United States Patent (19) 11) 4,207,300 Kestner et al. 45) Jun. 10, 1980

(54) PROCESS FOR THE PREPARATION OF 3,632,311 1/1972 Kovacs et al...... 423/316 ORTHOPHOSPHOROUSACD AND 3,679,374 7/1972 Kovacs ...... 423/36 OTHER PUBLICATIONS 75) Inventors: Mark O. Kestner, Mendham, N.J.; Pamela J. Teliszczak, Richardson, J. Chem. Soc. (London), vol. 51 (1887), pp. Carpentersville, Ill. 801-806. Jacobson, Encyclopedia of Chemical Reactions, vol. 5 (73) Assignee: Borg-Warner Corp., Chicago, Ill. (1953), p. 364. Mellor, Comprehensive Treatise on Inorganic & Theo (21) Appl. No.: 970,846 retical Chemistry, vol. 8 (1928), pp. 901-902. 22 Filed: Dec. 18, 1978 Primary Examiner-O. R. Vertiz 51) Int, C.2 ...... CO1B 25/06; C01B 25/163 Assistant Examiner-Thomas W. Roy 52 U.S. C...... 423/299; 423/316 Attorney, Agent, or Firn-Richard J. Schlott 58 Field of Search ...... 423/316, 299, 304 56 References Cited 57 ABSTRACT The direct reaction of elemental cata U.S. PATENT DOCUMENTS lyzed by produces orthophosphorus 3,437,438 4/1969 Carroll et al...... 423/316 3,437,439 4/1969 Carroll ...... 423/316 acid free of orthophosphoric acid and phosphine free of 3,437,440 4/1969 Carroll ...... 423/316 diphosphine. 3,528,772 9/1970 Whyte et al...... 423/316 3,532,461 10/1970 Whyte et al...... 423/316 5 Claims, No Drawings 4,207,300 1. 2 ing, less reactive substance known as red phosphorus. PROCESS FOR THE PREPARATION OF For the purposes of the process of this invention, only ORTHOPHOSPHOROUSACD AND PHOSPHINE the white phosphorus is useful. The elemental phospho rus may be employed as a finely divided solid or as a BACKGROUND OF THE INVENTION 5 melt, or it may be dissolved or dispersed in an inert This invention relates to a method for making ortho organic . and phosphine. More particularly, Elemental phosphorus is substantially insoluble in this invention is a method for the preparation of ortho water and does not react with water at any appreciable phosphorous acid and phosphine from elemental phos rate. In the presence of an acid and in particular in the phorus and water. Still more particularly, this invention 10 presence of aqueous hydroiodic acid, elemental phos is a method for the preparation of orthophosphorus acid phorus appears to undergo to form and phosphine by way of a hydroiodic acid-catalyzed phosphine and orthophosphorus acid. The reaction reaction of elemental phosphorus with water. proceeds best at elevated temperatures in the range of Methods for making orthophosphorus acid, H3PO3, 100' to 130 C, and appears to require that hydroiodic have long been known. More recently, practical meth acid be present in a ratio greater than 6 moles of hydro ods for preparing orthophosphorous acid have been gen (HI) for each phosphorus molecule (P4). At developed, including a process whereby the trivalent ratios below about 6:1, some of the white elemental oxide is formed by a controlled air oxidation of elemen phosphorus is converted to insoluble and inert red phos tal phosphorous and subsequently hydrolyzed, as is phorus, lowering the overall yield and contaminating disclosed in U.S. Pat, No. 3,528,772. Such processes 20 the final product. produce a mixture of containing orthophospho Hydroiodic acid forms a constant boiling azeotrope rous acid together with as much as 25% orthophos with water containing 57% HI which boils at 127 C. phoric acid, H3PO4, or more. Separating the orthophos The process of this invention may thus be conveniently phorous acid from the mixture in a highly purified form carried out by adding elemental phosphorus, in a con thus requires additional process steps such as those 25 tinuous stream or incrementally, to a pot containing disclosed in U.S. Pat, Nos. 3,632,311 and 3,679,374. Alternative prior art methods for obtaining ortho refluxing 57% aqueous hydroiodic acid and replenish phosphorous acid include the hydrolysis of a phospho ing the water as it is consumed or lost through evapora rous trihalide such as phosphorus (PI3) with tion to maintain the boiling temperature at or below water to produce orthophosphorous acid and the corre- 30 127 C. The reaction may be carried out in more