Sept., 1959
HEATCAPACITIES OF YTTRIUM, LANTHANUM AND NEODYMIUM OXIDES
acetate and the more dilute solutions of perchlorate, it is unlikely that a molecular mechanism was operative. It is more probable that the pyridine removed mercuric or HgOAc+ ions as Hg[CsH,N]z++ e.g. Hg++
+ 2CsHsN
Hg[CbHsN]z++
If the free mercuric ion only took part in the oxymercuration, the rate of which was proportional to [Hg++] = [Hg[C6H6N]2++)/K[C5H5NI2,then the retarded reaction would not have been of the first order with respect to mercuric over the whole range of pyridine/mercuric ratios and the rate constant would have fallen continuously with added pyridine. Thus it must be assumed that the complex ion Hg[C5H5N],++reacted slowly with the olefin, e . g . Hg[CSHsN]2++
+ C2H4 + BpO
+ + CIHBN
HOCzHiHgf CBHbNH+
The slower fall in rate constant toward a minimum value with the acetate may have been
1445
due to the fact that the salt is only partly dissociated in solution. With solutions of mercuric perchlorate, which did not contain excess acid originally, however, the minimum rate was not only much smaller but also occurred a t a higher relative concentration of base. Hydrolysis of mercuric ions occurs in perchlorate solutions in the absence of excess acid, the main species formed being Hg [OH], and the relative amount of HgOHf a t equilibrium being small, and the addition of ammonia to dilute mercuric perchlorate gives a pale yellow precipitate of a basic complex of indefinite composition, ie., zHgO. [l - a](Hg[C104J2. 2NHg).10 Thus with pyridine it is probable that a similar basic complex was formed and reacted more slowly with the olefins than Hg[C&N]z++ did. The complete complex formation in this case must have required a higher relative concentration of pyridine. The increase in rate at high pyridine concentrations was probably due to the increased solubility of the olefin in the pyridine-water mixtures. (9) S. Hietanen and L.G . Sillen, Acto. Chem. Seand., 6, 747 (1952). (IO) H. T. 6 . Britton and B. M. Wilson, J . Chern. Soc., 1045 (1933).
THE HEAT CAPACITIES OF YTTRIUM OXIDE (Y20a),LASTHANUM OXIDE (La203)'AND NEODYMIUM OXIDE (Nd20a)FROM 16 TO 3 O O 0 K 1 BY HAROLD W. GOLDSTEIN, E. I?. NEILSON,PATR~CK N. 'CVALSH A N D DAVIDWHITE Contribulion of the Cryogenic Laboratory, Department of Chemistry, The Ohio Stale U n i v e i d y , Colionbus, Ohio Received Februaru 19, 1969
The heat capacities of the sesquioxides of yttrium, lanthanum and neodymium have been determined in the temperature range 16 to 300°K. The entropies, enthalpies and free energy functions have been calculated from the heat capacity data and are tabulated for several temperatures. Yttrium oxide and lanthanum oxide exhibit typical sigmoidal heat capacity curves with no anomalies in the temperature range studied. The shape of the heat capacity curve for neodymium oxide is similar except that a t the lowest temperature there is evidence for the existence of an anomaly. At 298.16"K. the entropies are 23.693 0.07 and 30.580 f 0.07 cal. mole-' deg.-l for yttrium oxide and lanthanum oxide, respectively. For neodymium oxide S2gs.la - S I Bis 33.G07 cal. mole-' deg.-l. The free energy functions have been extended t o 2500'K. by the use of some higher temperature heat capacity data available in the literature.
