(E)-Stilbene

• Trans: 103-30-0
• Cis: 645-49-8

• Trans isomer: colorless crystals
• Cis isomer: colorless to yellowish liquid

• Trans: solid
• Cis: liquid

• Trans: 0.97 g · cm -3
• Cis: 1.01 g · cm -3

• Trans: 125 ° C
• Cis: 5.85 ° C

• Trans: 307 ° C
• Cis: 135 ° C ( 13 hPa)

Insoluble in water

Cis

Attention

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Stilbene (1,2- diphenylethylene ) is an unsaturated hydrocarbon, which can be seen as a symmetrical biphenyl derivatives of ethene. There are two geometric isomers compounds with the cis -and trans- stilbene. The asymmetric diphenyl derivative of ethene is the Constitution or structural isomer 1,1- diphenylethylene.

The name is derived stilbene in 1845 by the French chemist Auguste Laurent and refers to the Greek word for leg style shine, similar to the pearlescent mineral stilbite.

• 4.1 deposits
• 4.2 Use

Representation and extraction

The synthesis of trans-stilbene can be achieved by the reaction of benzaldehyde with Benzylphosphonsäurediethylester in a Horner-Wadsworth -Emmons reaction. The alkylated phosphonic acid can be obtained by a Michaelis -Arbuzov reaction of diethyl phosphite with benzyl bromide.

An alternative production variant is the reaction of benzaldehyde with benzyl magnesium bromide. The industrial production of trans-stilbene is carried out by a catalytic oxidative dimerization of toluene or by reductive dimerization of benzylidene chloride.

The preparation of cis-stilbene is performed by a photochemical isomerization of the trans -stilbene. The isomerization reaction is reversible. A reisomerization for trans-stilbene is thermally possible.

The synthesis of pure cis-stilbene is also achieved by metallation of diphenylacetylene ( tolan ) with lithium followed by reaction with methanol at -78 ° C. Another production possibility is the decarboxylation of 1- phenylcinnamic.

Properties

Physical Properties

Trans-stilbene forms colorless shiny crystals which melt at 125 ° C. The enthalpy of fusion of 27.37 kJ · mol -1, the entropy of fusion of 68.8 J · mol -1 · K -1. The molar heat capacity at 25 ° C a value of 235.0 J · mol -1 · K -1. For the molar enthalpy of combustion of a solid -7360.8 ± 3.9 kJ · mol -1 and a molar enthalpy of formation of 136.7 kJ · mol -1 was determined.

Cis -stilbene is a colorless liquid that crystallized to a solid below the melting point at 5.85 ° C. Under a reduced pressure of 13 hPa, a boiling point of 135 ° C was observed. The enthalpy of vaporization is 66 ± 1 kJ · mol -1. For the liquid molar enthalpy of combustion of a -7404.05 ± 0.75 kJ · mol -1 was determined.

Chemical Properties

Cis -stilbene can photochemically to 4a, 4b - dihydrophenanthrene be cyclized. The cyclization product is thermodynamically unstable and readily forms back the cis- stilbene. In the presence of oxidants, in the simplest case of atmospheric oxygen, the thermodynamically stable phenanthrene is formed rapidly.

Use

Trans-stilbene can be used as Monomerzusatz in copolymerizations. The crystals are suitable as scintillator materials. cis-stilbene is often used as olefinic test substance in order to elucidate the mechanism and stereospecificity in organic syntheses. It can also be used as a starting material in the synthesis of heterocycles and in cyclopropanation.

Stilbene derivatives

Occurrence

Stilbene derivatives are found in plants, they are product of two different biosynthetic pathways. A partially derived from the shikimic acid pathway, the other from the polyketide biosynthesis, while a Phenylpropanidbaustein is used as a starter unit for the iterative PKS synthesis of PKS III.

More stilbene derivatives are resveratrol, which is associated with health- promoting effects of red wine, rhaponticin, an isolable from rhubarb Phytoestrogen, and pinosylvin, one in the heartwood of pine occurring 3,5- Stilbendiol.

Use

A series of stilbene derivatives possess hormone-like effect. The substance diethylstilbestrol ( diethylstilbestrol, DES) was the first commercial oral estrogen product. Due to the anabolic effect of DES was used until the early 1980s in cattle and pig fattening than aids. However, DES is a carcinogen. Therefore, the use of stilbene and its derivatives in animals intended for food production in the EU is prohibited. In Germany this is legally regulated in the Ordinance on substances with pharmacological effects. In the context of hormone-treated meat scandals these stilbene derivatives were often referred to in media reports as " stilbenes ".

Stilbene derivatives are often used as optical brighteners, especially in fabrics made ​​of polymeric substances, and as laser dyes. The special feature of the stilbene compared to other aromatics and polyenes is exploited, that despite the absorption characterizing double bond fluoresce. This is due to the large change of the bonding in the excited state; the double bond in the excited S1 state receives strong single bond character, the single bonds to the rings on the other hand to win double-bond character. Thus, the torsional vibrations of the rings are strongly attenuated who have strong fluorescence-quenching character with other compounds of similar structure, resulting in the relatively strong fluorescence quantum yield of stilbene results.