Iowa State University Capstones, Theses and Retrospective Theses and Dissertations Dissertations 1973 The high-precision thermometric and coulometric assay of primary standard 4-aminopyridine William Charles Hoyle Iowa State University Follow this and additional works at: https://lib.dr.iastate.edu/rtd Part of the Analytical Chemistry Commons Recommended Citation Hoyle, William Charles, "The high-precision thermometric and coulometric assay of primary standard 4-aminopyridine " (1973). Retrospective Theses and Dissertations. 5017. https://lib.dr.iastate.edu/rtd/5017 This Dissertation is brought to you for free and open access by the Iowa State University Capstones, Theses and Dissertations at Iowa State University Digital Repository. It has been accepted for inclusion in Retrospective Theses and Dissertations by an authorized administrator of Iowa State University Digital Repository. For more information, please contact [email protected]. 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Xerox University Microfilms 300 North Zeeb Road Ann Arbor, Michigan 48106 74-545 HOYLE, William Chaises, 1944- THE HIGH-PRECISION THEEMOMETRIC AND CODLOMETRIC ASSAY OF PRIMARY STANDARD 4-AMINOPYRIDINE. Iowa State University, Ph.D., 1973 Chemistry, analytical University Microfilms, A XEROX Company, Ann Arbor, Michigan THIS DISSERTATION HAS BEEN MICROFILMED EXACTLY AS RECEIVED. The hîgh-precisîon thermometric and coulometrîc assay of primary standard 4-aminopyridIne by William Charles Hoyle A Dissertation Submitted to the Graduate Faculty in Partial Fulfillment of The Requirements for the Degree of DOCTOR OF PHILOSOPHY Department: Chemistry Major: Analytical Chemistry Approved: Signature was redacted for privacy. In Charge of Major Work Signature was redacted for privacy. Signature was redacted for privacy. For the Graduate College Iowa State University AmeS; Iowa 1973 TABLE OF CONTENTS Page QUOTATION vîî CHAPTER I. THE FARADAY AND HIGH-PRECISION COULOMETERS 1 Significance and History 1 The Silver Coulometer 4 Cou 1ometry 10 High-Precision Coulometric Titrations 11 CHAPTER II. PROPERTIES OF 4-AMINOPYRIDINE 17 Synthesis 17 Purification 18 Dissociation Constant 25 Latent Heat of Fusion 25 CHAPTER III. PURITY OF 4-AMINOPYRIDINE AS DETERMINED FROM 30 FREEZING CURVES Freezing Curves and Melting Curves as Criteria of Purity 30 General Description of the Instrument for Obtaining 35 Melting Curves and Freezing Curves Details of Construction 38 Electrical Components 42 Operation of the Instrument to Obtain a Freezing Curve 46 Freezing Curves Obtained on High-Purity 4-AmInopyridine 47 Melting Temperature of Pure 4-Aminopyridine 47 Melting Curve of 4-Aminopyridine and Latent Heat of 48 Fusion of 4-Aminopyridine Using the Instrument for Obtaining Melting Curves and Freezing Curves î i i Specific Heat of Liquid 4-Aniinopyridine Cryoscopic Constant of 4-Aminopyridine Genera] Treatment of Data Obtained from a Freezing Curve Interpretation of Data Obtained from Freezing Curves of 4-Aminopyridine Analyses Made on 4-Aminopyridine Recovered Following Freezing Curve Experiments CHAPTER IV. HIGH-PRECISION COULOMETRIC TITRATION OF 4-AMINOPYRIDINE Titration Cell, Electrodes, and Electrolytes Measurement of Current, Potential, Weight and Time Failure to Anodic Generation of Hydrogen Ion in Sodium Perch 1orate Electrolyte Attempts to Make an Anode 100 Percent Efficient for the Generation of Hydrogen Ion A Hydrazinium Sulfate-Platinum Anode as a Generator of Hydrogen Ion End-point Detection Using the Hydrazinium Sulfate- Platinum Anode for the Titration of a Base Working Potential of the Hydrazine Sulfate-Platinum Anode Combination Hydrazinium Sulfate-Platinum Anode and Cathode as a Generator of Hydrogen Ion Titration of 4-Aminopyridine Using the Hydrazinium Sulfate-Platinum Anode Titration of 4-Aminopyridine Using Perchloric Acid