Canadian Journal Journal canadien : of Chernistrv de chimie \ Published by Publii pa r $ THE NATIONAL RESEARCH COUNCIL OF CANADA LE CONSEIL NATIONAL DE RECHERCHES DU CANADA

Volume 52 Number 1 January 1, 1974 Volume 52 numCro 1 1 janvier 1974

i Kinetic Studies of the Reactions of Cyanide Ion and 1,3,5-Trinitrobenzene in Ethanol, n-Propanol, Isopropanol, and t-Butanol at 25.0 "C

$ Depnrtmenf of C/leinistiy, Qtreen's University, Ki~lgston, 0ntro.io Received July 3, 1973

The specific rate constants for the formation of the 1 : 1 1,3,5-trinitrobenzene - cyanide ion o-complex in ethanol, n-propanol, isopropanol, and t-butanol are 442 + 14, 932 + 30,2.45 + 0.10 x lo3 and 1.06 + 0.05 x lo5 M - Is-', respectively. A plot of log k us. Dirnroth'ssolvent parameter E, is linear with slope -0.25. The kinetics of thereactions of cyanide ion and 1,3,5-trinitrobenzene in ethanol and PI-propanol are complicated by alcoholysis of cyanide ion which yields the corresponding alkoxide ion and the 1 : I 1,3,5-trinitrobenzene - alkoxide ion o-complex.

Les constantes spkcifiques de vitesse pour la formation du cornplexe-o 1 : I trinitro-1,3,5 benzene - ion cyanure dans I'Cthanol, le n-propanol, isopropanol et le r-butanol sont respectivement egales a 442 + 14, 932 + 30, 2.45 + 0.10 x lo3 et 1.06 + 0.05 x lo5 M- ' s-'. Un graphique de log K us. le parametre de Dirnroth (solvant) E,, rCvele une ligne droite dont la pente est egale a -0.25. La cinetique des reactions de I'ion cyanure avec le trinitro-1,3,5 benzene dans I'Cthanol et le 11-propanol est perturbke par I'alcoolyse de I'ion cyanure qui conduit a I'ion alcoolate correspondant et au cornplexe-o 1 : 1 trinitro-1,3,5 benzene - ion alcoolate. [Traduit par le journal]

Can. J. Chem., 52, l(1974)

Introduction ions with a number of 1-X-2,4,6-trinitrobenzenes

Cyanide ion is known to react with 1,3,5- trinitrobenzene and related nitroaromatic com- pounds in a wide variety of solvents to form o- complexes (1-4). The visible absorption char- acteristics of o-complex 1 (X = CN), together with equilibrium constants and thermodynamic parameters associated with its formation, in a number of alcohols have been reported (5). The thermodynamic results were interpreted in terms of desolvation of the cyanide ion as being the primary factor affecting the enthalpies and entropies of formation (5).

o * N ~ O ~

NO2

1

As part of a series of kinetic studies of the reactions of sulfite, cyanide, and various alkoxide

(X = H, CH,O, CH,, CHO, NH,, NHCH,, and N(CH,),) (6, 7) and, as an extension to earlier equilibrium studies, we have investigated the kinetics of reaction of 1,3,5-trinitrobenzene and cyanide ion in several alcohols.

Specific rate constants for the formation of 1 (X = CN) at 25.0 "C in ethanol, n-propanol, isopropanol, and t-butanol have been deter- mined. Results are presented to show that in ethanol and n-propanol alcoholysis of cyanide ion is a significant side reaction and leads to the initial formation of 1 (X = RO) in these solvents.

Experimental Reagents

Eastrnan 1,3,5-trinitrobenzene was purified and dried as previously described (8), rn.p., 122 "C (lit., m.p. 122.5 "C (9)).

Eastman 1-(p-hydroxypheno1)-2,4,6-triphenylpyridin- ium betaine was converted to the perchlorate salt as described by Dirnroth er al. (10) and recrystallized from

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2 CAN. J . CHEM. VOL. 52, 1974

anhydrous methanol. After drying in uacuo over silica gel the pale yellow needle-shaped crystals had m.p. 250 "C.

Tetraphenylarsonium cyanide was prepared as described previously (5) and dried to constant weight in uacuo over phosphorus(V) pentoxide.

Absolute ethanol was distilled from magnesium and iodine according to the procedure described by Vogel(11). The remaining alcohols were dried by refluxing over Linde 4A Molecular Sieve overnight and then distilled under a dry nitrogen atmosphere. Only the middle portion of the distillate was retained in each case.

