2722
NOTES Interaction of n-Butylamine with Tetracyanoethylene and Chloranil
by William J. Lautenberger and John G. Miller John Harrison Laboralory of Chemistry and the Laboratory for Research on the Structure of Matter, University of Pennsylvania, Philadelphia, Pennsylvania 19104 (Received January 14, 1970)
AVERAGE
REACTANT ION
K E (eV)
Figure 2. Fractional yields as a function of average reactant ion kinetic energy, cyclopropane system.
study and those measured in the earlier pressure studies" are combined in Figures 1 and 2 as a plot of the fractional yields us. average reactant ion kinetic energy. The results from the pressure studies represent the appropriately weighted average for reactions of ions with energies ranging from zero to the final exit energy, E,, and we have taken as the average reactant ion kinetic energy I? = E,/3, which has been shownlato be valid for the low conversions attained. The solid points in Figure 1 represent the results obtained (using a tandem instrument) by Abramson and FutrellI4 for reaction of ions of 0.3 eV energy. The plots in Figures 1 and 2 clearly show that the reactant ion kinetic energy in the present study is quite low; indeed, the present data fit quite well with the higher energy data if we assume that the reactant ions in the zero-field and ICR experiments have thermal energies. This is to be expected for the ICR experiments and the good agreement between the ICR and zero-field results confirms that the latter also refer to thermal energy ions. Finally, we would point out that, as the results in Figures 1 and 2 clearly show, the relative product yields are strongly dependent on the ion kinetic energy, at least for unsaturated hydrocarbons. Clearly, this effect must be considered when results obtained by different techniques are to be compared. Acknowledgments. The work at the University of Toronto was supported by the Kational Research Council of Canada and that at the University of Sheffield by grants from the Science Research Council and from NATO. (13) P. Warneok, S. Chem. Phys., 46, 513 (1967). (14) F. P. Abramson and J. H. Futrell, J . Phys. Chem., 72, 1994 (1968).
The Journal of Physical Chemistry, Vol. 74, No. IS, 1070
The role of A and r (outer and inner) complexes in the nucleophilic substitution reactions of amines with tetracyanoethylene (TCNE) and chloranil (CA) has been studied at several laboratories recently. l-5 Evidence for the participation of the complexes has been obtained for the reactions of the aromatic amines, dime thy la nil in el^^ and aniline,6 with TCNE and CA. A major part of the evidence for the participation of u complexes as intermediates in the reactions has been based on kinetic measurements. The large difference between the rate of disappearance of the acceptor (TCNE or CA) or its T complex with the amine and the rate of formation of the product of reaction has indicated the existence of such intermediates in the reactions. No kinetic study has been made heretofore of the reaction of aliphatic amines with these acceptors, although it has been known that primary and secondary aliphatic amines form both mono- and disubstituted products readily with TCNE6 and CA.4"-9 Working with a large excess of amine, a condition used in the kinetic studies of the aromatic amines,l16we have made an ultraviolet-absorption spectroscopic rate study of the reactions of the n-butylamine with both acceptors. The results show that the formation of the monosubstituted product is practically immediate and that, although the subsequent formation of the disubstituted product has a smaller rate, no evidence for an intermediate of appreciable stability exists even in that second reaction since the rate of disappearance of the monosubstituted product is the same as the rate of formation of the disubstituted product. The ultraviolet absorption spectra of n-butylamine, TCNE, and a solution of the two with the amine in large excess, all in cyclohexane at 25", are shown in (1) 2. Rappoport, J . Chem. Soc., 4498 (1963). (2) R. Foster, Rec. Trav. Chim. Pays-Bas, 83, 711 (1964). (3) P. G . Farrell, J. Newton, and R. F. hf. White, J . Chem. Soc., B , 637 (1967). (4) B. K. Das and B. Majee, J . Indian Chem. SOC.,45, 1054 (1968). (5) T. Nogami, K. Yoshihara, H. Hosoya, and S. Nagakura, J. Phys. Chern., 73, 2670 (1969). (6) B. C. McKusick, R. E. Heckert, T. L. Cairns, D. D. Coffman, and H. F. Mower, J . Amer. Chem. Soc., 80, 2806 (1958). (7) L. F. Fieser, ibid., 48, 2936 (1926). (8) N. P. Buu-hoi, R. Royer, and B. Eckert, Rec. Trav. Chim. PaysBas, 71, 1059 (1962). (9) D. Buckley, N.B. Henbest, and P. Slade, J . Chem. Soe., 4891 (1957).
2723
NOTES
1
I
-
I
1
I
..
0.80
0.60-
w
0
z
2
0.40-
m
a
-
0.20
Figure 1. The ultraviolet absorption spectra of n-butylamine, TCNE, and their mixture in cyclohexane a t 25'; 1.69 X 10-1 M amine, - - -; 7.16 x 10-6 M TCNE, Solution of 1.69 x 10-1 M amine and 7.16 x 10-6 M T C N E a t different times after mixing: -., 1 min; -. .-, 35 min; . .-, 55 min; -. . .- , 96 min; . . . . . . . . . ., 2 days.
