A Technique in Nitration of Toluene using Ytterbium Triflate

This is my first post pertaining to my thesis. I am exploring the use of rare earth metals for the nitration of aromatic compounds. Previous research has shown that the use of lanthanides have environmental superiority over sulfuric acid (1). The use of corrosive acid is reduced, which greatly benefits the health of the environment. The question, however, about is economic use is still unanswered. In this specific project, I will attempt to recreate previous conditions that led to the creation of higher yields in toluene only. The last time this project was done, the reaction, while successful in nitrating activated arenes, did not yield high amounts of the product, the exception being toluene (2). A particular question that must be answered is whether this greener method of nitrating can only yield large amounts of the desired nitrated product when the substrate is an alkylbenzene? The reasoning as to why alkylbenzenes are the only activated arenes that nitrate successfully AND produce a high yield is caused by the electron donating nature of the alkyl group of toluene toward the ring. My hypothesis is that the bulkier alkyl group of cumene will have a higher yield than toluene.

 

Classical Nitration

 

Sulfuric acid is generally fond in the classical nitration method. The reaction begins with an aromatic compound reacting with an electrophile, such as the nitronium ion that is derived from nitric acid.The formation of the nitronium ion begins when nitric acid deprotonates sulfuric acid, which eventually forms water, sulfate anion, and the nitronium. The substitution of the nitronium ion into the aromatic ring forms two different isomers of nitrotoluene: ortho and para. In Green Chemistry Nitration of toluene, the lanthanide ytterbium triflate is the ideal environmental and economic method of obtaining nitrated aromatic products.

A Specific Technique Performed in my Project

I am being asked to describe a technique that I am doing for my research. One technique that I have done is the refluxing of my reactants.  I set up a reflux apparatus by obtaining a heating mantle, a condenser, and a 25 mL round bottom flask. After they were put together, I added my reagents according to optimum condition concentrations. This is important because under these conditions, I can maximize the amount of product created after the reaction. The temperature during reflux should be at a moderate level; just enough for there to be some boiling. Tubing should connect to the condenser and water should be flowing though so that the high temperature from the heating mantle does not evaporate the product. The length of the boiling is to be at least 14 hours. Refluxing at short time periods can cause the product to not be produced at high levels. It is imperative that all of the toluene be nitrated. Longer reflux time allows this to happen. The reaction is to be quenched with water, which will cause the reaction to cease. There should be two layers: the aqueous and organic layer. These layers will be separated with the help of a separatory funnel and undergo rotovaporization  in order to dry the catalyst and the product. The yields will then be calculated.

 

References

1) Braddock, C. Green Chemistry. 2001, 3, 26-32

2)Whitcomb, Tyler J. Using Recyclable Nitration Catalyst as an Environmental and Economical Alternative for the Nitration of Activated Aromatic Rings May 2009

 

(ALL IMAGES FROM THE PUBLIC DOMAIN)

TO BE CONTINUED…