Stock solutions of 1,3,5-trinitrobenzene and tetra- phenylarsonium cyanide were prepared by dissolving weighed quantities of each reagent in known volumes of the alcohol.

Instruments Ootical measurements in the eauilibrium studies were

carried out on a Cary 14 recording spectrophotometer using matched silica cells of 1.0-cm path length. The temperature in the cells was maintained constant to + 0.1 "C by circulating water from a constant temperature bath through a specially designed cell holder in the spectrophotometer.

Kinetic measurements were carried out on a Durrum- Gibson stopped-flow spectrophotometer.' A closed circuit temperature control system utilizing an Ultra Kryomat TK 30D constant temperature bath kept the temperature in the valve-block, drive syringes, and observation cell constant to k0.1 "C. Temperature-jump or conventional stopped-flow cells of 2.0-cm path length were used. Minimum "dead times" of the two cells were 10 and 2 ms, respectively. For some of the kinetic runs the normal mode of operation of the spectrophotometer was modified so as to yield an oscilloscope trace of absorbance as a function of time rather than % transmit- tance as a function of time (12). Standard solutions of potassium permanganate, whose absorbances at several different wavelengths had been determined on the Cary 14, were used to establish that the input signal to the vertical axis of the storage oscilloscope was directly proportional to absorbance over the range 0-0.10 absorbance units. One advantage of this method of operation was that over the range indicated absorbances could be accurately determined at very low noise to signal ratios.

Procedures Solutions containing 1,3,5-trinitrobenzene M )

and tetraphenylarsonium cyanide (10-4-10-2 M) were prepared immediately prior to each run by dilution of known volumes of the corresponding stock solutions with alcohol. Before each run each drive syringe was rinsed three times with the appropriate solution, filled to capacity, and allowed to stand for 20 min in order to reach thermal equilibrium with the bath. In the course of the kinetic studies the concentration of 1,3,5-trinitro- benzene was kept constant and only the solutions con- taining tetraphenylarsonium cyanide were changed. Each time this was done the drive syringe was thoroughly flushed with the new tetraphenylarsonium cyanide solu- tion before being filled for the kinetic run.

'Durrum Instrument Corporation. Palo Alto, Calif.

The stopped-flow spectrophotometer was used in the conventional way to obtain values of absorbance a t infinite time (A,) associated with the fast initial reactions in ethanol and n-propanol. The absorption characteristics of the species formed in the slow reactions were deter- mined by running the reactions under the same experi- mental conditions used in the kinetic runs and recording the resulting spectra of the solutions on the Cary 14.

Traces on the storage oscilloscope of absorbance o r transmittance us. time were recorded photographically when at least two consecutive runs gave identical traces. Absorbances or transmittances a t various times were read directly from the photographs and used to calculate values of In (A, - A,) as a function of time. A, and A, refer to absorbances at a specified wavelength a t times infinity and t, respectively.

Results and Discussion

When solutions containing 1,3,5-trinitroben- zene (TNB) in ethanol and tetraphenylarsonium cyanide in ethanol (in large excess) were mixed, the % transmittance us. time trace recorded o n the oscilloscope showed two distinct parts. The first portion of the trace rapidly reached a limiting absorbance value (A , ) ; there was then a further slow increase in absorbance. As the concentration of tetraphenylarsonium cyanide was reduced, separation of the trace into two distinct portions became less distinct.

The visible spectrum of the species formed in the first reaction was determined by recording, for solutions o f constant TNB and tetraphenyl- arsonium cyanide concentration, infinite absor- bance values as a function of wavelength. The resulting absorption spectrum (Fig. 1) showed

FIG. 1. Visible absorption spectrum (derived from A , values) of the colored species formed in the "fast" reaction observed in ethanol solutions containing 1,3,5- trinitrobenzeneand tetraphenylarsonium cyanide: [TNBlo = 1.02 x 1 0 4 M ; [ $ 4 ~ ~ ~ ~ ~ o = 1.15 x 10-2 M; T = 25.0 "C; I = 2.0 cm.

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GAN AND NORRIS: REACTIONS O F CYAN[DE ION AND TRINITROBENZENE 3

absorption maxima at 498 and 422 nm with E ~ ~ ~ / E ~ ~ ~ = 1.45. These absorption character- istics are very similar to those recorded for o- complex 1 (X = C2H50) (A,,, 497 and 424, E ~ ~ ~ / E ~ ~ ~ = 1.49) using the Cary 14 spectro- photometer (4, 6).

