Wittig Reaction: Synthesis of Trans-Stilbene

Topics: Wittig reaction, Aldehyde, Chemistry Pages: 3 (980 words) Published: June 16, 2008
The purpose of this experiment was to perform a wittig reaction, the horner-emmons wittig specifically, reacting an aldehyde with an ylide to make an alkene. This particular variation of the wittig reaction has several advantages: It gives only the trans product; it uses a much milder base that is easier to handle; and it gives a water soluble byproduct which is easy to separate from the product. The reason that these advantages occur is a change in the structure of the ylide. Instead of a tripheylphosphine ylide, we use a diethylphosphonate ylide. The protons are much more acidic and its byproduct is negatively charged. The reason why we chose to create trans-stilbene is become of its many practical applications. Stilbene exists as two possible isomers. The first is trans-1,2-diphenylethylene, called trans-stilbene. The second is cis-1,2-diphenylethylene, called cis-stilbene which is sterically hindered and less stable because the steric interactions force the aromatic rings out-of-plane and prevent conjugation. Z-stilbene has a melting point of 5°C to 6°C, while (E)-stilbene melts around 125°C, illustrating the two compounds are quite different. These two isomers can interconvert, however, under the influence of light. There are many ways the trans compound can be utilized. Trans-stilbene is related to the treatment of individuals afflicted with cancer or a precancerous condition, inflammatory disease or condition, and/or stroke or other ischemic disease or condition. The name stilbene was derived from the Greek word stilbos, which means shining, which is interesting considering that it is used to manufacture dyes and optical brighteners. It is also used as a gain medium in dye lasers. As a compound, stilbene is a diarylethene, or a conjugated alkene. This is a hydrocarbon consisting of an trans ethene double bond substituted with an phenyl group on both carbon atoms of the double bond. Please see outline of reaction and drawing of trans-stilbene below:...

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http://www.organic-chemistry.org/namedreactions/wittig-horner-reaction.shtm >
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