NOTES
368
Vol. 62
I
i c m.-'
*
Fig. lb.
a
among several authors in the observations near 300 cm.-l.*--6 The Raman spectrum was taken in the liquid phase without a filter. The far infrared spectrum was studied through the region of 23 to 60 p with a spectrometer described by Bohn, et al.' The usual rock salt region was studied with a Perkin-Elmer model 12C spectrometer. Both regions were measured in the gas phase under appropriate pressures. Results obtained were as follows: Raman: 164(0b), (e); 251(0b), (e); 334(0), (e); 414(lvb), (e&); 489(0b), (e); 530(0), (e$); 918(7), h e , + , f,g,k,i); 1105(lb), (k); 1142(lvb), (k); 1377(0), (k); 1392(0), (k); 1451(4vb), (e,k); 2814(10), (q,p,l,k,i,e,f,g); 2685(7), (k,i,e,) ; 2886(1), (e,k); 2918(5), (q,p,k,i,e) ; 2951 (4), (q,p,k,i,e) ; 2985(6), (q,p,k,i,e). Infrared (22-60 p ) : 210-270 (m,b), ca. 410(m). Infrared (2.5-15 p 8 ) : 921(m), 937(m), 1098(s), 1115(s), 1169(s), 1187(s), 1248(w), 1464 (m), 2022(w), 2047(w), 2098(m), 2430(w), 2630(w), 2710(w), 2845(s), 2900(s), 2980(s). Here, frequencies are expressed in cm.-l. (0), (7), etc., are the Raman intensities visually estimated on the plate; b or vb indicates that the line is broad or very broad; e, k, etc., denote the exciting mercury lines Hg-e, Hg-k, etc; w, m, and s denote weak, medium and strong infrared bands, respectively. The weakest Raman lines are on the border of detectability and cannot be taken as absolutely certain. A plot of the infrared absorption spectrum is shown in Fig. 1. In the lower frequency region there are five Raman Lines and an infrared band in addition to 414 cm.-', which is clearly the GO-C bending vibration. These are to be assigned as two modes of torsional vibration together with overtones and combinations. Assuming the point group of the molecule to be Cz,, one of these vibrations has a symmetry class Az (Raman active, infrared inactive) and the other Bz (Raman and infrared active). One can quite definitely assign 265 cm.-l to Bz, since A2 is infrared-inactive and 265 cm.-l is actually observed in the far infrared region. The peculiar infrared contour in the 200-270 cm.-l region is ascribed to a superposition of hot bands at lower frequencies on the 0-1 transition at 265 cm.-l. From a consideration of the vibrational motions, (4) S. C. Sirkar, Ind. J . Phys., 7 , 257 (1932). (5) N. G. Pai, dbid., 9, 121 (1934). (6) A. Hadni, Compl. rend., 289, 348 (1954). (7) C. R. Bohn, N. K. Freeman, W. D. Gwinn, J. L. Hollenberg and K. S. Piteer, J. Chem. Phys.. 21,719 (1953). (8) R. H. Pierson, A. N. Fletcher and E. 8. C. G a n t ~ Anal. . Cham., 28, 1218 (1956), present an infrared spectrum identical to our8 except f3r weak abflorptions near 1600 and 1875 om.-' which we did not find.
~-
Bz should be higher in frequency than An1v9thus leaving 164 cm.-l to be assigned as the latter. The BZ torsional motion is expected to be very anharmonic, hence it is reasonable to take the 0-1 transition at 265 cm.-l and hot bands in the 200-230 cm. -l region. Similarly, 164 cm. -l should be regarded as a lowered value of the true fundamental frequency because of the contributions of the corresponding hot bands t o the intensity of the Raman line. The true frequency was assumed to be 170 em. -I. We propose as the torsional energy level pattern of dimethyl ether the following formula, which is limited in applicability to levels well below the top of the barriers to rotation. E
-hc Eo = 1 7 0 ~ + ~ s2 6 5 ~ ~-2 3(vA,
-
- 21(VB,
I
C'
1)8A,
-
- 35 vA#B* where V A and ~ VB, are the quantum numbers of the 1)&p
two torsional vibrations. Thus, the remaining Raman bands at 334, 489 and 530 cm.-l have the V A ~and V B , values (2,0), (0,2) and (2,1), respectively, in their upper states. The expected (1,l) band a t 400 cm.-' would be buried under the strong 414 cm.-' band. This pattern of levels is a refinement of the assignment of HadniB He has shown that this assignment of torsional vibrational levels yields thermodynamic properties in approximate agreement with those observed We had hoped to discuss the vibrational assignment generally and to refine the thermodynamic calculations, but circumstances make it more feasible t o continue this work separately. Acknowledgment.-We wish to thank Dr. Roger Millikan and Dr. Edward Catalan0 for their aid in the far infrared measurements. (9) K. S. Pitzer, J . Chem. Phys., 12, 310 (1944).
