INDUSTRIAL AND ENGINEERING CHEMISTRY
1774
(6) DeBell, Goggin, and Gloor, “German Plastics Practice,” Spring-
(11)
field, Mass., DeBell and Richardson, 1946. Fieser, L. F., “Katural Products Relative to Phenanthrene,” 3rd ed., New York, Reinhold Publishing Corp., 1949. Flory, P. J., “Effect of Molecular Weight on Physical Properties,” Division of Paint, Varnish, and Plastics Chemistry, 117th Meeting, Anr. CHEM.,SOC., Detroit, April 1950. Fonrobert, E., Pette u. Seifen, 50, 514 (1943). Harris, G . C., J . Am. Chem. Sac., 70, 3671 (1948). Harris, G. C., T a p p i Monogrnph Ser., No. 6, Appleton, Wis., September 1947. Harris, G. C., and Sanderaon, T. F., J . Am. Chem. SOC., 70, 334
(12)
Hilditch, T. P., and Smith, C. J., J . SOC.Chem. Ind., 54, 1111
(6)
(7) (8) (9) (10)
Vol. 43, No. 8
Hultzsch, J., J . prakt. Chem., 158, 275 (1941). Krumbhaar, W., “Coating and Ink Resins,” New York, Reinhold Publishing Corp., 1947. (16) Krumbhaar, W., U. S.Patent 2,478,490 (Aug. 9 , 1949). (17) Mazzucchelli, A. P., Ibid., 2,413,412 (Dec. 31, 1946). (18) Oswald, F. G., Oficial Digest Federation P a i n t &: Varnish Produc(14) (15)
t i o n Clubs, KO. 608, 625 (1950). (19) Powers, P. O., IRD.ENG.CEIEM., 36, 1008 (1944). (20) Ibid., 42, 146 (1950). (21) Sprengling, G., Division of Paint, Varnish, and Plastics Chemistry, 118th Meeting, AM. CHEM.Soc., Chicago, September 1950.
(1948). (1935).
(13) Honel, H., J . Oil Colnw Ciicn. Assoc., 21, 247 (1938).
RECEIVEDSeptember 23, 1960. Presented before the Division of Paint, Varnish, and Plasticfi Chemistry a t the 118th Meeting of the AUERICAN CHE\IIC4L SOCIETY,Chicago, 111.
Autoxidation of Hydrazine J
EFFECT OF DISSOLVED METALS AND DEACTIVATORS L. F. AUDRlETH AND P. H. MOHR W . A . Noyes Laboratory of Chemistry, Unii:ersity of Illinois, Urbuna, I l l . Interest in the use of hydrazine as a specialty hydronitrogen fuel has made necessary a study of the stability of this substance, as both the aqueous and highly concentrated material, toward deterioration by atmospheric oxygen. Hydrazine undergoes autoxidation with the intermediate formation of hydrogen peroxide and eventual decomposition to nitrogen and water. This reaction is catalyzed markedly by dissolved copper. Metal deactivators which form very insoluble salts or stable complexes with copper can be employed as inhibitors. The more effective stabilizers include sulfide (added either as soluble sulfide or as elemental sulfur), Seques-
trene AA, dithizone, thiocyanate, potassium ethyl xanthate, p-tert-butylcatechol, and sodium diethyl thiothionophosphate. Polyamines are usable in dilute aqueous hydrazine, but are relatively ineffective in the highly concentrated material. It is recommended that 3 to 5 p.p.m. of the more effective deactivators be added to overcome the catalytic effects of any copper that may be introduced during the storage, shipment, and handling of hydrazine. Elimination of copper and copper alloys in equipment or apparatus designed for the manufacture, storage, handling, or use of hydrazine is desirable.
