What Is 4-Ethylphenylboronic Acid CAS 63139-21-9? Properties, Uses, and Buying Considerations

4-Ethylphenylboronic acid, identified by CAS 63139-21-9, is an aryl boronic acid used primarily as a synthetic building block in carbon–carbon bond-forming reactions. Its molecular formula is C₈H₁₁BO₂, and its calculated molecular weight is approximately 149.98 g/mol. In practical terms, I recommend viewing this material as a coupling intermediate for medicinal chemistry, pharmaceutical research, agrochemical development, and specialty organic synthesis rather than as a finished active ingredient.

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The molecule contains an ethyl-substituted aromatic ring and one boronic acid group. The boronic acid functionality can participate in Suzuki–Miyaura coupling with suitable aryl or heteroaryl halides, generally in the presence of a palladium catalyst and an appropriate base. Because performance can depend strongly on purity, moisture exposure, reaction conditions, and packaging, buyers should evaluate both the chemical identity and the supplier’s quality-control support.

Identity and Core Chemical Properties

4-Ethylphenylboronic acid is an organoboron compound derived from phenylboronic acid by introducing an ethyl group at the para, or 4-position, of the aromatic ring. The CAS number 63139-21-9 is an important identity reference for purchasing, documentation, and database matching. Buyers should still confirm the name, formula, molecular weight, structure, and analytical data together because similar aryl boronic acids can have closely related names.

The product is commonly handled as a research and synthesis chemical, but its exact physical appearance, melting behavior, and storage profile should be confirmed from the current specification and safety data sheet. I do not recommend relying on an appearance statement or a literature value alone when the material will be used in a regulated or scale-up project. Batch-specific documentation provides a more reliable basis for release and process planning.

What Does 4-Ethylphenylboronic Acid Do?

The main function of 4-ethylphenylboronic acid is to provide a transferable aryl group in cross-coupling chemistry. In a Suzuki–Miyaura reaction, the boronic acid group reacts with an aryl, heteroaryl, or vinyl halide under suitable catalytic and basic conditions to form a new carbon–carbon bond. This transformation is valuable because it allows chemists to connect two structurally different fragments in a relatively direct synthetic step.

Role in Synthetic Route Design

The para-ethyl substituent changes the electronic and steric profile of the aryl fragment compared with unsubstituted phenylboronic acid. It can be selected when a target molecule requires an ethyl-substituted aromatic ring for structure–activity studies, property optimization, or intermediate preparation. The actual effect on reaction yield and selectivity depends on the coupling partner, catalyst, solvent, base, temperature, concentration, and work-up procedure.

Like other boronic acids, this material can also serve as a building block for developing more complex aromatic compounds. However, the presence of a boronic acid group does not guarantee compatibility with every reaction sequence. I advise chemists to review functional-group tolerance and possible boronic acid degradation before committing the compound to a multi-step manufacturing route.

Application Scenarios

In medicinal chemistry, 4-ethylphenylboronic acid may be used to introduce a substituted aryl group into small-molecule libraries. Researchers can use this type of building block to prepare analogues for structure–activity relationship studies, where controlled changes to an aromatic substituent help evaluate biological response. Its suitability depends on the target structure and the development route, so it should be considered a synthesis option rather than a universal reagent.

In pharmaceutical intermediate research, the compound may be evaluated as one component of a route involving a halogenated intermediate. It can also be relevant to custom synthesis programs that require a defined aromatic fragment. For commercial development, the key questions are usually reproducibility, impurity control, supply continuity, and the ability to provide documentation for each production batch.

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Agrochemical and specialty chemical researchers may also consider this material when designing substituted aromatic intermediates. The same Suzuki coupling logic can support the preparation of molecules with different steric, electronic, or lipophilic characteristics. Before scale-up, I recommend confirming reaction conversion, impurity carryover, catalyst removal requirements, and downstream purification performance.

Material Options and Specification Considerations

Buyers may encounter different quality grades, pack sizes, and documentation packages for the same CAS number. A research-grade product may be suitable for early screening, while a development or production project may require tighter impurity controls, validated analytical methods, and more formal change-management support. The correct option depends on the intended use, batch size, regulatory environment, and process stage.

