Dec., 1961
PHOTOLYSIS OF
2-PENTANONE-4,5,5-&
2257
exchange half-time for fresh melts is expressed by Conclusions The following conclusions are drawn from this the equation log t l / n = -1.800 2092 -study which has determined the temperature deT pendence for the rate of isotopic exchange of Z d 5 between molten zinc and zinc chloride in the tem3. The controlling rate in the isotopic exchange perature range 433-681 O : mechanism is an interfacial process yhich involves 1. The temperature dependence for the isotopic the equilibrium between mono- and divalent zinc exchange half time for saturated melts is expressed ions which can exist in molten zinc chloride-zinc by the equation metal systems. Acknowledgment.-The author wishes to express 2120 log t1/* = -1.220 his appreciation to the Atomic Energy Commission T and Atomics International, under whose auspices 2. The temperature dependence for the isotopic this work was carried out.
+
+
INTRAMOLECULAR REARRANGEMENTS. IV. PHOTOLYSIS OF ~ - P E N T A N O N E - 4 , 5 , 5 - d 3 l
BY R. P. BORKOWSKI~ AND P. AUSLOOS Kational Bureau of Standards, Washington,D. C. Received August 7, 1961
The photolysis of 2-pentanone-4,5,5-da in the vapor and liquid states yields DzC=CHD and DHC=CHD. These ethylenes are formed by intramolecular rearrangements in which either an H or a D-atom is transferred to the carbonyl group. DzC=CHD CH3COCHs (I) e CH&OCH&HDCDZH hv DHCcCHD CHsCOCH2D (11) I n the vapor phase the quantum yield of ethylene is independent of concentration, temperature and intensity, whereas i t decreases with increasing wave length and oxygen pressure. The effect of oxygen is more pronounced a t longer wave lengths and lower temperatures, which indicates that oxygen interacts only with molecules excited to a low vibrational level. The ratio CZD~H&HZD? is independent of intensity, but increases with increasing wave length and ketone concentration, and diminishes m t h increasing temperature and oxygen pressure. These effects may be explained qualitatively in terms of the difference in the bond strength of C-D and C-H. In the liquid phase the quantum yield of ethylene increases, and the ratio C?DSH/CzH2Dzdecreases with increasing temperature. A difference of activation energy of about 1kcal./mole was obtained for D and H transfer in the intramolecular rearrangement.
+
+
+
Introduction effects of oxygen on the quantum yield of the intraIn addition to undergoing radical dissociative molecular rearrangement a t different wave lengths processes, ketones which have hydrogen atoms and temperatures. The compound chosen to be in the y-position relative to the carbonyl group investigated was 2-pentanone-4,5,5-d3 in the hope decompose photochemically by an intramolecular that a better understanding of the primary process rearrangement yielding olefins and simpler ke- may be obtained by studying the effect of various t o n e ~ . Recent ~ work on the photolysis of 2- parameters not only on the quantum yield of the he~anone-5,5-&,~in which indirect evidence has total ethylene, but also on the ratio of the two been obtained for the formation of the enol form of ethylenes produced in primary processes I and 11. acetone, suggests that the rearrangement takes D place via a six-membered ring. The isolation and identification of 1-methylcyclobutanol as a product from the photolysis of 2-pentanone in the liquid5J and vapor6 phases, respectively, provides further \ X support for the postulation of a six-membered cyclic CHz intermediate. OD It has been observed recently that oxygen and DHC=CHD + CH, =CH2 (I) nitric oxide inhibit the intramolecular rearrangement in the vapor-phase photolysis of 2-~entanone,~ H although no inhibition had been observed in earlier ,,' x 0 CDz work on 2-he~anone.~In order to clarify this + point a comprehensive study was undertaken of the CH~COCHZCHDCD~Hhv + CHnCI/
c,
~~
+
(1) This research was supported by a grant from the U. 5. Public Health Service, Department of Health, Education, and Welfare. (2) National Academy of Sciences-National Research Council Postdoctoral Research Associate 1961-1962. (3) For a review see: J. N. Pitts, Jr., J . Chem. E d w . , 3 4 , 112 (1957). (4) R. Srinivasan, J. A m . Chem. Soc., 81, 5061 (1959). (5) N. C. Yang and D-D. H. Yang, ibid., 80,2913 (1958). (6) P. Ausloos and R. E. Rebbert (to be published). (7) V. Brunet and W. A. Noyes, Jr., BdE. aoc. chin. France, 121 (1958).
hHD
'CZ
OH
D&=CHD
I + CHaC=CHz
(11)
The effect of temperature and wave length on the liquid phase photolysis of this compound also was investigated.