ONSIDERATZON of hydrazine as a specialty fuel has posed a number of problems with respect t o its stability during manufacturing operations, handling, storage, and use. Not only is hydrazine subject to catalytic decomposition by a number of active metals, specifically by nickel and cobalt ( I ) , but it also undergoes reaction with molecular oxygen. Such autoxidation of hydrazine results in deterioration of the product and loss in strcngtla both in dilute aqueous solution and in highly concentrated hydrazine. Although it was definitely proved by Cuy and Bray (4)that hydrazine reacts with molecular oxygen, no quantitative study of this phenomenon was made until Gilbert (6) and his students undertook to investigate autoxidation in dilute aqueous solution. Gilbert found that the autoxidation of dilute aqueous hydrazine always leads to the formation of some hydrogen peroxide as an intermediate, but that the over-all reaction yields nitrogen, water, and traces of ammonia; that the reaction is heterogeneous in nature; and that the rate of the reaction depende on the surface area of the solution, the partial pressure of oxygen above the solution, and the hydroxyl ion concentration. These observations were subsequently verified by Brown ( 2 ) in this laboratory and extended from the very dilute solutions employed by Gilbert (0.25 M ) to approximately 1 M solutions. Brown also established the fact that traces of copper exert a marked catalytic effect on the autoxidation of hydrazine, Actually, the dissolved copper content of distilled water, less than 0.5 p.p.m., greatly accelerated the autoxidation of dilute aqueous solutions. The experimental work presented below demonstrates that such autoxidation of hydrazine is markedly and uniquely catalyzed by dissolved copper; and that materials Fhich reduce the con-
centration of dissolved copper can be added to inhibit tlic catalytic effect, thus stabilizing both dilute and highly concentrated solutions of hvdrazine against deterioration and losa of qtrength. PROPERTI’ES OF HYDRAZINE
The physical properties of anhydrous hydrazinc are given in Table I. Hydrazine has a liquid range which is comparable to that of water, it has a relatively high density as compared with other fuels, especially hydrocarbon-type fuels, and its heat of combustion is high. The combustion products are nitrogen and water, whose average molecular weight is low compaied with products obtained when hydrocarbon fuels are used. Hydrazine is furthermore an endothermic compound, which factor contributes t o the energy value of hydrazine as a fuel but is, in part, an objectionable feature, as exothermic decomposition once initiated can be made to proceed most rapidly.
TABLE I. PROPERTIES OF HYDR~ZISE Melting point Boiling point , Density Heat of fusion Heat of vaporization Dielectric constant Heat of combustion
20
c.
113.5O C. (1 atm.) 1.014grams per cc. (15’ C.) 3 . 2 kg.-cal. per mole 10.7 kg.-cal. per mole (25“ C . ) 61.7 (25’ C.) 148.6 kg.-cal. per mole
The chemical properties of hydrazine must also be borne in mind during the handling and use of the material. Hydrazine is a powerful reducing agent and will effect reduction of many oxides, hydroxides, and compounds of the less active
August
1951
INDUSTRIAL AND ENGINEERING CHEMISTRY
metals to the metallic state. It is fortunate, however, that only nickel and cobalt among the common elements exert a catalytic effect on decomposition of hydrazine, so that even if corrosion products of copper, lead, bismuth, or silver should be present, reduction of these substances to the metallic states will not cause catalytic decomposition of hydrazine. Hydrazine is a basic substance, somewhat weaker than ammonia. It will therefore absorb carbon dioxide and other acidic gases from the atmosphere. Hydrazine is a strong coordinating agent, forming compounds containing hydrazine of crystallization, analogous to hydrates and ammoniates. Hydrazine is a hi hly polar substance, in contradistinction to such fuels as the hyjrocarbons. It is an excellent solvent for many inorganic and organic compounds, Pure hydrazine is a protophilic solvent. Hydrazine salts dissolve in anhydrous hydrazine and possess acidic character therein . From the Franklin point of view, hydrazine is a nitrogen analog of hydrogen peroxide, and is also related very closely to hydroxylamme. It is also one of the group of substances that are known as the hydronitrogens and may be considered the ethane analog in the hydronitrogen series. Consideration of hydrazine as a hydronitrogen fuel permits some rather interesting comparisons with the hydrocarbons. Both are susceptible to autoxidation and both will absorb oxygen with resulting deterioration. Small traces of dissolved copper catalyze tremendously the absorption of oxygen by both classes of fuels. In the case of the hydrocarbons, the catalytic activity of copper has been overcome by the addition of metal deactivators. The experimental work presented by the authors demonstrates that deterioration of hydrazine can also be inhibited, to the extent that dissolved copper catalyzes such reactions, by addition of suitable deactivators.