The progress of the fast reaction was followed at 480 nm. Plots of In (A, - A,) us. time were linear to at least 80% completion of reaction. If this first reaction involves the reversible forma- tion of l (X = C,H,O) according to the equation

k I

[ I ] TNB + CzH5O- 1 (X = CzH5O) k- 1

and the concentration of ethoxide ion in solution ([C2H,0-I) is much greater than the total concentration of 1,3,5-trinitrobenzene ([TNB],), the slope of the In (A, - A,) us. time plot (k,,,) should be related to the specific rate con- stants k, and k- , and [C2H50-] as follows:

value equal to 2020 M - ' was used in the calcula- tions (6). A typical set of data is given in Table 1.

The plot of k,,, for the fast reaction us. [C,H,O-] was linear with slope (k,) equal to 37 000 f 8000 M- ' s-I and intercept (k-,) of 11.9 f 1.7 s-', respectively. (Errors in k , and k- , are based on the errors associated with the "least-squares" slopes and intercepts of the k,,, us. [C2H50-] plots.) Values of k , and k- , for the interaction of sodium ethoxide with TNB in ethanol have been reported as 33 400 M- ' s-I and 27.5 s-' (13) and 49 500 f 1500 M-' s-' and 15.4 f 2.0 s-' (6), respectively. The good agreement in the k, and k- , values and the observed absorption characteristics of the species first formed leave little doubt that the fast initial reaction involves formation of o-complex 1 (X = C,H,O).

The visible absorption spectrum of the species formed at the termination of the slower second reaction showed absor~t ion maxima at 435 and

PI kobs = kl[C2H50-I + k- I 544 nm. The spectru& is consistent with the formulation of this species as the 1 : 1 1,3,5-

The [CiH50-] in the system was calculated trinitrobenzene - cyanide ion o-complex (1, 5).

using the equation2 The rate of formation of this species was followed at 580 nm where o-complex 1 (X =

C ~ I CCZHSO-I C2H50) has a negligible molar extinction co- - [I (X = C2HsO)I efficient (Fig. 2). Plots of In (A, - A,) us. time -

K{[TNBIo - [1 (X = C2H5O)I) for this second reaction were linear t o at least 90% co~npletion of reaction. For the reversible

A, formation of o-complex 1 (X = CN) in ethanol according to eq. 4 the k,,, obtained from the

k z TNB + C N - z l (X = CN)

k-7 where A, is the absorbance at infinite time associated with the fast reaction, 1 is the path length of the cell (2.0 cm), E is the molar extinc- tion coefficient of the complex at 480 nm (1.65 x lo4 M - ' cm-') and K(k,/k-,) is the equili- brium constant for complex formation. A K

ZThe equilibrium concentrations of CZH50- can be used to calculate an alcoholysis constant K' associated with the reaction

CN- + CZH50H+ C2H50- + HCN

where K' = [HCN] [CzH50-]/[CN-] [CzH50H] = [C2H50- J Z / {[CN-lo - [C2H50-I} [CzH5OH.]

The mean value of K' at 25.0 "C was 1.33 + 0.03 x The error limits on K' represent the standard

deviation of the mean for eight determinations over a range of 44AsCN concentrations 2.0 x to 5.48 x 10-3 M.

slope of the In (A, - A,) us. time plot is related to k,, I<-,, K, [TNB], and the total concentra- tion of cyanide ion in solution [CN-1, as shown in eq. 5.3

Values of k,,,, [C2H50-] and the term ([CN-I, - [C2H50-] + [TNB],)/(l + K[C2H50-I for a series of runs at different tetraphenylarsonium

31t is assumed in this deviation that the alcoholysis reaction is rapid and that the [C2H50-] is maintained constant throughout the course of the TNB - cyanide ion reaction. Also [CzH50-] >> [TNB],.

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C A N . .I. CHEM. VOL. 52, 1974

TABLE I . Pseudo first-order rate constants (k,,,) for the "fast reaction" observed in ethanol solutions containing

1,3,5-trinitrobenzene and tetraphenylarsonium cyanide: T = 25.0 "C; [TNBIo = 3.04 x M

[@+AsCN] x lo3 (M) [C2H,0-] x lo4 (M)" kabr ( s - ' ) ~

o[C~H,O-] calculated using eq. 3 with K = 2020 M-1 and = 1.65 X 104M-I cm-'. It is assumed that rapid alcoholysis o f cyanide ion maintains the [C2H,0-I constant throughout the course of reaction.

bk.o, values from the slopes of the In (A, - A,) us. time plots. Errors in kob. are based on the "least-squares" slopes of the plots.