R. P. BORKOWSKI AND P. AUSLOOS
22S8
Vol. 65
were used to interpret the mass spectra obtained from the CZ Experimental fraction. Apparatus.-The vapor-phase experiments were Results and Discussion conducted in a cylindrical quartz cell with a volume of approximately 175 cc. (10 cm. in length and 5 cm. in diameter). Vapor Phase. The Effect of Concentration.The cell was centered in an aluminum block furnace provided with double quartz windows. The temperature of the The rcplts in Table I indicate that at 3130 and furnace was controlled to f 2 ' . The cell was attached to a 2537 A. the quantum yield of ethylene is within standard type of vacuum system generally used in photo- experimental error independent of con~entration.~ chemical work. increases with An Osram-100 lamp was used in all of the diiect photolytic At 3130 A. the ratio C2D3H/CzH2D2 experiments. A combination of Cprning filters 7-54 and concentration of the ketone, indicating that the 0-54 was used, to obtain the 3130 A. group of lines, and a probability of a D atom transfer to the carbonyl filter composed of 1,4-diphenylbutadiene in diethyl ethers group decreases with increase in concentration. isolated the 2537-2650 A. lines. -4neutral density filter This observation may be interpreted in terms of a was used to vary the intensity by a factor of twenty. A low-pressure mercury arc in combination with Corning filter collision-induced vibrational deactivation of the 9-54 was used in the Hg(3P1)-sensitizedexperiments. Quan- excited ketone molecule. In view of the difference tum yields were determined a t 2537 and 3130 A. by measur- in bond strengths between C-H and C-D, it may ing the carbon monoxide yield from the photolysis of 3-pen- indeed be expected that the higher the level of tanone a t 87 and 145O, respectively. The short wave length experiments were carried out by vibrational excitation the more a D atom transfer using a Hanovia hydrogen discharge lamp. The space be- will be favored over a H atom transfer. tween the lamp and the cell was evacuated. The cell was It may be noted that methyl acetate is about as provided with thin hiah aualitv windows which trans- efficient a deactivator as the ketone itself. In con" ciuartz _ mit down to 1700 A. The 2000-Curie Co60 source a t the National Bureau of trast, carbon monoxide, which has been added a t a higher concentration of the ketone, had no noticeStandards was used to irradiate the vapor phase. The liquid-phase experiments were conducted in a quartz able effect on the ratio C:D3H/C2H21l2. However, cell having a volume of approximately 0.35 cc. (0.05 em. in the latter case the possibility exists that a t a in depth and 3 cm. in diameter). The cell was provided coilcentration of the ketone of 14 X moles/cc., with two outlets, one of which could be sealed after filling, has reached its maximum and the other with a breakseal. It was immersed in a Pyrex the ratio, C2D3H/C2HeD2, dewar flask xihich had double quartz windows. A water- value. It indeed can be seen that the value of the bath was used for experiments conducted above Oo, and ethylene ratio obtained a t this concentration is ethan21 was used as the refrigerant for those conducted be- comparable to the one obtained in the liquid phase low 0 A Hanovia SH-100 lamp was used in combination with Corning filter 0-53 to obtain the 3130 A . gloup of lines, photolysis a t approximately the same temperature. At 2537 the effect of Concentration on the whereas the 0-53 filter was replaced by the 1,4-diphenylbutadiene filter to obtain the 2537-2650 A. lines. The ratio of the ethylenes is small, but $he results folliquid phase work was conducted a t constant incident in- low the same trend as those a t 3130 A. tensity. The Effect of Wave Length.-The results in In the majority of the experiments conversions never exTable I show that the quantum yield of ethylene ceeded 0.5a/0. ( b ) Analysis.