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Ethanolamine
Ethanolamine
Ethanolamine
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Ethanolamine
Names
Preferred IUPAC name
2-Aminoethan-1-ol[1]
Other names
  • 2-Aminoethanol
  • 2-Amino-1-ethanol
  • Ethanolamine (not recommended[1])
  • Monoethanolamine
  • β-Aminoethanol
  • β-hydroxyethylamine
  • β-Aminoethyl alcohol
  • Glycinol
  • Olamine
  • MEA
  • Ethylolamine
  • 2-Hydroxyethylamine
  • Colamine
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
DrugBank
ECHA InfoCard 100.004.986 Edit this at Wikidata
EC Number
  • 205-483-3
KEGG
RTECS number
  • KJ5775000
UNII
  • InChI=1S/C2H7NO/c3-1-2-4/h4H,1-3H2 checkY
    Key: HZAXFHJVJLSVMW-UHFFFAOYSA-N checkY
  • InChI=1/C2H7NO/c3-1-2-4/h4H,1-3H2
    Key: HZAXFHJVJLSVMW-UHFFFAOYAD
  • NCCO
Properties
C2H7NO
Molar mass 61.084 g·mol−1
Appearance Viscous colourless liquid
Odor Unpleasant ammonia-like odour
Density 1.0117 g/cm3
Melting point 10.3 °C (50.5 °F; 283.4 K)
Boiling point 170 °C (338 °F; 443 K)
Miscible
Vapor pressure 64 Pa (20 °C)[2]
Acidity (pKa) 9.50[3]
1.4539 (20 °C)[4]
Hazards
GHS labelling:
GHS05: CorrosiveGHS07: Exclamation mark
Danger
H302, H312, H314, H332, H335, H412[5]
P261, P273, P303+P361+P353, P305+P351+P338[5]
NFPA 704 (fire diamond)
NFPA 704 four-colored diamondHealth 3: Short exposure could cause serious temporary or residual injury. E.g. chlorine gasFlammability 2: Must be moderately heated or exposed to relatively high ambient temperature before ignition can occur. Flash point between 38 and 93 °C (100 and 200 °F). E.g. diesel fuelInstability 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
3
2
0
Flash point 85 °C (185 °F; 358 K) (closed cup)
410 °C (770 °F; 683 K)
Explosive limits 5.5–17%
Lethal dose or concentration (LD, LC):
  • 3320 mg/kg (rat, oral)
  • 620 mg/kg (guinea pig, oral)
  • 2050 mg/kg (rat, oral)
  • 1475 mg/kg (mouse, oral)
  • 1000 mg/kg (rabbit, oral)
  • 700 mg/kg (mouse, oral)
  • 1720–1970 mg/kg (rat, oral)[7]
NIOSH (US health exposure limits):
PEL (Permissible)
 TWA: 3 ppm (6 mg/m3)[6]
REL (Recommended)
  • TWA: 3 ppm (8 mg/m3)
  • ST: 6 ppm (15 mg/m3)[6]
IDLH (Immediate danger)
 30 ppm[6]
Safety data sheet (SDS) Sigma[5]
Related compounds
Related compounds
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
checkY verify (what is checkY☒N ?)

Ethanolamine (2-aminoethanol, monoethanolamine, ETA, or MEA) is a naturally occurring organic chemical compound with the formula HOCH
2CH
2NH
2 or C
2H
7NO.[8] The molecule is bifunctional, containing both a primary amine and a primary alcohol. Ethanolamine is a colorless, viscous liquid with an odor reminiscent of ammonia.[9]

Ethanolamine is commonly called monoethanolamine or MEA in order to be distinguished from diethanolamine (DEA) and triethanolamine (TEOA). The ethanolamines comprise a group of amino alcohols. A class of antihistamines is identified as ethanolamines, which includes carbinoxamine, clemastine, dimenhydrinate, chlorphenoxamine, diphenhydramine and doxylamine.[10]

History

[edit]

Ethanolamines, or in particular, their salts, were discovered by Charles Adolphe Wurtz in 1860[11] by heating 2-chloroethanol with ammonia solution while studying derivatives of ethylene oxide he discovered a year earlier.[12] He wasn't able to separate the salts or isolate any free bases.

