Patented Dec. 22, 1953 2,663,621 UNITED STATES PATENT OFFICE 2,663,621 STA3EEZAON OF PERACDS Frank P. Greenspa, Buffalo, and Donald G. MacKeiai, Kentore, N. Y., assignors to Baf falo Electro-Chemical Company, Eric, Totaa warnia, N.Y. No Drawing. Application February, 2952, Seria No. 20,56 A Cairns. (C. 23-66) 2 This invention relates to the stabilization. Of It is a particular object of the present inven aqueous solutions of inorganic peracids. It is tion to stabilize peroxymonosulfuric acid by in particularly concerned with the stabilization of corporating small amounts of dipicolinic acid aqueous solutions of peroxymonosulfuric acid by therein. the employment of dipicolinic acid as a Stabilizer. Peracids differ in many in portant aspects from Peroxymonosulfuric acid, also known as Caro's peroxides, and the mechanism of decomposition acid, is an inportant and useful oxidizing agent. of the two classes of compounds also ShoWS pro Although known for a long time, peroxymonoSul nounced differences. In the special case of per furic acid has hardly found any technical use, oxymonosulfuric acid, decomposition may be rinainly because of the limited Stability of the acid O thought of as taking place in accordance With the as made heretofore. following general equations: Peroxymonosulfuric acid may be made by Var ious imethods, such as by treating a perOXydisul fate (such as the so-called potassium perSulfate) with concentrated sulfuric acid, by electrolysis of 5 a fairly concentrated Solution. Of Sulfuric acid, Or by direct action of concentrated hydrogen per oxide on concentrated sulfuric acid. This latter These equations explain why stabilizers here method has not received much attention in the tOfore employed and recognized as stabilizers for past, out today the commercial availability of hy 20 hydrogen peroxide are not effective as stabilizers drogen peroxide in concentrations as high as for peroxymonosulfuric acid. about 90%, concentrations not available in the past, makes this method particularly well Suited EXAMPLE for the preparation of peroxyimonosulfuric acid. Sodium stannate is an excellent stabilizer for We, therefore, prefer to make concentrated aque hydrogen peroxide; it is not, however, effective ous peroxymonosulfuric acid by the reaction be for stabilizing peroxynonOSulfuric acid, as shown tween 90% hydrogen peroxide and concentrated by the following: sulfuric acid, but other modes of preparation may be used. Concen- Percent Peroxymonosulfuric acid, as prepared by Our Stabilizer Tai IsferPeracid preferred method, may contain about 40% of FEFer Mith the inorganic peracid. In a typical case, the So Million 30° C. ution obtained when following Our preferred Sodium Stannate-------------------------- 50 29 method of preparation, contained 43% peroxy None-------------------------------------- None 24 monosulfuric acid, 3% hydrogen peroxide, 3% Water and 51% sulfuric acid. As With peracids 35 generally, increasing the resistance to deCOinpo EXAMPLE I sition, i. e., stabilization of the peroxymonosul A. Sample of relatively concentrated peroxy furic acid, has been found desirable. Inproved monoSulfuric acid Was prepared by reacting 1 stability of the peracid Solutions is not only in ino of hydrogen peroxide in form of its 90% portant in connection with handling, shipping 40 aqueous Solution. With i.5 rol. Sulfuric acid in and storing the moire concentrated Solutions of form of its 98% solution. The aqueous solution manufacture, but also in Connection. With the ac of perOXymonoSulfuric acid resulting within a tual use of the more diluted Solutions applied in few minutes time from this reaction was analyzed various reactions. and found to contain: It is a principal object of the present invention 45 Percent to provide an effective stabilizer for peroxy Peroxymonosulfuric acid ------------------ 43 monosulfuric acid of Substantially any strength, Hydrogen peroxide ----------------------- 3 but particularly for peroxymonosulfuric acid So Water ----------------------------------- 3 lutions containing substantial amounts of the Sulfuric acid ----------------------------- 51. peracid, whereby the same imay be handled, 50 A portion of this 43% peroxymonosulfuric acid shipped and stored in concentrations greater than Was divided into five partS. One of these served about 10% prior to dilution and Subsequent use, aS control or blank, the others were dosed with although the invention is applicable to the stabi Varying amounts of dipicolinic acid. All were lization of peroxymonosulfuric acid of any then stored in glass Stoppered Pyrex glass bottles strength. 