| HS Code | 728595 |
| Productname | Sodium Borohydride |
| Chemicalformula | NaBH4 |
| Casnumber | 16940-66-2 |
| Ecnumber | 241-004-4 |
| Unnumber | 1426 |
| Molarmass | 37.83 g/mol |
| Appearance | White to off-white crystalline powder or granules |
| Density | 1.07 g/cm3 |
| Meltingpoint | 400 °C (decomposes) |
| Decompositiontemperature | 400 °C |
| Solubilityinwater | 550 g/L at 25 °C (reacts slowly) |
| Solubilityinmethanol | 164 g/L at 20 °C |
| Solubilityinethanol | 43 g/L at 20 °C |
| Hazardclass | 4.3 (Water-reactive) |
| Packinggroup | I |
| Ph | About 11 (aqueous solution) |
| Hydrogencontent | 10.6 wt% |
As an accredited Sodium Borohydride factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Sodium borohydride packaged in sealed, moisture-resistant 25 kg steel drums with inner polyethylene liners, labeled corrosive and flammable. |
| Container Loading (20′ FCL) | Sodium Borohydride loaded into 20′ FCL in sealed palletized drums, kept dry, secured, with Class 4.3 UN 1426 DG labeling. |
| Shipping | Proper shipping name: Sodium borohydride; UN1426; Hazard Class 4.3; Packing Group I; subsidiary Class 8. It is water-reactive, releasing flammable hydrogen, and corrosive. Ship dry, sealed, away from water, acids, and oxidizers. Comply with DOT, IMDG, and IATA regulations, labels, and documentation. Emergency response information required. |
| Storage | Store sodium borohydride in a cool, dry, well-ventilated area away from water, moisture, acids, oxidizers, and heat or ignition sources. Keep containers tightly closed, preferably under dry nitrogen, and protect from physical damage. Store only in labeled, compatible containers. Use spark-proof equipment, avoid dust generation, separate from incompatible materials, and ensure ventilation to prevent hydrogen accumulation. Have appropriate firefighting and spill procedures available. |
| Shelf Life | Sodium borohydride shelf life: typically 2–5 years when stored dry, sealed, and moisture-free; hygroscopic and decomposes upon water contact. |
Pharmaceutical intermediate reduction consumes sodium borohydride at production scale because the hydride transfer can be stopped selectively at aldehyde or ketone functionality without reducing pendant esters, amides, or nitro groups under controlled conditions. A typical batch is executed in a glass-lined reactor equipped with a retreat-curve impeller, a nitrogen sweep, and jacket cooling. The carbonyl substrate is dissolved in methanol, ethanol, or a methanol/tetrahydrofuran mixture at 0.8–1.5 mol/L. Stabilised sodium borohydride solution containing 12% NaBH4 and 40% NaOH is metered at 0.25–0.6 mol NaBH4 per mole of carbonyl group; diaryl ketone reductions are commonly run at 0.3–0.4 mol NaBH4 per mole of ketone at 0–10°C. Addition is split or continuous over 30–90 min to manage the exotherm and to minimise solvent washout of hydrogen into the vent system. After conversion is confirmed by GC or UPLC, residual hydride is quenched with acetone at 1.0–2.0 mol acetone per mole of residual hydride, and the mixture is neutralised with citric acid to pH 6–7 before aqueous extraction or crystallisation. Batch records are governed by 21 CFR 210.3(b) and 21 CFR 211.100, and residual boron in the isolated intermediate is assessed under an ICH Q3D-driven elemental impurity risk assessment using ICP-MS or USP general chapter 621 chromatographic methods as appropriate to the matrix. The resulting diarylmethanol, chiral alcohol, and amino alcohol synthons are terminal intermediates for subsequent API salt formation or coupling steps.
Selectivity is maintained by solvent and temperature rather than by reagent excess alone. Protic solvents such as methanol attenuate ester reduction but also consume hydride slowly; therefore the borohydride charge is established by a development-stage design-of-experiment matrix that records endpoint aldehyde-ketone content, residual hydride, and borate ester formation. Temperature excursions above 25°C accelerate borohydride decomposition in alcohol and raise hydrogen evolution, requiring reactor vent sizing to handle peak gas flow. In production lines, the nitrogen sweep is interlocked with a flammable gas detector set to alarm at 25% of the lower explosion limit. Batch-to-batch variance is controlled by normalising the sodium borohydride charge against the limiting carbonyl assay, not against raw material weight alone.
