A Solventless Aldol Condensation Experiment for the Organic Chemistry Laboratory

Abstract

Aldol condensation reactions are routinely used in organic chemistry instructing labs. In this experiment, we made a greener method for the aldol condensation experiment of the Organic and natural Chemistry II lab at North Carolina Condition College. To do this, we used the twelve Rules of Green Chemistry, and altered our latest technique to match as lots of of them as doable. The primary strategy used all over this procedure was creating aldol condensation reactions that ended up entirely solventless. We at the moment have a technique that enables for all doable mixtures of two aldehydes: four-tolualdehyde and four-anisaldehyde, and two ketones: acetophenone and four-methylacetophenone. We have made a method that not only minimizes solvent usage, but also qualifies below 5 other green chemistry principles: avoidance of waste, significantly less hazardous chemical synthesis, reduction of derivatives, accident avoidance, and atom economic system. This new experimental layout enables pupils to select the compounds they would want to use from a record of readily available reagents therefore enabling a certain diploma of lab personalization.

1. Introduction

Green Chemistry is a speedily escalating willpower aimed at building chemical reactions and merchandise that minimize the generation of hazardous substances. ¹ The twelve principles of green chemistry lay the foundation for this intention and have to be utilized at all prospects to increase the greenness of the sought after response. The latest method of pondering about Green Chemistry was made in 1987 from the United Nations Commission on Environment and Enhancement. This commission outlined sustainable development as “…assembly the demands of the current with no compromising the capability of upcoming generations to fulfill their own demands.” ^two This commission paved the way to the advancement of the twelve principles of green chemistry, laid out below. ¹

two. Rules of Green Chemistry:

1. Protect against Squander

two. Atom Economy

three. Considerably less Hazardous Synthesis

four. Design and style Benign Chemical substances

5. Benign Solvents & Auxiliaries

6. Design and style for Energy Effectiveness

seven. Use of Renewable Feedstocks

8. Lessen Derivatives

nine. Catalysis

ten. Design and style for Degradation

eleven. Real-time Assessment for Pollution Avoidance

twelve. Inherently Benign Chemistry for Accident Avoidance.

In current a long time, the greening of organic chemistry instructing labs has been nicely underway, with many publications and presentations at conferences involving new lab experiments that integrated the principles of green chemistry. ^three From alkene isomerization to reduction of a ketone to oxidation of alcohols, lots of experimental methods have been made to alter the organic chemistry labs. ^two Even acylation reactions, this sort of as lidocaine synthesis, have been modified to put into action green chemistry. ^four Green Chemistry doesn’t just have software in organic chemistry even though, it can apply to nanotechnology and even into field. ^{5, 6} Introducing the principles of green chemistry into instructing or industrial labs is said to have lots of rewards further than just environmental. A person study famous that integrating green chemistry into instructing labs at an introductory collegiate level direct to an increase in students’ enthusiasm for equally chemistry and the green motion. ⁶

Aldol condensation reactions have been researched thoroughly, as they are one of the most considerable common methods for the formation of carbon-carbon bonds in organic chemistry. ^seven This response is a typical experiment performed in a sophomore level organic chemistry lab. While lots of scientists have aimed to combine green chemistry into the aldol response, they have commonly appear with a significant disadvantage, this sort of as significant hazards or significant waste generation. ⁸ Palleros (2004) revealed a thorough paper in the Journal of Chemical Education and learning that delivered quite a few illustrations of this response. ^nine From this, we aimed to make a functional source to use in just an undergraduate instructing lab.

We have been fascinated in the incorporation of green experiments in our organic chemistry lab curriculum. ^ten In this experiment, modifications have been made to the common aldol condensation used in labs on campus, in purchase to make it greener. These alterations outcome in a speedier response time (when in contrast to the common technique), an elimination of the want for a solvent, a reduction in the amount of money of waste made, and a easier response technique. ^{nine, eleven} The modifications satisfy 6 of the twelve principles of Green Chemistry: avoidance of waste, reduction of derivatives, safer solvents and auxiliaries, safer chemistry for accident avoidance, significantly less hazardous chemical synthesis, and maximization of atom economic system.

three. Experimental

three.1. Reagents Utilized

The following substances ended up utilized in this experiment: four-tolualdehyde, four-anisaldehyde, four-methylacetophenone, acetophenone, and sodium hydroxide pellets, as nicely as a ten{0841e0d75c8d746db04d650b1305ad3fcafc778b501ea82c6d7687ee4903b11a} aqueous HCl remedy. Reagents ended up purchased from Sigma-Aldrich and Fisher Scientific and used with no additional purification.

