[141-43-5] · C2H7NO · Ethanolamine · (MW 61.08)
Alternate Names: 2-aminoethanol; monoethanolamine; MEA.
Physical Data: viscous liquid; bp 170 °C; 58 °C/5 mmHg; mp 10.3 °C; d 1.018 g cm-3; pH = 12.1 (25 w/w % aqueous solution); pK
Solubility: sol H2O, alcohol, CHCl3; slightly sol ether, benzene; insol hydrocarbons.
Preparative Methods: large-scale preparation by ammonolysis of Ethylene Oxide.5
Purification: azeotrope with benzene followed by fractional distillation under reduced pressure.
Handling, Storage, and Precautions: hygroscopic; absorbs CO2 from atmosphere; corrosive.
MEA can be used to introduce b-hydroxyethylamino functionality onto aromatics containing electron-withdrawing groups (eq 1)6 or heterocycles (eq 2)7 by nucleophilic substitution. N-Alkyl or N,N-dialkylated derivatives of MEA can be obtained in good yields under mild conditions by alkylation (e.g. Benzyl Chloride, Sodium Hydroxide; mono, 68%; di, 72%)8 or reductive amination (e.g. Acetone, Platinum(IV) Oxide, 95%;9 Acetaldehyde, Sodium Borohydride, 76%1c). MEA derives its versatility by conversion to derivatives that serve in other transformations. Substituted ethanolamines are used in many asymmetric reactions.
MEA condenses with aldehydes and ketones to give oxazolidines (1),1 carbonates to give oxazolidinones (2),2 acids to give oxazolines (3),3 and standard acylating agents (eq 3). These heterocycles are used as intermediates in natural product and polymer synthesis. It selectively deacylates acyl glycosides10 and replaces hydrazine for cleavage of Gabriel synthesis intermediates.11
MEA aids hydroboration reaction workup by transesterifying the borate ester to give the product alcohol and a borinate precipitate (eq 4).4 MEA has also been used to increase optical purities by crystallization of the resulting MEA esters.12
Besides the heterocyclic systems shown in eq 3, different ring systems are obtained on reaction of MEA with CO2, CS2, isocyanates, nitriles, a-diketones [(4) and (5) depending on the reaction conditions],13 and with 1,4-butenediol to give (6).14
MEA is converted into a dienophile that has been used to prepare vicinal cis-amino alcohols (eq 5).15
MEA dealkylates quaternary ammonium salts (methyl groups) prepared during exhaustive methylation of amines (eq 6).15
Ethanolamine; In Kirk-Othmer Encyclopedia of Chemical Technology, 3rd ed.; Grayson, M., Ed.; Wiley: New York, 1984.
Kenneth C. Caster
Union Carbide Corporation, South Charleston, WV, USA