Essay about Wittig Reaction Synthesis of Trans-Stilbene

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†¦show more content†¦This modification is similar to a standard Wittig reaction in that the first step, which has already been done for you, is the reaction of a trialkyl phosphite with a suitable alkyl halide as shown below in two steps: In the first step the trialkyl phosphate acts as a nucleophile and, in a typical Sn2 reaction, forms a phosphonium salt. The salt is unstable and a halide ion X displaces R in the Sn2 manner to form a dialkylphosphonate. It is the phosphonate that, in the presence of base, is converted to a Wittig-like reagent. Normally the Wittig reagent is an ylid and neutral, but the modified Wittig is analogous to the carbanion of an aldol intermediate. Due to its resonance forms, the phosphonate anion is able to attack the carbonyl much like acarbanion in an aldol reaction to give an oxyanion species. This is where the analogy with the aldol reaction fails. The oxyanion undergoes a reaction analogous to nucleophilic substitution at an unsaturated center to form the olefin, normally as the E isomer, and a water soluble phosphonate anion. In this particular experiment, diethyl benzylphosphonate is used with benzaldehyde as the carbonyl component. Since phase transfer conditions are used, we can u se a weaker base, the hydroxide ion. The reactivity o the anion formed is very high, resulting in excellent yields of trans-stilbene. The trans form of Stilbene is more favored than the sterically hindered cis form. AlthoughShow MoreRelatedPreparation Of The ( 2 Nitrophenyl ) Acrylate Using The Wittig Reaction1287 Words   |  6 Pages3-(2-Nitrophenyl)acrylate Utilizing the Wittig Reaction Introduction: The Wittig reaction, named after Georg Wittig, produces an alkene from an aldehyde or ketone reacting with a phosphonium ylide (a Wittig reagent). The Wittig reaction is typically stereoselective, which makes the Wittig reagents more difficult to work with but use of the Wittig with different allyl substituents prove to make the Wittig more versatile which can lead to the synthesis of a wide range of alkenes, styrenes, stilbenes, and 1,3-dienes which