1775
sium iodate using amaranth as the internal indicator, (2) oxidation with iodine using starch as the indicator, and (3) neutralization with hydrochloric acid using methyl red or sodium alizarin sulfonate as indicators. Several complicating factors arose in the analysis of partially oxidized solutions of hydrazine. Ammonia and hydrogen peroxide form in small quantities. Ammonia causes no difficulty, as the iodate titration permits determination of hydrazine in the presence of other basic constituents. The combination acidimetric-oxidimetric procedure involving Methods 1 and 3 was used for the determination of both hydrazine and ammonia. The presence of any appreciable concentration of hydrogen peroxide does, however, lead to erroneous results, particularly if the iodate titration is used. Gilbert found that hydrogen peroxide in small quantities may be removed by adding sodium sulfite to an acid solution of the mixture. The excess of sulfite is then removed by boiling the solution to expel the sulfur dioxide. A new combination procedure was devised whereby both hydrogen peroxide and hydrazine can be determined conveniently in a single sample. Hydrogen peroxide was determined by making the solution 1 M in hydrochloric acid, adding potassium iodide, and titrating the released iodine with standard sodium thiosulfate. The iodine released under these conditions will not react with hydrazine at this low pH. The same solution is then made neutral with sodium bicarbonate and the hydrazine titrated with a standard iodine solution a t a controlled p H of 7 to 7.2. Hydrogen peroxide was present in such small amounts in most of the experimental runs that it did not create any appreciable error with respect to the hydrazine analysis. Only in a few experimental runs, where hydrogen peroxide was found to build up because of the presence of certain stabilizers, was it necessary to resort to this combination procedure.
AUTOXIDATION OF DILUTE AQUEOUS SOLUTIONS OF HYDRAZINE
In extension of the initial finding by Brown that traces of copper appear to catalyze the autoxidation of hydrazine, it seemed desirable to determine whether the effect of dissolved copper is unique or is shared by other dissolved metallic ions; whetherthe deterioration of hydrazine is a function of the copper concentration; and whether those substances which greatly reduce the concentration of dissolved copper, either because they serve as precipitants or as complexing agents or as adsorbents, might be added to hydrazine and thereby inhibit the catalytic activity of this particular metallic ion. EXPERIMENTAL PROCEDURES. A static test procedure was developed to evaluate these differcnt factors semiquantitatively. The tests were carried out using borosilicate glass volumetric flasks of 500-ml. capacity, filled with cylinder oxygen. A continuous flow of oxygen was maintained while various standard solutions were introduced into the flask to give a total liquid volume of 25 ml. After the final addition had been made, the oxygen tube was removed, and the flask was sealed and allowed to stand a t room temperature. usually for 24 hours; the liquid contents were then analyzed for unoxidized hydrazine, The original concentration of hydrazine was kept standard a t 0.5 M , thus allowing for a considerable excess of oxygen in the flask above that needed to effect complete autoxidation. ,411 containers were subjected to a thorough and uniform cleaning procedure. They were first given a 24-hour treatment with hot concentrated nitric acid, followed by repeated rinsin with redistilled water [ordinary distilled water contained too [igh a copper content (0.2 to 0.5 p.p.m.) to permit its use in this experimental work]. Before actual use the glass surfaces were conditioned by %-hour digestion with a dilute hydrazine solution. Only redistilled water was used to make additive solutions or dilutions. Any variation of this treatment was found to lead to irregular and unexplainable results. Furthermore, it was found necessary to discard reaction vessels from time t o time because of corrosive action of hydrazine and other reagents on the glass. ANALYTICAL METHODS(8). Three standard methods for the analysis of hydrazine were employed: (1) oxidation with potas-
TABLE11. EFFECT OF WATERAS DILUENTON AUTOXIDATION OF DILUTEHYDRAZINE (Hydrazine, 0.502 M ; sodium hydroxide, 0.02 M)’ Source of Water Redistilled
Laboratory distilled Redistilled Tap water
Copper Concentration
Nil
%
Time, Hours
Hydrazine Oxidized
11.0 25.0 47.5 72.5
26.6 59.8 83.0
Nil Nil Nil 8 X 10-6 iM 8 X 10-6 M 1 x 10-4 M
26.0 25.0 25.0
.......
25.0
99.8 97.4 96.0 99.6
89.8
EFFECTOF METALLICIONS.The importance of a source of pure water is evident from the data given in Table 11. Hydrazine samples were made up with laboratory distilled water; tap water; redistilled water;. and redistilled water to which was added an appropriate amount of copper(I1) chloride to correspond with the copper content of laboratory distilled water. Each solution was then made 0.02 M with respect to sodium hydroxide, as the reported maximum rate of autoxidation of dilute hydrazine occurs under these circumstances. Samples were analyzed for residual hydrazine. Examination of the data in Table I1 shows clearly the very potent effect of dissolved copper on the autoxidation of hydrazine. As little as 0.5 p.p.m. of copper exerts a marked influence on the extent of autoxidation. Extreme care had to be observed t o avoid the introduction of traces of copper with reagents and in the dilution of test solutions, as well as cleaning of test containers in order to obtain repioducible results. Copper is not necessarily unique in its catalytic action in other autoxidation processes. The static procedure was used t o test other metallicions, specifically those which are capable of existing in more than one valence state and are known to be reducible by hydrazine. Results are presented in Table 111. Dissolved cop-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1776
Vol. 43, No. 8
OF CONCEXTRATION OF DISSOLVED COPPER TABLE IV. EFFECT ON AUTOXIDATION OF DILUTE HYDRAZINE SOLUTICSWS
(Hydrazine, 0.5006 M : time, 6 hours) Molarity of Dissolved Hydrazine Copper" Oxidized
I 80
70
J
-
/IO-~M
cu
10-2 10-8
i o -4
-
a
10 - 5 10-5 Nil Added as copper(11) chloride.
