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In chemistry, a chemical trap is a chemical compound that is used to detect unstable compounds.^[1] The method relies on efficiency of bimolecular reactions with reagents to produce a more easily characterize trapped product. In some cases, the trapping agent is used in large excess.

Case studies

Cyclobutadiene

A famous example is the detection of cyclobutadiene released upon oxidation of cyclobutadieneiron tricarbonyl. When this degradation is conducted in the presence of an alkyne, the cyclobutadiene is trapped as a bicyclohexadiene. The requirement for this trapping experiment is that the oxidant (ceric ammonium nitrate) and the trapping agent be mutually compatible.^[2]

Diphosphorus

Diphosphorus is an old target of chemists since it is the heavy analogue of N₂. Its fleeting existence is inferred by the controlled degradation of certain niobium complexes in the presence of trapping agents. Again, a Diels-Alder strategy is employed in the trapping:^[3]

Silylene

Another classic but elusive family of targets are silylenes, analogues of carbenes. It was proposed that dechlorination of dimethyldichlorosilane generates dimethylsilylene:^[4]

SiCl₂(CH₃)₂ + 2 K → Si(CH₃)₂ + 2 KCl

This inference is supported by conducting the dechlorination in the presence of trimethylsilane, the trapped product being pentamethyldisilane:

Si(CH₃)₂ + HSi(CH₃)₃ → (CH₃)₂Si(H)-Si(CH₃)₃

Not that the trapping agent does not react with dimethyldichlorosilane or potassium metal.

Related meanings

In some cases, chemical trap is used to detect or infer a compound when present at concentrations below its detection limit or is present in a mixture, where other components interfere with its detection. The trapping agent, for example a dye, reacts with the chemical to be detected, giving a product that is more easily detected.

References

^ March, Jerry (1985), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure, 3rd edition, New York: Wiley, ISBN 9780471854722, OCLC 642506595
^ G. F. Emerson; L. Watts; R. Pettit (1965). "Cyclobutadiene- and Benzocyclobutadiene-Iron Tricarbonyl Complexes". J. Am. Chem. Soc. 87: 131–133. doi:10.1021/ja01079a032.
^ Piro, Nicholas A.; Figueroa, Joshua S.; McKellar, Jessica T.; Cumnins, Christopher C. (1 September 2006). "Triple-Bond Reactivity of Diphosphorus Molecules". Science. 313 (5791): 1276–1279. Bibcode:2006Sci...313.1276P. doi:10.1126/science.1129630. PMID 16946068. S2CID 27740669.
^ Skell, P. S.; Goldstein, E. J. (1964). "Dimethylsilene: CH₃SiCH₃". Journal of the American Chemical Society. 86 (7): 1442–1443. doi:10.1021/ja01061a040.

Category:

Analytical chemistry