-The analytical system consisted of a increases with decrease in wave length. However, solid nitrogen trap, a modified Ward Still, an automatic the sum @co10 @&hy;ene remains approximately Toepler pump and a Toepler-gas buret. The carbon mon- constant. oxide-methane fraction was removed a t -210". The C2 It can be seen that the ratio CiDaH/CzH2D2 fraction was removed a t -170'. At the lower temperatures this fraction contained mainly C2D8H, CZHZDZ and traces diminishes with decrease in wave length. This of C2HG. On a few occasions a C) fraction was removed a t trend is consistent with the view that the probabil- 150'. All of these fractions were analyzed mass spectrometrically using a Consolidated Mass Spectrometer Model ity of a D atom transfer to the carbonyl group as 21-101. The analyses for fractions boiling higher than Ca compared t o a H atom transfer increases with increase in absorbed energy. It is interesting to note were not attempted. (c) Materials.-2-Pentanone-4,5,5-d3 was obtained from that the ratios C2DSH/CsH2Dz obtained in the the Rlerck Company, Ltd. and was used without further Hg(3P1)-sensitized experiments are higher than purification. A chemical purity analysis by a PerkinElmer "A" column at 82" indicated that the compound was those obtained in the direct photolysis at 253708% pur(.. The 2% of impurity consisted mainly of com- 2650 This may be attributed to the possibility pounds having boiling points higher than that of' the 2 that not all of the energy absorbed by the Hg atom pentanone-4,5,5-da. Mass spectrometric analysis of this is transferred to the ketone as vibrational excitacompound indicatcd that it contained a maximum of 47, 2-pentanone-&. This impurity would contribute primarily tion energy. The laws of conservation of energy to the production of C2H2D2, and thus the C2D3H/C2H2D2 and momentum require that some of the energy ratios indicated in the paper may be lorn by as much as 470. will be imparted to the mercury atom as kinetic Since the amount of C2H2D2 produced from the impurity was energy. Consistent with this interpretation are not known, no correction was made for this error. 2-Pentnnone and 3-pentanone were obtained from East- the somewhat lower values for the ratio l-butene/2man Kodak Co. and were distilled on a spinning band butene recently found in the Hg(3P1)-sensitized column. In each case a middle fraction was used. decomposition of 4-methyl-2-hexanone as comOxygen of assayed reagent grade quality was obtained from Air Reduction Company, Inc. I t was contained in a pared$o the direct photolysis of this compound at one-liter bulb behind a mercury cut-off which mas attached 2537 A." directly to the reaction section. Experiments carried out with the hydrogen disThe t 4 o ethylenes, D&=CHD and DHC=CHD, were (9) I t may be noted that a twenty-fold reduction of the intensity has obtained from PyIerck Company, Ltd. and their mass specno effect on either the quantum yield of ethylene or on the ratio of the tiometric cracking patterns were determined. The D2C= CHD spectrum had to be corrected for an impurity of 8.2% ethylenes. (10) The quantum yields of CO were measured at temperatiirw CZHZDZ, and the DHC=CHD spectrum was corrected for an of 3.6% H2C-CHD. These cracking patterns above looo t o ensure that all of the C H G O farmed in the dissociative impurity process underwent thermal decomposition. (a)
- -
.
8.
+
8.
( 8 ) AI ICasha, J . O p t . SOC.Am., 88, Q2Q (1948).
(11) P. Ausloos,
J. Phys. Chem., 6 6 , 877 (1961).
Dec., 1961
2259
PHOTOLYSIS OF 2-PENThNONE-4,5,j-d3
TABLE I VAPORPHASEPHOTOLYSIS O F CHsCOCHzCHDCDzH. THE EFFECTO F CONCENTRATION, IXTENSITY, TEMPERATURE AND WAVELENGTH O N THE RATIOD2C=CHD/DHC=CHD Ketone concn. la (moles/cc.) (quanta/cc./sec.) x 106 x 10-d
(A) 3130A. (1) Effect of concn.
(2) Effect of temp.
(B) 2537-2650
A.
16.5
x
moles/cc.
