June, 1958
REACTIONS OF METHYLAMINE AND ETHYLAMINE WITH ATOMIC HYDROGEN
coal giving a type I isotherm. The heat of immersion for Graphon approaches zero near 0.8 g. of benzene per gram carbon, which is within experimental limits the saturation adsorption observed for a benzene i ~ o t h e r m . ~Whether the sharp bend ' in the curve a t this point is real or not cannot be determined, since the heat effects observed are much smaller than the bulb correction in this region. It is established beyond doubt, however.' that H, is very near zero for kt saturated sample. Graphite A also has capillary condensation between particles but here the situation is somewhat different than for Graphon. The particles are not attached to one another and may move apart as film builds up between them. Consequently some surface remains, even a t high relative pressure, and H , does not drop to zero as the pores fill. The heat of immersion levels off a t about 0.2 cal./g. The film area, obtained by dividing 0.2 cal./g. by 67.6 erg/cmm2,the enthalpy of b e n ~ e n e ,is~ about 12.5 m.2/g. This is only 15% of the original powder area, or some 85y0of the area lies in the filled pores. This result shows that the H J absolute area method must be used with caution. A true result was obtained for the coarse anatase powder they used, with area about 14 ma2/g.,which shows that the extent of capillary condensation between the anatase particles was small. When particles are smaller than theirs the effect of capillary condensation may be to make the film area much less than that of the dry powder, even though the H , curve
657
has apparently the same shape as found by Harkins and Jura. The point at 'which condensation in capillaries begins cannot be determined from the H , curve. One would anticiwate that since the maces between the particles are iuite wide except a i the points of contact, the condensation would not occur to any appreciable extent until a high relative pressure is attained. This view is supported by the fact that the nitrogen area of Graphon is in good agreement with the electron microscope area, and by recent work by Graham12 who finds that about 1% of the low pressure adsorption by Graphon occurs on high energy sites. He suggests that these high energy sites are the contact points where an adsorbed molecule is touching the surface of two particles. The writers believe that inter-particle condensation does not occur to any great extent until the film is two or three statistical layers in thickness, and that after this point condensation becomes increasingly important until it is responsible for most of the adsorption a t high relative pressure. If this interpretation is correct, previous views regarding film thickness on free surfaces must be re-examined because practically all the data for multilayer adsorption are based on isotherms for powdered samples. Acknowledgments.-This work was supported in part by the Office of Naval Research, through a contract with Pomona College. (12) D. Graham, THIB JOURNAL, 61, 1310 (1957).
THE REACTIONS O F METHYLAMINE AND ETHYLAMINE WITH ATOMIC HYDROGEN1 BY A. N. WRIGHT,~ J. W. S. JAMIESON~ AND C. A. WINKLER Contribution from the Physical Chemistry Laboratory, McGill University, Montreal, Canada Received November 16, 1867
The production of hydrogen cyanide from the reactions of hydrogen atoms with methyl- and ethylamines went through a maximum a8 the flow rate of amine was increased in the temperature range of 60 to 285'. Hydrogen cyanide production was considerably less, and ceased at lower flow rates in the ethylamine than in the methylamine reaction.
Introduction An early study of the reaction of methylamine4 with hydrogen atoms produced in a discharge tube indicated that ammonia was the main product. However, the production of hydrogen cyanide from the reactions of hydrogen atoms with ethylenimine and N-methylethylenimine6 suggested that aminehydrogen atom reactions might produce hydrogen cyanide under suitably controlled conditions. The present study was made t o investigate this possibility. Experimental The apparatus and techniques employed were similar ~(1) With financial assistance from the Consolidated Mining and Smelting Co., Trail. E. C . , and the National Research Council of Canada. (2) Holder of National Research Council Studentship. (3) Holder of Corninco Fellowship. (4) 0.C. Wetmore and H. A. Taylor, J . Chsm. Phya., 12, 61 (1944). ~ 60, 1542 (5) J. W. 5. Jamieson and C. A. Winkler, T H I JOURNAL, (1956).
to those described previously.6*8 Non-condensable products were analyzed with a mass spectrometer, and condensable products by low temperature distillationT and infrared analysis. The hydrogen atom flow rate was 5.3 X 10-6 mole/sec. a t 60" and 4.2 X 10-6 mole/sec. a t 275" as estimated from the production of hydrogen chloride when ethyl chloride was used as the reactant a t these temperatures.6
Results and Discussion Figures 1A and 2A show that, a t low flow rates of amine, the rate of production of hydrogen cyanide was linear and increased with temperature, while at higher flow rates of amine, it passed through a maximum and gradually decreased to zero. Over most of the range of flow rates used, HCN production was less from the ethylamine than from the methylamine reaction. The available hydrogen atom concentration corresponded to slightly less than the maximum amount of methylamine reacted and (6) D. M. Wiles and C. A. Winkler, ibid., 61, 620 (1957).
