Schweizer's reagent

Ball-and-stick model of the tetraamminediaquacopper (II) cation
Ball-and-stick model of the tetraamminediaquacopper (II) cation, [Cu(NH3)4(H2O)2]2+

Schweizer's reagent is the chemical complex tetraamminediaquacopper dihydroxide, [Cu(NH3)4(H2O)2](OH)2. It is prepared by precipitating copper(II) hydroxide from an aqueous solution of copper sulphate using sodium hydroxide or ammonia, then dissolving the precipitate in a solution of ammonia.

When the entire amount of copper is precipitated as hydroxide, it is advisable to filter it and dispose of the filtrate and rinse the precipitate from sulfate and other excess ions.

Water solution of tetraamminecopper(II) hydroxide.

It forms a deep azure solution. If the solution is evaporated, it leaves light blue precipitate of copper hydroxide. This is because the formation of the tetraminocupric complex is reversible and ammonia evaporates together with the water. If the evaporation is conducted under stream of ammonia, then deep blue needle-like crystals are formed. These crystals should be kept in isolation or in ammonia atmosphere. Besides, when the concentration of ammonia solutions is very high, divalent copper ions in presence of dioxygen, catalyze ammonia oxidation, giving rise to copper ammine nitrites: Cu(NO2)2(NH3)n;[1][2]

Schweizer's reagent finds use in production of cellulose products such as rayon and cellophane, because wood pulp, cotton fiber, and other natural cellulose sources are soluble in the solution. Dissolved cellulose precipitates when the solution is acidified. These properties of Schweizer's reagent were discovered by the Swiss chemist Matthias Eduard Schweizer (1818–1860),[3] after whom the reagent is named.

See also

Footnotes

  1. ↑ Cudennec, Y.; et al. (1995). "Étude cinétique de l'oxydation de l'ammoniac en présence d'ions cuivriques" [Kinetic study of the oxidation of ammonia in the presence of cupric ions]. Comptes Rendus Acad. Sci. Paris II 320 (6): 309–316.
  2. ↑ Cudennec, Y.; et al. (1993). "Synthesis and study of Cu(NO2)2(NH3)4 and Cu(NO2)2(NH3)2". Eur. J. Solid State Inorg. Chem. 30 (1–2): 77–85.
  3. ↑ (Schweizer, 1857), p. 110: "Dieselbe besitzt nämlich in ausgezeichnetem Grade das Vermögen, bei gewöhnlicher Temperatur Pflanzenfaser aufzulösen.
     Uebergiesst man gereinigte Baumwolle mit der blauen Flüssigkeit, so nimmt erstere bald eine gallertartige schlüpfrige Beschaffenheit an, die Fasern gehen auseinander und verschwinden und nach einigem Durcharbeiten mit einem Glasstabe hat sich das Ganze in eine schleimige Flüssigkeit verwandelt. Dabei findet nicht die geringste Wärmeentwicklung statt. Hat man nicht eine hinreichende Menge der Flüssigkeit angewendet, so bleibt ein Theil der Fasern noch sichtbar; setzt man dann aber einen Ueberschuss der Lösung hinzu und schüttelt um, so erhält man eine beinahe klare blaue Lösung, die sich, nachdem sie mit Wasser verdünnt worden ist, filtriren lässt."
    (It possesses, namely, to an outstanding degree the capacity to dissolve plant fibers at ordinary temperatures.
    If one pours the blue liquid over cleaned cotton, then the former soon assumes a gelatinous, slippery texture, the fibers separate and vanish, and after some kneading with a glass rod, the whole transformed into a slimy liquid. During this, not the least evolution of heat occurred. If one didn't use a sufficient quantity of liquid, then a portion of the fibers still remained visible; however, if one then adds an excess of the solution and shakes it, then one obtains a nearly clear blue solution, which, after it's been diluted with water, can be filtered.)

References


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