Patented Dec. 17, 1946 2,412,607 UNITED STATES PATENT OFFICE 2,412,607 AMMONIUM THIOSULFATE Henry V. Farr, Ferguson, Mo., and John R. Ruhoff, Bronxville, N. Y., assignors to Mallin ckrodt Chemical Works, St. Louis, Mo., a cor poration of Missouri No Drawing. Application October 2, 1943, Serial No. 507,178 Claims. (C. 23-5) 2 This invention relates to ammonium thio will not undergo decomposition under ap sulfate, and more particularly to methods for propriate storage conditions. the preparation of this compound. Ammonium thiosulfate is prepared in accord Among the objects of this invention are the ance with the present invention by the reaction provision of an improved method for the prepara of ammonium sulfite and sulfur in the presence tion of ammonium thiosulfate; the provision of of sulfide ions. The probable course of the re an improved method for preparing annonium action is as follows when ammonium Sulfide is thiosulfate in crystalline form; the provision of LSed: an improved method for the provision of a stable ammonium thiosulfate solution; the preparation O of anhydrous ammonium thiosulfate; the prepa Ammonium sulfite may be prepared by any ration of anhydrous annonium thiOSulfate in convenient means, such as by the reaction of stable form; and the provision of anhydrous sulfur dioxide with ammonia in the presence of ammonium thiOSulfate and ammoniuin thiOSul water to produce ammonium sulfite solution. fate solutions, both of which are stable and do Where ammonium thiosulfate has in the past not decompose under appropriate conditions of been prepared by the reaction of ammonium Storage. Other objects will be in part obvious sulfite and sulfur, the reaction has not pro and in part pointed out hereinafter. ceeded smoothly. The reaction is extremely slow, The invention accordingly comprises the steps and apparently requires conditions of tempera and sequence of steps, and features of manipu 20 ture and concentration which make it economi lation, which will be exemplified in the methods cally unfeasible. It has been found, however, and products hereinafter described, and the scope that where, as in the present invention, the re of the application of which will be indicated in action is carried out in the presence of Sulfide the following claims. ions, the reaction itself takes place easily in a Ammonium thiosulfate has long been known comparatively short time interval and may be to be a superior photographic fixing agent. It carried out at a Wide range of temperatures. has the advantage that it will fix the photo Since, as indicated in the foregoing reaction, the graphic image at a much more rapid rate than ammonium sulfide is not consumed by the re sodium thiosulfate, the customarily employed fiX 30 action, only a relatively small proportion is re ing agent. Ammonium thiosulfate, however, has quired. The ammonium sulfide apparently acts not been widely used because it has been ex as a carrier or solubilizer for the sulfur which pensive to produce and because a product sufi reacts with the ammonium Sulfite to form an ciently free from impurities for photographic use monium thiosulfate. has not been available. Such Small quantities 35 The above reaction is, however, preferably car of ammonium thiosulfate as have been used have ried out by keeping the reaction temperature customarily been marketed in the form of a con low, and by having present in the reaction mix centrated solution, chiefly because economical ture an excess of ammonium hydroxide. The methods of preparing a stable crystalline product, reaction is preferably carried out between sulfur, particularly one in the anhydrous state, have not 40 ammonium sulfide and ammonium sulfite in the been known. The transportation of a Solution presence of such an amount of ammonium hy is difficult because it has, in the case of am droxide that the final reaction solution is about monium thiosulfate, been shipped in glass car 1N in ammonium hydroxide. Ammonium Sulfide boys, which adds greatly to the cost because the is preferably employed to provide the sulfide ions, carboys themselves are expensive and must be 45 since it does not introduce an undesired cation. shipped back to the manufacturer when empty. Other sulfides could be substituted but would in This greatly increases transportation costs. effect contaminate the reaction product. The It has now been found that in accordance with reaction is preferably carried out at a tempera the present invention, ammonium thiosulfate can ture of from 30 to 55° C. be easily and economically prepared as a product 50 At the end of the reaction, the liquors con of great purity, and that it may, if desired, be tain ammonium hydroxide, ammonium sulfide made in the form of an anhydrous crystalline or polysulfide, and excess sulfur, in addition to solid. The ammonium thiosulfate prepared in the ammonium thiOSulfate product, the am accordance with the present