65 61 64
44 21
4
z
0 60l-
a
0
pX 5 0 3
a
T I M E I N HOURS
Figure 1. Effect of Concentration of Dissolved Copper on Autoxidation of Dilute Aqueous Hydrazine Temperature 25' C.
per is by far the most active catalyst. Only vanadium appears to approach copper in itJs ability to catalyze the autoxidation reaction.
OF METALLIC IONS ox AUTOXIDATION OF TABLE 111. EFFECT DILUTEHYDRAZINE SOLUTIONS
(Hydrazine, 0.5045 M ; dissolved metal Concentration, 10-6 AM; time, 19 hours) To Hydrazine Oxidized Metal Added a8 39 None 40 Tungsten, WOd-42 Nickel, S i + + 46 Manganese, Mn + 48 Iron, Fe 49 Cobalt C o + + 50 Molybbenurn, &fool-52 Chromium, Cr 86 Vanadium, VOa85 Copper, Cu +
+
+
+
+
++
The catalytic behavior EFFECT OF COPPERCOKCENTRATION. of copper was studied in more detail in order to evaluate such factors as time and concentration with respect to the extent of autoxidation of dilute hydrazine solutions. I n the f i s t series, the concentration of added copper (as cupric chloride) was varied from 10-2 to 10-8 M . A blank of pure hydrazine diluted with redistilled water was included in order to permit ready comparison. The initial concentration of hydrazine was 0.5006 M . The percentages of hydrazine oxidized in each test sample after 6 hours are given in Table IV.
n'ithin certain limits the extent of autoxidation is definitely a function of the concentration of copper. The percentage of hydrazine undergoing oxidation increased up to a concentration of about 10-4 M added copper; increase in copper concentrations beyond this value had no effect. Visual observation of changeb in the appearance of the test solutions may explain these results M with respect t o disThe blank and solutions 10-6 and solved copper remained perfectly dear. A trace of red precipitate developed in the sample contaifiing PO-4 copper. Proportionally greater quantities of precipitate formed in the sarnplep containing still higher concentrations of dissolved copper. Thk observation indicates that concentrations of dissolved copper probably in the cuprous state, cannot exceed 10-4 iM in such hydrazine solutions. The extent of autoxidation of dilute hydrazine solutions colitaining copper, as a function of time, was next investigated. REsults, depicted graphically in Figure 1, show conclusively that an increase in the concentration of dissolved copper causes more rapid deterioration of dilute hydrazine solutions. The blank (containing no added copper) is particularly interesting, because the autoxidation is relatively slow initially, suggesting that 811 induction period precedes the normal reaction. Results given above show EFFECT OF COPPERDEACTIVATORS. conclusively that the deterioration of hydrazine becomes more serious as the concentration of dissolved copper in the solution it. increased. It may therefore be assumed that any substance which will greatly reduce the concentration of the catalytirallj active species, be it copper in the cupric or cuprous state, should be effective in retarding or inhibiting the autoxidation of hydrazine, Three classes of substances were considered: reagentc which form compounds whose solubility product constants are 60 small as to preclude the existence of any appreciable concentrstion of copper ions in solution; substances which are known to form very stable complexes with either cupric or cuprous ion; and materials which presumably adsorb metallic ions and thereby re move them from active participation in any mechanism involving the reaction of hydrazine with oxygen. A preliminary investigation was first undertaken t o determinr the effect of certain complexing agents as copper deactivatom The static procedure was again employed. Laboratory distilled water (containing approximately 8 X 10-5 LM dissolved copper) was used as a source of copper ions; the inhibitor concentration of approximately 10-2 M was chosen arbitrarily to give better than a, thousandfold molar excess of complexing agent over the copper content. Test solutions nere made up with a hydrazine concenis, pertration of 0.635 M . The extent of autoxidation-that centage hydrazine oxidized-was determined after 24 hours These data are summarized in Table V. The various complexing agents are listed in the order of decreasing effectiveness. The peroxide content of residual hydrazine solutions was also determined. Peroxide content was found to be very low, except when 8-quinolinol (8-hydroxyquinoline) was used as an inhibitoi In this case the hydrazine and peroxide concentrations in the residual solution were found by analysis to be 0.369 and 0.097 M , respectively. For every mole of hydrazine that had been oxidized, 0.365 mole of peroxide had heen formed.
