Scientific Russia: Scientists from St Petersburg University make sulphur behave like metal
Russian scientists have synthesised organic sulphur-containing compounds that can significantly speed up chemical reactions. The resulting substances are potentially less toxic and more stable than many other catalysts, such as those containing metals or metalloids. Because of this, the novel compounds can be used in pharmaceuticals for the synthesis of drugs.
Organic-based catalysts have a number of advantages over other types of catalysts, for example, those containing metal cations. They are resistant to oxidation in air and to moisture, less toxic and significantly more environmentally friendly. They are therefore widely used in the pharmaceutical and chemical industries for the synthesis of drugs and polymers.
The findings of the research supported by a grant from the Russian Science Foundation are published in The Journal of Organic Chemistry.
It is not easy to create a catalyst in which a non-metal atom exhibits the metal properties necessary to bind to a molecule, activate it and thereby accelerate the conversion. As a consequence, in most cases, the catalytic properties of organic compounds are ensured by the activity of metalloid atoms, i.e. compounds that can exhibit both metal and non-metal properties. Metalloids are among the chalcogens, elements in group 16 of Mendeleev’s periodic table, and include selenium, tellurium, and polonium. It is possible to use them to create analogues of catalysts containing real metals, but these elements are very toxic, which contradicts the very idea of green catalysts. Until recently it was thought impossible to obtain safe organic catalysts based on other chalcogens − oxygen and sulphur − because these chemical elements are typical non-metals and do not exhibit metallic properties in compounds.
St Petersburg University scientists synthesised stable and safe organic catalysts in which the sulphur atom behaves like a metal. The authors evaluated the ability of the proposed substances to accelerate chemical conversions by performing a synthesis reaction of nitrogen-containing compounds, which is used in the creation of many drugs. It turned out that the obtained catalysts accelerate the studied reaction by an order of magnitude.
Although experiments showed that sulphur-based compounds are less active than their sulphur-based counterparts, they may be considered more promising for use in organic synthesis because they are more environmentally friendly. For example, if further recycled and disposed of, the proposed catalysts could be converted into hydrogen sulphide or sulphur oxide, which are many times less toxic than similar selenium compounds (just as dangerous as arsenicals). Additionally, calculations of the chemical reaction parameters showed that the activity of the novel compounds is higher than that of catalysts containing tellurium, often used to accelerate conversions.
‘Our research focuses on making non-metals behave like metals. This expanded understanding of the reactivity of the elements on the periodic table will enable the use of toxic compounds to be phased out and a wide range of environmentally benign catalysts to be used in future. This is undoubtedly important both for our and future generations,’ said Dmitrii Bolotin, Doctor of Chemistry, Associate Professor in the Department of Physical Organic Chemistry at St Petersburg University, Principal Investigator of the project supported by the grant from the Russian Science Foundation.