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Application BulOf interest to: General analytical laboratories; organic chemistry; plastics

Automated determination of the hydroxyl(HN) according to ASTM E 1899-08 and D

Summary

The hydroxyl group is an important functional group and knowledge of the hydrohydroxyl group content, is required for the production of intermediate and finishepolyols, resins, paint resins and lubricants (petroleum industry). In the method pand secondary hydroxyl groups are determined. The hydroxyl number (HN) is dof potassium hydroxide in milligrams that is equivalent to the hydroxyl amount ople.The most frequently described method for determining the hydroxyl number is thanhydride in pyridine with subsequent titration of the free acetic acid:

H3C-CO-O-CO-CH3+ R-OHR-O-CO-CH3+ CH3COO

However, this method has the following disadvantages:

The sample must be boiled under reflux for 1 hour (long reaction time acated handling)

The method cannot be automated

Small hydroxyl numbers cannot be determined exactly

Toxic pyridine, which is unpleasant to use, is required

Both standards, ASTM E 1899 and DIN 53240-2, describe an alternative methosample preparation and can therefore be fully automated.

The method described in ASTM E 1899 is based on the reaction of the primary droxyl groups with excess p-toluenesulfonyl isocyanate (TSI) with the formationbamate. This latter can then be titrated with the strongly basic tetra-n-butylammsolution (TBAOH) under non-aqueous conditions.

The method proposed in DIN 53240-2 is based on the catalytic acetylation of thhydrolysis of the intermediate product, the remaining acetic acid is titrated with aunder non-aqueous conditions.

This paper demonstrates and discusses a simple analysis method for determini

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Application Bulletin

Potentiometric determination of the hydroxyl number as per ASTM

Instruments and accessories

Both methods require the following equipment:

Pos. Order No. Description

1 2.814.0130 814 USB Sample Processor (2T / 0P)

2 6.1458.040 Titration head

3 6.9914.158 Titration head with Dis-Cover

4 6.2041.470 Rack 22 x 120 mL PP beakers

5 6.1459.300 120 mL PP Beakers (100 pieces)

6 6.9920.164 Dis-Cover Lids for beakers (6.1459.300) 7 2.800.0010 800 Dosino

8 6.1805.120 FEP tubing /M 6/100 cm

9 2.741.0010 741 Magnetic stirrer for sample changers

10 6.1903.030 stirring bars/25 mm

11 6.0229.100 Solvotrode (LiCl sat. in EtOH)

12 6.2104.030 Electrode Cable 2 m/F

13 2.809.0010 809 Titrando

14 6.2151.000 Controller cable USB

15 6.6056.122 tiamo 1.3 full

To comply with the requirements of the ASTM standard, the following additionalrequired:

1 6.3032.250 50 mL Dosing Unit for acetonitrile

2 6.3032.220 20 mL Dosing Unit for TSI reagent and titrant *

3 6.3032.120 2 mL Dosing Unit for deionized water

* For the results presented here two 10-mL dosing units were used; it may be nesizes of the dosing units.

To comply with the requirements of the DIN standard, the following additional doquired:

1 6.3032.250 50 mL Dosing Unit for catalyst solution and titrant

2 6.3032.210 10 mL Dosing Unit for acetylation mixture and deionize

Reagents

This Bulletin contains no information about handling the reagents mentioned; nosafety measures that have to be observed. Please obtain the necessary informapriate regulations and safety data sheets.

Reagents for ASTM method

Acetonitrile, purity > 99.5%

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Reagents for the DIN method

N-Methylpyrrolidone (1-methyl-2-pyrrolidone,NMP)Acetic anhydride4-N-Dimethylaminopyridine1-Octanol as reference material, hydroxyl number (HN) = 430.08 mg KOH/gEthanol (electrode rinsing solution), purity > 99.8%Water, deionized (electrode rinsing solution)

Titrant:Potassium hydroxide solution, 0.5 mol/L in methanol (ready to use)

Acetylation mixture:Acetic anhydride solution, 10% in NMP (store in amber g

Catalyst solution:4-N-Dimethylaminopyridine, 1% in NMP

Calculation

ASTM

HN ASTM= (EP2 - EP1) x CONC x TITER x 56.106 / Sample size

HN: Hydroxyl number [mg KOH per g sample]EP2: Titrant consumption up to second potentiometric endpoint [mL]EP1: Titrant consumption up to first potentiometric endpoint [mL]CONC Concentration of titrant [mol/L]56.106 Molecular weight of KOH [g/mol]Titer Titer of titrant used [ - ]

Sample size: Weight [g]

DIN

HN DIN= [(Blank - EP1) x CONC x TITER x 56.106 / Sample size] + TAN

HN: Hydroxyl number [mg KOH per g sample]EP1: Titrant consumption up to first potentiometric endpoint [mL]

Blank* Blank value of solvent and reagents [mL]CONC Concentration of titrant [mol/L]56.106 Molecular weight of KOH [g/mol]Titer: Titer of titrant used [ - ]Sample size: Weight [g]TAN: Previously determined acid number (TAN) of sample [mg KOH/

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Calculating the sample weight for 1-octanol

