ASTM E1899-23

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
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Designation: E1899 − 16 E1899 − 23
Standard Test Method for
Hydroxyl Groups Using Reaction with p-Toluenesulfonyl
Isocyanate (TSI) and Potentiometric Titration with
Tetrabutylammonium Hydroxide
This standard is issued under the fixed designation E1899; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This test method covers the determination of hydroxyl groups attached to primary and secondary carbon atoms in aliphatic
and cyclic compounds and phenols. phenols from 0.5 to 367 hydroxyl number. It is not suitable for determination of hydroxyl
groups attached to tertiary carbon atoms. This test method is applicable to polyacetals, temperature sensitive materials, high solids
polymer polyols, and rigid polyols. Other available test methods listed in Note 1 are not suitable for many of the sample types listed
above.
1.1.1 This test method is currently recommended for neutral refined products. Successful application has been made, however, to
some in-process samples that contain an excess of acidic species. Proper validation must be performed, of course, to show that the
acidic species either does not interfere, or that the acidic species interference has been obviated.
NOTE 1—Other methods for determination of hydroxyl groups are given in Test Methods D817, D871, D1957, D2195, D4252, D4273, D4274, E222,
E326, and E335.
1.2 The Limit of Detection (LOD) is 0.18 units and the Limit of Quantitation (LOQ) is 0.59 units. Unit = hydroxyl number (OH#).
NOTE 2—LOD and LOQ were calculated using Standard deviations from 14.1.2.1.
1.3 Review the current appropriate Safety Data Sheets (SDS) for detailed information concerning toxicity, first aid procedures, and
safety precautions.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 The following applies for the purposes of determining the conformance of the test results using this test method to applicable
specifications. Results shall be rounded off in accordance with the rounding-off method of Practice E29.
1.6 This standard does not purport to address all of the safety concerns, if any, associated, with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use. For specific hazards see Section 9.
This test method is under the jurisdiction of ASTM Committee D16 on Aromatic, Industrial, Specialty and Related Chemicals and is the direct responsibility of
Subcommittee D16.12 on Caustics and Peroxides.
Current edition approved April 1, 2016April 1, 2023. Published May 2016June 2023. Originally approved in 1997. Last previous edition approved in 20082016 as
E1899 – 08.E1899 – 16. DOI: 10.1520/E1899-16.10.1520/E1899-23.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
E1899 − 23
1.7 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D817 Test Methods of Testing Cellulose Acetate Propionate and Cellulose Acetate Butyrate
D871 Test Methods of Testing Cellulose Acetate
D1193 Specification for Reagent Water
D1957 Test Method for Hydroxyl Value of Fatty Oils and Acids (Withdrawn 2007)
D2195 Test Methods for Pentaerythritol (Withdrawn 2011)
D4252 Test Methods for Chemical Analysis of Alcohol Ethoxylates and Alkylphenol Ethoxylates
D4273 Test Method for Polyurethane Raw Materials: Determination of Primary Hydroxyl Content of Polyether Polyols
D4274 Test Methods for Testing Polyurethane Raw Materials: Determination of Hydroxyl Numbers of Polyols
D6809 Guide for Quality Control and Quality Assurance Procedures for Aromatic Hydrocarbons and Related Materials
E29 Practice for Using Significant Digits in Test Data to Determine Conformance with Specifications
E180 Practice for Determining the Precision of ASTM Methods for Analysis and Testing of Industrial and Specialty Chemicals
(Withdrawn 2009)
E222 Test Methods for Hydroxyl Groups Using Acetic Anhydride Acetylation
E300 Practice for Sampling Industrial Chemicals
E326 Test Method for Hydroxyl Groups by Phthalic Anhydride Esterification (Withdrawn 2001)
E335 Test Method for Hydroxyl Groups by Pyromellitic Dianhydride Esterification (Withdrawn 2002)
3. Terminology
3.1 Definitions:
3.1.1 hydroxyl number (OH#)—the milligrams of potassium hydroxide equivalent to the hydroxyl content of 1 g of sample.
