TAKERU HIGUCHIAND JUNHASEGAM-A
796
Rate of Exchange of Chlorine between Dimethylchloramine and Succinimide'
by Takeru Higuchi and Jun Hasegawa School of Pharmacy, University of Wisconsin, Madison, Wisconsin (Received February 18, 1964)
Data are presented to show that the exchange of chlorine for hydrogen between succinimide and dimethylchloramine occurs directly and not through intermediate forrnation of hypochlorous acid. The pH profiles of the reaction rates in both directions have been determined.
Introduction Formation of dialkylchloramine in mixed aqueous solutions of dialkylamine and a halogenating agent may result either from a direct exchange of chlorine or through an intermediate formation of hypochlorous acid. Thus, for example, production of dimethylchloramine from dimethylamine and N-chlorosuccinimide (NCSI) may be written Me2NH
+ chlorosuccinimide
ki
k-
I
succinimide
+ Me2NCl
(1)
or
+ succinimide Me2NCl + H 2 0
chlorosuccinimide E HOCl
(2)
+ Me2NH
(3)
HOCl
Results of experimental measurement of these reactions suggest that (1) is normally the primary route. Values of kland L1 are reported as functions of pH. I . Formation of Dimethylchloramine from N-Chlorosuccznimide and Dimethylamine. The reaction can be readily followed spectrophotometrically since the end product absorbs strongly a t 263 mM. Figure 1 shows the approximate changes in the absorption spectrum of a mixture of the organohalogenating agent and the amine in water a t pH 2.9 and 25'. The curve shown for zero time is that corresponding to the sum of individual spectra of the reactants. The equilibrium values shown are based on the molar absorbancy, essentially, as given by Weil and Morris2 and as confirnied by our own work. I n Figure 2 the initial rates of appearance of dimethylchlonnline in these systems are shown for several molar ratios of dimethylamine to chlorosucThe Journal of Physical Chemietry
cinimide a t a constant initial chlorosuccinimide concentration. The linear plot clearly indicates that the rate is directly dependent on the amine. The usual z / z ( a - 2) plots against time, however, showed substantial departure from linearity for equiconcentration of the reacting species. This is ascribed to the reverse reaction corresponding to L1. All evidence available clearly rules out the possibility of the exchange reaction taking place through hypochlorous acid mediation as set forth in reactions 2 and 3. The formation of dimethylchloramine in freshly prepared solution of chlorosuccinimide and the amine exhibits no lag time. There is no spectral evidence of intermediate production of hypochlorous acid. The kinetic dependency on the amine as described above would not, moreover, be compatible with reaction 2 being rate determining. A recent separate study in these laboratories3 has indicated, in addition, that the forward reaction3 is apparently extremely slow in the pH range covered in the present study. These facts, taken together with the observation that the k l / k - l values calculated from the initial phases of the corresponding reactions agree with the observed equilibrium constant, are only consistent with the first mechanisms4 The second-order constant, kl, for the system calculated from initial rate of concentration charge is shown in Figure 3 plotted against the pH of the buf(1) This study was supported in part by the U. S. Army Research and Development Laboratories under Grant No. DA-CXIL-18-10861-G22 and DA-CML 18- 108-G-53. (2) I. Weil and J. C. Morris, J . Am. Chem. Soc., 71, 3123 (1949). (3) T. Higuchi, A. Hussain, and A . Hurwitz, private communication. (4) At the request of one of t h e referees, this conclusion was further substantiated by showing t h a t addition of succinimide had no significant effect on the forward reaction rate.
RATEOF EXCHANGE OF CHLORINE BETWEEN DIMETHYLCHLORAMINE AND SUCCINIMIDE
797
301
I
I
I
I
I
2
3
4
5
PH
I 6
+
Figure 3. pH rate profiles of C4H40zNC1 ki
+ C ~ H ~ O Z N[I]H and LMezNCl+ C~H~OZN .-H ,MezNH + C4H4OZNCl [11]. MezNHt+
WAVE LENGTH
-+
MezNCl
k- 1
Figure 1 . Spectral changes during reaction of dimethylamine with N-chlorosuccinimide in 0.05 M phosphate buffer at, pH 2.9 and 25". [Me2NH]i n i t i a l = [C4H402NC1] initial = 5.0 X 10-3 M . 0, before mixing; 1, 4, 8, 22, and 40, after mixing of Me2NH,in min. Yield,, = 35Tob.
