The Beckmann rearrangement involves the use of a strong acid to rearrange an oxime (aldoxime or ketoxime) to an amide. First the oxime hydroxyl group receives a proton from the acid, forming a leaving group. A [1,2]-shift of the R group, which is anti to the leaving group, then promotes its departure, resulting in a nitrilium ion, which reacts with water. Deprotonation of oxygen, protonation of the nitrogen and tautomerization produces the final amide product.
- Reagents: Strong Brӧnsted or Lewis Acid (H2SO4)
- Reactant: Oxime
- Product: N-Substituted Amide
- Type of Reaction: Rearrangement
Lab Tips
- Forcing conditions (high temperatures (> 130°C) and large amounts of a strong Brӧnsted/Lewis acid) are usually required. Sensitive substrates should be avoided. [1]
- Check that the oxime does not isomerize under the reaction conditions, otherwise a mixture of two possible amides is obtained. Reagents p-toluenesulfonyl chloride and phosphorus pentachloride have been found least likely to cause competing isomerization. [2]
- Since the hydrogen atom never migrates, N-unsubstituted amides cannot be made. [1]
2. Carey, F.A., Sundberg, R.J. (2001). Advanced Organic Chemistry Part B: Reactions and Synthesis (4th ed.). New York: Kluwer Academic/Plenum Publishers.
Mechanism
Top Citations
Original Paper
Related Reactions
- Curtius Rearrangement
- Schmidt Reaction
Related Compounds
- Oximes
- Acids
Reference
Jiang, Yuejing, Juan Cheng, Chengyu Yang, Yongzhou Hu, Jia Li, Yifeng Han, Yi Zang, and Xin Li. "An ultrasensitive fluorogenic probe for revealing the role of glutathione in chemotherapy resistance." Chemical science 8, no. 12 (2017): 8012-8018.
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