dilute sponding halide. An improved process em hydroiodic acid solutions if desired, and at any conve ploying this scheme is disclosed in U.S. Pat. No. nient temperature in the range of 100 to 130° C., how 3,437,439, and includes the steps of in situ generation of ever, at temperatures above about 127 C., phospho PI3 from phosphorous and in the presence of an nium iodide, PHI, sublimes from the reaction mixture, oxidizing agent and a solvent, followed by hydrolysis to 35 leading to a substantial reduction in the concentration of form orthophosphorous acid. As with the air oxidation hydroiodic acid. processes previously discussed, this process forms a It is absolutely essential that the reaction be carried mixture containing a substantial proportion of ortho out in an inert gas atmosphere. Elemental phosphorus is which must then be subjected to a spontaneously flammable in moist air, and the phos separation process step if pure orthophosphorous acid is 40 phine produced is flammable and forms potentially desired. explosive mixtures with air or oxygen. For reasons of safety, the reaction vessel will thus be purged with an SUMMARY OF THE INVENTION inert gas such as nitrogen or argon and a slight positive In the process of this invention, orthophosphorous pressure of inert gas will preferably be maintained acid free of orthophosphoric acid is produced in high 45 throughout the reaction period to prevent air from yield by the reaction of elemental phosphorus with entering the vessel. water in the presence of hydroiodic acid. More particu An inert organic solvent for the elemental phospho larly, elemental phosphorus readily reacts with water in rus may optionally be included to aid in dispersing the the presence of hydroiodic acid and, optionally, an phosphorus. The useful for the purposes of this organic solvent, by a disproportionation to produce 50 invention will be inert organic liquids which boil at a equimolar amounts of phosphine (PH3) and orthophos temperature within or slightly above the preferred tem phorous acid, apparently according to the equation: perature range and which may be readily distilled from the pot mixture at the end of the reaction period, includ 2P+3H2O H PH3+H3PO3. ing, for example, anhydrous, C1 to C6 aliphatic carbox 55 ylic acids. The solvent may be employed directly in the Phosphine, being a gas under the reaction conditions, reaction mixture with the aqueous hydroiodic acid, or evolves from the reaction mixture and may be collected alternatively the elemental phosphorus may be dis for other uses. The reaction mixture, after distillation to persed in the solvent and added therewith in a steady remove hydroiodic acid, water and any solvent present, stream. Because of its stability, convenient boiling tem consists of a clear viscous orthophosphorous acid con- 60 perature of 118 C. and ready availability, acetic acid taining no detectable amounts of orthophosphoric acid will be preferred for these purposes. The proportion of or other acids of phosphorus. solvent employed is not critical; when added directly to DETALED DESCRIPTION OF THE the reaction mixture, approximately equal volumes of INVENTION the solvent and aqueous hydroiodic acid may be conve 65 niently employed. The common forms of elemental phosphorous in The products of the reaction are orthophosphorous clude the clear or whitish-yellow waxy solid melting at acid, which remains in the reaction mass, and gaseous 44' known as white phosphorus, and a red, high melt phosphine which is evolved and may be conducted out 4,207,300 3 4. of the reaction vessel, optionally water-scrubbed to tain the boiling temperature of the reaction mass below remove HI, then collected by any convenient method 127 C. such as cold trapping and gas-liquid displacement. As phosphine evolved, it was passed through a water Phosphine is both flammable and highly-toxic, and pre filled gas scrubber, then collected by trapping in a so cautions must be taken to prevent its escape into the air dium hypochlorite solution. The total phosphine gener and to ensure that no exposure to phosphine can occur. ated amounted to 51 g (89% yield). The