Fragrance-grade citral reduction illustrates a different borohydride duty: the conjugated aldehyde groups in geranial and neral are reduced to geraniol and nerol without saturating the olefinic bond under standard sodium borohydride conditions, but the reaction exotherm must be suppressed to avoid aldehyde isomerisation and headspace defects in the finished material. A typical charge is 0.27–0.30 mol NaBH4 per mole of citral in ethanol at -5°C to +5°C; the borohydride is added as a 12% alkaline solution over 45–90 min. The resulting geraniol/nerol mixture is quenched into water, neutralised, and extracted, followed by brine washing and vacuum fractionation. Process gas chromatographic analysis adapted from ISO 7609:1985 monitors total residual citral below 0.1% area, because residual aldehyde shortens shelf life and distorts the odour profile in downstream compounding. The same reactor configuration is used for acetophenone reductions to 1-phenylethanol at 0.25–0.30 mol NaBH4 per mole of ketone and 10–20°C. Terminal products enter fragrance, flavour, and solvent-grade alcohol streams where release is based on gas chromatographic purity specifications rather than pharmacopoeial monographs.
Borate ester handling is a distinct feature in these non-pharmaceutical reductions. The crude alcohol is washed with dilute sodium hydroxide at 2–3% concentration to hydrolyse borate esters, reduce neutral oil turbidity, and improve phase separation. Failure to control the quench pH below 8 can retain borate in the organic phase and cause haze after distillation. The process is operated in stainless steel or glass-lined stirred tanks with condenser loading sized for simultaneous hydrogen and solvent vapour evolution during the addition period.
In sodium borohydride-reduced electroless nickel plating, the reducing agent concentration is maintained between 0.5 g/L and 1.0 g/L, while nickel sulphate hexahydrate is held at 20–30 g/L. Ethylenediamine or sodium gluconate complexes the nickel at a pH of 12–14, and the bath is heated to 90–95°C. Under these conditions, deposition proceeds at 8–15 μm/h and yields a nickel-boron alloy containing 3–8 wt% boron. The as-deposited hardness falls between 550 HV0.1 and 750 HV0.1 when measured with ISO 6507-1:2018; post-deposition heat treatment at 380–400°C for 1 h under vacuum or inert atmosphere raises hardness into the 900–1100 HV0.1 range through nickel boride precipitation. Coating thickness is verified by cross-sectional microscopy according to ISO 1463:2021. Parts processed in this bath include valve spools, pump sleeves, textile guides, and electronic connector bodies that require wear resistance without post-machining.
The principal process conflict is borate accumulation. Each hydride transfer converts borohydride to borate, and when borate exceeds roughly 30 g/L as sodium borate, plating rate falls and deposit tensile stress rises. The bath is therefore operated at a defined metal turnover, commonly 3–5 nickel turnovers, before partial decant or replacement becomes necessary. Hydrogen evolution at the part surface causes gas pitting unless air or mechanical agitation is intense, and drag-out of complexing agent shifts pH and nickel solubility. Replenishment uses separate additions of nickel sulphate solution and sodium borohydride solution, never a mixed concentrate, because unmixed concentrates can precipitate nickel boride fines in the feed lines. Users without a dedicated plating line for nickel-boron frequently avoid this bath because its operating window and waste stream differ from conventional nickel-phosphorus systems.
| Control parameter | Operating range | Measurement method |
|---|---|---|
| Nickel sulphate hexahydrate | 20–30 g/L | EDTA complexometric titration |
| Sodium borohydride | 0.5–1.0 g/L | Iodometric titration |
| Bath pH | 12–14 | High-temperature pH electrode |
| Bath temperature | 90–95°C | Calibrated Pt100 probe |
| Boron content in deposit | 3–8 wt% | ICP-OES after acid dissolution |
In thermomechanical pulp and chemi-thermomechanical pulp mills, sodium borohydride is not applied directly to fibre but is converted into sodium dithionite shortly before the bleach tower by reaction with sodium bisulfite at a molar ratio of 1:8 NaBH4 to NaHSO3. The generated dithionite reduces quinonoid and carbonyl chromophores in the fibre, and because the route is sulphur-based and oxygen-free rather than chlorine-based, the bleaching effluent contains no measurable AOX from the reduction reaction. A typical dithionite charge is 0.5–1.0 wt% on oven-dry fibre, applied at stock consistency 8–12%, pH 5.5–6.5, and temperature 60–80°C for 30–60 min. Brightness response is measured on handsheets using ISO 2470-1:2016; opacity and yellowness are monitored with ISO 2471 and ISO 5631 respectively. The borohydride-to-dithionite reactor is a compact in-line mixing loop installed upstream of the upflow tower, and steam injection holds tower temperature because the conversion exotherm is modest. Stock line residence time before bleaching is limited to 10–20 s to minimise dithionite oxidation by dissolved air.