INDUSTRIAL AND ENGINEERING CHEMISTRY
August 1951
T.4BLE
v.
AUTOXIDATION O F DILUTE HYDRAZINE SOLUTIONS
ACTIOri OF INHIBITORS ON
(Hydrazine, 0.635 M ; inhibitor, 10-2 M ; copper concentration, 8 X 10-6 M ; time, 24 hours) Hydrp en % . ~eroxitfee~, Hydrasine Molarity Oxidized Inhibitor 4 0.001 Thiourea 0.004 6 Sodium thiocyanate 0.001 Propylenediamine 0,001 16 Ethylenediamine 0,001 10 Diethylenetriamine 0.010 a-Phenanthroline 16 0.001 16 Bip yridine 0,001 17 Glycine 0.002 31 Sodium citrate 0.004 36 Sodium tartrate 0.097 42 8-Quinolinol 0.001 61 Pyridine 59 0.001 Blank After 24 hours in residual solution.
1777
quantity of copper present. Several of the inhibitors appear to be outstanding: potassium ethyl xanthate, thiourea, sodium cyanide, sodium stearate, sodium sulfide, and sodium thiocyanate. The polyamines, propylenediamine, ethylenediamine, and diethylenetriamine, do not appear to be so effective. Gelatin, o-phenanthroline, bipyridine, potassium ferrocyanide, and glycine may be classed as intermediate in effectiveness. The others, which include stannic chloride, acetanilide, sodium pyrophosphate, ammonia, sodium dithionate, ammonium aluminum sulfate, mannitol, and sodium sulfite, appear to have little or no inhibitory properties. Only small amounts of hydrogen peroxide were formed in these particular runs. A very small quantity of red sediment was also detected in some of the samples. Formation of this red sediment seemed qualitatively to occur more readily and more frequently in the more completely oxidized samples. AUTOXIDATION OF HIGHLY CONCENTRATED HYDRAZINE
The amazing and surprising effect of 8-quinolinol and several d h e r materials, among them plert-butylcatechol, on the stabilization of hydrogen peroxide, even in the presence of hydrazine, was checked subsequently by a series of qualitative experiments. tnteraction of equimolar dilute aqueous solutions of hydrazine and hydrogen peroxide is fairly rapid, as evidenced by vigorous evolution of nitrogen gas (7). If, during the course of this reaction, a crystal of 8- uinoljnol is added to the solution, the rate of gas evolution is magedly decreased. If 8-quinolinol is added to either the hydrazine or the hydrogen peroxide solution prior to mixing, the evolution of gas decreases markedly. Actually it takes but a very small amount of this particular material to stop completely the reaction between hydrogen peroxide and hydrazine. This most unusual and perhaps very significant finding is heing subjected to study, in the hope that the mechanism of autoxidation reactions in general can be thereby elucidated. In a more extensive series of experiments the copper concentration was raised t o lo-'; the concentration of inhibitor was not changed ( l o + M). Test solutions now contained a 100 M excess of inhibitor over dissolved copper. This change was made to bring out greater differences in evaluating the effectiveness of these materials in removing copper. Results of these experiments are summarized in Table VI. For the same inhibitors the extent of autoxidation is slightly higher than in the previous series. This may be attributed to the relatively smaller excess of the inhibiting agent used over the
In extending this investigation from dilute hydrazine solutions to the highly concentrated base, it was recognized that the change in the nature of the medium might produce effects different from those observed previously. Highly concentrated hydrazine constitutes a solution of water in hydrazine as the solvent. Metallic ions are hydrated in aqueous solution, but are converted into hydrazine complexes in concentrated hydrazine. In highly concentrated hydrazine it remained to be determined if those agents which served as inhibitors in dilute aqueous hydrazine, because of their complexing action for copper, could still do so in competition with the enormously greater solvent concentration, the solvent itself being an excellent coordinating agent. The study of the autoxidation of concentrated hydrazine was patterned after the investigation in dilute solutions. The effects of various metallic ions on the oxidation rate and of inhibitore (metal deactivators) to counteract these catalytic effects were studied. EXPERIMENTAL PROCEDURES. A dynamic procedure wae employed to study autoxidation of highly concentrated solutions
