Synthesis of an Alkene from an Aldehyde – The Wittig Reaction
Abstract
The Wittig Reaction, discovered and named after Nobel prize winner Georg Wittig, can synthesise an alkene from an aldehyde1 by overall substitution of C=C for C=O in the presence of a base and a phosphonium ylide (negative and positive charges on adjacent atoms)2. The objective of this experiment was to investigate the effect of different aldehyde substituents on the cis:trans ratio of alkenes in the product and to determine the influence of different bases on the total yield.3 It was determined that stronger bases result in a higher total yield than weaker bases, and that the presence of a benzene substituent on the aldehyde (in benzaldehyde) resulted in trans-selectivity, however the results for a 4-methoxybenzene substituent were inconclusive.
Experimental
The objective of this experiment was to determine the effect of different aldehyde substituents and different bases on the structure/yield of product in the Wittig reaction. The aldehydes which were chosen to…show more content… Theoretically this cannot occur, so the fault must lie in experimental error. It is likely that this discrepancy has occurred due to the fact that the product was crude so impurities remained, and also due to poor drying of the sample by vacuum filtration. This means that that the masses have been reported as more than that of the product alone due to the mass of water and mass of impurity in the sample. The impurity present could be the other product produced in this reaction, Ph3PO. However, due to the fact that each sample was dried using the same technique and should contain the same impurities, it can still be concluded that, with both benzaldehyde and 4-methoxybenzaldehyde, the total yields of crude product were highest with sodium hydroxide, lower with sodium carbonate, and lowest with sodium