Pdf greening the wittig and other reactions for the undergraduate. Mar 18, 2014 its time for the wittig reaction mechanism to be made easy. Why is the wittig reaction generally considered a green. He was also awarded the 1979 nobel prize in chemistry for this discovery. If a potassium base was used to generate the phosphine oxide anion, the reaction with a carbonyl compound proceeded as in the wittig reaction to give an alkene. Background the ability to prepare alkenes is an extremely valuable reaction in organic synthesis. The reaction of an aldehyde or ketone with a phosphonium ylide to an alkene and a phosphine oxide is known as wittig reaction or wittig olefination reaction this reaction was discovered in 1954 by georg wittig, for which he was awarded the nobel prize in chemistry in 1979. In 1958, horner and coworkers described the use of phosphine oxides in wittigtype reactions. Wittig reactions are more general in that the product carbonyl does not need to have an attached carbonyl. Teaching green chemistry in organic teaching laboratories green experiments in the organic teaching lab. A highly versatile onepot aqueous wittig reaction sciep. The wittig reaction described within this report is an excellent example of how traditional organic chemistry experiments can be modified to ensure that green principles are being discussed and promoted within a traditionally non green discipline. No waste from this lab should be poured down the sink. Synthesis of stilbene by the wittig and hornerwadsworth.
Green chemistry, the wittig reaction green chemistry. Follow me in my walkthrough video and we can do the mechanism together. The formation of a phosphine oxide with its strong po bond is the driving force for the classical wittig reaction, but is wasteful and can pose problems during purification. We disseminate green chemistry concepts and best practices globally to science educators, scientists and the public at large through our education programs that are designed to teach and demonstrate green chemistry. The wittig reaction or wittig olefination is a chemical reaction of an aldehyde or ketonewith a triphenyl phosphonium ylide often called a wittig reagent to give an alkene andtriphenylphosphine oxide. Wittighorner reaction proceeds through stepwise p p cleavage of an oxadiphosphetane intermediate, followed by a 2,3. Mar, 2014 hey guys, have you ever heard of the wittig reaction. Nov 30, 2016 azawittig reactions are similar to wittig reactions in that they also involve the reaction of a phosphonium ylide, in this case an iminophosphorane or phosphinimide such as 39, with a carbonyl group containing compound to form the carbonnitrogen double bond of an imine along with a byproduct phosphine oxide such as 2 scheme 12. The wittig reaction is named after georg wittig 18971987 and was so useful as a cc bond formation reaction that he won the nobel prize in 1979. Experiment 27 a solvent free wittig reaction page 2 of 5 figure 3. Each group member will perform the wittig reaction with commercially available ylide carbethoxymethylenetriphenylphosphorane and one of the three aldehydes 2, 3, or 4 chlorobenzaldehyde below.
The wittig reaction is an important chemical reaction that is used to convert ketones or aldehydes into alkenes. Further development of the wittig reaction in carbohydrate chemistry is demonstrated by the many publications each year on this topic. When the r group of the ylide is a simple alkyl, the species is called an unstabilized ylide and the z double bond isomer predominates in the products. If you want to know why check out barry trosts concept of atom economy. Synthesis of stilbene by the wittig and hornerwadsworthemmons reactions. The reaction is easy to carry out and proceeds under mild conditions. Beyond benign is a nonprofit organization dedicated to green chemistry education. This reaction is a very common method used in the organic synthesis of alkenes. The double bond forms specifically at the location of the original aldehyde or ketone.
Pdf green experiments in the organic teaching lab are a vital part of. You will work in a small group to carry out variations of the wittig reaction and to answer the focus questions below. A variation of the wittig reaction, called the hornerwadsworthemmons hwe reaction gives e alkenes. The wittig reaction is the addition of a ylide to an aldehyde or ketone to form an alkene. The wittig reaction 1 is perhaps the most commonly used method for the synthesis of alkenes.
I used the original lab manual pages while making the video. Catalytic wittig and azawittig reactions beilstein journals. The driving force is the formation of a very stable phosphine oxide. A solvent free wittig reaction west virginia university. The mechanism beings with attack of the pph 3 on the alkyl halide which releases the halide anion and forms a phosphonium ion. This reaction was discovered in 1954 by georg wittig, for which he was awarded the nobel prize in chemistry in 1979. Its a really really cool and useful reaction that you all will learn in organic chemistry ii that involves ketones and aldehydes. Green synthesis of morpholino cinnamides using sodium lauryl. We disseminate green chemistry concepts and best practices globally to science educators, scientists and the public at large through our education programs that are designed to teach and demonstrate green chemistry principles. This reaction is important because it allows us to couple two carbon fragments together and is very useful for the generation of alkenes, which are very adaptive starting material. The reaction is effected by grinding the reactants in a mortar with a pestle.
