NOTES
1904
Vol. 65
TABLE I EMPIRICAL CONSTANTS AND MOLARPOLARIZATIONS IN BENZENE SOLUTION AT 25' Compound
Ethyl nitrate l,%Dinitroxyethane 1,3-Dinitroxypropane 1,4-Dinitroxybutane 1,SDinitroxypentane 1,6Dinitroxyhexane 1,2-Dinitroxypropane l,>Dinitroxypentane Nitroglycerin 2,%Bis-.(nitroxymethyl)1-nitroxypropane 2,>Bisr:nitroxymethyl)3-nitroxy-1-propanol
tD
b
a
VP
Pm
E: (obsd.)
II
(obsd.)
2.2584 2.2524 2.2019 2.2133 2.2397 2.2519 2.2469 2.2727 2.2597
1.14494 1.14474 1.15254 1.14450 1.14537 1.14509 1.14375 1.14524 1.14558
10.06 8.91 7.77 7.38 7.48 7.15 9.92 9.26 5.33
-0.19 .47 .52 .39 - .36 .33 .40 - .36 .51
199.3 287.6 282.7 296.4 322.2 332.8 349.6 384.8 272.0
20.4 26.4 30.0 35.2 39.9
41.7 39.1
2.96 3.58 3.52 3.58 3.72 3.76 3.95 4.10 3.38
2.2673
1.14531
4.76
.46
281.5
47.1
3.39
2.2690
1.14609
5.57
.49
337.6
48.4
3.76
-
44.0 30.8
p
(lit.)
2.911 3.28' 3.14'
3.72* 3.16'
normal aliphatic mononitrate esters occurs a t n- encies in the literature concerning the possible propyl nitrate ( p = 2.98 D ) . l 0 This would give a hydrates of Cu(en)eS04. Werner2 prepared Culimiting value for the polymethylene series as p = (en)$Oc by decomposing the ion formed when ex4.1 D. Table I, based on the present study, shows cess ethylenediamine was added to aqueous copper sulfate: he considered this ion to be Cu(en)a++. the observed increase for the series O&O-(CH,)nUpon dilution of this solution and addition of exONOZ, as n goes from 2 to 6. A second general trend is not*iced among the cess ethanol, a violet crystalline solid was formed dipole moments of the compounds: 1,2dinitroxy- which was assigned the composition Cu(en)$O~ ethane ( p = 3.58 D), 1,Zdinitroxypropane ( p = 2H20 by Werner. Johnson and Bryant3 observed 3.95 D) and l12-dinitroxypentane ( p = 4.10 0). that addition of ethanol to an aqueous solution of Here, evidently, the dipole moments increase as the ethylenediamine and copper sulfate gave a violet size of the a,ttached chain increases. De Kreuk2 crystalline substance which they analysed to be measured thie dipole moment of 2,3dinitroxy- C ~ ( e n ) B 0 ~ . 4 ~ / ~ This H ~ 0 substance . slowly efflobutane a t 20° and found a value of p = 4.12 D. resced to give the anhydrous salt a t room temperaThis lends same support to the simple assumption ture. I n addition, both workers found that the t,hnt increased side-chain size is accompanied by an other solids of various blue colors were obtained increased dipole moment. This effect ha.- been ob- by the addition of ethanol under various conditions, among which was a material to which Johnson and served also with aliphatic dihalides. 11,12 The dipole moments of nitroglycerin, 2,Z-bis- Bryant ascribed the composition of C ~ ( e n ) ~ S 0 ~ . (nitroxymethy1)-1-nitroxypropane and 2,2-bis-(ni- 2Hz0. Some time ago there were reported4 the magnetic troxyme th yl) -3-nit rox y- 1-propanol were cd(:ulat,ed by assuming free a nitroxy group moment properties at low temperatures of Cu(en)$O4 of 2.73,? n C--0 bond moment of 1.14, and a, NOC and its stable hydrate, which we found to be lmitd niiglc of 110'. The respective values of 4.78, Cu(en)B04.4H20. More recently Gordon and 4.74 and 3.06 indicate considerable restric1,ion of Birdwhistel15reported a study of the complexes of copper with ethylenediamine, in which they stated free rotation in these compounds. that they were unable to obtain a stable hydrate of (10) C . P. Sinyth, "Dielectric Behavior and Structure," McGrawCu(en)B04. I n view of the uncertainty about the Itill Book Co., In?., New York. N. Y., 1955, p. 288. (11) M . I,. Flierrill, M. E. Smith and D. D. Thompson, J . Am. cxistence of this hydrate, we are reporting its Chem. S o c . . 66, ( i l l (193-11. preparation and properties in detail. We take (12) A. A. hlsryott, M. E. Ihbbs and P. M. Gross, ibid.. 63, 059 this opportunity also to present further observa( 1941). tions on the interesting magnetic properties of (13) 11. Eyring. P h y s . Reo., 39, 746 (1932). the anhydrous material.
