780
G. R. F'RET"M.~N AND C. A. WINKLER
VOl. 50
decomposition of an arsine molecule at an arsenic surface include
The calculations suggest also that, a t very low temperatures, a zero-order reaction would result, the arsenic surface being largely covered with AsH(a). AsHs(g) = AsHa(a) (1) The quantitative evaluation of this mechanism and AsH8(a) = AsHz(a) H(-As) (2) that of other hydrides already studied, including AsH2(a) = AsH(a) H(-As) (3) GeH4 and SbH3, will be separately communicated. AsH(a) = As H(a) (4) Acknowledgment.-This work was carried out on 2H(a) = Hdg) (5) a post-doctoral fellowship kindly provided to where reaction (1) is the physical adsorption and Princeton University by the Shell Fellowship Comthe reaction (5) is the desorption of physically ad- mittee of the Shell Companies Foundation, Inc., sorbed hydrogen. Theoretical considerations of New York City. We wish to express our apprecithe total sequences of the reactions lead to a con- ation of this support. The work in question is clusion that either reaction (1) or (2) can be com- also a part of a program of research supported by patible with the experimental results as the rate- the Office of Naval Research N6onr-27018 on Solid determining step of the over-all reaction. Because State Properties and Catalytic Activity. Aclmowlthe physical process of adsorption (1) is in general edgment is made also to this research project for more rapid than the process of chemisorption (2), facilities used and for consultation with workers stage (2) or the chemisorption of arsine is actually in the project, and to Dean Hugh Taylor for rate determining in the experimental region studied. advice and assistance.
+
+ +
THE REACTION OF ACTIVE NITROGEN WITH METHYLAXIINE' BY G. R. FREEMAN A N D C. A. WINKLER Contribution from the Physical Chemislru Laboratory, McGill University, Monlreal, Caruida Received March Id. 1966
Plctive nitrogen reacted with methylamine to produce hydrogen cyanide, hydrogen and a polymer, with smaller amounts of ammonia and C2 hydrocarbons. The rates of methylamine destruction and hydrogen cyanide production increased with increasing temperature, while polymer formation increased with decreasing temperature. Comparison of the maximum rates of hydrogen cyanide production from methylamine and from ethylene during reaction with active nitrogen indicates that methylamine undergoes both ammonia and hydrocarbon type reactions.
The relative extents of reaction of ammonia and hydroxide solution were cooled to lo", and mixed in a flask, ethylene with active nitrogen2 indicated that a t nitrogen was bubbled through the mixture and the gas stream passed through a condenser cooled with Dry Ice least two reactive species are present in active into a similarly cooled receiver containing potassium hynitrogen. It appeared that ammonia reacted with droxide pellets. About 10% of the recovered methylamine only one of these while ethylene (and presumably was removed by distillation under vacuum and diwarded, and the residue distilled twice, with rejection each time of the other hydrocarbons, e.g., propylene,ja p r ~ p a n e , ~ blast 20% to remove traces of water. Infrared analyses? b ~ t a n e ,etc.) ~ reacted with the other or both. of the final distillate showed that it contained 98.7% Since methylamine might be expected to undergo methylamine and 1.3% ammonia The amount of methylamine passed into the reaction both ammonia and hydrocarbon type reactions, it vessel was estimated from the change in pressure in a storage was obviously of interest to examine the reaction vessel of known volume. Condensable products of the of active nitrogen with this compound. reaction were collected in a trap containing 10 ml. of standard sulfuric acid, immersed in liquid nitrogen, and their Experimental base content determined by titration to methyl red endThe apparatus used was essentially the same as that described in earlier papers.686 The molecular nitrogen flow rate was 9.2 X 1 0 - 6 mole/ sec., corresponding to a pressure of 1.43mm. in the reaction vessel. In several experiments, the reaction vessel was surrounded by powdered Dry Ice. While the wall temperature may be assumed to have been approximately -78", the temperature of the gases in the reaction vessel, as indicated by a glass encased thermocouple, was about -5' during the active nitrogen-methylamine reaction. To obtain methylamine, equal volumes of 25% methylamine solution (C.P.Fisher Scientific Co.) and 50% sodium
(1) Financial assistance froin the National Rewarch Council of Canada. (2) G. R . Freeman and C. A. Winkler, THISJOURNAL,59, 371 (1955). (3) (a) G. S. Triok and C. A. Winkler, Can. J . Chem., SO, 915 (1952); (b) I?.Onyszchuk, L. Breitman and C. A. Winkler, ibid., 32, 351 (1954). (4) R. A. Back and C. A. Winkler, ibid., 32, 718 (1954). (6) J. H. Creenblatt and C. A. Winkler, Can. J . Rea., B87, 721 (1949). (6) H. Blades and C. A. Winkler, Can. J . Ch~m.,49, 1022 (1951).
