2-Chloro-4-methylbenzoic acid
[CAS# 7697-25-8]

Identification

• Classification: Chemical reagent >> Organic reagent >> Aromatic acid
• Name: 2-Chloro-4-methylbenzoic acid
• Molecular Formula: C₈H₇ClO₂
• Molecular Weight: 170.59
• CAS Registry Number: 7697-25-8
• EC Number: 630-125-1
• SMILES: CC1=CC(=C(C=C1)C(=O)O)Cl

Properties

• Density: 1.3±0.1 g/cm³ Calc.^*
• Melting point: 155 - 157 ºC (Expl.)
• Boiling point: 303.5±22.0 ºC 760 mmHg (Calc.)^*
• Flash point: 137.4±22.3 ºC (Calc.)^*
• Index of refraction: 1.573 (Calc.)^*

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

Safety Data

• Hazard Symbols: GHS05;GHS07 Danger
• Hazard Statements: H315-H318-H319-H335
• Precautionary Statements: P261-P264-P264+P265-P271-P280-P302+P352-P304+P340-P305+P351+P338-P305+P354+P338-P317-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
Specific target organ toxicity - single exposure	STOT SE	3	H335
Eye irritation	Eye Irrit.	2	H319
Serious eye damage	Eye Dam.	1	H318

Discovory and Applicatios

2-Chloro-4-methylbenzoic acid is an aromatic monocarboxylic acid bearing a chlorine substituent at the ortho (2-) position and a methyl group at the para (4-) position relative to the carboxyl function. Its molecular formula is C₈H₇ClO₂ and it appears in chemical databases with a CAS registry number (e.g., 2735755 in PubChem). It is typically described as a white to off-white solid with moderate solubility in organic solvents.

The compound arises as an intermediate in aromatic substitution chemistry and in the manufacture of fine-chemicals. The direct discovery of this specific isomer is not well chronicled in early literature; rather, it emerges from systematic studies of chlorinated toluic and benzoic acid derivatives. Historically, benzoic acid derivatives were oxidised from methylbenzenes (such as toluene and its substituted analogues), and subsequent halogenation or methylation yielded substituted benzoic acids such as 2-chloro-4-methylbenzoic acid. For instance, the oxidation of o-methyl chlorotoluene derivatives, or chlorination of methylbenzoic acid derivatives, would lead to this compound. Its presence in databases and supplier catalogues confirms that it is commercially available as a synthetic intermediate.

In terms of application, 2-chloro-4-methylbenzoic acid serves primarily as a building block or intermediate in organic synthesis rather than as a final consumer product. Through its carboxyl function it can be converted to acid chlorides, esters, or amides; via the chlorine and methyl substituents it offers selective reactivity for further functionalisation. For example, the chloro substituent can participate in nucleophilic substitution or cross-coupling reactions, enabling the synthesis of more complex molecules such as agrochemical agents, pharmaceutical intermediates, or dye precursors. Some supplier information highlights its utility in specialty polymers and materials where substituted benzoic acid moieties are incorporated for tuneable properties (although peer-reviewed literature specifically about polymers derived from this compound is sparse).

From a practical standpoint, the presence of both the methyl and chloro groups impacts the physical and chemical behavior of the molecule. The methyl group contributes to hydrophobic character and electron-donating influence, while the chlorine is electron-withdrawing and can enable further reaction. The carboxylic acid group makes the compound reactive under typical carboxylic acid chemistry—such as dehydration to form anhydrides, formation of esters or amides, or metal salt formation. In synthetic workflows, it is often employed where a para-methyl substituent and an ortho-chlorine are needed to control steric and electronic parameters in subsequent transformations.

Safety and handling information indicate that like many aromatic carboxylic acids, 2-chloro-4-methylbenzoic acid should be handled with standard organic chemistry precautions: avoiding inhalation of dust, using gloves and eye protection, and storing in a cool, dry area away from strong oxidisers. There is limited publicly available toxicological data specific to this compound, implying that standard laboratory safety practices should apply.

In summary, 2-chloro-4-methylbenzoic acid is a chemically versatile intermediate discovered through the broader historical development of substituted benzoic acids and benzoic acid derivatives. Its key value lies in its dual substituents (chloro and methyl) plus a carboxylic acid function, enabling downstream transformations in fine chemical and materials synthesis. While not typically an end product, its role in synthetic chains makes it a valuable component in the manufacture of advanced chemical products.

References

2023. Synthesis, Crystal Structure, and DFT Study of 2-Chloro-N-cyclopropyl-4-methyl-5-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzamide. Russian Journal of General Chemistry, 93(4).
DOI: 10.1134/s1070363223040230

2015. A new and improved process for C-aryl glucoside SGLT2 inhibitors. Monatshefte f�r Chemie - Chemical Monthly.
DOI: 10.1007/s00706-015-1458-z