June, 1956 ing with the linear portion of the BET plot that includes the relative pressure at which a statistical monolayer is obtained. T H E DECOMPOSITION OF MALONIC ACID IN GLYCEROL AND I N DIMETHYL SULFOXIDE
NOTES
825
the solvent and the evolved gas messured aa described above. The experiment waa repeated at five dflerent temperatures between 130-140'. Every sample invariably yielded the stoichiometric volume of carbon dioxide allomng for the experimental error. For example, the final observed volume at STP produced by one sample at 129.8" wan 36.1 ml.; at 134.3 , 35.5 ml.; at 138.8 , 36.0 ml. Reproducibility was excellent.
Results and Discussion The experimental data were converted to standB Y LOUIS WATTS CLARK ard conditions and milliliters'of evolved gm was plotted against time for each temperature. Values Conlribslion from the Department of Chemiatry, Saint Joseph Collsge. Emmilaburg, Maruland of x corresponding to different values of t were obReceived January 18. 1066 tained from the resulting isotherms. Log (a A number of investigators have made kinetic x) was then plotted against t (a is the theoretical studies on the thermal decomposition of malonic stoichiometric volume of carbon dioxide, 36.0 ml.). acid alone and in solution.' Although it is well The points thus obtained for the middle 80% of the known that malonic acid, like oxalic acid, is reaction fell on perfectly straight lines in every exsmoothly decarboxylated in glycerol, the kinetics of periment. This fact indicates that the decomposithe reaction in that solvent have not been previ- tion of malonic acid in glycerol, m well as in dimethyl sulfoxide, is a first-order reaction. ously reported. From the slopes of the lines thus obtained the Preliminary studies in this Laboratory revealed the interesting fact that the solvent, dimethyl sul- specific reaction velocity constants for the decomfoxide, likewise promotes the decomposition of position of malonic acid in the two solvents were malonic acid, and does so even more efficiently calculated for the various temperatures. For the cme of the decomposition of malonic acid than glycerol. The kinetics of the decomposition of malonic acid in glycerol, the temperatures studied, as well as the in these two solvents have been carefully studied corresponding speciiic reaction velocity constants in in this Laboratory, and results of this investigation sec.-l, were M follows: 152.2")0.00364; 154.1°, 0.00413; 155.7",0.00470;156.3', 0.00483; 158.1", are reported herein.
-
0.00513; 159.0",0.00570; 159.9",0.00578; 161.0°, Experimental Rea ents.-C.P. malonic acid was further purified by re- 0.00666. Results for the case of the decomposition crystafiisation from ether The purity of the reagent was of malonic acid in dimethyl sulfoxide were as foldemonstrated by the fact that the volume of carbon dioxide lows: 129.8", 0.00416; 131.3", 0.00490; 134.3", evolved from every quantitative sample in the decarboxyla- 0.00618; 137.0°,0.00740; 138.8",0.00845. tion experiments was invariably stoichiometric. A straight line was obtained in each case when Dimethyl Sulfoxide (99.9% ure), and glycerol, Analytical Reagent Grade, 95% by vofume, were also used in these log k was plotted against 1/T according to the Arexperiments. rhenius equation. From the slopes of the lines Apparatus and Technique.-The apparatus and technique thus obtained the energy of activation and the freused in these experiments have been previously described.2 Decomposition of Malonic Acid in Glycerol.