NOTES
2023
Table I1 : Comparison of Calculated and Experimental Compressibility Factors for Air Compressibility faciors----Calcd. from Calcd. from t o t d pressure partial pressure From equations z factors z factors of statea
law a t low pressures, the partial pressure method cannot be presumed in general to be more accurate. (7) J . A. Beattie and 0. C. Bridgeman, Proc. Am. Acad. Arts Sci., 6 3 , 229 (1928). (8) J. Hilsenratz,. et al., "Tables of Thermal Properties of Gases," National Bureau of Standards Circular KO. 564, U. S. Government Printing Office, Washington, D. C., 1955.
_ _ I -
Temp.,
Pressure,
OK.
atm. p
100
1
0.980
0.9813
0.9809
200
1
0 99769 0 9768 0 9086 0 810
0 0 0 0
0 99767 0 97666 0 9080
0 0 0 0
0 99986
10 40 100 300
1 10
40 100 a
99972 99741 9920 9941
99856 9857 9441 878
0 99872 0 99130 0 9972
(9) C. W. Solbrig and R. T . Ellington, A.I.Ch.E. Chern. E n g . Progr. Series, 59, 127 (1963).
0 8105
0 0 0 0
99970 99717 99135 9933
Ref. 8
A Color Reaction between Trinitrobenzoic Acid and Acetone
by John E. Neufer, Rloshe H. Zirin, and Dan Trivich Depwtment of Chemistry, W a y n e State University, Detroit 8. Michigan (Received February 1 4 , 1964)
A review of the results of comparison in Table I1 will show that, in all cases presented, the use of component x values a t total mixture pressures will give results closely approximating the experimentally derived values, and in most (if not all) cases within experimental accuracy. The use of the partial pressure method is converse1:y shown to be apparently much more unreliable iii estimating compressibility factors for air, and in most cases gives results considerably outside experimental error. If it is assumed that the total pressure method is more valid for pressures down to 1 atm., the rather theoretical question may be raised as to whether or not that method would also be more valid for pressures under 1 atm. This (question can be answered by considering the low pressure isothermal x curves for air, and the components of air, vs. pressure. These isothermals at all except extremely low temperatures are found to be essentially linear, converging as expected to unity a t zero pres~,ure.~''The deviation from unity of an isothermal would then be essentially proportional to pressure. Therefore, if the total pressure x values of components were used and were more valid in determining the z values for a gas a t l atm., they would also be more valid a t any lower pressure down to zero. The foregoing analysis does not prove, of course, that use of total pressure component x values would always give answers closer to experimentally derived z values for mixtures than would the partial pressure method, for moderate and low pressures. For example, mixtures of hydrogen and ethane under moderate pressures apparently do not follow Amagat's law.g It would appear, however, that lacking more experimental data which would contradict Amagat's
We have found that dilute solutions of 2,4,6-trinitrobenzoic acid (TH) in acetone, which are nearly colorless when freshly prepared, develop green to red colors on standing in the dark. Exposure to strong visible light bleaches the color and the darkening-bleaching cycle can be repeated a large number of times. This suggests that TH forms a complex with acetone since solutions of TH in water, alcohol, and dioxane do not produce similar colors. A number of color-forming reactions have been reported involving nitro compounds and acetone, e.g., by Willgerodt,l Janovsky, and others. 3--6 An extensive study of this field has been reported by C a n b a ~ k . ~ I n contrast with the present reaction between T H and acetone, the previously reported methods for the development of color invariably required the presence of base and, further, the colored solutions obtained were not reported as being sensitive to exposure to light. Extensive tabulations of complexes formed by nitro compounds are included in reviews by Andrew8 and Briegleb.9 It is pointed out that usually nitro aromatic ~
~~
(1) C. Willgerodt, Ber., 14, 2451 (1881); 25, 608 (1892). (2) (a) J. V. Janovsky and L. Erb, ihid., 19, 2155 (1886); (b) ihid., 24, 971 (1891).
(3) M . Jaffe, Z. physiol. Chem., 10, 390 (1886). (4) C. L. Jackson and R. S.Robinson. Am. Chem. J . , 1 1 , 93 (1889). ( 5 ) V. Meyer, Ber., 29, 848 (1896). (6) R. W. Bost and F. Nicholson, I n d . Eng. Chem., A n a l . Ed., 7 , 190 (1935). (These authors mention in a table that T H forms a color with acetone in the presence of alkali.) (7) T. Canbick, Farm. Revy, 48, 153, 217, 234, 249 (1949). ( 8 ) L. S.Andrews, Chem. Rev., 54, 713 (1954). (9) , G . Briegleb, "Elektronen-Donator-Acceptnr-Komplexe," Springer-Verlag, Berlin, 1961.