invention, either in monium Sulfite, having been substantially Com the form of a solution or as a solid, is stable and 55 pletely converted to the thiosulfate. The am 2,412,607 3 4 monium thiosulfate could be isolated directly proves the stability of the ammonium thiosulfate, from this solution. However, from an economic and also aids in the subsequent drying step. The viewpoint it is preferable to treat the solution ammonium sulfite need not be present in the So that more anamonium thiosulfate is formed at mother liquor, but the salt can be Washed with the expense of the impurities present in the ammonium sulfite Solution if it is desired to reaction solution. This is accomplished by the introduce additional proportions of ammonium careful addition of an Incinium bisulfite Solution Sulfite to stabilize the drying step. to the reaction mixture. This addition neutral The factors pointed out above for the evapora izes the excess ammonia, to form ammonium tion of ammonium thiOSulfate Solutions also sulfite, and the ammonium sulfite is converted to 10 apply to the drying of moist crystalline ann ammonium thiosulfate by reaction. With the ann monium thiosulfate. Ammonium thiosulfate is monium sulfide remaining in the Solution. Neu not a stable product, and dissociates substan tralization of the ammonia, favors the reaction of tially over normal drying temperature ranges. the ammoniuin Sulfide and the ammonium sulfite, It has been customary therefore, where Such Which may thereby be made to take place readily 5 drying has been carried out, to effect it in a and Substantially completely, isy proper selec vacuum over a drying agent, such as sulfuric tion of the reaction conditions and concentra acid, and at a temperature of about room tem tions, and by careful addition of the ammonium perature. bisulfite, the final Solution will contain insig In accordance with the present invention it nificant amounts of annonium sulfide, am 20 has been found that ammonium thiosulfate can monia, and alinmonium sulfite, When considered be dried at temperatures above those at which in the light Cf Corinnercial Specifications for am decomposition. Would ordinarily occur, if a.m.- monium thiosulfate. The percentages inay be of nonia is present in sufficient quantity in the the order of from 0 to 1% annonium sulfide, atmosphere in the drying chamber. The higher from 0 to 1.5% ammonia, and from 0.5 to 1% 25 the temperature of drying, the greater the pro annonium Sullfite. portion of ammonia, which must be present in The solution may contain a Small amount, of the atmosphere in order to prevent the dissocia colloidal sulfur, and is preferably therefore fil tion of the ammonium thiosulfate. We believe tered, With or without 2, prior adjustment by that the partial pressure of the annonia present the addition of annonium bisulfite. At this 30 must be at least as great as the dissociation point a controlled annount of annonium hy pressure of the ammonium thiosulfate at the ten droxide is preferably also added to aid in the perature of treatment in order to prevent dis preservation and stabilization of the annonium. sociation of the ammonium thiosulfate. As long thiOSulfate. The filtered Solution is ten ready as the ammonia, is present to at least this ex for sale as such, or may be used as feed for tent, the ammonium thiosulfate Will dry With the evaporator if crystalline anhydrous ann out, decomposition. However, Whatever the cor monium thiosulfate is desired. rect explanation may be, this drying may be Annonium thiOSulfate Solutions are unstabie carried out at atmospheric pressures, or under in the presence of heat, and concentration of vacuum, or by placing the thiosulfate in a cabi such solutions has in the past been carried out 40 net containing trays of a drying agent, such usually at temperatures in the neighborhood of as calcium oxide or merely in an ordinary heated 30° C. by operation under a high Vacuum. pipe drier, provided always that Sufficient an It has been found, however, that in accord monia, is present in the atmosphere. ance with the present invention, anmonillin In all of the above processes in which ammonia thiosulfate solutions can be concentrated at at is employed, the ammonia, is of course preferably mospheric pressure if this is carried out in the recovered from the moisture-laden atmosphere presence of ammonia, or of ammonium sulfite removed from the concentrating or drying cham or both. Pressures below atmospheric may be bers. employed if desired, but this is not necessary. The following description is given by Way of Aminonium thiosulfate Solutions may thus be example to indicate one form in which the in concentrated under at nospheric pressure by vention can be carried out: heating and simultaneously blowing annonia, 1800 pounds of water, 2890 pounds of am gas into the solution. The ammonia, is recovered Incrhium sulfite and 140 pounds of 28% ammo from the vapors.