The pressure of oxygen over the test solution was kept constant a t 1 atmosphere during each experimental run. Because large numbers of copper deactivators were to be evaluated, an apparatus was designed so that six different samples could be subjected to the action of oxygen a t the same time. Ten-milliliter weighing bottles, each containing 5.1 ml. of 96% hydrazine (30 M),were placed in a small aluminum desiccator, the cover of which was fitted with an inlet tube extending t o within a few millimeters of the bottom. A small outlet hole was located in the TABLEVI. COMPARATIVE EFFECTIVENESS OF VARIOUS COPPER desiccator cover. This apparatus was placed in a constant ON AUTOXIDATION OF DILUTE HYDRAZINE temperature bath a t 25' C. A stream of oxygen was passed DEACTIVATORS SOLUTIONS through this apparatus at a regulated rate of 25 cc. per minute. The surface area of each test solution was 4.5 sq. cm. Samples of (Original hydrazine concentration, 0.500 M : deactivator concentration, 1 0 - p M ; copper concentration, 10-4 M ; time, 24 bours) test solutions were removed a t definite time intervals for analysia. Two standard samples, one consisting of pure hydrazine and Qm. Hydrazine another containing 10-4 M dissolved copper, were included in Copper Deactivator Oxidized each series of six test solutions. Because slight variations did Potassium ethyl xanthate 4 occur from series to series it was considered desirable to compare Sodium stearate 8 results within a single seAes. It was felt, however, that reasonThiourea 11 ably reproducible results could be attained by the experimental Sodium cyanide 13 Sodium sulfide 14 procedure used in the present investigation. For eleven different Sodium thiocyanate 14 series the percentage hydrazine oxidized after 120 hours averaged ProDvlenediamine 19 44.2 =t4.2%; for samples containing lo-* M added copper, Ethblenedianiine 20 Dietbylenetriamine 22 oxidation amounted to 91.1 * 3y0. Gelatin. o-Phenanthroline Di yridyl & i o n ,BU Potassium ferrocvanide Glycine Trilon ~ ....Ab ~~
Sodium formate Stannic chloride Acetanilide Sodium pyrophosphate Ammonia Sodium dithionate Ammonium aluminum sulfate Mannitol Sodium sulfite Blank a Derivative of ethylenediaminetetraacetic acid. b Derivative of nitrogen triacetic acid.
30 31 34 41 46 48
53 ._
80 80 84 87 95 96 96 96 98 98
EXPERIMENTAL RESULTS. Data presented in Table VI1 show that highly concentrated hydrazine undergoes a reaction with oxygen which is catalyzed by the presence of dissolved copper [added as copper( 11) chloride]. The catalytic effect becomes evident when the concentration of dissolved copper is greater than 10-8 M . Addition of soluble iron(II), cobalt(II), chromium(III), vanadium(V), and nickel( 11) compounds does not accelerate the autoxidation of hydrazine. Dissolved copper is therefore unique among those metals tested in its catalytic effect. Figures given in Table VI1 represent the per cent hydrazine oxidized after 120 hours of exposure to oxygen a t a pressure of 1 atmosphere a t 25" C.
INDUSTRIAL AND ENGINEERING CHEMISTRY
1778
Vol. 43, No. 8
most useful deactivator 011 a n eight basis and would thus bc pieferred over sodium sulfide. Complexing agents for both divalent and univalent copper (a preliminary polarographic study of dissolved copper in hydrazine ievealed that the metal is picsent in the univalent state) ale 81.0 vert effective and constitutc the majority of the better deactivatois. These include Sequestrcne AB (ethylenediamine tetraacetic arid), dithizone, thiocyanate, potassium ethyl xanthate, thiouiea, p-kit-butylcatechol, sodium diethyl thiothionophosphatc,. tetiarthyl dithionotrithiodipliosphate. Solutions containing sodiuni c I niiidr and ethylenediaminc 10veal interesting differences fioin their behavior in dilute aqurous hydrazine. The cyanide ion i q initially a good inhibitor, but gradually appears to undergo oxidation, after v, hich it is no longcar effective. Ethylenediamine does not become effective until aftrr the concentration of hydiazine has been reduced by oxidation It is evident that i t cannot displace initially coordinated hydrazine from the hydrazine-copper(1) complex, which must be present in highly concentrated hydrazine and must represriit the catalytically active Epeciet
32t
TABIX
VII. EFFECTOF -4DL)ITIT'ES ON AUTOXIDATIOK HIGHLY CONOBNTRATED HYDRAZINE (Teiiip., 25'
Additive
25
50 75 TIME I N HOURS
IO0
None Copper(I1) chloride, 10-7 Ji' Copper(I1) chloride, 10-6 ,tl Copper(I1) chloride, 1 0 - 6 M Copper(I1) ohloride, 10-4 L ' Copper(I1) chloride, 1 0 - 8 31 Iron(I1) ammonium sulfate * Cobalt(I1) chloride6 Chromium(II1) chlorideh Ammonium metavanadatc'l Nickel(I1) ohlorideb Potassium iodide Catalase, 2% 8-Quinolinol Average of eleven runs. Concentration, 10-4 M .
