CH3COOH` (Acetic acid)
- (IV) `PhCOOH` (Benzoic acid)

2. **Understand Decarboxylation**:
- Decarboxylation involves the removal of CO2 from the carboxylic acid. The ease of this reaction is influenced by the stability of the carbanion formed after the loss of CO2.
- Electron-withdrawing groups (EWGs) stabilize the carbanion, making decarboxylation easier.

3. **Evaluate the Effects of Substituents**:
- **Trichloroacetic Acid (I)**: The three chlorine atoms exert a strong −I effect, significantly stabilizing the carbanion, leading to easier decarboxylation.
- **Tribromoacetic Acid (II)**: The three bromine atoms also exert a −I effect, but it is weaker than that of chlorine. Thus, it is less effective than trichloroacetic acid but still promotes decarboxylation.
- **Acetic Acid (III)**: The methyl group (−CH3) has a +I effect, which destabilizes the carbanion, making decarboxylation less favorable compared to the previous two acids.
- **Benzoic Acid (IV)**: The phenyl group (−Ph) is aromatic and has a weak −I effect. However, due to its aromatic nature, it is less favorable for decarboxylation compared to the aliphatic acids.

4. **Rank the Acids**:
- Based on the above analysis, the order of ease of decarboxylation is:
1. `Cl3C-COOH` (most favorable due to strong −I effect)
2. `Br3C-COOH` (less favorable than trichloro but still favorable)
3. `PhCOOH` (less favorable due to aromatic stabilization)
4. `CH3COOH` (least favorable due to +I effect)

5. **Final Order**:
- The final decreasing order of ease of decarboxylation is:
- (I) `Cl3C-COOH` > (II) `Br3C-COOH` > (IV) `PhCOOH` > (III) `CH3COOH`

### Answer:
The decreasing order of ease of decarboxylation is:
(I) `Cl3C-COOH` > (II) `Br3C-COOH` > (IV) `PhCOOH` > (III) `CH3COOH`