Y
+
action, chlorosuccininiide free dimethylamine succininiide (CH&NCl, calculated for several pH values at 25' and based on a pKb value of 3.22 for dimethylamine6are given in Table I.
+
c? i
c
o
X
s
Table I : Second-Order Rate Constant for Reaction of N-Chlorosuccinimide with Free Dimethylamine
I
I
PH 4.90
3.90 2.90
Rate constant X lo-', 1. mole-' sec.-l 1.5 1 9 1.3
Mean 1 . 6 X lo7 1. mole-' sec.
-
MOL. RATIO
Figure 2. Initial rate us. molar ratio for the reaction, MezNH C~H~OZ+ N CMezNCl ~ C4H40zNH,a t pH 2.9 (0.05 M phosphate buffer solution) and 25". The concentration of chlorosuccinimide was 2.29 X 10-3 M in every instance.
+
+
fered systems. The pH dependency suggests that the reaction probably involves only the free form of the amine. The second-order rate constants for the re-
I I . Formation of N-Chlorosuccinimidefrom Dimethylchloramine and Succinimide. Spectral changes following mixing of equiconcentration solutions of diniethylchloramine and succininiide at pH 3.01 and 25' are shown in Figure 4. The second-order rate constant obtained directly on this system from initial changes was 0.86 1. mole-' set.-'. The value is shown as a solid square in Figure 3. The reniaining two points for the reverse reaction were calculated from the equilibrium concentration of the halogenating species ( 5 ) D. H. Everett and W. F. K. Wynne-Jones, Proc. Roy. Soc. (London), A177, 499 (1941).
Volume 69,Number 9
March 1966
TAKERU HIGUCHI AND JUNHASEGAWA
798
k-
- -kl=
' - Ki
kl (~~ZNC~)~,(C~H~O~NH)~~ (C4H402NC1),,(Me2NH2+)eq
It is evident that this reaction is largely pH independent, as would be expected from the nature of the reactants. The second-order rate constants calculated as above from the equilibrium constants a t pH 3.90 and 4.90 were 0.88 and 0.92 1. mole-' sec.-l, respectively, in good agreement with those determined directly. The corresponding K1values based on total remaining amine concentration (essentially MezNH2+) as given previously are shown in Table 11. The value at pH 3.01 was determined from kl and k-1 obtained from initial rates, and the remaining two values were obtained from equilibrium concentrations. The constant decreases inversely with hydrogen ion as expected. Other studies over pH range 2-6 are consistent with this relationship.
Experimental Reagents. All reagents used were of the highest grade commonly available and were normally subjected to further purification before use. N-Chlorosucciniinide was recrystallized twice from benzene and stored in a blackened desiccator. Succinimide was recrystallized from acetone. Dirnethylamine solution was prepared fiom the hydrochloride salt (Eastman Kodak, A.R. grade). The reagents used for preparation of the buffer solutions were recrystallized from solutions treated with hypochlorous acid to remove oxidizable material, Water used in the studies was prepared by redistilling tap distilled water from an acid permanganate solution. This procedure was found to reduce oxidizable residue to a negligible level. The hypochlorous acid solutions were prepared by dilution of distillate obtained from sodium hypochlorite solution under reduced pressure. Fifteen grams of boric acid, 250 ml. of sodium hypochlorite (Fisher Scientific, 5-6% available chlorine), and 500 ml. of water were distilled together. The first 50 ml. of the distillate was discarded, and the following 500 ml. was collected to yield a solution containing 0.04-0.08 mole of hypochlorous acid/l. Table I1 : Equilibrium Constant for the Exchange Reaction a t 25', CIH4OZNC1 CaH4O2NH Me2NCI
+
+ lCIezNHz+
KI
PH
KI
3.01 3.90 4.90
0.32 2.5 23.0
The Journal of Physical Chemistry
I
I
220
1
I
240
WAVE
I
1
260
280
1
300
w
LENGTH
Figure 4. Changes in ultraviolet absorption during the
+
k- I
+
reaction, C4H40zNH MeZNCl- C4H402NC1 Me2NH, in 0.05 M phosphate buffer solution at pH 3.24 and 25'. Curve B corresponds to 5.0 X 10-3 M MezNC1by itself, and curve A corresponds to 5.0 X 10-8 M succinimide only. That marked 0 corresponds to the arithmetic sum of A and B. Others correspond to spectra obtained 1, 4, 8, 15, and 30 min. after mixing the reactants to yield individual concentrations of 5.0 X 10-3 M .
