OXIDATION I'.Îethods for the VOLUMETRIC DETERMINATION of HYP0PHÜ5PHATE, PHOSPHITE, and Hïpofhosphite
Total Page：16
File Type：pdf, Size：1020Kb
OXIDATION i'.îETHODS FOR THE VOLUMETRIC DETERMINATION OF HYP0PHÜ5PHATE, PHOSPHITE, AND HïPOFHOSPHITE By Stanley J. Carlyon A THESIS Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. OXIDATION METHODS FOR THE V0LUI-4ETRIG DETERMINATION OF HYPOPHOSPHATE, PHOSPHITE, AI'D HYPOPHOSPHITE By Stanley J. Carlyon AN ABSTRACT Submitted to the School of Graduate Studies of Michigan State College of Agriculture and Applied Science in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY Department of Chemistry Year 1953 Approved Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Stanley d. Carlyon THISIS IBSTrtAGT Volnmetrlc oxidation methods were developed for tlie determination of hypopnosphste J phosphite and hypophosptilte using standard solutions of sodium hypochlorite, potassium dlchromate, and cerlc ammonium sulfate under suitable conditions. The compounds used for the anal;yses were dlsodlum dlhydrogen liypophosphate hexaliydra.te which was prepared by the method of Lelnlnger and Chulskl,^ reagent grade phosphorous acid, and purified sodium hypophosphlte. The compositions of the phosphorous acid end sodium hypophosphlte were established by a gravimetric procedure In which the compounds were oxidized to orthophosphate by repeated evaporations with aqua, regia, and the orthophosphate converted to mag nesium pyrophosphate. iiypophosphate , phosphite, and hypophosphlte were quantitatively oxidized to phosphate by an excess of standard potassium dlchromate In 12 normal sulfuric acid at the temperature of a. boiling water bath. The oxidations were complete In one hour. The excess dlchromate was determined lodometrlcally after adjusting the sulfuric acid concentration to approximately three normal by the addition of sodium hydroxide solu tion. The excess dlclirornate was also determined by adding an excess of standard ferrous anmionlum sulfate solution and backtltratlng the excess ferrous Ion with standard dlchromate . It was found that there was a loss of 0.01 to 0.03 ml. of 0.1 normal dlchromate during the oxidations and corrections were applied to compensate for this loss. 1 Lelnlnger, Z ., end Ghulskl, T., J. Am. Cliem. Soc ., 71, 238$ (I9k9). — 1 — Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Stanley J. Carlyon iiypophosphate J phosphite ^ ano Irypophospliite were quantitatively to phosphate uno.er sue.tsole conditions by an excess of standard sodiuiri hypochlorite , Hypopliosphate was determined vjith an excess of standard sodium hypochlorite in a solution made neutral >ri.th sodium bicarbonate . The excess hypochlorite was determined after jO minutes by adding an excess of standard sodium arsenite and beckti.trating the excess arsenite with standard sodium hypochlorite using Bordeaux as indicator. Tiie excess hypochlorite was also determined by titrations with standard arsenite in wïrich the endpoint was determined either potentiometrically or by the deadstop technique. The iodometric de termination of hypochlorite in the presence of bicarbonate or buffers gave unsatisfactory results. Phosphite was determined by a sligiit excess of standard sodium hypochlorite in a solution containing bicarbonate and bromide, or essentially by hypobromite. The oxidation was sufficiently rapid under these conditions tha,t a direct titration of the phosphite with hypo chlorite was possible if the equivalence point in the titration was determined by the deadstop technique. The use of Bordeaux as indicator in this titration was not satisfactory. HypophospMte was only very slowly oxidized by an excess of sodium hypochlorite in neutral solution but was quantitatively oxidized to phosphate by excess hypochlorite in one normal sulfuric acid in ten hours. Phosphite and hypophospliite were quantitatively oxidized to phos phate by an excess of standard eerie ammonium sulfate in dilute sulfuric - 2 - Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Stanley J. Carlyon acid solution in one hour at boiling temperature. Hypopliosphate was incompletely oxidioed under these conditions, à small loss of eerie suH-fate during the oxidations required the use of blank eorrections . -3- Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 11 AGKNŒ'JLil.DŒ'iENT The writer wishes to express his sincere appreciation to Doctor Elmer Leininger for his most helpfxil counsel and guidance dur ing the course of this work. Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. Ill T;aLE OF C01\iTi!;i\iTS PÎGE I . B3TR0DUCTI0N............................... 1 II. HISTORICAL................................................ 3 III. itiiFiGENTS AND STANDiUtD SOLUTIONS........................... 16 A , Preparation of Standard Solutions.................. 16 B. Standardization of Solutions ...... .............. Ifa G. Indicators......................................... 19 IV. DETERiilNATION OF HYPOPHOSPHiVfE............................ 21 A. Oxidation of Hypophosphate by Excess Potassium Diciiromate in Sulfuric Acid Solution............ 21 3. Oxidation of Hypopliosphate By Excess Sodium Hypochlorite..................................... 32 0, Oxidation of Hypopliosphate With Sodium Hypochlorite in a Solution Containing Bromide....... U? D . Oxidation of iîÿpophosphate by Excess Ceric Sulfate in Sulfuric Acid Solution....................... 32 Summary of Results of Hypophosphate Determination... 33 V. DETERHIiLlTION OF PHOSPHITE................................ 37 A. Oxidation of Phosphite By Excess Potassium Bichrom ate in 5u].furic Acid Solution................... 60 B. Oxidation of Phospliite by Excess Hypochlorite in the Presence of Bromide.............. 6U C. Oxidation of Phosphite vrith Sodium Hypochlorite 69 D. Oxidation of Phosphite By Excess Ceric Sulfate in Sulfuric Acid Solution.......................... 76 Summary of Volumetric Methods for the Determination of Phosphite..................................... 60 VI. DETERMINATION OF HYPOPHOSPHITE............................ 62 A. Oxidation of Hypophosphlte by Excess Bichromate in Sulfuric Ac id Solution....................... 83 B. Oxidation of Hypophospliite by Excess Sodium Hypochlorite in a Bicarbonate Medium............. 8? C. Oxidation of Hypophospliite by Excess Hypochlorite in the Presence of Bromide...................... 87 D . Oxidation of Hypophospliite by Excess Hypochlorite in Sulfuric Acid Solution....................... 68 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. IV Tj-iBLE OF CONTENTS - Continued PAGE E. Oxidation of iiypophospliite by Excess Ceric Sulfate in Nitric i cid Solution........................... 91 F , Oxidation of Hypophospliite By Excess Ceric Sulfate in Sulfuric Acid Solution......................... 93 Summary of Volumetric Methods for the Determination of Hypophosphite ................................. 97 VII. DISCUSSION................................................ 99 VIII. SUfilARY................................................. 106 LITliltATURE CITED...................................................108 Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. 1 I. INTRODUCTION Phosphorus forms a series of oxy scids and salts of these acids. The first tiiree members of this series include hypophosphorous ^ Ji, phosphorous acid, and hypophosphoric acid in wliich the oxidation numbers of phosphorus are positive one, positive tliree, and positive four respectively. Some of the properties of these acids and their salts such as their physical properties, molecular structure, stability, acid strength, and preparation have been fairly well established but accurate rapid methods for their determination are not available. Better analyti cal methods for the determination of the members of this series would assist greatly in further studies made of the series . Theoretically, phosphorous and hypophosphorous acids and their salts are powerful reducing agents; however, reactions of these acids and their salts with even the strongest oxidants are slow, and in many cases require several hours for completion. The slow oxidation of hypophos phate by strong oxidants has been explained by the presence of P-P bonds in its structure and in some cases by the time required for its hydrolysis to phosphite and phosphate before the oxidation can proceed. An equi librium between tautomeric forms of the compound has been suggested as the reason for the slow oxidation of phosphite and hypophosphite. An appreciable amount of work has been done on the development of analytical methods for hypophosphite largely because of its use in medicine. The literature describes the work of several investigators Reproduced with permission of the copyright owner. Further reproduction prohibited without permission. who proposed methods for the determination of phosphite out very little has been published on the determination of 1 ijp op ho sph at e . Much of what has been written on the determination of these acids, especially on the first two members of the series, is often misleading