*
Introduction The present study is part of a series of investigations being carried out in this Laboratory dealing with the thermodynamic properties of some rare earth oxides. Yttrium oxide has been included in these studies because of its similarity to these compounds. The heat capacities of many of the rare earth oxides can be expected to exhibit anomalies that are presumably related to their magnetic behavior. The magnetic properties of many salts of the rare earth metals have been investigated, and these properties correlated with tJhe electronic structure of the rare earth ions. Because of the structural similarity of the rare earth oxides, and the relatively small variations in molecular weight and lattice dimensions in this series3 it seems reasonable to assume that the lattice heat capacities of all these compounds will be very similar, and that the major (1) This work was supported by the Air Force Office of Scientific Research, Washington, D. C . (2) J. H. Van Vleck, "The Theory of Electric and Magnetic Susceptibilities," Oxford University Press, London, 1932. (3) W. Zaclmriasen, 2. p k u s i k . Chem., 123, 131 (1920).
differences will be due to the magnetic contributions associated with the degenerate ground states of the lanthanide ions. The total heat capacity of lanthanum oxide should be due entirely to lattice vibrations, as the La+3 ion has a 'So ground state. Hence, the heat capacity of Laz03may be used as an approximation for the lattice contribution to the heat capacities of the other rare earth oxides. Addition of the magnetic coiitributioii characteristic of any other member of the series should yield a reasonable estimate for the total heat capacity of that oxide. Of course, not a11 of the entropy, R In (2J l), associated with the ground state degeneracy, will necessarily be developed a t any given temperature. It was of interest, therefore, to study the heat capacity of neodymium oxide to determine the fraction of the magnetic entropy, resulting from the 419,2 ground state, that is developed a t room tempemture.
+
Apparatus and Procedure The equipment employed in this research and the procedure for the heat capacity measurements have been de-
1446
Vol. 63
H. W. GOLDSTEIN, E. F. NEILSON, P. N. WALSHAND D. WHITE
scribed by Johnston and Kerr.4 The temperatures reported are based on a thermodynamic temperature scale established by Rubin, Johnston and Altman.6 For all the rare earth heat capacity measurements, calorimeter "No. 3" was used. It is one of a group of seven calorimeters of identical design in use in this Laboratory. Although the calorimeter had been calibrated previously over the temperature range 16 to 300'K., the calibration was rechecked, before and after use, over the entire temperature range. Immediately before filling the calorimeter, the samples were heated to constant weight in a platinum dish at 950' in air, to decompose any hydroxide or carbonate present. The transfer of the sample to the calorimeter was carried out in a dry box with a helium atmosphere. After the heat capacity measurements were completed the calorimeter was emptied in the dry box. Portions of the sample were taken from the top, middle and bottom of the calorimeter and heated t o determine whether any contamination occurred during handling. In all cases these samples showed no weight change upon being heated for 24 hours a t 950' in air.
Materials Y20s.-The yttrium oxide, obtained from the Lindsay Chemical Company, West Chicago, Illinois, had a reported purity of greater than 99.9%. Analysis of the sample showed these impurities: Gd203, less than 0.01%; Dy203, less than 0.01%; and HotOs, less than 0.02%.6 A powder X-ray pattern of the heat treated material showed only the cubic, Mn203 ty e, sequioxide structure.' La203.-The inthanurn oxide, obtained from the Lindsay Chemical Company, had a reported purity of 99.997%. Analysis of the sam le showed only 1.5 p.p.m. of Fez03 as impurity.6 A pow%er X-ray pattern of the heat-treated material showed only the A-form sesquioxide structure.6 Ndz03.-The neodymium oxide, obtained from the Lindsay Chemical Company, had a reported purity of 99.9%. Analysis of the sample showed as impurities: PrsOll, less than 0.1%; SmzOa, less than O.l'%.6 A powder X-ray pattern of the heat-treated material showed only the A-form sesquioxide structure.*
