| HS Code | 844310 |
| Chemical Name | Crotonaldehyde |
| Chemical Formula | C4H6O |
| Molecular Weight | 70.09 g/mol |
| Cas Number | 4170-30-3 |
| Appearance | Colorless to pale yellow liquid |
| Odor | Pungent, suffocating, acrid odor |
| Density | 0.846 g/cm3 at 20 °C |
| Melting Point | -76.5 °C |
| Boiling Point | 104 °C |
| Flash Point | -1 °C (closed cup) |
| Solubility In Water | 150 g/L (20 °C) |
| Vapor Pressure | 22.6 mmHg at 20 °C |
As an accredited Crotonaldehyde factory, we enforce strict quality protocols—every batch undergoes rigorous testing to ensure consistent efficacy and safety standards.
| Packing | Crotonaldehyde is packaged in 150 kg steel drums under nitrogen, with hazard labeling and leak-proof seals. |
| Container Loading (20′ FCL) | Load 20′ FCL with crotonaldehyde in approved UN drums, secure upright, ventilate, segregate from oxidizers, label flammable/poisonous. |
| Shipping | Crotonaldehyde (UN 1143, Hazard Class 6.1/3, Packing Group I) must ship in approved, tightly sealed containers under dangerous goods regulations. Use UN-certified drums or tanks, with toxic and flammable labels. Segregate from oxidizers and foodstuffs. Ensure proper ventilation, ground-vehicle bonding, and secure containment to prevent leaks, vapor exposure, or fire risk. |
| Storage | Store crotonaldehyde in tightly sealed, corrosion-resistant containers under inert gas in a cool, dry, well-ventilated area away from heat, flames, sparks, and direct sunlight. Isolate from oxidizers, acids, bases, and foodstuffs. Use explosion-proof equipment, grounded containers, and secondary containment to prevent spills. Monitor for polymerization; store under nitrogen if possible. |
| Shelf Life | Shelf life is limited; store under inert nitrogen in a cool, dark place. Stabilized Crotonaldehyde typically lasts up to 6 months. |
Production of sorbic acid from crotonaldehyde starts with ketene absorption into a cooled reaction mass. Crotonaldehyde (CAS 123-73-9) is metered under closed-loop conditions because its flash point is 13 °C, its vapour pressure at 20 °C is approximately 3.2 kPa, and its flammable range spans 2.1 vol% to 15.5 vol% in air. The jacketed reactor contains toluene as diluent and a zinc carboxylate catalyst; in-line Karl Fischer instrumentation maintains water below 500 ppm because residual moisture converts ketene to acetic acid and reduces molar balance. The ketene-to-crotonaldehyde molar ratio is held between 1.00:1 and 1.08:1 to offset ketene losses to diketene dimerization. Reaction temperature is kept between 40 °C and 85 °C under nitrogen. Turbine agitation is required because the polyester intermediate increases sharply in viscosity as conversion passes 70%. On production-scale lines, oligomeric polyester deposits on cooling coils and reactor walls lower heat transfer coefficients and force solvent recirculation between batches. The crude polyester is hydrolysed with aqueous hydrochloric or sulfuric acid, steam-distilled, and crystallized to yield sorbic acid or converted to its potassium salt. The finished preservatives are tested against Commission Regulation (EU) No 231/2012 for E 200/E 202, the JECFA sorbic acid and potassium sorbate specifications, and the applicable FCC monograph. In finished food matrices, sorbic acid or potassium sorbate is typically added at 0.025 wt% to 0.1 wt%, with the upper limit set by product category regulations. Terminal product types include preservative-treated bakery goods, processed cheese, dry sausage casings, wine and beverage stabilization, and animal feed preservation. Crotonaldehyde itself is not a direct food additive and is consumed as a captive intermediate.