point of the excess acid after it had been allowed to melt in the trap. The presence of hydrogen cyanide did not affect the titration. Ammonia was determined by infrared analysis. The condensable reaction products were collected in an evacuated bulb immersed in liquid nitrogen, then distilled into an evacuated 10 cm. absorption cell. The wave numbers of the absorption peaks used were 968 cm.-* for ammonia and 2930 crn.-l for methylamine. The hydrogen cyanide content of the condensable products was determined by the Liebig DBnighs method.B In some experiments, these products were also analyzed for cyanogen. To do this, condensable products were collected in a trap containing 20 ml. of 0.5 N silver nitrate solution and 0.5 ml. of 6 N nitric acid, immersed in liquid nitrogen. The cyanogen was flushed out of the melted solution with nitrogen (1 hr.), and the cyanogen removed from the nitrogen stream by bubbling it through potassium hydroxide (7) We are indebted to the Central Research Laboratory, Canadian Xndustries (1954) Ltd., McMasterville, Que., and to Ayerst McKenna and Harrison, Ltd., Montreal, Que., for the infrared analyses reported in this paper. (8) I. M. Kolthoff and E. B. Sandell, "Textbook of Quantitative Inorganic Analysis," The Macmillan Co., New York, N. Y., 1946.
REACTION OF ACTIVENITROGEN WITH METHYLAMINE
August, 1955
78 1
solution. The potassium hydroxide solution was then analyzed for cyanide. The total CI frastion in the products was estimated with a Le Roy still, and its composition determined with the mass spectrometer.0 The non-condensable products were similarly analyzed for methane and hydrogen.
Results and Discussion The products of the reaction between active nitrogen and methylamine were found to be hydrogen cyanide and hydrogen, with smaller amounts of ammonia and a polymer, and traces of cyanogen, methane, ethane, ethylene and acetylene. In Fig. 1 the flow rate of methylamine is plotted for 10 (0.
Q
TEMP-OC.
x
0477
y
0 307
8-
A
ad
A-0-
2
0 A 43263 70 7
W
V 2 6-
n
8 a 4-
-0-
a
1-
TEMP-%
263
z 0 I
I
A
99
0
-7
A
1
I
2/
3r
0
','-"--o
14"
8 IO I2 F L O W R A T E - M O L E / S E C . X IO6.
CH3NH,
Fig. 2.-Freeman
-1
0
rn
4
6"
16
and Winkle!, active nitrogen with methylamine.
of Cz hydrocarbons produced at methylamine flow rates below about 8 X 10-6 mole/sec. increased with decreasing temperature. CH3NH,
Fig. 1.-Freeman
F L O W RATE - M O L E / S E C XIOb. and Winlcle~,active nitrogen with methylaniine.
different temperatures against (i) the flow rate of ammonia produced and (ii) a quantity, A (Base), defined as the flow rate of methylamine introduced minus the flow rate of total base found in the condensable products (Le., residual methylamine plus ammonia produced). Obviously, (ii) plus (i) gives the rate of destruction of methylamine. The relations between the methylamine flow rate, the rate of destruction of methylamine, and the rate of production of hydrogen cyanide are shown in Fig. 2 for different temperatures. The rates of production of hydrogen, methane, cyanogen and Cz hydrocarbons are shown in Table I. The C? hydrocarbons were approximately 20% ethane, 30% ethylene and 50% acetylene. Yearly two moles of hydrogen were produced for each mole of methylamine destroyed. Methane was not produced at methylamine flow rates below about 8 X mole/sec., and the amount produced above that flow rate increased with increasing temperature. Cyanogen production decreased with increasing methylamine flow rate and iticreased with increasing temperature. The amount (9) We a r e grateful t o D r . H. I. Schiff, of this department, for w r niiasion to use the mass spectrometer, and to Mr. D. A. Aiiustiong foi the analyses.
TABLE I
PRODUCTION OF HP, CH,, C2Nz AND CZHYDROCARBONS (.411 units except temperature are mole X 10-B/sec.) T ("C.)
468
CHIN& flow
480 482
7.01 10.4 10.4
96 74 106 101 108 130
0.56 1.57 7.11 7.23 10.29 12.47
-6 -2 +2 -2
0.90 1.68 7 10 7.55
Hl
13.7 17.7
CHI
CiNz
C1
0.00 0.18
0.010 0.003
0.010 .092 .118
.OO
.015 .010 ,003
(3.2
.I1
1.88
.OO
3.04
.OO
,000 .000
,041
,031 ,095
.02
.e5
The difference between the amount of methylamine destroyed and the ammountof hydrogen cyanide produced at 477 O corresponded closely to the amount of ammonia produced. The amount of carbon in this difference is much more than that contained in the methane, cyanogen and Cz hydrocarbons. As the temperature was decreased, the amount of carbon which was measured in the products decreased progressively, and at Dry Ice temperature (gas phase temperature about - 5 ")
G. R. FREEMAN AND C. A. WINKLER
782
.