Experimental Results The heat capacity measurements were made using GO.8GSO g. (0.26952 mole) of yttrium oxide, 98.9526 g. (0.30368 mole) of lanthanum oxide and 97.9633 g. (0.29109 mole) of neodymium oxide. The molecular weights were taken as 225.84, 325.84 and 336.54, respectively. The experimental heat capacities, expressed in terms of the defined thermochemical calorie, equal to 4.1840 absolute joules, are listed in Tables I, I11 and V. Values of the heat capacities a t selected temperatures, read from smooth curves through the experimental points, together with derived thermodynamic functions, are given in Tables 11,IV and VI, for yttrium oxide, lanthanum oxide and neodymium oxide, respectively. As evidence exists for an anomaly in the specific heat curve of neodymium oxide below lG°K., thermodynamic functions for this substance are given relative to lG°K. The entropy of yttrium oxide a t 298.16"K. is 23.693 cal. mole-I deg.-', of which 0.112 cal. mole-' deg-l is contributed by extrapolation below 1 G 0 K A Debye 0 of 178 degrees, est,imated from the lowest temperature heat capacities, was used for the extrapolation. The uncertainty in the entropy is estimated to be k0.07 cal. mole-' deg.-l, of which 2tO.02 cal. mole-' deg.-' is due to the extrapolation (4) H. L. Johnston and E. C. Kerr, J . Ant. Ckena. SOC.,72, 4733 (1950). (5) T. Rubin, H. L. Johnston and H.Altman, ibid., 73,3401 (1951). (0) Analyses supplied b y Lindsay Chemical Co. (7) H. W. Swanson, R . I
So
9
oal. mole-' des.-'
cal. mole-] deg. - 1
0.323 .405 ,777 1.717 2.796 3.966 5.236 6.545 7.854 9.152 11.66 13.06 16.03 17.86 19.37 20.64 21.75 22.77 23.70 24.50 24.58
0.1120 ,1928 ,4120 ,7575 1.255 1.867 2.572 3.357 4.204 5.098 6.991 8.965 10.966 12.963 14,925 16.833 18.677 20.459 22.181 23.693 23.846
-
H Q Hoo, cal. mole-'
1,342 2.796 8.320 20.56 43.06 76.77 122.71 181.61 252.88 338.66 547.07 803.70 1103.9 1443.3 1816.1 2216.6 2640.6 3086.1 3550.9 3989.3 4033.7
-(P oal .mole HoOyT, deg. - 1
0.02812 ,05300 .1347 .2436 .3941 ,5873 ,8194 1.0867 1.3937 1.7117 2.4324 3.2240 4.0666 4.9443 5.8447 6.7573 7.6742 8.5895 9.4992 10.313 10.400
below 16'K. The entropy of lanthanum oxide a t 298.16"K. is 30.580 cal. mole-' deg.-*, of which 0.1535 cal. mole-' deg.-' is contributed by extrapolation between 16"K., using a Debye e of 160 degrees. The uncertaint,y in the entropy is estimated to he 2t0.07 cnl. mole-' deg-', of which 2tO.02 cnl.
TABLE V HEATCAPACITY OF NEODYMIUM OxIm
TABLE I11 HEATCAPACITY OF LANTHANUM OXIDE Mean
T,
OK.
16.91 19.55 '31.27 23.35 25.36 27.78 30.39 33.12 36.13 39.73 43.95 48.52 53.73 58.49 69.81 75.77 82.12 88.71 92.13 98.17 104.46 110.89 117.22 123.45
CP
Mean
cal. m61e-1 deg. - 1
T,
OK.
0.501 0.850 1.067 1.278 1.469 1.870 2.111 2.552 3.184 3.764 4.357 5.071 6.187 6.991 8.683 9.681 10.475 11.450 11.930 12.668 13.488 14.239 14.980 15.757
129.80 136.48 142.67 148.65 155.04 166.03 171.57 177.35 183.07 188.81 201.66 215.03 221.90 228.54 235.16 241.61 254.11 260.07 272.36 279.79 287.18 294.27 300.30
CP 8
cal. mole-' deg. -1
&lean T,
16.376 17.110 17.647 18.200 18.661 19.534 20.070 20.364 20.680 21.236 21.967 22.675 23.123 23.330 23.633 23.910 24.529 24.687 25.066 25.277 25.395 25.662 25.640
18.26 20.28 22.34 24.27 26.05 27.78 29.43 31.37 33.43 35.71 36.94 37.70 39.43 40.25 42.46 42.86 45.58 48.91 52.63 55.47 56.72 60.47 60.97 65.67 72.70 78.53 84.78 90.89
TABLE IV THERNODY NAMIC FUNCTIONS FOR LANTHANUM OXIDE HO - Ho', -(Fo - HoO)/T, CP, so I
T,OK.
