1096
J. C . Tou, L. B. Westover, and L. F. Sonnabend
( 1 2 ) P. Frarizo5.ini and 12.Sinistri. Ric. S c i . . A3, 439 ( 1 9 6 3 ) . (13) J, 1-urnsden, "Themodynarnics of Molten Salt Mixtures," Academic Press, London. 19156, (14) D. 13, Stul: and H . Prophet, Nat. Ref. Data Ser.. Nat. Bur. Stand.. No. 37 (1971).
(15) F. D. Rossini, eta/.. Nat. Bur. Stand. Circ.. No. 500 (1952). (16) G . A. Bukhalova and D V. Sementsova, Russ. J. lnorcl. Chem. 10. 1027 ( 1965). (17) M . L. Sholokhovich, D. S. Lesnykh, G. A . Bukhaiova, and A . G . Bergman, Dokl. Akad. Nauk. S S S R , 103, 267 (1955).
inetic Studies of Bis(chlorornethy1) Ether Hydrolysis by Mass Spectrometr J.
c. Tw,*
L. B. Westover,
Analytical Laboratories
and L. F. Sonnabend Designed Polymers Research, Dow Chemical U.S. A , , Midiand, Michigan 48640 (Received October 10, 1973) Publication costs assisted by the Dow Chemical Co.
The hydrolysis of bis(chloromethy1) ether (bis-CME) was studied in 2 N NaOH, 1 N NaOEI, water, 1 N HCl, and 3 N HC1. From the measured values of A&* and E*, it was interpreted that the mechanism of the hydrolysis of bis-CME was S N 1 in character in basic solution and shifted to an S N like ~ mechanism in acidic solution.
htroductior.. 160-cc vessel filled with the appropriate solution in which the hydrolysis rate was to be determined. Assuming no Ghloroniethy! methyl ether (CMME) is a commonly prior hydrolysis took place, the concentration so prepared used chlorornethylating agent in the manufacturing of was ca. 1 ppm. The vessel was placed in a thermal bath nic resins. One of the impurities present in and completely filled with the appropriate solution so that en found to be bis(chloromethy1) ether (bisno air space remained into which bis-CME might volatize GME). B.is-CME 'has been shown recently to be a very thus changing the concentration of the solution. The solustrong carcic.ogen in experiments involving skin painting,l tion was constantly stirred. The syringe used for injecting subcutaneow iajection,l and inhalation.2 Since these the bis-CME-acetone solution served for sealing the openfindings. possible industrial exposure to this simple moleing used for the injection. To avoid any bis-CME escaping cule has been of very much concern. Analytical techniques into the atmosphere, the syringe was not removed until for analysis of ppb levels of bis-CME in air have then after the bis-CME in the aqueous solution reached an unbeen developed quite r e ~ e n t l y . ~ , ~ Unlike CMME, which has been extensively ~ t u d i e d , ~ detectable level. The concentration of bis-CME in the aqueous solution was monitored using a CEC 21-110 douthe hydrolysis of bis-CME in solution has not been invesble focusing mass spectrometer coupled with a 15-head tigated to the best of our knowledge. In this report, the rates of b i s C M E hydrolysis were determined in 2 AT semi-membrane silicone fiber probe. The development of the fiber probe was published elsewhere by Westover, NaOH, 1 N NaOFI, water, 1 N HC1, and 3 N HC1. The Tou, and Mark.6 In order to detect the anticipated weak Arrhenius expressions for the hydrolysis rates were also signals, an amplifier with a gain of about 30 was installed determined. The systematic changes of the determined to amplify further the mass spectrometer output. values of A&* and E* from basic solution to acidic soluA few milligrams of benzene in a 500-cc reservoir a t Lion are disc'assed in terms of the changes of the hydroly200" was bled int,o the mass spectrometer through a mosis mechanisms. lecular leak. The purpose for this was twofold. One was The least-squares linear fits of the rate and arrhenius for cali.bration as an internal mass marker for the peaks to plots were achieved with use of an IBM 1130 computer. be monitored. The second was for checking whether or not Experimentill Section there were variations of the instrum.ent sensitivity during Due to thl? high toxicity of bis-CME, any exposure to each experiment. The resolution of the mass Spectrometer this molecul? must be avoided. The rate determinations was adjusted to ca. 2000; which was enough to resolve a were, therefc're, carried out a t very low concentration levdoublet peak at m / e 79 due to C5P3CHs+and C2H4QC1+-. els of the orlder of I ppm. Bis-CME dissolves in aqueous The former ion is the I3C molecular ion of benzene. The solution very slowly. To facilitate a fast dispersion of bislatter ion, C2H40C1+, which was monitored, is the most ChlE in aqui-.ous solution, a 1% bis-CME-acetone solution intense ion in the mass spectrum of bis-CME and is genwas used. &re, acetone acted as a carrier for dispersion. erated from the molecular ion, ClCM2QCH2C1.t The hydrolyhi apparatus is shown In Figure 1. The bisClCHzQ+=CHz C .C1. The intensity of the C2H40CI-k peak is directly proportional to the concentration of bisCME-acet,one solution (20 pl) was injected into a sealed
-
The Joilr-rai o f Pi:vs,cai Chernstry. Voi. 78. No 7 7 . 7974
Kinetic: Studieij oi B i s j c h l o r o m e t h y l ) Ether Hydrolysis
15.80
59.48
146.84
103.16 t.
