| HS Code | 973409 |
| Product Name | Boron Methoxide |
| Chemical Formula | C3H9BO3 |
| Cas Number | 121-43-7 |
| Molecular Weight | 119.91 g/mol |
| Appearance | Colorless liquid |
| Odor | Sweet, aromatic |
| Density | 0.915 g/cm3 at 25 °C |
| Melting Point | -34 °C |
| Boiling Point | 68-69 °C |
| Flash Point | 8 °C |
| Vapor Pressure | 121 mmHg at 20 °C |
| Solubility | Decomposes in water; soluble in organic solvents |
| Refractive Index | 1.358 (n20/D) |
| Autoignition Temperature | 340 °C |
As an accredited Boron Methoxide factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Boron Methoxide supplied in 500 mL amber glass bottles, nitrogen-purged, with PTFE-lined caps, sealed and labeled as moisture-sensitive/flammable. |
| Container Loading (20′ FCL) | Load Boron Methoxide in 20′ FCL: moisture-sensitive, flammable liquid; use sealed drums, secure stowage, ventilated dry container, proper hazardous labels. |
| Shipping | Boron Methoxide (trimethyl borate) is shipped as UN2416, Trimethyl Borate, Hazard Class 3 Flammable Liquid, Packing Group II. Use approved sealed containers, keep cool, dry, away from ignition sources, oxidizers, acids, and moisture. Label flammable liquid; include SDS, shipping papers, and emergency response information. Handle with PPE and avoid contact. |
| Storage | Store Boron Methoxide (trimethyl borate) in a cool, dry, well-ventilated flammable-liquid cabinet, away from heat, sparks, flames, oxidizers, acids, and moisture. Keep containers tightly closed, preferably under inert gas, because it hydrolyzes with water. Use grounded, compatible containers with secondary containment and clear hazard labeling. |
| Shelf Life | Boron methoxide shelf life is typically two years if kept sealed, dry, cool, and moisture-free; hydrolysis can degrade it. |
Pharmaceutical routes that require arylboronic acid building blocks for palladium-catalysed coupling commonly use boron methoxide (trimethyl borate, CAS 121-43-7) as the boron electrophile for arylmagnesium halide quench reactions. In plant-scale operation the solvent is 2-methyltetrahydrofuran dried to <10 mg/kg water, the reactor is inerted with nitrogen until oxygen is <0.5 vol%, and boron methoxide is charged at 1.1–1.5 molar equivalents relative to the Grignard species to compensate for trace hydrolysis and ester cleavage. The Grignard feed is dosed at −25 °C to −10 °C over 6–8 h under jacket brine cooling; the resulting aryl dimethoxyborate intermediate is hydrolysed with 10–15 wt% sulfuric acid while the batch is maintained below 5 °C, which limits protodeboronation of electron-rich arylboronic acids. The crude product is extracted into methyl tert-butyl ether, washed with brine, crystallised from heptane/water, and isolated by bottom-discharge centrifuge. This route is used where downstream crystallisation requires a boron source that leaves methanol as the principal hydrolytic residue rather than higher alcohols.
Residual methanol from the methoxide ligands is managed under ICH Q3C; methanol is a Class 2 solvent with a PDE of 30 mg/day and a concentration limit of 3,000 ppm in single-solvent cases, making late-stage vacuum drying below 50 mbar at 40–50 °C a standard release condition. Manufacturers supplying registered intermediates operate under ICH Q7 and validate cleaning for boron and palladium in accordance with ICH Q3D; residual solvents are tested by headspace GC against USP <467>, and elemental impurities are measured by ICP-MS using matrix-matched calibration. Terminal product types include free arylboronic acids, pinacol esters, and potassium trifluoroborate salts that enter downstream routes to sartan antihypertensives, oncology kinase inhibitors, and peptide boronic acid proteasome inhibitors.
