Ethylamine, also known as ethanamine, is an organic compound with the molecular formula C₂H₇N or CH₃CH₂NH₂, classified as the simplest primary aliphatic amine and a direct ethyl derivative of ammonia.[1] This colorless, flammable gas or low-boiling liquid exhibits a strong ammonia-like odor and serves as a key intermediate in organic synthesis across various industries.[1]Ethylamine has a molecular weight of 45.08 g/mol, a boiling point of 16.6 °C, a melting point of -81.2 °C, and a density of 0.689 g/cm³ at 15 °C.[1] It is highly soluble in water (miscible), as well as in ethanol and ether, and possesses a pKa of 10.7 at 25 °C, reflecting its basic nature similar to ammonia.[2] With a flash point below -18 °C and vapor density of 1.55 relative to air, it forms explosive mixtures with air (LEL 3.5%, UEL 14%) and reacts vigorously with oxidizing agents, acids, and certain metals like copper or zinc.[1]Industrially, ethylamine is produced primarily through the amination of ethanol with ammonia over an alumina catalyst at 350–400 °C or via the catalytic hydrogenation of acetaldehyde in the presence of ammonia and a nickel catalyst.[2] Alternative synthesis routes include the hydrogenation of nitroethane, the reaction of ethyl chloride with alcoholic ammonia under heat and pressure, or the catalytic hydrogenation of aziridines, often yielding it as a pure gas or 40–50% aqueous solution.[3]Ethylamine finds extensive applications as a building block in the manufacture of triazine herbicides such as atrazine and simazine, as well as in the production of dyes, pharmaceuticals, surfactants, detergents, emulsifiers, cosmetics, fibers, resins, and organic paints.[1] It is also employed in oil refining as an additive, as a stabilizer for rubber latex, and in the synthesis of rubber accelerators and medicinal preparations, underscoring its versatility in chemical and material sciences.[3]
Structure and Nomenclature
Molecular Structure
Ethylamine, with the structural formula CH₃CH₂NH₂, is a primary aliphatic amine consisting of an ethyl group (CH₃CH₂-) bonded to an NH₂ group. Both carbon atoms and the nitrogen atom exhibit sp³ hybridization, leading to tetrahedral local geometries around these atoms.The Lewis structure depicts a single bond between the two carbon atoms, a single C-N bond, two N-H bonds, and a lone pair on the nitrogen atom, which contributes to its nucleophilic character. In three-dimensional space, ethylamine adopts a staggered conformation around both the C-C and C-N bonds to minimize torsional strain and steric interactions between the methyl group and the amino hydrogens.Experimental gas-phase structural parameters, determined by electron diffraction, show the C-C bond length as approximately 1.53 Å and the C-N bond length as approximately 1.47 Å, with minor differences between the trans (C-C 1.531 Å, C-N 1.470 Å) and gauche (C-C 1.524 Å, C-N 1.475 Å) conformers. The H-N-H bond angle measures about 107°, reflecting the influence of the lone pair repulsion on the nitrogen pyramidality.[4]Relative to ammonia (NH₃), the ethyl group in ethylamine acts as an electron-donating substituent via inductive effects, slightly enhancing the basicity of the amine; the pKₐ of the ethylammonium ion is 10.6, compared to 9.2 for the ammonium ion.
Names and Identifiers
Ethylamine, with the molecular formula C₂H₇N, is systematically named ethanamine as the preferred IUPAC name.[1] This nomenclature treats the compound as a derivative of ethane, replacing the terminal "-e" with "-amine" to indicate the primary amino group.[5]Common names for the compound include ethylamine and monoethylamine, the latter emphasizing its status as a simple primary amine.[1]In chemical databases and regulatory contexts, ethylamine is assigned the CAS Registry Number 75-04-7, the EC (EINECS) number 200-834-7, and the UN number 1036 for transport classification as a flammable gas. Additional identifiers include PubChem CID 6341 and the InChI string InChI=1S/C2H7N/c1-2-3/h3H2,1-2H3.Historically, the compound was commonly referred to as ethylamine in early chemical literature, reflecting its derivation from ethyl alcohol; however, the preferred IUPAC name ethanamine was formally established in the 1979 Recommendations of the International Union of Pure and Applied Chemistry (IUPAC) for the Nomenclature of Organic Chemistry, promoting systematic alkanamine naming for primary amines.