- -
-t
-1-
19052
234.20
sec
Figure 2. Hydrolysis of bis-CME in 3 N HCI at 294.5'K. 2.97041
F i ~ 1.~Bis-CME r ~ hydrolysis
apparatus
CNIE in solution. The doublet a t m/e 79 was repetitively scanned a t a rate of 1.3 sec per data point and recorded using a light kiearn oscillograph.
I 2.51496 a
l
.
-J
Results and IIIiscussion The monitored intensity of the CZH40C1+ peak was found ,to be dependent upon rates of mixing and hydrolysis. In order to determine the rate of mixing, acetone was used and the rate measured by monitoring the molecular ion of acetone. Acetone was found to reach equilibrium in the solution in cn. 20 sec. The recorded intensity change o f the C&4OCl peak can be considered to be solely due to hydrolysis only after bis-CME is uniformly dispersed in the solution. The rate of mixing was found to be dependent on temperature and viscosity of the solutions being studied. These depentlences are easily recognizable from the intensity changes of the CzH40C1+ peak. The peak intensities monitored gradually increased to their maxima as mixing occurred and then followed a decay controlled by the bis-CME hydrolysis rate in solution a t the experimental temperature. The log of the intensity of the C2W4OCl+ peak after reaching its maximum was plotted against time. The rate of hydrolysis can then be derived from the slope 0' a lea t-squares fit straight line. Two rate c u v e s are shown in F p r e s 2 and 3 to serve as representative i:ases. Because the signals monitored are weak: scatteriiig of the data points is expected. Generally speaking, the lower the temperature and the weaker the signal, the larger the scattering. These are clearly demonstrated in Figures 2 and 3 . Even though the data points are scattered, :1 1inea.r plot was obtained in every case studied which indicates the hydrolysis is a pseudo-first-order reaction. The rates determined a t different temperatures can be expressed in the Arrhenius form k = A~-E*;RT 2.1 1~10~e,5S"!Re-~Ev/RT (1) where k is the rate a t temperature T, A the Arrhenius frequency factor, R the gas constant, AS* the entropy of activation. and E* the energy of activation. Hence the plot of log k against i / T will yield a straight line, from which E" can be derived from the slope and A from the intercept. The Arrhenius plot with least-squares fit is shown in Figure 4 for the hydrolysis of bis-CME in 3 N HC1 as a representative case. The values of A, A&,*, and E* along I
2.05950
In I C ~ H ~ O C I ' 1.14860
i
lJ.e9314-~~ 23.14
@ I
I
87 11
151 08
21505
27902
34298
t, sec
Figure 3. Hydrolysis of bis-CME in 3 N HCI at 288.4'K
11~~103
Figure 4. Arrhenius plot of bis-CME hydrolysis in 3 N HCI.
with the standard deviations were calculated and are summarized in Table I. As shown in 'Table I, a systematic change in A, A&*, and E* is clearly demonstrated as the hydrolysis media changed from being basic to being acidic. The decrease of the activation energy from acidic solution to basic solution highly suggests that the hydrolysis of bis-CME is a nucleophilic reaction. It has been reported that the soivolysis of CMME, similar to that of terf-butyl chloride in many respects. has an unusually low activation energy and entropy of activation. Values of E* from 8.6 t o 13 kcal mol-I and of ASo* from -43.7 to -15.6 eu have been re-
J. C.Tou, L. B. Westover, and L. F. Sonnabend
1Q98
TABLE C: A, ASo*, and E* for the Hydrolysis of bis-CME in NaOH (aqueous), HzO, and WCI (aqueous) l l l _ .