Qco
C*DaH/CnHnDn
*ethylene
1.57 1.57 1.57 1.57 1.57 1.57 0.078 0.078 1.57 1.57
305 305 305 306 307 305 305 306 30G 305
0.27 .27 .29 .34
2.00 2 00 2.30 2.72
. . .23
2 41 2 G3
.27 .29 .27 .24
2.69 2 72 2 67 2.72
I .60 1.60 10.2 10.2 10.2
1.57 1.57 1.57 1.57 1.57
305 420 306 359 420
.29 .32 .27 .26 .28
2.30 1.47 2.60 1 .93 1.42
1.38 2.82 14.1 10.8
0.1 .1 .I .1
306 306 308 398
.39
0.90 0.96 1.oo 0.92
1.65 14.3 CH&OOCHa added.
0.5s
...
0.42
...
*
306 307 28.2 X lo-' moles/cc. CO added.
...
charge lamp (1700-1900 A,) a t 300'K. gave a value of 0.65 for the ratio C2D3H/C2H2D:,whereas radiolysis in the vapor phase gave a value of 0.58. It thus can be seen that a t high energies the ratio C2D3H/CzH2Dz approaches the statistical value of 0.5. In this connection it is of interest to point out that the mass-spectrum of 2-pentanone-4,5,5-da at low energies (13 e.v.) yielded a value of 0.50 for the mass ratio 58/59. Because the masses 58 and 59
OH
I
may be ascribed to the ions CH3C=CH2+ and OD
I
(OK.)
0.27 0.85 1.60 1.65" 3.74 14.1 14.1 14.2 14. lb 14.2
(C) Hg( *P1)-sensitiaed a
T
CHsC=CH2+, respectively, it thus may be concluded there is no isotope effect for the olefin splitout process which the ketone ion undergoes. Effect of Temperature.-The results of Table I indicate that at 3130 A. an increase in temperature leads to a pronounced decrease in the ratio C2D8H/ CrH2Dr. The decrease, which is due to an increase in vibrational energy is, as may be expected, considerably less at the shorter wave lengths. It can be seen also that the effect of concentration on the ratio of the ethylenes is less a t 420 than at 305'K. The latter observation indicates a shorter dissociative lifetime of the excited ketone molecule at the higher temperatures. Effect of Oxygen.-The results in Table I1 show that, a t the wave lengths used in this work, the quantum yield of ethylene and the ratio CzD&H/ C2D2Hzdecrease with increase in the pressure of oxygen. The effect of oxygen is considerably more pronounqed a t 3130 than at 2537 A. It also is more important at 305 than at 420'. Thus, it
.40 .42 e . .
...
1.01 1.16
appears that oxygen preferentially interacts with molecules excited to lower vibrational levels. TABLE I1 VAPOR PHASEPHOTOLYSIS OF CHsCOCHzCHDCD2H. THEEFFECT OF OXYGEN (A) 3130A. Ketone pressure = 26.5 mm. P a , mm. T. OK.
...
0.36 .39 .75 1.5 5.5 26.2 53.5 56.0 1.25 28.0
305 305 305 305 305 305 305 305 305 420 420
Is = 1.57 X 10'8, uanta/cc.
?kDaH/C*fkUI
0.28 .24 .24 .18 .16 -10 .07 .08
2.62 2.62 2.62 2.36 2.22 1.96 1.78 1.65 1.71 1.44 1.40
.06
.18
.I4
(B) 2537-2650 A. Ketone pressure = 26.5 mm.
...
1.25 33.0 2.7
308 307 307 423
see.
hhvlena
la= 0.1
x
0.40 .42 .36 .39
1018,quanta/oc./sec.
1.00 1.oo 0.92 0.88
The effect of oxygen on the quantum yield of ethylene in the photolysis of 2-pentanone has been reinvestigated at 3130 k. and 305' K. The results (Table 111), which are in good agreement with those recently reported,6 show that the inhibitory effect of oxygen is not of the same magnitude as in the case of 2-pentanone-4,5,5-d3, under the same experimental conditions. This difference may be due to a shorter dissociative lifetime of 2-
NOTES
2260
pentanone as compared to that of 2-pentanone4,5,5-d3. Since Z-pentanone has three H atoms in the y-position, while 2-pentanone-4,5,5-d3 has only one H atom and two more strongly bonded D atoms in this position, 2-pentanone would have a relatively higher probability of undergoing a molecular elimination than 2-pentanone-4,5,5-d8. TABLE I11 VAPORPHASEPHOTOLYSIS OF CH3COCH2CH2CH8. THE EFFECT OF OXYGENAT 3130 1. Ketone pressure = 26.5 mm.
la
1.57 X IO" quanta/cc./sec.
Poi, mm.