Production of sodium borohydride from boron methoxide follows the stoichiometry 4 NaH + B(OCH3)3 → NaBH4 + 3 NaOCH3, requiring exactly 4.0 mol sodium hydride per 1.0 mol boron methoxide; in practice sodium hydride is maintained at 2–5 mol% excess to compensate for surface oxidation and unreacted oil-wet hydride. The reaction is run as a mineral-oil slurry in a stirred high-pressure reactor with gas-tight mechanical seals, because protic impurities in boron methoxide, particularly water above 0.05 wt% and methanol above 0.1 wt%, release hydrogen when contacting sodium hydride and reduce yield by consuming NaH before the borate ester is added. The batch is heated to 250–275 °C under nitrogen; at this temperature the slurry remains stirrable only with high-torque helical agitation, and the reactor is designed for rapid external cooling because the reaction is highly exothermic once initiated.
After the reaction mass is cooled below 80 °C, sodium borohydride is separated from sodium methoxide by solvent extraction and the product is dried under vacuum to a free-flowing powder with assay above 98% by iodometric titration. Process safety management for sodium hydride falls under OSHA 29 CFR 1910.119 in the United States; in the EU the operation is managed under Directive 2012/18/EU where sodium hydride inventories exceed threshold quantities for major-accident hazards. Downstream users in pharmaceutical synthesis require trace metal content below 50 mg/kg for Pd, Ni, and Fe, tested by ICP-OES after acid digestion. Terminal products include sodium borohydride used as a chemoselective reducing agent for prostaglandin intermediates, as a stabiliser in precious metal recovery, and as a solid hydrogen carrier in portable fuel cell power systems where the liberated hydrogen is fed to a PEM stack.
Boron methoxide enters fibre-preform manufacturing as a volatile boron oxide precursor that is delivered from a heated bubbler at 25–40 °C using nitrogen or argon carrier gas, then mixed with silicon tetrachloride, germanium tetrachloride, and oxygen before combustion in a hydrogen-oxygen torch at 1,500–1,800 °C. In modified chemical vapour deposition and outside vapour deposition systems, the oxidation product B2O3 is incorporated into the cladding layer at typical loadings between 5 wt% and 15 wt%; this doping depresses the refractive index below that of the silica core and allows the cladding to be matched to a germania-doped core with relative index difference near 0.3–0.4%. The preform is subsequently drawn in a graphite resistance furnace at 2,000–2,200 °C under tension control, with fibre diameter held to 125 ± 1 µm by laser gauge feedback.
Product specification for the single-mode fibre is defined by ITU-T G.652.D and IEC 60793-2-50; attenuation, chromatic dispersion, and cut-off wavelength are measured according to IEC 60793-1-40, IEC 60793-1-45, and IEC 60793-1-44 respectively. Manufacturing facilities supplying telecom-grade fibre are qualified to ISO 9001:2015, and raw-material traceability includes gas chromatographic purity checks of the boron methoxide feed with ethanol and water specified below 0.1 wt% each to avoid particulate hydroxyborate formation in vaporiser lines. Terminal products include standard single-mode optical fibre for underground metropolitan cables, bend-insensitive fibre for FTTH drop cable, and dispersion-shifted fibre for long-haul transmission.
In dry-room electrolyte compounding for NMC/graphite lithium-ion cells, boron methoxide is blended into carbonate-based electrolytes at addition levels from 0.5 wt% to 2.0 wt% relative to total electrolyte mass, with the dry room dew point held below −50 °C to limit hydrolysis of both LiPF6 and trimethyl borate. The compound is added after the lithium salt is fully dissolved and the solution is filtered through 0.2 µm PTFE membranes before filling; published data indicate that the methoxide functions as a sacrificial additive that participates in the formation of a borate-containing solid electrolyte interphase on the cathode, suppresses transition metal dissolution, and reduces free HF in the electrolyte. At loadings above 5.0 wt%, studies report a marked increase in charge-transfer resistance and lithium plating risk on graphite anodes, setting an upper practical boundary for this additive in high-energy cells.