Volume 6 8 , *Yurnher 7
Julu, 1964
NOTES
2024
compounds act as electron acceptors although in some few cases another nitro compound takes the role of donor. Czekall, et U L . , ' ~ have studied the donoracceptor complex between hexaniethylbenzene and TH, while Yainada and Kozima" have studied the behavior of acetone as a donor toward iodine, Shellhas reported complexes of nitro compounds with acetone and iodide ions and he nientions light sensitivity of 2,4,6-trinitrotoluene in the solid stmateand in acetone solution. Gold and Rochester13 have studied a photochemical reaction of 1,3,5-trinitrobenzene with aqueous alkali. Wettermark and ~ t h e r s 'have ~ reported that illumination of certain substituted oriitrotoluenes, especially 2-(2',4'-dinitrobenzyl)pyridine, produces colors which fade on standing in the dark. Another well-known characteristic reaction of T H is that of decarboxylation. Some authors'6,'B have noted the effect of changing the solvent upon the rate of decarboxylation, and showed that the rate-controlling step involves the decomposition of the trinitrobenzoate ion.16,17 The present research was undertaken to determine some of the characteristics of the color-forming reaction as well as to elucidate the nature of the bleaching phenomenon.
Experimental Eastman Kodak White Label 2,4,6-trinitrobenzoic acid was purified by the procedure of Smith and Wilkins,18 followed by recrystallization performed by saturating ethyl ether a t room temperature with the acid and then cooling the solution to -6.5'. The crystals, after filtering, were dried in air and then placed in a desiccator over Drierite. Reagent grade acetone (Fisher or Baker and Adamson) was further purified by the method of Riddick and T o ~ p s . ' ~ Spectrophotometric measurements were made with a Beckinan DU spectrophotometer or a Warren Spectracord using 1- and IO-cm. cells. The bleaching was effected with incandescent light, e.g., a 150-w. bulb, 2.5 cm. from the sample vessel in the thermostat, was used for the rate experiments. The samples were analyzed by titration with XaOH, after dilution of the sample with water and sweeping out the COz with S,. The separation of the conipounds remaining after partial decomposition was effected by taking the acetone solution to dryness a t room temperature by evacuation and then treating the mixture with a n~inimumquantity of water to dissolve the TH. The insoluble part consisted almost entircly of 1,3,5-trinitrobenzene. After further puriThe Journal of Physical Chemistry
fication, the compounds were characterized by infrared, titration, and mixture melting points.
Results Color Formation.
Figure 1 shows the spectrum of a solution of T H in acetone on standing in the dark and after bleaching. The absorbances of the two peaks of the complex, a t 450 and 590 mp, are in the ratio of'2.2 to I, indicating that the peaks represent the same compound. The absorbances of such solutions increase with time in the dark and approach a limiting value indicating a tendency to approach equilibrium. The rate of color development is sensitive to small amounts of impurities, being accelerated by bases and retarded by st,rong acids. When the ratio (base),/ (TH) is greater than 0.02, an additional but transient peak occurs a t 520 mg. The absence of this peak was used in the selection of grades of acetone, which were further purified in any case. Similar color formation (with absorption peaks a t -450 and --580-610 mp) and bleaching were observed for solutions of T H (ranging from 0.02 to 0.08 in mesityl oxide, propionaldehyde, 2,4-pentanedione, ethyl acetoacetate, acetophenone, cyclopeiitanone, and cyclohexanone, but not in methyl acetate or purified benzophenone. No other similar nitro compounds tested gave significant amounts of color when dissolved in pure acetone. The dependence of the a,niount of color upon the concentration of T H in purified acetone was investigated to in several series of solutions ranging from 5 X 1 . 5 M TH. It was found that absorbance, e.y., after (10) J. Czekall, G . Briegleb, TV. Herre, and R. Glier, 2. Elektrochem., 61, 537 (1957).