16 20 30 40 50 60 70 80 90 100 120 140 160 180 200 220 240 260 280 298.16 300
1447
LANTHANUM AND NEODYMIUM OXIDES HEATCAPACITIES OF YTTRIUM,
Sept., 1959
cal. mole-' deg.-l
cal. mole-] deg.-l
cal. mo1e-I
cal. mole-1 deg. -1
0.526 0.800 2.094 3.742 5.480 7.135 8.697 10.18 11.60 12.94 15.35 17.39 19.08 20.57 21.86 22.91 23.83 24.61 25.27 25.79 25.84
0.1535 .3049 .8713 1.6920 2.7143 3.8612 5.0794 6.3390 7.6209 8.9131 11.491 14.016 16.451 18.787 21.022 23.157 25.191 27.130 28.979 30.580 30.742
1.838 4.576 18.600 47.525 93.662 156.82 236.05 330.54 439.51 562.28 845.79 1173.9 1539.0 1935.9 2360.6 2808.7 3276.3 3761.0 4260.0 4724.2 4771.2
0.03862 .07610 .2513 .5039 ,8411 1.2475 1.7073 2.2072 2.7375 3.2903 4.4427 5.6310 6.8322 8.0320 9.2190 10.390 11.540 12.665 13.765 14.735 14.838
mole-1 deg.-' is due to the extrapolation below 16°K. For neodymium oxide, S298.1a - SIC, is 33.607 cal. mole-' deg.-'. Discussion Yttrium oxide and lanthanum oxide show typical sigmoidal variations with temperature and exhibit no anomalies in the temperature range studied. The heat capacity of lanthanum oxide, however, a t any given temperature, is greater than that of yttrium oxide. Although yttrium oxide is classified with the rare earth oxides, its heat capacity can be
OK.
CP
Mean
oal. m h e - 1 deg. -1
T,
OK.
96.86 103.38 109.57 115.67 121.88 128.14 134.41 141 .OO 147.30 161.32 167.68 173.97 180.27 186.97 193.54 200.02 206.45 212.45 222.88 229.88 236.50 243.29 250.12 263.43 277. GO 284.76 291.49 298.13
2,200 2.422 2.673 2.889 3.106 3.308 3.542 3.755 4.064 4.384 4.689 4.785 5.105 5.239 5.586 5.644 5.929 6.421 7.036 7.541 7.750 8.221 8.351 9 .a04 10.083 10.801 11.711 12.625
CP v
cal. mole-' deg.-l
13.202 14,126
14.882 15.610 16.394 16.998 17.589 18.218 18.819 20.017 20.440 20.935 21.354 21.866 22.316 22.590 23.007 23.302 23,742 24.195 24.467 24.728 24.834 25.401 25.910 26.205 26.390 26.401
TABLE VI THERMODYNAMIC FUNCTIONS FOR NEODYMIUM OXIDE
16 20 30 40 50 60 70 80 90 100 120 140 160 180 200 220 240 260 280 298.16 300
-
cal. mole-1 deg.-l
ST Sla, cal. mole-) deg.-l
1.988 2.394 3.619 5.105 6.680 8.202 9.666 11.07 12.44 13.74 16.10 18.14 19.88 21.37 22.65 23.72 24.58 25.32 26.01 26.59 26.65
0.4863 1.6785 2.9186 4.2271 5.5805 6.9556 8.3382 9.7216 11.100 13.819 16.458 18.997 21.426 23.746 25.957 28.058 30.056 31.958 33.607 33.774
Cp,
T,O I L
HT
- Hi8
cal. mole-i
8.748 38.563 82.024 140.95 215.42 304.82 408.51 526.09 657.06 955.99 1298.9 1679.6 2092.4 2533.0 2997.0 3480.3 3979.4 4492.8 4970.9 5019.4
-(FT
- Hld/T,
cal. mole-' deg. -1
0.04890 ,3931 .8680 1.4081 1.9902 2.6010 3.2318 3.8762 4,5294 5.8524 7.1801 8.4995 9.8016 11.081 12.334 13.557 14.751 15.912 16.935 17.043
expected to be considerably lower than that of lanthanum oxide, owing to the large difference in molecular weight, if one assumes the heat capacity to result only from lattice vibrations. This is not the case when one compares the rare earth oxides, neodymia and lanthann. Due to the small difference in mass of these compounds and the similarity of
1448
H. W. GOLDSTEIN, E. F. NEILSON,P. N. WALSHAND D. WHITE
their crystal structure^,^ one should expect their lattice heat capacities to be nearly equal. The greater heat capacity exhibited by neodymium oxide a t any given temperature can therefore be attributed to a magnetic effect associated with the presence of Nd+3ions in the lattice. This is consistent with the observed paramagnetism of many salts of neodymium. Blomeke and Zieglerg have determined the heat capacities of neodymium oxide and lanthanum oxide between 30 and 900". Their results suggest that even a t the highest temperatures there is still a considerable magnetic contribution to the heat capacity of neodymium oxide. Assuming that the lattice heat capacity of neodymium oxide is identical with that of lanthanum oxide, the magnetic contribution can be obtained by comparing the heat capacity differences at any temperature. This magnetic heat capacity is shown in Table VII. Unfortunately there exists no specTABLE VI1 MAGNETIC HEAT CAPACITY O F CPS
NEODYNIIUM
OXIDE
CP s
T,OK.