The e isomer is isolated by crystallization with ethanol in this experiment. Mechanism of the wittig reaction the ez selectivity of the wittig reaction depends upon the structure of the ylide that is used. The driving force of this reaction is the formation of phosphine oxide product. It is widely used in organic synthesis for the preparation of alkenes. Synthesis of stilbene by the wittig and hornerwadsworthemmons reactions important concepts synthetic methods for making double bonds olefins phosphonium salt, ylide, phosphonate ester transition state controls wittig stereochemistry cis. This reaction is named after its discoverer, the german chemist georg wittig. I also provide some useful tips that you guys should try to. Mechanism of the phosphawittighorner reaction arkhypchuk. There are a number of reactions that can be used to prepare alkenes, but one of the most important is the wittig reaction.
The reaction utilizes a carbonyl compound as an electrophile, which is. The wittig reaction is the reaction of a wittig reagent with an aldehyde or a ketone to afford an alkene as the organic product. Wittig reaction article about wittig reaction by the free. Both the e and z isomers of the product are produced as evidenced by thinlayer chromatography and 1h nmr analysis.
The wittig reaction was discovered in 1954 by georg wittig, for which he was awarded the nobel prize in chemistry in 1979. Dispose of all waste in the designated waste container. Mechanism the general mechanism of the wittig reaction is shown above. The work discussed here focuses on a series of wittig reactions that are carried. This is followed by a presentation of the current state of the art regarding phosphinecatalyzed wittig reactions. Green experiments in the organic teaching lab are a vital part of training a new generation of scientists. Cohen used the known axial preference of the formation of organolithiums by reduction of 2alkylthiopyrans 23 to produce the organolithium 24 diastereoselectively, the vinylic and lithio substituents lying trans. Kirchhoff summer school on green chemistry and sustainable energy 23 july 20. The reaction between a phosphorane and an aldehyde or a ketone to form a phosphine oxide and an alkene is known as the wittig reaction fig. The result of a wittig reaction is the replacement of the carbonyl oxygen of an aldehyde by the carbon group.
The mechanism of the hwe reaction resembles that of the wittig reaction. Alkenes from carbonyl compounds study questions 1 why is it important that the aldehydes added to the ylide be free of carboxylic acids. The wittig reaction chem 115 fan liu stabilized ylides are proposed to have a later and more productlike transition state with 1e thermodynamically favored over 1z. Mar 01, 20 the wittig reaction or wittig olefination is a chemical reaction of an aldehyde or ketonewith a triphenyl phosphonium ylide often called a wittig reagent to give an alkene andtriphenylphosphine oxide. In addition to learning about the wittig reaction, students are also introduced to the ideas of mechanochemistry and green chemistry. The alkene product 4 that you make today is the one that was used a few weeks ago as the colorizer for the chemiluminscence experiment it gave the green solution. Because the acidic proton on the carboxylic acid will protonate the negatively charged carbon, destroying the ylide. George wittig, the german chemist, has first showed the value of this procedure in the synthesis of alkenes. For example, it has low atom economy due to its requirement of one molar equivalent of a phosphine reagent, and. Wittig olefination also known as the wittig reaction was developed by georg wittig in 1954. The wittig reaction was discovered by the german chemists g.
The wittig, hornerwadsworthemmons, kabachnikfields, arbuzov and michaelis reactions are considered as examples. Though the wittig reaction was published 60 years ago, there has been and continues to be a wealth of research into the subjects, mostly directed toward extending it for the general stereospeci c synthesis of arbitrary alkenes. We will discuss the mechanism in greater detail in chapter 23, when we discuss the chemistry of hydrogens that are. This organic chemistry video tutorial provides a basic introduction into the wittig. Reactive ylides give rapid reaction and subsequent rapid ring opening to give the zalkene. Because of its reliability and wide applicability, the wittig reaction has become a standard tool for synthetic organic chemists. The synthesis of vitamin a is based on the wittig reaction, which may also be used to prepare squalene a precursor of cholesterol, lycopene, bixin esters, and so on. The green wittig reaction described within this report was performed at ambient temperature and in an aqueous medium. Greening the wittig and other reactions for the undergraduate organic teaching laboratory. Green chemistry is the design of chemical products and processes that reduce or eliminate the use and. In this experiment e and z14bromophenyl2phenylethene are synthesized by a solventfree wittig reaction.
