(3,5-Difluoro-4-(hydroxymethyl)phenyl)boronic Acid: Lab Guide

(3,5-Difluoro-4-(hydroxymethyl)phenyl)boronic acid(Contains varying amounts of anhydride) is a fluorinated arylboronic acid reagent used in transition-metal-catalyzed cross-coupling reactions and other synthetic transformations, supplied by Aladdin Scientific as SKU P732186.

Product Name

(3,5-Difluoro-4-(hydroxymethyl)phenyl)boronic acid (Contains varying amounts of anhydride)

SKU

P732186

Functional Groups

Boronic acid (–B(OH)₂), hydroxymethyl (–CH₂OH), and two ring fluorine substituents

Anhydride Content

Contains varying amounts of boroxine (cyclic anhydride); actual boronic acid content should be determined prior to stoichiometry-sensitive applications

Primary Application

Suzuki–Miyaura cross-coupling, Chan–Lam coupling, and related organoboron transformations

Storage Recommendation

Store in a cool, dry place away from moisture; seal tightly after each use to minimise hydrolysis and anhydride formation

Chemical Identity and Structural Features

(3,5-Difluoro-4-(hydroxymethyl)phenyl)boronic acid is an arylboronic acid bearing two ortho-like fluorine atoms at the 3- and 5-positions of the phenyl ring and a hydroxymethyl (–CH₂OH) group at the 4-position. The boronic acid group (–B(OH)₂) at the 1-position provides the reactivity typical of arylboronic acids, including participation in transmetalation steps of palladium-catalyzed Suzuki–Miyaura couplings and copper-mediated Chan–Lam reactions.

The hydroxymethyl group introduces an additional handle for further functionalization, for example through esterification, oxidation to the aldehyde, or conversion to a leaving group, making this compound a versatile building block in medicinal chemistry and materials science. The two flanking fluorine atoms alter the electronic density of the aromatic ring and can influence the pKa of the boronic acid, its transmetalation rate, and the lipophilicity of downstream products.

Note on anhydride content: Arylboronic acids can partially dehydrate to form cyclic trimeric anhydrides (boroxines) during synthesis, concentration, or storage. This compound is labelled as containing varying amounts of anhydride. In practice, the boroxine and the free boronic acid are often interconvertible under reaction conditions; however, the actual boronic acid equivalent weight will differ from the molecular weight of the pure boronic acid form. Researchers performing stoichiometry-sensitive reactions should determine effective boronic acid content experimentally or use an excess corrected for the estimated anhydride fraction.

Handling, Storage, and Safety Guidelines

General handling: Use standard laboratory personal protective equipment (PPE), including chemical-resistant gloves, safety glasses, and a laboratory coat. Weigh the compound in a well-ventilated area or under a fume hood to avoid inhalation of fine particulates. Avoid contact with skin and eyes.

Moisture sensitivity: Boronic acids are susceptible to protodeboronation and additional anhydride formation upon prolonged exposure to humid air. Always work under inert atmosphere conditions (nitrogen or argon) when precise stoichiometry is required. Return unused material to the original container immediately and seal tightly.

Storage conditions: Store at room temperature (or as specified on the product label) in a cool, dry location away from direct sunlight and incompatible materials such as strong oxidisers and strong bases. Desiccant sachets inside the storage container are recommended to prolong shelf life.

Stability considerations: The presence of the hydroxymethyl group means that care should be taken to avoid strong oxidising conditions that could convert –CH₂OH to –CHO or –COOH inadvertently during storage or workup. The compound should be inspected visually before use; significant colour change or clumping may indicate degradation.

Disposal: Dispose of waste in accordance with local, regional, and national environmental regulations. Do not pour organoboron waste down the drain without appropriate treatment.

Application Protocol: Suzuki–Miyaura Cross-Coupling

The Suzuki–Miyaura reaction is one of the most common applications for arylboronic acids. The following provides general guidance; specific conditions should be optimised for each substrate pair.

1. Reagent preparation: Weigh out (3,5-Difluoro-4-(hydroxymethyl)phenyl)boronic acid (P732186) accounting for the anhydride content. If the anhydride fraction is unknown, use 1.5–2.0 equivalents relative to the electrophilic coupling partner to ensure sufficient boronic acid equivalents are present. Dissolve in an appropriate solvent (e.g., DMF, dioxane, THF, or aqueous ethanol mixtures).
2. Catalyst and base selection: Palladium catalysts such as Pd(PPh₃)₄, Pd(dppf)Cl₂, or Pd(OAc)₂ with a suitable phosphine ligand are commonly employed. Bases such as K₂CO₃, Cs₂CO₃, or K₃PO₄ in aqueous or mixed solvent systems promote transmetalation. The electron-withdrawing fluorine substituents may influence the optimal base and temperature.
3. Reaction conditions: Combine the aryl halide or pseudohalide electrophile, the boronic acid, catalyst (typically 1–5 mol%), base (2–3 equivalents), and solvent under inert atmosphere. Heat to 60–100 °C as appropriate. Monitor reaction progress by TLC or LC-MS.
4. Workup: After completion, cool the reaction mixture, dilute with ethyl acetate or another suitable solvent, wash with aqueous base and brine, dry over anhydrous MgSO₄ or Na₂SO₄, filter, and concentrate. Purify the product by column chromatography or recrystallization as required. The free –CH₂OH group in the product may necessitate careful choice of silica gel conditions to avoid streaking.