In 1897 Ludwig Knorr developed the modern industrial route (see below) and separated the products, including MEA, by fractional distillation, for the first time studying their properties.[13]

None of the ethanolamines were of any commercial importance until after the WWII industrial production of ethylene oxide took off.[12]

Occurrence in nature

[edit]

MEA molecules are a component in the formation of cellular membranes and are thus a molecular building block for life. Ethanolamine is the second-most-abundant head group for phospholipids, substances found in biological membranes (particularly those of prokaryotes); e.g., phosphatidylethanolamine. It is also used in messenger molecules such as palmitoylethanolamide, which has an effect on CB1 receptors.[14]

MEA was thought to exist only on Earth and on certain asteroids, but in 2021 evidence was found that these molecules exist in interstellar space.[15]

Ethanolamine is biosynthesized by decarboxylation of serine:[16]

HOCH
2CH(CO
2H)NH
2 → HOCH
2CH
2NH
2 + CO2

Derivatives of ethanolamine are widespread in nature; e.g., lipids, as precursor of a variety of N-acylethanolamines (NAEs), that modulate several animal and plant physiological processes such as seed germination, plant–pathogen interactions, chloroplast development and flowering,[17] as well as precursor, combined with arachidonic acid C
20H
32O
2 20:4, ω-6), to form the endocannabinoid anandamide (AEA: C
22H
37NO
2; 20:4, ω-6).[18]

MEA is biodegraded by ethanolamine ammonia-lyase, a B12-dependent enzyme. It is converted to acetaldehyde and ammonia via initial H-atom abstraction.[19]

H2NCH2CH2OH → NH3 + CH3CHO

Industrial production

[edit]

Monoethanolamine is produced by treating ethylene oxide with aqueous ammonia; the reaction also produces diethanolamine and triethanolamine. The ratio of the products can be controlled by the stoichiometry of the reactants.[20]

Applications

[edit]

MEA is used as feedstock in the production of detergents, emulsifiers, polishes, pharmaceuticals, corrosion inhibitors, and chemical intermediates.[9]

For example, reacting ethanolamine with ammonia gives ethylenediamine, a precursor of the commonly used chelating agent, EDTA.[20]

Gas stream scrubbing

[edit]
See also: carbon dioxide scrubber and sour gas

Monoethanolamines can scrub combusted-coal, combusted-methane and combusted-biogas flue emissions of carbon dioxide (CO2) very efficiently. MEA carbon dioxide scrubbing is also used to regenerate the air on submarines.

Solutions of MEA in water are used as a gas stream scrubbing liquid in amine treaters.[21] For example, aqueous MEA is used to remove carbon dioxide (CO2) and hydrogen sulfide (H2S) from various gas streams; e.g., flue gas and sour natural gas.[22] The MEA ionizes dissolved acidic compounds, making them polar and considerably more soluble.

MEA scrubbing solutions can be recycled through a regeneration unit. When heated, MEA, being a rather weak base, will release dissolved H2S or CO2 gas resulting in a pure MEA solution.[20][23]

Other uses

[edit]

In pharmaceutical formulations, MEA is used primarily for buffering or preparation of emulsions. MEA can be used as pH regulator in cosmetics.[24]

It is an injectable sclerosant as a treatment option of symptomatic hemorrhoids. 2–5 ml of ethanolamine oleate can be injected into the mucosa just above the hemorrhoids to cause ulceration and mucosal fixation thus preventing hemorrhoids from descending out of the anal canal.

It is also an ingredient in cleaning fluid for automobile windshields.[25]

pH-control amine

[edit]

Ethanolamine is often used for alkalinization of water in steam cycles of power plants, including nuclear power plants with pressurized water reactors. This alkalinization is performed to control corrosion of metal components. ETA (or sometimes a similar organic amine; e.g., morpholine) is selected because it does not accumulate in steam generators (boilers) and crevices due to its volatility, but rather distributes relatively uniformly throughout the entire steam cycle. In such application, ETA is a key ingredient of so-called "all-volatile treatment" of water (AVT).[citation needed]

Reactions

[edit]

Upon reaction with carbon dioxide, 2 equivalents of ethanolamine react through the intermediacy of carbonic acid to form a carbamate salt,[26] which when heated usually reforms back to ethanolamine and carbon dioxide but occasionally can also cyclizate to 2-oxazolidone, generating amine gas treatment wastes.[27]

References

[edit]
[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Ethanolamine

View on Grokipedia
from Grokipedia
Ethanolamine, also known as 2-aminoethanol or monoethanolamine, is an organic with the molecular formula C₂H₇NO or HOCH₂CH₂NH₂, featuring both a (-NH₂) and a (-OH) that enable its bifunctional reactivity. This colorless, viscous liquid has an ammonia-like odor, a of 171 °C, a of 10.5 °C, and is fully miscible with , , acetone, and other polar solvents, reflecting its alkaline and hygroscopic nature. It is industrially produced primarily through the of with aqueous , yielding a mixture of ethanolamines including monoethanolamine, , and , which are subsequently separated by . Ethanolamine serves as a key intermediate in the manufacture of surfactants, emulsifiers, and chelating agents used in detergents, like shampoos and soaps, and cleaning formulations where it aids in adjustment and dirt removal. In industrial applications, it is employed for gas scrubbing to remove (CO₂) and (H₂S) from and process streams, as well as in pharmaceuticals, textiles, leather processing, and as a in boiler systems. The U.S. (FDA) approves its use as an indirect and washing agent, while the Cosmetic Ingredient Review deems it safe in rinse-off cosmetics at low concentrations. Despite its utility, ethanolamine is corrosive to and eyes, moderately toxic upon , , or absorption, and can cause respiratory irritation, with occupational exposure limits set by the (OSHA) at 3 ppm over an 8-hour time-weighted average. First prepared in the laboratory in 1860, with large-scale synthesis developed in 1897 by Ludwig Knorr, it has also been detected in , suggesting potential roles in prebiotic chemistry.