Sodium bisulfite and stabilised sodium borohydride are metered through static mixers in separate feed lines and combined immediately before the stock mixing point. The pH at the injection point controls dithionite stability; slurry pH below 5.5 can decompose dithionite before fibre contact, while pH above 6.5 reduces brightening response. Terminal products include newsprint, directory paper, and lightweight coated mechanical paper where dithionite brightening preserves optical yield without the fibre strength loss associated with peroxide stages run at higher pH.
Alkaline sodium borohydride solutions are selected for compact hydrogen generation when a proton exchange membrane fuel cell requires a low-carbon-monoxide hydrogen feed. The hydrolysis reactor consists of a jacketed packed column loaded with a ruthenium-on-carbon catalyst, with total ruthenium loading between 0.5 wt% and 5 wt%. Sodium borohydride solution containing 15–20 wt% NaBH4 and 5–10 wt% NaOH is metered at 0.5–3.0 mL/min through the catalyst bed at 40–80°C and 0.1–0.3 MPa. Hydrolysis releases 4 mol hydrogen per mole of NaBH4, corresponding to a hydrogen content of 10.8 wt% relative to NaBH4 mass; the practical system-level density is lower because stabiliser water, catalyst bed mass, and product borate capture add weight and volume.
The generated hydrogen stream passes through a coalescing filter, a silica-gel dryer, and a palladium-silver membrane or pressure swing adsorption module before entering the fuel cell. The final hydrogen must meet ISO 14687:2019 limits for PEM fuel cell feed; carbon monoxide is controlled below 2 μmol/mol, carbon dioxide below 5 μmol/mol, and the water dew point below -40°C. Reactor integrity is monitored with hydrogen detectors compliant with ISO 26142:2010. Because hydrolysis is exothermic and gas release accelerates if catalyst activity is uncontrolled, the system is configured with a pH-controlled feed interlock that closes the borohydride supply when outlet pH drops below 11 or when reactor pressure exceeds 0.5 MPa.
| Hydrogen attribute | PEM fuel cell feed limit | Analytical reference |
|---|---|---|
| Carbon monoxide | ≤2 μmol/mol | ISO 14687:2019 |
| Carbon dioxide | ≤5 μmol/mol | ISO 14687:2019 |
| Water dew point | ≤-40°C | ISO 14687:2019 |
| Hydrogen leak detection alarm | 25% LFL | ISO 26142:2010 |
In a closed continuous stirred-tank reactor fitted with a vent scrubber, sodium borohydride is used to reduce dissolved mercury, silver, palladium, and copper from electroplating and chlor-alkali effluents. The wastewater is pre-neutralised to pH 6–8 because acidic feeds accelerate borohydride hydrolysis and hydrogen evolution. A stabilised sodium borohydride solution at 0.5 mol/L in 1 mol/L NaOH is then metered at 1.1–1.3 times the theoretical reducing demand based on the molar reduction of each metal ion to the metallic state. For copper, the theoretical ratio is 0.25 mol NaBH4 per mole Cu²⁺; for mercury and silver the same stoichiometric principle applies, but side consumption by dissolved oxygen and hydrogen formation requires the excess. Reduced solids are separated in a lamella clarifier and dewatered in a plate-and-frame filter press.
Clarified effluent is monitored for total mercury with US EPA Method 7470A and for total dissolved metals with ISO 11885:2007 or US EPA Method 6020B. The recovered metal-bearing sludge is sent to a permitted metal reclamation furnace, while the treated water is discharged under NPDES permit limits. The operational boundary is strict: borohydride must not be added directly to tanks containing hypochlorite or acidic oxidising drops because rapid hydrogen release can exceed tank vent capacity. Terminal outputs are treated wastewater meeting the facility discharge permit and a concentrated metal-bearing residual for off-site metals recovery.