FIG. 2. Visible absorption spectra in ethanol at 25.0 "C of (i) the 1 :1 1,3,5-trinitrobenzene -cyanide ion o-complex and (ii) the 1 : I 1,3,5-trinitrobenzene - ethoxide ion o-complex.

cyanide concentrations are given in Table 2. The plot ofk,,, vs. ([CN-1, - [C,H,O-] + [TNB],)/ (1 + K[C,H,O-I) was linear with "least- squares" slope (k2) and intercept (k-,) of 442 i 14 M- ' s-I and 0.042 + 0.033 s-I, respectively.

When solutions of tetraphenylarsonium cya- nide in n-propanol and 1,3,5-trinitrobenzene in n-propanol were mixed the % transmittance vs. time traces on the oscilloscope again indicated that "fast" and "slow" reactions were taking place in solution. By analogy to what was found to occur in the ethanol system, the fast reaction in n-propanol was considered to be associated with the formation of a-complex 1 (X = n-C3H70).

The progress of the fast reaction was followed at 505 nm. Plots of In (A, - A,) us. time were linear to about 80% completion of reaction. Values of k,,, were not as reproducible in this

system as for the fast reaction in ethanol, average reproducibility in kob, being i. 13% in n-propanol as compared to +5% in ethanol. The [n-C,H70-] was calculated as in eq. 3 using a K for a-complex formation of 7.8 x lo3 M - I (6) and a molar extinction coefficient (E) of the a-complex at 505 nm of 1.74 lo4 M - I cm-l. The plot of kObs vs. [n-C3H70-] was linear with slope (k,) equal to 7.3 5 3.0 x lo4 M-' s- ' and intercept (k-,) equal to 5.8 4 3.6 s-I. The agreement between these values of k , and k - , and the k, of 9.26 i. 0.17 x lo4 M-I s-' and k, of 11.9 i 1.1 s-' determined from a study of the interaction of 1,3,5-trinitro- benzene and n-propoxide ion in n-propanol (6) is reasonable and confirms that the fast reaction involves the formation of a-complex 1 (X = n-C3H70).

The alcoholysis constant K' for the reaction of cyanide ion and n-propanol at 25.0 "C was determined to be 1.56 i. 0.05 x The error limits on Kt represent the standard devia- tion of the mean of nine determinations carried out over the tetraphenylarsonium cyanide con- centration range 1.24 x to 8.28 x M.

The species present at the completion of the slow reaction in n-propanol possessed absorp- tion maxima a t 435 and 542 nm. This is con- sistent with the formulation of this species as a-complex 1 (X = CN) (5). The rate of forma- tion of this complex was followed at 580 nm since at this wavelength a-complex 1 (X = n-C3H70) has negligible absorption. Treatment of the rate data was identical to that employed for the reaction of cyanide ion and TNB in ethanol. A linear kobs vs. ([CN-] - [n-C3H70-]

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GAN AND NORRIS: REACTIONS OF CYANIDE ION AND TRINITROBENZENE

TABLE 2. Pseudo first-order rate constants (kobs) for the 1,3,5-trinitrobenzene - cyanide ion reaction in ethanol: T = 25.0 "C; [TNBIo = 8.03 x M

x lo3 [Ij14AsCN] x lo3 (M-l) [CIH,O-] x lo4 (M)" 1 + K [CzH50-] kobs (s-'lb

"[C2H50-I calculated using eq. 3 and the experimentally determined A, associated with the first (fast) reaction. Alternatively, [C2H50- was calculated using K' for the alcoholysis o f CN- ion in ethanol.

bSlope o f the In (A, - A,) us. time plot. Error in k.,, based on the error associated with the "least-squares" slope o f the plot.

FIG. 3. Values of kOb, for the formation of the 1 :1 1,3,5-trinitrobenzene - cyanide ion o-complex in n- propanol as a function of ([CN-lo - [n-C3H70-] + [TNB],)/(I + K[n-C3H70-I): T = 25.0 "C; [TNB], = 9.62 x M; [IjI4AsCNIo = 1.78 x to 1.10 x

M.

+ [TNB],)/(l + K[n-C3H70-I) plot was ob- tained (Fig. 3) whose slope (k,) was 932 + 30 M-' s-'. The intercept of the plot was too small (<0.01) to be assessed with any real accuracy by this method.

