YOTES
April, 1900 e.v. to less than 4.06 C . V . would quench the re:Ict ion. 7'hc. differciicr. in the quenching for the differeat foreign gases is explained by their different effectiveness in producing vibrational deUnfortunately, little of quantitative significance can be said on this point for two reasons. First, vibrational deactivation appears to be quite sensitive to traces of certain impurities, especially water. l 2 Second, experimental information on vibratioixil deactivation of Or comes from sound dispersion measurements, in which the lower vibrational levels of the X3Z,- state are involved and not tlte upper ones of the ]Ag state. Cross sections in A.z for quenching of Hg(3P1) hy the gases in question ares: He, 0; Ar, 0; Sz, 6.0; O,, G2-70; CO?, 11.1. X2 and CO, could theitfore also decrease the reaction rate by decreasing the concentration of Hg(3P1) as well as by dencti.;ating the 1-ihrationally excited O2('AP). In conrlusion. we wish to suggest that the O?* which occurs in the process is likely to be a molecule i i the lZU-state Tvhich passes over into the l& state tiy pressure-induced predissociation. This mechanisni satisfies the main arguments given by Gill :uid Laidler and also satisfies T'olman's points on thc effect of foreign gases. Further experimental n-orli TI-ouldbe most valuable. Acknow1edgrnent.-The authors wish to thank Professor B. de B Darnent for helpful discussions mid comn3eiitq.
-
-
507
Fig. 1.
over a range of temperatures near to the melting point are generally available, the molar volume change on fusion AT; may be obtained. Experimental The measurements consist of the determination as a function of temperature of the free volume inside a vessel containing a known weight of salt in a platinum crucible. A constant volume manometer (temperature T , and containing gas of volume 0,) is connected by a capillary of negligible volume t o the salt container situated inside a furnace at temperature Tr. A calibration bulb of known volume ub may be connected to the system, or to a vacuum line by a two-way stopcock. The free volume in the salt container, vi, is obtained from the change in pressure in th'. system when i t is connected to the evacuated calibration bulb. If p l and p , , respectively, are the pressures in the system before and after the expansion, i t can he shown that
(12) J . C \I((onbr~~ nnd K D. 3IcGrsth Quart. Rets., 11, 87 (1057).
is ohtained by weighing; and is determined by measuring the change of pressure in the system n i t h the capillarv sealed off just above the level of the furnace. The change in 211 n4th temperature is due to the combined expansions of the T'ycor vessel, platinum crucible and the salt. Thus, at any temperature t the densitv of the salt, p t , may be calculated from the expression 1 = -1+ Av, - AvC - At'i (2)
L'b
DEKSITIES O F SOLID SALTS AT ELEVATED TEMPERATURES BKD MOLAR VOLUME CHhSGE OK FUSIOX BY
J. 0'11.BOCKRIS, .%. PILLAAND J. L. B.4RToN
John Hairiso:? Laboratory of Chemistry, Gnicersili~of Pennsylvania, i'hiladelphin, Penna. Rereired S o v e m h r r 19, lD6Q
Dat,al-Yfor the molar volume change on fusion of simple inorganic salts are sparse and discrepant ; those for the bulk densities of solid salts at elevated temperatures have not been reported. Knowledge of the change of volume on fusion is of use as a basis for the eva,luationof structural models for the liquid pure electrolytes4; that of densities indicates changes in crystal structure in the solid which must he known before interpretation of the structural implications of the volume change on fusion can be evaluated. Here, a high temperature gas densitometer is described, Jvhich has been used to measure the expansion of a solid salt from room temperat'ure t'o just helox the melting point'. As t'he solid densities a t room temperature and the liquid densities ( 1 ) G . J . T,an(lon and A . R. Ubbelohde, T r a n s . Faraday Soc., 62, 617 il936). 121 TI. Fciiiiihc a n d F. Sariorwald, Z. a n o w . allgem. Chem., 287, 313
