The Wittig reaction is an important organic chemistry reaction in which an alkylidene phosphonium ylide is used to convert an aldehyde or ketone into an alkene. This reaction is named after Georg Wittig, who was awarded the Nobel Prize in Chemistry in 1979 for his work on this and related reactions.
In a Wittig reaction, the alkylidene phosphonium ylide is typically synthesized by reacting a phosphorous halide (such as phosphorous pentachloride or phosphorous trichloride) with an alkyl halide (such as an alkyl bromide or alkyl iodide). The resulting ylide can then be treated with an aldehyde or ketone to produce an alkene, with the loss of a molecule of HCl.
One of the key advantages of the Wittig reaction is that it allows for the synthesis of alkenes with a high degree of control over the configuration of the double bond. This is because the alkylidene phosphonium ylide is a chiral molecule, and the reaction produces a single enantiomer of the alkene. This can be useful in the synthesis of optically active compounds, which are important in the pharmaceutical and fine chemical industries.
In a Wittig reaction lab report, the discussion section should summarize the main findings of the experiment, including any observations or data collected during the reaction. It should also discuss the mechanisms of the reaction, highlighting any key intermediates or transition states that were identified. The discussion should also compare the results of the experiment with those reported in the literature, and discuss any discrepancies or unexpected results that were observed.
The discussion should also address any limitations of the experiment, such as the purity of the starting materials, the conditions of the reaction, or the yield of the product. The discussion should also consider any potential applications or future directions for the reaction, based on the results of the experiment.
Overall, the discussion section of a Wittig reaction lab report should provide a clear and concise summary of the main findings of the experiment, along with an analysis of the mechanisms and limitations of the reaction, and a discussion of its potential applications.
Lab # 5 Wittig Reaction
This product is also recycled back into the reaction after it is created. The remainder of the organic solution was then placed in a warm water bath in order to evaporate the dichloromethane. The NMR displayed strong peaks between 6 ppm and 7 ppm, as well as between 7 and 7 ppm. The stable 5 valencies are met in compounds like phosphoric Figure 1. Even though the melting point that was observed was lower than the literature value for this isomer, it is likely that it was still formed.
It was not clear if a pure product had been formed because time constraints did not allow us to perform thin layer chromatography. The weight of the product decreased as it dried because water and dichloromethane were removed from it in the drying process. The reaction produced very low yield of 6. Can you distinguish them using the available characterization methods in 216? Isolated Product Mixture 0. Thus, the intermediate in the reaction is stabilized by resonance 2. Alkenes are less polar than the trans-cinnamaldehyde so that is why they appear higher on the TLC plate since they have a higher affinity for the mobile phase petroleum ether. The organic solution formed was then compared to trans-cinnamaldehyde using TLC.
The product was allowed to dry and the weight and melting point were determined. Figure 1: The mechanism shown below shows the formation of an alkene using the Wittig reaction. Stereochemistry with vinyl halides are maintained, while inversion of stereochemistry happens… Wittig Reaction Lab Report Discovered by Georg Wittig in 1954, the Wittig reaction is a robust organic synthesis method for preparing stereospecific alkenes. The specific isomer which forms is dependent on the transition state of the reaction. One major milestone in this regard is the Horner-Wadsworth-Emmons HWE reaction, a slightly different approach to the Wittig reaction that is based on a modified Wittig Scheme 2: Primary Reaction Mechanism of the Wittig Reaction The primary mechanism of the Wittig reaction involves the reaction of the benzalde- hyde 1 with the methyl triphenylphosphoranylidene acetate ylide 2 to form a 4- membered ring intermediate 5. The palladium catalyst couples with the p-iodophenol which results in an organopalladium complex.
The Z,Z isomer is the isomer that is not formed. The potential isomers formed in this reaction are E, E -1,4- diphenyl-1,3-butadiene and E, Z -1,4-diphenyl-1,3-butadiene 1. Once the stirring was complete, the mixture was transferred to a conical tube. Draw a structure of this isomer. When Z-Stilbene underwent photoisomerization with iodine for 1 hour it reconfigured almost exclusively into its more stable counterpart E-Stilbene. An improvement to this experiment could be to use plane polarized light in order to further determine which isomer was present in the reaction.