IIY1)ltATED AND ANHYDROUS ~ISETkIlrlLENE~IAMINE-COPI~ER(11) SULFATE BY L. V. (GREGOR,J. J. FRITZ AND P. E. FIELI) Publicofion No. 120 from the Cryogenic Laboratmy. College of Chemisfry and Physics, The Pennsylvania State Unioemty, Unisersifg Park, Pcnna. Raeiocd A p d 14. 1961
The complex ion bisethylenediamine-copper(II), abbreviated to Cu(en)z++,is quite stable in aqueous solution, and many of its salts have been prepared and studied.' However, there have been inconsist(1) N . V. Sidgvrick, "Tho Chemical Elements and Their Cornpounds," Vol. 1, Oxford. 1950, pp. lfi3--lGk,A. Martell and M. Calvin, "Chemistry of the Metal Chelate Compounds," Prentice-Hall, New York. N. T. 1952, p. 286.
Preparation of Bisethylenediamine-copper(I1) Sulfate.-The hydrate of Cu(en)rS04was prepared from an aqueous solution containing reagent grade copper sulfate pentahydrate and redistilled ethylenediamine (h.p. 116.9", lit. 118.0') in a 1:2 mole ratio. A typical preparation involved 2.5 moles of copper sulfate pentahydrate and 5.0 moles of ethylenediamine in 700 ml. of H20. After evaporation on a steam-bath to about 100 ml., the solution was cooled in ice for several hours, resulting in the formation of several hundred grams of large blue-violet, crystrtls. These crystals were filtered on a Buchner funnel by suction, pressed dry with filter paper, and dried further by shaking in a box lined with absorbent paper. Although stable in a stoppered (2) A. Werner, 2. anorg. u. allgem. Chcm., 11, 201 (1899). (3) C. H. Johnson and 9. A . Bryant, J . Chem. Soc.. 1783 (1934). (4) J. J. Fritz, R. V. G . Rao and S. Seki. J . Phgs. Chem., 61,703 (1 968). ( 5 ) G . Gordon and H. Birdwhistell. J . Am. C h e w Soc., 81, 3567 (1959).