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Sodium borohydride (CAS 16940-66-2, EC 241-004-4) is supplied as a white crystalline powder, a densified granular solid, or a stabilised aqueous solution containing 12% NaBH4 and 40% NaOH. The molecular weight is 37.83 g/mol, the solid density is approximately 1.07 g/cm³, and the water solubility is near 55 g/100 mL at 25 °C. Product designations are supplier-specific and commonly encode physical form and assay; a granular grade may be described as NaBH4-G-98, a fine powder as NaBH4-P-98, and a solution as NaBH4-S-12/40. Typical solid grades specify ≥98.0% NaBH4, with high-purity material at ≥99.0%. Trace-metal limits are reported in mg/kg on the supplier certificate of analysis. Transport classification is UN 1426, hazard class 4.3, packing group I.
The principal side reaction is hydrolysis, in which water donates protons to the borohydride anion and releases hydrogen. This reaction is strongly pH-dependent. In alkaline solution at pH 12 or above, the half-life of sodium borohydride at ambient temperature is sufficient for controlled reductions; below pH 9, gas evolution accelerates and can dominate over carbonyl reduction. Commercial aqueous solutions are therefore stabilised with 40% NaOH, and batch reductions in water or methanol typically add sodium hydroxide or sodium methoxide to keep pH above 11.
Temperature is the second kinetic control. Hydrolysis accelerates with increasing temperature, and many methanol reductions are run at 0–5 °C to limit the adiabatic temperature rise from both hydrolysis and reduction. Cobalt, nickel, and copper ions lower the kinetic barrier further. This creates an operational boundary: brass fittings, copper transfer lines, and damaged glass-lined reactor surfaces with exposed nickel are excluded from sodium borohydride service. Production-scale failures commonly involve localised dead zones where caustic dosing is delayed or pH probe fouling occurs. In such zones, rapid gas generation can produce foam, pressure rise, and hydrogen-rich headspace. The lower explosive limit of hydrogen in air is 4% v/v, so reactor headspace oxygen is normally kept below 5% v/v by nitrogen inerting. Emergency relief sizing for this scenario follows DIERS methodology, with the design case usually based on uncontrolled water reaction rather than normal reduction exotherm.
Solid sodium borohydride is offered in at least two morphologies that affect material handling and dissolution rate. Fine powder grades are milled to a median particle size below 50 µm; granular grades are densified to D50 values of 150–300 µm. Fine powder dissolves faster in methanol and water but is more hygroscopic and dust-prone. Granular material reduces dust generation and feeds more consistently through screw feeders, but complete dissolution may require several minutes longer at low temperature.
| Parameter | Typical specification | Reference method |
|---|---|---|
| Assay NaBH4 | ≥98.0% powder; ≥99.0% high-purity | Iodometric titration, supplier CoA |
| Moisture | ≤0.50% | ISO 760 Karl Fischer |
| Particle size D50 | 10–50 µm fine; 150–300 µm granular | ISO 13320 laser diffraction |
| Bulk density | 0.40–0.70 g/cm³ | ASTM D4164 tapped density |
| Elemental impurities | Fe, Ni, Cu controlled to low mg/kg limits | USP 233 ICP-MS |
Stabilised solution grades eliminate exothermic dissolution at the use site and are preferred for continuous processes. The 12% NaBH4/40% NaOH solution remains pumpable at ambient temperature but may require heat tracing or indoor storage where winter temperatures fall below 0 °C. Storage tanks are fabricated from carbon steel with appropriate caustic service rating or from stainless steel; nickel-alloy trim is selected where high-velocity erosion at pump impellers is expected. Because the solution is corrosive and water-reactive, secondary containment and segregation from acids and oxidising agents are mandatory.
Reduction of a sterically hindered ketone in the presence of an ethyl ester is often operated as a solid-liquid reaction in a glass-lined pilot reactor. The substrate is dissolved in methanol or ethanol, cooled to −5 °C to 0 °C, and held under nitrogen while granular NaBH4 is metered through a rotary valve or screw feeder. A pre-charge of sodium hydroxide or sodium methoxide maintains pH above 11. Under these conditions, the ketone is reduced to the secondary alcohol while the ethyl ester remains substantially unchanged. Charge ratios of 0.25–0.50 mol NaBH4 per mole of carbonyl are common, accounting for hydride losses from hydrolysis. Published calorimetric data for each specific substrate configuration are limited; process development normally relies on reaction calorimetry to quantify heat release before scale-up. Bulk density differences between fine and granular grades affect feeder mass flow and are controlled by gravimetric feeding rather than volumetric feeding.