ASTM DIN

Equation E= 40/HNe E= 300/HNe

1-Octanol ASTM DIN

Sampleweight

40/430.08 = 0.093 g 300/430.08 = 0.698 g

The following diagram is intended to clarify the automated analytical steps of thmethods:

ASTM DIN

Sample & stirring bar

Add 30 mL catalystsolution and 10 mLacetylation mixture

Stir sealed for 15 min

Add 3 mL deion. water


Dynamic endpoint titration(DET U) with c(KOH)=0.5

mol/L in methanol

Sample & magnetic stirrer

Add 10 mL acetonitrile

Stir sealed for 30 s

Add 10 mL TSI


Add 0.5 mL deion. water

Stir sealed for 60 s

Add 40 mL acetonitrile

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Detailed description of the working steps for the ASTM method

The manually homogenized sample is weighed out into a 120-mL PP beaker, a and the beaker is sealed with a Dis-Cover lid. The beaker is placed on the sampmethod has been started, 10 mL acetonitrile is added automatically. After a stirrand dissolution of the sample, 10 mL TSI is added. Then the beaker is resealed5 more minutes.The chemical reaction is interrupted by opening the lid and adding 0.5 mL deionthen closed again and the resealed beaker is stirred for 60 more seconds. The sreopened and 40 mL acetonitrile is added. After resealing the beaker, the sampmoderate speed and the titration with 0.1 mol/L TBAOH in 2-propanol/ methanoThe two equivalence points are determined using the conditioned Solvotrode. Tparticular care.At the end of the titration the Solvotrode is first immersed in a PP beaker contairemains until the next measurement with only the membrane immersed in deionof a series of measurements the electrode is automatically immersed in a beakeuntil the start of the next analysis. When not in use for longer periods, the Solvosat. in EtOH.

Modification in comparison with the ASTM standard

For automation, the acetonitrile addition at the end of the analysis is increased fin order to ensure that the Solvotrode is immersed to a sufficient depth.

Detailed description of the working steps for the DIN method

The calculated amount of sample is weighed out directly into a 120-mL PP beakDis-Cover lid are added and the beaker is placed on the sample rack. The lid isby using a magnet, 30 mL catalyst solution and 10 mL acetylation mixture are aresealed. The sealed sample is stirred for at least 15 minutes (the reaction timeof sample). The lid is then again raised automatically and the reaction is interrupmL deionized water. The beaker is resealed and stirred for a further 12 minutesautomatically cleaned and conditioned by immersing it in ethanol and then in detitration for determining the hydroxyl number is carried out using 0.5 mol/L KOHend of the titration the electrode is automatically cleaned in ethanol and conditiowater.

Examples of measurements

The following customer samples were analyzed for the development of the autothe hydroxyl number according to ASTM/DIN methods:

Sample name Sample composition Gui

Oxooil 9N Hydroformylation product ofC8-alkenes

120..(ideal valu

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Statistical evaluation of the results for the ASTM method

Sample: Oxooil 13 expected value: 120...130 mg KOH/g and titrati

Sample Oxooil 13

Weight [g] HN [mg KOH/g]

0.3217 128

0.2961 132

0.2958 134

0.3077 127

Mean 130.0

RSD 2.54%

Sample:Lupranol 2090 expected value: 30 mg KOH/g and titration curv

Sample Lupranol 2090


1.2742 29.8

1.3323 29.9

1.2533 29.9

1.3030 29.7

Mean 29.6

RSD 1.39%

When the sample weights are taken into account, a constant consumption of 0.7

tained for the ASTM method.

Statistical evaluation of the results for theDIN method

Sample:Oxooil 9N expected value: ~100 mg KOH/g and titration c

Sample Oxooil 9N


1.3057 1021.2262 104

1.1109 103

Mean 103

RSD 0.97%

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General remarks

The use of a fully automatic system for this type of analysis is highly recommenway contact with toxic solvents is minimized. Electrode treatment is very importtitrations. An automated system ensures that electrode handling is always carriesame way.

Summary

The titration system presented here is able to carry out a fully automatic determ

number (HN) according to ASTM or DIN. The method permits the analysis of powithout boiling under reflux and is therefore an enormous step forward for laboranalyze a large number of such samples every day. Above all, the ASTM methoits simple handling without blank value determination and much, much shorter r

Expression of thanks

We kindly thank BASF in Ludwigshafen for providing the samples.

Literature

ASTM E 1899-08, Standard Test Method for Hydroxyl Groups Using Reaction wIsocyanate (TSI) and Potentiometric Titration with Tetrabutylammonium Hydrox

DIN 53240-2, Bestimmung der Hydroxylzahl Teil 2: Verfahren mit Katalysator

AB-206, Titer determination in potentiometry (http://products.metrohm.com, sea

AB-080, Determination of the acid and base numbers in petroleum products, T

electrode(s), control of the electrodes slope (http://products.metrohm.com, sear

81091586, 6.0279.300 LL Solvotrode Combined pH electrode for non-aqueous (http://products.metrohm.com, search for 81091586)

Tips for handling the Solvotrode, Metrohm Information 1/2007, Vol. 36 (www.me

AB-200, Determination of the acid number, hydroxyl number and isocyanates infabrication of plastics by automatic potentiometric titration (http://products.metro

AB-200)

Annex

Method and titration parameters, ASTM/DIN

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