Properties

Physical properties

Ethanolamine (C₂H₇NO) is a bifunctional with a molecular weight of 61.08 g/mol. It appears as a colorless, at , exhibiting an ammonia-like . This physical state influences its handling in industrial and settings, where it remains liquid over a moderate temperature range. Key physical characteristics include a of 10.3 °C and a of 170.8 °C, indicating stability under ambient conditions but requiring caution during heating processes. The is 1.012 g/cm³ at 20 °C, contributing to its syrupy consistency. Ethanolamine is fully miscible with and , facilitating its use in aqueous solutions, while it shows limited in organic solvents such as . Additional properties include a refractive index of 1.4538 at 20 °C, a flash point of 85 °C, and a vapor pressure of 0.4 mmHg at 20 °C, which inform safety protocols for storage and transport. Its viscosity measures approximately 18.0 cP at 25 °C, and the specific heat capacity is about 3.20 J/g·K. Regarding acid-base behavior, the pKa of the amine group is 9.50, while that of the alcohol group is approximately 15.5.
PropertyValueConditions
Molecular formulaC₂H₇NO-
Molecular weight61.08 g/mol-
AppearanceColorless viscous liquid, ammonia-like odorRoom temperature
Melting point10.3 °C-
Boiling point170.8 °C760 mmHg
Density1.012 g/cm³20 °C
Refractive index1.453820 °C
Flash point85 °CClosed cup
Vapor pressure0.4 mmHg20 °C
Viscosity18.0 cP25 °C
Specific heat capacity3.20 J/g·KLiquid phase
pKa (amine)9.5025 °C
pKa (alcohol)≈15.5-
Solubility in waterFully miscible-
Solubility in ethanolFully miscible-
Solubility in etherSlightly soluble-

Chemical properties

Ethanolamine is a bifunctional possessing a (-NH₂) group and a (-OH) group attached to adjacent carbon atoms. This arrangement confers amphoteric character, enabling it to behave as a base via the (with the pKa of its conjugate at 9.5 at 25°C) and as a weak via the alcohol (pKa ≈ 15.5). The molecule's ability to form extensive bonds, both intramolecularly and intermolecularly, through its -NH₂ and -OH groups results in strong associations that elevate its to 170°C—significantly higher than expected for a compound of its 61 g/mol molecular weight. Ethanolamine demonstrates good under ambient conditions but is hygroscopic, readily absorbing moisture and from air to form carbonates. It undergoes slow oxidative degradation in the presence of oxygen, yielding products such as and . begins above approximately 200°C, producing hazardous gases including nitrogen oxides and carbon oxides. Key spectroscopic properties reflect the contributions of its and alcohol functionalities. (IR) spectra exhibit broad overlapping stretches for O-H and N-H at 3200–3600 cm⁻¹, N-H bending near 1600 cm⁻¹, and C-O stretching around 1050–1100 cm⁻¹. In ¹H (NMR), the CH₂NH₂ protons appear at 2.7–3.1 ppm and CH₂OH at 3.5–3.8 ppm (in D₂O), while ¹³C NMR shows distinct signals at ≈42 ppm (CH₂NH₂) and ≈61 ppm (CH₂OH). (UV) absorption is weak, with a maximum near 226 nm attributable to n→σ* transitions.

Nomenclature and Structure

Naming conventions

Ethanolamine is systematically named based on its bifunctional nature, incorporating both an alcohol and an group. The is 2-aminoethan-1-ol, reflecting the higher precedence of the as the principal characteristic group, with the amino at position 2 on the ethane chain. An alternative retained IUPAC name for general is 2-aminoethanol. When the amine function is considered principal, the systematic name becomes 2-hydroxyethanamine, though this is less commonly used due to seniority rules favoring alcohols. In common usage, the compound is referred to as ethanolamine or monoethanolamine (MEA), the latter emphasizing its role as the simplest member of the ethanolamines series to distinguish it from and , which feature additional hydroxyethyl groups on the atom. The etymology of "ethanolamine" stems directly from its structural components: "ethanol" for the C2H4OH moiety and "" for the NH2 group, a convention that highlights its hybrid organic functional groups. Standard chemical identifiers for ethanolamine include the CAS Registry Number 141-43-5 and the EC (EINECS) number 205-483-3, which are used internationally for regulatory and inventory purposes. These identifiers ensure precise referencing in scientific literature, patents, and safety data sheets across the ethanolamine family.