(IO) G. B. Kistiakowsky and W. W, Rice, zbzd., 8, 618 (1940). (11) R. 111. Kennedy, M. Sagenkahn and J. G.Aston, J . Am. Chem.
I
; t
I
t I
-t
! I I P "
I
Sac., 63,2267 (1941).
(12) A. Eucken and E. U. Franck, 2.Elektrochsm., 52, 195 (1948).
THE EFFECT OF AROMATIC NITRO COMPOUNDS ON MALONIC ACID BYLOUISWATTSCLARK Departmant of Chemistry, Saint Joeeph CoZleqa, Emmilaburg, Maryland Received October $1, 1967
Studies on the decarboxylation of malonic acid in non-aqueous, basic type solvents* have con(1) L. W. Clark, THISJOURNAL, 62, 79 (1958).
i
360
March, 1968
NOTES
firmed the hypothesis of Fraenkel and co-workers2 that malonic acid and the solvent form an intermediate transition complex, an electrophilic atom of the acid coordinating with a nucleophilic atom of the solvent. Analysis of the kinetic data for the reaction in 24 solvents indicated that, within the range of basicity where the malonic acid remains undissociated, the activation energy for the reaction decreases as the effective negative charge on the nucleophilic atom of the solvent increases. A consideration of the structure of nitrobenzene and other aromatic nitro compounds suggested the possibility that such compounds possess sufficient nucleophilic character to coordinate with malonic acid and promote the decarboxylation reaction. Preliminary tests confirmed this suggestion. In order to obtain further information on the mechanism and energetics of the reaction kinetic studies were carried out in this Laboratory on the decomposition of malonic acid in four aromatic nitro compounds. The results of this investigation are reported herein.
TABLEI APPARENTFIRST-ORDER RATECONSTANTSFOR THE DECARBOXYLATION OF MALONIC ACID I N SEVERAL AROMATIC
Experimental Reagents.-( 1) The malonic acid was analytical reagent grade, 100.0% assay. (2) plvents: (a) nitrobenzene, reagent grade, b.p. 210-212 ; (b) o-nitrotoluene, reagent grade, m.p. -4 to -3O, sp. gr. 1.163; (c) m-nitrotoluene, highest purity grade, m.p. 15-16'; (d) 1,3-dimethy1-2nitrobenzene, highest purity grade, m.p. 13-15'. Each sampIe of each liquid was distilled into the reaction flask immediately before the beginning of the decarboxylation experiment. Apparatus and Technique.-The kinetic experiments were conducted in a constant-temperature oil-bath ( i ~ 0 . 1 " )by the technique previously described .* Temperatures were determined by means of a thermometer calibrated by the U. S. Bureau of Standards. In each experiment a 0.1857-g. sample of malonic acid (the amount required to produce 40.0 ml. of COS a t STP on complete reaction) was introduced in the usual manner into the reaction flask containing 50.0 ml. of solvent saturated with dry COz gas.
KINETICDATAFOR THE DECOMPOSITION OF MALONIC ACID I N SEVERAL AROMATICNITROCOMPOUNDS AND AMINES
NITRO COMPOUNDS Solvent
AT
VARIOUS
Temp. ("C.) (cor.)