(11) N. H . Yarnada and K. Koaima, J . Am. Chem. Soc., 82, 1543 (1960). (12) R. W. Shellman. J . Org. Chem., 22, 818 (1957). (13) V. Gold and C. H. Rochester, Proc. Chem. Soc., 403 (1960). (14) (a) G. Wettermark and € L Ricci, J . Chem. Phys,, 39, 1218 (1963); (b) G . Wettermark and J. Sousa, J . Phys. Chem., 67, 874 (1963); ( e ) G. Wettermark, {hid., 66, 2560 (1962); (d) G. Wettermark, S a t u r s , 194, 677 (1962); (e) J. D. Margerum, L. J. Miller, E. Saito, XI. S. Brown, H. S.Mosher, and It. Hardwick, J. Phys. Chem., 6 6 , 2434 (1962); (f) G . Korttim, 11;Kortfini-Seiler, and S.D. Bailey, ihid. 66, 2439 (1962); (g) G. Wettermark, J . B m . Chem. Soc., 84, 3658 (1962): (h) J. A. Soma and J. Weinstein, ,I. O r g . Chem,., 27, 3155 (1962j; (i) R. Hardwick, H. S. Mosher, and F. Passailaigue, Trans. F a m d a y Soc., 56, 44 (1960): (j) H . 8. Mosher and C. Souers, J . Chem. Phys.. 32, 1888 (1960). (15) E. A4. Moelwyn-Hughes and C. N. Hinshelwood. Proc. Roy. SOc. (London). A131, 186 (1931). (16) D. Trivich and F. H . Verhoek, J . Am. Chem. Soc., 6 5 , 1919 (1943). (17) F. H. Verhoek, ibid., 61, 186 (1939). (18) G. F. Smith and D. H. Wilkins. Anal. Chim. Acta, 8 , 209 (1953). (19) J. A. Riddick and E. E. Toops, Jr., "Technique of Organic Chemistry." Vol. 1'11, "Organic Solvents," 2nd Ed., Interscience 1955, p. 382. Publishers, Inc.. New York. N. T.,
NOTES
Figure 1. Typical spectra of a 0.04 M solution of 2,4,6-trinitrobenzoxc acid in acetone after standing in t h e dark. Spectra were recorded on a Warren Spectracord, using 1-cm. cells. Times after mixing for curves A, B, C, D and E were 1, 31, 80, 190, and 549 min., respectively. Curve F was taken just after subjecting to illumination by strong visible light the solution which gave curve E.
the solutions were kept in the dark for 1 day, increased with initial [TH] up to 0.1 M beyond which the absorbance decreased with increasing [TH]. Below the maximum, the absorbance was found to be proportional to [TH]”’. Almost all of the other experiments reported in this paper were done with solutions of concentrations less than 0.1 M . Titration of T H solutions in acetone, both before and after standing in the dark, showed no change in acid concentration. The apparent molecular weight of T H in acetophenone, determined by freezing point depression, was found to be 276 f 15, which indicated that T H is largely present in such solvents as the undissociated monomer (17101. wt. 257). The concentration of the complex was inferred from spectrophotometric measurements. In very dilute solutions of TH(w3 X M ) , spectra taken at various times during the darkening reaction exhibit an isosbestic point at 385 mp. The decrease in absorbance at 360 mh was found to be directly proportional to the increase at 450 mp with a proportionality constant of 0.150. The molar extinction coefficient of T H in fresh solutions of acetone is 280 a t 360 mp. Assuming that the complex does not absorb at 360 mp and that the concentration of complex is equal to the decrease in the concentration of TH, one calculates exti17ction coefficient Of a Of 1870 for the the complex a t 450 m p . This leads to estimates for
2025
the amount of conversion of T H into complex, after 1 day’s standing, of 57, for 4 X l o p 4 M T H to 0.6% a t 0.1 M TH. Since the most likely departure from the assumptions made and implied here is that the complex may also absorb to some degree at 360 mp, the estimated value of the extinction coefficient of the complex is likely to be a maximum value and the real value may be lower. Also, the estimates of the concentrations of the complex are likely to be minimum values and the real values may be higher. An attempt was made to determine the number of moles of acetone associated with the complex by dilution of the acetone with hexane. Various constant concentrations of T H were used, varying from about 0.01 to 0.03 M for the various series, and in each series the acetone concentration was varied from 2.73 to 13.6 M . The appropriate plots based on a procedure proposed by Benesi and HildebrandZ0for 1 : l complexes were not linear so that a 1: 1 complex is not proved. A more general treatment, suggested by Foster, et Q Z . , ~ ~was also employed and this also did not yield linear plots over the entire concentration range. At high acetone concentrations, above 7 M , the data did tend toward a linear plot of AB/[HA]2 us. A,, where A , is the absorbance of the solution and [HA] is the acetone concentration. This suggests that the complex formation may require 2 moles of acetone. The Foster treatment in this range leads t o a value for the extinction coefficient of 214 f 75 and a formation equilibrium constant of 0.004. In view of the uncertainties involved, the previously mentioned value for E of 1870 mill be used in further discussion. Since the absorbance in pure acetone solutions is proportional to [TH ]”’, this suggests a dissociation reaction in the color formation. Since the molecular weight in acetophenone is normal, it is unlikely that the reaction involves dimers and their dissociation. Thus one is led to postulate an ionization mechanism for the color formation process: H T HA + HT.HA and HT.HA HA + TH,4-H*A+ in which HA represents acetone and T I L - represents the colored complex. An equivalent mechanism can be written for a reaction of TH with enolate ion, A-. If an ionic mechanism is involved, this would explain the difficulty of quantitatively applying the Benesi-Hildebrand or Foster treatments to the acetone-hexane solutions since a low and varying dielectric constant is encountered in these solvent mixtures. It should be
+
+ +
(20) H. A. Benesi and J. H . Rildobrand, .I. Am. Cham SOC.,71, 2703 (1949); cf. ref. 9, p. 199. (21) H. Foster, D. L Hammick, and A. A. Wardleg, J . Chem. Soc., 3817 (1953).
