THEREACTION OF O( T) WITH DIDEUTERIOACETYLENE step. It is apparent, however, from our studies and from studies of calcium-doped NaCl and KCI crystals that point defects at the crystal surface play an all important role in the sublimation of alkali halides. Minute changes in the ion vacancy concentrations can markedly change the sublimation rate. The nonstoichiometry at the surface that i s characteristic of the ionic compound or that i s created by the incorporation of impurities seems to control the sublimation rates. This nonstoichiometry appears to remain constant during the sublimation process. Variation of the dislocation density of LiF apparently has not changed the sublimation rate. Similar insensi-
The Reaction of 0 (")
4053
tivity of the sublimation rate to changes of dislocation density was found for KC1.6 On the other hand, it was shown that for NaCl the increascd concentration of dislocations has increased the sublimation rate. It appears that the annealing rate of excess dislocations that were introduced by stress determines whether high dislocation densities can be maintaincd at thc subliming surface. The annealing rates of excess dislocations are probably more rapid in LiF and KC1 crystals than in NaC1.
Acknowledgment. This work was performed under the auspices of the U. S. Atomic Energy Commission.
with Dideuterioacetylene'
by David G. Williamson Department of Chemistry, California State Polytechnic College, San Luis Obispo, California 93401 (Received M a y $1- 1971) Publication costs assisted by the U.S. Air Force Ofice of Scientific Reaearch
The reaction of atomic oxygen, O(aP),with CZDZwas studied to determine the importance of D atom production in this reaction. By measuring the yield of HD from the exchange reaction of D atoms with Hz, the D atom yield was estimated to be (42 * 10%) based on the number of O(aP)atoms generated.
Introduction In an earlier study of the reaction of ground-state oxygen atoms with acetylene, various reactions were considered.2 The possible exothermic reactions, rewritten for deuterated acetylene, are shown below.
0
+ CzDz
(CzDzO")
(1)
(CZDZO")
+CDZ + CO
(2)
(CZDzO")
.---t D
(3)
---+
+ DCzO
(CzDzO") --+D2 (CzDzO")
M
---+
+ C20
(C2D20)
+ (CZDZO") *CzDzO + A 1
the importance of D atom production. If all of the D atoms formed in reaction 3 could be trapped in another compound, this would provide a measure of reaction 3. Few D atom scavengers which do not react rapidly with O(3P)atoms are known. Therefore, the exchange reaction 7
D
+ Hz
HD
+H
(7) was chosen as a way to trap D atoms from reaction 3, since the attack of O(3P)on H2is quite S ~ O W . ~ -3
(4)
Experimental Section
(5)
Ground-state oxygen atoms were generated in a static system by the mercury-photosensitized decomposition of nitrous oxideV3 All experiments were done at 130,6 f 0.5" in an air furnace. Two oblong quartz vessels of about 35 a n a volume were used.
(6)
(CzUzO*) is an unstable complex, analogous to that proposed for oxygen atom-olefin reactions. Reactions 2 and 4 were estimated to account for 25 and 0.3%, respectively, of the original oxygen atoms formed. Reaction 5 was postulated as a possible isomerization or intersystem crossing. The previous work demonstrated the importance of reaction 3, but the yield could not be measured quantitatively. The object of the present investigation is to estimate
(1) Contribution No. 2844 from the Department of Chemistry, University of California, Los Angeles. (2) D. G. Williamson and K. D. Bayes, J . Phys. Chem., 73, 1232 (1969). (3) R . J . Cvetanovic, Advan. Photochem., 1, 115 (1963). (4) K. Schofield, Planet. Space Sci., 15, 643 (1967).