-.
-.
.
WAVELENGTH, my.
Figure 3. The ultraviolet absorption spectra of n-butylamine, CA, and their mixture in cyclohexane a t 25': 6.76 X M amine, -; 2.71 X 10-6 M CA, Solution of 6.76 X 10+ M amine and 2.71 X 10-6 M CA a t different times after , 1 min; -. 6 min; -. . .-, 25 min. mixing:
--
-.
-e-
9-,
:z::
0
20
60 80 TlME IMIN.)
40
100
v
0.2
120
TIME IMIN.)
Figure 2. Pseudo-first-order rate plots of 1.69 X 10-1 M 'ih T C X E in cyclohexane: 0, n-butylamine and 7.16 X k = 0.00893 0.00015 min-'; 0, k = 0.00846 =k 0.00015 min-'.
Figure 4. Pseudo-first-order rate plots of 6.76 X M n-butylamine and 2.71 X iM chloranil in cyclohexane 0, IC = 0.2388 & 0.0039 min,-l; 0, k = 0.2276 i: 0.0002 min.-1
Figure 1. In 1min after mixing, the prominent TCNE band has disappeared and an intense new band has appeared at 324 mp. This new band is due to the monosubstituted product, N-tricyanovinyl-n-butylamine,6 and not to a complex. Apparently, the replacement of one cyanide group of TCNE by the amine is extremely rapid. A new band has started to form a t 269 mp and grows as the band at 324 mp diminishes. We have synthesized the disubstituted product, 1 , l bis(n-butylamino)-2,2-dicyanoethylene(Anal. Calcd for C I ~ H ~ O C, N ~65.4; : H, 9.2;N, 25.4. Found: C, 65.1;
H,9.5; N,25.4),and have found that its absorption band in cyclohexane is at 269 mp. First-order rate constants for the disappearance of the monosubstituted product and for the formation of the disubstituted product were obtained from the rates of change of the absorbance values at 324 and 269 mp by plotting the quantities - IogA, and -log ( A , A $),respectively, against time, where A I is the absorbance at time t and A , is the value at the end of reaction. The absorbance values were corrected for overlap of the bands. Figure 2 shows the results obtained. The Journal of Physical Chemistry,Val. 74,hTo.13, 1970
KOTES
2724 The k values and their standard errors were computed by a least-squares procedure. Over the period studied, the reaction went two-thirds to completion and the rates of the two processes were closely the same, showing no evidence for the existence of any intermediate of appreciable stability. Similar results were obtained with n-butylamine and CA, as shown in Figures 3 and 4. The monosubstituted product has its maximum absorption at 289 mp, the same as for CA itself, but with a smaller extinction coefficient. The growing band at 354 mp is caused by the disubstituted product, 2,5-dichloro-3,6-bis(n-butylamino)-p-benzoquinone, which was identified as the final product of reaction (mp 200-202', lit.e mp 201202'; Anal. Calcd for C14H20NzC1202: C, 52.7; H, 6.3; N, 8.8; C1, 22.2; 0, 10.0. Found: C, 52.7; H, 6.3; IS,8.2; C1, 20.7; 0, 9.6. Uv and visible maxima (cyclohexane) 225, 354, 525 mp; lit.e (dioxane) 224, 355,520 mp). The near equality of the rates given in Figure 4 indicates that there is no stable intermediate in the reaction. The reaction is remarkably rapid, production of the disubstituted compound being 92% complete in 11 min. Foster2 earlier found that ethylamine also reacts rapidly with CA in aqueous ethanol. Although he did not evaluate the rates, the spectral changes observed resembled closely those shown in Figure 3. The band of the monosubstituted product occurred a t 303 mp and replaced the CA band (285 mp) practically instantly and then decayed rapidly. The disubstituted product had its growing band at 356 mMu. Due to the high speed of these reactions, Slifkinl0 was probably unaware of the reactions of ethylamine and diethylamine with CA and for that reason misinterpreted the spectra he obtained for those systems. Aclcnowledgments. This research was supported in part by the Advanced Research Projects Agency, Office of the Secretary of Defense, and by a Public Health Service Fellowship (5-F1-GM-32, 638-02, awarded to W. J . 11.)from the Xational Institute of General Medical Sciences. We also wish to acknowledge the assistance given by Mr. John W. Schulhoff. (10) M. A . Slifkin, Nature, 195, 635 (1962); J. B. Birks and M. A , Slifkin, ibid., 197, 42 (1963); lf.A. Slifkin, ibid., 198, 1301 (1963).
The Determination of the Pressure Dependence of Transference Numbers
by Robert L. Ray, I
