The Gattermann reaction, (also known as the Gattermann salicylaldehyde synthesis) is a chemical reaction in which aromatic compounds are formylated by hydrogen cyanide in the presence of a Friedel–Crafts catalyst (e.g. AlCl3). It is named for the German chemist Ludwig Gattermann and is similar to the Friedel-Crafts reaction.
The reaction can be simplified by replacing the HCN/AlCl3 combination with zinc cyanide. Although it is also highly toxic, Zn(CN)2 is a solid, making it safer to work with than gaseous HCN; additionally, because the reaction uses HCl, Zn(CN)2 also supplies the reaction with ZnCl2 in-situ, where it acts as a Lewis acid catalyst. Examples of Zn(CN)2 being used in this way include the synthesis of 2-Hydroxy-1-nafthaldehyde and Mesitaldehyde.
The Gattermann–Koch reaction, named after the German chemists Ludwig Gattermann and Julius Arnold Koch, refers to a Friedel–Crafts acylation reaction in which carbon monoxide, hydrochloric acid, and a Friedel–Crafts catalyst (e.g. AlCl3) are used to produce aromatic aldehydes from various aromatic compounds, including derivatives of benzene and naphthalene:
The applicability of the reaction includes many substituted aromatic derivatives, for example the conversion of toluene (The reaction above displays benzene to p-tolualdehyde) to p-tolualdehyde. However, unlike the Gattermann reaction with HCN, this reaction is not applicable to phenol and phenol ether substrates. Additionally, when Zinc chloride is used as the catalyst, the presence of traces of copper(I) chloride co-catalyst is often necessary.
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