| Boron methoxide loading | Interfacial effect reported | Test basis |
|---|---|---|
| 0.5 wt% | Increased high-voltage cycling stability on NMC532; modest impedance rise | IEC 62660-1:2018 cycle test |
| 1.0 wt% | Reduced Mn dissolution on high-voltage cathodes; stabilised capacity retention at 45 °C | IEC 62660-1:2018 plus ICP-OES separator analysis |
| 2.0 wt% | Thicker borate-rich SEI; improved thermal abuse behaviour in some cells | IEC 62133-2:2017 safety screening |
| 5.0 wt% and above | Excessive interfacial impedance; poor low-temperature discharge | UN 38.3 transport and IEC 62660-1:2018 |
Compliance for cells containing such electrolyte blends is governed by UN 38.3 for transport, IEC 62660-1:2018 for traction cell performance, and IEC 62133-2:2017 for portable sealed cell safety. Downstream production frames include vacuum-filling of prismatic and cylindrical cells in automated lines with electrolyte hold time below 2 h after additive introduction, because trimethyl borate can slowly react with trace water and form boric acid particles that block electrode wetting. Terminal product types are lithium-ion cells for electric buses, energy storage system modules, and marine powertrain packs where high-temperature cycle stability is specified.
Vapour-phase wood preservation uses boron methoxide as a penetrating boron carrier that hydrolyses in the presence of cell-wall moisture to deposit boric acid, thereby avoiding the drying time and surface crust associated with aqueous borate diffusion. In a sealed retort, the ester is vaporised at 60–80 °C under reduced pressure, and the vapour is held against the timber for 2–6 h depending on thickness; the final boric acid equivalent loading is controlled between 0.5 kg/m³ and 2.0 kg/m³ for interior joinery and structural timber in use class UC1/UC2. Because trimethyl borate has a flash point near −8 °C, the retort is maintained oxygen-deficient and continuous LEL monitoring below 25% is used; methanol released by hydrolysis is condensed and incinerated or recycled.
The treated wood is specified according to EN 599-1 for biological efficacy and factory production control is maintained under ISO 9001:2015; boric acid as an active substance falls under the EU Biocidal Products Regulation (EU) No 528/2012 for product-type 8, and in North America the retention and penetration requirements are verified against AWPA P5-19. Published data for vapour-phase trimethyl borate treatment of refractory species such as spruce and pine are available for laboratory and pilot retorts, but long-term field performance data for ground-contact applications is limited. Terminal products include interior framing timber, door and window core stock, timber packaging for archival storage, and protected museum shelving where leachable mineral preservatives are undesirable.
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Commercial boron methoxide (trimethyl borate, boric acid trimethyl ester, CAS 121-43-7) is an anhydrous liquid organoboron compound with the formula B(OCH3)3 and a molecular weight of 103.91 g/mol. The material is supplied as a clear, colorless, mobile liquid with a density of 0.932 g/mL at 25 °C as measured by ASTM D4052-22, a boiling point of 68–69 °C at 101.3 kPa, a refractive index n20/D of 1.355–1.357, and a closed-cup flash point of -8 °C. The compound carries the transport classification UN 2416, Class 3, Packing Group II. Unlike boric acid, the methoxide is monomeric and volatile because all three hydroxyl positions are capped with methyl groups, leaving no hydrogen-bonded network to suppress vapour pressure.
Manufacturer-specific catalog identifiers replace universal model numbers for this product. Typical order codes distinguish a synthesis grade, an anhydrous grade, and a high-purity electronic grade. Representative synthesis-grade certificates report an assay of not less than 99.0% by GC-FID area percent, water content below 500 mg/kg by ASTM E203-16, and a Pt-Co color below 10 APHA by ASTM D1209-05. High-purity grades intended for vapour deposition are additionally specified for trace metals by inductively coupled plasma mass spectrometry, with sodium, iron, and calcium limits commonly below 1 mg/kg each. Package sizes from 1 L glass containers to 200 L steel drums are used, with inert-gas headspace maintained to exclude moisture and reduce vapour accumulation.