(7) D.J. LeRoy, Can. J . Research, 28B,492 (1950).
658
A, N. WRIGHT,J. W. S. JAMIESON AND C. A. WINKLER
Vol. 62
A 6
2
4
4t
2
I
6 ' O 8
0
6
x
4
ti
2
2
W' 0
-x
2
4
2
4
B A S E FLOW R A T E
6
8
6
8
MOLE/SEC.X
IO'
C
W
v) \
8
W -I
0 *
16
24
32
I
C 8
6 4 2
4
8
I2
16
AMINE F L O W RATE MOLEISEC. X I 0 6 Fig. 1.-Methylamine-hydrogen atom reaction, HCN produced: 0, 61 f 8"; 0 , 180 f 6'; A, 285 f 5 (B) Abase: 0, 61 f 8'; 0 , 180 f 6'; A, 285 & 5'. (C) products of reaction at 61 f 8 " : 0, methylamine reacted; 0 , CHI formed; A, NHI formed; A, HCN formed; 0, CzHe formed; . , "no titer."
(4).
slightly more than the amount of ethylamine reacted (Figs. 1C and 2C). The quantity (ABase) in Figs. 1B and 2B represents the amount of amine reacted if other basic products are not formed diiring the reaction. Figure 2B is plotted with flow rate of base rather than ethylamine since later experiments showed that the ethylamine used contained about 8% ammonia as impurity. Ethylamine that had been laboriously purified by low temperature distillation dia not yield significantly different results. Products of the reactions at room temperature were aiialysed and the results are shown in Figs. 1C and 2, C and D. Ammonia and amine distilled partly as cyanides when the total base exceeded the amount of hydrogen cyanide produced ana free hydrogen cyanide was recovered only when it exceeded the total amount of base. A small amount of an unidentified substance, recovered above -80" from both reactions, gave neither basic nor cyanide titration. This "no titer" fraction was estimated (Figs. 1C and 2D) by subtracting the amount of titratable material from the total amount in the fraction obtained above -SOo, inferred from pressure-volume measurements. In both reactions, relatively large quantities of methane were produced which decreased a t higher amine flow rates. Ethane formation appeared to attain a constant value,
A M I N E FLOW RATE MOLEISEC. X IO6, Fig. 2.-Etliylnmine-hydrogen atom reaction. (A) HCN produced: 0, 65 f 8 " ; 0 , 121 f 2'; A, 288 f 4". (El) Abase: 0, 65 f 8 " ; 0 , 121 f 2'; A, 288 f 4 ' . (Carld D) roducts of reaction a t 65 f 8 " : 0, ethylamine reacted; 0 , 8H4formed; A, F,H3 formed; A, HCN formed; 0 , C$He formed; ,. "no titer.
ammonia production to increase, with flow rates of the two amines. As in most other reactions of hydrogen atoms, hydrogen abstraction is the most probable primary step. Since the strengths of carbon-hydrogen and nitrogen-hydrogen bonds are almost equal,*-1° it may be assumed that hydrogen abstraction from nitrogen and carbon sites should occur with approximately equal facility. The possible primary reactions for methylamine are
+ H +CH3NH + Hz AH = -9 kcal.
CHaNHz
----f
CHzNHz -+ Hz AH = -9 kcal.
(1A)" (1B)
and for ethylamine CH3CHzNHz
+ H +CHiCHzNH f Hz
AH = -9 kcal.
(1C) f Hz AH = -9 kcal. (1D) +CHzCHzNHz Hz A H = -9 kcal. (1E)
+CHaCHNHz
-+
(8) J. 8. Watson and B. deB Darwent, J . Chem. P h y s . , 20, 1041 (1952). (9) A. F. Trotman-Dickenson and E. W. R. Steacie, {bid., 19, 329 (1951). (IO) C. Keniball and F. J. Wolf, Trans. Faraday Soc., 61, 1111 (1955). (11) Heats of reaction were calculated using the following values. Accepted heats of formation of gaseous substances (U.8. Natl. Bur. Standards, Circular 500, "Selected Values of Chemical Thermodynamic Properties," Washington (1952)) a t 25'; heat of formation of NHI and the NHz radical (A. P. Altshuller, J . Chem. Phys., 22, 1947 (1954)); heat of formation of the ethyl radical (hi. Szwarc, Disc. Faraday Soc., 10, 330 (1951)). Heats of formation have been estimated for the CHaNH (or CHzNHz), CHaCHzNH (or CHiCHNHz or CHaCH2NHz) radicals and the CHaN biradical and for methylmethylenimine and ethylethylidenimine from a consideration of values for bond dissociation energies (M. Szwarc, Chem. Reus., 4T, 75 (1950)).
