Green Aqueous Wittig Reaction: Teaching Green Chemistry in Organic Teaching Laboratories

Abstract

Green experiments in the organic teaching lab are a vital part of training a new generation of scientists. 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 work discussed here focuses on a series of Wittig reactions that are carried out in aqueous conditions, at room temperature, and in less than one hour. The reactions have been applied to a variety of starting aldehydes. Results for this work and strategies for implementing a green chemistry case study into the laboratory curriculum are presented.

A Safe and Green Benzylic Radical Bromination Experiment

“…Interestingly, the bromination of p -toluic acid can be used as a starting material of subsequent reactions, such as S N 2 , and Wittig , reactions, allowing the synthesis of more complex products (Scheme ). This affords the opportunity to compare different reactions with radical and polar mechanisms in the same experiment.…”

Re-casting traditional organic experiments into green guided-inquiry based experiments: student perceptions

“…A collaboration of Organic chemistry educators presented a comprehensive summary of experimental and theoretical applications of green chemistry in Organic experiments in a publication edited by Dicks (2). A small subset of articles shows a variety of greener principles or methods are used in these new or revised experiments such as microwave irradiation, solvent-free conditions, and safer reagents or solvents (3)(4)(5)(6)(7)(8)(9). Montes et al (3) have developed a greener synthesis of aspirin using microwave irradiation.…”

“…Students determine the effect of catalysts on reaction time, purity, yield, and secondary products. Morsch et al (4) implemented a greener Wittig reaction carried out in aqueous conditions at room temperature. Palleros (5) used a solvent-free aldol reaction to form a variety of chalcones.…”

A microwave-assisted highly stereoselective one-pot Wittig reaction undersolvent-free conditions

“…Despite widespread prominence and recognition, it suffers from various difficulties like selectivity, separation, multistep protocol, and less atom economy. 4,5 The main difficulty of this reaction in the solution phase is the removal of the side product TPP oxide. Another drawback of the Wittig reaction is the need for two-pot synthesis that involves preparation of the phosphonium ylide using alkyl halides and an external base (which leads to the formation of halide salts that require separation and disposal) and successive reaction of ylide with carbonyl to produce alkene.…”

“…6 In recent years, there have been several successful attempts to overcome these drawbacks and to enhance the green aspects of the Wittig reaction, which include ball-milling, 7 one-pot synthesis, 8 microwave irradiation, 2,5 and reaction in aqueous media. 4,9 From the first implementation of microwave technology in organic synthesis by Giguere and Gedye in 1986, microwave-assisted organic chemistry has experienced a revolutionizing growth. This unconventional energy source eliminated the difficulties related to conventional heating, which include slow and time-consuming heating, unexpected decomposition of components, overheating of substrate or product, and loss of energy, thereby reducing reaction times from hours to minutes and increasing yields and selectivity.…”