I25
Figure 2. Effect of Copper Deactivators on Autoxidation of Highly Concentrated Hydrazine Hydrazine 30 M Deactivator 10-2 M Copper 10-4 M Temperature 25' C.
Because the reaction between highly concentrated hydraline and oxygen presumably proceeds with the intermediate formation of hydrogen peroxide, the enzyme catalase (obtained from the Vita-Zyme Laboratories, h e . , 546 West Washington Boulevard, Chicago 6, Ill.) was added in very low concentration to bring about more rapid destruction of the peroxide. Potassium iodidck has also been found to catalyze oxidation reactions involving hydrogen peroxide. &Quinolinol had been shown to stabilize thtb hydrogen peroxide formed as an intermediate in the autoxidation of dilute aqueous hydrazine solutions. Each of these was added directly to samples of pure hydrazine. The data show that the basic oxidation rate is not influenced by 8-quinolinol, potassium iodide, or catalase in pure hydrazine solutions. No evidence of peroxide formation was found in the sample containing 8-quinolinOl.
Complete data were collected relating extent of autoxidation under given experimental conditions against time. Typical curves depicting the course of the autoxidation process are given in Figure 2. Figures foi the per cent hydrazine oxidized after 120 hours were arbitrarily interpolated from such curves to permit comparison of the influence of various additives and inhibitors. As hydrazine is replaced upon oxidation by a somewhat larger weight of water (32 grams of NzHl +36 grams of H20), the nature of the medium undergoes a profound change as autoxidation proceeds-from essentially anhydrous hydrazine to a mixed solvent containing increasingly greater amounts of water. The data given in Table VI11 show that complexing agents and/or precipitants are again the most effective copper deactivators. Elemental sulfur is soluble in hydrazine and reacts to yield a solution containing sulfide ion (6). I t would appear to ti(, t h r
C.)
OF
% Hydraeine Oxidized after 120 Hours 44.2 ~ t 4 . 2 ~ 43 44
63 91.1 i 3" 97 40 39 43 38 40 38 40 39
Benzaldehyde, as M t j pic2il riltit41yde, is converted Into the azine by hydrazine. Thew wl-wtaricaeb form very stable coniplexeb with copper and may thub berve as inhibitors. Sodium monothiodiethyl phosphatr ifi riot Qopffective as an inbibitor aa the related thionothiophosphate. 0ctamethylpyrophosphor:c mlde, diethyl phosphite, and riipfei ron are ineffective.
'Y-~BTIE VIII.
COPPER D~.%C'PI-\~ATo€LS AND AUTOXIDATIOS OF HIGHLY C O S C D V T R 4 T E D HYDRAZINE
(Inhibitor concentration 10-2 .If. dlssolved copper, 10-4 iM ea oovver(I1) cdloride. t&mnerature, 2.5' C.) Hydrazine xidized after 120 Hours Inhibitor 44.2 f4.2 Blanka 91.1 f3 Noneb 49,42 p-tert-Butylcatechol 45 Sodium sulfide 42 Potassium ethyl xanthate 46 Dithizone 42 Sequestrene AA 40 Sulfur 46 Sodium thiocyanate 53 Sodium diethyl thiothionopnusynate Thiourea 56 57 Tetraethyl dithionotrithiodiphmphate 59 8-Quinolinol 61 Benzaldehyde 67 Ethylenediamine 72 Sodium dieth,yl thiophosphsre 75 Sodium cyanide 81 Diethyl hosphite 86 Ootamet~ylpyrophobphoralnlrie 88 Cupferron Contains no added cop er 1 0 - i .V dissolred copper. h Contains no inhibitor,
6
Q
INDUSTRIAL A N D ENGINEERING CHEMISTRY
August 1951
As hydrazine undergoes autoionization in accordance with the equilibrium 2N2H4
* NzH6+ + N2Ha-
(2Hz0
F=
H30+
+ OH-)
it is the hydrazonium ion which is the analog of the hydronium ion and represents the solvated proton (acid species) in hydrazine. Solutions of hydrazine salts in hydrazine are therefore acidic in character. Neither the nitrate nor the chloride brings about a change in the basic autoxidation rate of hydrazine. The data given in Table I X demonstrate that solutions of hydrazine salts in highly concentrated hydrazine inhibit somewhat the catalytic action of added copper salt.
