| HS Code | 313195 |
| Product Name | Potassium Tert-Butoxide |
| Iupac Name | Potassium 2-methylpropan-2-olate |
| Cas Number | 865-47-4 |
| Ec Number | 212-740-3 |
| Molecular Formula | C4H9KO |
| Molar Mass | 112.21 g/mol |
| Appearance | White to off-white crystalline solid |
| Odor | Odorless to slight characteristic odor |
| Density | 1.025 g/cm3 |
| Melting Point | 256-258 °C |
| Boiling Point | 275 °C (decomposes) |
| Solubility | Soluble in tetrahydrofuran, diethyl ether, and dimethyl sulfoxide; reacts with water |
| Pka Conjugate Acid | 16.5 |
| Basicity | Strong base |
| Moisture Sensitivity | Moisture sensitive |
| Air Sensitivity | Air sensitive |
| Hygroscopic | Yes |
| Flammability | Flammable solid |
As an accredited Potassium Tert-Butoxide factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Potassium tert-butoxide, 100 g, supplied in a sealed amber glass bottle under inert gas with clear hazard labels. |
| Container Loading (20′ FCL) | 20′ FCL loading: Potassium tert-butoxide packed in UN-approved sealed drums, palletized, moisture-protected, secured, and compliant with IMDG hazardous cargo rules. |
| Shipping | Potassium tert-butoxide is shipped as a moisture-sensitive, corrosive solid under UN 3263, Class 8, PG II. THF solutions are UN 2924, Class 3(8), PG II. Use sealed, chemically resistant packaging under inert gas, labeled corrosive/flammable, segregated from water, acids, and oxidizers. |
| Storage | Store potassium tert-butoxide in a cool, dry, well-ventilated, fire-resistant area away from water, moisture, acids, oxidizers, heat, and ignition sources. Keep containers tightly closed, preferably under inert gas such as nitrogen or argon, to prevent hydrolysis and degradation. Use labeled, corrosion-resistant containers, handle moisture-free, and segregate from incompatible materials. |
| Shelf Life | Stable approximately two years when kept dry, tightly sealed, and under inert gas; hygroscopic, moisture-sensitive, and decomposes upon air exposure. |
Potassium tert-butoxide (CAS 865-47-4, molecular weight 112.21) functions downstream as a sterically hindered alkoxide base. Pharmaceutical intermediate synthesis with potassium tert-butoxide is concentrated in dehydrohalogenation and enolate-mediated alkylation steps. A typical glass-lined reactor charge for dehydrochlorination of a 17α-chloro ketosteroid uses 1.05–1.40 molar equivalents of potassium tert-butoxide relative to the chlorosteroid. The solvent is tetrahydrofuran or 2-methyltetrahydrofuran at an initial temperature of 0–5°C. Addition is controlled over 45–90 minutes to hold internal temperature below 15°C. Production-scale lines with poor agitator clearance can lose conversion when the solid base is added through the manway and remains on the baffle; a nitrogen pad at 50–80 mm H₂O gauge is maintained during the entire operation. The terminal product is a Δ17(20) steroidal alkene intermediate that is then subjected to epoxidation and dihydroxylation. Residual potassium is removed by an aqueous quench with 5% acetic acid followed by water washing until the organic layer conductivity falls below 50 µS/cm. The relevant compliance framework is ICH Q3D for elemental impurities and 21 CFR 210/211 for API intermediates; potassium is not a Class 1 or Class 2 element but must be controlled below the permitted daily exposure limit of the downstream drug. Published data for this specific configuration is limited.
In palladium-catalyzed C–N coupling of aryl halides with primary or secondary amines, potassium tert-butoxide is added at 1.4–2.0 molar equivalents relative to the limiting aryl halide, not to the amine. The excess is required because the tert-butoxide neutralizes hydrohalic acid released from oxidative addition and deprotonates the amine hydrochloride in situ. Toluene and 1,4-dioxane are preferred solvents at 85–100°C under reflux. Water levels above 200 ppm in the reactor lead to palladium hydroxide species and a drop in turnover number. Production-scale campaigns in 2,000–6,300 L glass-lined reactors use vacuum-purge cycles to less than 500 ppm oxygen. The terminal products are N-aryl piperazine or N-aryl imidazole building blocks used in kinase inhibitor and central nervous system active pharmaceutical ingredient synthesis. Compliance under REACH requires registration of the isolated intermediate when it is placed on the market as a transport-isolated compound. Analytical release follows HPLC at 210–254 nm with area percent purity ≥98.0%. Residual tert-butyl alcohol is measured by headspace GC because its carryover into the next step cannot exceed 0.10%.