1 os(;). ( 3 ) 11.-1.Eredig and .J. IT. Johnson. ORNL-1940 p. 19. ( 4 ) J. 0'11.Bockris a m l K. E. Richards, PTUC. Roy. Soc. (London). 241, 41 (1957) (5) E. A. Moelwyn-Hughes, "Pliysical Chemistry," Pergamon Press, London, 1957, p. 728-735. I
1
Pt
Ptr
3
~
w
nhere W is the weight of the salt, p t r is its density a t room temperature; ALL, Azic and Avi are the changes in volume between room temperature, t,, and temperature t of the s'ycor vessel, the platinum crucible and vi, respertively. A v , is calculated from the total internal volume of the Vycor vessel using the expansion coefficirnt 8.0 X lo-'. A i c is calculated from the weight of the crucible using the dcnsity values of Shartsis and Spinner.G Usuall> , (Av, Aut) is about 4% of At f. The crucible A (Fig. 1) is 36 mm. o.d., 50 mni. high, 1 mm. thick. The Vwor vessel, B, encases the crncible to within c.2 mm. so (hat expansion of the salt reduces the free volume bv a significant fraction. T h r volume z'f is about 25 rc. and the salt volume about 40 cc. The eapillary D between the vessel. and the constant vohime manometer G is 1 mm. i.d., vr ic: about 8.5 cc. The calibration bulb E of 15 cc. reduces the pressure by a fartor of ahout one half. The furnace is water jacketed and its winding (Kanthal A-1) is tapped a t six points to allow a temperature uniformity of j=0.lo to be obtained in the region of the container (surro;inded by .41?01). The temperature i c mcasurcd to 1 0 2 . The molten salt is introduced through an orifice in 13 into A , after the latter has been sealed into B. The apparatus is evaruated Kith the sample a t room temperature, and then filled with Ar purified by passage through Ka-K. Determinations of z'i are made a t a series of temperatures, the highest being about 10' below the melting ( 6 ) L. Shartsis and 170 (1061).
S.Spinner, J. Reseaich .Vall Bur. Standards, 46,
KOTES
508
Yol. 64 TABLE I NCI
:4-1 42
-
.I
al*r,’I; 0. IT(’1
h l ct hoti
2 5 . 5 8 rt 0.07 20.20 =k 0 . 0 3 1’restwt nir:isiirenic3nts 22.8 .7 lii.8 =k . 5 T,inearex~)nriPiorrio 23.0 hTotspecified” 30.0 C!rystallization pycnom25.0 rt . 5 1 7 . 3 rt . 5 etry2 23.2 rt 2.0 17.5 rt 2 . 0 Ext,rapolatrd density data3 21 .O i 0 . 5 Crystallizat.ion pycnometry’
liquid salts concerned of about 10+ mole cc.-’. Grimes, et aZ.,12f13have shown that the solubility 0 200 400 600 800 1000 of noble gases in various molten salt systems is of this order. The method might thus he adapted to Temp. (“C.). the measurement of gas solubilities in molten salts. Fig. 2. Acknowledgment.-Thanks are due to the point. At each temperature, three measurements are made Atomic Energy Commission, Contract KO.&4t30-1using different initial pressures in the range 300-700 mm. 1769, for financial support of this 1%-ork.
Fine adjustment in pressure measurement is made by applying pressure to the tubing with the adjustable clamp I until the needle F just touches the mercury surface. Pressure measurements are reproducible to rt0.05 mm. and of measurements a t a given temperature to r t O . l % . I n general it is found about 1 min. is required for equilibration after expansion and about 45 min. for equilibration after change in temperature. T o test for the presence of cavities in the sample as normally prepared, it was melted in situ and allowed to cool slowly from the bottom upward. Values of ur obtained before and after the re-freezing agreed to within the normal experimental error (*0.3%). The form of the apparatus is similar to that employed by Nachtrieb and Clement.’ The procedure, however, involves no measurements with the salt in the molten state so that difficulties which arise from the solubility of Ar in the fused salt are avoided. Moreover, i t is unnecessary to apply vacuum to the salt at elevated temperatures, thus avoiding clogging of the capillary.
