2-Ethyl-2-oxazoline 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. Propanal reacts with 2-aminoethanol in "t"-butanol to 2-ethyl-2-oxazoline in the presence of the iodinating reagent 1,3-diiodo-5,5-dimethylhydantoin (DIH) and potassium carbonate. 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
2-Ethyl-2-oxazoline 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. Copolymers with other 2-alkyl-2-oxazolines and other monomers allow the preparation of random copolymers and block copolymers. The copolymers obtained can be used as biocompatible drug carriers, in coatings and adhesives, and in many other applications. The elimination of the propionyl group from poly (2-ethyl-2-oxazoline) yields linear polyethyleneimine. 2-Ethyl-2-oxazoline