Separation of Amines by Hoffmann’s Method

Table of Contents

The separation of amines by Hoffmann’s method can be carried out via the treatment of the mixture of amines with diethyl oxalate. The whole separation can be carried out by the following diagram:

separation of primary. secondary, and tertiary amine by Hoffmann's method

Separation of Primary, secondary, and tertiary amines by Hoffmann’s method

Diethyl oxalate reacts with the mixture of amines as:

1o amine forms crystalline solid, dialkyloxamide

separation of primary amines

2o amine forms an oily liquid, dialkyloxamic ester

separation of secondary amines

No reaction with 3o amine as it lacks replaceable hydrogen atom

Filtration of mixture

Filtration is carried out on a reaction mixture containing dialkyl oxamide, dialkyloxamic ester, tertiary amine, and ethyl alcohol to obtain solid dialkyl oxamide, which is then heated with aqueous KOH to liberate primary (1o) amine.

separation of amines

The remaining mixture containing 3o amine, dialkyloxamic ester, and ethanol is now fractionally distilled. Because tertiary amine is more volatile than alcohol, it is distilled first. Finally, to recover secondary 2o amine, the dialkyloxamic ester that remains as the residue is treated with aqueous KOH. These are distilled to produce two fractions of amine and alcohol.

separation of amines by Hoffmann's method

In this way, primary, secondary, and tertiary amines can be separated via Hoffmann’s method.

Separation of 1o, 2o, and 3o amines Video

References

  • Morrison, R. T., & Boyd, R. N., Organic chemistry, Allyn and Bacon, Inc. 1987.
  • Ghosh, S.K., Advanced General Organic Chemistry, Second Edition, New Central Book Agency Pvt. Ltd., Kolkatta, 2007.
  • Bahl, B.S., A., Advanced Organic Chemistry, S. Chand and company Ltd, New Delhi, 1992.
  • Finar, I. L., Organic Chemistry, Vol. I and Vol. II, Prentice Hall, London, 1995.

Separation of amines by Hoffmann's method

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