55 at 30° C. for one month, whereupon the percent 2,668,821. 3 age loss of peracid was determined with the foll tion of about 250 to 750 parts per million of dipic lowing results as shown in the table. olinic acid will usually suffice in the average Table CaSe, Dipicolinic acid is generally recommended as Percent a stabilizer in the form of the pure acid; how TDipicolinic Peracid ever, the soluble salts, such as the alkali metal Sample Acid, Parts Loss Per Per Million Month at Salts, may be employed to this end, as can certain. 30° C. gouble salts, such as the double Salt with potas sium nitrate. It is believed that in Solution in 43% Peroxymonosulfuric acid.----------- None 24 the peracid dipicolinic acid itself is produced and D - 10 2. 100 0.0 functons as the stabilizer and, hence, is preferred, 500 10.2 By means of the present invention it is possible 1,000 80 to obtain stabilities for peroxyimonosulfuric acid which are not obtainable with any known per The amount of stabilizer to be employed Yay oxygen stabilizer. It is further possible to en vary considerably and may be from about 5 pairts ploy standard grade chemicals in the preparation per million to about 1000 parts per million, de of the peracid and by addition of dipicolinic acid pending upon the stability desired in the product, thereto form a peracid of commercially accept with the average quantity required to Stabilize able, highly improved stability. being in the neighborhood of 250 to 750 parts per 20 From the practical viewpoint, the in Veintion million of dipicolinic acid. will find wide applicability for the stabilization of The dipicolinic acid may be added to the ma commercial solutions of peroxyl ionosulfuric acid teral subsequent to its formation or inay be added from about 10% to about 43% strength. It Will to the ingredients prior to their reaction. No be understood, however, that the invention is material difference in effectiveness of stabilization 25 suitable for stabilizing peroxyisonoSulfuric acid appears to result from the enploymaent of these of ainy strength. modifications of manufacture. The production of a stabilizei peroxy incinoSull The following test shows that the dipicolinic furic acid inakes noise feasible those chemical acid is effective as a stabilizer in Substantially any reactions where Caro's acid finds specific applica dilution of the peracid. 30 tion, namely, the oxidation of primary armines to nitroso and to nitro compounds and as an oxidiz EXAMPLE ing agent for organic compounds of olefinic A further portion of the sane 43% solution of nature. w peroxymonosulfuric acid, as described in Ex What is claired is: ample II, was diluted with water to yield a 20% 3 5 1. The method of stabilizing percxynchoSul solution of the peracid. This 20% solution of the furic acid which comprises incorporating at least peracid was divided into two parts; one part Serv 5 parts per million dipicolinic acid therein. ing as a blank; to the other part was added an 2. A stabilized peroxyronosulfuric acid aque amount of dipicolinic acid corresponding to 000 ous solution containing at least 5 parts per Kail parts per inillion parts of the peracid. The 40 lion of dipicolinic acid as a stabilizer. samples were then stored in glass stoppered Pyrex 3. A stabilized peroxyria010Sulfuric acid ague glass bottles at 30° C. for one inonth, whereupon ous solution containing firona 250 to 750 paits per the percentage loss of peracid was determined million of dipicolinic acid as a stabilizer. with the following results: 4. A Stabilized per'OxynonOSulfuric acid aque ous solution containing from 10% to 43% peroxy monosulfuric acid and at least 5 parts per million Dipicolinic E. of dipicolinic acid. Sample Acirarts S.W.O. Er FRANK EP. GREENSPAN. Million ai". DONALD G. MiACKELAR. 20%. Peroxymonosulfuric acid ----------- None 17.0 D0---------------------------------- 1,000 9.0 References Cited in the file of this patent UNITED STATES PATENTS In general, the greater the amount of dipicolinic Nunbel Naine Date acid, the greater the stabilizing effect. The 5 5 2,363,778 amount of dipicolinic acid required to inpart a Pedersen ----------- Nov. 28, 1944 commercially acceptable degree of stability to the O'HER REFERENCES peracid will further depend on the initial in Yost and Russell 'Systematic Inorganic Cheta stability of the per'acid and the degree of Stability istry', page 372, 1944 Prentice-Hall, Inc., New desired in the final product. However, an addi York, N. Y. .