k , sec -1
Solutior
A
1.16 x 105 1.34 x 108 1 08 X loxo 1 . 9 4 x 10'1 8.37 x 10"
2 N NaOM 1 N NaOH
HZO 1°C 3 N EEC
E*, kcal/mol
ASo*, BU
-35.2 -21.2 --12.5
8.96 i 0 . 3 12.9 5 1.0 15.8 i: 0 . 4
-6.73
17.5 5 0.05 18.6 i 0.11
-3.82
__ see - 1
20'
403
0.0079 0.0064
0.024 0.032
0.002
0.0025 0.0019 0.0011
0.01.8
0.064 0.13 0.10 0.12 0,088
0.002
00
0 ,018 0.011
& dk,
0.003 0,006 0,002
of about 0.92. The positive slope indicates that energies of activation and entropies tend to compensate each other, so that the changes in free energy are small. The irregular variations of the rate constants calculated in different solvents at different temperatures, as shown in Table I, are believed to be real and to be caused by the alleged compensation effects which determines both the slopes ( E * ) and the intercepts (AS*) in the Arrhenius rate plots. The directions of the variations in the rate constants determined in different solvents are controlled by the crossings of the rate curves in the Arrhenius plots.
6
Figure 5. The
8
10
12 14 E', KCsllMale
16
IS
20
com'pensation effect plot of T A P against E* at
0""
ported in various solvents.5a,7 In the case of solvolysis of primary alkyl halides, values of E* are ca 20 to 25 kcal . former ~ case is mol-I and ,f ea. -4 to -12 e ~ The typical of the transition state involving an ion-pair like mechanism), and the latter case inconfiguration (SN~ volves a covalenl bond like configuration ( S N ~mechanism). Comparing our values shown in Table I with those discussed above, the mechanism of the hydrolysis of bisCME is Sh1 in character in basic solutions and shifts to an Sx2 like mechanism in acidic solutions. In basic solutions, the formation of the ion-pair like transition state would be facilitated by charge delocalization, [ClCW20CI-I2-~Cl- --r [ClCH2-O+=CH2]Cl-. However, the carbonium ioris will be destabilized due to the protonation on thcb ether oxygen atom in acidic solutions. In this case, the attack of a nucleophile, -OH, on the cy carbon is ~ is favored. anticipated and. therefore, the S N reaction In a considerable number of kinetic studies involving a series of sclvenls, plots of TAS* against E* have been found to be straight lines of approximately unit slope.s As shown in Figure 5, the linear relationship was indeed found to be true in the present case and exhibited a slope
Tho Journal 5 f Physical Chemistry. Vol 78. No 1 1 1974
Conclusion The hydrolysis of bis-CME was found to be a pseudofirst-order reaction in all of the cases investigated. The decrease of the activation energy from acidic solution to basic solution highly suggests that the hydrolysis of bisCME is a nucleophilic reaction. Comparing the values of ASo* and E* measured for bis-CME with those for CMME and primary alkyl halides, it can be rationalized that the mechanism of the hydrolysis of bis-CME is S N ~ in character in basic solutions and shifts to an S N like ~ mechanism in acidic solutions.
Acknowledgment. The authors would like to express their great appreciations to T. Alfrey, 6. J . Kallos, and D. R. Carter for their helpful discussions. References and Notes B. L. VanBuuren, A. Sivak, B. M Gold Schmidt, C . Katz, and S . Milchonne, J . Nat. Cancer Inst., 43. 481 (1969). S. Laskin, M . Kuschner, R. T. Drew, V. P Cappielle, and N. Nelson, Arch. Environ. Health, 23(5), 135 (1971). L. Collier, Environ. Sei. Tech., 6, 980 (1972). L. A . Shadoff, G. J. Kallos, and J. S. Woods, Anal. Chem., 45, 2341 (1973). (a) T. C. Jones and E. R. Thornlon, J , Amer. Chem. Soc., 89, 4863 (19671, and the references therein: (b) T J, Ribar and M. J. Glavas, Glas. H e m . Drus., Beograd, 33, 517 (19683, L. B. Westover, J. C . TOU, and J. H. Mark, Anal. Cirem., 46, 568 (1974). P. Salomaa, Ann. Univ. Turku., A14 (1953). K. J. Laidler, "Chemical Kinetics," McGraw-Hi!l, New YorK, N. Y . , 1965, p 251.
