Wittig Reaction Lab Report
Introduction
Discovered by Georg Wittig in 1954, the Wittig reaction is a robust organic synthesis method for preparing stereospecific alkenes. In general, Wittig reactions involve an aldehyde or ketone and a Wittig reagent (triphenylphosphonium ylide) and result in the formation of an alkene product and triphenylphosphine oxide (side product). Stereospecific alkene products can be synthesized by adjusting the reaction reagents and conditions.
In the 60 years since the Wittig reaction was discovered, many articles have expanded upon its mechanism. For example, Bryne, et al.1 describe in a review how our understanding of the Wittig reaction mechanism has changed with new computational and experimental studies. Recent evidence suggests Wittig reactions run in lithium-salt-free conditions occur solely under kinetic control via an oxaphosphetane intermediate. This finding applies to all phosphonium ylides, stabilized or unstabilized, and is contrary to many previously reported mechanisms. …show more content…
Although the yield of our reaction was mediocre, the purity of the sample (as analyzed by 1H and 13C NMR) was poor. There are many factors that may have caused poor purity, of which include reaction incompletion during exposure to microwave radiation, poor mixing, and poor product isolation during column chromatography. As seen in the 1H NMR spectrum, impurity peaks (>10%) corresponding to methyl (triphenylphosphoranylidene) acetate, acetone, ethyl acetate, and hexane were identified. The phosphonium ylide peak indicates that the reaction did not go to completion (leftover starting material). Meanwhile, the acetone, ethyl acetate, and hexane peaks show there was residual solvent in the sample submitted for NMR analysis (compounds were not in reaction scheme). Because acetone, ethyl acetate, and hexane are volatile, we deduced that our evaporation of the final product was
Discovered by Georg Wittig in 1954, the Wittig reaction is a robust organic synthesis method for preparing stereospecific alkenes. In general, Wittig reactions involve an aldehyde or ketone and a Wittig reagent (triphenylphosphonium ylide) and result in the formation of an alkene product and triphenylphosphine oxide (side product). Stereospecific alkene products can be synthesized by adjusting the reaction reagents and conditions.
In the 60 years since the Wittig reaction was discovered, many articles have expanded upon its mechanism. For example, Bryne, et al.1 describe in a review how our understanding of the Wittig reaction mechanism has changed with new computational and experimental studies. Recent evidence suggests Wittig reactions run in lithium-salt-free conditions occur solely under kinetic control via an oxaphosphetane intermediate. This finding applies to all phosphonium ylides, stabilized or unstabilized, and is contrary to many previously reported mechanisms. …show more content…
Although the yield of our reaction was mediocre, the purity of the sample (as analyzed by 1H and 13C NMR) was poor. There are many factors that may have caused poor purity, of which include reaction incompletion during exposure to microwave radiation, poor mixing, and poor product isolation during column chromatography. As seen in the 1H NMR spectrum, impurity peaks (>10%) corresponding to methyl (triphenylphosphoranylidene) acetate, acetone, ethyl acetate, and hexane were identified. The phosphonium ylide peak indicates that the reaction did not go to completion (leftover starting material). Meanwhile, the acetone, ethyl acetate, and hexane peaks show there was residual solvent in the sample submitted for NMR analysis (compounds were not in reaction scheme). Because acetone, ethyl acetate, and hexane are volatile, we deduced that our evaporation of the final product was