Properties
Physical Properties
Ethylamine is a colorless gas at standard temperature and pressure, exhibiting a strong ammoniacal odor often described as fishy.[1][6] Its molecular weight is 45.08 g/mol.[1]The liquid density of ethylamine is 0.687 g/cm³ at 15 °C, while its vapor density relative to air is 1.56.[1] It has a melting point of -81 °C and a boiling point of 16.6 °C.[1][3]Ethylamine is miscible with water, ethanol, and diethyl ether, and it shows good solubility in organic solvents such as benzene.[1][2] The refractive index of the liquid is 1.366 at 20 °C.[1] Its liquid viscosity is approximately 0.3 cP near 0 °C, decreasing with temperature.[7]
Chemical Properties
Ethylamine acts as a weak base in aqueous solution, characterized by a pK_b value of 3.36, corresponding to a pK_a of 10.64 for its conjugate acid at 25°C. This basicity arises from the lone pair on the nitrogen atom, enabling protonation according to the equilibrium:\mathrm{CH_3CH_2NH_2 + H_2O \rightleftharpoons CH_3CH_2NH_3^+ + OH^-}The compound exhibits high stability under ambient conditions but undergoes thermal decomposition at temperatures exceeding 300°C, primarily yielding ethylene and ammonia through unimolecular pathways involving hydrogen, ammonia, or methane elimination.[8]Spectroscopically, ethylamine displays a characteristic N-H stretching band in the infrared spectrum at approximately 3300 cm⁻¹, indicative of its primary amine functionality.[9] In the ¹H NMR spectrum, the methyl protons appear as a triplet at 1.1 ppm, the methylene protons as a quartet at 2.6 ppm, and the amino protons as a broad singlet at 1.2 ppm, reflecting the expected splitting patterns and hydrogen bonding effects.[10]The polarity of ethylamine stems from the electronegative nitrogen, resulting in a dipole moment of approximately 1.3 D.[11] This property contributes to its moderate solubility in water and role as a nucleophile in various chemical processes.
Thermodynamic Properties
Ethylamine's thermodynamic properties are crucial for applications in process design, equilibrium predictions, and energy balance calculations in chemical engineering and synthesis. In the gas phase, the standard enthalpy of formation (ΔH_f°) is -50.03 kJ/mol at 298.15 K, reflecting the energy change when forming the compound from its elements in their standard states.[12] The standard Gibbs free energy of formation (ΔG_f°) is 36.3 kJ/mol, indicating the spontaneity of formation under standard conditions.[13]The standard entropy (S°) in the gas phase is 283.8 J/mol·K at 298 K, providing insight into the disorder associated with the molecule.[13] The molar heat capacity at constant pressure (C_p) for the gas is 71.5 J/mol·K at 25°C, while the enthalpy of vaporization (ΔH_vap) is 26.8 kJ/mol at the boiling point of approximately 289 K.[13][14] These values enable accurate modeling of phase changes and thermal behaviors.The C-N bond dissociation energy is approximately 305 kJ/mol, a key parameter for assessing molecular stability during bond-breaking processes.
These parameters relate to the overall stability of ethylamine, as explored in its chemical properties.
