4-Cyanobenzoic Acid: Properties, Handling & Lab Use Guide

4-Cyanobenzoic acid is a bifunctional aromatic compound bearing both a carboxylic acid and a nitrile group on a para-substituted benzene ring, making it a versatile building block in organic synthesis, medicinal chemistry, and materials science.

CAS Number

619-65-8

Molecular Formula

C₈H₅NO₂

Molecular Weight

147.13 g/mol

Appearance

White to off-white crystalline powder

Melting Point

~216–219 °C (literature)

Functional Groups

Carboxylic acid (–COOH) and nitrile (–CN)

Solubility

Sparingly soluble in water; soluble in ethanol, DMSO, and DMF

Chemical Identity and Physical Properties

4-Cyanobenzoic acid (CAS 619-65-8) is an aromatic compound with the molecular formula C₈H₅NO₂ and a molecular weight of 147.13 g/mol. Its structure features a benzene ring substituted at the para (4-) position with a carboxylic acid (–COOH) group and a nitrile (–CN) group, making it a bifunctional molecule of considerable synthetic utility.

The compound typically appears as a white to off-white crystalline solid with a reported melting point in the range of approximately 216–219 °C. It is sparingly soluble in water but dissolves readily in polar aprotic solvents such as dimethyl sulfoxide (DMSO) and dimethylformamide (DMF), and in protic solvents such as ethanol. These solubility characteristics should be taken into account when designing reaction conditions or preparing stock solutions for biological assays.

The nitrile group is electron-withdrawing, which activates the ring toward nucleophilic aromatic substitution and moderates the acidity of the carboxylic acid group relative to benzoic acid. Both functional groups are independently reactive, enabling selective derivatization under appropriate conditions.

Research Applications

4-Cyanobenzoic acid serves as a versatile intermediate in multiple areas of chemical research:

• Medicinal Chemistry and Drug Discovery: The compound is frequently employed as a building block for the synthesis of pharmaceutically relevant heterocycles, including tetrazoles, amidines, and oxazolines, which are important pharmacophores. The nitrile group can be transformed into amidines or tetrazoles via cycloaddition with azides, while the carboxylic acid can be converted to amides, esters, or acyl chlorides to introduce additional pharmacophoric elements.
• Coordination Chemistry and Metal–Organic Frameworks (MOFs): The carboxylate moiety is a well-established ligand donor for metal coordination. 4-Cyanobenzoic acid and its deprotonated form are used as linkers or modifiers in the construction of coordination polymers and MOFs, where the pendant nitrile group may participate in secondary coordination or post-synthetic modification.
• Polymer and Materials Science: The compound is used as a monomer or chain-end modifier in the synthesis of functional polymers. Its nitrile group can be hydrolyzed to amide or carboxylic acid functions, or used directly to impart dielectric properties.
• Bioconjugation and Surface Chemistry: Activated esters derived from 4-cyanobenzoic acid are used to label biomolecules such as peptides, proteins, and oligonucleotides. The nitrile group also offers a handle for further chemical modification after conjugation.

Safe Handling and Storage Guidelines

Although 4-cyanobenzoic acid is a solid reagent that presents lower acute volatility hazards than liquid nitriles, appropriate precautions must be observed in the laboratory:

• Personal Protective Equipment (PPE): Always wear chemical-resistant gloves (e.g., nitrile or neoprene), a laboratory coat, and safety goggles when handling this reagent. Avoid generating fine dust during weighing.
• Ventilation: Handle the compound in a well-ventilated area or under a fume hood. Although the solid has low vapor pressure at room temperature, dust inhalation should be minimized.
• First Aid: In case of skin or eye contact, flush immediately with copious amounts of water for at least 15 minutes and seek medical attention. If ingested or inhaled in significant quantity, seek immediate medical advice.
• Storage Conditions: Store in a tightly sealed container in a cool, dry, and well-ventilated location, away from strong oxidizers, strong bases, and reducing agents. Recommended storage temperature is 2–25 °C. Keep the container closed when not in use to prevent moisture uptake and maintain purity.
• Waste Disposal: Dispose of waste material in accordance with local, regional, and national environmental regulations. Do not pour down drains.

Consult the Safety Data Sheet (SDS) supplied by Aladdin Scientific for complete hazard information before use.

Preparation of Stock Solutions and Reaction Tips

Researchers frequently need to prepare stock solutions or set up reactions using 4-cyanobenzoic acid. The following practical guidelines help ensure reproducibility and reagent integrity:

• Solvent Selection: For aqueous biological assays requiring a co-solvent, DMSO is the preferred choice (typical stock concentration 10–100 mM). For synthetic reactions, DMF, acetonitrile, THF, or ethanol are suitable solvents depending on the downstream chemistry.
• pH Adjustment: When preparing aqueous solutions, the carboxylic acid group (pKa approximately 3.5–4.0 for electron-deficient benzoic acids) will be partially or fully deprotonated at physiological pH. Adjust pH as appropriate for the intended application.
• Activation of the Carboxylic Acid: For amide bond formation or bioconjugation, the carboxylic acid can be activated using standard coupling reagents such as EDC/NHS, DCC/DMAP, or HATU in the presence of a base (e.g., DIPEA or triethylamine) in an aprotic solvent.
• Nitrile Hydrolysis: Controlled hydrolysis of the nitrile group to an amide can be achieved under mild conditions (e.g., aqueous H₂O₂/K₂CO₃ or enzymatic conditions). Full hydrolysis to the carboxylic acid requires stronger acidic or basic aqueous conditions.
• Tetrazole Synthesis: Cycloaddition of the nitrile with sodium azide in the presence of an ammonium salt or Lewis acid catalyst (e.g., ZnBr₂) in DMF at elevated temperature yields the corresponding 5-substituted tetrazole, a common bioisostere of carboxylic acids in drug design.