In fact, the discoverer of this reaction, george wittig, was awarded the 1979. This reaction is important because it allows us to couple two carbon fragments together and is very useful for the generation of alkenes, which are very adaptive starting material and are able to generate lots of other compounds. An example of the wittig reaction is provided below. This experiment can be extended to include 1 h nmr analysis of the products. The versatility of this method has been demonstrated by several syntheses of such biologically important products as sialic acids, 2deoxy sugars, and sphingosines.
The wittig reaction experiment chemistry libretexts. The most popular use of the wittig reaction is for the introduction of a methylene group using methylenetriphenylphosphorane ph 3 pch 2. This reaction will also form an alkene as a product. Pdf greening the wittig and other reactions for the. Apr 23, 2015 there are ways to make alkenes that are green, but the wittig reaction is not one of them, in its classical formulation. Wittig and wittig horner reactions under phase transfer catalysis conditions article pdf available in central european journal of chemistry 14. The first section summarizes how arsenic and telluriumbased catalytic wittig type reaction systems were developed first due to the relatively easy reduction of the oxides involved. Aza wittig reactions are similar to wittig reactions in that they also involve the reaction of a phosphonium ylide, in this case an iminophosphorane or phosphinimide such as 39, with a carbonyl group containing compound to form the carbonnitrogen double bond of an imine along with a byproduct phosphine oxide such as 2. It is one of the most direct methods for the synthesis of alkenes with the fewest isomeric products. Green chemistry and sustainability green chemistry is a tool in. The geometry of the resulting alkene depends on the reactivity of the ylide. Procedure method 1 to be completed by one of the group members.
Introduction to the wittig reaction and discussion of the. Betaines may be stabilized by lithium salts leading to side products. In the previous post, we discussed the principle and mechanism of the wittig reaction go over those if you need to and in the following practice problem, we will work on proposing a synthesis for wittig reagents as well as preparing alkenes using the wittig reagent and alternative methods. In fact, george wittig, was awarded the 1979 nobel prize in chemistry for. There are a number of reactions that can be used to prepare alkenes with one of the most important being the wittig reaction. The reaction of an aldehyde or ketone with a phosphonium ylide to an alkene and a phosphine oxide is known as wittig reaction or wittig olefination reaction. Not only do they make the lab experience safer and produce less costly waste, they allow students an opportunity to examine and consider potentially hazardous chemical methodologies and develop alternatives. The most important use of ylides in synthesis comes from their reactions with aldehydes and ketones, which are initiated in every case by a covalent bonding of the nucleophilic alphacarbon to the electrophilic carbonyl carbon. While initially it was supposed that all wittig olefination reactions lead via 1,2 addition to. Industrial applications of the wittig reaction springerlink. To demonstrate the ease of introducing green chemistry principles into the organic chemistry teaching lab a wittig reaction was chosen to be greened. The wittig reaction is an organic reaction used to convert a primary or secondary alkyl halide and an aldehyde or ketone to an olefin using triphenylphosphine and base. This is the third and final quarter of the organic chemistry series.
The wittig reaction is an important method for the formation of alkenes. The reaction of stabilized phosphonium ylides with aldehydes favors ealkene products. Intro the wittig reaction is one of the premier methods for the synthesis of alkenes. The wittig reaction or wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide often called a wittig reagent to give an alkene and triphenylphosphine oxide the wittig reaction was discovered in 1954 by georg wittig, for which he was awarded the nobel prize in chemistry in 1979. The first evidence that the 2,3 wittig rearrangement of organolithiums proceeds with inversion followed theoretical work 23 predicting that this should be the case.
In 1958, horner and coworkers described the use of phosphine oxides in wittig type reactions. Students can observe the difference in the coupling. Fundamental concepts relating to carbon compounds with emphasis on structural theory and the nature of chemical bonding, stereochemistry, reaction mechanisms, and spectroscopic, physical, and chemical properties of the principal classes. There are ways to make alkenes that are green, but the wittig reaction is not one of them, in its classical formulation. Wittig reaction is so important and it gives a new cc bond. This organic chemistry video tutorial provides a basic introduction into the wittig reaction mechanism. Parrick, in comprehensive heterocyclic chemistry iii, 2008. The wittig reaction or wittig olefination is a chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide often called a wittig reagent to give an alkene and triphenylphosphine oxide. This video is a follow up to the first wittig reaction video. The wittig reaction allows the preparation of an alkene by the reaction of an aldehyde or ketone with the ylide generated from a phosphonium salt. The wittig reaction in carbohydrate chemistry pdf free.
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