3.1.1.1 Discussion—
In the case of a pure compound, the hydroxyl number is inversely proportional to the hydroxyl equivalent weight and the molecular
weight:
equivalent weight ~g/equivalent!5 (1)
OH#
and:
56100 ×number of OH groups per molecule
molecular weight ~g/mol!5
OH#
4. Summary of Test Method
4.1 According to a reaction given in Manser et al. (see Fig. 1) the hydroxyl group is reacted with excess p-toluenesulfonylp-
toluenesulfonyl isocyanate (TSI), to form an acidic carbamate. Water is added to convert unreacted isocyanate to sulfonamide,
followed by direct potentiometric titration of the acidic carbamate with tetrabutylammonium hydroxide (Bu NOH) in nonaqueous
medium.
FIG. 1 Hydroxyl Group Reaction
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
The last approved version of this historical standard is referenced on www.astm.org.
Manser, G.E., Fletcher, R.W., and Knight, M.R., High Energy Binders Final Report, Defense Technical Information Center, Ft. Belvoir, VA, Contract No.
N00014-82-C-0800, p. 1-3 of Appendix A, August, 1985.
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5. Significance and Use
5.1 Hydroxyl is an important functional group and knowledge of its content is required in many intermediate and end use
applications. This test method is for the determination of primary and secondary hydroxyl groups and can be used for the assay
of compounds containing them.
5.2 This test method has the following advantages over other hydroxyl number methods: It is rapid (10 min), pyridine-free,
ambient temperature, small sample size, applicable to extremely low hydroxyl numbers (<1), and is amenable to automation.
6. Interferences
6.1 Primary and secondary amines derivatize quantitatively with the TSI reagent and contribute to the hydroxyl value.
6.2 High levels of water in the sample can interfere by consuming reagent. The amount of excess TSI reagent prescribed by this
test method is quite large, however, so that rather high water levels can be accommodated. Optimum titration curves are obtained,
however, when the water is <1 %.
6.3 Any acidic species with a pKa value close to that of the acidic carbamate (formed between TSI and the hydroxyl compound),
will contribute to the hydroxyl number and cause high values. Excess base in a sample may potentially react with the acidic
carbamate to cause low hydroxyl number values. If this test method is to be used for samples other than neutral refined products,
the analyst must first validate this test method on a case by case case-by-case basis. For example, an in-process sample containing
excess acid or base may be analyzed using Test Method B of Test Methods E222, to establish concordance of results with the
current TSI test method for that particular matrix. The identities of acidic or basic species contained in in-process samples are
frequently known, so that known addition of these moieties to the sample can establish whether or not there is interference
exhibited. For example, methane sulfonic acid titrates sufficiently before the acidic carbamate formed between TSI and ROH, and
therefore does not interfere. At the other extreme, methacrylic acid titrates well after the acidic carbamate of interest and thus
causes no interference.
7. Apparatus
7.1 Potentiometric Autotitrator, equipped with a 10- or 20-mL10 mL or 20 mL delivery buret. Ideally, the autotitrator should be
capable of generating the potentiometric titration curve in the normal and derivative modes with automatic marking of end points.
However, an older model titrator without automatic marking of end points was shown to give excellent hydroxyl number results
obtained by manually evaluating the mid-point of the normal “S” shaped curve.
7.2 Glass Combination pH Electrode, consisting of a glass sensing membrane and Ag/AgCl internal reference element.
7.3 Automatic Pipetter, 500 μL.
7.4 Glass or Plastic Beakers, 100 mL.
7.5 Magnetic Stirrer and Stirring Bars,Bars (3-cm(3 cm length is optimum).
7.6 Glass Pipet, 10 and 20 mL, 10 mL and 20 mL, Class A.
7.7 Volumetric Flasks, 500 and 1000 mL.500 mL and 1000 mL.
7.8 Analytical Balance, accurate to 0.1 mg.
7.9 Standard Bulb Transfer Pipets, plastic, approximately 15-cm15 cm length.
7.10 Graduated Cylinder, 10 mL, or Bottle Type Volumetric Dispenser.
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8. Reagents
8.1 Purity of Reagents—Unless otherwise indicated, it is intended that all reagents shall conform to the specifications of the
Committee on Analytical Reagents of the American Chemical Society, where such specifications are available. Other grades may
be used, provided it is first ascertained that the reagent is of sufficiently high purity to permit its use without lessening the accuracy
of the determination.