Agrochemical intermediates prepared by O-alkylation with potassium tert-butoxide require a polar aprotic solvent that is stable against strong base. Dimethyl sulfoxide is used only below 80°C because potassium tert-butoxide slowly decomposes in DMSO at higher temperatures. N,N-dimethylacetamide and N-methyl-2-pyrrolidone are alternatives for phenol deprotonation at 60–90°C. The molar charge ratio is 1.05–1.15 equivalents of potassium tert-butoxide relative to the substituted phenol or alcohol, leaving minimal excess base to be quenched. In the synthesis of aryloxypropionate herbicide intermediates, a chloromethyl heterocycle is added after the phenoxide has formed. The terminal product is the corresponding aryloxypropionate ester, used in the manufacture of selective post-emergence herbicides. Residual potassium salts are removed by filtration and water washing until conductivity of the organic layer remains below 100 µS/cm. Compliance with FAO/WHO specifications for active ingredient purity applies only after hydrolysis and further reaction. Equipment is normally glass-lined or 316L stainless steel with a dimple jacket.
In propylene oxide and ethylene oxide ring-opening polymerization, potassium tert-butoxide is converted to the corresponding potassium alkoxide of the polyol initiator in a separate pre-reactor. The initiator charge is 0.2–1.0 mol% relative to epoxide monomer. After dehydration at 105–110°C under vacuum, potassium tert-butoxide is added and the reactor is blanketed with nitrogen. Polymerization is carried out in a stainless steel autoclave with a rupture disc set at 10 bar. The reaction temperature is 100–130°C and pressure is maintained at 2.0–5.0 bar during oxide addition. The terminal products are polyether polyols with hydroxyl numbers between 20 and 400 mg KOH/g, used in polyurethane flexible slabstock and rigid foam systems. Free potassium content in the final polyol is neutralized with acetic acid or phosphoric acid. Hydroxyl value is tested under ASTM D4274-16, moisture under ASTM D4672-12, and acid number under ASTM D4662-08. The requirement for manufacture of food-contact polyurethane articles in Europe is EC 1935/2004; formulation-specific migration limits are assessed in the final cured article.
Transesterification of refined vegetable oils with methanol uses potassium tert-butoxide as an anhydrous alkaline catalyst at 0.7–1.2 wt% of oil mass. The catalyst is first dissolved in methanol at 25–35°C to generate methoxide; dissolution is exothermic and must be controlled below 40°C to prevent boiling. The reaction is run at 55–65°C for 1–2 h in a closed stainless steel reactor with a reflux condenser. Free fatty acid content in the incoming oil must be kept below 0.05–0.10 wt% because carboxylate salts are the main yield loss and emulsifier. The terminal product is fatty acid methyl ester, tested under EN 14214:2012+A1:2014 and ASTM D6751-20a. Total glycerol must be below 0.25 mol% and ester content above 96.5% under EN 14214. The lower water content of potassium tert-butoxide compared with potassium hydroxide reduces soap formation during initial dispersion, but large-scale comparative data for this specific configuration is limited. Excess potassium is removed by water washing and adsorption with magnesium silicate.
In Wittig olefination of β-ionylideneacetaldehyde with a phosphonium salt, potassium tert-butoxide generates the reactive ylide in situ. The charge is 1.0–1.2 molar equivalents relative to the phosphonium salt. The solvent is toluene–tetrahydrofuran at -15 to 0°C. Conditions are kept below 5°C during addition because premature ylide decomposition gives triphenylphosphine oxide and the starting aldehyde. The terminal product is a polyene intermediate used in vitamin A and carotenoid synthesis. The organic layer is washed with water and 10% sodium chloride to remove potassium salts. The isolated product is assayed by UV–Vis at 325–450 nm depending on polyene length. Compliance follows food additive regulations for the final product rather than the isolated intermediate.
