Metrohm provides automatic determination of the hydroxyl number (HN) according to ASTM E 1899-08 and DIN 53240-2.
Knowledge of hydroxyl content is required in many intermediate and end-use products such as polyols, resins, lacquer raw materials and fats (petroleum industry).
The hydroxyl number is defined as the mg of KOH equivalent to the hydroxyl content of 1g of sample.
The most frequently described method for determining the hydroxyl number is the conversion with acetic anhydride in pyridine with subsequent titration of the acetic acid released: H3C-CO-O-CO-CH3 + R-OH - R-O-CO-CH3 + CH3COOH.
However, this method suffers from the following drawbacks: the sample must be boiled under reflux for one hour (long reaction time and laborious, expensive sample handling); the method cannot be automated; small hydroxyl numbers cannot be determined exactly; and pyridine has to be used.
Both standards, ASTM E 1899-08 and DIN 53240-2, offer alternative methods that do not require manual sample preparation and can be fully automated.
The method suggested in ASTM E 1899-08 is based on the reaction of the hydroxyl groups attached to primary and secondary carbon atoms with excess toluene-4-sulfonyl-isocyanate (TSI) to form an acidic species.
The latter can then be titrated in a non-aqueous medium with the strong base tetrabutylammonium hydroxide (TBAOH).
The method suggested in DIN 53240-2 is based on the catalysed acetylation of the hydroxyl group.
After hydrolysis of the intermediate, the remaining acetic acid is titrated in a non-aqueous medium with alcoholic KOH solution.
The system used to carry out the test consists of the: Metrohm 814 USB Sample Processor, 905 Titrando, 800 Dosino, Solvotrode and Tiamo software.
The Metrohm system automates these two methods for determining polyols.
This setup eliminates manual tasks and offers an immediate return on investment to laboratories that analyse a large number of samples per day.
