A research team from the UniSysCat Cluster of Excellence at TU Berlin has synthesised silicon-based super Lewis acids containing an additional halogen atom for the first time.<\/p>\n
These compounds rank among the strongest Lewis acids<\/a> known to date and can attack highly stable chemical bonds such as the carbon\u2013fluorine linkages in PFAS.<\/p>\n The new compounds are not consumed during the reaction, and instead, can regenerate. Therefore, they act catalytically, which presents a decisive advantage for potential applications in recycling processes and green chemistry.<\/p>\n Why are PFAS bonds so difficult to break down?<\/p>\n The extreme difficulty of breaking down PFAS bonds comes down to a single, incredibly strong chemical bond: the carbon-fluorine (C-F) bond. This bond is one of the strongest in organic chemistry due to fluorine\u2019s high electronegativity, enabling the creation of a very stable and short covalent bond with carbon.<\/p>\n Due to this unique chemical stability, a substantial amount of energy is required to break it. Traditional chemical and biological degradation processes, which can break down many other organic compounds, are simply not powerful enough.<\/p>\n This is why PFAS are known as \u201cforever chemicals,\u201d as they persist in the environment for decades, if not longer, leading to widespread contamination of soil and water. The C-F bond\u2019s strength makes it a key challenge for scientists developing new remediation technologies.<\/p>\n Electron hunger enables PFAS degradation<\/p>\n The stability of PFAS is due to their particularly strong carbon\u2013fluorine bonds, and breaking them requires substances with an exceptionally high affinity for electron pairs.<\/p>\n The newly developed super Lewis acids meet this requirement: the combination of a silicon atom with a halogen atom generates an extreme electron deficiency, enabling the breakdown of PFAS bonds<\/a>.<\/p>\n The synthesis process is complex, as the substances must be handled under inert conditions to prevent contamination. Neither oxygen nor water can encounter the compounds.<\/p>\n The breakthrough was achieved using protolysis, a method previously applied in carbon chemistry and now adapted for use in silicon chemistry.<\/p>\n Regeneration of Lewis acids provides predictive power<\/p>\n In addition to experimental work, theoretical calculations played a crucial role. Quantum chemical methods allowed the researchers to predict the acidity of the molecules purely from their structure, and these predictions were later verified experimentally using NMR spectroscopy.<\/p>\n