I OXIDATION METHODS FOR THE DETERMINATIGN Q3“ HYP‘OPHOSPHATE i‘l A NEW METHOD FOR‘FHE PREPARATION OF SQDEUM DIHYDROGEN HYPOPHOSFHATE Thesis for Eh-e Degrae M. S. MHCHIGAN STATE COLLEGE Thomas Chuiski I '37:? 4-7 This is to certify that the thesis entitled I Oxidation Methods for the Determination of Hypophosphate II A New Method for the Preparation of Sodium Dihydrogen Hy ophosphate presented 9 Thomas Chulski has been accepted towards fulfillment of the requirements for __l_~ . S . _degree in_Qh 63:1ij (Analytical) _6 WGth Major profeJr Date Ivzarch 10, 19h? M495 v—‘iwr -— — — »— w'7'* ‘- _ ___—_- — ——-——~'r— -— <- Amwwow—f I OXIDATION METHODS FOR THE DETERMINATION OF HYPOPHOSPHATE II A NEW METHOD FOR THE PREPARATION OF SODIUM DIHYDROGEN HYPOPHOSPHATE by ihomas Ohulski A THESIS Summittea 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 MASTER OF SCIENCE Department of Chemistry l947 ACKNOWLEDGEMENT Grateful appreciation is expressed to Doctor Elmer Leininger under whose kind and efficient direction this work was carried out. TABLE OF CONTENTS Oxidation methods for the determination of Page hypophosphate. A. introduction. 1 B. Historical. 2 C. Preparation of Sodium dihydrogen. 8 hypophosphate. D. Stability of 0.05000 normal solution of 14 sodium dihydrogen hypophOSphate. E. Quantitative determination of hypophosphate by oxidation with potassium dichromate. 16 Quantitative determination of hypophosphate by oxidation with SOdium hypochlorite. 25 Quantitative determination of hypophosphate by oxidation with potassium permanganate. 33 H. Oxidizing agents that do not react quantitatively with nypophosphate. 36 l. Potassium bromate in hydrochloric acid. 2. bromine. 3. Chlorine. 4. Iocine. 5. Potassium bromate in sulfuric acid. 6. Potassium periocate. 1. oxidizing agents that do not react xith hypophOSphate. 44 l. Sedium chlorite. 2. Chloramine T. 11. A new method for the preparation of souium 47 dihydrogen hypophosphate. Ill. Conclusion. 54 IV. Literature cited. 56 INTRODUCTION Hypophosphoric acid, H4P206, is a.member of a series of cxyacids of phosphorus. In hypOphoSphorous acid, h3P02, phosphorus exhibits a valence number of positive one; in phosporous acid, H3P03, positive three; in hypophOSphoric acid, H4P305, positive four; and in phOSphoric acid, H3PO4, positive five. Such a series is a fruitful field of study. For example, phosphite is rapidly and quantitatively oxidized to phosphate by iodine in a neutral solution. HypophOSphite does net interfere. However if the reaction sclution is acidified, hypophospnite is oxidized to a.mixture of phosphite and phosphate. It can be made quantitative by neutralizing and oxidizing the phOSphite so formed to phosphatetES). However at pH 5.7 to 4.6 phoSphite is oxidized to hypophosphate with a yield of from 37tll) to 55tl2) per cent. before further studies of the series can be made the chemistry of the individual members must be better known. The literature contains more information on phosphite than on hypophOSphite or hypOphosphate. What has been written on hyp0ph05phite is often vague and misleading while information on hypophosphate is to a large extent entirely lacking. Hence the purpose oi this work is twofOld, to work out methods of determining hypophosphate and to more fully characterize it. HISTORICAL Pelletiertld) identified two acids of phoSphorus. One he called 'l'acice phosphorique", and the other 'l‘acide phoSphoreux'. The acid “l'acide phosphoreux" was commonly known as ”Pelletier's acid" until Salzer in le77 identified it as suhphosphoric acid\22), now called hypophosphoric acid, H4P306. The classical method of preparation is by the slow oxidation of yellow phosphorus. Sticks of yellow phos- phorus are half sucmerged in water and oxidation is allowed to proceed for several weeks. A mixture of phOSphorous, hypophosphoric, anu phosphoric acids is Obtained. brom 6 to l6 percent of the phosphorus is converted to hypophosphate. SalzerQZS) reported 6 to 7 per cent of the phosphorus oxidized to hypophosphate, Jelyt7) reported l2 to 14 per cent, and van Name and huff (31) reported l0 to l6 per cent conversion. In all cases the hypophoSphate was isolated as sodium dihydrogen hypophoSphate hexahydrate, Na2H2P206°6HgO. Hosenheim and PinsxertZO) prepared hypophOSphate by the oxidation of yellow phosphorus with cupric ion in dilute nitric acid sclution. This method was later modified by Jungte). Rosenheim and Pinsker reported a yield of 10 per cent of the theoretical, Jung reported l8.l per cent. Hosenheim and Pinsker (20) also prepared hypophos- phate by the electrOlysis of a l to 2 per cent sulfuric acid sclution using anodes of copper, nickel, or silver phOSphide and the corresponding metal as the cathode. They reported