July, 1962
XOTES
involves a contraction of about 10% (that is, 20 om.~/molefor dodecane) and this contraction would clearly outweigh the expansion which accompanies the formation of micelles of sodium dodecyl sulfate at low pressures (11 ~m.~/rnole). If this hypothesis is correct it should be possible to vary the freezing pressure, and hence the c.m.c. inversion pressure, by altering the temperature and the hydrocarbon chain length, and by dissolving short chain alcohols in the micelles. It is hoped to study the effects of some of these changes in future work.
l1
1361
t
10 L 30 Fig. 1.-log
BATE OF SPREADING AND EQUILIBRIUM SPREADING PRESSURE OF THE MONOLAYERS OF n-FATTY ALCOHOLS AND n-ALICOXY ETHAKOLS BY A. V. DEO,S. B. KULKARNI, M. I(. GHARPUREY, AND A. B. BISWAS Contribotion No. 486 from the Nattonal Chemical Laboratory, Poona-O, Indza Received December 19, 1961
In recent communications,'V2 we reported the superior water evaporation retarding power of the alkoxy ethanols (glycolmonoalkyl ethers) to those of the commonly used cetyl and stearyl alcohols. With a view to understand this evaporation retardation behavior we have been studying their physico-chemical properties; and in what follows, preliminary results on the rate of spreading from the solid onto a clean water surface and on equilibrium spreading pressure a t 25' are reported. The Rate of Spreading.-For measuring this rate, the alcohol or the alkoxy ethanol sample was prepared by gently withdrawing a glass rod of uniform diameter irom the melt of the substance kept 10' above its melting point. The rod then was left overnight at room temperature (-25'). The perimeter of the coated rod was measured with the help of a traveling microscope. It then was half-immersed vertically in a known area of clean water surface in a thermostated Langmuir trough fitted with a horizontal film pressure balance. The time required for the film pressure to rise to the low value of X dyne/cm. was noted. From such data and from the previously determined values of the area/molecule of the various substances a t 1 dyne/cm., the rate of spreading in terms of the number of molecules entering the water surface from 1 cm. of the triple interface perimeter in 1 sec. was calculated. The values a t 25' are given in Table I. From the above it may be noticed that a modification of the terminal -OH group to -OCH2CH20H has considerably decreased the melting point and increased the rate of spreading. Again, in s homologous series the rate of spreading is decreased as the melting point is increased along with the chain length. It is interesting to compare the log dN/dt us. melting point curves for the two series as given in Fig. 1. (1) A. V. Deo, N. R. Sanjma. S. B. Kulkarni, M. K. Gharpurey, and A. B. Biswas, Nature, 187, 870 (1960). (2) A. V. Deo, S. B. Xulkami, M. K. Gharpurey, and A. B. Biswas. ibid.. 191, 378 (1961).
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60 90 120 Time, min. Fig, 2.-Surface pressure vs. time: 0, cetyl alcoholA = 308.5 cm.2; T = 25.3'; p = 2.12 cm. A, octadecoxyethanol-A = 308.5 cm.2; T = 24.7'; p = 2.15 Cm. 0
30
TABLE I MELTINGPOINT,RATEOF SPREADING (dN/dt, NUMBER OF MOLECULES/CM./SEC.), AND EQUILIBRIUM SPREADING PRESSURE (DYNES/CM.) -n-Fatty M.P., OC.
Cic Ci6 CIS Czo Czz 0
alcoholsdN/dt
11.
7 - n - A l k o x y ethanolsM.P., oc. dN/dt
39.5 2.1 X 10" 46.5 35.0 49.5 2 . 8 X 10l3 39.6 43.5 59.4 1.1 X 10l2 35.2 51.7 64.5 7.6 X loll 32.6 60.5" 71.0 6.0 X 10" 27.6 65.6 Compound not extremely pure.
5.2 X 2.3 X 1.8 X 1.2 X 1.5 X
10" 10" 10" 10'' 1012
IIe
48.6 50.4 48.9 49.0 47.2
In the intermediate range the curves run roughly parallel and here the rate of spreading of the nalkoxy ethanol is about ten times higher than that of the n-alcohol. This may be attributed to the higher escaping tendency of the former compounds from the solid together with the enhanced interaction of the -OCH&H20H group with the water subphase compared to the -OH. The film pressure vs. time curves for the Ciaalcohol and the Cle-alkoxyethanol at 2.5' are shown in Fig. 2. The points of discontinuity in the curves naturally correspond to those in the 11-A curves and are a consequence of the sudden change in the film compressibility, and do not signify a sudden change in the rate of spreading at the corresponding pressure.