T , OK.
*ethylem
1.4 6.4 56.5
305 306 303 305
0.30 .25 .20 -13
...
Vol. 65
from which decomposition occurs does, however, depend on the equilibrium temperature. It is ipteresting t o note that in the vapor phase at 3130 A. the effect of temperature on the ratio C2D3H/ CaHzDs is of the same order of magnitude. This is not surprising in view of the fact, as was pointed out before, that the ratios of the ethylenes in the two phases are comparable. TABLE IV LIQUIDPHASE PHOTOLYSIS OF CH2COCH2CHDCD2H A,
A.
3130 3130 3130 2537 3130
Liquid Phase.-In the liquid phase (Table IV) the ratio CzD3H/C2H2D2decreases with an increase in temperature. A plot of log CZD3H/ C2HsDz against 1/T yields a difference of 1.15 0.15 kcal./mole in the activation energy for the transfer of a D atom a2d an H atom. Since the point obtained a t 2537 A. lies on the same line of the Arrhenius plot, the ratio CzDsH/CzH2Dz is independent of wave length. It may indeed be expected that in the liquid phase, collisional deactivation is important. The mean energy level
*
T,OK.
198 214 273 296 343
Rethyleas X IO' (co./min.)
5.40 6.55 27.8
...
26.2
CzDaH/ChHzDi
6.40 5.37 3.44 2.76 2.12
The relative quantum yield of ethylene is within experimental error constant from 343 to 273OK. At temperatures below 273'K., however, there is a pronounced decrease in the yield of ethylene. Because ethylene can be formed only by a molecular elimination process, cage recombination cannot be invoked to explain the reduction in quantum yield. It is more likely that an activation energy of a few kcal./mole is required for the decomposition process.
NOTES THE ELECTRODE POTENTIALS OF GERMANIUM: SOME COMMENTS ON THE INTERPRETATION BY LOVRECEK AND BOCKRIS
atm. for brown GeO and about atm. for yellow GeO.) Such low hydrogen pressures might well have been attained in the solutions which LovreEek and Bockris swept with helium. However, replacement of the atmosphere of helium by one of BY J. I. CARASSO, M. M. FAKTOR AND H. HOLLOWAY hydrogen would render the postulated corrosion reaction 3 impossible. Yet the authors have rePost Ofice Research Stataon, DoEZzs H i l l , London N.W. 8, England ported that the measured potentials were unaffected Received March 80,1961 by sweeping with hydrogen. The only possible I n a recent paper' Lovrerek and Bockris have conclusion appears to be that at least one of the described measurements of the electrode potentials two postulated electrode reactions 1, 2 does not of germanium over a range of pH in deoxygenat,ed contribute to the measured Potentials, and that, solutions. These potentials were interpreted as if corrosion does occur in deoxygenated solutions, mixed potentials arising from the simultaneous it does so by a process other than the postulated occurrence of the two electrode reactions corrosion reaction 3. A further objection to the interpretation by Ge + HzO +GeO + 2H+ + 2e(1) LovreEek and Bockris concerns their claim that 2Hf + 2e- +Hz (2) the difference between the measured mixed poThese authors showed that the resultant over- tentials and the reversible potentials for the anodic all corrosion reaction reaction is not more than 20 mv. This result was derived from the assumption that the corrosion Ge + H20 ---+ GeO + H2 (3) current in deoxygenated solutions and the exchange would be thermodynamically feasible only in solu- current for the anodic reaction are both about 2 X tions which are in equilibrium with a low pressure amp. cm.-2. of hydrogen. (The maximum hydrogen pressure The value assumed for the corrosion current for which the postulated process is possible depends was derived from the results of Brattain and Garupon the form of GeO involved, being about rett? who do not appear to have deoxygenated (1) B. LovreEek and J. O ' M . Bockris, J (1959).
Phya. Chem.. 68, 1368
(2) W. H. Brattain and C. G. B. Garrett, Phys. Rev., 94, 750 (1954): BelZ System Tech. J . , Sl. 129 (1956).
