5-Bromo-2-chlorobenzoic acid
[CAS 21739-92-4]

Identification

• Classification: Chemical reagent >> Organic reagent >> Aromatic acid
• Name: 5-Bromo-2-chlorobenzoic acid
• Molecular Formula: C₇H₄BrClO₂
• Molecular Weight: 235.46
• CAS Registry Number: 21739-92-4
• EC Number: 244-558-5
• SMILES: C1=CC(=C(C=C1Br)C(=O)O)Cl

Properties

• Density: 1.8±0.1 g/cm³ Calc.^*
• Melting point: 154 - 156 °C (Expl.)
• Boiling point: 324.5±27.0 °C 760 mmHg (Calc.)^*
• Flash point: 150.1±23.7 °C (Calc.)^*
• Index of refraction: 1.621 (Calc.)^*

^* Calculated using Advanced Chemistry Development (ACD/Labs) Software.

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319-H335
• Safety Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P319-P321-P332+P317-P337+P317-P362+P364-P403+P233-P405-P501

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Skin irritation	Skin Irrit.	2	H315
Eye irritation	Eye Irrit.	2	H319
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2A	H319

Discovery and Applications

5-Bromo-2-chlorobenzoic acid is a halogenated aromatic carboxylic acid with the molecular formula C₇H₄BrClO₂. It is derived from benzoic acid and contains bromine and chlorine substituents on the aromatic ring. The compound belongs to the broader class of substituted benzoic acids, which are important intermediates in synthetic organic chemistry.

The core structural feature is the benzoic acid framework, consisting of a benzene ring bonded to a carboxylic acid group (–COOH). The carboxylic acid functionality contains a carbonyl group and a hydroxyl group attached to the same carbon atom. Through resonance, electron density is distributed between the two oxygen atoms, giving the carboxyl group its characteristic acidity and hydrogen-bonding properties. Under basic conditions, the proton can dissociate to generate a carboxylate anion.

In this molecule, chlorine occupies the 2-position of the aromatic ring relative to the carboxylic acid group, while bromine occupies the 5-position. This substitution pattern creates a chemically modified aromatic system in which both halogens influence the electronic behavior of the ring.

Chlorine and bromine are both electron-withdrawing substituents through inductive effects because of their relatively high electronegativity. At the same time, they can donate electron density weakly through resonance interactions involving lone-pair electrons. The overall influence of halogens on aromatic systems is complex, but inductive withdrawal generally dominates for many properties.

The chlorine atom at the ortho position lies adjacent to the carboxylic acid functionality and can create steric effects that influence the orientation of neighboring groups and alter intermolecular interactions. The bromine atom at the 5-position contributes substantial molecular polarizability because of its larger atomic size and more diffuse electron cloud.

The aromatic ring itself is planar and contains a delocalized π-electron system characteristic of benzene derivatives. The carboxylic acid group is typically oriented somewhat out of perfect coplanarity because of steric and electronic influences from neighboring substituents. The ortho chlorine substituent may contribute additional steric interactions that affect the preferred conformation.

From a physicochemical standpoint, 5-bromo-2-chlorobenzoic acid contains both hydrophobic and polar regions. The aromatic ring and halogen substituents contribute hydrophobic character, while the carboxylic acid group provides polarity and hydrogen-bonding capability. In the solid state, carboxylic acids frequently form hydrogen-bonded dimers through interactions between hydroxyl and carbonyl oxygen atoms.

Chemically, the carboxylic acid group represents the most reactive functionality under typical conditions. It can undergo esterification, amidation, salt formation, and other transformations commonly associated with carboxylic acids. The aromatic halogens are generally stable under ordinary conditions but can serve as useful functional handles in synthetic reactions. Carbon–bromine bonds are often more reactive than carbon–chlorine bonds in substitution and transition-metal-catalyzed coupling reactions because bromide is a better leaving group.

The aromatic ring itself can undergo electrophilic substitution reactions, although the combined effects of the carboxylic acid and halogen substituents alter both the rate and orientation of such reactions.

Overall, 5-bromo-2-chlorobenzoic acid is a substituted aromatic carboxylic acid characterized by a benzoic acid core bearing bromine and chlorine substituents. Its structure combines the acidity and hydrogen-bonding properties of a carboxylic acid with the electronic and steric influences introduced by halogen substitution, producing a chemically versatile aromatic compound.

References

2025. Bexagliflozin. Pharmaceutical Substances.
URL: https://pharmaceutical-substances.thieme.com/lexicon/KD-02-0193