Occurrence and Production
Natural Occurrence
Ethylamine has been tentatively detected in the interstellar medium toward the Galactic center molecular cloud G+0.693−0.027 through radio astronomical observations, marking it as one of the complex organic molecules present in such environments.[15] The derived column density corresponds to an abundance of (1.9 ± 0.5) × 10^{-10} relative to H₂, indicating its rarity but significance in astrochemistry.[15]Laboratory simulations replicating interstellar conditions further support its natural formation, showing that ethylamine arises from the irradiation of ices composed of ammonia (NH₃) and methane (CH₄) with energetic particles, such as those from cosmic rays.[16] This process highlights ethylamine's potential role as a prebiotic building block, contributing to the synthesis of proteinogenic α-amino acids in extraterrestrial settings.[16]On Earth, ethylamine functions as a metabolite in biological systems, primarily generated via the decarboxylation of alanine catalyzed by alanine decarboxylase (AlaDC).[17] In humans, it appears as a normal constituent of urine and is derived from amino acid breakdown, though in trace quantities.[1] Similarly, plants such as tea (Camellia sinensis) produce ethylamine through AlaDC-mediated alaninedecarboxylation, where it serves as a precursor for compounds like theanine.[18] Microorganisms also generate ethylamine in small amounts during metabolic processes, underscoring its widespread but minor presence in terrestrial biochemistry.[19]In environmental contexts, ethylamine exists at low atmospheric concentrations, typically below levels that pose significant pollution risks, due to its short half-life of about 14 hours in the presence of hydroxyl radicals.[1] It emerges as a minor byproduct in natural fermentation, accumulating in trace amounts in beverages like wine, beer, and vinegar through microbial activity on amino acids.[20] These occurrences reflect its incidental role in organic decay and food-related processes rather than as a dominant environmental compound.[1]
Industrial Production
Ethylamine is primarily produced industrially through the catalytic amination of ethanol with ammonia in the presence of hydrogen. This process employs a heterogeneous catalyst, typically consisting of copper, cobalt, and nickel supported on gamma-alumina (Al₂O₃), at temperatures ranging from 200 to 300°C. The reaction proceeds as CH₃CH₂OH + NH₃ → CH₃CH₂NH₂ + H₂O, achieving a selectivity of approximately 70% toward ethylamine under optimized conditions.[21]Alternative production routes include the reductive amination of acetaldehyde with ammonia and hydrogen over a suitable catalyst, represented by CH₃CHO + NH₃ + H₂ → CH₃CH₂NH₂.[22]In these processes, particularly the ethanol amination, diethylamine and triethylamine form as significant byproducts due to further alkylation of the primary amine. These are managed through distillation and decantation steps, with portions recirculated to the reactor to convert intermediates into higher-boiling compounds and prevent accumulation, ensuring efficient separation and recovery of the target ethylamine.[22]Global production of ethylamine stands at approximately 152,000 metric tons per year as of 2025, with major producers concentrated in Europe (e.g., BASF in Germany) and Asia (e.g., Balaji Amines in India). The overall ethylamine market, encompassing mono-, di-, and triethylamine variants, was valued at USD 3.17 billion in 2024.[23][24]
Reactions
Acid-Base Reactions
Ethylamine acts as a base through protonation of its nitrogen atom, forming the ethylammonium ion according to the equilibrium CH₃CH₂NH₂ + H⁺ ⇌ CH₃CH₂NH₃⁺, where the acid dissociation constant for the conjugate acid is K_a = 10^{-10.63} (pK_a = 10.63 at 25°C).[25] This protonation is reversible and reflects the compound's moderate basicity in aqueous solutions.The protonated form readily forms salts with acids, such as hydrochloric acid, yielding ethylammonium chloride (CH₃CH₂NH₃Cl) via the reaction CH₃CH₂NH₂ + HCl → CH₃CH₂NH₃⁺ Cl⁻. This salt is highly soluble in water (approximately 280 g/100 g at 25°C), facilitating its use in the purification of ethylamine by converting the free base to a crystalline or soluble ionic form that can be separated from non-polar impurities, followed by basification to regenerate the amine.[26]Aqueous solutions of ethylamine exhibit basic pH values due to partial protonation of water, with a 0.1 M solution having a pH of approximately 11.8, calculated from its base dissociation constant K_b = 4.3 × 10^{-4}.[27] In acid-base titrations with HCl, the pH starts high (around 12), decreases gradually as the base is protonated, and shows a sharp drop near the equivalence point (pH ≈ 5.5–6.5), where the solution becomes dominated by the ethylammonium ion acting as a weak acid.[28]Compared to ammonia (pK_a of NH₄⁺ = 9.25), ethylamine is a slightly stronger base, as the electron-donating inductive effect (+I) of the ethyl group increases the electron density on the nitrogen, enhancing its ability to accept a proton.[29]
