Wittig reaction mechanism of benzyltriphenylphosphonium chloride. Wittig Reaction Lab Report 2022-11-06

The Wittig Reaction

This reaction uses a phosphate ester instead of a phosphine, manufacturing a more reactive ylid. Journal of the American Chemical Society. Using the techniques of separation, elimination, extraction and crystallization it is intended that an alkene will be formed with the reaction of the aldehyde used and the phosphonium ylide reagent to achieve a stronger organic reaction. Inserted a magnetic stir bar to the flask and turned the stir speed on to about 5 for a few minutes. .

Wittig Reaction Mechanism with Reagent Preparation

The main source of error in the experiment performed was the over heating of the yellow organic material in the step to dissolve the solvent material to achieve pure crystallized product. The organic bottom layer was extracted and placed in a test tube. Taylor, Leonie Campbell, and Graeme D. This is because bromobenzene is very stable, and contains allylic and vinyllic bromine, which is also very stable, and cannot be a good nucleophile. The oxygen takes both the bonding electrons and forms a new double bond with the phosphorus which loses the bonding pair of electrons to the carbon atom.

Study of the Wittig reaction of benzyltriphenylphosphonium salt and benzaldehyde via ylide

Many reactions are performed in a homogenous solution but in this experiment the 9-anthraldehyde is very hydrophobic and the sodium hydroxide reactant is very hydrophilic. In 1979, Wittig won a Nobel Prize in Chemistry due to the. Wittig Reagent Preparation Wittig Reagent is a term used to refer to an organo-phosphorus ylide. This joining allows the molecules that are growing in size and complexity to assemble faster and gives it no uncertainty for where the double bond forms; alleviating the elimination reactions mixture of more or less substituted isomers. The phosphorous ylide is the nucleophile and is stabilized through resonance with the triphenylphosphonium group.

Wittig reaction

The path used to obtain a reaction of alcohols or alkyl halides to alkenes can usually be obtained using E1 or E elimination reactions but in the Wittig reaction the two carbon units are small and are joined to make the desired alkene. Let the lower yellow layer run out again and then discarded the unwanted aqueous layer into aqueous waste container. . After approximately 15, minutes a solid had formed and 3 ml of 1-propanol were added and heated on a hot plate in the hood. This leads to the formation of a charge-separated and dipolar intermediate called a betaine.

Wittig Reaction Lab Report

The intermediate disassembles to hopefully accomplish the formation of the alkene and phospineoxide product. A percent yield has been calculated below for reference. We used 2cm3 of 0. He was born in Berlin, on June 16, 1897, and died August 26, 1987 1. Olofson, "Stereochemistry and Mechanism of the Wittig Reaction. After 30 minutes of reaction time, the solution was removed and 1.

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The crystals were gold or silver-yellow metallic in nature. This step can be illustrated as follows: Step 2: The betaine intermediate which is formed in step 1 is now subject to the formation of a new oxygen phosphorus bond, yielding another intermediate which has a four-membered ring structure. Cooled the flask in a beaker of ice along with the 2- propanol the product was still not able to be achieved. When discussing a pure product the IR spectroscopy would result in a strong band at 960cm-1 due to a trans group from the trans-9- 2- phenylethenyl anthracene product. Ordinarily, the E -enoate α,β-unsaturated ester , just as the Wittig reaction does. Trialkylphosphines or the presence of groups that stabilize the ylide tends to give E- Trans geometry 2.

If we have a more acidic H to abstract a weaker base such as NaOEt or even Na could be used in the reaction. The Wittig reaction is intended to make larger molecules with carbon-carbon double bonds. The additional spectrographic information from IR, MS or NMR was not needed due to the melting point achieved. Carruthers, Some Modern Methods of Organic Synthesis, Cambridge University Press, Cambridge, UK, 1971, 81—90. This stabilized ylide will allow for the desired stereochemistry of trans E product rather than the cis Z product. The concerted asynchronous cycloaddition mechanism involving a four-centered transition state is suggested to be operating in these systems. This step is illustrated below.

The alkene in the final product contains unsaturation of the olefinic pi bond thus enabling the product to possess the ability to absorb light. How to make alkenes using the Wittig reaction 1 This reaction goes so well due in part to the formation of the immensely strong P-O bond. . Some of these limitations can be overcome by following a variation of the Wittig reaction such as the Schlosser modification. M-nitrobenzaldehydeEthyl-3- 4-nitrophenyl acrylate from P-nitrobenzaldehydeIn 1954, Georg Wittig, a German chemist, discovered the Wittig Reaction.

The reaction is completed using an SN2 reaction of the phosphorous compound with the primary alkyl halide and the generation of ylide using a strong base when deprotonated. The strong bases used to make the ylid can be the sodium hydride NaH , and sodium amide NaNH. The powerful force used in The Wittig reaction is for the desired formation of the strong bond of the phophine oxide. Wittig became an emeritus professor in 1967, where he remained until the end of his notable career 1. The stable 5 valencies are met in compounds like phosphoric acid and PCL 1. Stereochemistry, mechanism, and selected synthetic aspects".

It was evident that the product did form or the melting point would have not been as close as it was. . The residue was heated too fast and started to sublime so about 4 mL of 2-propanol was added instead of the 2mL required in hopes to salvage product. Conclusion: The goal of performing the experiment was to use the Wittig reaction to form a stereoselective alkene. The experiment allowed for the preparation of trans 9— 2—phenylethenyl anthracene, the formation a crystallized product and the confirmation of the products identity through its melting point. Introduction: The Wittig Reaction performed in this lab is good method used to synthesize alkenes.