Table 1. Representative specification framework for boron methoxide grades.
| Specification parameter | Synthesis grade | High-purity electronic grade | Test method |
|---|---|---|---|
| Assay (GC area %) | ≥ 99.0 | ≥ 99.9 | GC-FID |
| Water content (mg/kg) | ≤ 500 | ≤ 100 | ASTM E203-16 |
| Color (Pt-Co, APHA) | ≤ 10 | ≤ 5 | ASTM D1209-05 |
| Methanol content (%) | ≤ 0.5 | ≤ 0.1 | GC-FID |
| Sodium, iron, calcium (mg/kg each) | Not specified | ≤ 1 | ICP-MS |
| Total chloride (mg/kg) | Not specified | ≤ 5 | Ion chromatography after hydrolysis |
The values above are representative of published technical bulletins and supplier certificates; batch-specific limits may differ and should be verified against the delivered certificate of analysis.
In comparisons with other liquid boron alkoxides, the methoxide has the lowest molecular weight and the highest boron mass fraction. The theoretical boron contents are 10.40% for B(OCH3)3, 7.40% for B(OCH2CH3)3, and 5.75% for B[OCH(CH3)2]3. The boiling point of 68–69 °C places the methoxide well below the ethoxide at 117–118 °C and the isopropoxide at 139–140 °C, allowing methoxide to be used as a room-temperature vapour source.
Table 2. Comparative physical data for common homoleptic trialkyl borates.
| Parameter | Boron methoxide | Boron ethoxide | Boron isopropoxide |
|---|---|---|---|
| Boiling point at 101.3 kPa (°C) | 68–69 | 117–118 | 139–140 |
| Density at 25 °C (g/mL) | 0.932 | 0.858 | 0.815 |
| Boron mass fraction (%) | 10.40 | 7.40 | 5.75 |
In a vapour delivery system, the liquid is held in a stainless steel bubbler at 20–35 °C with nitrogen or argon carrier gas controlled by a mass flow controller. Downstream lines are maintained at 25–40 °C because the methoxide can condense in unheated segments below its dew point, producing feed instability and droplet carryover. This is a more severe constraint than with boron ethoxide or boron isopropoxide, whose lower vapour pressures require higher bubbler temperatures but tolerate ambient downstream lines more readily. The methoxide also hydrolyzes rapidly upon exposure to humid air, generating methanol; closed transfer under a nitrogen blanket is mandatory in processes where the residual water content of the final product must remain below 100 mg/kg.
Sol-gel processing exploits the rapid hydrolysis of boron methoxide to produce borosilicate glass and oxide powders. The reaction with water releases three moles of methanol per mole of ester, corresponding to 925 g of methanol per kilogram of boron methoxide. Hydrolysis is exothermic and is normally controlled by slow addition into a water-alcohol mixture under agitation. A typical pilot-scale reactor uses a jacketed glass-lined vessel with nitrogen purge at 0.5–1.0 L/min and a circulating chiller set to 10 °C during the addition phase. If the internal temperature exceeds 30 °C, the condensation rate accelerates and the sol may gel prematurely. The water-to-alkoxide ratio is usually set between 3:1 and 4:1; at ratios below 3:1, partially condensed methoxy-bridged boron species persist, while higher ratios favour more complete hydrolysis and boric acid formation. Acidic catalysis with hydrochloric acid or nitric acid shifts the reaction toward silanol condensation, whereas neutral conditions can leave borate-rich domains that alter the thermal expansion of the final oxide.
Batch-to-batch variation in gelation time is frequently controlled by drying the alcohol co-solvent. Solvents should be dried to a water content below 200 mg/kg by activated molecular sieves or azeotropic distillation before combination; otherwise the gelation time can shift by more than 20% under constant pH and temperature. Because the released methanol lowers the flash point of the mixed solvent, explosion-proof ventilation and vapour monitoring are required. No single ASTM method defines gel time for this system; process control usually relies on inline rotational rheometry or a falling-needle viscometer.
