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A new method to discharge phosphorus by ultraviolet radiation

Phosphorus, a mineral element found in rocks and bones, is an important component in fertilizers, pesticides, cleaning products and other industrial and household materials. The assimilation of the phosphorus in these materials, after it is extracted from the rocks, is dangerous and expensive, and for decades chemists have been trying to simplify this process.

The properties of the phosphorus atom
The properties of the phosphorus atom

Chemistry professor Christopher Cummins from MIT University and his research team have developed a new method for attaching phosphorus to organic compounds by first splitting the phosphorus with ultraviolet radiation. Their new method, described in the scientific journal Angewandte Chemie, eliminates the need for chlorine compounds, which are often required in these reactions and which present health risks to the workers who use them.

Scientist Guy Bertrand, professor of chemistry at the University of California (Riverside), explains that the beauty of the discovery is its simplicity. - Phosphorus is indeed urgent and required, since the old chemistry of chlorine-based phosphorus has many undesirable consequences for the environment." Although the new reaction is not capable of producing the quantities needed to make phosphorus compounds on a large scale, it opens the door to a new field of research which could lead to such industrial applications, says the scientist Bertrand.

Most of the natural phosphorus comes from fossilized fossils, which are often found in dried up seabeds. These phosphorus deposits exist as phosphate rocks (phosphate, the anion of a phosphorous salt), which usually include impurities such as calcium and other metals, which must be kept away. Purification of these rocks yields white phosphorus, a fragment containing four phosphorus atoms. The structure of white phosphorus is tetrahedral, i.e. square pyramid-like when each atom located in the corner is connected to the other three atoms. White phosphorus (P4) is the most stable form of molecular phosphorus (several polymeric forms also exist, with the most common being black phosphorus and red phosphorus, which consist of long chains of quaternary phosphorus units).

In most of its industrial uses, the phosphor must be joined atom by atom, so it is necessary to tear single atoms out of the P4 compound. This process is usually carried out in two stages: the first - three of the phosphorus atoms are converted into chlorine atoms to obtain the isolated PCl3 - a single phosphorus atom attached to three chlorine atoms. These chlorine atoms are then removed by organic compounds, obtaining a wide variety of organo-phosphorus compounds similar to those found in pesticides. However, this process was both wasteful and dangerous - chlorine gas was used as a chemical weapon during the First World War - so chemists tried to find new ways to connect phosphorus atoms to organic compounds without the need to use chlorine.

Scientist Cummins has long been fascinated by the element phosphorus, in part because of its unusual tetrahedral structure. The element phosphorus is found in the same column as nitrogen in the periodic table of the elements, whose most stable form is N2, so the chemists expected that phosphorus should form a stable structure of P2. However, the reality is not like that.

For several years this research group has been exploring ways to split the P4 fragment into a P2 fragment in the hope of attaching smaller phosphorus fragments to organic compounds. In his new study, the scientist was inspired by an old, neglected paper published in 1937, describing the ability to split the four-atomic structure into two diatomic structures using ultraviolet radiation. In the old study, P2 was next polymerized to obtain red phosphorus.

The researcher decided to test what would happen if he cleaved the P4 compound using ultraviolet radiation in the presence of active organic compounds (in this case - compounds with a carbon-carbon double bond). After 12 hours of exposure to ultraviolet radiation, he found that the compound known as tetra-organo-di-phosphate was formed, which consists of two phosphorus atoms attached to two units of the organic compound.

This finding implies, although it does not absolutely prove, that the P2 form was indeed formed and immediately afterwards it was bound to the organic compound. In future studies, the research group hopes to directly observe the presence of the P2 form, if it does exist. The research team also plans to test whether other organophosphorus compounds can be produced using ultraviolet radiation, including metallic compounds. In addition, the team has already created an organophosphorus compound containing nickel, which could be used in electronic applications.

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