Liquid-phase oxidation of crotonaldehyde to crotonic acid is carried out in a bubble column or stirred gas-liquid reactor charged with acetic acid diluent and a manganese/cobalt acetate catalyst. Air or oxygen-lean air is staged through the sparger so that oxygen-to-crotonaldehyde molar delivery remains below the stoichiometric acid-formation demand and off-gas oxygen concentration is held below 8 vol%. The oxidation mass is maintained at 40–70 °C and 0.2–0.6 MPa; higher oxygen partial pressure accelerates over-oxidation to acetic acid and carbon dioxide, while lower oxygen loading increases residence time. Unreacted crotonaldehyde is recovered in vent condensers and recycled to the oxidation feed. Quantitative kinetic data for proprietary manganese/cobalt catalyst packages are not uniformly published; verified plant documentation should be consulted for catalyst-specific oxygen uptake curves. Crude crotonic acid is purified by vacuum distillation and controlled for residual aldehyde, water, and polymerizable impurities. The monomer is released under REACH (EC) No 1907/2006 registration and ISO 9001:2015 quality control. In vinyl acetate-ethylene copolymer emulsions, crotonic acid is incorporated at 0.5–5 wt% of total monomer to introduce carboxyl functionality; loadings above 8 wt% typically increase emulsion viscosity and coagulum formation in production batches. Terminal finished products include crotonic acid and methyl/ethyl crotonate monomers, vinyl acetate-crotonic acid copolymer emulsions for textile sizing, hair fixative resins, and waterborne coating binders.
When aniline and crotonaldehyde are condensed in an acid-catalysed Doebner-Miller ring closure, the feed molar ratio of aniline to crotonaldehyde is maintained between 1.0:1 and 1.2:1 to limit high-boiling tar formation. The reaction is conducted in a glass-lined or acid-resistant stainless vessel charged with aqueous sulfuric acid; crotonaldehyde is added below 60 °C because fast dosing creates localized exotherms and polymerized by-products. After the addition is complete, the batch is heated to 95–110 °C to close the quinoline ring, then neutralized and steam-distilled. Production-scale distillation columns are operated under vacuum because quinaldine and residual aniline form azeotropic mixtures; wiped-film evaporation is used when tar content exceeds 1% of batch mass. The distilled quinaldine is verified by gas chromatography and falls under the supplier’s REACH (EC) No 1907/2006 intermediate registration and ISO 9001:2015 release testing. Terminal product types include 2-methylquinoline derivatives for quinophthalone dyes, antimalarial and veterinary drug intermediates, quinoline-based agrochemical building blocks, and corrosion inhibitor packages used in oilfield acidizing formulations.
Methanol addition to crotonaldehyde produces 3-methoxybutyraldehyde, which is then hydrogenated to 3-methoxybutanol. In the addition step, methanol-to-crotonaldehyde molar ratio is controlled between 1.05:1 and 1.25:1 with sodium methoxide added at 0.1–0.5 mol% relative to crotonaldehyde. The reactor is held at 30–60 °C with external cooling because the addition is exothermic; methanol must be pre-dried to 200 ppm water to avoid hydrolysis and aldol condensation on downstream catalyst acid sites. The intermediate is hydrogenated in a fixed-bed reactor over nickel-on-silica catalyst at 100–150 °C and 2–6 MPa. Production-scale operation must monitor pressure drop across the catalyst bed; aldol-derived heavies increase differential pressure and reduce cycle length. Crude 3-methoxybutanol is purified by vacuum distillation and tested under ASTM D1078-21 for distillation range, ASTM E203-24 for water content, and gas chromatographic purity specifications. Terminal finished product types include 3-methoxybutanol and its acetate ester used as specialty solvents in printing inks, coil coatings, adhesive formulations, and agricultural formulation carriers.