.
June, 1958
REACTIONS OF METHYLAMINE AND ETHYLAMINE WITH ATOMIC HYDROGEN
659
The formation and levelling out of ethane at high A radical formed in reaction 1 at lower amine flow rates could then add a hydrogen atom to form the flow rates of both amines can be explained by the corresponding activated amine, CH3NH2*or CH3- recombination of methyl radicals and perhaps CHZNHZ"which, with about 85 kcal. excess energy, 2CH3.CH2.NH +2C2H6+ Nz AH = - 102 kcal. (6) might dissociate together with stabilization by collision of energy CHINH~*+CHIN Hz AH = -9 kcal. (2A) rich ethane molecules formed as a first step in the +CHI + NHz AH = -15 koal. (2B) hydrogen atom reaction with ethyl radicals to yield CH&HzNHz* +CHaCHz + NH2 methyl radicals. Formation of trace amounts of AH = -18 kcal. (2C) nitrogen could be the result of reactions 5 and 6 +CHI CHzNHz at high amine flow rates. AH = -15 kcal. (2D) The net consumption of amine at high flow rates +CHXCHzN Hz might be decreased by stabilization by collision of AH = -9 kcal. (2E) Reaction 2B is similar to the cleavage of the carbon- the activated amines that would otherwise undergo nitrogen bond postulated by Emeleus and Jolley12 reaction 2. Consumption of methylamine in during the thermal decomposition of methylamine excess of the hydrogen atom concentration could above 550". The CH3N radical produced in (2A) be explained by the formation of additional hydrogen atoms by the reactions of CHI and NH2 could decompose to yield hydrogen cyanide radicals with niolecular hydrogen. These reCH3N --it HCN + Hz AH = -48 kcal. (3) actions, normally endothermic, could occur if The low yield of hydrogen cyanide from ethylamine radicals from (2B) carried some excess energy, and and its gradual decrease to zero at relatively high would be favored by the high mole fraction of flow rates of amine suggests that, unlike CH3N,the molecular hydrogen in the system. Further eviC2HsN radical may not yield hydrogen cyanide dence for the presence of additional hydrogen directly, but might undergo further reaction with atoms is seen in the approximate linearity of hyhydrogen atoms, possibly after rearrangement to drogen cyanide yield up to amine flow rates well ethylenimine, which has been shown6 to react beyond the point where reaction 1 should be rereadily with hydrogen atoms to produce hydrogen placed by slower reactions. The increase in ammonia production in both cyanide. The decrease in hydrogen cyanide production at cases can be attributed to the reactions relatively high flow rates of methylamine is thought CHZNH CHzNHz +CH3NxCHa + NH3 to be due to the increased significance of the disproAH = -65 kcal. (7A) portionation reaction. CHaCHzNH + CH3CHNHI +
+
+
+
+
CHI"
+ CHI"
+CHlNHz + CHIN
AH = 0
CHaCH2N=CHCHa
(4)
and recombination of CH3N radicals before they suffer decomposition to hydrogen cyanide CHIN
+ CH3N +CzH6 + Nz
AH = -94 kcal.
(5)
Formation of methane as the major product, in both reactions probably is due to the reactions of methyl and ethyl radicals with hydrogen atoms, and hydrogen abstraction from the parent amine by methyl radicals. The decrease in methane production a t higher flow rates of methyl- and ethylamine can be ascribed to the replacement of the radical-hydrogen atom reactions by the slower abstraction reactions. (12) H. J . Enieleus and L. J. Jolley, J . Chem. Soc., 929 (1935).
+ NH3
A H = -55 kcal.
(7B)
The results obtained from investigations in this Laboratory indicate that, under suitable conditions, biradicals containing nitrogen may decompose to form hydrogen cyanide. The radicals produced in successive hydrogen atom reactions with amines may not be identical with the reaction complexes postulated for the reactions of active nitrogen with organic but there is at least an interesting similarity in their behavior. The active nitrogen complexes are formed in highly exothermic processes and contain excess energy which probably accounts for their invariable decomposition to hydrogen cyanide. (13) H. G. V. Evans, G. R. Freeman and C. A. Winkler, Can. J . Chem., 34, 1271 (1956).