Oct., 1961
NOTES
1905
2 . A reverse titration was made a t 0’ in which the water content wfts reduced in five steps to 3.84 moles of water per mole of salt. Above 4.0 moles of water the vapor pressure was 3.9 mm.; below this composition it fell sharply to 2.4 mm. 3. The vapor pressures of a mixture containing 4.45 moles water/mole salt (tetrahydrate-solution) and of a mixture containing 3.85 moles water/mole salt (anhydrous-tetrahydrate) were measured a t five points between 0 and 25’. In both titrations and the vapor pressure measurement it was found necessary to wait a t least an hour for equilibrium after each addition of water or change of temperature. I n all cases the pressures were observed for at least three hours to ensure equilibrium. The vapor pressures of the anhydrous-tetrahydrate system obeyed the linear equation log P mm. = -2685/T 10.214 within their expected accuracy (0.1 to 0.2 mm.), with only random deviations. From this we conclude that the heat of dehydration is about 49,200 cal: per mole of tetrahydrate (12,300 cal. per mole of water) and that the Analytical Results.-The determination of Cu entropy change of the dehydration reaction is about iv:ts carried out electrolytically,6 by using a Fisher 33 gibbs per mole of water. (Since the vapor presElectroanalyzer and platinum electrodes. The sures were measured primarily to establish the difficulty of drying the hydrate completely without nature of the phases present, they were not measdecomposition. caused the percentage of Cu in this ured as accurately as possible, we estimate the material to vary over a much wider limit than would uncertainty of the heat of dehydration as about 3% be expected for such a relatively accurate deter- and that of the entropy change as 5%.) The vapor mination. Tlie results are given in Table I. pressure at 2 5 O , from the log P-l/T plot, is 16.3 rt 0.3 mm. TABLE I The vapor pressures of the tetrahydrate-satuCalcd. Cnnipound Exr. % cu % Cu No. of dctns. rated solution system also fitted a log p us. 1/T Cu(er1)nSOa 22.55 f 0.10 22.79 4 plot and corresponded within 0.1 nim. to the equaCu(eri)~SO4~4II2O 17.89 I 0.20 18.07 11 tion log P mm. = -2267/T +8.899. Coniparison of the two vapor pressure equations indicates that Loss of water on heating in an oven a t 105’ or the tetrahydrate should become unstable with decomposition into a vacuum gave an avrragc of respect to anhydrous material and saturated solu20.7y0 HzO (calcd. for C ~ ( e n ) ~ S 0 ~ . 420.487Q). H~0 tion somewhat below 45’. Cooling curves on a It was not found possible to obtain a sharp end- mixture of salt and saturated solution established point in a potentiometric titration (against HCl) the transition point as 42.8’. for ethylenediamine, but the amount of the amine Discussion was found to be about 36% (calculated value 34%). The vapor prc’ssure invcstiga tion dtwx3xd Phase Behavior.-In order to establish clearly the composition and range of stability of the hy- above indieatcs clearly that Cu(en)&3Oa 4IIzO is drated salt, a phase study was made of the system the stable hyclratctl phase of Cu(en)zS04a t ordiCu(en)2S04-Hz0 between 0 and 25’. This investi- nary temperatures, and that the water caii bc added or removed readily and reversibly. The gation consisted of three parts: 1. A specimen of anhydrous Cu(en)$04 was nature of the results gives hints as to why other inthoroughly dried on a vacuum line and then vestigators of this system have obtained negative “titrated” with water a t 24.90’. Tlie vapor prossure or ambiguoiis results in their efforts to obtain of the system was observed after each of 13 small hydrates. In the first place, the relatively low increments of water had been distilled in. The ob- decomposition temperature of the tetrahydrate servations covered the range of 0 to 4.5 moles (about 50’) will prevent getting the hydrate by water per mole of salt; the amounts added were evaporation of solutions above this temperature. observed volumetrically, and checked by weighing Second, the vapor pressure of the tetrahydrate at 1.86, 3.88 and 4.45 moles per mole of salt, with (16.8 mm.) a t 25’ is rather high. (The vapor presvolumetric obs,ervations used only for interpolation. sure of pure water a t this temperature is only 23.8 The vapor pressure of the system remained con- mm.) Consequently the addition of a material stant from the first addition to 4.0 (+0.05) moles such as ethanol to precipitate the salt a t room temof water per mole of salt, then rose sharply to a perature is quite likely to reduce the activity of second plat,eau where it again remained constant as water below that required for the hydrat(A. Finally, the extreme solubility of the salt mnkcs it solution was formed. difficult to prepare the hydrate from solutiun. (6) H. H. Willard and N. 11. Furman, “Eleirientary Quantitative We could do so only by chilling a solution preAnalyais,” 3rd Ed.. D. Van Nostrand Co., New York, N. Y.,1940, viously concentrated by evaporation. We have p. 431.