Electrophilic Reactions
Ethylamine, as a primary aliphatic amine, readily undergoes acylation reactions with electrophilic acid chlorides to form N-ethylamides. The nucleophilic nitrogen attacks the carbonyl carbon of the acid chloride, displacing the chloride ion and yielding an amide after deprotonation. For example, the reaction of ethylamine with acetyl chloride proceeds as follows:\text{CH}_3\text{CH}_2\text{NH}_2 + \text{CH}_3\text{COCl} \rightarrow \text{CH}_3\text{CH}_2\text{NHCOCH}_3 + \text{HCl}This reaction is typically conducted in the presence of a base to neutralize the HCl byproduct and is a standard method for amide synthesis from primary amines.[30][31]Alkylation of ethylamine with alkyl halides occurs via nucleophilic substitution, where the amine acts as a nucleophile to displace the halide, forming higher-substituted amines. A representative example is the reaction with methyl iodide:\text{CH}_3\text{CH}_2\text{NH}_2 + \text{CH}_3\text{I} \rightarrow (\text{CH}_3\text{CH}_2)(\text{CH}_3)\text{NH} + \text{HI}However, due to the increased nucleophilicity of the resulting secondary amine, overalkylation to tertiary amines and quaternary ammonium salts is a common challenge, often requiring excess amine or protective strategies to control selectivity.[32][33]Ethylamine reacts with carbonyl compounds such as aldehydes to form imines, commonly known as Schiff bases, through nucleophilic addition followed by dehydration. This condensation typically requires mild acidic conditions or removal of water to drive the equilibrium toward the imine product. For instance, ethylamine and benzaldehyde form N-benzylideneethylamine. These imines serve as versatile intermediates in organic synthesis. In reductive amination, ethylamine condenses with an aldehyde or ketone to form an imine intermediate, which is then reduced (e.g., with NaBH₃CN or H₂) to yield a secondary amine, providing a selective route to alkylated products without overalkylation issues.[34][35]Among other electrophilic reactions, ethylamine reacts with carbon dioxide to form ethylcarbamic acid, which can exist in equilibrium or as a carbamatesalt under basic conditions. The mechanism involves nucleophilic attack by the amine nitrogen on CO₂, followed by proton transfer, often facilitated by a second amine molecule or solvent effects in aqueous media.[36] Additionally, ethylamine can be oxidized by hydrogen peroxide, typically under copper catalysis, to the corresponding imine, acetaldimine (CH₃CH=NH), via dehydrogenation, though this product is unstable and prone to hydrolysis.[37]
Reaction with Nitrous Acid
Primary aliphatic amines like ethylamine react with nitrous acid (HNO₂) to form unstable diazonium ions that decompose to nitrogen gas and alcohols. The reaction is:CH₃CH₂NH₂ + HNO₂ + HCl → CH₃CH₂OH + N₂ + 2H₂O + NaCl (in aqueous conditions)This is a distinguishing test for primary aliphatic amines and is used synthetically to convert amines to alcohols with retention of configuration at the carbon bearing the nitrogen.[38]
Applications
Synthetic Applications
Ethylamine serves as a vital precursor in the laboratory synthesis of pharmaceuticals, particularly antihistamines.In dye chemistry, ethylamine functions as a key intermediate, contributing to the formation of azo dyes via diazotization processes. Aromatic amines derived from or incorporating ethylamine groups are diazotized to generate diazonium salts, which then couple with nucleophilic components like phenols or additional amines to produce vibrant azo compounds. This role underscores ethylamine's utility in fine chemicalsynthesis for colorants, where its reactivity facilitates the assembly of conjugated systems responsible for dye absorbance properties.[39]Ethylamine is also valued as a solvent in specialized laboratory reductions, notably lithium-mediated dissolving metal reactions. For instance, in the conversion of ketones to secondary alcohols, ethylamine acts as a low-molecular-weight aminesolvent that stabilizes the reactive lithiumspecies, promoting selective reduction while minimizing side reactions. This application is particularly useful for hindered substrates, offering an alternative to traditional hydride reagents in organic synthesis.
