palico - 7-2-2024 at 11:36
Hello people,
I am back to chemcycle something else tonight, let's find out !
In this episode of my waste to resource serie, we will see the esterification of the terephtalic acid prepared last time from a waste PET water bottle.
The reaction is a simple Fisher esterification of the acid in ethanol, catalyzed by sulfuric acid. The reaction time is very long, also because I used
a big excess of solvent.
Procedure
5.82g of terephthalic acid are place in a 250 ml round bottomed flask along with a stirbar. 150 ml of ethanol and 2 ml of concentrated sulfuric acid
are added, the reaction mixture kept at 80 Celsius in oil bath under stirring for 4 days. The white suspension become a limpid solution, that
indicates reaction finished. The flask is removed from bath, let cool to room temperature. Once cool, the reaction mixture is poured into a solution
made by dissolving 17 g of potassium carbonate in 300 ml of water. A little froating is detected. Then, the opalescent solution is evaporated off to
300 ml of volume on hotplate at 60 Celsius. Once cool, a solid precipitate. The suspension is vacuum filtered, washed with water, residue pump dried.
The residue is furtherly dried by pressing on paper. The product smell of mint feebly. It looks single spot on TLC. 3.25 g of off-white crystalline
solid is obtained, corresponding to 41.77% of yield.
m.p.: 40-42 Celsius.
Discussion
The reaction has been so long, because I used an extremely exagerated amount of solvent. The proper amount had to be just 50 ml. I did it because I
had no running water that time, so I could not reflux. In fact, after 4 days a bit of ethanol had evaporated off. The product has been analyzed at
proton NMR and looked very pure.
In summary, from 20 g of PET, one waste water bottle we have got 3.25 g of diethyl terephthalate. And all with household, readily available reagent
and simple glassware. Imagine that, ethanol can be bioethanol, carbonate from other scrap, the energy renewable and all process of chemical recycling
of PET almost 100% a total upcycling.
References
1. Org. Syn., vol. 26, pp. 95, 1946
2. Eur. J. Med. Chem., vol. 44, pp. 3552-3559, 2009
As usual, I link to my YT video for more detailed prodecure, both preparation and analysis.
thank you for attention,
palico
[Edited on 7-2-2024 by palico]