Specifications I Recommend Reviewing

• Identity: Confirm the CAS number, chemical name, molecular formula, molecular weight, and structure.
• Assay or purity: Define the minimum acceptable value for your application; for example, a project may request 98.0% or higher, but the correct limit should be agreed with the technical team.
• Related substances: Ask which organic, inorganic, or residual process impurities are monitored.
• Water and residual solvents: These may affect reaction reproducibility and should be controlled when moisture-sensitive chemistry is involved.
• Analytical evidence: Request appropriate chromatographic and spectroscopic data, such as HPLC, NMR, or other methods included in the supplier’s certificate of analysis.
• Packaging: Confirm the container type, sealing method, label information, and protection against unsuitable storage conditions.

The value of a specification is not only the number printed on the certificate; it is also the consistency of the test method and the traceability of the result. A buyer should ask whether the reported purity is area percentage, assay by another method, or a different basis. Clear terminology helps prevent an apparent specification match from becoming a technical problem during incoming inspection.

Handling and Storage Considerations

4-Ethylphenylboronic acid should be handled according to its current safety data sheet and the procedures established by the user’s laboratory or plant. Personnel should use suitable protective equipment, minimize dust generation, and work with appropriate ventilation. The SDS should be reviewed before opening the package because hazard classification, first-aid guidance, and disposal requirements must be based on the current product data.

Storage conditions should be confirmed with the supplier rather than assumed from the chemical name. Keep the container tightly closed, clearly labeled, and protected from conditions that may compromise material quality, such as excessive moisture, heat, or contamination. If the product will be stored for an extended period, I recommend defining an approved storage range and a retest policy in the purchasing specification.

How Buyers Should Select a Supplier

For a small research order, availability and appropriate analytical documentation may be the main priorities. For repeated purchasing or process development, I place greater emphasis on lot-to-lot consistency, production capacity, lead-time transparency, packaging control, and technical communication. A low unit price is not necessarily the lowest total cost if inconsistent material causes failed experiments, additional purification, or schedule delays.

Practical Supplier Evaluation Checklist

1. Confirm that the supplier can provide 4-Ethylphenylboronic acid under CAS 63139-21-9 with a clearly defined specification.
2. Request a recent certificate of analysis and representative analytical data before approving the source.
3. Ask about available pack sizes, minimum order quantity, production lead time, and stock status.
4. Clarify whether custom packaging, retesting, or additional impurity testing is available.
5. Review shipping documentation, labeling, safety information, and export requirements for the destination country.
6. Discuss a sample or qualification batch before placing a larger or recurring order.

At Maison Chemical, I support B2B buyers by organizing product identity information, specification discussions, documentation review, packaging coordination, and quotation planning for organic boronic acids. The exact supply solution should be matched to the buyer’s application, quantity, delivery schedule, and quality requirements. Where a standard specification is not sufficient, I recommend discussing the required analytical items before the order is finalized.

Key Takeaways

• 4-Ethylphenylboronic acid CAS 63139-21-9 is an aryl boronic acid used mainly as a carbon–carbon coupling building block.
• Its molecular formula is C₈H₁₁BO₂, with an approximate molecular weight of 149.98 g/mol.
• Its principal application is Suzuki–Miyaura and related synthetic chemistry, subject to suitable reaction conditions.
• Purity, water content, related substances, analytical documentation, packaging, and supply continuity should be evaluated together.
• Storage and handling decisions should follow the current SDS and the supplier’s confirmed product specification.

Conclusion: Is It the Right Material for Your Project?

4-Ethylphenylboronic acid CAS 63139-21-9 is a practical choice when a synthesis requires a para-ethyl-substituted aryl fragment that can participate in boronic acid coupling chemistry. It is most relevant to research, pharmaceutical, agrochemical, and specialty chemical programs where aromatic carbon–carbon bond formation is part of the route. Its final suitability should be confirmed through reaction screening and an agreed quality specification.

My recommended next step is to define the required quantity, purity target, analytical documentation, packaging, and delivery schedule before requesting a quotation. Maison Chemical can help review these requirements and coordinate a suitable supply plan for your project. Send us your target specification and purchasing timeline so we can prepare a focused B2B quotation and technical response.

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