Fc'pt., l % i l
FLUOHESCESCE AX 11 PHOSPHORESCENCE OF THIFLCOROACETONE TT.4po~
1519
Heat of Deaquation by DTA.-The A H of the TABLE 1 FIRST-ORDER KATE CONSTANTS AND ACTIVATIOK ENERGIESdeaquation reaction was determined by the method of quantitative DTA. This method is FOR T E E !lQUOPENTA\IMIKECOBALT( 111) COMPLEXES Ttmp., C.
-log
E*,
k
Order
kcal.
86 90 95
3 37 3 24 3.10
1
19f2
[ C O ( S H : ) ~ H ~ O ] B ~ ~ 85 90
1
25&2
93.7
3 32 3 12 2 94
[ C O ( ; I ; H ~ ) ~ H ~ O ] ( X O82 ~)~ 85 88
3.77 3 60 3 45
1
31k3
Compound
[Co(NHa)sHzO]CIA
Dissociation Pressure Measurements.--illthough Lamb aiid nlarden5 concluded that the transformation illustration in equation 1 was noiireversible in the solid state, hIori, et aZ.,'assumed that they obtained equilibrium dissociation pressures for the chloride complex in the 21 to 48" temperature range. They reported a dissociation pressure of 2.15 mm. a t 25" and 6.93 mm. a t 48". Previous rough measurements5 yielded values of approximately 5 , 4 and 4 mrn. for the chloride, bromide and nitrate compkxes. respectively, at 25". I n this investigation, ~ i attempt i TVRS made to confirm the results of Nori, et al.,s and establish the reversibilitg of the reaction. For the [Co(SH3)5&O]Cl3 complex, 2.fter 100 hr. a t 28.0", a dissociation pressure of 38.0 mm. was obtained. The temperature then was lom-ered to 25.0" and after 500 hr. the preseure did not change from its initial Yalue. Similar results were obtained for the bromide and nitrate complexes. ilIoriZ4stated that the system reached an equilibrium dissociation pressure after about 12 hr. a t any specific temperature. Howes~er, it is apparent from the above results that the system is not reversible. (24) RI. 3Iori private communication.
based upon the premise that under certain experimental conditions, the heat of reaction can be evaluated by integration of the differential curve peak of peaks. From the various theories on quantitative DTX, that of Speil, et a1.,25 states that the peak area is
where tl and t:! are the time limits of the peak, 0 is the differential temperature, AH is the heat of reaction involved in the chemical change, M is the mass of reactive sample present, X is the thermal conductAvity of the sample, and g is a constant dependent, on the furnace and sample holder geometry. To det'ermine the above constant's, the apparat,us was calibrated by studying reactions of known hhermal effects. The heat's of deaquation, a t 108", obt'ained by use of the above method were 6.1 and 7.8 kcal. mole-' for [Co(XH3)5H*O]C13 and [CojKH3)5HzO]Br3, respectively. Because of the many variable factors involved, no great accuracy is claimed for the above results. However, the values obtained are probably indicative of the true heats of deaquatioii. Acknowledgments.-The assistance of T. D. George, W. Robinson and P. Ruhii is gratefully acknowledged. This work was supported iii part by t'he U. S. Air Force, Office of Research aiid Development, t'hrough Coiit'ract X o . AF-49(638)787. (2,5) S. Speil, L. H. Berkelhamer, J. A. Pask and B. Davis. Bureau of Mines, Tech. Paper 664 (1945). (26) 31. J. Vold. A n d . Chem.. 21, 683 (1949). (27) S. L. Roersma, J . Am. Ceyam. Soc., 38, 281 (1955).
I?, S.
THE FLUORESCEKCE AKD PHOSPHORESCESCE OF TRIFLUOROACETOSE VAPOR1 BY P. A c s ~ o o sAND E. MVRAU* iYatzonal Bureau o j Standards, Washington, D.C. Recezued Febi u a r y 28, I 9 6 1
The fluorrscence and phosphorescence of trifluoroacetone has been investigatd at 2652, 2804, 3025, 3130 and 3341 A. The effect of concentration and temperature on the yields of triplet and single-state emissions are comparable to those obP P ~ V Rfor ~ acetone The emissions from 2-butanone and 2-pentanone have been investigated briefly Both compounds phosphoresce v e x TI eakly and their fluorescence yields are nearly identical with those observed for acetone and trifluoroacetone.
Introduction Recent studies3$ on t,he fluorescence of hexafluoroac:et,onc: have c l ~ n r l yyhown that the emis11) 'I'liis I C Q C ~ ~ C I I Has supliortril iii ljai't tJy a g i a n t from tile U. R. l'Lil,lic llriiltli , S ~ r v i v v , I ~ v ~ ~ a , t , i t< ~> f~ Irl ri ut l t l i , I G I i i c ~ t i o n ,an(l \VPIfaie.
