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
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This methodology is utilized because of its many industrial applications. Some of these include: Elimination of dangerous, inconvenient, and expensive reactants; high reactivity of the active species, high yield and purity of products, and simplicity of the procedure. The phase transfer catalyst facilitates the migration of a reactant in a two-part system from one phase to the other where the main reaction is taking place. During this reaction the PTC brought the OH anion (from KOH in aqueous layer) into contact with the two organic wittig reagents in the hexane layer. The phase transfer catalyst works by holding the ion within a hydrophobic exterior. The PTC for anion reactants are usually quaternary ammonium salts and the catalysts for cations are commonly known ethers. Removal of the PTC was carried out by recrystallization and washings of cold water and cold ethanol. Both washings were needed to take care of both kinds of contaminants.
When the crude stilbene is ready to be recrystallized from EtOH, when the cooling begins, it is necessary to carry out the procedure slowly because if this is done too quickly impurities will be trapped within the crystals. This error will become apparent when one takes the melting point of the product, which is a good method to test the purity of the product. The melting point of trans-stilbene is 122.4