Wittig reaction Essay Example | Topics and Well Written Essays - 1500 words

Wittig reaction - Essay Example The latter chemical agent is commonly known as the witting reagent, it results into chemical agents known as alkene as well as triphenylphosphine oxide (Carrutthers, 1971). Discovered in 1954 by Georg Witting, it continues to be vastly used in the organic synthesis of alkene preparation. This procedure should not be misunderstood with, the Witting rearrangement chemical procedure which is based on a different theory. The witting reaction is normally applicable in the coupling of aldehydes and kentones, is the single substitution of phosphine ylides. The out coming data from the ylides test results is nearly exclusive with the z-alkene chemical agent product. As such for one to obtain the E-alkene chemical agent, there is need to apply ylides under stabilization which can also be substituted with unstablised ylides. This can be undertaken with the application of the Schlosser modification chemical tests, after which the Witting reaction chemical test can be performed (Vedejs et al, 20 00). The witting reaction has a variation known as the classical mechanism; this is the established theoratical procedure of the witting reaction chemical test. It involves the bulk steric of ylide, this interacts with sterochemicals to produce nucleophilic addittives. This gives rise to betaine, the carbon-carbon bond rotation produces betaine tht in turn produces oxaphosphetane. By eliminating the desireable z-alkene in addittion to triphenylphosphine oxide components, the simplified witting reagents are used in a sequenced procedure. The first sequence of this procedure begins with a combination of aldehyes and ketones, this is followed by the decomposition of betaine. This decomposition occurs to the fifth form, this stage is also known as the rate-determination level. However, with ylides under stablization the initial sequence is noticed to be the slowest. As such the general alkene formation rate is reduced with time, this results into a sizeable proportion of the akene produ ct in which case being the E-isomer. This creates an understanding of the reasons, behind the failure of the stablizing reagents in proper reaction with sterical hindered ketones (Vedejs et al. 2000). Witting reagents such as phosphorus ylides, are prepared in a formulated procedure. Phosphium salt is the known derivative of preparation; it is also a resulting chemical agent from the reaction of triphenylphosphine and alkyl halide. As such in order to create the witting reagent being ylide, phosphonium salt must undergo suspension in a solvent such like diethyl ether with treatment of strong base chemicals like phenyllithium which can also be substituted with butyllitium. This can be shown with the following chemical equation Ph3P+CH2R X? + C4H9Li > Ph3P=CH?R + LiX + C4H10, in this chemical procedure methylenetriphenylphosphorane is the simplified ylide in use (Vedejs and Marth, 1998). This yield is also a precursor to a more defined elaboration of the witting reagents, alkylation o ccurs as seen in this chemical equation Ph3P=CH2 by the main alkyl halide that creates a phosphonium salt substitution. The formulation of these salts, is deprotonated in the normal matter resulting into a chemical agent as identified by the following chemical equation Ph3P=CH?CH2R. The ylide which is the witting reagent is structured in such a way that is identified as phosphorane in written form. This is an established representation of the ylide form, being a vital contributor as carbon remains mildly nucleophilic. Its chemical structure is comprised of a ball-and-stick model arrangement, that is takes the physical form of a crystal structure. In terms of its reactivity, simplified phosphoranes are highly reactive and very unstable in