Do hvz chlorination follow the same mechanism of hvz bromination ?

No, HVZ chlorination does not follow the exact same mechanism as HVZ bromination. Let's analyze the mechanisms in detail.

Hell-Volhard-Zelinsky (HVZ) Reaction:
The HVZ reaction is used for the α-halogenation of carboxylic acids. It involves the substitution of a hydrogen atom at the α-position with a halogen (Cl, Br, or I) in the presence of a halogen and a catalyst (usually phosphorus-based, such as PCl₃, PBr₃, or red phosphorus).

Mechanism of HVZ Bromination:
Formation of Enol or Enolate Intermediate:

The carboxylic acid first reacts with phosphorus tribromide (PBr₃) or elemental phosphorus and bromine (Br₂) to form an acyl bromide.
The acyl bromide undergoes tautomerization to form an enol.
Electrophilic Halogenation:

The enol reacts with bromine (Br₂), leading to the formation of an α-bromo acyl bromide.
Hydrolysis:

Upon hydrolysis, the α-bromo acyl bromide converts back to the α-bromo carboxylic acid.
Mechanism of HVZ Chlorination:
Formation of Enol or Enolate Intermediate:

Similar to bromination, the carboxylic acid reacts with phosphorus trichloride (PCl₃) or phosphorus and chlorine (Cl₂) to form an acyl chloride.
The acyl chloride tautomerizes to its enol form.
Electrophilic Halogenation:

The enol reacts with chlorine (Cl₂), leading to the formation of an α-chloro acyl chloride.
Hydrolysis:

The α-chloro acyl chloride undergoes hydrolysis, yielding the α-chloro carboxylic acid.
Differences Between HVZ Chlorination and Bromination:
Reactivity of Halogens:

Chlorine (Cl₂) is more reactive and less selective than bromine (Br₂). This can lead to multiple chlorination products if conditions are not controlled properly.
Bromine (Br₂) is more selective, favoring monobromination at the α-position.
Reaction Conditions:

HVZ bromination typically proceeds more smoothly due to the better leaving ability of bromine.
HVZ chlorination may require stricter control of reaction conditions to avoid excessive chlorination.
Intermediate Stability:

The α-chloro intermediates are generally less stable than α-bromo intermediates due to the stronger C-Cl bond compared to the C-Br bond.
Conclusion:
While both HVZ chlorination and bromination follow a similar general mechanism (via enol formation, halogenation, and hydrolysis), chlorination is less selective and may lead to over-chlorination. Additionally, the stability of intermediates and reaction conditions differ slightly.