When solutions of 1,3,5-trinitrobenzene in isopropanol and tetraphenylarsonium cyanide in isopropanol were mixed only a single reaction trace of % transmittance vs. time was observed. The resulting solutions possessed absorption maxima at 436 and 546 nm consistent with the formulation of the species in solution as o- complex 1 (X = CN) (5).

The progress of the reaction was followed at 540 nm. Plots of In (A, - A,) vs. time were linear to greater than 90% completion of reaction over the entire range of cyanide ion concentra- tions employed. Plots of k,,, vs. [CN-1, were

linear in the range 2.0 x M to 3.0 x M but curved slightly upward between 3.0 x

and 7.0 x M [CN-]o.4 The value of k, at 25.0 "C obtained from the slope of the k,,, vs. [CN-1, plot, for runs carried out at low concentrations of cyanide ion, was 2.45 + 0.10 x lo3 M-' s-'. The value of k-, was too small to be accurately estimated from the inter- cept of the plot. Using the reported K (k,/k-,) for complex formation of 10.0 f 0.3 x lo3 M-' at 25.0 "C (5), k-, is calculated to be 0.25 s-'.

The reaction of 1,3,5-trinitrobenzene and cyanide ion in t-butanol also gave rise to only a single reaction trace of % transmittance vs. time. The species formed in solution possessed absorp- tion maxima at 437 and 539 nm consistent with its formulation as o-complex 1 (X = CN)(5).

The progress of the reaction was followed at 545 nm. Plots of In (A, - A,) vs. time were linear to greater than 90% completion of reaction at all cyanide ion concentrations employed. A plot of k,,, vs. [CN-1, was linear over the range 2.0 x to 5.0 x M but curved slightly upward between 5.0 x

and 7.0 x M [CN-I,. From the linear portion of the plot at low [CN-I,, k, and k-, were found to be 1.06 + 0.05 x lo5 M-' s-' and 2.5 f 1.2 s-', respectively.

Specific rate constants for the formation of 1 (X = CN) decrease in the order k,(t-C4H50H) > k2(iso-C3H70H) > k,(n-C3H70H) > k2- (C,H,OH). A plot of log k, vs. the solvent parameter E, (10) is linear with slope -0.25.

40ver a comparable range of tetraphenylarsonium cyanide concentrations the curvature in the kOb, us. [CN-Io plots was more pronounced the higher the temperature. A study of this phenomenon is reported in the following paper.

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6 CAN. J . CHEM

Linear log k 27s. E, plots of comparable slopes have also been reported for the formation of 1 (X = RO) in ROH, where R = CH,, C2H5, n- and iso-C3H7, and n-C4Hg (6), and for the formation of the 2,4,6-trinitrobenzyl anion (2) by reaction of 2,4,6-trinitrotoluene with RO- in the corresponding alcohol (R = C,H5, n- and iso-C3H7) (14).

0,. + No.

NO2

It has been argued that for the formation of 1 (X = OR) free energy changes associated with the desolvation of the anion play a critical role in determining the magnitudes of the specific rate constants (15, 6). The similarity in the slopes of the above log k us. E, plots suggests that, for the limited range of alcohols studied, cyanide ion and RO- respond similarly to the changing solvation characteristics of the different alcohols.

Little can be said on the basis of our results concerning trends in k-, for decomposition of 1 (X = CN), k-, values in ethanol and n- propanol are both small (<0.05 s-l) and cannot be determined with any accuracy using the method described; k-, values in isopropanol and t-butanol are approximately 0.3 and 2.5 s- l , respectively. The trend in k - , values is opposite to that which is observed for the decompositions of 1 (X = RO) in the alcohols where the higher values of k-, are associated with the ethanol and n-propanol systems.

The ratios of the rate constants for formation of 1 (X = OR) and 1 (X = CN) in ethanol, n-propanol, isopropanol, and t-butanol are 116, 112, 43, and 0.27, respectively. The straight chain alkoxides are about 100 times more reactive than cyanide ion in the corresponding alcohol whereas isopropoxide is only about 40 times as reactive. A steric hindrance associated with a methyl group in isopropoxide would account for its lower reactivity compared to n-propoxide. This steric effect is sufficiently pronounced that in t-butanol cyanide is a better nucleophile towards the aromatic carbon center than is t-butoxide ion.

