YOME CATALYTIC REACTIONS1
L
A. J. CURRIER The Pennsylvania State College, State College, Pennsylvania
W
HEN the velocity of a reaction expressed as cc. of gas absorbed in a given time is plotted as a function of time, a curve passing through a maximum is obtained (Figures 2 and 3). "The time P r e s e n t e d before the physical Science Section of the pennsyl. vania Academy of Science, State College, Pa., April 7, 1939.
necessary for the reaction to reach its maximum velocity" is called the induction period (1). It is obvious that the general effect of a catalyst is to decrease the length of the induction period in a given reaction. The "autocatal~tic" suggests that the effect is developed as the reaction proceeds. Several cata-
lytic reactions are to he considered in some of which "antocatalysis" is apparently involved. The first reaction to be considered is the so-called .-.. .---"dninc" of linseed oil ( 2 ) . I n this investigation, , " known weights of linseed bii, with and without drier, were placed successively on strips of cloth from the same sample. These strips, of the same size, were stretched upon wire frames and placed in a closed system which supplied oxygen at atmospheric pressure ~
Other curves shown by Nicholson and Holley indicate that variation in the quantity of metal (cobalt) used in the drier caused a variation in the length of the
OWESALT L I N O L E A T E A M A N G A N E S E LINOLEATE O LEAD LINOLEATE P R A W 01 L
ui
2
2 X
6
G
2
0
50
100
Time, Min.
FIG-
oa AssortPlIoN
%--RATES
OF OXYGEN
BY
LWSEEDOIL USING LINOLEATES OF COBALT, MANGANESE, AND LEAD-H 0.1 PERCENT.CONCENTRATION OF METAL IN EACH SAMPLE
FEL-RE 1.-APPARATUS ABSOXPTION O F
MEASURINGTHE RATE OXYGEN BV LINSEED OIL FOR
OF
(Figure 1). The reaction vessel containing the cloth was immersed in boiling water so that a temperature of approximately 10O0C. was maintained. By working a t 100°C. i t was possible to carry through a given experiment within one hundred minutes. Figure 2 shows the curves for data obtained with raw linseed oil alone and with driers. Driers used were linoleates of cobalt, manganese, and lead containing 0.1 per cent. of metal calculated on the weicht of the on used in each case. It will be observed that the maxima were much higher and the induction period was much shorter in the experiments in which driers were used. In an investigation of the rate of drying of linseed oil naint.. Nicholson and Holley (3) obtained results closely analogous t o those of ~ u ' & e r and Kagarise, although, a different technic was employed. The method was essentially a gravimetric one, in which the sample of paint, of known weight, was spread upon a glass plate in a film of known thickness. The glass plate was placed upon the balance pan of a chainomatic balance which was housed in a specially constructed chamber through which pure dry oxygen was passed at a known rate. Special devices for manipulating the chain, beam, and pan from the outside made i t ~ossibleto weiah the samples in situ. Figure 3 shows 'the velocity-time curves for two samples containing respectively cobalt resinate and cobalt naphthenate with the same concentration (0.038 per cent.) .of cobalt in each.
~.
induction period, a fact which was also observed by Currier and Kagarise (2). Although the chemical mechanism of drier action and the changes that take place in the drying of oils is not fully understood, two fairly well-defined processes are known t o take place, wiz., ((1absorption of oxygen with the formation of a peroxide type of structure, 0-0
I I
-c-c-
I I
(4)
H H
and (2) polymerization resulting id -the formation of polydimensional molecules of high molecular weight,
5
24
V COBALT RESINATE 0 COBALT NAPHTHENATE
d
%3
&. 2
2
.-ii
I
100
300
500
700
1000
1400
Time, Min.
F I G 3.-RATES ~ OF ABSORPTIONOP OXYGENBY LwseEn OIL PAINTCONTAINING COBALTRESINATE AND COBuT NdPHTAENATE COBALT BY WEIGHT
CE~T,
of the resin type and insoluble. It has been postulated also that the energy necessary to initiate polymerization is supplied by the oxidation process. Another factor not hitherto considered in the problem of the mecbanism of the drying of oils is the interface effect. The writer suggests that "autocatalytic" effects in the case of the drying oils, may be developed a t the interface between the liquid oil phase and the resulting solid resin phase composed of the oxidized polymerized product. It may be that the oxygen or the oil or both are activated a t this interface. As a basis for this view, attention is now directed to some experiments on the reduction of nickelons oxide by hydrogen (5). Benton and Emmett ascribe an "autocatalytic" effect, in the case of the reduction of nickelons oxide, to the nickel-nickel oxide interface which is developed during the reaction. This reaction appears to be analogous to the reduction of copper oxide by hydrogen, investigated by Pease and Taylor (6), and others. During the course of this reaction, copper nuclei were observed to form rapidly and thus set up an increasing copper-copper oxide interface. It was observed that when reduced copper was placed in contact with the copper oxide before reduction was started, the induction period was of shorter duration. The snpposition is made by these investigators that "the oxygen atoms of the oxide are rendered more active by contact with free metal." Benton and Emmett refer also to earlier work by Langmnir (7), in which it is shown that in the decomposition of calcium carbonate by heat, an interface is formed between the two heterogeneous
phases, calcium carbonate and calcium oxide, which accelerates the rate of decomposition. It is of interest to note here that a somewhat analogous case was investigated by G. N. Lewis (8) ("Zersetzung von Silberoxyd durch Autokatalyse"), in which he states that the "autocatalyst" is metallic silver. The oxidation of cyclohexene is of interest because other factors are apparently involved in the reaction. Stevens (9) concludes from his study of this reaction that the induction period is not due to autocatalysis but is caused by inhibitors (impuritiesg) which retard the attainment of the maximum rate. This view is supported by the fact that if the increase in rate with time is due to antocatalysis, the rate of oxidation a t a given time ought to be a function of the amount of oxygen which bas been absorbed. No such relationship was found. It was shown, on the contrary, that the rate was essentially of zero order with respect to oxygen-a fact which suggests the effect of some ratedetermining factor independent of the concentration of oxygen. This rate-determining factor was considered to be the rate of activation of the hydrocarbon molecules a t the walls of the vessel. From this brief survey, it is apparent that reactions of the so-called autocatalytic type are extremely complicated. In these reactions, as in many other catalytic reactions, a complete explanation of the mecbanism is difficultto attain because of the transitory intermediate steps in the gross process. 'The most exhaustive purification failed to eliminate the induction period entirely.
.. LITERATURE CITED
(1 (21 (3) (4) (5)
MIUS. Chew. RNieus, 10,308 (1932). CURRIER AND KAOARISE, Ind. Eng. Chem., 29,467 (1937). NICHOLSON AND HOLLEY, ibid., 30, 114 (1938). LONOAND CHATTAWAY, Oid., 23, 53 (1931). BENTON AND E ~ E T T I., A m . Chcm. Sac., 46, 2728 (1924).
(6) PEASEAND TAYLOR, J. A m .
Chem. Soc.,
(1921).
(7) LANGMUIR, ibid., 38, 2263 (1916). (8)
(9)
LEWIS, 2. physik. Chem., 52,310 (1905). STEVENS, 1.A m . Chem. Soc., S$,.219 (1936).
43,
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