Note: These are general guidelines. Always consult the primary literature for substrate-specific optimisation.

Quantification of Effective Boronic Acid Content

Because this product contains varying amounts of cyclic boronic anhydride (boroxine), the effective molarity of boronic acid in a weighed sample can differ from that calculated using the molecular weight of the pure boronic acid. Several practical approaches are available to address this:

• ¹H NMR in DMSO-d₆ or D₂O: Integration of diagnostic aromatic or benzylic protons relative to an internal standard (e.g., 1,3,5-trimethoxybenzene) allows quantification of total aryl species. Comparison with a known standard can give the effective purity in boronic acid equivalents.
• Titration methods: Boronic acids can be quantified by potentiometric or colorimetric titration using appropriate indicators or complexing agents (e.g., mannitol complexation to shift pKa followed by base titration). Consult the analytical literature for validated protocols.
• Empirical excess strategy: For reactions tolerant of excess boronic acid, use 1.5–2.5 equivalents and optimise from there. This is the simplest approach in routine synthetic work.
• Karl Fischer / TGA: Thermogravimetric analysis (TGA) or Karl Fischer titration can estimate water content and thus provide an indirect indication of the boroxine-to-boronic acid ratio, though these methods require careful interpretation.

Document the lot-specific anhydride content in your lab notebook and in any experimental reports to ensure reproducibility across experiments and between laboratories.

Frequently asked questions

Why does this boronic acid contain anhydride, and does it affect reactivity?

Arylboronic acids readily dehydrate to form cyclic trimeric anhydrides (boroxines) under conditions of heat, reduced pressure, or low humidity during manufacture or storage. In most palladium-catalyzed coupling reactions, boroxines are competent coupling partners because they regenerate the boronic acid under aqueous basic conditions; however, for stoichiometry-sensitive applications, the effective boronic acid content should be determined or an empirical excess applied.

What are the recommended storage conditions for P732186 to minimise anhydride formation?

Store P732186 in a tightly sealed container in a cool, dry location away from moisture and direct light. Including a desiccant sachet inside the storage container and working under inert atmosphere when opening the vial will help minimise additional anhydride formation and protodeboronation over time.

Can (3,5-Difluoro-4-(hydroxymethyl)phenyl)boronic acid be used in Chan–Lam coupling reactions?

Yes, arylboronic acids including fluorinated variants are established reagents for copper-mediated Chan–Lam C–N, C–O, and C–S bond-forming reactions. The fluorine substituents and hydroxymethyl group may influence reactivity and selectivity, so reaction conditions including copper source, base, solvent, and temperature should be optimised for the specific substrate combination.

How should I account for the hydroxymethyl group during purification of coupling products?

The –CH₂OH group increases the polarity of the product and can cause streaking on standard silica gel columns. It is advisable to use a gradient elution with increasing proportions of ethyl acetate or incorporate a small percentage of methanol. Reversed-phase HPLC or recrystallisation from polar solvents may also be suitable for final purification.

Is P732186 suitable for use as a building block in medicinal chemistry?

Yes, the combination of ring fluorine atoms (which modulate lipophilicity, metabolic stability, and electronic properties) with a boronic acid coupling handle and a functionalizable hydroxymethyl group makes P732186 an attractive building block for the synthesis of fluorinated biaryls and drug-like scaffolds. The hydroxymethyl group can be further elaborated to introduce diverse functional groups.

References

1. Miyaura, N.; Suzuki, A. Palladium-Catalyzed Cross-Coupling Reactions of Organoboron Compounds. Chem. Rev. 1995, 95, 2457–2483. doi:10.1021/cr00039a007
2. Chan, D. M. T.; Monaco, K. L.; Wang, R.-P.; Winters, M. P. New N- and O-arylations with phenylboronic acids and cupric acetate. Tetrahedron Lett. 1998, 39, 2933–2936. doi:10.1016/S0040-4039(98)00503-6
3. Hall, D. G. (Ed.) Boronic Acids: Preparation and Applications in Organic Synthesis, Medicine and Materials. Wiley-VCH, 2011.
4. Lennox, A. J. J.; Lloyd-Jones, G. C. Selection of boron reagents for Suzuki–Miyaura coupling. Chem. Soc. Rev. 2014, 43, 412–443. doi:10.1039/C3CS60197H

Products are supplied for research and development use only. Not for use in humans, animals, diagnosis, or therapy.