In this laboratory, we will prepare an aromatic heterocyclic molecule from the class of molecules called quinoxalines. These rings are rare in nature; however, they have been found to be useful products for medicinal purposes.
In this laboratory experience you will examine the synthesis of heterocyclic molecules. In addition you will see some ways that green chemistry principles can be used to prepare the products more safely than has been done previously. In specific you are using a safe substance (thiamine, Vitamin B1) as a catalyst. We are also speeding the reaction by the use of ultrasound. Lastly, the published procedure from which this method was derived uses more hazardous solvents and produces a larger amount of waste.
1. Convert the amount of diamine and diketone from moles to mass.
2. Calculate the amount of thiamine needed; multiply the number of moles of the limiting reagent by 5% and convert from moles of thiamine to mass of thiamine.
3. Go online to find the Twelve Principles of Green Chemistry. List the principles that this laboratory seems to incorporate.
In a standard sized test tube, dissolve 4-nitro-o-phenylenediamine (1.1 mmol), benzil (1 mmol), and thiamine catalyst (see question above) in 5 mL of ethanol. Clamp the test tube into an ultrasonic bath at room temperature and sonicate for 1 hour. Add 10 mL water to the resulting mixture. Chill, stir well and collect the product by vacuum filtration. If the product is orange, it can be purified by recrystallization from 70% ethanol. After the product has dried obtain IR spectrum and melting point (literature value = 193-195 °C).
Aghapoor, K.; Mohsenzadeh, F; Talebian, S.; Tehrani, M. J.; Balavar, Y; Khanalizadeh, G.; Darabi, H. R. Vitamin B1 as a metal-ion-free natural catalyst for sustainable quinoxaline ring condensation under sonochemical conditions. Montash. Chem. 2011, 142, 619-624. link
Mohsenzadeh, F; Aghapoor, K.; Darabi, H. R. Benign Approaches for the Microwave-assisted Synthesis of Quinoxalines. J. Braz. Chem. Soc. 2007, 18, 297-303.