2-Ethyl-2-oxazoline

Last updated
2-Ethyl-2-oxazoline
2-Ethyl-2-oxazoline structure01.svg
Names
Preferred IUPAC name
2-Ethyl-4,5-dihydro-1,3-oxazole
Other names
2-Ethyloxazoline
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.030.817 OOjs UI icon edit-ltr-progressive.svg
PubChem CID
UNII
  • InChI=1S/C5H9NO/c1-2-5-6-3-4-7-5/h2-4H2,1H3
    Key: NYEZZYQZRQDLEH-UHFFFAOYSA-N
  • CCC1=NCCO1
Properties
C5H9NO
Molar mass 99.133 g·mol−1
Density 0.982 g/mL [1]
Melting point −62 °C (−80 °F; 211 K) [1]
Boiling point 128.4 °C (263.1 °F; 401.5 K) [1]
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. [2] This type of polymers are under investigation as readily water-soluble and biocompatible materials for biomedical applications. [3]

Contents

Production

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.

Synthese von 2-Ethyl-2-oxazolin aus Carbonsaurederivaten 2-Oxazoline Synthese aus Carbonsaurederivaten.svg
Synthese von 2-Ethyl-2-oxazolin aus Carbonsäurederivaten

For example N-(2-hydroxyethyl)propionamide is first formed from propionic acid and ethanolamine in 74% yield which can be dehydrated to give 2-ethyl-2-oxazoline in about 75% yield. [4]

Synthese von 2-Ethyl-2-oxazolin uber N-(2-Hydroxyethyl)propionamid 2-Ethyl-2-oxazolin uber N-(2-hydroxyethyl)propionamid.svg
Synthese von 2-Ethyl-2-oxazolin über N-(2-Hydroxyethyl)propionamid

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. [5] An even higher yield of 96.2% is obtained by heating with zinc acetate. [6]

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. [6] From the water-containing distillate pure 2-ethyl-2-oxazoline can be isolated by extraction with diethylbenzene and subsequent distillation [6] or by distillation only after addition of diethyl phosphite or dimethyldichlorosilane. The product can be dried to a residual water content of 10 ppm. [7]

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. [8]

Synthese von 2-Ethyl-2-oxazolin uber Boratester 2-Ethyl-2-oxazolin uber Boratester.svg
Synthese von 2-Ethyl-2-oxazolin über Boratester

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 due to the tendency of oxazolines towards ring-opening by chloride ions during protonation of the imine nitrogen. [9]

Synthese von 2-Ethyl-2-oxazolin uber Propionsaureaurechlorid 2-Ethyl-2-oxazolin uber Saurechlorid.svg
Synthese von 2-Ethyl-2-oxazolin über Propionsäureäurechlorid

The direct reaction of propanoyl chloride with 2-chloroethylamine hydrochloride in the presence of triethylamine avoids the formation of water.

Synthese von 2-Ethyl-2-oxazolin mit Chlorethylamin 2-Ethyl-2-oxazolin mit Chlorethylamin.svg
Synthese von 2-Ethyl-2-oxazolin mit Chlorethylamin

From propanal

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. [10]

Synthese von 2-Ethyl-2-oxazolin aus Propionaldehyd 2-Ethyl-2-oxazolin aus Propionaldehyd.svg
Synthese von 2-Ethyl-2-oxazolin aus Propionaldehyd

Properties

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. [11] Aqueous solutions react alkaline. The compound is stable in alkaline but hydrolyses under acid action.

Applications

In anhydrous form, 2-ethyl-2-oxazoline is mostly used as a monomer. [2]

The cationic ring-opening polymerization of 2-ethyl-2-oxazoline [12] 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. [13]

Kationische lebende Polymerisation von 2-Ethyl-2-oxazolin 2-Ethyl-2-oxazolin Polymerisation.svg
Kationische lebende Polymerisation von 2-Ethyl-2-oxazolin

The polymerization of 2-ethyl-2-oxazoline can also be carried out as living cationic polymerization. [14]

Copolymers with other 2-alkyl-2-oxazolines [15] and other monomers [16] allow the preparation of random copolymers and block copolymers.

The copolymers obtained can be used as biocompatible drug carriers, [17] in coatings and adhesives, and in many other applications. [18]

The elimination of the propionyl group from poly (2-ethyl-2-oxazoline) yields linear polyethyleneimine. [19] [20]

Herstellung von Linearem Polyethylenimin aus Poly(2-ethyloxazolin) Lineares PEI aus PEOx.svg
Herstellung von Linearem Polyethylenimin aus Poly(2-ethyloxazolin)

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References

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