16.4 What does the Dean and Stark distillation measure?
Description
This article is from the Chemistry FAQ, by Bruce Hamilton B.Hamilton@irl.cri.nz with numerous contributions by others.
16.4 What does the Dean and Stark distillation measure?
The Dean and Stark procedure can be used to measure the water content of
a diverse range of samples, and has been extensively used in industrial
laboratories to measure water in petroleum oils. The technique can measure
% levels of water, but is not as accurate as the Karl Fischer titration,
and is not applicable to samples where the water is not liberated by the
solvent. The sample is mixed with a solvent ( usually a toluene/xylene mix )
and refluxed under a condenser using a special receiver. There are two common
designs of receivers, one for solvents that are heavier than water, and the
more common one for solvents that are lighter than water - illustrations will
be shown in most laboratory glassware supplier catalogues.
The water and solvent are refluxed, and as they condense the two phases
separate as they run into the receiver. The water remains in the receiver
while the solvent returns to the flask. The Dean and Stark technique is also
useful for removing unwanted water from reactions, eg the synthesis of
dibutyl ether by the elimination of water from two molecules of n-butanol
using acidic conditions. An example of this is provided in the preparation
of dibutyl ether described in Vogel, and detailed procedures for the
determination of water using Dean and Stark are provided in ASTM and AOAC.
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