After the reduction, excess hydride is destroyed in a controlled quench. Acetone or dilute acid is added slowly at 0–5 °C, because acid quench generates hydrogen and requires venting. Borate salts are then removed by aqueous extraction or precipitation. The waste stream is alkaline and contains borates; discharge limits are site-specific. In active pharmaceutical ingredient manufacture, residual boron is monitored in the final drug substance where the relevant compendial monograph or ICH Q3D elemental impurity risk assessment includes boron as an element of interest.
Lithium aluminium hydride is a stronger and less selective hydride donor. It reduces esters, amides, nitriles, and carboxylic acids, but requires rigorously dried ether or tetrahydrofuran and reacts violently with protic solvents. Sodium borohydride can be used in methanol, ethanol, and water at controlled pH, allowing aldehyde and ketone reductions in multifunctional molecules where an ester or secondary amide must survive. Sodium cyanoborohydride is preferred for reductive amination at pH 6–8, but its aqueous workup generates cyanide-containing waste; sodium borohydride is less selective for iminium reduction unless the pH and solvent are carefully adjusted.
| Property | NaBH4 | LiAlH4 | NaBH3CN |
|---|---|---|---|
| Substrate selectivity | Aldehydes, ketones, acid chlorides; esters generally not reduced in protic media at ambient conditions | Broad, including esters, amides, nitriles, carboxylic acids | Iminium ions in reductive amination |
| Solvent compatibility | Water, methanol, ethanol at pH 10–12 | Dry diethyl ether, THF | Methanol or acetonitrile with acid |
| Water reactivity | Moderate, pH-dependent | Violent | Low, but acid quench releases cyanide |
| Residue | Borate salts | Lithium and aluminium hydroxides | Cyanide-containing waste |
Compared with catalytic hydrogenation, sodium borohydride does not require pressure-rated vessels, hydrogen gas logistics, or catalyst activation and filtration. However, catalytic hydrogenation can reduce aromatic rings, nitriles, and certain olefins under optimised conditions, and it avoids stoichiometric borate waste. The choice between the two is therefore governed by chemoselectivity, equipment class, and waste disposal costs. Borane complexes such as borane-tetrahydrofuran and borane-dimethyl sulfide reduce carboxylic acids and some amides, but they are moisture-sensitive, flammable, and require refrigerated storage. Sodium borohydride offers lower acute flammability and simpler handling, although it remains water-reactive and must be kept dry.
In mechanical pulp brightening, stabilised 12% NaBH4/40% NaOH solution is reacted with sulfur dioxide and sodium hydroxide in a continuous static mixer to generate sodium dithionite. The generated dithionite solution is cooled to 5–10 °C and injected into the pulp stock at pH 6.5–7.5 under oxygen exclusion. Brightness response is measured according to ISO 2470-1:2016. Because dithionite decomposes rapidly below pH 6, in-line pH sensors and automatic caustic trimming are required; dead legs in the injection ring must be eliminated to prevent local sulfur dioxide formation and fibre yellowing.
This application differs fundamentally from small-molecule synthesis: sodium borohydride is not added directly as a reducing agent for pulp fibre but serves as a precursor to an unstable dithionite reducing species. The conversion is operated continuously, with narrow residence-time control, because the generated dithionite has a half-life on the order of minutes in neutral aqueous solution at ambient temperature. The process avoids direct borohydride contact with acidic pulp and therefore reduces hydrogen formation risk compared with uncontrolled acidification.
Solid sodium borohydride is hygroscopic and must be stored in tightly closed containers under nitrogen where relative humidity exceeds 60%. Storage temperature is normally maintained below 40 °C. Contact with acids, oxidising agents, and transition metal salts must be prevented because rapid hydrogen evolution can create an explosive atmosphere. Small spills are covered with dry sodium carbonate or sand; water must not be used. Aqueous solution grades present a caustic corrosion hazard in addition to water reactivity, and they must be segregated from alcohol and acid storage. For bulk transfers, nitrogen padding and pressure-vacuum vents are used, and transfer lines are sloped to avoid low-point pockets where decomposition can occur.