The Journal of Physical Chemistry, Vol. 76, No. 26, 1971
DAVIDG. WILLIAMSON
4054 Table I: Nz/HD Values as a Function of C2D2/H2; Temperature 130.6 CzDs,Torr
Hz,Torr
0.95 9.91 1.83 0.96 6.06 3.27 0.96 0.96 0.96 0.96 0.95 0.96 1.76 1.76 0.88 0.88 0.97 0.97 0.95 0.96
56 B5 50 53 53 24 10.2 31 19 40 25 22 104 145 205 88 84 78 104
58
0.5""
Na, Torr/min
Nl/HD
CzDdHz
Photolysiv time, min
0.127 0.216 0.136 0.0093 0,327 0.163 0,143 0.120 0.110 0.140 0.113 0.0090 0.153 0.090 0.140 0.100 0.110 0.126 0.113 0.130
5.18 f 0 . 4 25.8 f 6 6.03 -I: 0.6 5.02 f 0 . 5 24.6 & 3 10.7 f 1 7.58 rt 0 . 8 16.3 f. 3.2 7.0 k 0 . 9 9.40 f 1 5.76 f: 1 . 1 6.45 2c 0.9 15.7 2 3.52 f 0.4 2.01 f.0 . 1 1.81 f 0.1 3.56 f 0.5 4.36 rt 0 . 5 4.23 -I 0.3 3.59 f 0.3
0.0126 0.163 0.0282 0.0156 0.103 0.0557 0.0287 0,0735 0.0242 0,0363 0.0185 0.032 0.0655 0.0155 0.00517 0.00355 0.00870 0.00865 0.00912 0.00663
3 3 3 30 3 3 3 3 3 3 3 30 3 3 2 2 3 3 3 3
+
The NnO pressure was 500 rt 65 Torr in all runs.
-
Both had a freeze-out tube about 10 cm X 0.4 cm which contained a small drop of Hg at the bottom. The freeEe-out tubes were a t room temperature during photolysis and were shielded from thc photolysis light. A G E G25T8 25-watt germicidal lamp provided sufficient 2537-A light intensity for the experiments. Measurements of H D and Kzwere made with a CEC 21-620 mass spectrometer. After photolysis, the freezeout tubes of the reaction vessels were cooled to liquid nitrogen temperature for about 0.5 hr. Samples of noncondensable gases were introduced directly from the cells into the mass spectrometer. Mixtures of H2Nz,and Dz-N2 were used to calibrate the instrument. Using 70-eV ionizing electrons, the sensitivity of the instrument to Nz was 1.29 f 0.05 times that of Hz, and 1.25 + 0.05 that of D2. An ascrage of these two figures, 1.27 f 0.05, was used for the sensitivity of N2relative to HD.
Table I, the C2Dz/H2 ratios shown are the average values during photolysis. Consumption of CzHz was the same with or without Hz present. The observed ratio of CO/N2 = 0.44 at 1 Torr CzDz,500 Torr NzO, and at 130' was the same as the CO/Nz ratio measured previously at room temperatures2 Carbon monoxide yields for CzDg pressures other than 1 Torr were taken to be the same as those found at room temperature. Thus, the contribution by CO to the m/e = 28 peak could be calculated. Kitrogen yields in Table I have been corrected for the CO yield, the N2+peak from N& and the m/e = 28 peak from the background of the instrument.
Discussion A simple mechanism can account for the dependence of HD/N2 on the ratio CZDz/Hs.
D
Mass spectrometric determination of HD yields from reaction 7 and Nzyields from reaction 8 NzO
+ Hg(3P~)
-+
Nz I- O W )
+Hg
The Journal ~f Physical Chemiatrg, Vol. 76, N o . 26, l W l
-
-3
+ C2D2
D
+ DCzO
CzDa
+ H2 H D + H H + CzDz +CzD2H
D
(8)
showed that the ratio HD/N, depends very strongly on the ratio of CzDz/Hz. At low C2D2/H2, yield of H D (as measured by HD/Na) is highest. Increasing CzD2/Hz decreases the H D yield (see Table I). Values of C2Dz/H2 in Table I have been corrected for the depletion of C2D2during photolysis. By mass spectral analysis of samples of CzHzand NzO before and after photolysis, it was determined that for 0.39 Torr of NZ generated, 0.47 Torr of @& was consumed. In
+ CzDz
O(T)
Result
---f
(3)
(9) (7) ( 10)
Applying the steady-state approximation to oxygen atoms and deuterium atoms yields
where
4055
THEREACTION OB O( T )WITH DIDEUTERIOACETYLENE
least-squares line. At high Hz pressures, some additional pathway for the formation of H D appears to become important. One possible disturbance is the sensitized dissociation of Hz, which will generate in-
30
Hg”
25
+ H2 +Hg + 2H
(12)
creasing amounts of hydrogen atoms as the H2 pressure ie increased. If the H atoms then exchange with C2Dz according to eq 13 and 14, this could cause the observed 20
+ CzD2 +CzDzH CzDzH CzDH + D H
--ic
N, -
15
HD
IO
5
7 0 5
0
IO
IO2 x
15
20
Figure 1.
