3D model (JSmol)
|Molar mass||g·mol−1 99.133|
|Melting point||−62 °C (−80 °F; 211 K)|
|Boiling point||128.4 °C (263.1 °F; 401.5 K)|
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
2-Ethyl-2-oxazoline (EtOx) is an oxazoline which is used particularly as a monomer for the cationic ring-opening polymerization to poly(2-alkyloxazoline)s. This type of polymers are under investigation as readily water-soluble and biocompatible materials for biomedical applications.
From propionic acid and derivatives
Carboxylic acids, carboxylic esters, carboxylic amides and nitriles can react with 2-amino alcohols at 200 °C upon dehydration to the corresponding N-(2-hydroxy)carbamide, which react further at 260–280 °C upon dehydration to the 2-alkyl-2-oxazoline.
Less drastic reaction conditions require the dehydration of the N-(2-hydroxyethyl)propionamide in vacuo in the presence of iron(III)chloride, which delivers the product in 90% yield. An even higher yield of 96.2% is obtained by heating with zinc acetate.
An economic one-pot reaction is heating the salt of propionic acid with ethanolamine at 200 °C in vacuo in the presence of zinc chloride yielding 82% 2-ethyl-2-oxazoline. From the water-containing distillate pure 2-ethyl-2-oxazoline can be isolated by extraction with diethylbenzene and subsequent distillation or by distillation only after addition of diethyl phosphite or dimethyldichlorosilane. The product can be dried to a residual water content of 10 ppm.
In another one-pot reaction propionic acid is converted first with 2-aminoethanol to 2-hydroxyethylamide, than reacted with boric acid at 130 °C yielding a boric acid ester which is finally thermolyzed at 280 °C in 92% yield to 2-ethyl-2-oxazoline.
From propionic acid and thionyl chloride can be obtained propanoyl chloride, which reacts with ethanolamine in the presence of an acid scavenger (for example pyridine) to N-propionyl-2-aminoethanol. With further thionyl chloride this reacts further to 2-chloroethylamide. With the chloride ion as a better leaving group, this intermediate is cyclized by simple heating to the oxazoline. Water must be excluded du to the tendency of oxazolines towards ring-opening by chloride ions during protonation of the imine nitrogen.
The direct reaction of propanoyl chloride with 2-chloroethylamine hydrochloride in the presence of triethylamine avoids the formation of water.
2-Ethyl-2-oxazoline is a readily water-soluble, colorless liquid which is also soluble in a variety of organic solvents and possesses an amine-like smell. Aqueous solutions react alkaline. The compound is stable in alkaline but hydrolyses under acid action.
In anhydrous form, 2-ethyl-2-oxazoline is mostly used as a monomer.
The cationic ring-opening polymerization of 2-ethyl-2-oxazoline can be initiated by alkylation with e.g. methyl tosylate or triflates (in particular methyl triflate) and leads to the water-soluble poly(2-ethyl-2-oxazoline) which is a propionyl-substituted linear polyethylenimine and can also be seen as a pseudo-polypeptide.
The polymerization of 2-ethyl-2-oxazoline can also be carried out as living cationic polymerization.
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