Molecular structure and isomers

Ethanolamine, with the molecular formula C₂H₇NO, possesses the structural formula HOCH₂CH₂NH₂, consisting of a vicinal amino alcohol where the hydroxyl and amino groups are attached to adjacent carbon atoms in an ethylene chain. The C-O bond length is approximately 1.43 Å, and the C-N bond length is about 1.47 Å, based on computational geometry optimizations, while the C-C bond is around 1.53 Å; bond angles at the methylene carbons approach tetrahedral values of 109°–110° as determined by electron diffraction and ab initio calculations. These structural parameters reflect the single bonds typical of aliphatic alcohols and primary amines, with no unusual distortions in the gas phase or solution. The molecule contains no stereocenters, rendering it achiral and incapable of existing as enantiomers. Conformational flexibility arises primarily around the central C-C bond, allowing gauche and anti arrangements of the OH and NH₂ groups; the gauche conformer predominates due to stabilizing intramolecular hydrogen bonding between the oxygen and atoms, with studies showing gauche populations exceeding 80% across various solvents. Within the ethanolamine series, (HN(CH₂CH₂OH)₂) and (N(CH₂CH₂OH)₃) serve as key derivatives, featuring additional hydroxyethyl groups on the nitrogen atom rather than true positional isomers of the parent compound. Tautomerism is negligible, as the stable amino-alcohol form lacks viable alternatives like or tautomers under standard conditions.

Synthesis and Production

Laboratory synthesis

Ethanolamine can be synthesized in the laboratory through the of chlorohydrin with , a classical method first demonstrated by Charles-Adolphe Wurtz in 1860 by heating the reactants in a sealed tube with aqueous . The reaction is represented as: \ceClCH2CH2OH+NH3−>HOCH2CH2NH2+HCl\ce{ClCH2CH2OH + NH3 -> HOCH2CH2NH2 + HCl} This process is typically conducted at 100–150 °C under pressure to maintain ammonia in solution, producing ethanolamine alongside ammonium chloride as a byproduct. The crude mixture is treated with a base such as sodium hydroxide to liberate the free ethanolamine, followed by extraction into an organic solvent or direct distillation for isolation. A more contemporary laboratory approach involves the ring-opening reaction of ethylene oxide with ammonia, adapted from larger-scale processes but suitable for benchtop execution with controlled addition of reactants. The primary reaction is: \ce(CH2)2O+NH3−>HOCH2CH2NH2\ce{(CH2)2O + NH3 -> HOCH2CH2NH2} Excess ammonia (molar ratio of 10:1 to 20:1) is employed to favor monoethanolamine formation over di- and triethanolamines, with the reaction performed at 50–100 °C and 5–15 bar in a pressure reactor. Typical laboratory yields for monoethanolamine reach 70–80% based on ethylene oxide conversion, which is nearly complete under these conditions. Purification of the product mixture commonly entails fractional distillation under reduced pressure, exploiting the boiling point differences: ethanolamine at approximately 170 °C, diethanolamine at 268 °C, and triethanolamine at 335 °C (at atmospheric pressure). This step isolates high-purity ethanolamine while recycling unreacted ammonia. An alternative route utilizes the reduction of glycolamide (2-hydroxyacetamide), prepared from and , using lithium aluminum hydride in or catalytic with . The is reduced to a methylene unit, yielding ethanolamine after and purification. This method provides good yields (around 60–75%) but is less frequently used due to the availability of simpler precursors. Reduction of serine derivatives, such as the ethyl ester of N-protected serine, with lithium aluminum hydride followed by deprotection, offers another synthetic option, though it requires additional steps for side-chain management and typically achieves moderate yields (50–70%).

Industrial production

Ethanolamine is produced industrially on a large scale through the liquid-phase reaction of with excess aqueous , typically at temperatures of 50–100 °C and pressures of 1–10 . This yields a mixture of monoethanolamine (MEA), (DEA), and (TEA) in proportions that can be adjusted by controlling the -to- molar (often 10:1 to 20:1) and reaction conditions, with a typical unoptimized approaching 1:1:1 by weight. The process operates without catalysts, relying on in the aqueous (45–55 wt%) to facilitate the reaction and excess to enhance selectivity toward MEA while minimizing higher analogs. Byproducts are minimized through recycling of unreacted and small amounts of MEA and DEA to the , achieving overall yields of 98–99%. Separation of the product mixture occurs via in a series of columns, leveraging the significant differences in boiling points (MEA at 170 °C, DEA at 269 °C, at 335 °C) to isolate high-purity fractions after initial ammonia stripping and removal. Global production of ethanolamines totals approximately 2.5 million metric tons annually in the 2020s, led by major manufacturers such as and SE. The process economics are influenced by feedstocks, with derived from the of and synthesized via the energy-intensive Haber-Bosch process.

