Enolether
As enol ethers of the general structure with enols R1R2C = CR3 -O -R4 are referred to. Of particular importance in industry are of this group of the vinyl ether H2C = CH -O -R, where a vinyl group ( ethenyl ) is connected via an oxygen atom with a variable R.
Production and representation
Enol ether can be represented for example by reacting the carboxylic ester with Tebbe reagent in the laboratory.
The preparation of vinyl ethers on an industrial scale is usually done by reacting the corresponding alcohols with acetylene in the presence of basic catalysts ( Reppe synthesis).
Vinylation can be carried out both in liquid and in the gas phase. In the vinylation in the gas phase basic heterogeneous catalysts, such as potassium hydroxide can be used on activated carbon or magnesium / calcium oxide. In the liquid phase of the highly exothermic reaction is generally conducted in the presence of alkali metal hydroxide, or alkali metal alkoxide catalysts.
Properties and Uses
Enol ethers and enamines are also referred to as electron-rich or activated alkenes, because the adjacent oxygen atom of the double bond ( oxonium ion structure) emits electrons to form a resonance structure. This property gives the enol a special reactivity, for example, the Diels- Alder reaction. An enol ether may be interpreted as the corresponding ether of the enolate. Enol ethers serve as starting material for the preparation of α - bromocarboxylic esters, which can be important starting materials for the Reformatsky reaction on their part.
Allyl vinyl ethers are the starting substrates for Claisen rearrangements to γ, δ -unsaturated carbonyl compounds.
Vinyl ethers find used mainly as a monomer in polymers and copolymers, in coatings, adhesives, printing inks and in radiation- curing coatings. Furthermore, they are used for the production of odor and flavorings, pharmaceuticals and intermediates in the chemical industry. The simplest representative of this group of substances, methyl vinyl ether, is often called himself simply " vinyl ether ".