Industrial Applications
Ethylamine plays a significant role in various industrial sectors, with its global market valued at approximately USD 2.3 billion in 2025 and projected to reach USD 3.6 billion by 2035, reflecting a compound annual growth rate (CAGR) of 4.4%. This growth is primarily driven by demand from the agrochemical industry, where ethylamine serves as a critical raw material for herbicidemanufacturing, alongside applications in rubber processing and pharmaceuticals.[40]In herbicide production, ethylamine is an essential intermediate for synthesizing triazine-based compounds such as atrazine and simazine. Atrazine, chemically known as 2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine, is produced through the nucleophilic substitution of cyanuric chloride with ethylamine and isopropylamine, enabling effective control of broadleaf and grassy weeds in crops like corn and sorghum. Global production of atrazine is estimated at around 70,000 tons annually, underscoring ethylamine's substantial contribution to this sector. Similarly, simazine (2-chloro-4,6-bis(ethylamino)-1,3,5-triazine) incorporates two molecules of ethylamine per unit via sequential reactions with cyanuric chloride, supporting its use in non-crop areas and certain orchards. These herbicides account for a major portion of ethylamine consumption, bolstering agricultural productivity worldwide.[41][42][43][44]Within the rubber industry, ethylamine functions as a precursor for vulcanization accelerators and antioxidants, enhancing the durability and performance of rubber products. As a building block, it contributes to the synthesis of amine-based accelerators that speed up the cross-linking of sulfur with rubber polymers during vulcanization, allowing for efficient production of tires, hoses, and belts. Additionally, ethylamine-derived compounds act as antioxidants, protecting rubber from oxidative degradation caused by heat, oxygen, and ozone exposure, thereby extending product lifespan in automotive and industrial applications. These uses highlight ethylamine's importance in supporting the high-volume rubber processing sector.[23][45]In pharmaceutical manufacturing, ethylamine is employed in the bulk synthesis of intermediates for various drugs. Ethylamine's role facilitates the large-scale production of these compounds, meeting the demands of the growing pharmaceutical industry.[46]Ethylamine is also used in the production of surfactants, detergents, emulsifiers, cosmetics, fibers, resins, and organic paints, as well as an additive in oil refining and a stabilizer for rubber latex.[1][3]
Safety and Hazards
Health and Toxicity
Ethylamine exhibits moderate acute toxicity via multiple exposure routes. The oral LD50 in rats is 400 mg/kg, while the dermal LD50 in rabbits is 265 mg/kg.[47]Inhalation toxicity is evidenced by an LCLO of 4,000 ppm for 4 hours in rats, where exposure killed 1 of 6 animals.[48] Occupational exposure limits include an OSHA permissible exposure limit (PEL) of 10 ppm (18 mg/m³) as an 8-hour time-weighted average (TWA), a NIOSH recommended exposure limit (REL) of 10 ppm (18 mg/m³) TWA, and an immediately dangerous to life or health (IDLH) value of 600 ppm.[48]Exposure to ethylamine causes severe irritation to the eyes, skin, and respiratory tract, with corrosive effects at high concentrations leading to burns and potential pulmonary edema.[49] Inhaled vapors may result in dyspnea, laryngeal and bronchial edema, nausea, vomiting, chemical pneumonia, and corneal ulceration, with pulmonary edema potentially fatal.[3]Chronic exposure to ethylamine can lead to damage in the liver, kidneys, and heart, as well as irritation of the lungs potentially causing bronchitis with symptoms including cough, phlegm, and shortness of breath.[50] It is classified under the Globally Harmonized System as corrosive, causing severe skin burns and eye damage (Skin Corr. 1; H314).[47] Ethylamine is not classified as carcinogenic by the International Agency for Research on Cancer (IARC Group 3).[51]Ethylamine is rapidly absorbed through oral, dermal, and inhalation routes, with toxic effects observed across these pathways. It is partially metabolized by oxidation to acetaldehyde and then acetic acid, with portions excreted unchanged via the lungs and urine primarily as ethylammonium ions; no significant bioaccumulation occurs due to its low molecular weight and high watersolubility.[39] Ethylamine is toxic to aquatic life (GHS Aquatic Acute 3; H402), with a 96-hour LC50 of approximately 46–198 mg/L in fish species such as golden orfe or rainbow trout.[47]
Flammability and Handling
