Biocatalytic hydrolysis of di-urethane model compounds in ionic liquid reaction media

The suitability of different enzymes to carry out the hydrolysis of two-different toluene-based urethane model compounds (i.e. bis(2-methoxyethyl) (4-methyl-1,3-phenylene)dicarbamate, and bis(2-methoxyethyl) (2-methyl-1,3-phenylene)dicarbamate) has been demonstrated for the first time by taking advantage of ionic liquid (IL) technologies. Toluene-based urethane compounds were prepared from usual substrates in polyurethane industrial synthesis. Afterwards, their carbamate groups were target of a biocatalytic hydrolysis by means of different commercial hydrolases (i.e. lipase, urease and proteases) in either water, hydrophilic organic solvents (i.e. ethylene glycol or 1,2-dimethyl-1,3-dioxolane-4-methanol, (solketal)), or hydrophobic ILs (e.g. [C4mim][NTf2], etc.) as reaction media. Because of the insolubility of these compounds in water, most of the enzymes were unable to catalyse the hydrolysis of the di-urethane substrates in pure water, being clearly improved (up to 31.6 mU/mg for the urease case) in solketal:water (90:10, v/v) reaction media. When hydrophobic ILs were added into this reaction medium, the urease activity increased by more than twice (74.1 mU/mg). The most promising results for the hydrolysis of these urethane compounds were obtained by combining lipase and urease biocatalysts in a IL:solketal:H2O (70:25:5, v/v/v) reaction medium. These results demonstrate a possible biocatalytic approach for the hydrolytic depolymerization of polyurethane foam wastes.