Journal of the Arkansas Academy of Science Volume 55 Article 21 2001 Moisture Determination by Thermal Titrimetry Using the Enthalpy of Reaction of 2,2-Dimethoxypropane with Water Edmond W. Wilson Jr. Harding University Reagan Baber Harding University Follow this and additional works at: http://scholarworks.uark.edu/jaas Part of the Environmental Chemistry Commons, and the Fresh Water Studies Commons Recommended Citation Wilson, Edmond W. Jr. and Baber, Reagan (2001) "Moisture Determination by Thermal Titrimetry Using the Enthalpy of Reaction of 2,2-Dimethoxypropane with Water," Journal of the Arkansas Academy of Science: Vol. 55 , Article 21. Available at: http://scholarworks.uark.edu/jaas/vol55/iss1/21 This article is available for use under the Creative Commons license: Attribution-NoDerivatives 4.0 International (CC BY-ND 4.0). Users are able to read, download, copy, print, distribute, search, link to the full texts of these articles, or use them for any other lawful purpose, without asking prior permission from the publisher or the author. This Article is brought to you for free and open access by ScholarWorks@UARK. It has been accepted for inclusion in Journal of the Arkansas Academy of Science by an authorized editor of ScholarWorks@UARK. For more information, please contact [email protected], [email protected]. Journal of the Arkansas Academy of Science, Vol. 55 [2001], Art. 21 Moisture Determination by Thermal Titrimetry Using the Enthalpy of Reaction of 2,2-Dimethoxypropane with Water Edmond W. Wilson,Jr.* and Reagan Baber Department of Physical Science Harding University Searcy, AR 72149 ""Corresponding Author Abstract Assays for water content can be readily and simply carried out using the technique of thermal titrations. The method is based onmeasuring the endothermic heat of reaction exhibited when 2,2-dimethoxypropane is brought into contact with water in the presence of an acid catalyst. The apparatus is simple, requiring a constant delivery rate buret, a recording thermistor thermometer, and a stirred, thermally insulated reaction container. The 2,2-dimethoxypropane reagent used for the water assays is environmentally friendly ("green"). Itis stable, pleasant smelling and economical. Working curves in three solvents, acetonitrile, tetrahydrofuran and 1,4-dioxane, show excellent precision and linearity withincreasing water concentrations to at least 0.07 M.Four different kinds ofsamples were subjected to this method of water assay to demonstrate its versatility: ethanol, nickel (II) nitrate hexahydrate, concentrated sulfuric acid, and two kinds of fuels. Ineach case, the method worked accurately and reproducibly witha minimum of time required. Introduction reagent, one could readily quantitate the amount of water in a sample. The Karl Fischer Method for the quantitative There are some obvious benefits to such a method. The determination of the amount of water in a sample is consid- reagent, 2,2-dimethoxypropane, is not affected by many ered tobe the standard method of analysis. This is due to its substances that interfere with Karl Fischer reagent. For wide range of applicability compared with numerous other example, ferric and cupric ions interfere in Karl Fischer methods available. Substances that react with Karl Fischer water analysis. Acids that react to produce esters with the reagents, of course, preclude its use. Several excellent dis- methanol present in KarlFischer reagents preclude its use. cussions of this method and its limitations have been pub- The shelf life of 2,2-dimethoxypropane is much longer than lished (Kolthoffand Elving, 1961). We describe a method for Karl Fischer reagent. Although 2,2-dimethoxypropane moisture determination that also appears to be widely reacts with water, it does so only when heated or catalyzed applicable, particularly in some of those cases where the with acid. Moreover, it is not necessary for the concentra- KarlFischer method fails. Our method involves measuring tions of 2,2-dimethoxypropane to be known in order to the heat produced when 2,2-dimethoxypropane reacts with determine the amount of water present. The enthalpy of water as described by Equation 1. reaction can be used instead. The Karl Fischer reagent is a Extensive use has been made of 2,2-dimethoxypropane moisture-sensitive mixture ofmaterials that contains, among other things, the toxic substances sulfur dioxide and pyri- dine. The 2,2-dimethoxypropane, on the other hand, is a OCH, O pleasant smelling, harmless, relatively liquid is + + (1) stable that CH3CCH3 HOH ;=± CH3CCH3 2CH3OH I easily and inexpensively obtainable inpure form. OCH3 Earlier investigators proposed methods that used 2,2- dimethoxypropane to accurately determine the amount of to dehydrate various samples containing water. The dehy- water in a sample. For example, Critchfield and Bishop dration is easily carried out bypouring an excess of the ketal measured the amount of acetone produced after reacting a over the substance to be dried and warming gently. The moisture-containing sample with 