In
chemistry, a chemical trap is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one ele ...
that is used to detect unstable compounds. 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.
:
Diphosphorus
Diphosphorus is an old target of chemists since it is the heavy analogue of N
2. 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:
:
Silylene
Another classic but elusive family of targets are
silylene
Silylene is a chemical compound with the formula SiH2. It is the silicon analog of methylene, the simplest carbene. Silylene is a stable molecule as a gas but rapidly reacts in a bimolecular manner when condensed. Unlike carbenes, which can exis ...
s,
analogues of carbenes. It was proposed that dechlorination of
dimethyldichlorosilane generates dimethylsilylene:
:SiCl
2(CH
3)
2 + 2 K → Si(CH
3)
2 + 2 KCl
This inference is supported by conducting the dechlorination in the presence of
trimethylsilane, the trapped product being pentamethyldisilane:
:Si(CH
3)
2 + HSi(CH
3)
3 → (CH
3)
2Si(H)-Si(CH
3)
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
concentration
In chemistry, concentration is the abundance of a constituent divided by the total volume of a mixture. Several types of mathematical description can be distinguished: '' mass concentration'', '' molar concentration'', '' number concentration'' ...
s 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
{{Reflist
Analytical chemistry