For recovered crotonaldehyde routed to oxo-alcohol recycle streams, selective hydrogenation converts the unsaturated aldehyde to n-butyraldehyde over a palladium or nickel fixed-bed catalyst. The hydrogen-to-crotonaldehyde molar ratio at the reactor inlet is held between 1.00:1 and 1.10:1; excess hydrogen above 1.20:1 promotes over-reduction to n-butanol and reduces aldehyde yield. Bed temperature is segmented between 120 °C and 180 °C to manage the strong exotherm, and hot spots above 220 °C cause methane formation and carbon deposition. The n-butyraldehyde effluent is condensed, flashed, and then sent to aldolization and hydrogenation for 2-ethylhexanol or to oxidation and esterification for butyric acid derivatives. The n-butanol fraction is tested against ASTM D304-11(2020) for n-butyl alcohol and relevant butanol purity specifications. Terminal finished product types include 2-ethylhexanol-derived non-phthalate plasticizers, butyl acrylate, butyl acetate, amino resins, and solvent-grade n-butanol for coatings and industrial cleaners.
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Crotonaldehyde, also referred to as 2-butenal, is an α,β-unsaturated aldehyde with the formula CH₃CH=CHCHO, relative molecular mass 70.09 g/mol, CAS registry designation 123-73-9 for the mixed isomeric product, and CAS 4170-30-3 for the E-isomer. Common commercial variants include the stabilised technical grade, a low-moisture synthesis grade for water-sensitive downstream chemistry, and a low-acidity grade for esterification or catalyst-sensitive hydrogenation. A typical stabilised technical-grade material is controlled to assay not less than 99.0% area by GC, water content not more than 0.05 wt% by ASTM D1364, color not more than 15 Pt-Co by ASTM D1209, and distillation range from 102.0 °C to 104.0 °C at 101.3 kPa by ASTM D1078. The closed-cup flash point is approximately 13 °C, and the lower and upper explosive limits in air are approximately 2.1 vol% and 15.5 vol%, respectively. Vapor pressure at 20 °C is approximately 3.9 kPa. Because the aldehyde function is conjugated with the carbon-carbon double bond, crotonaldehyde exhibits both aldehyde-typical condensation behavior and β-carbon Michael addition chemistry; this dual reactivity differentiates it from saturated C₄ aldehydes in downstream processing.
| Parameter | Typical specification | Test method |
|---|---|---|
| Assay, sum of isomers | ≥ 99.0% area | Gas chromatography |
| Water content | ≤ 0.05 wt% | ASTM D1364 |
| Color | ≤ 15 Pt-Co | ASTM D1209 |
| Distillation range | 102.0–104.0 °C at 101.3 kPa | ASTM D1078 |
| Acidity as acetic acid | ≤ 0.05 wt% | ASTM D1613 |
| Inhibitor, hydroquinone | 0.1–0.5 wt% | Internal spectrophotometric method |
Compared with acrolein, crotonaldehyde has a higher normal boiling point and lower vapor pressure, so liquid-phase reactor and condenser systems can often operate with coolant temperatures of 10–15 °C rather than refrigerated brine. Compared with saturated C₄ aldehydes such as n-butyraldehyde and isobutyraldehyde, crotonaldehyde is more electrophilic at the β-carbon and participates in Michael addition reactions that are not accessible to the saturated analogues. In catalytic hydrogenation, this unsaturation makes selectivity more difficult to control: unmodified nickel catalysts can promote decarbonylation and aldol side reactions, so copper-based or modified copper-zinc oxide systems are typically preferred. The comparative property differences are summarised in the following table.