Natural Occurrence and Biological Role

Occurrence in nature

Ethanolamine has been detected in the , highlighting its potential role as a prebiotic compound. In 2021, observations using the IRAM 30 m and Yebes 40 m radio telescopes identified it in the G+0.693–0.027, part of the Sagittarius B2 complex near the , with column densities on the order of 10^{13} to 10^{14} cm^{-2}. This marks the first astronomical detection of ethanolamine , suggesting formation pathways involving neutral-neutral reactions or ion-molecule processes in star-forming regions. Extraterrestrial samples also reveal its presence in natural geological contexts. Ethanolamine was identified in the Almahata Sitta meteorite, fragments of the ureilite from asteroid that fell in in 2008, at a concentration of 19 ppb. Its detection alongside other and amines indicates possible abiotic origins through processes like Strecker synthesis or hydrolysis in asteroidal materials. On , ethanolamine appears in trace amounts in certain natural settings, such as a degradation product from breakdown in under . During such conditions, phospholipases hydrolyze , releasing free ethanolamine to facilitate recycling.

Biological functions

Ethanolamine serves as a crucial component in the of (PE), a major that constitutes approximately 20-25% of the total mass in eukaryotic cell membranes, contributing to membrane structure, fluidity, and curvature. PE is particularly enriched in the inner leaflet of the plasma membrane and plays essential roles in cellular processes such as membrane fusion, , and the assembly of membrane proteins. In eukaryotic cells, ethanolamine is incorporated into PE primarily through the Kennedy pathway, a de novo biosynthetic route. The process begins with the of ethanolamine by ethanolamine to form phosphoethanolamine, followed by the action of CTP:phosphoethanolamine cytidylyltransferase to generate CDP-ethanolamine, and concludes with the transfer of the phosphoethanolamine moiety to diacylglycerol by ethanolaminephosphotransferase, yielding PE. This pathway is conserved across eukaryotes and is vital for maintaining , with disruptions leading to impaired integrity and cellular dysfunction. In neurological contexts, ethanolamine functions as a precursor to choline through methylation pathways in certain neural cells, enabling the subsequent synthesis of acetylcholine, a key neurotransmitter involved in synaptic transmission and cognitive processes. This conversion supports neurotransmission by providing substrates for cholinergic signaling, and ethanolamine-derived PE in neuronal membranes further facilitates ion channel function and vesicle trafficking essential for neural activity. In , ethanolamine is essential for the growth and survival of various , particularly pathogens, where it acts as a source derived from host cell membranes. Mutants deficient in ethanolamine utilization exhibit reduced growth rates and attenuated in host environments, highlighting its role in bacterial adaptation and colonization. For instance, in phylogenetically diverse such as and , ethanolamine catabolism supports metabolic fitness during infection. Bacterial metabolism of ethanolamine often involves oxidation to by ethanolamine oxidase, an that catalyzes the reaction with oxygen to produce , , and , providing carbon and energy sources under nutrient-limited conditions. This oxidase-dependent pathway is observed in species like , contrasting with the more common ammonia-lyase route but underscoring ethanolamine's versatility in prokaryotic metabolism.

Applications

Gas stream scrubbing

Ethanolamine, commonly referred to as monoethanolamine (MEA), is primarily utilized in aqueous solutions at concentrations of 10-30 wt% for the absorption of acidic gases such as (CO₂) and (H₂S) in processes, particularly in to purify raw gas streams. This method, known as gas sweetening, involves contacting the gas stream with the MEA solution in an absorber column, where the amines react chemically with the acid gases to form soluble compounds. The absorption mechanism relies on the formation of a reversible with CO₂, following the pathway: 2MEA+CO2⇌MEACOO−+MEAH+2 \text{MEA} + \text{CO}_2 \rightleftharpoons \text{MEACOO}^- + \text{MEAH}^+ This reaction enables high reactivity and selectivity for CO₂ and H₂S removal. The loaded solution, or "rich amine," is then directed to a regenerator (stripper) column where heat is applied at 100-120 °C to reverse the reaction, releasing the captured gases for venting or further processing while recovering the lean for reuse. MEA exhibits a high absorption capacity of approximately 0.5 mol CO₂ per mol MEA, stemming from the of the formation, and is a standard solvent in the majority of amine-based gas treating operations due to its rapid kinetics and effectiveness in bulk removal. To optimize performance, MEA is often blended with (DEA) or (MDEA); for instance, MEA-DEA mixtures enhance absorption rates, while MEA-MDEA formulations improve H₂S selectivity and reduce corrosion in selective removal scenarios. These systems typically consume 2-3 GJ of per of CO₂ captured, primarily for steam generation in the regenerator. In post-combustion CO₂ capture applications at power plants, MEA-based scrubbing has been scaled to facilities handling capacities up to several million tons of CO₂ per year, such as proposed projects capturing from coal-fired units, demonstrating its viability for large-scale carbon mitigation.