cal. mole-1 deg.-l
T,O K .
cal. mole-' deg.-l
16 20 30 40 50 60 70 80 90 100 120 140 160 180
1.46 1.53 1.53 1.36 1.20 1.07 0.97 .89 .84 .80 .75 .75 .80 .80 .79
220 240 260 280 300 400 500 600 700 800 900 1000 1100 1200
0.81 .75
200
.71
.74 .78 .81 1.12 1.49 1.83 2.14 2.43 2.72 3.02 3.29
troscopic data for neodymium oxide which can be used to compute the magnetic heat capacity. The absorption spectrum of the salt Ndz(S04)34Hz0 has been observed by Spedding, Hamlin and Nutting.'O Although the two observed electronic levels, 77 and 260 cm.-l, are in agreement with the heat capacity datal1 (assuming the ground state of the Nd+3 ion is 41e/2)the situation in neodymium oxide can be expected to be considerably different. Not only are the electric fields in these two crystals quite different but the closer proximity of the Nd+a ions in the oxide could give rise to large magnetic interactions at temperatures considerably above absolute zero, This might result in an increase in the heat capacity, as suggested by our data a t the lowest temperatures. If the ground state of the Nd+a ion is 419/2,then the magnetic entropy of neodymium oxide a t high temperature is 9.16 cal. mole-' deg.-1. From the experimental data it is found that the magnetic contribution to the entropy between 16 and (9) J. 0. Blomeke and W. T. Ziegler, J . Am. Chem. Soo., 73, 5099
(1951).
(10) F. H. Spedding, H. F. Hamlin a n d G. C. Nutting, J . Chem. Phys., 6 , 191 (1937). (11) J . E. Ahlberg, E. R. Blanohard and W. 0. Lundberg, i b i d . , 6,
552 (1937).
Vol. 63
298.16"K. is 3.17 cal. mole-' deg.-'. (The lattice entropy is assumed equal to that of lanthanum OXide.) Not only is this a small fraction of the total possible magnetic entropy but it is considerably less than the spin-only value (2R In (28 1) = 5.50 cal. mole-l deg.-'). The absolute magnetic entropy, however, may be considerably larger than 3.17 cal. mole-1 deg.-' when the entropy below 16°K. is taken into account. In order to establish a reasonable estimate for the absolute entropy of neodymium oxide a t 298.16"K., a comparison with the actinides has been made. In neptunium dioxide (possible ground state 41s/2)it has been found that the spin-only value of the magnetic entropy is attained a t 95"K.12 I n uranium dioxide (possible ground state 3H4) the spin-only value is attained at 73°K.12 As a first approximation, it has been assumed that for neodymium oxide, ground state 419/2, the spin-only value of the magnetic entropy is attained at 100°K. Combining this with the lattice contribution, the entropy of lanthanum oxide a t this temperature, one obtains a value for the absolute entropy of neodymium oxide a t 100°K. of 14.413 cal. mole-' deg.-l, which, when combined with the increase in the entropy between 100 and 298.16"K. calculated from the experimental data, gives 36.92 cal. mole-' deg.