| Property | Crotonaldehyde | Acrolein | n-Butyraldehyde |
|---|---|---|---|
| CAS registry number | 123-73-9 / 4170-30-3 | 107-02-8 | 123-72-8 |
| Boiling point at 101.3 kPa | 102–104 °C | 52.5 °C | 74.8 °C |
| Flash point, closed cup | 13 °C | -26 °C | -7 °C |
| Vapor pressure at 20 °C | approx. 3.9 kPa | approx. 29.3 kPa | approx. 10.5 kPa |
| Water solubility | approx. 18.1 g/100 mL at 20 °C | approx. 20.6 g/100 mL at 20 °C | approx. 7.1 g/100 mL at 25 °C |
Continuous acetaldehyde condensation units for crotonaldehyde manufacture generally use an agitated reactor cascade with residence times of 20–60 min at 15–35 °C and aqueous sodium hydroxide addition of 0.5–1.5 mol% relative to acetaldehyde feed. The exotherm is removed by internal cooling coils, and the resulting aldol stream is dehydrated in a thin-film evaporator at 70–90 °C under 200–400 mbar absolute. Crude crotonaldehyde is then distilled through a 316L stainless steel column with structured packing. On production lines, rising reboiler pressure drop at constant bottom temperature is frequently caused by aldol polymer fouling; control strategies include limiting total nitrogen-containing impurities below 50 mg/kg, maintaining reboiler temperature below 120 °C, and keeping oxygen ingress low. Hydroquinone dose is maintained at 100–500 mg/kg in the finished distillate to suppress polymerization during storage.
Inhibitor selection modifies downstream behavior. Hydroquinone at 0.1–0.5 wt% retards free-radical propagation but can interfere with peroxide-initiated polymerizations if crotonaldehyde is used as a comonomer. Hydroquinone monomethyl ether is substituted in some synthesis grades because it is less acidic and less prone to color development in esterification batches. Acidity limits are set at or below 0.05 wt% as acetic acid by ASTM D1613 because residual acid accelerates acetal formation and aldol condensation during storage. Water below 0.05 wt% by ASTM D1364 prevents hydrate formation that shifts the carbonyl equilibrium and depresses GC assay intensity. A low-moisture grade with water below 0.03 wt% is used where water consumes ketene or hydrolyzes water-sensitive intermediates.
Hydrogenation of crotonaldehyde to n-butyraldehyde or n-butanol is performed in fixed-bed reactors containing copper-zinc oxide or copper-chromite catalysts at 150–220 °C and 1.0–3.0 MPa hydrogen partial pressure. Selectivity to n-butanol depends on temperature, hydrogen-to-aldehyde ratio, and alkali metal content of the catalyst. Nickel-based catalysts are generally not preferred because decarbonylation and aldol side reactions reduce C₄ selectivity. In sorbic acid production, crotonaldehyde is condensed with ketene at 20–50 °C over zinc carboxylate catalysts, and the resulting intermediate is hydrolyzed under acidic conditions at 80–100 °C. The water content of crotonaldehyde is critical in this route because water consumes ketene. Crotonaldehyde also enters Michael addition pathways with thiols and active methylene compounds to yield 3-substituted butyraldehydes; these applications require low acidity to avoid premature acid-catalysed aldol condensation. Published data for some specific downstream reaction configurations is limited, but the general hydrogenation and condensation behavior is documented in industrial catalyst literature.
Distillation of inhibited grades is required for applications where hydroquinone poisons hydrogenation catalysts or discolors condensation resins. A wiped-film evaporation stage at 90–110 °C and 20–40 mbar absolute removes non-volatile inhibitor; the distillate is then used within 24–48 h or re-inhibited at 5–10 mg/kg to prevent rapid viscosity rise. Bulk tanks should use nitrogen blanketing at 5–10 kPa gauge, 10 kPa pressure/vacuum relief, and 316L stainless steel or lined carbon steel construction. Carbon steel is acceptable for dry, inhibited material, but stainless-clad storage is recommended for long-term service. The material is incompatible with strong alkalis, primary and secondary amines, strong oxidizers, and copper alloys. Uninhibited crotonaldehyde can undergo exothermic polymerization; material stripped of hydroquinone for catalyst-sensitive processes must be consumed promptly or stabilised. Reboiler temperatures should not exceed 120 °C to prevent polymer film formation during distillation. For storage and handling compliance, the material is classified under flammable liquid rules in NFPA 30 and is subject to registration and risk-management measures under REACH.