three.two. Treatment

This technique is written for all doable mixtures of the two aldehydes and two ketones previously outlined in the Reagents Utilized part. Using a volumetric pipet, .50 mL of the picked aldehyde and .40 mL of the picked ketone ended up extra to a mortar. Close to .ten g of stable NaOH was extra to the response and then using a pestle, was crushed up in just the remedy. The response was ground till the formation of a stable was observed. Immediately after the stable started to type, the mixture was authorized to sit for ten minutes, to assure completion. As soon as the ten minutes experienced handed, two mL of ten{0841e0d75c8d746db04d650b1305ad3fcafc778b501ea82c6d7687ee4903b11a} aqueous HCl ended up extra to neutralize any residual NaOH. This mixture was then authorized to sit for an additional ten minutes, before vacuum filtration was performed. The sample was washed with a smaller amount of money of chilly 90{0841e0d75c8d746db04d650b1305ad3fcafc778b501ea82c6d7687ee4903b11a} ethanol.

three.three. Hazards

The use of right individual protective tools, this sort of as eye security, by scientists was required at all instances in the laboratory. Ethanol was managed with caution due to flammability. Each aldehydes (four-anisaldehyde and four-tolualdehyde) are air delicate, so the containers ended up coated with parafilm to keep away from contamination. In addition to this, the reagents used are eye, pores and skin, and respiratory irritants and ended up dispensed in just a fume hood. Utilized solvents and filtrate ended up disposed of in the organic undesirable liquid content container, whilst stable merchandise was disposed of in the organic undesirable stable content container.

four. Benefits and Dialogue

This experiment was intended to provide a green substitute to common aldol condensation reactions in just a 2nd semester organic chemistry lab. Introducing a technique that incorporates quite a few principles of green chemistry, this sort of as lowered auxiliaries, atom economic system, and waste reduction, could be beneficial to pupils. The common technique involves pupils to mix acetone and acetophenone with a 1:1 ninety five{0841e0d75c8d746db04d650b1305ad3fcafc778b501ea82c6d7687ee4903b11a} ethanol: 3M sodium hydroxide remedy in an Erlenmeyer flask. The pupils then stir intermittently for 15 minutes, isolate the merchandise, and recrystallize. This technique sales opportunities to very low yields and impure merchandise (as decided through melting level assessment). ^eleven The proposed technique will call for pupils to mix one of two aldehydes (four-tolualdehyde or four-anisaldehyde) with one of two ketones (acetophenone or four-methylacetophenone) in the presence of a pellet of sodium hydroxide in a mortar. The pupils then grind the remedy till a stable is observed. Upcoming, they use a smaller amount of money of ten{0841e0d75c8d746db04d650b1305ad3fcafc778b501ea82c6d7687ee4903b11a} HCl to neutralize the merchandise, adopted by filtering and washing with chilly 90{0841e0d75c8d746db04d650b1305ad3fcafc778b501ea82c6d7687ee4903b11a} ethanol. No recrystallization was needed with these merchandise as they have reasonable to significant purity primarily based on IR spectroscopy and melting level assessment, with the exception of the combination of anisaldehyde and acetophenone, which did not react.

Table 1 displays the 3 mixtures of aldehydes and ketones that ended up examined in this experiment. These mixtures (options 1-three) are then in contrast to the common aldol response performed with benzaldehyde and acetone in Table two.

Table two below displays a comparative assessment of the greenness of the two treatments. The comparison was minimal to the 6 principles of green chemistry that the proposed technique enhanced from the prior method.

As witnessed in Table two, the proposed method gives lots of green rewards when in contrast to the latest one, this sort of as the elimination of solvent, reduction of waste and derivatives, curtailment of hazardous risks, advancement of atom economic system, and improvement of accident avoidance. An additional benefit of the proposed technique is that with the several choices and reduction of response time, pupils are able to synthesize a lot more than one merchandise, so giving them a lot more observe with the different strategies used. Learners also have a lot more time to review the IR spectra and melting level knowledge to determine the relative purity of the merchandise.

5. Conclusion

The aldol condensation is a quite helpful response in organic chemistry for its capability to type carbon-carbon bonds it is also a rather straightforward technique in use in lots of instructing labs. Some latest methods have a tendency to outcome in very low yields and purity. In this experiment, we redesigned this method to increase the green chemistry facet of the response and elevated the selection of doable reagents in purchase to give pupils a diploma of alternative when completing the experiment. The modifications of the experiment to fulfill the principles of green chemistry resulted in a new technique that not only made significant yields and purity, but also removed the use of solvents, lowered derivative formation, lowered chemical risks, elevated atom economic system, and lowered the probability of mishaps.

Acknowledgments

We thank the Office of Chemistry at North Carolina Condition College for financial guidance of this challenge.

References