Other industrial uses

Ethanolamine functions as a and emulsifier in the formulation of detergents and cleaning products, where it enhances wetting and foaming properties. It is commonly incorporated into shampoos, soaps, and household cleaners at concentrations typically ranging from 5% to 10%, contributing to effective soil removal and product stability. In the pharmaceutical sector, ethanolamine serves as a key intermediate in the synthesis of ethanolamine-class antihistamines, such as diphenhydramine, which are used to treat allergic reactions and . Additionally, it acts as a adjuster and buffering agent in various formulations, ensuring stability and compatibility. Ethanolamine finds application in and for adjustment, helping to maintain optimal alkalinity in formulations like dyes and lotions. In dyes, it often replaces to swell the and facilitate color penetration, while its properties aid in moisture retention in lotions and creams. In the textile industry, ethanolamine is utilized as a softening agent to impart antistatic and smooth properties to fabrics during pre- and post-treatment processes. It also serves as a wetting agent and dye stabilizer, promoting even color distribution and improved dye uptake on fibers. Similar roles extend to paper production, where it acts as a softening additive in pulp processing and dye formulations. Beyond these, ethanolamine is employed in herbicide formulations, notably as the ethanolamine salt of glyphosate, which enhances solubility and efficacy in agricultural applications. In cement manufacturing, ethanolamine salts function as grinding aids, reducing surface tension to improve dispersion and mill efficiency while influencing hydration rates for better mechanical properties. In metalworking fluids, it provides corrosion inhibition, pH stabilization, and alkalinity boosting, extending fluid life and protecting metal surfaces during machining.

Reactions

Reactions with acids and CO₂

Ethanolamine, a primary with a pKa of 9.5 for its conjugate acid at 25 °C, readily undergoes in acidic media to form the ethanolammonium (HOCH₂CH₂NH₃⁺). This acid-base reaction is characterized by the equilibrium HOCH₂CH₂NH₂ + H⁺ ⇌ HOCH₂CH₂NH₃⁺, where the constant is derived from the pKa value reported in standard compilations of dissociation constants. The resulting conjugate acid is a cationic that influences ethanolamine's in aqueous solutions, particularly in buffering applications. Ethanolamine forms salts with various acids, including inorganic and organic species. With , it produces ethanolamine hydrochloride, a white crystalline solid with a of 82–84 °C, of approximately 1.07 g/cm³ at 20–25 °C, and in of approximately 33 g/100 mL at 20 °C, though it is only slightly soluble in DMSO when heated. This salt is hygroscopic and used in biochemical assays due to its role as a buffering agent near physiological . With fatty acids, such as oleic or , ethanolamine reacts to form soaps, which are neutral carboxylates (e.g., HOCH₂CH₂NH₃⁺ RCOO⁻, where R is a long-chain ). These soaps exhibit emulsifying properties, aiding in the dispersion of oils in -based formulations, and are valued for their mildness compared to soaps in . A key reaction of ethanolamine involves carbon dioxide, where two molecules of the amine react to form a carbamate salt via the zwitterionic mechanism: 2\ceHOCH2CH2NH2+\ceCO2⇌\ceHOCH2CH2NH3++\ceHOCH2CH2NHCOO−2 \ce{HOCH2CH2NH2} + \ce{CO2} \rightleftharpoons \ce{HOCH2CH2NH3+} + \ce{HOCH2CH2NHCOO-} This carbamate formation is exothermic, with an enthalpy of reaction approximately -85.4 kJ/mol CO₂ in aqueous solution at typical absorption conditions. The equilibrium constant for carbamate formation (K_c = [HOCH₂CH₂NH₃⁺][HOCH₂CH₂NHCOO⁻] / [HOCH₂CH₂NH₂]²[CO₂]) is about 12.5 M⁻¹ at 298 K, decreasing with increasing temperature (e.g., to 4.8 M⁻¹ at 328 K), which reflects the endothermic nature of the reverse dissociation. Kinetically, the reaction proceeds via a zwitterion intermediate, with the overall second-order rate constant for the forward reaction around 4.6 × 10³ M⁻¹ s⁻¹ at 293 K in aqueous media, governed by the base-catalyzed hydrolysis of CO₂ followed by amine attack. These properties underpin ethanolamine's use in CO₂ scrubbing processes. Ethanolamine reacts analogously with hydrogen sulfide (H₂S) through proton transfer, forming ethanolammonium hydrosulfide (HOCH₂CH₂NH₃⁺ HS⁻) in aqueous solutions, similar to its interaction with CO₂ but without carbamate formation. The reaction is rapid and essentially irreversible under absorption conditions due to the weak acidity of H₂S (pKa ≈ 7), yielding stable sulfide salts that facilitate H₂S removal from gas streams. The mechanism involves direct protonation of the amine by H₂S, with equilibrium favoring the salt at low partial pressures of H₂S.

