Phosphorus

Phosphorus deposits come from fossilized animals skeletons. Purifying these deposits produces white phosphorus, a tetrahedral P₄ molecule.

Organophosphorus compounds such as those found in pesticides are produced commercially in a two step process:

1. three of the atoms in P₄ are replaced with chlorine atoms to produce PCl₃
2. chlorine atoms are then displaced by organic molecules

This process is both wasteful and dangerous, chlorine is a toxic gas. It would be very beneficial if scientists could find a way of producing organophosphorus compounds without the need for chlorine.

It has been known since 1937 that P₄ can be broken into two molecules of P₂ using ultraviolet light and that the P₂ will polymerize into red phosphorus.

Massachusetts Institute of Technology (MIT) Chemists have just used UV light to break P4 molecules apart in the presence of unsaturated organic molecules in order to form tetra-organo diphosphane, a molecule made up of 2 atoms of phosphorus attached to 2 molecules of the organic compound.

Reference:
Daniel Tofan, Christopher C. Cummins. Photochemical Incorporation of Diphosphorus Units into Organic Molecules. Angewandte Chemie International Edition, 2010; DOI: 10.1002/anie.201004385

Further Reading
Allotropes

Study Questions

1. Name the allotropes of phosphorus
2. Explain the ways in which these allotropes of phosphorus are similar and the ways in which they are different to each other.
3. Write a sequence of chemical equations to represent the series of stages in the two step process to produce commercial organophosphorus compounds.
4. Write a chemical equation to represent the breaking up of P₄ molecules into P₂ molecules using UV light.
5. Explain what is meant by the term polymerize.
6. Explain the difference between saturated and unsaturated organic compounds.
   
7. Why do you think that MIT chemists used unsaturated rather than saturated organic compounds in their experiment with P₄?