DISCONTINUITIES IN ADSORPTION ISOTHERMS
Dee., 1954
1089
DISCONTINUITIES IN ADSORPTION ISOTHERMS BY M. L. CORRINAND C. P. RUTKOWSKI General Electric Research Laboratory, Schenectady, N . Y . Received M a y $6, 1064
Adsorption isotherms of krypton on calcium halophosphate under certain conditions exhibit discontinuities; under other conditions, the isotherms are smooth. The smooth isotherm is probably the equilibrium isotherm. The very marked effect of the time allowed for adsorption of the first increment on the later points is indicated.
The existence of discontinuities in adsorption isotherms, which are equivalent to first-order phase transitions in the adsorbed film, has been a matter of controversy. Such transitions have been reported by Harkins, Jura and their co-workers,l and by Ross and Boyd2; work on similar but not identical systems by Smith,a Young, Beebe and B i e n e ~and , ~ CorriiP has failed to confirm the earlier findings. These later workers point out that it was quite possible equilibrium was not attained in those experiments in which discontinuities were observed. Recently Ross and his co-workers6 have reported the existence of first-order transitions and supersaturation effects on sodium chloride, potassium chloride and asbestos. We have observed an apparent first-order phase transition for the adsorption of krypton on a calcium halophosphate a t 77.3OK. The general
experimental setup was that of a surface area system; stopcocks were employed and a thermistor gage served as the pressure measuring device. The sample was contained in a cylindrical glass container 12 mm. in diameter and was degassed 16 hours a t 350". Gage readings are plotted against time in Fig. 1; the readings are sensitive to h0.05 pa. or, in the pressure region of interest, 1 0 . 3 micron. It should be noted from these plots that apparently equilibrium has been attained in two hours; ie., with the sensitive pressure measuring system employed, the pressure is apparently then constant with time. The two hour points are plotted in Fig. 2 (open circles) as an isotherm; one marked first-order transition occurs and there are indications that at least two more discontinuities exist. 0
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- MINUTES.
120
Fig. l.-Rates
of adsorption in cylindrical bulb system. (Only 1 point, V, shown in transition region.)
W. D.
Harkins and E. H. Loeser, J. Chem. Phys., 14, 344 (1946); G. Jura, E. H. Loeser, P. R. Basford and W. D. Harkins, dbid., 14, 117 (1946). (2) S. Ross and G. E. Boyd, M D D C Report 864 (1947). (3) L. N. Smith, J. Am. Chem. SOC.,74, 3477 (1952). (4) D. A. Young, R. A. Beebe and H. Bienes, Trans. Faraday SOC., 49, 1086 (1953). ( 5 ) 1\1. L. Corrin, THIS JOURNAL, in press. (6) H. Clark and 9. Ross, J . Am. Chem. S O L , 76, 6081 (1953); S. Ross and W. Winkler, paper presented American Chem. SOC. Meeting, Kansas City, Mo., 1954. (1) G. Jura,
I
I
I
,0025
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,0075
Fig. 2.-Isotherms obtained: open circles, 2-hour points in cylindrical bulb: closed circles in tray system; 16-hour equilibration time for initial point.
A similar sample was then placed in the tray system described by Jura and Criddle.' The apparent rates of adsorption appeared less than with the cylindrical bulb and the pressure was still decreasing markedly a t the end of two hours. (7) G. J u r a a n d D. Griddle, THIS JOURNAL, 56, 163 (1951).