TABLEIX.
EFFECTOF HYDRAZINE SALTS ON AUTOXIDATION ow HIGHLYCONCENTRATED HYDRAZINE
(Time, 120 hours; added co per catalyst, 10-4 M , as CuCla; hydrazine salt, 1 2 . temperature, 250 c.)
Catalyst CU.Cl, CUCll Cl’dll
...
Hydrazine Salt
....... .......
NaH4. HCl N2Hd. HCl NnHp. HNOa NzHi. HNOa
75.
Hydrazine Oxidized 39 92 59
37 65
1779
times greater on a molar basis than the amount of copper used-in order to test the effectiveness of potential inhibitors. Experimental tests to inhibit autoxidation of solutions containing dissolved copper concentrations of the order of 0.1 to 0.5 p.p.m. were not carried out. It may be assumed, however, that the data with respect to the effectiveness of inhibitors will hold equally well for the much smaller copper concentrations encountered in practice and that additions of the order of 3 to 5 p.p.m. of inhibitor will be more than sufficient under all normal conditions to overcome the catalytic effect of any copper which may inadvertently be introduced during the storage, shipment, and handling of hydrazine. Byrkit and Michalek (3) state that “copper is satisfactory [for use with hydrazine] if provision is made for padding with nitrogen.’, Where contact with the atmosphere cannot be avoided, however, it is desirable t o eliminate use of copper tubing, copper alloys, such as brass and bronze, and copper and copper alloy fittings in any equipment or apparatus used for the manufacture, storage, handling, or use of hydrazine. It is certainly desirable that air be replaced by nitrogen in containers that are t o be used for shipment or storage of hydrazine. This is recommended not only to prevent oxidation of hydrazine, but also as a safety measure toeliminate the possibility of explosive decomposition.
40 ACKNOWLEDGMENT
The unique catalytic effect of dissolved copper on the reaction between hydrazine and oxygen can most simply be explained by a copper( I)-copper( 11)redox equilibrium. The catalytically active species is assumed to be copper(1) hydrazine complex, which serves as an oxygen molecule acceptor. Intramolecular decomposition would yield initially the 0 2 - ion and the Cu(I1) ion. The latter immediately oxidizes hydrazine and is thereby reduced to the Cu(1) state. RECOMMENDATIONS FOR HANDLING HYDRAZINE
The experimental results presented above lead to definite conclusions with respect to the storage and stability characteristics of highly concentrated hydrazine. Because it may be difficult t o avoid exposure to the atmosphere a t some stage during the handling or use of highly concentrated hydrazine, additions of 3 to 5 p.p.m. of some of the more effective inhibitors may serve to overcome the catalytic effect of traces of dissolved copper. The experimental work carried out by the authors made use of copper concentratiohs which are of the order of a hundred to a thousand tinies greater than normally found in tap water or distilled water. The amounts of inhibitors used in these tests were a hundred
The authors desire to express their gratitude for a fellowship grant made available (to P. H. M.) by the Western Cartridge Co. Division of Olin Industries, to the Victof Chemical Works for furnishing samples of various phosphorus chemicals, and to the Ordnance Corps of the Department of the Army in sponsoring the final phases of this research program. LITERATURE CITED
Audrieth, L. F., and Jolly, W. L., J . Phys. and Colloid Chem., 55, 524-31 (1951). Brown, E. A., thesis, University of Illinois, 1947. Byrkit, G. D., and Michalek, G. A., IND.ENG.CHEM.,42,1862-75 (1950).
Cuy, E. J., and Bray, W. C., J . Am. Chem. SOC., 46, 1786-95 (1924).
Ephraim, F., and Piotrowski, H., Ber., 44, 386-894 (1911). Gilbert, E. C., J . A m . Chem. SOC.,51,2744-51 (1929). Gordon, J. S., “Reaction between Hydranine and Hydrogen Peroxide in the Liquid Phase,” presented a t Third Symposium on Combustion, Flame and Explosion Phenomena, University of Wisconsin, Sept. 7 to 11, 1948. Penneman, R.A.,and Audrieth, L. F., Anal. Chem., 20, 1058-61 (1948). RECEIVED November 10,1950. Abstracted from a thesis submitted by P. H. Mohr to the Graduate School of the University of Illinois, June 1950.
Artist’s Conception of Army Air Force Supersonic Rocket-Propelled Airplane
