Beilstein trial

from Wikipedia, the free encyclopedia

The Beilstein test , named after Friedrich Konrad Beilstein (also known by the Russian name Fedor Fedorovich Beilstein ) is a method of analytical chemistry to organic compounds on halogens to test. With this sensitive qualitative detection, low-molecular and high-molecular organic compounds can be examined, including plastics or organic pigments. The detectable polymers include polyvinyl chloride, polyvinylidene chloride, chloroprene and epichlorohydrin rubber, polychlorotrifluoroethylene, ethylene-chlorotrifluoro copolymers, chlorinated polyethylene, chlorosulfonated polyethylene, chlorinated polypropylene and various copolymers containing polyvinyl chloride.

execution

First, a sheet of copper or a copper eyelet is annealed until no blue or green color of the flame can be seen. This is absolutely necessary because even traces of halogens can cause a false-positive result. For example, ammonium chloride can easily form from hydrochloric acid and ammonia , which - if deposited unnoticed on copper sheet or wire - also causes a blue-green flame color .

Next, the sample is applied to the annealed - still hot - copper sheet or the copper eyelet and held in the non-luminous area of ​​a gas burner flame . If the flame turns green to blue-green in the process, it is very likely that the sample contains a halogen.

Explanation

The organic halogen compounds decompose during pyrolysis and form z. B. hydrogen chloride or hydrogen bromide . These form volatile copper-halogen compounds with copper, which discolor the flame.

Security concerns

Since dioxins can form in this reaction, even if only in very small quantities, the experiment must be carried out under a fume cupboard. For this reason, this experiment may no longer be carried out at some schools in North Rhine-Westphalia and Lower Saxony .

Individual evidence

  1. ^ Entry on Beilstein test. In: Römpp Online . Georg Thieme Verlag, accessed on June 16, 2014.
  2. ^ MD Lechner, K. Gehrke and EH Nordmeier: Makromolekulare Chemie , 4th edition, Birkhäuser Verlag, 2010, p. 473, ISBN 978-3-7643-8890-4 .
  3. ↑ Detection of different ions
  4. ↑ Hans Beyer and Wolfgang Walter : Organische Chemie , S. Hirzel Verlag, Stuttgart, 22nd edition, 1991, p. 12, ISBN 3-7776-0485-2 .