(10) A. Eucken and E. Dannohl, Z. Elektrochem., 4 0 , 814 (1934). (111 A. Eucken, 2. angeu. Chem., 66, 103 (1942). (12) W. R. Grinies, N. V . Smith and G. AI. Watson, Tmn JOCRXAL, 62, 862 (1958). (13) M. Blander, ‘Ar. R. Grimes, N . V. Smith ani1 G . A f . Watson, i b i d . , 6 3 , 1104 (1959).
THE EFFECT OF ALKAKOLS O?: ;\lhLOSIC ACID BY
L O U I S ~ ~ A T CLARK T S
Contitbution f r o m the Department of Chemistry, Saint I f a i i i o i t h e Plains College, Dodge Ctfy, Kansas Receioed Soceniber 80, 1969
When malonic acid is placed in contact with a nucleophilic solvent a t a suitable temperature it decomposes into acetic acid and carbon dioxide. Results From room temperature densities8 and the meas- To date this reaction has been studied kinetically ured expansivities these equations were found in 41 polar liquids comprising representatives of 13 homologous series.’ These studies have amply for density of the solid salts confirmed the mechanism of the reaction proposed PKCI = 1.985 - 5.459 X 10-5 t - 1.836 X 10-7 t 2 by Fraenkel and co-workers,2 namely, the forma(rtO.001 g. cc. -1) tion, prior to cleavage, of a transition complex pYnri = 2.168 - 1.267 X l o v 4t - 1.754 X 10+ t 2 involving coordination between the electrophilic ( f 0 . 0 0 2 g. cc. -1) carbonyl carbon atom of the malonic acid and the where t is the temperature in “C. Hence, the molar unshared pair of electrons on the nucleophilic volumes of the solid a t the melting point, V,, may atom of the solvent molecule. In addition these be calculated and compared with those obtained studies have contributed to a better understanding from the corresponding density data for the liquidsg of the electron properties of the solvent molecules. Although the reaction has been studied preto give the molar expansion on fusion AVf. Values of AVf expressed as a fraction of the solid viously in several hydroxy compounds, namely, molar volume are given, together with the values four monocarboxylic acids,3 one phen01,~one alicyclic alcohol‘, and one aromatic alcohol’, it has obtained by other investigators, in Table I. Figure 2 shows the variation of molar volume of not been studied in any of the aliphatic alcohols. KC1 from room temperature to above the melting Because of the unique position of the alkanols in the family of polar liquids it was deemed advisable to point. ilttempts to measure AVf from the change in investigate the reaction in several representatives pressure over the melting point were not successful. of this group in order t o fill this hiatus. The The app:trent changes were 3040% lower than present paper describes the results of kinetic those found by other methods. The discrepancy studies carried out in this Laboratory on the decan be awounted for by a solubility of Ar in the carboxylation of malonic acid in six aliphatic alco(7) N. H Nachtrieb and N. Clement, THISJOURNAL, 62, 747 (1958). (8) “International Critical Tables.” Vol. 3, McGraa-Hill Book Co., New York, N. Y., 1928, p. 43. (9) I. S. I’affe a n d E. R. Van Artsdalen, THISJOURNAL,60, 1125 (1956).
(1) L. W. Clark, T i m J O L R Y A L64, , in prers (1900). and rx-e\ioiis papers in this aeries. (2) G. Fraenkel, R. L. Beiford and P. E. YanLaich, J . Am. Chem. S O C . , 15 ~ ~(1954). , (3) L. W. Clark, THIS JOURNAL,64, 4 1 (1960). (4) L. W. Clark. abad.. 6 2 , 1468 (1058).