gas stream was Phosphine is commercially useful as a synthesis inter completely free of diphosphine (P2H4). mediate. Alternatively, phosphine may be readily oxi The pot mixture was fractionally distilled to remove dized to form phosphoric acid. Prior art methods for the the acetic acid and hydroiodic acid azeotrope. The pot preparation of phosphine generally produce phosphine 10 residue, amounting to 105 g (76.6% yield) was a clear contaminated with significant amounts of diphosphine, viscous liquid. Chromatographic analysis showed this P2H4 which is considerably more flammable and poten product to be H3PO3, with no detectable trace of tially more of an explosion hazard than phosphine. Sur H3PO4 or other phosphorus acids. prisingly, the instant process results in very pure phos The invention will thus be seen to be a method for the phine containing no detectable amounts of diphosphine. 15 preparation of orthophophorus acid and phosphine The process of this invention thus also provides a very comprising the steps of adding elemental white phos practical and convenient method for the production of phorus to aqueous hydroiodic acid, optimally in the very pure phosphine. presence of a solvent, at a reaction temperature of about The reaction vessel, after the addition of phosphorus 100 to 130 C., collecting phosphine as it is evolved, is complete and the evolution of phosphine has ceased, 20 stripping hydroiodic acid, water and any solvent from contains orthophosphorous acid and aqueous hydroi the reaction mixture, thereby providing orthophospho odic acid, together with the solvent, if employed. The rous acid. mixture is then distilled to strip off the hydroiodic acid We claim: as the azeotrope which may be re-used directly. The pot 1. A process for preparing orthophosphorous acid mixture after distillation contains only clear viscous 25 and phosphine comprising orthophosphorus acid with no other acids of phospho adding elemental phosphorus to a reaction vessel rus such as orthophosphoric acid. The mass is readily containing a mixture consisting of water, a C1-C6 crystallized if desired. aliphatic carboxylic acid and hydroiodic acid at a The process of this invention may be carried out temperature between about 100 and 130° C. under either as a batch or continuous flow process. In a con 30 an inert gas atmosphere; tinuous process, molten phosphorous would be continu collecting phosphine from the reaction vessel; and ously added under an inert atmosphere to the pot mix distilling aqueous hydroiodic acid, said carboxylic ture of 57% aqueous hydroiodic acid and solvent acid and water from the reaction vessel. heated to a temperature of 127 C. Phosphine would be 2. The process of claim 1 wherein said carboxylic collected as it evolved, and pot mixture would be con 35 acid is acetic acid. tinuously removed to a second heated vessel and 3. The process of claim 1 wherein said elemental stripped of solvent and hydroiodic acid azeotrope. The phosphorus is charged at a rate such that the ratio of azeotrope would be returned to the reaction vessel. hydroiodic acid to elemental phosphorus is maintained The process of this invention will be better under at a value greater than 6:1. stood by consideration of the following Example: 4. A process for the preparation of orthophosphorus acid and phosphine consisting of combining acetic acid, EXAMPLE aqueous hydroiodic acid and elemental phosphorus at a To a 0.51 round bottom flask fitted with a stirrer, a temperature between about 100 and 130 C, collecting reflux condenser and a thermometer were added 0.15 phosphine and stripping the acetic acid, hydroiodic acid of glacial acetic acid and 0.1181 of 57% aqueous hydroi 45 and water from the orthophosphorous acid. odic acid. The mixture was slowly stirred, purged with 5. The process of claim 4 wherein the hydroiodic acid nitrogen, and heated to 125-129' C. Elemental phos and elemental phosphorus are in a ratio greater than . phorus (105 g) was added incrementally over a period about 6:1. of 30 days, and water was periodically added to main k k sk s 50

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