Ethylene

CH2=CH2

[74-85-1]  · C2H4  · Ethylene  · (MW 28.06)

(used in photochemical and thermal cycloadditions, Friedel-Crafts and other alkylations, vinylation reactions, and as an alkene in electrophilic addition reactions)

Physical Data: mp -169 °C; bp -104 °C; vapor density 0.97; flammable gas.

Solubility: insol H2O; sol THF, pet ether, benzene.

Form Supplied in: gas (lecture bottle); widely available.

Handling, Storage, and Precautions: store and use with adequate ventilation. Explosions involving ethylene have occurred: when mixed with aluminum chloride at 30-60 bar pressure in the presence of supported nickel catalysts, methyl chloride, or nitromethane; when mixed with trifluoromethyl hypofluorite without diluent; when reacted with chlorine, ozone, or nitrogen oxide; when passed through 5 Å molecular sieves.1

Photochemical Cycloadditions.

Ethylene has been utilized extensively in intermolecular [2 + 2] photocycloaddition reactions with enones.2 Cyclohexenones (eq 1),3 cyclopentenones (eq 2),4 and functionalized enones (eqs 3 and 4)5,6 undergo cycloaddition with ethylene in high yield.

Thermal Cycloadditions.

Ethylene is a relatively poor dienophile but can be used in the Diels-Alder reaction with active dienes or under forced conditions such as high pressure (eqs 5-8).7-9 Nitrone cycloadditions can also be carried out with ethylene under high pressure (eq 9).10

Friedel-Crafts Reactions.

Ethylene alkylates a variety of aromatic systems in the presence of Lewis acids (eqs 10 and 11).11 2-Tetralones can be prepared from aromatic acetyl chlorides and ethylene in the presence of Aluminum Chloride (eqs 12 and 13).12

Ethylene reacts with aromatic acid chlorides (eq 14),13 aliphatic acid chlorides (eqs 15 and 16),14 and anhydrides (eq 17)15 under Lewis acid catalysis to produce a,b-unsaturated ketones and 3-chloroethyl ketones. Ethylene also condenses with haloalkanes to effect a formal ethylene insertion (eqs 18 and 19).16

Other Alkylation Reactions.

Alkylbenzenes containing at least one benzylic hydrogen may be alkylated with ethylene in the presence of catalysts such as sodium or Potassium-Graphite (eqs 20 and 21).17 Ethylene can alkylate aromatic rings ortho to heteroatoms using aluminum catalysts (eqs 22 and 23).18

Organometallic Catalyzed Reactions and Heck Reactions.

Palladium-catalyzed oxidation of ethylene is an important industrial process. Ethylene is oxidized to vinyl acetate19 by Palladium(II) Acetate in acetic acid and to acetaldehyde (the Wacker process).20 In the presence of bis(acetonitrile)dichloropalladium(II), indoles are converted to vinyl indoles (eq 24).21 Silyl enol ethers are alkylated by ethylene in the presence of Bis(benzonitrile)dichloropalladium(II) (eq 25).22 Stabilized carbanions are also vinylated by ethylene with the assistance of PdCl2(MeCN)2 (eqs 26 and 27).23 Substituted o-bromonitrobenzene derivatives react with ethylene to yield the corresponding indole derivative or vinyl derivative (eq 28).24

An efficient asymmetric hydrovinylation of cyclohexa-1,3-dienes catalyzed by nickel complexes in the presence of a chiral aminophosphine ligand has been reported (eq 29).25 Acrylamides can be prepared through the reaction of isocyanates with ethylene in the presence of Bis(1,5-cyclooctadiene)nickel(0) (eq 30).26 Bis(1,5-cyclooctadiene)nickel also catalyzes the conversion of styrene to 5-phenyl-4-pentenoic acid (eq 31).27

Rhodium catalysts (e.g. Dodecacarbonyltetrarhodium) have also been used for carbonylation-alkylation reactions of alkynes with ethylene to form ketones (eq 32) and lactones (eq 33).28

Other Organometallic Reactions.

Diallylic organozinc derivatives and allylic magnesium halides react with ethylene to afford the corresponding zinc or Grignard derivatives (eqs 34 and 35).29 The conditions for the organozinc addition are milder than those needed for the Grignard addition. Secondary and tertiary alkyllithium reagents also add to ethylene to give primary alkyllithium reagents that are inert to further addition to ethylene (eq 36).30 An example of an intramolecular addition of a lithium reagent generated from the addition to ethylene has also been reported (eq 37).31 Ethylene can be deprotonated and added to benzaldehyde to obtain the allylic alcohol in high yield (eq 38).32

Alkene Polymerization.

Ethylene is used extensively in polymerization reactions (Ziegler-Natta). Titanium(IV) Chloride and Triethylaluminum catalyzed the conversion of ethylene to polyethylene (eq 39).33

Miscellaneous Reactions.

Ethylene has been used in cycloadditions with Chlorosulfonyl Isocyanate to form 2-(2-chloroethyl)-3-oxoisothiazolidine 1,1-dioxides (eq 40).34 Compared to other alkenes, ethylene provides substituted cyclopentenones with modest results under Pauson-Khand reaction conditions (eqs 41 and 42).35 Perchlorovinylcarbene (formed from the thermal ring opening of tetrachlorocyclopropene) adds efficiently to form 1-chloro-1-(trichloroethenyl)cyclopropane (eq 43).36 Electrophilic addition of sulfenyl chlorides and chlorine sulfate to ethylene provides chloroethyl sulfides (eq 44)37 and chloroalkyl sulfonate (eq 45).38


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Michael T. Crimmins & Agnes S. Kim-Meade

University of North Carolina at Chapel Hill, NC, USA



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