it corresponded to only about 10% of the total amount of methylamine destroyed. However, at this low temperature, the walls of the reaction vessel became coated with a solid white polymer which melted upon warming to room temperature. The liquid turned light yellow upon standing. During the course of several experiments in the uncleaned reaction vessel, the polymer turned into a light brown solid, which did not melt at room temperature. It was assumed that, at all temperatures, the polymer accounted for the carbon which was not measured in the products. The active nitrogen concentration, estimated from the amount of hydrogen cyanide produced by the reaction of active nitrogen with ethylene at 360°, was 12.3 f 0.4 X 10-6 mole/sec. If it is assumed that the component in active nitrogen which reacted with ammonia2 would react in a similar manner with the NH2 group in methylamine, and that the other component reacted with the CH3 group, the experimental results may be explained by the following type of mechanism'o
CH3
+ CH,NHz --+
VOl. 59 CHI
+CH,
CHI"
(
+ CH3NH + CHzNI-12
+ possibly CHzNH,)
----f
=
+Nz
+ 2H2
+CzH6
(5a)
(5b)
polymer
( + possibly HZ
2NHz 2CH3
-6 -6
+
"I)
-89.4 -83
(6)
(7) (8)
At high methylamine flow rates, the N, concentration would be depleted by reaction (2), thus allowing reactions (5) and (8) to compete to a certain extent with reaction (3) for methyl radicals. Since nearly two molecules of hydrogen were produced for each molecule of methylamine destroyed, the polymer must contain a low percentage of hydrogen. The formation of some polymer at higher temperatures in the presence of excess active nitrogen indicates that polymerization occurs quite rapidly. The photochemical (direct and mercury-sensitized) decomposition of methylamine has been i n ~ e s t i g a t e d . ~ ~The ~ ~ 9 ~products ~0 from the decomposition of one mole of methylamine were found AH1' (kcal.) to be one mole of hydrogen, 0.5 mole of ammonia, CHaNHt N +CHI Nz + Hz -78.2 (1) 0.02-0.04 mole of methane, and a polymer. The CHJNHI Ns+ HCN Ha NH? - (34.4 - 2) (2) mechanism of the photochemical reaction has not CH, NI + [CHIN] Na +HCN + Hz Nt been definitely established, but the fate of the -(113.4 - 5 ) (3) CH3NH (or CH2NH2)radicals is probably similar in both the photochemical and active nitrogen NH2 CHINHz+NH3 + CHINH = -12 (4a) reactions, since in both cases they appear to form a +NHs + CHzNH2 z -12 (4b) similar polymer with a low hydrogen content. (10) For the uurpose of illustrating the typo of mechanism, it is When the reactjon vessel was surrounded by aasunied that N and Ns are the reactive specias, since there is some reaDry Ice the value of A(Base) was the same as the son to believe that excited molecules probably contribute little to the G. R. Freeman and C. A. chemical activity of active nitrogen: amount of ammonia destroyed by active nitrogen Winkler, Can J . Chem., in print. under similar conditions (1.8 X 10-6 mole/sec.2). (11) These heats of reaction were calculated using the following However, the maximum rate of destruction of values: D N - N = 225 kcal.,la DE-H = 102.7 kcal.,18 D H - C B ~= IO1 methylamine was 3.0 X mole/sec., with the = ~79 kcal.," DE-":, = 107 koal.,lb AHf(HCN) = kcal.,14 D C H ~ - N E 30.1 kcal.,16 AHf(CHs) = 3 1 kcal.,l4 AHr(NH8) = -10.9 kcal.,16 production of. only 0.2 X mole/sec. HCN. A H combustion (CHaNHz gas) = -262.0 kcal.". Using the ailThis can be explained if it is assumed that reaction propriate values from above, it WBS calculated that AHf (CHaNHz) = -3.3 kcal., AHr ("2) = 44.7 kcal. It was assumed that DB-HNCH~ = (2) does not occur appreciably a t this temperature, and that the collision complex formed in reaction DE-CH~NH =~ 95 kcal. z = D N - N in ~ Na. (3) (Le., [CH3N]) reacts with methylamine and (12) J. M. Hendrie, J . Clrem. Phyr., 2!2, 1503 (1954). (13) H. Beutler, Z. p h y s i k . Chem., B29,315 (1935). itself to produce ammonia, hydrogen and a polymer.
+ +
+ +
+ + + +
+
(14) M. Szwarc, Chem. Reus., 41, 7 5 (1950). (15) J. C. Devins and M. Burton, J . A m . Chem. Soc., 16, 2F18
(1954).
(16) "Handbook of Chemistry and Physics." (17) T. L. Cottrell and J. E. Gill, J . Chem. Soc., 1798 (1951).
(18) 0. C. Wetmore and H. A. Taylor, J . Chem. Phys.. 12, 61 (1944). (19) C. I. Johnson and H. A. Taylor, ibid., 19, 613 (1951). (20) J. 6. Watson and B. de B. Darwent, ibid., 20, 1041 (1952).