-' for the entropy a t 298.16"K. The entropies and free energy functions of yttrium oxide, lanthanum oxide and neodymium oxide from 298.16 to 2500°K. are given in Table VIII. In the case of lanthanum oxide, these thermal functions were computed from the results of this research and that of Blomeke and Ziegler,$ extrapolated to 2500°K. As no high temperature heat capacities have been reported for yttrium oxide, the low temperature data were extrapolated on the assumption that the temperature dependence of the heat capacity above 300°K. is identical with that of lanthanum oxide. In the case of neodymium oxide, a simple extrapolation cannot be employed to obtain the thermal functions a t high temperatures. This is evident when one examines the data in Table VII. At the higher temperatures, it appears that a magnetic anomaly, possibly attributable to excitation to the 4111/2 state, may be developing. Although there is no informatioii on the energy difference between the 4 1 y / ~ and the 4111/2 states of Nd+++ in crystalline Nd& a value of 0.2 e.v. was assumed in order to estimate the heat capacity at 2500°K. (This is approximately the value found for dilute salts13 and dilute solution^'^ of N d + + + and should be considered only a first approximation.) Assuming the lattice heat capacity a t 2500°K. to be that of La203,one finds the heat capacity of Nd203a t this temperature to be 37.00 cal. mole-l deg.-l. For the calculation of the thermal functions of Ndz03 between 1200"K., the limit of the Blomeke and Ziegler data, and 2500"K., an arbitrary smooth curve was drawn linking the heat capacity data of the former with the value calculated a t 2500"K., such that the heat capacities a t 1500,1800 and 2000"B. were 36.71, 36.89 and 36.85 cal. mole-l deg.-', respectively.
+
(12) D. W. Osborne and E. F. Westrnm, Jr., ibid., 21, 1884 (1953). (13) W. 0. Penny and R. Sohalpp, P h y ~Rev., . 41,202 (1932). (14) 8. P. Keller and 0. D. Pettit, J . Chem. Phya., S O , 434 (1959).
Sept., 1959
RADIOLYSIS OF METHANOL AND METHANOLIC SOLUTIONS BY COBALT ?-RAYS
1449
TABLE VI11
---
HIGHTEMPERATURE ENTROPIES A N D FREE ENERGY FUNCTIONS
-
I
Temp., OK.
298.16 500 1000 1500 2000 2500
.
YrOa LanOa Nd203 So, - ( P o - Hoo)/T, SO, -(FO HoQ)/T, S O -(FO - Hoo)/T, cal. mole-’ deg.-l cal. mole-’ deg.-l cal. mole-1 deg.-l cal. mole-’ deg.-l cal. mole’’ deg.-l cal. mole-’deg.-l
23.69 37.98 59.04 72.18 82.00 89.07
10.31 18.75 34.15 44.76 52.89 59,52
30.58 45.02 66.08 79.22 89.04 97.01
14.74 24.39 40.49 51.33 59.58 66.28
36.92 51.44 73.80 88.26 98.86 107.08
20.21 30.16 46.94 58.44 67.28 74 45
Acknowledgments.-The authors wish to ac- some of the experiments and of Mr. John Farnham knowledge the assistance of Mr. Donald Flynn in in carrying out preliminary measurements.
RADIOLYSIS OF METHANOL AND METHANOLIC SOLUTIONS BY Co60 7-RAYS AND 1.95 X 10‘ VOLT VAN DE GRAAFF ELECTRONS’ BY NORMAN N. LICHTIN~ Contribution frono the Department of Chemistry, Brookhaven National Laboratory, Upton, N . Y . Receioed Februaru 1 9 , 1969
Yields of hydrogen, formaldehyde, ethylene glycol (determined by means of an improved procedure), methane and carbon monoxide per 100 e.v. of absorbed radiation obtained on irradiation of methanol are compared with values reported in the literature. The several sets of data are not in good agreement with each other. Initial study of the effects of several solutes suggests a variety of modes of intervention in the radiolytic process.