bottle, the crystals lost water in dry air, giving the anhydrous Cu(en)2SOr, a violet-blue solid. (Note: While the colors of the two solids were clearly distinguishable, both were between blue and violet, aa just indicated. For convenience the color near blue will hereafter be designated simply “blue” and that near violet aa “violet.”) The violet and blue forma were reversibly interconvertiblc by passing dry or water-saturated air or nitrogen over the solid. Anhydrous C’u(en)*SO, wm prepared by allowing the hydrate to dry either in a desiccator for a few days or in an oven at 105” for several hours. Both the hydrate and the anhydrous compound were extremely soluble in water to give intensely colored violet solutions. The solution of the anhydrous salt in water, after evaporating and cooling in ice, gave back the violet rrystals of the hydrat,e. Both forms were insoluble in ethylenediamine, pyridine, aniline, ethanol, ethyl ether, and aliphatic or aromatic hydrocarbons. Attempts to precipitate Cu(en)k304from solution by addition of absolute ethanol resulted in a lustrous pale-blue solid whose solubility in water was considerably less than that of the hydrate of anhydrous material: moreover, the solutions were of a different color. Occasionally, dark sludges were formed which could not be recrystallized. It thus appeared that the evaporation method waa distinctly more reliable for preparation of anhydrous material than the ethanol precipitation.
+
Vol. 65
NOTES
19%
observed, but not reported, similar behavior previously7 with C:U(NH~)~SO~.H~O. I n this case we found that ethanol precipitation of the complex resulted in material either uncertain in composition or too finely (divided for our purposes, whereas chilling of a solution previously concentrated by evaporation gave excellent yields of large crystals of the desired material. It is ironical that the hydrate which is so difficult to prepare directly for the reaction mixture can be made easily by hydration of the anhydrous material, provided that a sufficiently high partial pressure of water vapor is provided. Magnetic Properties of the Complex Salt.In previously reported measurements4 of the low t>emperat'ure magnetic properties of Cu(en)zSOc and Cu(en)eSOlq.4H20,we observed that the hydrate was relatively ideal magnetically even below 4.2'K., whereas the anhydrous material had a maximum in its magnetic susceptibility somewhere bet,ween 4 and 10'K. At that time it appeared possible tJhat the decrease in susceptibility a t and below 4' might have been due to relaxation effects in the dynamic (400 cycle) susceptibilit,y we observed, rather than a decrease in the static aerofrequency susreptibility. We have since repeated these measurements, confirming previous mea.;curement,s a t 400 cycles, and found no dependence of susceptibility on frequency up to 1000 cycles. Thus the observed maximum in susceptibility rannot, be due to relaxation effects. It is probably aiised tiy stmng exchange interactions between copper ions, such as those previously adduced by Eisensteiri* t o explain our observat,ioris on Cu?j H3)4S04.H20. The magnetic behavior of the two Cu(en)z++ rompounds offers additional indirect, evidence on the nature of the hydrated material. The magnetic anomalies displayed by the anhydrous material are greater than those shown by Cu(NHJ4S04. &(I. This is not surprising since the ethylenediamine group:; could well be more effective in promoting exchange interactions between copper LLtoms bhan are ammonia molecules. The fact t,hatt t'he hydrate Cu(en).,SO4.4H20 shows nearly ideal behavior (about, as ideal as CuS04.5H2C),in fact') indicates that the water of hydration interfcrw with t,hesc int,rract,ions eit)her by a specific: i~ht~micnl cffcd or possibly just by dilut,ion. Additional et,hyIeriediaminf. as in Gordon and Uird\vhistp!l'.: cmlpoun,l Cu(en)3S04.1120, shodtl ren1 t w the suhstancc as momalous or more anomaious I h i :inhy(irrru:.: C'h(en)&04. Thus t.he magiirt'iv (,vi(Icnccx CLISO. strongly supportas tht. composition 'grid t ( I t Iw hgtfrat,cv-l mat.rri:LI: it. was in farf I ) I K of tlicl c~lucswhich It:d 11s t.o roinplrtt- t.ho itIc.?it,iticatioiiof thv mat,ci.i:rlas a hydrati.. ;
