Zinc-copper pair

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In chemistry, an activated form of metallic zinc is referred to as the zinc-copper pair (also called activated zinc ) .

background

Highly pure zinc develops almost no hydrogen when exposed to acids at room temperature . The reason for this is that the first positively charged zinc ions (Zn → Zn 2+ + 2 e - ) formed during the dissolution prevent the approach and discharge of the also positively charged protons of the acid on the zinc (2 H + + 2 e - → H 2 ). If, on the other hand, the zinc comes into contact with a more noble metal - such as copper  , for example - electrons can flow off onto this metal and form hydrogen there with the protons of the acid. For the sake of simplicity, the more noble metal can also be added in the form of ions, for example in the form of copper sulfate . The less noble zinc then deposits the metallic copper on its surface (Cu 2+ + Zn → Cu + Zn 2+ ), from where the charges can be derived. Tiny local elements form on the surface between the copper impurities and the zinc .

This activates the zinc and can be used for reduction purposes.

An example of the use of the zinc-copper pair is the Reformatzki reaction . The Simmons-Smith reaction can also be carried out with the zinc-copper pair.

Manufacturing

The classic zinc-copper pair is obtained by treating metallic zinc with dilute hydrochloric acid and then adding a copper sulfate solution and repeatedly washing the treated zinc with water.

Individual evidence

  1. ^ AF Holleman , E. Wiberg , N. Wiberg : Textbook of Inorganic Chemistry . 101st edition. Walter de Gruyter, Berlin 1995, ISBN 3-11-012641-9 , p. 1370.
  2. ↑ E. Santaniello, A. Manzocchi, Synthesis 1977, pp. 698-9.
  3. ↑ A. Siegel, H. Keckeis, On a modified form of the Reformatski reaction. In: Monatshefte fur Chemie , 84/1953, pp 910-8.
  4. ↑ S. Lang u. a., Highly reactive zinc form, method for the production thereof, and use of the same. In: WO2007 / 020298 , February 22, 2007