Hydroxyl Number in Polyols and Oxo Alcohols in Accordance with ASTM E1899

It is known that primary and secondary hydroxyl groups form acidic carbamates when reacted with an excess of p-toluenesulfonyl isocyanate (TSI). This product is titrated using tetra-n-butylammonium hydroxide solution (TBAOH) which is strongly basic, under non-aqueous conditions using the Solvotrode.

Sample

Polyol

Oxo alcohol

Sample Preparation

The sample is well homogenized.

Configuration

Solutions

Analysis

The manually homogenized sample is weighed precisely directly into a 120-mL PP beaker, and a stirring bar is placed inside. A Dis-Cover lid is added to seal the beaker and it is put on the sample changer.  After the addition of 10 mL acetonitrile it is stirred for 30 seconds to completely dissolve the sample, following which 10 mL TSI is added. The beaker is resealed, and a slow stirring is performed for 5 minutes.

At this point 0.5 mL deionized water is added and the solution is stirred again for 60 seconds. Now 40 mL acetonitrile is added. The sample is now titrated with c(TBAOH) = 0.1 mol/L in 2-propanol/methanol until the second equivalence point is passed.

At the end of the titration the Solvotrode easyClean is placed in a PP beaker of acetonitrile, in which it remains immersed until it is time for the next measurement. The membrane is immersed in deionized water.

After a series of measurements is completed the machine automatically immerses the electrode in a beaker containing acetonitrile until it is required for the next analysis.

Parameters

Results

This information has been sourced, reviewed and adapted from materials provided by Metrohm AG.

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