Volume 68, ,Vumber 7
J u l y , I964
NOTES
2026
mentioned that the colored compound formed by illumination of 2- (2’-nitro-4’-cyano benzyl)pyri dine in ether-isopentane-ethanol solutions exhibits siinilar absorption peaks to those of the T H complex shown in Fig. 1 and that Wettermark and have suggested that the color is due to an ionic species produced by dissociation of an aci form of the nitro compound. Bleaching. A solution of 0.02 M T H in purified acetone was subjected a t room temperature to 30 cycles of darkening and quick bleaching with no measurable loss in acid concentration. Since the total amount of complex formed was estimated to be a t least 5 mmoles/l. as calculated from the sum of the absorbances developed and using E = 1870, this suggests that the bleaching reaction may be predominantly a reversal of the color-forming reaction. At somewhat elevated temperatures and in the presence of continuous illumination, some decomposition occurs. The decomposition reaction consists of decarboxylation since 1,3,5-trinitrobenzene (TNB) was found to be the principal product, as identified by infrared spectra and mixture melting point determinations. The rate of decarboxylation under illumination was studied using various initial concentrations of TH, ranging from 0.01 to 0.05 M , and was found to be first order with rate constants of 5.05 X lo-? sec.-? a t 3 5 O , 14.3 X lo-? set.-' at 4 5 O , and 69.7 X lo-? sec.-l a t 56’ (b.p. of acetone). It is interesting to note that solutions of T H in acetone showed no change in acid concentration upon being refluxed in the dark for more than 1day. The bleaching reactions may be summarized thus
€ITAHi!HA
(I) bleaching to form acid, possibly reversal
1 A\
+
(11) decarboxylation, ie., T S B C02 solvent
+
An attempt was made to determine the proportions contributed by paths I and I1 to the total bleaching. This involved comparing the initial darkening rate a t room temperature with an extrapolated value of the decarboxylation rate. This leads to the very tentative estimate that reaction II represents less than 1% of the bleaching reaction a t 25’. T h e Journal of Physical Chemistry
Proton Magnetic Resonance Spectrum of
1,1,2,2,4,4,5,5-0ctadeuteriocyclohexane
by Xorbert Muller and Peter J. Schultz Department of Chemistry, Purdue University, Lafayetle, Indiana (Received February 17,1.964)
It is known1 that the proton magnetic resonance spectrum of cyclohexane a t low temperatures shows much partially resolved hyperfine structure arising from magnetic nonequivalance of the axial and equatorial hydrogen atoms. Because of inadequate resolution it has not been possible to obtain accurate values for the chemical shifts of the axial and equatorial species or for the various spin-spin coupling constants. The chemical-shift values are needed to test predictions based on theoretical models which have been proposed to explain n.m.r. data21a and also to make it possible to refer shifts found for substituted cyclohexanes4~5to logical “standard” values. With this in mind we prepared 1,1,2,2,4,4,5,5-octadeuteriocyclohexane (ODCH) which was expected to yield a proton CD2-C D2
/ \
CH2
\ CH2
/
CD2-CD2
resonance spectrum much simpler than that of ordinary cyclohexane.
Experimental The preparation of ODCH is described in detail elsewhere.‘j Briefly, the procedure used was to exchange all hydrogens of 1,4-cycl~hexanedione~ by refluxing with three portions of D 2 0 to which a trace of acetic anhydride had been added to provide a catalyst. The extent of exchange was monitored by n.m.r. spectroscopy, and it was estimated that the diketone eventually obtained was 96% deuterated. This material was converted to the corresponding bisdithioketal (1) I?. R. Jensen, D. S.Noyce, C. H. Sederholm, and A. J. Berlin, J . Am. Chem. SOC.,82, 1256 (1960); 84, 386 (1962). (2) J . I. Musher, J . Chem. Phys., 35, 1159 (1961). (3) A. G. Moritz and N. Sheppard, Mol. Phys., 5 , 361 (1962). (4) N. Muller and W. C. Tosch, J . Chem. Phys., 37, 1167 (1962). (5) E. L. Eliel, M. H. Gianni, and T. H. Williams, Tetrahedron Letters, 741 (1962). (6) P. J. Schultz, M.S. Thesis, Purdue University, in preparation. (7) Obtained from Columbia Organic Chemicals.