2,2-dimethoxypropane reaction is driven to completion by removing the low boil- (Critchfield and Bishop, 1961). The amount of acetone was ngproducts, acetone and methanol. While in the process of determined spectroscopically by measuring its absorbance drying various reagents with 2,2-dimethoxypropane, we at 5.87 micrometers. When utilizing their method, one must noted that its reaction with water was accompanied by a take into account any carbonyl compounds that also absorb considerable absorption of heat. Itis a strongly endothermic at this wavelength. Other workers have used 2,2- reaction. We felt that by applying the method of thermal dimethoxypropane to determine the amount of water in a titrations, using 2,2-dimethoxypropane as the analytical sample with the aid of a gas chromatograph (Badinad et al., Journal of the Arkansas Academy of Science, Vol. 55, 2001 154 Published by Arkansas Academy of Science, 2001 154 Journal of the Arkansas Academy of Science, Vol. 55 [2001], Art. 21 z,z-Dimetnoxypropane with Water 1965; Martin and Knevel, 1965). Martin and Knevel equili- brated different known amounts of water with 2,2- Materials and Methods dimethoxypropane. Aliquots from each of these solutions were withdrawn witha syringe and injected into a gas chro- Two thermal titrationsystems were used for these analy- matograph. The peak heights of the ketal were measured on ses. The system used for obtaining calorimetry data and the chromatogram and a relationship between the ratios of some of the water calibration measurements have been these peak heights to the initial water concentration was described in detail (Wilson, 1968). The remaining measure- determined. Once this relationship was known, the amount ments were made using a FACTS Titration System, com- of water in other samples could be obtained using the same posed of a Sanda Dual Titration Station, F.A.C.T.S. Ce2010 method. Data Processing Module, National Instruments Lab-PC The quantitative determination of the amount of water 1200 Control Board and PC computer (Sadder, 1999). This in a sample by thermal titrimetry is not new. Greathouse et latter instrument was used to make the majority ofmeasure- al. determined the amount of water in acetic acid by reac- ments. The instrumentation in both cases is similar in that tion with acetic anhydride (Greathouse et al., 1956). A what is required is an accurate constant rate delivery buret, known amount of excess acetic anhydride was titrated with a stable, sensitive thermistor thermometer, a stirred titration small increments of water in a dewar flask until no further vessel that is thermally insulated, and a means of recording > temperature rise was observed on a thermometer. the resulting thermogram. The FACTS system is particular- Alternatively, acetic anhydride and the sample were mixed lyuseful because of the sophisticated data handling that pro- > in a Dewar flask and the temperature noted. Then catalyst duces a thermogram on which the temperature versus milli- was added that allowed the hydrolysis reaction to take place liters of titrant is plotted along with the first and second ? quickly. The maximum temperature was observed and com- derivatives of temperature versus milliliters. The derivative pared with a working curve of temperature rise versus water plots greatly enhance the ability to measure the endpoint of > content. This latter technique was a precursor of what is now the thermogram accurately without having to resort to termed Direct Injection Enthalpimetry, DIE (Wasilewski et graphical extrapolations. i al., 1964). Spink and Spink used DIE to determine the Inorder to determine the amount of water in a sample amount of water inorganic liquids (Spink and Spink, 1968). by thermal titration with 2,2-dimethoxypropane, it is Their method involved injecting 80% wt/wt sulfuric acid necessary to have a solvent capable of dissolving both the into a dewar flask containing the sample and noting the tem- sample to be analyzed and the 2,2-dimethoxypropane. perature rise. A working curve was prepared relating the Ideally, one would like to have a solvent with low vapor amount of water to the temperature rise. Itis interesting to pressure, no unpleasant odor, a low cost, and one that would note that the heat produced by the addition of water to sul- dissolve a wide variety of inorganic and organic materials. furic acid was used by Somiya to determine the water con- Acetone and methanol are unsuitable because they are the tent of sulfuric acid (Somiya, 1927). Finally, Wasilewski and products of the reaction between water and 2,2- Miller used DIE to do moisture analysis (Wasilewski and dimethoxypropane. Moreover, alcohols, ketones, acid anhy- Miller,1966). They used the heat produced when water is drides, and acid chlorides, as well as amines cannot be used added to Karl Fischer reagent. First, they added a known since they may react with the 2,2-dimethoxypropane excess of KarlFischer reagent to the sample and noted the (Killian et al; Baum and Hennion, 1938; Kreevoy and Taft, temperature.