-At the be- quency factor for the reaction in each solvent was ginning of each experiment 100 ml. of glycerol was placed calculated. For the decomposition of malonic acid in the dry reaction flask in the thermostated oil-bath. A in glycerol these were found t o be 25,500 cal., and 0.1671- sample of malonic acid (sufficient t o eld 36.0 5.3 X respectively; for the decomposition of ml. of 80,a t STP on complete reaction) was pcced in a thin glass capsule (blown from 6 mm. soft glass tubing and malonic acid in dimethyl sulfoxide corresponding weighing approximately 0.29.) and introduced at the proper values were 23,350 cal., and 2.3 X lO*O, respecmoment into the solvent in the manner previously de- tively. scribed. The rapidly rotating mercury seal stirrer immediThe temperature coefficient for the reaction in ately crushed the capsule, the contents were dissolved and mixed in the solvent, and reaction began. The evolved glycerol was found to be 2.11,in dimethyl sulfoxide carbon dioxide was measured at constant pressure. 2.26. The above procedure was repeated at eight different temThe enthalpy of activation, entropy of activation peratures between 150-160". Every sample of malonic and free energy of activation at 140°,according to acid yielded the stoichiometric volume of carbon dioxide within ex erimental error. For example, the final observed the Eyring equation, were found to be as follom: volume ofgas at STP produced by one sample at 154.3' was for the decomposition of malonic acid in glycerol, 35.6 ml.; a t 156.0", 36.0 ml.; a t 156.3', 35.9 ml.; at 24,600 Gal., -12.2 e.u., and 29,650 cal., respec159.9', 36.0 ml.; at 161.0°,36.0 ml. Duplicate and triplicate runs a t the same temperature showed excellent repro- tively; for the decomposition of malonic acid in dimethyl sulfoxide, 22,300 cal., -15.0 e.u., and ducibility. Decomposition of Malonic Acid in Dimethyl Sulfoxide.28,350cal., respectively. At the beginning of each experiment 100 ml. of dimethyl It is of interest to compare the rate of reaction in sulfoxide was saturated with dry carbon dioxide gas and the two solvents a t some particular temperature. laced in the reaction flask in the thermostated oil-bath. gamples of malonic acid weighing 0.1671 g. were added to At 140",k for malonic acid in glycerol is 0.0013,for
lo"',
(1) (a) J. Laskin, Trans. Sib. Acad. Agr. Po?., 6, No. 1 (1928); C.A., 13, 1804 (1928); (b) J. Bigeleisen and L. Friedman, J . Chem. Phus., 17, 998 (1941); ( 0 ) G. A. Hall, Jr., J . Am. Chsm. Soc., 71, 2891 (1949); (d) J. G. Lindsey, A. N. Bournes and H. G. Thode, Can. J . Chsm., 19, 192 (1951); (e) J. G. Lindsey, A. N. Bournes and H. G. Thode, ibid., 80, 183 (1952). (2) (a) H. N. Barham and L. W. Clark, J . A m . Chsm. Soc., 73, 4638 (1951): (b) L. W. Clark, ibid., 77, 3130 (1955); (c) 77, 6191 (1955).
malonic acid in dimethyl sulfoxide it is 0.0092. Therefore, malonic acid decomposes seven times aa fast in dimethyl sulfoxide as it does in glycerol at this temperature. It is also of interest to ascertain how the values of k in these two solvents compare with that for the pure acid for a given temperature. By melting one-half mole (53 g.) of the pure acid
NOTES
826
and measuring the evolved gas at 140" a value of k of 0.00025 see. - l was obtained, a result which agrees with that reported by J. Laskin.la Therefore, at this temperature, malonic acid decomposes about five times as fast in glycerol, and 37 times as fast in dimethyl sulfoxide, as it does alone.
BOILING POINT-COMPOSITION DIAGRAM FOR THE SYSTEM 1,4-DIOXANE-n-BUTYL ALCOHOL BY JAMESB. MCCORMACK, JOHNH . WALKUPAND
Vol. 60
carried out in an Othmer equilibrium stilL2 The pressure was maintained a t 760 mm. of mercury by means of a Cartesian m a n ~ s t a t . ~ Equilibrium was assumed to be attained when samples checked on the refractometer had a constant reading, and the composition of the samples was determined from a refractive index-composition curve. The boiling point was read with an accuracy of 10.05O. The data secured are given in Table I and also presented graphically. ( 2 ) D. F. Othmer, Anal. Chem., 80, 763 (1948). R. Gilmont, Ind. Eng. Chem., Anal. Ed., 18, 633 (144R).