| Downstream application | Primary compliance reference | Critical control limit |
|---|---|---|
| Pharmaceutical dehydrohalogenation | ICH Q3D, 21 CFR 210/211 | Residual potassium < 50 ppm in isolated intermediate |
| Buchwald–Hartwig amination | REACH, internal cGMP release | Water < 200 ppm, residual tert-butanol < 0.10% |
| Aryl etherification | FAO/WHO active ingredient specifications | Conductivity < 100 µS/cm after washing |
| Polyether polyol initiation | ASTM D4274-16, ASTM D4672-12, EC 1935/2004 | Hydroxyl number 20–400 mg KOH/g |
| Fatty acid methyl ester production | EN 14214:2012+A1:2014, ASTM D6751-20a | Free fatty acid < 0.10 wt%, ester content > 96.5% |
| Wittig olefination for polyene intermediates | FDA 21 CFR 117 for final food ingredient | Ylide addition temperature < 5°C |
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Potassium tert-butoxide is an anhydrous, strongly basic alkali metal alkoxide used predominantly as a non-nucleophilic, sterically hindered base in organic synthesis. The compound is identified by CAS Registry Number 865-47-4, empirical formula C4H9KO, and formula mass 112.21 g/mol. Commercial material does not carry a unified industry model code; it is supplied under supplier-specific article designations that encode physical form, packaging, and solvent matrix, such as anhydrous powder, granular solid, or 1.0 M solution in tetrahydrofuran. A typical powder-grade specification includes an assay ≥98.0% as C4H9KO, free potassium hydroxide ≤1.5%, water ≤0.50% by ASTM E203-16, and a white to off-white crystalline appearance. The material is produced commercially by treatment of tert-butanol with potassium metal or potassium hydride under inert gas, followed by solvent evaporation and size reduction; the product is delivered as a free-flowing solid or as a filtered, low-water solution.
The dominant application of potassium tert-butoxide is deprotonation of carbon, oxygen, and nitrogen acids in aprotic media. It is used to generate enolates from ketones, esters, amides, and nitriles; to promote dehydrohalogenation to alkenes; to abstract acidic protons from phosphonium salts in Wittig olefination; and to serve as the base component in palladium-catalyzed cross-coupling reactions where a strong, non-coordinating alkoxide is required. Because the conjugate acid tert-butanol has an approximate DMSO pKa of 32.2 on the Bordwell scale, the reagent deprotonates substrates with pKa values below approximately 31 under controlled conditions. The steric bulk of the tert-butoxy anion suppresses nucleophilic substitution at carbon, which accounts for its higher elimination-to-substitution selectivity relative to sodium methoxide and potassium hydroxide.
The selectivity profile of potassium tert-butoxide is determined by three variables: cation identity, alkoxide structure, and solvation state. Compared with sodium methoxide, potassium tert-butoxide is a stronger base and a poorer nucleophile. Sodium methoxide has a conjugate acid DMSO pKa near 29.0, whereas tert-butanol has a DMSO pKa near 32.2; the difference of approximately 3 pKa units translates into a thermodynamically more favorable deprotonation for weakly acidic substrates. The tert-butoxy group is also more sterically hindered than methoxide, so the rate of bimolecular substitution at primary and secondary carbon centers is lower. Potassium hydroxide is a strong but often heterogeneous inorganic base in organic media; it provides hydroxide as the active species, has limited solubility in tetrahydrofuran and methyl tert-butyl ether, and introduces water or alcohol after proton transfer. Potassium tert-butoxide dissolves in ethereal and dipolar aprotic solvents, allows homogeneous reactions, and generates tert-butanol as the protonated byproduct.
Compared with lithium diisopropylamide, potassium tert-butoxide is a weaker base but provides lower reactivity toward substrate self-condensation in certain enolate formations and avoids the need for low-temperature amide handling. Lithium diisopropylamide has a conjugate amine DMSO pKa near 35.7, and is often used at −78°C to 0°C; potassium tert-butoxide can be used at more moderate temperatures for many deprotonations. The counterion also influences aggregation. Potassium alkoxides in tetrahydrofuran form contact ion pairs and higher aggregates at higher concentration, whereas lithium alkoxides form more covalent aggregates. This aggregation difference can alter deprotonation rates and enolate regiochemistry in ketone substrates.
| Reagent | Conjugate acid pKa in DMSO | Typical organic solubility | Active species | Nucleophilicity profile |
|---|---|---|---|---|
| Potassium tert-butoxide | 32.2 | THF, DMSO, MTBE, tert-butanol | tBuO− | Low; hindered |
| Sodium methoxide | 29.0 | Methanol, dimethyl sulfoxide | MeO− | Moderate; less hindered |
| Potassium hydroxide | 31.4 | Water, alcohols; limited in THF | HO− | Moderate; water co-product |
| Lithium diisopropylamide | 35.7 | THF, hexane, ethers | iPr2N− | Very low; hindered amide |
Specifications for potassium tert-butoxide vary by manufacturer, but the following ranges are typical for industrial anhydrous powder and for a 1.0 M solution in tetrahydrofuran. The solid is usually assayed by non-aqueous acid-base titration, with water determined by volumetric Karl Fischer titration according to ASTM E203-16. Free potassium hydroxide is reported as a separate alkalinity value because residual hydroxide changes reaction stoichiometry in anhydrous systems. Chloride and sodium are monitored in high-purity grades where downstream catalyst performance is sensitive to halide contamination.