Other reactions

Ethanolamine undergoes reactions with alkyl halides, primarily at the atom, leading to N-alkylated derivatives such as N-methylethanolamine upon treatment with methyl iodide. This N-alkylation can be achieved selectively under phase transfer catalysis conditions, where the of reagents influences toward monoalkylation products, minimizing over-alkylation or O-alkylation side products. The hydroxyl group of ethanolamine can participate in esterification reactions with s to form 2-(acyloxy)ethylamines, but the presence of the adjacent group poses significant challenges, as it promotes competing formation or intramolecular O-to-N acyl migration, converting the initial to an . To achieve selective esterification, temporary protection of the functionality, such as through or , is often required prior to reaction with the under acidic . Oxidation of ethanolamine typically targets the C-C bond adjacent to the amino and hydroxyl groups, yielding as the primary product. serves as an effective oxidant for this cleavage, proceeding rapidly in aqueous media at neutral to mildly acidic to produce and . Enzymatic oxidation by ethanolamine , found in certain , also converts ethanolamine to under physiological conditions, facilitating its role in metabolic pathways. Additionally, exposure to air leads to slow auto-oxidation, generating degradation products like through radical-mediated processes. In polyurethane synthesis, ethanolamine acts as a difunctional precursor, reacting primarily at the hydroxyl group with isocyanates to form urethane linkages, while the group can form linkages, enabling its use as a chain extender or crosslinker in networks. This reactivity contributes to the formation of rigid foams when combined with polyisocyanates and catalysts, enhancing mechanical properties through hydrogen bonding in the resulting urethanes. Thermal dehydration of ethanolamine at elevated temperatures above 200 °C, typically 350–450 °C in the gas phase over solid catalysts like metal oxides, cyclizes the molecule to via intramolecular elimination of . This operates under reduced to favor the volatile product, achieving high selectivity with catalysts that balance acidity and basicity to promote over .

Safety, Toxicity, and Environmental Impact

Health and safety

Ethanolamine is corrosive to the skin and eyes, causing severe burns and irritation upon contact. It is also an irritant to the when inhaled. The oral LD50 in rats is 1.72 g/kg, indicating moderate via ingestion. Exposure to ethanolamine primarily occurs through inhalation, skin contact, or ingestion in occupational settings. The odor threshold is approximately 2.6 ppm, providing some warning of presence, though it may not detect levels above exposure limits. The (OSHA) (PEL) is 3 ppm (6 mg/m³) as an 8-hour time-weighted average (), while the American Conference of Governmental Industrial Hygienists (ACGIH) (TLV) is 3 ppm with a (STEL) of 6 ppm. The National Institute for Occupational Safety and Health (NIOSH) immediately dangerous to life or health (IDLH) value is 30 ppm. Safe handling of ethanolamine requires (PPE), including chemical-resistant gloves, safety goggles, and protective clothing to prevent skin and eye contact. It should be used in well-ventilated areas or under a to minimize risks. Storage must occur in a cool, dry, ventilated location away from heat sources and incompatible materials, such as strong oxidizers, which can lead to violent reactions. In case of exposure, first aid measures include immediately flushing affected skin or eyes with large amounts of water for at least 15 minutes and seeking medical attention. For , move the person to and provide oxygen if breathing is difficult; professional medical evaluation is recommended. If ingested, do not induce vomiting and obtain immediate medical help. Ethanolamine is not classified as a carcinogen by the International Agency for Research on Cancer (IARC Group 3) and shows minimal based on available data.