( 2 ) Natiorial Academy of Sciences-National Research Council Postdoctoral Research Associate 19.59-1960. (3) H. Okabe and E . W.R. Steacie, Can. J . Chem., 36, 137 (1958). (4) G . Oiacometti, II. Okabe and E . W.R . Steacie, Proc. R o y . SOC. (London), A260, 287 (1959).
sioii from this compouiid differs considerably froin that reported for a c e t , ~ n e . ~For # ~ inst'ance, iii the case of hexafluoroacetone, emission was observed from t h e upper singlet-stat,e, arid t,he yield pas: st,ror~glydrpendrnt, on tempr,rat,ure and pressure. 111 coiit i~ast, \vit,li t,liis I x h v i o r , t,he p}iohphorrsc.c.l,c.~~ of acetone niay be quite strong, depending 011 (5) For a review s e e : IT. A . N o y e s , Jr., G. B. Porter and J. E. Jolle>-, Chem. Reus., 6 6 , 49 (1956). (6) J. ISeicklen, J . Am. Chem. Soc., 81,3863 (1959).
TABLE I1 EFFECT OF CONCEKTRATION o s THE R E L A T ~ V E PHOSPHORESCENCE YIELDOF CF3COCH2AT 30""
temperature and prcssure, whereas the fluorescence is independent of pressure and temperature. Although the photochemistry of trifluoroacetone has been invest~gated,~,~ no information is available in the literature on the emission of the excited state of this compound. Experimental Trifluoroacetone was obtained from Merck and Company and was purified by g.1.c. techniques. Acetone (Spectrograde), 2-butanone and 2-pentanone were obtained from Eastman Kodak Company and were purified by distilling on a spinning band column. No biacetyl could be detected in the fractions used in this work. AJl compounds were thoroughly degassed and stored at -80 . The cell was made of quartz and was T-shaped. It was 56 mm. in length and 28 mm. in diameter. The light source was a Hanovia SEI-type mercury lamp. il Bausch and Lomb grating monochromator with a focal length of 250 mm. was used. The widths of the exit and entrance slits were 0.5 mm. The emitted light passed through a Corning No. 3850 filter to a 1.P28 photomultiplier tube. The phototube used to measure the transmitted ligklt was calibrated against a thermopile at the NBS. The relative fluorescence yields were obtained from an equation identical with the one used in the study3 of CFaCOCF3. No correction has been applied to readings made a t large absorbed intensities.
Concn., mo!e/l.
x
9.78 7.05 5.05 3.62 2.59 1.85 1.326 0.95 .68 ,485 ,348 ,249 .178 .091
hIoLAR EXTINCTION COEFFICIENTS AT 25' Wave length,
A.
2537 2652 2804 2594 3025 3130 3341
CHSCOCHa
7.7 11.2 12 4 10 3 6.32 2.86 < 0.1
CHsCOCFn
CHsCOCFa'
3 2 5.58 8.15 8.35 6.55 3.95 0 61
1.4 2.8 5.6
8.1 7 0 2 6
In this paper the emission which is not inhibited by oxygen is designated as fluorescence, The phosphorescence is thus the total emission minus the fluorescence. The numbers given in Tables 11, 111 and IV represent relative emission yields. The absolute emission yields are approximately 1/100 as large. The values obtained at 3341 A. may be slightly in error by a constant factor, because of the inaccuracy of the low extinction coefficient measured a t this wave length. Although no detailed analysis has been made of the fluorescence and phosphorescence spectra of trifluoroacetone, it may be pointed out that they are both displaced to longer wave lengths as compared to the emission spectra obtained for acetone under identical conditions. The displacement is (7) R. A . Sieger a n d J. G. Calvert, ibzd., 7 6 , 5197 (1954). ( 8 ) U . M. Smith a n d J. G. Calveit, zbid., 78, 2345 (1956).
2652 A. 1 . 6 1 10.52) 1.36 ,324) 1 . 0 5 ( 186) 0 . 7 5 5 ( .09) ,503 (.042) ,295 ,184
2R04 A. 1.83 1.88 1.64 1.385 0.77 ,345 ,318 ,221
3!25 A. 1.80 1.96 2.06 2.06 1.98 1.85 1.70 1 54 1.23 1,11
0.96 .81 ,605
3130 A. 1.58(1.59) 1.67 1 . 7 9 (1.67) 1.88 1 . 9 2 (1.71) L96 l.YZ(1.73) 1 92 l.gS(1.66) 1.82 1 . 7 1 (1.59) 1.66 1.60(1.47) 1.40
3341 A. 1.38 1.47 1.60 1.62 1.70
1.71 1.72
a The values given in parentheses are the phosphorescence yields of acetone.
TABLE I11 EFFECT OF TEMPERATURE ON THE RELATIVE PHOPPHORESCENCE YIELDS OF CF3COCHp Temp.. "C.
Results The absorption of trifliuoroacetone follows Beer's law over the concentration range reported in this work. The molar extinction coefficients, k(1. mole-' cm.-l) measured a t several wave lengths are given in Table I. For comparison, the extinction coefficients of acetone and hexafluor~acetone~ are included in the same table. It can be seen that the maxima of absorption for trifluoroacetone lie between the maxima for acetone and hexafluoroacetone. TABLE I
108
26528.
23 1.93 64 1.17 94 0.66 126 .. . Concn. 9.8 x 10-3
28048.
30258.
3130.k.
3341 A.
2.12 1.36 0.75 0.158 mole/i.
2.00 1.28 0.765 0.203
1.74 1.25 0.75 0.23
1.54 1.24 0.74 .22
TABLE IV T , 30' Compound
Phosphorescence
Fluorescence
CHiCOCFs CH3COCHs CH3COC2H5 CH3COCsH.i
1.92 1.73 0.12
