Kobe, Japan – The solvent tetrachloroethylene (also known as perchloroethylene, or Perc) is used extensively for dry cleaning, and also as a metal degreaser. Now, a team of chemists at Kobe University has found a way to use it to make urethane derivatives.
The Kobe team developed a photo-oxidation method to transform the solvent into useful building blocks. First, they took the tetrachloroethylene and an amine, and simply shone a UV light on it, with the resulting reaction making N-substituted trichloroacetamides.
While they originally developed this process a decade ago, it was not very practical: the yield was low, and toxic, corrosive by-products were also made. Working alongside the Japanese chemicals and glass manufacturer ACG Inc, they worked out how the reaction could be made more efficient, and also safer.
The key was a change to the reaction conditions. The reaction had been run at below room temperature, but they found that by heating it to above 70°C, the resulting gas-phase photooxidation reaction was extremely fast, and a single product was made. They believe that a radical chain reaction is occurring, with the tetrachloroethylene first forming trichloroacetyl chloride, which then reacts with the amine to form a N-substituted trichloroacetamide.
These building blocks were then used to make eight different urethane derivatives via base-catalysed substitution reactions with alcohols or amines, and even a fluorinated polyurethane. They also made 11 different urea derivatives that have potential uses in pharmaceutical manufacturing.
The team suggest that this synthetic method could have potential for the recycling of tetrachloroethylene. As a result, the sustainability of the dry cleaning process might be improved.
Patents have already been filed, and the work has been published in the journal ACS Omega.