Environmental considerations

Ethanolamine is readily biodegradable in aerobic environments, with studies demonstrating greater than 70% degradation within 28 days under 301 test conditions, such as the modified Sturm test (301B) and closed bottle test (301D). This rapid breakdown occurs primarily through microbial action, resulting in mineralization to and . Its low bioaccumulation potential further limits long-term ecological buildup, as indicated by an (log Kow) of -1.31 and a bioconcentration factor (BCF) estimated at 3.2, both well below thresholds for concern (log Kow < 3 and BCF < 100). Ecotoxicity assessments reveal moderate impacts on aquatic life. For fish, the 96-hour LC50 values range from 114 to 196 mg/L in species like rainbow trout (Oncorhynchus mykiss), indicating potential acute toxicity at elevated concentrations. Algal species show higher sensitivity, with 72-hour EC50 values around 15 mg/L for green algae such as Pseudokirchneriella subcapitata, suggesting inhibition of growth at levels exceeding 10 mg/L. These effects are attributed to ethanolamine's interference with cellular processes in primary producers, though chronic risks are mitigated by its biodegradability. Regulatory frameworks address ethanolamine's environmental release. In the , it is registered under REACH (EC 205-483-3), classified as harmful to aquatic life with long-lasting effects (Aquatic Chronic 3, H412), requiring risk assessments for manufacturers and importers exceeding one tonne annually. In the United States, it is listed on the TSCA inventory as an active substance, subject to reporting under the Clean Water Act for industrial discharges. Effluent limitations for industrial discharges, including those from gas processing, are site-specific under NPDES permits and may include restrictions on and related compounds to protect receiving waters. Industrial emissions of ethanolamine primarily stem from gas scrubbing and chemical manufacturing, but its low environmental persistence minimizes accumulation. In water, aerobic biodegradation half-lives range from 10 to 58 hours, driven by kinetics in systems, ensuring rapid removal in plants (75-90% efficiency). Atmospheric half-lives are similarly short, around 11-27 hours due to . Sustainability efforts focus on reducing ethanolamine's environmental footprint in CO2 capture applications. Greener alternatives, such as deep eutectic solvents (e.g., choline chloride-based mixtures) and piperazine-promoted amines, offer lower volatility, reduced energy for regeneration, and decreased degradation products compared to traditional 30% aqueous ethanolamine solutions. Process , including thermal reclaiming and ion-exchange purification of spent amine streams, recovers up to 95% of ethanolamine, minimizing waste and emissions in closed-loop systems.

History

Discovery

Ethanolamine was first synthesized in 1860 by the French chemist Charles-Adolphe Wurtz, who prepared it and its salts by heating ethylene chlorohydrin with aqueous ammonia in a sealed tube. This laboratory synthesis marked the initial identification of the compound as a simple amino alcohol, though the reaction also produced diethanolamine and triethanolamine as byproducts. Wurtz's work built on his earlier studies of ethylene derivatives and ammonia reactions, providing one of the earliest examples of synthesizing beta-amino alcohols. However, the first deliberate isolation of ethanolamine from natural sources occurred in 1884 by biochemist Johann Ludwig Wilhelm Thudichum, who extracted it from cephalin during and processes. Thudichum mistakenly considered the isolated ethanolamine a decomposition artifact of choline but documented its presence in tissue, linking it to structures. The first isolation of the ethanolamine was achieved in 1897 by German chemist Ludwig Knorr at the , who reacted chlorohydrin with to produce the compound. This method laid the groundwork for later industrial processes, though initial production remained limited to small-scale applications. Structural confirmation of ethanolamine came in the 1880s through degradation studies on cephalin by Thudichum and contemporaries, involving and oxidation to yield identifiable fragments like and , verifying the 2-aminoethanol formula. These analyses established its role as the polar head group in . Initially named "colamine," a term derived from its association with "glue-like" lipid extracts (from Greek kolla, meaning glue), reflecting its origin in viscous brain substances.

Commercial development

Commercial production of ethanolamine began in the early via reaction of with , but it gained significant scale only after in the 1940s and 1950s, coinciding with the expansion of manufacturing. The modern oxide-ammonia route was integrated into large-scale operations, improving efficiency and reducing costs compared to earlier methods, positioning ethanolamine as a key intermediate in chemical manufacturing. By the , production expanded rapidly to meet demand in detergents and gas treating applications, where ethanolamine served as a surfactant precursor and absorbent, respectively. The 1970s oil crisis further accelerated its use in gas scrubbing to purify streams, enhancing recovery and compliance with stricter environmental standards amid energy shortages. In the , research intensified on ethanolamine-based solvents for CO₂ capture, marking its entry into treatment processes. The saw a focus on applications, with ethanolamine incorporated into sustainable formulations for eco-friendly detergents and reduced-emission processes. Today, ethanolamine production is tightly integrated with the global ethylene industry, relying on as a feedstock, and experiences annual growth of 5.2% (as of ) driven primarily by demand in gas purification and (CCS) technologies for mitigating industrial emissions.

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