(3)
R. I. RUSH
Chemistry Laboratory, Centre College of Kentucky, D a n d l e . K y . Received January 23, 1966
I n order to extena information previously obtained in this Laboratory' the boiling point-composition diagram for the system 1,4-dioxane-n-
RADIOLYSIS OF ETHANE: MOLECULAR DETACHMENT OF HYDROGEN BY LEONM. DORFMAN Qeneral EEectric Research Laboratory Schenectady, New York Received January S4# 1966
118
The chief products in the radiolysis of ethane are hydrogen and a polymeric liquid,lp2 the yield for hydrogen formation being approximately 3.9 molecules/lOO e . ~ . This ~ , ~note reports the results of experiments which show that a large fraction of the 112 hydrogen is formed intramolecularly by direct de9 tachment of molecular hydrogen without the apparent intermediate formation of single atoms of a hydrogen. ri Molecular detachment of hydrogen is inherent 106 in one of the seven primary processes suggested ,~ direct formation by Williams and E s s ~ xnamely, of hydrogen and ethylene ion, based on the observed5 mass spectral pattern of ethane. The hydrogen may be released from an excited ethane molecule or ion. It may originate from more com100 I I I I I 0 20 40 60 80 100 plex ions which can be formed in ion-molecule reactions which occur with high efficiency as shown n-Butyl alcoli,l, T . Fig. I -Boiling point-cwnposition diagram for the system recently by Steverison and Schissler.6 1,Pdiosane-n-butyl alcohol. The data which follow provide no information concerning the nature of the transitory entity butyl alcohol has been determined. The dioxane from which the hydrogen is released. They indiand n-butyl alcohol were purified by methods de- cate only the fraction of the total hydrogen formed scribed elsewhere, ' and the determinations were by molecular detachment. In these experiments a number of mixtures of TABLE I BOILINGPOINT-COMPOSITION DATA FOR THE n-BuTYL deuteroethane and normal ethane have been irALCOHOL-1,4-DIOXANE SYSTEM AT ONE ATMOSPHERE radiated in a 1 MeV. electron beam and the hydrogen isotope fraction analyzed mass spectrometriPRESSURE cally. The degree of isotopic randomization of the Composition Composition !.p.. (wt. % alcohol) B.p (wt. Sr, alcohol) is a measure of the relative occurrence hydrogen C. Vapor Liquid Vi' Vapor Liquid of single-atom reactions and molecular detachment 101.1 0.0 0.0 109.3 48.9 ti5.4 if it is known that secondary exchange produces no 101.5 3.0 4.5 110.55 55.4 73.2 appreciable isotopic mixing. 101.8 4.9 6.7 110.8 57.8 74.2 Experimental 102.2 7 . 5 10.7 111.25 59.8 75.8 105.0 106.25 106.5 106.95 107.35 107.4 107.55 108.5 108.8
22.2 31.9 31.6 33.8 38.0 38.8 37.2 43.8 45.6
36.8 47.5 46.1 52.1 54.4 54.4 53.6 60.8 62.2
111.65 112.3 112.65 113.8 115.1 116.0 116.5 117.5
62.3 67.0 67.0 75.8 85.0 90.6 94.2 100.0
76.3 80.1 81.1 85.9 91.2 94.2 96.4 100.0
(1) R. I. Rush, D. C. Ames, R. W. Horst and J. R. McKay, THIS JOUBNAL,
in press (18513).
The deuteroethane was obtained from Tracerlati, Inr. It contained 98 f 1 isotopic per cent. deuterium as determined mass spectrometrically . The deuteroethane was degassed at - 195", then fractionated twice by bulb-to-bull) (1) W. M u n d a n d W. Koch, BdE. 8 0 0 . chim. Belg., S4, 119 (1925). ( 2 ) S. Lind and Bardwell, J . A m . Chem. Soc.. 48, 2335 (142G).
C.
D. C.
(3) L. M. Dorfinan, F. J. Shipko and C. F. Pachucki, to be publiahed. (4) N. T. Williams and H. Esaex, J . Chem. Phgs., 17, 995 (1949). ( 5 ) J. A. Hipple, Jr., Phys. Rev., S3, 530 (1938). ( G ) D. P. Stevenson and D. 0. Schissler. J . Chem. Phys.. 2 3 , 1353 (1955).
c
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