TEMPERATURES Specific reaction velocity constant (sec.-L)
Nitrobenzene
139.31 153.05 161.78
0.000268 .000859 .001711
o-Nitrotoluene
149.65 161.55 167.37
0.000671 .001487 ,002168
m-Nitrotoluene
128.29 144.11 149.94
0.000910 .003310 ,005210
2-Ni tro-m-xylene
147.50 159.38 167.67
0.000398 .001132 .002260
TABLE I1
Solvent
(1) (2) (3) (4) (5) (ti)
2-Nitro-nz-xylene Nitrobenzene Aniline' m-Nitrotoluene m-Toluidine1 o-Nitrotoluene
$2, 30,000 28,100 26,900 26,200 26,100 23,500
AS$ (e.u.1
-
3.12 7.15 4.45 - 7.46 - 5.80 -17.92
-
kiao' X los (set.-*)
16.2 28.3 500.0 237.0 592.0 33.6
The enthalpies of activation for the reaction in 2nitro-m-xylene and in nitrobenzene (lines 1 and 2 of Table 11) are higher than in aniline (line 3), suggesting that in these first two solvents the effective negative charge on the nucleophilic atom of the solvent is lower than in ani1ine.l I n mResults and Discussion nitrotoluene and in o-nitrotoluene the enthalpies of The rate of reaction was measured in each solvent a t three different temperatures over a 20" activation are lower than in aniline, suggesting temperature range (Table I). When log (a - z) that in these solvents the effective negative charge was plotted against t (a being the h a 1 or maxi- on the nucleophilic atom of the solvent is higher mum volume of GO:! produced in an experiment and than in aniline. A methyl group in the metaz the volume of GO2 produced a t the time t ) position (line 4) increases the effective negative straight lines resulted over the greater part of the charge on the nucleophilic atom of the nitro group, reaction, indicating that the decomposition of by a posit,ive inductive effect, sufficient to lower malonic acid in aromatic nitro compounds is the enthalpy of activation below that of aniline, but has a relatively small steric effect as shown by pseudo-first-order. the relative values of AS$ for nitrobenzene and mThe parameters of the Eyring equation are listed in Table 11. Data for aniline and m-toluidine are nitrotoluene (lines 2 and 4). The large decrease in A H $ and the slight change in entropy results in a included for comparison. Nitrobenzene resembles aniline structurally in large increase in the rate of reaction on going from having a nitrogen atom joined to the benzene ring nitrobenzene to m-nitrotoluene. A methyl group and to two other identical atoms. It differs from in the ortho-position (line 6) decreases A H $ consideraniline in that oxygen is much more electronegn- ably due to the +I effect, and a t the same time has tive than hydrogen and that resonance occurs in the a pronounced effect on ASS, a result which is connitro group but not in the amino group. The sistent with the orlho e f f e ~ t . ~ The effect of substitution of methyl groups in essential condition for the formation of a transition complex between malonic acid and solvent is that both ortho positions (line 1) appears to be anomathe molecule of the solvent be sufficiently nucleo- lous, and suggests a possible difference in orientaphilic to coordinate with the malonic acid but not tion of the solute molecules with respect to malonic acid between this liquid and the other nitro comsufficientlynucleophilic to ionize the acid.2 pounds studied. (2) G. Fraenkel, R. L. Belford and P. E. Yankwich. J . Am. Chem.
Soc., 76, 15 (1954).
(3) L.
W. Clark, Txm JOURNAL,
60, 1150 (1956).
(4) L. P. Hammett, "Physical Organic Chemistry," McGraw-Hill Book Co., Inc., New York, N.Y..1940,p. 204.
370
NOTES
Acknowledgments.-The support of this research by the National Science Foundation, Washington, D. C., is gratefully acknowledged. Distillations of the solvents were carried out by Miss Dolores Sicilia. ON T H E INTERPRETATION OF HYDRODYNAMIC DATA FOR DILUTE PROTEIN SOLUTIONS BYHAROLD A. SCHERAUA AND LEOMANDELKERN Department of Chemistyy, Cornell University, Ithaca, N e w Y o r k , and Polumer Structure Sectzon, Natzonal Bureau of Standards, Washington 36,D. C. Rereived September SO, 1967
Several questions have recently been raised’ about our method of interpretation of hydrodynamic data on dilute protein solutions,2and about a recent application of this method to measurements on bovine serum a l b ~ m i n . ~We believe that the argument developed by Tanford,’ in this connection, is misleading and thus necessitates further clarification. As stated in his equation 1, Tanford chooses to express the effective hydrodynamic volume of a dissolved protein molecule in terms of its partial specific volume and a quantity 61,which he defines4 as “the number of grams of solvent incorporated in the hydrodynamic particle per gram of dry protein.” The arbitrariness of this assumption and its disregard of physical reality have already been