| Parameter | Anhydrous powder | 1.0 M THF solution | Test method |
|---|---|---|---|
| Assay as C4H9KO | ≥98.0% | 0.95–1.05 M | Non-aqueous titration |
| Free potassium hydroxide | ≤1.5% | ≤0.10% | Acid titration after precipitation |
| Water | ≤0.50% | ≤0.10% | ASTM E203-16 |
| Appearance | White to off-white crystalline solid | Clear to slightly hazy | Visual inspection |
Incoming quality control should include assay, water, free potassium hydroxide, and for solution grades, peroxide and solvent identity. Tetrahydrofuran solutions require inhibitor levels to be stated because residual peroxide can react with the alkoxide and generate heat or degrade the base. Manufacturing sites are typically certified to ISO 9001:2015, and the material is placed on the market under the requirements of REACH Regulation (EC) No 1907/2006. Safety data sheets in the European Union classify the substance under Regulation (EC) No 1272/2008 as Skin Corrosive Category 1B, Hazard Statement H314, Flammable Solid Category 2, Hazard Statement H228, and EUH014 for violent reaction with water. These classifications define mandatory labeling, storage, and spill-control measures.
Temperature control is the principal process variable in manufacturing applications. In polar aprotic solvents such as tetrahydrofuran, 2-methyltetrahydrofuran, and dimethyl sulfoxide, the deprotonation of a ketone with potassium tert-butoxide is fast and exothermic. Uncontrolled addition can raise the batch temperature beyond the region where the desired enolate is kinetically stable. When the substrate bears a leaving group at a secondary carbon, raising the internal temperature above 30°C in tetrahydrofuran increases β-hydride elimination; at 0°C to 5°C, deprotonation at a less hindered site can be kinetically favored. The processing window is therefore narrow for substrates that can undergo both enolate formation and elimination. Process descriptions in pilot-plant literature commonly specify jacket set points between −10°C and 5°C, with potassium tert-butoxide solids added incrementally to maintain internal temperature within a 5°C band. For large-scale batches, a cooled brine jacket at −20°C to −10°C and controlled solid addition over 60–120 min are used to limit adiabatic temperature rise.
On production-scale equipment, potassium tert-butoxide powder is charged through nitrogen-purged solids addition funnels, split-valve systems, or glovebox transfer ports. In agitated reactors, a bottom-discharge filter dryer with nitrogen blanket reduces lumping during solvent wash. Batch-to-batch variance in free potassium hydroxide is controlled by using potassium metal of defined sodium content and by avoiding exposure of the solid to ambient air during packaging. Powder handling systems should avoid electrostatic discharge, and the solid should not be allowed to accumulate in screw conveyors or rotary valves because frictional heating can initiate decomposition and corrosive dust formation. Glass-lined reactors are preferred over stainless steel when chloride contamination must be minimized, although stainless steel is acceptable for processes where trace iron does not affect catalyst performance.
Storage stability is governed by moisture, carbon dioxide, and solvent quality. The solid should be stored in tightly closed containers under inert gas at temperatures below 25°C and relative humidity below 50%. Exposure to atmospheric moisture liberates tert-butanol and forms potassium hydroxide; exposure to carbon dioxide generates potassium tert-butyl carbonate and potassium carbonate, reducing active assay and producing insoluble fines that interfere with downstream filtration. In solution, the reagent is stabilized by low water and peroxide levels in the solvent; tetrahydrofuran containing ≥50 ppm water can reduce effective base concentration through hydrolysis. Solutions should be assayed before use by titration or by reaction with a standardized acid. Chlorinated solvents are generally incompatible: chloroform and dichloromethane can generate carbene intermediates under strongly basic conditions, with exothermic decomposition. Alcohols other than tert-butanol, aqueous acids, and oxidizing agents should be excluded from all process lines.
In cross-coupling applications, potassium tert-butoxide is used as a stoichiometric base in palladium-catalyzed amination and C–C bond formation. It deprotonates amine substrates or neutralizes acid byproducts without introducing sodium or lithium counterions that can alter catalyst selectivity. However, its strong basicity can also deprotonate solvent or ligand C–H bonds under forcing conditions. For substrates with acidic functional groups outside the target pKa range, potassium tert-butoxide may generate off-target enolates or initiate polymerization. Published data for specific continuous-flow configurations using potassium tert-butoxide in carbon–nitrogen bond formation is limited, but laboratory batch data indicate that stoichiometry between 1.05 and 1.30 equivalents is often required to compensate for residual moisture and free potassium hydroxide. Any process deviation should be supported by reaction calorimetry and in-process assay rather than by extrapolation from small-scale screening.
