Neßler reaction

Reaction of Neßler's reagent with ammonia solution: Precipitation of the iodide of Millon's base

The Neßler reaction was first described by Julius Neßler (1827–1905) in his inaugural dissertation published in 1856 on the behavior of mercury iodine and mercury compounds in general to ammonia and a new reaction to ammonia .

The Neßler reagent potassium tetraiodomercurate (II) : K ₂ [HgI ₄ ], which forms the red-brown color complex [Hg ₂ N] I, the iodide of the cation of Millon's base , with ammonia is used in this reaction .

${\displaystyle \mathrm {NH_{4}^{+}+2\ K_{2}[HgI_{4}]+3\ NaOH+OH^{-}\longrightarrow {[Hg_{2}N]I\downarrow }+4\ KI+3\ NaI+4\ H_{2}O} }$

Ammonium ions, potassium tetraiodomercurate (II), sodium hydroxide solution and hydroxide ions react to form the iodide salt of Millon's base, which flocculates in aqueous solution, potassium iodide , sodium iodide and water.

The detection is very sensitive to ammonium / ammonia and is used in water analysis for its photometric quantitative determination. The disadvantage is the cross-sensitivity to simple amines , which occur in abundance in strongly revitalized water (e.g. fish ponds, waste water). The Neßler reaction is also used to measure ammonia immission using the Nessler method .

In addition, attempts are made to avoid laboratory waste that contains mercury and is therefore toxic. Therefore, according to DIN 38 406 E5, today the Berthelot reaction is used almost exclusively for the determination of ammonium.

Web links

Wikibooks: Practical course in inorganic chemistry / ammonium  - learning and teaching materials

Individual evidence

1. ↑ Julius Neßler: About the behavior of iodine mercury and mercury compounds in general to ammonia and about a new reaction to ammonia . University book printer of Hermann Meinhard Poppen , Freiburg i. Br. 1856 ( full view in the Google book search).
2. ^ Siegfried Ebel and Hermann J. Roth (eds.): Lexicon of Pharmacy . 1st edition. Georg Thieme Verlag , Stuttgart 1987, ISBN 3-13-672201-9 , p. 461 .
3. ^ Bruno Lange, Zdeněk J. Vejdělek: Photometric analysis . 1st edition. Verlag Chemie , Weinheim / Deerfield Beach (Florida) / Basel 1980, ISBN 3-527-25853-1 , p. 327 .
4. ↑ VDI 2461 sheet 2: 1976-05 measurement of gaseous immissions; Measuring ammonia concentration; NESSLER method. VDI-Verlag, Düsseldorf, p. 2.