discussed in great detail both by us2 and by Sadron15 whose treatment is essentially equivalent to ours. In addition to this arbitrary division of the effective hydrodynamic volume into two terms ( M / N ) G and 6I(M/N)vlo,Tanford’s procedure is also very misleading since one is thereby tempted to attach reality to 6’ as the mass of water actually bound to one gram of protein. Tanford, in fact, is inconsistent on this point since he makes this latter identity when he asserts’ that the validity of his equation 1 is confirmed by Wanq’s considerationsB of the self-diffusion of water in dilute aqueous protein solutions. It is incorrect to obtain 61 from self-diffusion since it is clearly stated by Wang and quite apparent in his theoretical development that the hydrodynamic behavior of the dissolved protein molecule does not enter into his calculation. Thus, it is not surprising that in Wang’s treatment the appropriate and correct volume to be considered is that which describes the domain of the molecule, with &, in this instance, being the specific solvation of the actual protein molecule. However, this latter conclusion is limited to problems involving the self-diffusion of water and has no application to the present matter concerned with the interpretation of the hydrodynamic data of protein solutions. A similar error is committed by Tanford and Buzzell,4 who assume that the value of 61 obtained from intrinsic viscosity data and the afore(1) C. Tanford, THISJOURNAL, 61, 1023 (1957). (2) H.A. Scheraga and L. Mandelkern, J . Am. Chem. Soc., 76, 179 (1953). (3) G. I. Loeb and H. A. Scheraga, THISJOURNAL, 60, 1633 (1956). (4) C. Tanford and J. G. Buzsell, THISJOURNAL, 60, 225 (1956). (5) C. Sadron, Prou. in Biophys.. 3, 237 (1953). (6) J. H. Wan& J . Am. Chem. Soc., ‘76,4755 (1954).
Vol. 62
mentioned definition of the effective hydrodynamic volume is comparable with the value obtained from self-diff usion experiments. Hence, we re-affirm the statement3 that “it is impossible to relate the effective hydrodynamic volume of a dissolved protein molecule to its partial specific volume.” Tanford agrees that two hydrodynamic properties have to be measured in order to deduce both the size and the shape of the effective hydrodynamic particle. However, he tries t o imply a greater senhitivity in the interpretation of hydrodynamic data than actually exists by stating that our 0 (and presumably also our 6) function represents a poor choice of measurements. As emphasized previ0us1y,~Jwhereas a single property (such as viscosity) varies considerably with axial ratio for constant volume, one doesn’t know in advance what the volume is. Hence, one must use a function (e.g., our p or 6 function, or any other equivalent one) which depends on a pair of hydrodynamic measurements. A few calculations will show that any such function, which combines two hydrodynamic measurements, is very insensitive to changes in axial ratio.
I
. I
1 I
a*. ?
t
EXTRACTION OF INORGANIC SALTS BY 2-OCTANOL. 111. ZINC AND CADMIUM CHLORIDES. AQUEOUS PHASE ACTIVITIES‘ BY T. E. MOORE,NORMAN G. RHODEAND ROBERTE. WILLIAMS The Department of Chemistry, Oklahoma State University, Stallwater, Oklahoma Received October 10, 1967
Preliminary experiments in these laboratories have shown that the extraction of both Zn(C104)z and Cd(C104)2from aqueous solutions (4 m) occurs readily. When solubilities of ZnC12 and CdClz in 2-octanol are compared? however, a large difference is found, ZnCL being over 1000 times as soluble at 25”. This suggested that effective separation might be achieved through the 2-octanol extraction of aqueous mixtures of the chlorides. This is in general agreement with earlier observations regarding the non-specificity of 2-octanol as an extraction solvent for metal perchlorates contrasted to the much more specific behavior of the corresponding chlorides.2 To test this theory, six series of solutions were extracted with the octanol at 25”. Figure 1 presents the variation of the distribution coefficients, kd, of ZnClz and CdClz in the different series. The distrlbution coefficient is here defined as the ratio of the molal concentration in the non-aqueous phase to the molal concentration in the aqueous phase. The equilibrium mixtures of octanol and water are considered as solvents in each phase. It is evident from the figure that separation factors, s, of the order of 50-60 (s = kd(ZnClz)/ kd(CdClz)) are obtained with the ZnClz-CdCln mixtures investigated. These values, however, are only about 50y0 of the values calculated from (1) Supported under Contract AT(11-1)-71 No. 1 with the U. 8. Atomic Energy Commission. (2) T.E. Moore, Roy J. Laran and Paul C. Yates, THISJOURNAL, 19, 90 (1955).
c
*.