+ NzO +OH + Nz OH + C2Dz DCzO + H D ---+
Figure 1 is a graph of the data in Table I plotted according to eq I. A least-squares line through all the data points has been drawn in Figure 1. Experiments at about 54 Torr of hydrogen and varying C2Dz pressures are in reasonable agreement with those points at constant CnDz. Therefore, it is the ratio of C2Dz/H2which is important in determining the ratio of N2/HD as required by eq I. The line in Figure 1 yields l/f = 2.4 =t0.6 o r f = 0.42 f 0.10 and ks/kl = 20. Thus the yield of D atoms from the reaction 77 of 0 with C2Dzis about 40%, which means that reaction 3 is of major importance. It is not possible to compare directly the ratio of k g / k 7 determined from Figure 1 with literature values, since the rate constant ks has not been observed directly. However, the reaction of D with normal acetylene, reaction 11, has been studied as a function of temperD
+ CzH2
+CzHzD
(11)
ature.6 Since one would not expect a large isotope effect on the rate of reaction 9 compared to reaction 11, the ratio lcn/k7 should be comparable to kg/k7. At 130” the calculated ratio of lc11/k7 is 73, which is to be compared to k#/k7 of (70 f 20) from the slope and intercept of Figure 1. The agreement between these values supports the proposed mechanism. The points in Figure 1 corresponding to runs with Hz pressures above 100 Torr tend to fall below the
(14)
deviations, since the D atoms would go on and exchange with Hz.However, experiments in which the NzO was replaced with an equivalent pressure of N2, but with the same high pressures of Hz, showed H D levels that were no greater than 2% of the HD formed during the oxygen atom reactions. Exchange of H with CzDzdoes not appear to be the cause of the low values of NZ/HD. Another possible source of HD would be the attack of H on N20, reaction 15,s followed by the recently suggested reaction 16.’ This possibility can be ruled out by comparing the known rate of reaction 15 with the rate of the alternate reaction 13. Approximating
H
(C,D,/H,)
(13)
(15) (16)
the rate of combination of H with CzDz by its rate of combination with C2Hz, one can show that only one H atom in 300 reacts with KZO according to reaction 15. The ratio of NzO to CzDzwill have to be several powers of ten larger than those in Table I in order for reactions 15 and 16 to generate more H D than reactions 3 and 7. By similar reasoning, the reaction of oxygen atoms with Hz can be ruled out as a source of OH in these experiments, since even at the lowest ratio of CzDz/Hzapproximately 6% of the O(3P) atoms generated react with Hz.4 The excess HD at high Hi pressures may be coming from exchange reactions of the type
DCzO
+ Hz +HCzO + HD
(17)
or the reaction s e q ~ e n c e ~ , ~
+ Hz +CDzH + H H + CDzH CDzHz +D + CDHz CD2
--f
(18) (19)
followed by reaction 7. Another possible source of H D at high H2 may be reaction 20 followed by reaction (5) K. Houermann, H. G g . Wagner, and ‘J. Wolfrum, Ber. Bunsenges. Phys. Chem., 72, 1004 (1968). (6) G. S. Bahn, “Reaction Rate Compilations for the H-O-N System,” Gordon and Breach, New Yorlr, N . Y., 1968, p 128. (7) J. E.Breenrtnd G. P. Glass, Int. J . Chem. Kinet., 3, 145 (1970). (8) W. Braun, A. Bass, and M. Pilling, J . Chem. Phys., 52, 5131 (1970).
