W. C.PERKINE ANP W. 5.KMKI
474
Val. 66
and the rate constant ratio, for instance k,/L1- The relative effects of perchlorates and sulfates GN~o-. It in implausible to consider that G ~ ~ o - i n - on k4/kl agree quantitatively with the observations creases with the square root of the ionic strength of Indelli, Solan and ArnW for the alkaline hyin one system, decreases in another and remains drolysis of potassium malonate in which two reunchanged in the third. actants with unit negative charge are reacting. The enhanced effect of LaCI3 agrees qualitatively Discussion The usual form of the equation relating rate with the observation of Indelli and Pruel2 in their of the persulfate oxidation of iodide, They constants and ionic strength, obtained from the study a larger positive deviation than we observe, Bronsted model of ionic reactions and the extended observed which agrees with the higher charge on the actiDebye theory of ionic solutions, isg,lo vated complex in the I-, SzOs- reaction. Such k p1/2 deviations have been discussed by Scatchardli3 log - = 1.022,Zb ____ (V) ko 1 + up1/% who finds them in agreement with predictions where k is the rate constant a t ionic strength p, based on the Mayer theory of electrolytes. ko is the rate constant at infinite dilution of ions, Two other observations on the nature of H202, and Zb are the algebraic numbers of charges on may be made on the basis of these data. First, the reactants and a is a parameter near unity and the species is thermal, otherwise the ionic strength taken as such. Thus, the rate constant will in- effect would not be observed. The derivation of crease, decrease, or remain the same with increasing equation V depends upon maintaining a Boltsmann ionic strength, depending on whether the reactants distribution of the concentration of charges around have the same sign, opposite signs or whether one an ion. Secondly, HzO- must move slowly enough reactant is neutral. ill1 three types of behavior to maintain its ion atmosphere, Le., it must be are seen in Fig. 1. The lines drawn are for slopes solvated. If it moved rapidly, the charge distriof 1.02, 0 and - 1.02, respectively, corresponding bution surrounding the activated complex would to a unit negative charge on H20-. The agree- resemble that of' a univalent ion and the change in ment with the data is excellent. the activity coefficient of the activated complex Deviations from equation V are observed in would only be half of that for a divalent ion. One Fig. 4, where the ionic strength is varied by the other observation on the nature of HzO-, not based addition of multivalent ions. These deviations on the present data, perhaps is in order. It is are expected and lend support to the interpretation. known that HzO- reacts quantitatively with reaRate constants for reactions between ions of the gents such as H202and O2present in low concentrasame charge depend more upon the concentration tions of the order of several ph.l without undergoing of ions of opposite charge than on ions of similar a first-order reaction to produce a hydrogen charge, Hence replacing perchlorate by sulfate at0m.2~~4This suggests that HzO- is quite stable, does not have much effect on the rate constants, the rate constant for the reaction H20- + H while it increases the ionic strength by a factor of OH- probably being less than lo4sec.-l. two. Similarly, as lanthanum is a triply charged A. Indelli, G. Xolan, Jr., and E. S. Amis, J. A m . Chem. Soc., positive ion, it exhibits an abnormally large effect. 84,(11) 3237 (1960).
+
+
(9) H. A. Schwarz, J . A m . Chem. Soc., 77, 4960 (1955). (IO) S. E. Benson, "The Foundations of Chemical Kinetics," MeGraw-Hill Book Co., New York, N. Y.,1960, p. 525.
(12) A. Indelli and J. E. Prue, J . Chem. Soc., 107 (1959). (13) G. Soatchard, Natl. Bur. Standards Circ. 524, 1953, p. 185. (14) H. A Sohware, J . Phys. Chem , 6 6 , 255 (1962).
NX3-L,4BELEDPRODCCTS FROM C1' (d,n) REACTION IN ALCOHOLS BY W. C. PERKINS AND W. S . KOSKI Department of Chemistry, The John Hopkins University, Baltimore 18, Maryland Received September $3, 1961
The W-labeled compounds produced when gaseous methane, methanol, or ethanol are bombarded with 2 Mev. deuterons have been investigated. HCNI3 and CH&N1* are the gaseous aqtivities found for CHd and CHaOH. These activities plus CzHsCN13 were found in ethanol bombardments. Experiments with rare gas additives and Brs suggest that cyanogen ion or radical is the B13 carrier and that the HCN is formed by reaction with materials on the wall of the vessel, whereas the CHsCN is formed by reaction with target gas molecules in the gas phase.
arose from the reactions of Yi3 recoils with the alkyl halide, This could not be determined with In a previous investigation2 the radioactive NI3 certainty because of the possible role of radiationproducts, formed when alkyl halide derivatives damage products. rn this paper an extension undergo C12(d,n)N13reactions in the gas Phase, of these studies to methanol and ethanol is dewere identified. Indications were obtained that scribed. Through the use of B~~as % scavenger, the radioactive products such as HCN and c1Cx from the effect of rare gas additives on the reaction and from a careful examination of the products (1) Work done under the auspices of the United States Atomic Enobtained from deuteron bombardment of methane ergy Commission. a better insight has been Obtained and the (2) H. Scbmied and W. S. Koski, J . A m . Chem. Soc., 81, 4706 into the nature of these reactions. (1960).