Ethylamine is a highly flammable gas at room temperature, with a flash point below -18°C, making it prone to ignition from sparks, flames, or static electricity.[1] Its autoignition temperature is 385°C, and it forms explosive mixtures with air in concentrations ranging from 3.5% to 14% by volume.[1] During combustion, it releases irritating and toxic nitrogen oxides, and vapors, being heavier than air, can travel along the ground to distant ignition sources, potentially causing flash fires or explosions.[49]For safe storage, ethylamine should be kept in tightly closed containers made of compatible materials such as glass or steel, in cool, well-ventilated areas away from heat sources, direct sunlight, and ignition points.[52] It is typically stored under an inert atmosphere like nitrogen to prevent oxidation or reaction, and is incompatible with strong acids, oxidizing agents, and certain metals including copper, zinc, and nickel, which can lead to violent reactions or corrosion.[50]Handling ethylamine requires strict precautions to minimize fire and exposure risks, including use in well-ventilated fume hoods or explosion-proof equipment, and employment of non-sparking tools to avoid static discharge.[52]Personal protective equipment (PPE) must include chemical-resistant gloves (e.g., butyl rubber or chloroprene), safety goggles or face shields, flame-retardant clothing, and, where vapors may exceed safe levels, a respirator with an appropriate filter or self-contained breathing apparatus.[50] In case of spills, evacuate the area, eliminate ignition sources, ventilate to disperse vapors, and dilute with large quantities of water while containing the liquid with inert absorbents like vermiculite; professional hazardous waste disposal is recommended.[49]Under regulatory frameworks, pure ethylamine is classified by the U.S. Department of Transportation (DOT) as a flammable gas in Hazard Class 2.1 (UN 1036), while its aqueous solutions are treated as flammable liquids in Class 3 (UN 2270).[50] The Globally Harmonized System (GHS) designates it with pictograms for flammability (flame) and corrosion, emphasizing hazards of extreme flammability, potential explosion under pressure or heat, and severe skin/eye damage.[52]
History
Discovery
Ethylamine was first synthesized in 1849 by the French chemist Charles Adolphe Wurtz, marking it as the inaugural organic derivative of ammonia and a key advancement in understanding amine chemistry. Wurtz achieved this through the alkaline hydrolysis of ethyl isocyanate (also known as cyanic ether of ethyl), treating the compound with potassa (potassium hydroxide) and water in a reaction that replaced the oxygen in the isocyanate group to yield the amine. The process involved heating the mixture, followed by distillation to isolate the product, demonstrating Wurtz's innovative approach to substituting organic radicals for hydrogen atoms in ammonia.[53][54]Wurtz described ethylamine as a colorless, volatile liquid possessing a strong ammoniacal odor, which readily absorbed carbon dioxide from the air to form a carbonate. He measured its boiling point at approximately 17°C, noting its high solubility in water and its behavior as a strong base comparable to ammonia. These observations were pivotal in characterizing ethylamine's physical and chemical properties, confirming its composition through elemental analysis that aligned with the formula C₂H₅NH₂.[53]This discovery occurred within the broader context of mid-19th-century organic chemistry, building on the foundational understanding of ammonia as a type compound and extending Wurtz's investigations into alkyl substitutions, including his parallel work on alkyl halides. Ethylamine's synthesis exemplified the emerging "ammonia type" theory, which posited that organic bases could be derived systematically from ammonia by radical replacement, influencing subsequent amine research. At the time, its applications were confined to academic pursuits, such as exploring the reactivity of organic bases and their salts in fundamental studies of nitrogen-containing compounds.[54][55]
Commercial Development
The commercial development of ethylamine originated from its initial laboratory synthesis in 1849.[54] Industrial production of ethylamine began in the mid-20th century, primarily through the amination of ethanol with ammonia over catalysts. Post-World War II, production expanded rapidly alongside the petrochemical boom, as inexpensive feedstocks like ethanol and acetaldehyde became widely available, scaling global output to support emerging industrial applications in agrochemicals and other sectors.Economic growth has been propelled by demand in the agrochemical sector for pesticide and pharmaceutical intermediates, with global annual production estimated at approximately 185,000 metric tons as of 2021 and the market projected to expand at a compound annual growth rate (CAGR) of 4.4% through 2035.[56][40]