The radiolysis of methanol and methanolic solutions has been the subject of an increasing number of investigatioma Two recent reports4f6dealing with the action of Co60 y-rays on pure dry methanol and on ZL variety of solutions in this solvent include extensive discussions of the mechanisms of the radiolytic processes. These two reports are not in good agreement with each other or with earlier with respect to the G-yields of the principal of radiolysis of pure methanol, Hz, CH,, CO, CHzO and HOCH2CH20H, nor as t o the effect of small amounts of water. Although the work described below does not provide a basis for mechanistic interpretation, it presents additional extensive data on the radiolysis of pure methanol. These data are not in complete accord with any one of the previously published reports. The results of a preliminary survey of the yields of the five principal products obtained on radiolysis of solutions containing a wide variety of solutes are also reported and discussed. Experimental Methanol.-Mallinckrodt AR anhydrous grade material was employed. This was generally subjected to rectification by means of a 50 theoretical plate glass-helix packed column protected from atmospheric moisture; the first ( 1 ) Research carried out under the auspices of the U. S. Atomic Energy Commission. (2) Visiting Chemist at the Brookhaven National Laboratory, 19571958. Department of Chemistry, Boston University, Boston, Mass. (3) (a) W. J. Skraba, J. C. Burr, J r . , and D. N. Hess. J. Chem. Phys., 21, 1296 (1953)’ (b) W. R . McDonell and A. S. Newton, J . Am. Chem. Soc., 76, 4651 (1954); ( 0 ) W. R . McDonell and S. Gordon, J . Chem. Phys., 28, 208 (1955); (d) W. R . McDonell, zbid., 28, 208 (1955); (e) G. Meahitsuka, K . Ouchi, K . Hirota and G . Kosumoto,J. CAem.Soc. J a p a n , 78, 129 (1957). (4) G. Meshitsuka and M . Burton, Rndzdtion Research, 8, 285 (1958). (5) G . E. Adrtms and J . H. Baxendale, J . A m . Chem. Soc., 80, 4125 (19581.
third of the distillate routinely was discarded. (The methanol employed in half of the Van de Graaff runs was not rectified. No systematic difference in results distinguished these runs from the other experiments.) Eastman 99.9% “Grignard Grade” magnesium (1 to 2 g./lOO ml. methanol) was added and the flask containin the methanol then was attached via a T joint to a manifo% used in drying and degassing the methanol and filling the radiation cells. After dissolution of the magnesium was complete, the methanolic Mg(0CHa)t was refluxed for a minimum of three hours. Tubes containing silica gel and “Ascarite” protected the solution so long as H, was venting. Degassing was next accomplished by alternately pumping with a diffusion pump while the methanol was frozen in liquid nitrogen and permitting the methanol to warm t o room temperature under autogenous pressure. A minimum of three such cycles was always employed. Each aliquot of dry degassed methanol was distilled at autogenous pressure through a trapping system into a radiation cell (chilled to -80”) which was attached to the manifold via a T joint. The cell then was sealed off a t a constriction. Sample sizes were determined by weight. The density of methanol was taken as 0.790 in calculations. . Solutes and Preparation of Solutions.-Magnesium methoxide solution was prepared by distilling dry degassed methanol onto magnesium metal (Eastman “Grignard Grade”) maintained a t -80”. Dissolution of the metal did not apear t o begin until the solvent warmed to room temperature. hydrogen evolved into an isolated portion of the manifold and was removed rigorously by a degassing procedure like that described above. Water and heptaldehyde (Eastman “White Label”) were introduced into cells equip ed with stopcocks and were separately degassed in the uauarway before the solvent was distilled in. Cells containing samples of benzoquinone (Eastman “Practical,” recrystallized from ligroin and then sublimed) and maleic anhydride (Pfanstiehl, “Pure”) were also equipped with stopcocks and were subjected t o prolonged pumping while maintained a t -80’ before distilling in the solvent. Cells containing lithium chloride (Baker “Analyzed”), pyrogallol (Eastman “White Label”), anthracene (Eastman “Fluorescent Grade”), sulfuric acid (concd. B. and A . , C.P.), FeCl3.6H?O(B. and A . “Reagent” grade) and boric oxide (B. and A . “purified grade”) were subjected to prolonged pumping at room temperature. A trace of the anthracene and a substantial fraction of the ferric chloride (estimated as 10-207& of added solute) did not dissolve even after prolonged shaking a t
