Tiemann rearrangement

What is Tiemann rearrangement?

The Tiemann rearrangement is a chemical process that involves the transformation of amidoximes into monosubstituted ureas through the use of benzenesulfonyl chloride and water. To initiate the reaction, oximes are first prepared from nitriles and hydroxylamine.

Tiemann rearrangement - general reaction scheme - Tiemann amidoxime-urea rearrangement
Tiemann rearrangement

R = H, alkyl, aryl (see list of acronyms)

This reaction was discovered by Tiemann and Pinnow in 1891 and is often referred to as the Tiemann amidoxime-urea rearrangement. The Tiemann rearrangement can be induced by treating amidoximes with benzenesulfonyl chloride or acetic anhydride followed by hydrolysis.

For example, N-phenyliminoforyl-N-phenylhydroxylamine can be converted into N,N-diphenylurea in high yield using acetic anhydride.

While the rearrangement typically occurs with amidoximes, it has been observed that benzamidoxime does not undergo the Tiemann rearrangement when heated or treated with an acid or a base. However, when a suspension of benzamidoxime and Na2CO3 in CHCl3 is treated with benzenesulfonyl chloride, the corresponding urea is produced.

Amidoximes are a type of molecule that can exist in two tautomeric forms, with the amino iminoxime form being predominant. They can be prepared using a Tiemann cyanohydrin amination, which involves the reaction between nitrile and hydroxylamine. Amidoximes contain both NH2 and NOH groups, which allows them to form salts with metals and mineral acids and evolve nitrous oxide when treated with nitrous acid. The amidoxime was first elucidated and named by Tiemann in 1891.

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