Quality, Purity and Specification Considerations

For reliable experimental results, the purity and specification of 4-cyanobenzoic acid are critical parameters to verify before use:

• Typical Purity: Research-grade 4-cyanobenzoic acid from Aladdin Scientific is typically supplied at ≥98% purity as determined by HPLC or titration methods. Verify the Certificate of Analysis (CoA) for the specific lot used.
• Identity Confirmation: Identity can be confirmed by melting point determination (expected ~216–219 °C), ¹H NMR spectroscopy (characteristic aromatic doublets and absence of aldehyde or other impurity signals), and IR spectroscopy (strong nitrile stretch ~2230 cm⁻¹; broad carbonyl stretch ~1680–1700 cm⁻¹).
• Common Impurities: Potential impurities include 4-aminobenzoic acid (from partial nitrile reduction), isophthalic acid derivatives, or unreacted starting materials from synthesis. These can interfere with sensitive biological assays or asymmetric catalysis, so purity verification is advisable for critical applications.
• Moisture Sensitivity: The compound is not classified as highly moisture-sensitive but should be stored with a desiccant and resealed promptly after use to maintain declared purity over time.
• Available SKU: Aladdin Scientific supplies 4-cyanobenzoic acid under SKU C108511. Contact your regional Aladdin representative for available pack sizes, bulk quantities, and current pricing.

Frequently asked questions

What solvents are recommended for dissolving 4-cyanobenzoic acid in laboratory applications?

4-Cyanobenzoic acid is sparingly soluble in water but dissolves well in polar aprotic solvents such as DMSO and DMF, and in protic solvents such as ethanol. For biological assays, DMSO is the preferred co-solvent, typically used to prepare stock solutions at 10–100 mM before dilution into aqueous buffer. For synthetic reactions, DMF, acetonitrile, or THF are commonly employed.

How can the nitrile group of 4-cyanobenzoic acid be converted to a tetrazole?

The nitrile group can be converted to a 5-substituted 1H-tetrazole via [3+2] cycloaddition with sodium azide in the presence of an ammonium salt or a Lewis acid catalyst such as zinc bromide (ZnBr₂) in DMF at elevated temperature (typically 100–120 °C). The resulting tetrazole is widely used as a carboxylic acid bioisostere in medicinal chemistry.

What are the recommended storage conditions for 4-cyanobenzoic acid (SKU C108511)?

4-Cyanobenzoic acid should be stored in a tightly sealed container in a cool, dry, and well-ventilated area at 2–25 °C, away from strong oxidizers, strong bases, and reducing agents. A desiccant is recommended to prevent moisture uptake. Always reseal the container promptly after use to maintain purity over the shelf life of the reagent.

Can 4-cyanobenzoic acid be used directly for amide coupling reactions?

Yes. The carboxylic acid group of 4-cyanobenzoic acid can be activated using standard coupling reagents such as EDC/NHS, DCC/DMAP, or HATU in an aprotic solvent (e.g., DMF or DCM) with a non-nucleophilic base such as DIPEA or triethylamine. The activated ester intermediate then reacts with primary or secondary amines to afford the corresponding amide product. Care should be taken to avoid conditions that might concurrently hydrolyze or react with the nitrile group.

What analytical methods confirm the identity and purity of 4-cyanobenzoic acid?

Identity can be confirmed by melting point determination (expected approximately 216–219 °C), ¹H NMR spectroscopy showing characteristic para-substituted aromatic doublets, and IR spectroscopy displaying a strong nitrile stretch near 2230 cm⁻¹ and a carbonyl stretch near 1680–1700 cm⁻¹. Purity is typically assessed by HPLC with UV detection. Always verify the lot-specific Certificate of Analysis provided by Aladdin Scientific before use.

References

1. March, J. Advanced Organic Chemistry: Reactions, Mechanisms, and Structure. Wiley-Interscience. General reference for nitrile and carboxylic acid reactivity.
2. Demko, Z. P.; Sharpless, K. B. Preparation of 5-Substituted 1H-Tetrazoles from Nitriles in Water. J. Org. Chem. 2001, 66, 7945–7950. doi:10.1021/jo0107017
3. Larock, R. C. Comprehensive Organic Transformations. Wiley-VCH. General reference for functional group interconversion including nitrile hydrolysis and amide coupling.
4. Aladdin Scientific Certificate of Analysis, 4-Cyanobenzoic acid, SKU C108511. Aladdin Scientific (Shanghai) Co., Ltd.

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