Determination of the Forward Rate. Fresh 5.00 X M Y-chlorosuccinimide solution was prepared by mixing 50 ml. of 0.2 M acetate buffer and 5.0 ml. of 0.01 M N-chlorosuccinimide (0.1336 g. in 100 ml.) just before use in a 100-cc. volumetric flask. A second solution consisting of 50 ml. of 0.2 M acetate buffer solution and 5.49 i d . of 0.00910 M dimethylamine solution was prepared and diluted to 100 ml. Both solutions were then brought to 25.0 f 0.1". An equivolume mixture of these was prepared as rapidly as possible in a 10-cm. light path silica cell, and the change in absorbance at 263 nip was followed in a Cary Model 11 spectrophotometer. After the run was completed, the pH of the reaction mixture was determined. Determination of the Reverse Rate. A 5.00 X M dimethylchloramine solution was prepared by mixing 50 ml. of 0.1 M phosphate buffer, 11.0 nil. of 0.0901
CHEMICAL SYNTHESIS WITH IONBEAMS
M dimethylamine, and 15.3 ml. of 0.0654 M hypochlorous acid and water to the mark in a 100-ml. volumetric flask. A second solution consisting of 5.0 ml. of 0.01 M succinimide solution and 50 ml. of 0.1 M phosphate buffer solution was diluted to 100 ml. with water. Mixtures of the two solutions were prepared and allowed to react in a 10-cm. cell as above, and the decrease in absorbancy at 263 mp was determined as described before.
799
Determination of Equzlibrium Constant. Appropriate amounts of 5.00 X lo-* M N-chlorosuccinimide and dimethylamine solutions were mixed, and the change in absorbance at 263 mp was followed in appropriate buffer solutions. An equilibrium state was usually reached in 30-60 min. The equilibrium constant was arrived a t from the independently determined molar absorbancy of dimethylchloramine and the absorbancy at equilibrium.
Chemical Synthesis with Ion Beams
by Stanley Singer,* N. G . Kim,*A. W. Merkl, and M. Farber Maremont Corporation, Research Division, Pasadena, Cdifornia (Received March 8,1964)
A method of chemical synthesis by gas phase ion-molecule reactions analogous to known liquid phase reactions is described. The synthesis of nitrobenzene by the reaction of NOz+ and benzene is reported. The interaction of a beam of NO2+ ions with maximum energies of 1 e.v. with gaseous benzene gave nitrobenzene in high yield. A 1-ma. ion current consisting of 99% NO2+ was formed by electron impact with nitrogen dioxide in a concentric dual-anode magnetron.
This paper describes the use of low kinetic energy ion beams for chemical synthesis. Gas phase ion-molecule reactions have been the subject of numerous investigations.’ In the usual method of study the ionic products are determined in a mass spectrometer over the range of conditions available. Neutralization of the ionic species can lead to compounds produced in the usual gas or liquid phase reactions. Many different ions have been formed in electron bombardment of chemical compounds.2 The ability to produce high currents of selected ions a t controlled energies would make possible study of interesting gas phase reactions. For example, reactions which proceed through ionic intermediates in the liquid phase could be investigated in the gas phase as ion-n~olecule reactions. Three ion beams containing as major species NOz+,NF2+,and OF+ have been r e p ~ r t e d . ~ A molecular beam method in which the ion beam is directed into a reaction zone containing the neutral
target molecules can be used to study such reactions. In the apparatus shown in Figure 1, for example, a plasma is generated in the ion source. The ion beam is extracted by an electrostatic potential on the control grid. Ions passing through this grid enter the reaction zone where they encounter the neutral molecules flowing into the zone. The apparatus thus consists of three major parts: (1) the ion source for forming the ions from a suitable gas, (2) the electrostatic grid for ex-
* Correspondence may be addressed to these authors at Dynamic Science Corp., South Pasadena, Calif. (1) F . W. Lampe, J. L. Franklin, and F. H . Field, Progr. Reaction Kinetics, 1, 67 (1961). (2) F. H. Field and J. L. Franklin, “Electron Impact Phenomena,” Academic Press, Inc., New York, N. Y., 1957. (3) S. Singer, N. G. Kim, A: W. Merkl, L. B. Marantz, and C. Bodai, “The Formation of Plaama Beams Containing Ionic Species,” presented before the Division of Fuel Chemistry, 147th National Meeting of the American Chemical Society, Philadelphia, Pa., April 1964; Division of Fuel Chemistry Preprints of Papers, Vol. 8, NO.2, 1964, pp. 1-5. Volume 69. Number 3 March 1966