The primary advantage of boron methoxide in low-pressure deposition is the absence of halides. In comparison with boron trichloride, boron methoxide decomposes in oxygen or water vapour to boron oxide and methanol without generating hydrogen chloride, which corrodes vacuum pump seals and exhaust ducting. In semiconductor-adjacent processes the halide-free route prevents chloride incorporation in the film and avoids the need for high-temperature post-deposition scavenging. A delivery manifold commonly operates with a heated bubbler at 30 °C, a pressure of 100–200 Torr, and a carrier flow of 50–200 sccm. The deposition chamber may be held at 0.5–2.0 Torr with substrate temperatures between 300 °C and 450 °C. Under these conditions the methoxide reacts with water or ozone to form boron oxide glass; the B-O infrared band near 1400 cm-1 is commonly monitored for thickness and composition.
Atomic layer deposition sequences separate the methoxide pulse from the water or ozone pulse with inert-gas purges. Laboratory reactors using precursor pulse times of 1–3 s and purge times of 5–15 s produce sub-angstrom growth per cycle, but the exact growth rate depends on surface hydroxyl density and chamber geometry. Published data for this specific configuration is limited; uniformity is influenced more by precursor dose and purge efficiency than by chemical purity alone. High-purity electronic grade material is specified with transition metals below 1 mg/kg each and total chloride below 5 mg/kg. Metal impurities are determined by ICP-MS of the neat liquid or an aqueous extract, and chloride by ion chromatography after hydrolysis.
Compared with boric acid, boron methoxide is a liquid at ambient temperature and can be metered continuously without dust-handling or dissolution steps. Its hydrolysis generates only methanol and boric acid or boron oxide, whereas boron phosphate, borax, or alkali borosilicate frit feedstocks introduce sodium, calcium, or phosphorus side streams. In electronic-grade borosilicate batches an alkali contamination above 1 mg/kg can shift dielectric loss and reduce the reproducibility of the glass transition. Boron methoxide is also distinct from trialkylboranes such as triethylborane; it is flammable with a flash point of -8 °C, but it is not pyrophoric under normal storage. The lower flash point requires grounding, sealed transfer, and storage below 25 °C. In contrast, boron ethoxide and boron isopropoxide have higher flash points and lower hydrolysis rates, which may be preferred where slower gelation or lower vapour pressure is needed.
Transesterification with higher alcohols converts boron methoxide to less volatile borate esters used as anti-wear additives and corrosion inhibitors. Neat methoxide is generally not retained in lubricant formulations because its volatility and flammability create handling constraints and because it hydrolyzes too quickly in the presence of dissolved water. This product difference does not exclude methoxide as an intermediate; the methoxide is reacted with a long-chain alcohol under nitrogen to displace methanol, which is removed by distillation. The completeness of transesterification can be followed by gas chromatography of the liberated methanol or by refractive index change.
Storage stability is governed by moisture ingress. The as-received material should be kept under nitrogen in a tightly sealed container at 0–25 °C and protected from light; prolonged storage above 25 °C increases methanol vapour pressure and can distort container headspace. Exposure to ambient humidity produces boric acid precipitate and free methanol, raising the water content and reducing assay. For synthesis-grade material the water content should not exceed 500 mg/kg before use; if it does, the product may be re-purified by distillation over sodium methoxide or by reaction with a low-water methanol stream, but such operations must be performed under inert conditions.
In lithium-ion electrolyte formulations, trimethyl borate has been examined as a sacrificial film-forming additive at mass fractions of 0.5–2.0% in carbonate solvents. The additive can promote the formation of a borate-containing surface layer on high-voltage layered-oxide cathodes, but it reacts with residual water and therefore requires electrolyte solvents dried to below 20 mg/kg of water. Qualification for battery use includes electrochemical cycling in coin or pouch cells with LiPF6-based electrolytes; no ASTM method governs this electrochemical performance, so cell-level data are vendor- and application-specific. The water sensitivity also means that methoxide-containing electrolyte solutions should be stored in sealed glass or fluoropolymer vessels and cannot be exposed to open-air mixing lines.