1090
L. K. J. TONG
Vol. 58
The sample was then degassed and the first incre- point was measured after 16 hours. The isotherm ment of gas allowed to remain in contact with the was continuous. Isotherms (1) and (3) coincide a t solid for 16 hours. With succeeding increments higher pressures; a t equal pressures the amount the rate of adsorption was quite high and apparently adsorbed by isotherm (3) is equal to or greater than equilibrium attained in five minutes. The isotherm the amount adsorbed by isotherm (1). thus obtained is plotted as partially filled circles It would appear that the continuous isotherm in Fig. 2. It should be noted that this isotherm is (3) rather than the discontinuous isotherm (1) smooth and coincides with the discontinuous represents the equilibrium state. It is not possible, isotherm a t pressures exceeding 7.5 microns. however, to rule out the possibility that (3) repreWe thus have looked a t three systems: (1) sents a “supersaturation” phenomenon and that Two-hour points with a cylindrical sample con- the discontinuous isotherm has significance. The tainer. Apparent equilibrium was attained ; the marked dependence of the rates of adsorption on isotherm was discontinuous. (2) Two-hour points the time allowed for attainment of equilibrium of with a tray sample container. Apparent equilib- the first point is evident; no explanation can be rium was not attained and adsorption rates were offered a t the present time. These findings suggest slow as compared to (1). (3) Apparent equilibrium that any measurements yielding discontinuous points with a tray sample container; the initial isotherms be carefully checked.
KINETICS OF DEAMINATION OF OXIDIZED N,N-DISUBSTITUTED p-PHENYLENEDIAMIIVJES BY L. K. J. TONG Communication No. 1849 f r o m the Kodak Research Laboratories, Research Laboratories, Eastman Kodak Company, Rochester, N . Y. Received May $9, 1964
An experimental technique is described for following the reactions of the deamination of oxidized N,N-disubstituted pphenylenediamines. Over a pH range of 7 to 12, the deamination of the substituted amino group fits the second-order rate equation involving the product of the concentrations of hydroxide ion and quinonediimine. The deamination of the unsubstituted amino group fits the first-order rate equation in buffered solutions, and the rate constants are insensitive to the change in pH. The variations in reactivity due to substitution can be largely accounted for by inductive effects.
Introduction the main reaction involved a t high pH is the deamMany of the processes of color photography ination of the substituted imino group. employ a substituted p-phenylenediamine type of Experimental developing agent to obtain a reduced silver image Materials.-For convenience, the developing agents will from the exposed silver halide emulsion. I n the be referred t o in this article by roman numerals as given in reduction of silver halide, the diamine is oxidized Table I . These N,N-disubstituted phenylenediamines beto the diimine, which then undergoes a coupling long to a class of color-developing agents commonly used. reaction with a suitable agent, called a coupler, The samples were as prepared for earlier experiments5 and to form an appropriate dye.’ I n any study of the have been stored under refrigeration. Compound IX was mechanism of the dye-forming reactions, a knowlTABLE I edge of the stability and reactivity of the diimines STRUCTURE OF DEVELOPING AGENTS is a prerequisite. This paper describes the development of suitable techniques for studying in solution the kinetics of the reactions involved, the application of these techniques to the specific problem of the rate of deamination of the diimines, Y (salt) No. and the interpretation of the results obtained. 2HC1 I It has been known for a long time that both HCI I1 substituted and unsubstituted qiiinonediimines HCI I11 undergo deamination reactions in acid s0lutions.~~3 I V HCI In alkaline solutions, N-substituted quinonedi2HCI V imine has been shown by Cameron4 to be highly VI unstable, but the reactions involved were not VI1 1/zHzS04 specified. We shall show in a later section that (1) C. E. IC. Mees, “The Theory of the Photographic Process,” rev. ed., The Maomillan Co., New York, N. Y.,1954, p. 586. R. M. Evans. W. T. Hanson, Jr., and W. L. Brewer, “Prinoiplea of Color Photography,” John Wiley and Sons, Inc., New York, N. Y.. 1953, p. 257; P. W. Vittum and A. Weissberger, J . Phot. Science, in press (1954). (2) R. WillstQtter and E. Mayer, Ber., 37, 1499, 1501 (1904); R. Willstatter and J. Piccard, ibid., 41, 1473 (1908). (3) L. F. Fieser. J. Am. Chem. Soc., 62, 4915 (1930). (4) A. E. Cameron. THISJOURNAL, 42, 1217 (1938).
VIII
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IX
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