Standardized Coulometrically Titration of Tris(hydroxymethyl)aminomethane Using the Hydrazinium Sulfate-Platinum Anode îv Page CHAPTER V. CALCULATION OF A VALUE FOR THE FARADAY 93 Molecular Weight of 4-Aminopyridine 93 Possible Effects on Molecular Weight of Chemical 95 Processing Calculation Using Data Obtained in the Various 96 Coulometric Titrations CHAPTER VI. SUMMARY 105 ACKNOWLEDGEMENTS 111 LITERATURE CITED 112 APPENDIX 119 V LIST OF TABLES Page Table 1. High-precision coulometric titrations 15 Table 2. Dissociation constant of 4-aminopyridine in 22 solutions of sodium perchlorate of various concentrations. 24.4°C Table 3. Dissociation constant of 4-amInopyridine at 22 various temperatures in 1.00 M sodium perchlorate Table 4. Depression of the freezing point, AT^, of 4- 65 aminopyridine as a function of time of contact in the molten state with the gold of the crucible Table 5. Coulometric titration of 4-aminopyridine with 98 acid generated at the hydrazinium su 1 fate- platinum anode. Series 1 Table 6. Coulometric titration of 4-aminopyridine with 99 perchloric acid (coulometric end-point) and standardization of perchloric acid coulo- metrically. Series 2 Table 7- Coulometric titration of 4-aminopyridine with 101 perchloric acid (coulometric end-point) and standardization of perchloric acid. Series 3 Table 8. Summary of recent values for the Faraday 104 vî LIST OF FIGURES Page Figure 1. Sublimation apparatus. 21 Figure 2. Calorimeter used in the determination of the 24 latent heat of fusion of 4-aminopyridine. Figure 3. Instrument for obtaining melting curves and 37 freezing curves. Figure 4. Stages in the assembly of the instrument for 4l obtaining melting curves and freezing curves. Figure 5. Components of the electrical measurement 44 system. Figure 6. Freezing curves. 56 Figure 7. Shield tube. 72 Figure 8. External, "drip" electrode. 74 vî î QUOTATION "Mosques fall, palaces crumble into dust but knowledge remains." Ulug Beg, the great Uzbet astronomer of the fifteenth century. 1 CHAPTER I. THE FARADAY AND HIGH-PRECISION COULOMETERS Significance and History The laws governing the relationship between electric current, time and the amount of chemical change effected by the electric current were discovered by Michael Faraday in 1833. Faraday expressed the relations In a series of statements, introducing at the same time a new terminology. 21 The principal of these statements are: 783. The chemical power of a current of electricity is in direct proportion to the absolute quantity of electricity which passes. 824. The numbers representing the proportions in which they (anions, cations) are evolved I propose to call electro­ chemical equivalents. 835. Electro-chemical equivalents are always consistent; I.e., the same number which represents the equivalent of substance A when it is separated from substance B, will also represent A when separating from a third substance C. 836. Electro-chemical equivalents coincide, and are the same, with ordinary chemical equivalents. Curiously, the text books for over a hundred years continued this non- symbolic statement of the laws and it was only about 1950 that the laws appeared in a textbook in the algebraic formulation ^ 1 Mol. Wt. 2 G being the weight of chemical undergoing change, in grams; I being the current, in amperes; t being the time, in seconds; Mol. wt./n being the equivalent weight, that is, the molecular weight divided by the number of electrons involved in the change (change in valence at the electrode). The proportionality factor, F, is appropriately called the "faraday." The work described in the present thesis deals with measurements leading to a numerical value of this constant. It is common in physical science that the evaluation of a proportion­ ality constant is tied up intimately with the establishment of units of measurement of the