Zeisel determination

What is Zeisel determination?

The Zeisel reaction, discovered by Zeisel in 1885, is a quantitative method for determining the number of alkyl groups attached to the oxygen atom of an ether or ester. This is accomplished by heating a mixture of the substrate with hydriodic acid and trapping the evolving alkyl iodide with silver nitrate.

The Zeisel determination is also referred to as the Zeisel method, Zeisel reaction, Zeisel alkoxyl determination, Zeisel methoxy determination, Zeisel methoxyl method, or Zeisel alkoxyl reaction.

 

Zeisel determination - general reaction scheme
Zeisel determination
Zeisel determination - general reaction scheme
Zeisel determination

The determined number of alkoxyl groups, especially methoxyl, may vary and may be higher than the actual number of alkoxyl groups depending on factors such as the concentration of hydriodic acid, reaction time, solvent, and temperature.

In certain instances, the determined number of alkoxyl groups may be lower than the theoretical value, such as with O-methyl or O-ethyl substituted celluloses, due to the formation of ethylene and propylene. Conversely, the use of xylene during the Zeisel determination of cellulose ether may result in a slightly higher substitution number. The Zeisel determination may also be employed for the qualitative detection of existing alkoxyl groups by observing the appearance of red or scarlet red HgI2 on a piece of test paper saturated with mercury nitrate Hg(NO3)2 hung above a test tube containing the sample.

References

Zeisel, S., Monatsh. Chem., 1885, 6, 989

 

Shares