a yield of 60 per cent. With iron phos- phide only phosphate was formed. Speter(27) prepared hypophOSphate by the oxidation of red phoSphorus with bleaching powder, calcium chloride hypochlorite. Five g. of red phosphorus was heated with l liter of lO per cent solution of practical grade bleaching powder. After filtering, the acids formed were nearly neutralized with solid calcium carbonate. Calcium phOSphite, hypophosphate, and phOSphate precipi- tate with standing. A solution of the pure acids was Obtained by dissolving the precipitate in the smallest possible volume of dilute sulfuric acid. Calcium sulfate settles out. Speter did not isolate the hypophOSphate but used the solution of mixed acids as a test reagent for thorium. He reported that 64 per cent of the phOSphorus was oxidized, with hypophosphoric acid predominating. Probst(19) modified Speter's method by utilizing an alkaline solution of sodium hypochlorite instead of the bleaching powder, thus entirely eliminating the calcium ion. He reported a yield of 25 per cent. Kclitowska(ll) prepared hypophosphoric acid by oxidizing the hydrolysis products of phOSphorus tetraiodide, P314, and pnOSphoruS triiodide, P13, with iouine at approximately pH 6.7. He reported a yield of 44.6 per cent from the tetraiodide and 37.3 per cent from the triiodide. Kolitowska(l0) also prepared hypophosphoric acid by the oxidation of the hydrolysis products of phosphorus trichloride, PCls, with iodine at a pH of 5.7. Kolitowska(l2) also prepared hypophosphoric acid from the hydrolysis products of phOSphorus tribromide by the oxidation with iodine in a solution buffered with sodium acetate and sodium bicarbonate. He reported a yield of 55 per cent. Hilobedzike, Kolitowska, and Berxan(l6) prepared hypophOSphoric acid by the oxidation of red phOSphorus with iodine at a pH of 5.7 to 4.6 with a yield of 34 per cent. Salzer(24) determined hypophoSphate by direct titration With potassium permanganate. Satisfactory results could by obtained only if the potassium permanganate was standardized against pure sodium dihydrogen hypophOSphate. Hypophosphate can be hydrolyzed to phosphite and phosphate with hydrochloric acid and the phosphite so formed ddermined(30). Treadwell and Schwarzenbach(29) determined hypophOSphate by titration with a standard solution of uranous sulfate, U(SO4)3, in an atmOSphere of carbon dioxide obtaining the end point electrometrically. uranous hypophOSphate, UPZOG, is insoluble. Silver hypophoSphate is insoluble over a pH range of l to 2 while silver hypophosphite, phOSphite and pnOSphate are scluble. Hence the separation of hypophosphate as silver hypophosphate can be used as a method of determination. Wolf and Jung(34) buffered a solution containing hypophosphite, phOSphite, and hypothSphate with phosphoric or formic acid. Excess Standard silver nitrate solution was added. The silver hypOphOSphate was filtered off and the excess silver determined by titrating the filtrate with standard potassium thiocyanate solution. Wolf, Jung, and Uspenskaja(35} modified the method by titrating directly with silver nitrate solution obtaining the end point potentiometrically in a solution buffered by dideium phoSphate. Exclusion of air was not necessary. A qualitative test for hypophOSphoric acid and its salts is the formation of a precipitate with guanidine carbonate, 2NHC(NH3)2-H2003. Mfiller(20) assigned the formula (CN3H6)2P05+H30 to the precipitate. Rosenheim and Pinsker(21) said it was (0N335)4H2P03+5Hbo. Bell and Sugden(l) in a more recent work determined the formula of guanidine hypophospnate to be 4(CN3H4)-g§:865- Hypophosphoric acid and its salts form a curdy precipitate with thorium which is insoluble in boiling hydrochloric acid. The reaction was used by Speter(27) -b— as a qualitative test for thorium. The precipitate formed is the normal thorium hypophosphate, ThPZOG'llHBO. The doubled formula, (H2P03)2 or H4P205, for hypophosphoric acid was established by conductance and freezing point data. Treadwell and Schwarzenbach(29) obtained the ionization constants of the acid by electrometrio methods. Kl has the value of 10'2‘2, K2 of 10-2.81, K3 of 10’7'27. and K4 of 10-10.03. However Rosenheim and Pinsker<2l) found that the freezing points of sclutions of hypophosphoric acid were not in accord with Treadwell and Schwarzenbach's values for K1 and KB. Moreover, the molar conductances of pyrophosphoric acid, H4P207, are approximately the same as those for hypophoSphoric acid. But pyrophos- phoric acid is considered to be a stronger acid with ionization constants K1 of lO-O°85. Kg 0f 10‘1'96. is of 10‘5-54, and K4 of 10‘8'44. Although the data is not in good agreement the determination of four ionization constants substantiates