The Journal of Physical Chemistry, Vol. 76,N o . 86,1971
NOTEB
4056
7.9 Since these rate constants have not been measured, CD2
+ Hz +CDHz + D
(20)
quantitative estimates of their importance cannot be made at this time. In conclusion, it has been shown that the yield of D atoms from the reaction of oxygen atoms with CzDz is about 40%, and this yield has been interpreted as a direct measure of the primary reaction 3. This result means that the alternative reaction 2, formation of CD2 and CO, cannot be the only major primary step in the reaction, as several previous workers have assumed.lO-lz Previous results from similar staticsystem experiments2 indicated that approximately 25% of the oxygen atoms generated produced methylene and CO, or CzO and Dz. Therefore, only about two-thirds of the oxygen atoms produced can bc accounted for by gas phase reaction products,
Attempts to detect ketenc in the gas phase have failed, and so thc remaining fraction of oxygen atoms must end up in the polymer, which is observed in the present experiments as well as those at room termperature. Acknowledgments. The experimental work reported above was carricd out in the Department of Chemistry, University of California at LOSAngcles. Thc financial support of the Air Force Office of Scientific Research, under Grant AFOSR 70-1872, is gratefully acknowledged. (9) J. Bell and G . B. Kistiakowsky, J . Amer. Chem. Soc., 84, 8417 (1962). (10) C. P. Fenimore and G . W. Jones, J . Chem. Phys., 39, 1514 (1963). (11) C, A. Arrington, W.Brennen, G. P. Glass, J. V. Michael, and H. Niki, ibid., 43,525 (1965). (12) J. M.Brown and B. A. Thrush, Trans, Faraday Soc., 63, 630 (1967).
NOTES A Nuclear Magnetic Resonance Study of the Protolysis Kinetics of 5-Dimethylaminonaphthalene-1-sulfonic Acid and Its N-Methylsulfonamide
by J. F. Whidby,*latcD. E. Leyden,l" C. h4. Himel,Ib and R. T. Mayer'b Department of Chemistry and Department of Entomology, University of Georgia, Athens, Georgia (Received March 11, 1971) Pubticution costs borne completely by The Journal of Physical Chemistrg
Sulfonamides are an important class of compounds because of their biological activity and use as fluorescent probes in the study of enzyme active sitesS2 We report the results of an nmr study of thc protolysis of 5-dimethylaminonaphthalene-1-sulfonic acid (I) and its N-mcthylsulfonamide (11). Proton exchange studies on the 5-dimethylamino group of I and I1 were performed in aqueous HzS04, whereas proton exchange of the N-methylsulfonamide moiety in I1 was carried
A
N C&
/ \
'CH,
CH, CH3
I
I1
The Journal of Physical Chemistry, Vol. 76,No. 36,1971
out in 16.0 mol % lert-butyl alcohol in water. The pK, of thc dimethylamino group of I was determined to be 3.5 in 16% tert-butyl alcohol by nmr spectroscopy during this investigation and to be 4 3 2 + 0.03 in HzO by spectrofluorescence measurements.$ Lagunoff and Ottolenghi4 report the pK, for I and I1 in IIzO to be 4.55 and 3.85, respectively, from spectrofluorometric data. Nmr studies with I1 in 16% ted-butyl alcohol gave a pK, of 2.1.* Several studies of the sitc of protonation of carboxylic acid amides have been performcd.5-' Each study concluded that the major protonation of these compounds occurs at the oxygen atom. However, aliphatic and aromatic N-substituted sulfonamides have been shown to protonate on the nitrogen atom8rgin concen(1) (a) Department of Chemistry; (b) Department of Entomology; (c) correspondence should be addressed t o 500 B Bexfield Drive, Dugway, Utah 84022. The authors acknowledge support in part by Research Grants from the National Institute of Health ES00207, GM-13935, Agricultural Research Service 12-14-100-9148(33) and Federal Water Pollution Control Agency 16020EAO. (2) C. M.Himel, R. T. Mayer, and L. L. Cook, J. Polym. 9 c L Part A - l , 8 , 2219 (1970). (3) C . Himel, R. T. Mayer, J. F. Whidby, and D. E. Leyden, unpublished results. (4) D. Lagunoff and P. Ottolenghi, C. R. Trav. Lab. Carlsberg, 35, 63 (1966). ( 5 ) R. J. Gillespie and T. Birchall, Can. J. Chem., 41,2642 (1963). (6) D. Herbison-Evans and R. E. Richards, Trans. Faraday Soc., 58,845 (1962). (7) C. A. Bunton, B. N. Figgis, and B. Nayak, Proc. Int. Meeting Mol. Spectra., 4th, Bologna, 1969, 3, 1209 (1962). (8) R. G. Laughlin, J. Amer. Chem. SOC.,89,4268 (1967).