Introduction
March, 1962
T LABELED PRODUCT^
FROM
C'z(d,n) REACTIONS IS ALCOHOLS o,p.rn. 5000
Experimental The bombardments were made with 2 Mev. deuterons
from a n electrostatic generator in our Laboratory Beam currents and bombardment timm were kept as lorn as OB-
eible to Inimmize complications through radiation damage. Currents as low as 0 03 pamp. and irradiation times of 2 min. can be taken as the lower limits used for these parameters. The irradiations were made through a 0.0001-inch nickel foil. The irrahation cells mere made of brass and of glass and ranged from 2-7 om. in diameter and were about 16 em. long. The methyl alcohol used was the Baker analyzed reagent grade product and the absolute ethyl alcohol was a U. S. Industrial product. The methane was Phillips rcsearch grade. The gas chromatograph was an allglass instrument operated from 80-115". It contained a 12-ft. colitmn of "Celite" coated with silicone oil. Helium was used as a carrier gas and a flow of 40 cc ./min . was maintained by a pressure regulator. Detection of macro amounts of materisl was realized with a thermal-conductivity cell. The radiaoactive gases were detected with two 2~ methane proportional counters viewing diametrically opposite Mylar windom of a glass cell through which the gas passed on exit from the chromatograph. The responses of the detectors were recorded with a two-pen recorder. Identification of the compounds was made through. a comparison of their retention times with those of the reference compounds.
475
4000
3000 2000
1000 h
.-dd 2 4s
4 c.p.m. 5000
-3 .4 4s
Results and Discussion 4000 Typical radioactive gas chromatograms obtained for deuteron irradiation of methyl and ethyl alcohol 3000 in a glass cell are given in Fig. 1. Peak I has been identified as due to Nzand arises by reaction of Xi3 with residual amounts of nitrogen gas present 2000 as an impurity on the walls of the cell or in the target gas. Peak I1 is due to HCN, I11 to CH3CN, and IV to C2HGCN. In similar irradiations of CH4, 3000 peaks I, 11, and I11 also appear. KOammonia or amines were detected in spite of a careful search. One can vary the relative intensity of these peaks by changing experimental conditions. For ex1 2 3 4 5 ample, addition of 6 mm. of to 75 mm. of CHsOH 'Time (min.). in a brass cell caused the activity of peak I to inFig. 1.-Gas chromatograms of compounds formed crease from 370 (no Kzadded) to 7000 c.p.m. In- by deuteron bombardment of methanol (upper) and ethanol creasing the alcohol pressure resulted in a reduc- (lower). tion in absolute amount of Nz radioactivity. In for reaction vessels completely removes the gaseous view of extensive attempts to free the target gas of HCN yield and the activity is found on the wall Nz, it is concluded that the bulk of the radioactive of the cell. The alcohol system differs in one point nitrogen, in the case where no N2 was deliberately from the alkyl halide system previously reported.2 added, comes from the reaction of N13with ad- In the latter case, it was found possible t o condisorbed Nz on the walls of the irradiation cell. This tion the metal surfa,ce by extensive irradiation of exchange reaction apparently also can occur with the alkyl halide so that such cells did give a gaseous nitrogen molecules in the gas phase. The idea that HCN yield. This presumably arises from the the wall plays an important role in the formation protective polymer coating that is put on the walls of residual nitrogen molecule activity is supported of the metal vessel. In the case of the alcohols by the following observation. On extensive ir- studied here, such conditioning of the metal surfaces radiation, polymeric material from radiation- could not be realized and no HCN was detected damage effects can be deposited on the walls of when brass cells were used. the glass reaction vessel. Under such conditions, A second factor that influences drastically the the adsorbed nitrogen is covered and subsequent HCN yield is the addition of small amounts of irradiations of methanol give no radioactive Nz. gaseous XZ. The addition of 5 mm. of Na to 110 On the other hand, when this polymer coating is mm. CH30H in a glass irradiation cell resulted in removed and an irradiation is made, the radioactive a fall in HCN activity from 16,000 t o 4500 c.p.m. nitrogen again appears even though no Nz was with a corresponding increase of the radio Nz activadded to the system. The behavior of the radio- ity. There was no discernible effect on the CH&N nitrogen yield as a function of target gas pressure yield. also tends to support the view that it results from The cell size also has an influence on radio HCN a wall reaction. yield. Increasing the glass cell radius by a factor The amount of HCK yield also is considerably of three decreased the ratio of HCN/CH&N by influenced by various experimental parameters, a factor of five. Such changes favored CH3CN The role of metal cells has been mentioned2 pre- production and reduced the HCN yield to the extent viously and similar observations have been made that now the CH&N was the dominant gaseous with the present system. Use of clean brass cells activity,
476
of this type that were run, all indicated thiB rise in HCN yield and a corresponding fall in CHaCN yield as one proceeded from no rare gas additive
2000 1500 1000
2
500
0
4 8000 6000
4000 2000
1
Pressure (mm.). Fig. 2.-Pressure variation of CHyCN18 (upper) and HCNl3 (lower) yield from deuteron bombarded methanol and ethanol, respectively.