A comparison of the autopyrolysis constant of ethanol (pK, = 18.88) (16) with the dissocia- tion of hydrocyanic acid in ethanol (pK, 1: 13)

. VOL. 52, 1974

determined above indicates that in ethanol ethoxide ion is about lo6 times more basic than is cyanide ion. Comparable differences in hydrogen basicity may be expected to operate in the other alcohols. However, based on the reported equilibrium constants for formation of 1 (X = OR) and 1 (X = CN), carbon basicity towards the aromatic carbon center favors the alkoxide over the cyanide by less than a factor of 10 for R = C2H5, n- and iso-C3H7, and n-C4Hg (5, 6, 13).

Alcoholysis of cyanide ion was observed in ethanol and n-propanol but not in isopropanol and t-butanol. Combining the alcoholysis con- stants K' obtained in this study with the reported autopyrolysis constants of ethanol and n- propanol (16) one can calculate the dissociation constants (K,) of HCN in ethanol and n-propanol at 25.0 "C as 9.92 x 10-l4 and 1.72 x 10-14, respectively. The constant (K,) of HCN in water at 25.0 "C is 8.82 x 10-l2 (17). This order of dissociation constants Kd (H,O) > Kd (C2H50H) > K,, (n-C3H70H) is in quali- tative agreement with the calculated pKBH+ values of water (-3.43), ethanol (- 1.93), and n-propanol (-1.91) reported by Levitt and Levitt (18). Isopropanol and t-butanol (pKBH+ value - 1.70 and - 1.49, respectively) are too weakly acidic to undergo any substantial alcoholysis reaction. Although kinetic studies in methanol and n-butanol were not investigated, the pKBH+ values of these alcohols (- 2.17 and - 1.90, respectively) suggest that complications due to cyanide ion alcoholysis would also be observed in these solvents.

The alcoholysis reactions of cyanide ion in methanol and ethanol may have been responsible in part for the experimental difficulties which lead to the placing of high error limits on the equilibrium constants for formation of 1 (X = CN) in methanol and the difficulties experienced in obtaining a good AH,,, for the formation of 1 (X = CN) in ethanol (5). In fact since the reaction to form 1 (X = OR) is always signifi- cantly faster than the reaction to form 1 (X = CN) in the same ROH, the slow secondary reactions referred to by Buncel et al. (5) may, in part, have been associated with the formation of the desired TNB - cyanide ion o-complexes. More accurate values of k-, for the decomposi- tion of 1 (X = CN) in ethanol and n-propanol are required before any definitive statements can be made regarding possible errors in the re-

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CAN AND NORRIS: REACTIONS O F CYANIDE ION AND TRINITROBENZENE 7

ported K and AH0 for the formation of 1 (X = 9. J. R. A. POLLOCK and R. STEVENS (Editors). Dictio-

CN) in ethanol and n-propanol introduced nary of organic compounds. 4th Ed. Eyre and Spot- tiswoode Ltd., London. 1965. through of the alcohol~sis reactions in 10. K. DIMROTH. C, REICHARDT. T. SIEPMANN. and F.

these solvents. BOHEMANN. iiebigs Ann. hem. 661, 1 (1963). 11. A. I. VOGEL. A textbook of practical organic chem-

Financial s u ~ p o r t by the National Research Council istry. 3rd Ed. Longmans, Green, London. 1956. of Canada is g;atefull; acknowledged.

1. A. R. NORRIS. Can. J. Chem. 45, 2703 (1967). 2. A. R. NORRIS. Can. J. Chem. 47, 2895 (1969). 3. E. BUNCEL, A. R. NORRIS, and W. PROUDLOCK. Can.

J. Chem. 46, 2759 (1968). 4. E. BUNCEL, A. R. NORRIS, and K. E. RUSSELL. Q.

Rev. Lond. 22, 123 (1968). 5. E. BUNCEL, A. R. NORRIS, W. PROUDLOCK, and K. E.

RUSSELL. Can. J. Chem. 47, 4129 (1969). 6. L. H. GAN and A. R. NORRIS. Can. J . Chem. 49,2490

(1971). 7. E. BUNCEL, A. R. NORRIS, K. E. RUSSELL, and R.

TUCKER. J. Am. Chem. Soc. 94, 1646 (1972). 8. A. R. NORRIS. Can. J . Chem. 45, 175 (1967).

p. 169. 12. P. G. ASHMORE, B. P. LEVITT, and B. A. THRUSH.

Trans. Faraday Soc. 52. 530 (1956). 13. C. F . BERNASCONI. J . A ~ . ~ h e k . Soc. 92, 4682

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