The lower melting point could be due to impurities in the solution or the reaction not reaching completion and therefore allowing intermediates to be found in the product. The first step is the formation of a phosphonium salt by an SN2 reaction in which a nucleophilic phosphorus compound reacts with an alkyl halide 1. Even though the product was impure, the data still provided enough evidence that this isomer was the major product of the reaction. The experimental melting point was above 200 degrees as we expected it to agree with the literature value 241-245C which helped us identify our product. There is a strong indication of E, E -1,4-diphenyl-1,3-butadiene, but weaker peaks can be attributed to the E, Z isomer.
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. This intermediate then undergoes a bond rearrange- ment which leads directly to the products: an alkene, methyl 2E -3- 2-nitrophenyl acrylate 3 , and triphenylphosphine oxide 4. Purify the crude product using a microscale wet column. Group members will work together to identify appropriate solvents for use in TLC and purification by microscale wet column chromatography. The final melting point of the product was 154 degrees Celsius. Wittig was educated originally at Tubingen; Wittig spent periods at Braunschweig, Freigurg, back to Tubingen again before taking up the post as director of the organic The foundation of the Wittig reaction is not complex. This generates the phorphorus ylide known as the Wittig reagent.
Stereospecific alkene products can be synthesized by adjusting the reaction reagents and conditions. Transfer the solution to a clean vial and evaporate the majority of the solvent. A stir bar was placed in the flask and then 0 mL of sodium hydroxide was added while the mixture was stirring on the stir plate. Figure 2: The reactions below show the formation of the ylide that will be used in the experiment in order to form the final product. The ylide will be formed using benzyltriphenylphosphonium chloride with sodium hydroxide. Reflux mechanism was used for the reaction to occur. The key step of the mechanism of the ylide reaction is the nucleophilic addition of the ylide to the electrophilic carbonyl group, forming a 4-membered ring that dissociates into the product molecules.
For this specific experiment, we will use benzyltriphenylphosphonium chloride to synthesize the ylide. Because ylides contain by definition adjacent positive and negative charges a positive on the phosphonium, and a negative on the carbon adjacent to the residue , R groups that can better stabilize the adjacent negative charge produce more stable ylides. TLC plate 1 is for the organic layer and tans- cinnamaldehyde and TLC plate 2 is for the product dissolved in dichloromethane and trans-cinnamaldehyde. The melting point for the product was determined to be 123°C. Organic Chemistry II Lab. These molecules allow the synthesis of large molecules from smaller organic compounds through carbon-carbon double bonds.
The remaining product was submitted for NMR analysis 2. Ylides are the resonance stabilized intermediates in this reaction that allow the attachment of the two smaller molecules to form the larger molecules with the creation of a double bond 1. An air condenser was then added to the top of the flask and the reaction sat at room temperature and was stirred for 40 minutes. When the reaction is complete evaporate the dichloromethane solvent with a stream of N 2 gas and dissolve the reaction mixture in 25% diethyl ether in hexanes 2-3 mL. This is most likely attributable to an error in our lab procedure where we erroneously selected later fractions of our elution for purification rather than earlier fractions, leading to samples that by the very nature of the chromatographic setup con- tained small amounts of product and large amounts of impurities. Figure 3: The two drawings below represent the TLC plates that were obtained in the process of this experiment.
Do not let it come in contact with the skin. The stereoselectivity of the reaction is predicated on the stability of triphenylphosphonium ylide, which determines which of two ring intermediates form: the sterically-unfavoredcisintermediate that forms via a fast yet reversible process, or the slow, irreversibletransintermediate. Organic Chemistry II Lab. A small amount of the solid was collected and dissolved in CH2Cl2 for TLC analysis. This molecule has two stereocenters allowing more than one product i.