8.2 Purity of Water—Unless otherwise indicated, references to water shall be understood to mean Type III or Type IIIII reagent
water as defined in Specification D1193.
8.3 Acetonitrile, HPLC Grade must be used as it is sufficiently low in moisture so that molecular sieves are not needed to dry this
solvent.
8.4 2-Propanol, HPLC Grade.
8.5 p-Toluenesulfonyl Isocyanate (TSI), 96 %—Maintain a nitrogen pad above this reagent after opening bottle.
8.6 TSI Reagent—Pipet 20 mL of TSI into a dry 500-mL500 mL volumetric flask half filled with acetonitrile. Dilute to the mark
with acetonitrile and mix well. This reagent should be prepared fresh monthly.
8.7 Potassium Hydrogen Phthalate, Primary Standard.
8.8 Tetrabutylammonium Hydroxide (Bu NOH), 1M Solution in Methanol, 100 mL.
8.9 Tetrabutylammonium Hydroxide (Titrant), 0.1 meq/mL—Prepare by transferring the entire 100 mL of 1M Bu NOH in
methanol (see 8.8) into a 1-L1 L volumetric flask that is half filled with 2-propanol. Rinse the emptied bottle that contained the
solution in 8.8 and transfer the rinsings to the contents of the 1-L1 L volumetric flask. Swirl contents and dilute to the mark with
2-propanol. Stopper the flask and mix well. Finally, transfer the flask contents to the buret reservoir of a potentiometric autotitrator
and standardize the titrate versus dried (2 h, 120°C) (2 h, 120 °C) potassium hydrogen phthalate (KHP) as follows: dissolve
approximately 0.18 g of KHP, weighed to 0.1 mg, in about 60 mL of water contained in a 100-mL100 mL beaker. Stir several
minutes to ensure complete dissolution of the KHP. Perform a potentiometric titration directly on the KHP solution using the 0.1
meq/mL Bu NOH titrant. Perform three to five standardization titrations to obtain a reliable average value for the 0.1 meq/mL
Bu NOH concentration.
KHP, g
N 5 (2)
0.20423 ×Bu NOH, mL
where:
N = concentration of the 0.1 meq/mL Bu NOH expressed to four decimal places, and
Bu NOH, mL = mL of this titrant to reach a potentiometric end point in the reaction with KHP.
8.10 Methanol.
8.11 Acetone.
9. Hazards
9.1 p-Toluenesulfonyl Isocyanate (TSI) is harmful by inhalation, in contact with skin, and if swallowed. It may cause sensitization
by inhalation and skin contact. It reacts violently with water. It causes severe irritation. It is a Lachrymator. In case of contact with
eyes, rinse immediately with plenty of water and seek medical advice. Never add water to this product.
Reagent Chemicals, American Chemical Society Specifications,ACS Reagent Chemicals, Specifications and Procedures for Reagents and Standard-Grade Reference
Materials, American Chemical Society, Washington, DC. For Suggestionssuggestions on the testing of reagents not listed by the American Chemical Society, see Analar
Standards for Laboratory Chemicals, BDH Ltd., Poole, Dorset, U.K., and the United States Pharmacopeia and National Formulary, U.S. Pharmacopeial Convention, Inc.
(USP),(USPC), Rockville, MD.
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9.2 Wear suitable protective clothing, gloves and eye/face protection when handling p-Toluenesulfonyl Isocyanate. Use only in a
chemical fume hood. Do not breathe vapor.
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