1362
NOTES
The ourves flatten at the higher pressures due to the balance between spreading and loss of molecules (by di~solution3~~ and evaporatioiP-6). The steady-state spreading pressure value has been found to be a function of the perimeter/surface area ratio, the pressure tending to the equilibrium value for higher values of the ratio only, which is in agreement with the earlier work.3 However, for the same perimeter-area ratio, a remarkably higher steady-state spreading pressure value of the C18alkoxy ethanol than that of the Cle-alcohol may be noted. Equilibrium Spreading Pressure (e.s.p.).-The measurements were carried out by dropping a large number of solid specks of the pure compounds on a clean distilled water surface using a vertical film pressure balance. The e.s.p. at 25' of the fatty alcohols and the corresponding alkoxy ethanols are given in Table I. It is seen that the alkoxy ethanols exhibit considerably higher pressure and that in this range the value does not fall a$ rapidly on increasing the chain length as in the case of the alcohols. The value for Clralkoxy ethanol may be lower than the true e.s.p., probably due to its higher rate of dissolution into the water. This also may be attributed to the greater escaping tendency of the alkoxy ethanol molecules from the solid state and to the increased interaction between their polar groups and the water surface. The superior evaporation retardation1 exhibited by the alkoxy ethanols thus could be attributed to their higher evaporation resistance2 at high surface pressures and higher equilibrium pressure values as well as higher rates of spreading. (3) A. Roylanoe and T. G. Jones, J . AppZ. Chem., 9, 621 (1959). (4) A. Roylance and T. G. Jones, 3rd Intern. Congr. of Surface Activity. (5) W. W. Mansfield, Australian J . Appl. Sci., 10,73 (1959). (6) A. Roylance and T. G. Jones, J . Appl. Chem , 11, 329 (1961).
Vol. 66
is the only species present which may react to consume nitric oxide, and secondly, that one nitrogen atom destroys one molecule of nitric oxide. There is almost no real evidence either to support or to contradict these assumptions, since the measurement of absolute atom concentrations by other means (mass ~pectrometry,2~4.8 e.p.r.,6 calor i m e t r ~ Wrede ,~ gage1*) has not been sufficiently accurate to indicate anything more than a very crude proportionality between atom concentration and nitric oxide consumption.11 Despite this lack of evidence, many authors have assumed, usually tacitly, that these assumptions were well-proven facts. Verbeke and Winkler,12 on the other hand, in order to account for the considerable discrepancy between nitric oxide consumption and hydrogen cyanide production from the reaction with ethylene, have suggested that nitric oxide might also be destroyed by reaction with excited nitrogen molecules present in active nitrogen. It was suggested that in addition to the simple atomic reaction N
there also occurred the process Nz*
Division of Pure Chemistry, Sational Research Councd Laboratories, Ottawa, Canadala Received December $3, 1961
The reaction of active nitrogen with nitric oxide has been used in a number of laboratories in the last few years to estimate nitrogen atom concentration,%-e usually using the now-familiar gasphase titration first described by Spealman and Rodebush? The validity of this method depends upon two assumptions, first, that atomic nitrogen (1) Summer reseal-oh assistant, 1961. (1%)Issued a4 N. R. C. No. 6867. (2) G. B. Kistiakowsky and G. G. V d p i , J . Chsm. Phys., 97, 1141 (1957). (3) P. Earteck, R. R. Reeves, and G. Mannella, abid., 29, 608 (1958). (4) J. T. Herron, J. TJ. Franklin, P. Bradt, and V. H. Dibeler, zbad., 30,879 (1959). (5) J. Iiaplan, W. J. &hade, C. A. Barth, and A. F. Hildebrandt, Can* J . Chem,, 38, 1688 (1960). (6) M. A. A. Clyne and B. A. Thrush, Pioc Roy. SOC.(London), A261, 259 (1961). (71 M. L. Spealman and W.H. Rodebush, J . A m . Chem. Sac., 57, 1174 (1935).
+ NO+Nz
+N +0
(1) (2)
followed by reaction 1. If the velocity of reaction 2 were not much different from that of (l), then the occurrence of (2) would not have been detected in previous studies of the reaction. The present work was undertaken to test this possibility by studying the reaction with N160 and examining the isotopic composition of the nitrogen produced. If the atomic reaction (1) is the only important one, then the nitrogen product should be all T\J15N14. If, however, reaction 2 occurs, free atoms should be produced, which, with an excess of N150 present, should react by reaction 1to give N215. The atomic exchange reactions "4
THE REACTIONS OF ACTIVE NITROGEN WITH "'0 AND N215 BYR. A. BACKAND J. Y. P. Mu11
+ NO +Nz + 0
f" 6 0
+N16 + N140
(3)
and
+ S16Nl4 (4) could, if they occurred, cause some confusion, so these reactions also were investigated. "6
f N214+N14
Experimental Active nitrogen was generated in a fast-flow system with a condensed discharge operating at 60 discharges per second which, with a 5-liter ballast volume just before the pump, gave a steady, non-pulsating flow. The flow system between the discharge tube and the product traps was poisoned with 5 % Hap04 solution. The reactions r i t h nitric oxide and ethylene were studied in a cylindrical reaction vessel of 18 mm. 0.d. Pyrex tubing about 30 em. below the discharge tube, which could be heated to 300". The reagent gases were admitted to the stream of active nitrogen through a cone-shaped axial nozzle designed to assure rapid mixing. The nitric oxide conaumption was measured by the gas-phase titration method, while the hydrogen cyanide from the ethylene reaction wab trapped a t - 196" and titrated with silver nitrate. (8) D. Jacksonand H. I. Schiff, J . Chem. Phys., as, 2333 (1955). (9) M. H. Saxe and N. K. Liohtin. Abstracts, 135th National Meeting, Am. Chem. Soo., 1959. (IO) R. A. Back and C. A. Winkler, unpublished results. (11) K. R. Jennings, Quart. REU.(London), 1 5 , 237 (1961). (12) G. J. Verbeke and C. A. Winkler, J . Phys. Chem., 64, 319 (1960).