The influence of alcohol pressure on the yield of HCN and CH3CN is shown in Fig. 2. The radio CH3CN yield increases with alcohol pressure and is approximately linear. The accuracy of the measurements is such that one would not detect a relatively small curvature in the plot. On the other hand, the yield of HCN goes through a definite maximum if one makes measurements at sufficiently low pressures. The general increase of the CH3CN yield as a function of alcohol pressure is expected if the material is produced in the gas phase since the greater the number of carbon atoms present the greater the El3production and its subsequent products. On the other hand, the HCN yield us. pressure curve could be explained best if the bulk of the HCN production occurs on the walls of the vessel since, with increased pressure, fewer of the N13 carriers would get to the walls prior to reacting in the gas phase. Another parameter that influences the HCN yield is the presence of rare gases. These experiments were performed by adding 15 mm. of alcohol to 5-50 mm. of rare gas and comparing the HCN yield to the case where no additive was present. Examples of typical results obtained are the following. When no rare gas was added to a certain run, the HCN peak was 220 c.p.m.; the addition of 51 mm. of argon gave a peak of 280 c.p.m.; and 51 mm. of Kr gave 570 c.p.m. The corresponding figures for the CH&N peak were 250, 170, and 130 c.p.m., respectively. Of the number of experiments
to argon and then to krypton. Rare gases can have several possible effects and two that are probably of pertinent interest here are moderation and charge exchange. Both argon and krypton can act as moderators; Le., the radioactive carrier, be it NI3or CNISin ion or radical form, will undergo collisions with the moderator and be slowed down to thermal energies. There is also the possibility of charge exchange if the ionization potentials are favorable. For example, the first ionization po~ tentials of argon, nitrogen, CN r a d i ~ a l , and krypton are 15.7, 14.5, 14.5, and 13.9 volts, respectively. Consequently, charge exchange would be expected to occur between krypton and N + or CN+ but not with argon. If moderation and charge exchange are the contributing factors to the variation of the yield of radioactive products, one would conclude that HCN is produced by a thermal reaction involving a neutral reactant since addition of rare gases results in more effective thermalization of the N13 carrier. Kr would be expected to be a less efficient thermalizer than Ar; however, the enhancement of the HCN yield realized with Kr can result from a charge transfer process producing more radical carriers, which are presumably one of the reactants. The fall of the CH&N yield with rare gas addition can be explained best if the reactant is an ionic N13 carrier with greater than thermal energies. Considerable attention has been given to the possible role that radiation-damage products might play as far as the yield of radioactive products is concerned. Measurements were made with varying beam currents, pressures, and times of irradiation. In these runs, the beam current was as low as 0.03 pamp. and irradiation time as short as 2 min. Under such conditions, less that 1% of the target gas was destroyed. In general, the yield was linear with increasing beam current and time until a large amount (>30%) of the target gas was destroyed. Even under conditions of minimum amount of radiation damage compatible with obtaining a detectable amount of radioactive products, one has a considerable amount of damage along the beam path. Consequently, the Nla produced by the nuclear reaction has a high probability of undergoing a number of collisions with ions and free radicals in the beam path. The question then arises whether a significant amount of the final products arise from the reaction of the "3 carrier with free radicals or ions resulting from radiation damage, or is the reaction between NL3 carrier and target gas molecules. An experiment which has some bearing on this question is one in which Brz was added to the target gas. Bromine is an efficient scavenger for organic free radicals; consequently, its presence should reduce the radioactive product yield if the radiation-damage fragments were one of the reactants. Experiments in which there was as much as 20 mole % ' Brt in methanol showed that the yield of CHaCN was not (3) V. R. Dibeler, R. M. Reese, and J. L. Franklin, J . Am. Cham. SOC.88, 1813 (1981).
March, 1962
ELECTROPHORETIC CONTRIBUTION TO ELECTROLYTE CONDUCTANCE
477
influenced appreciably, whereas the HCN yield rise to CNf: This CN+ ion can react in the gas was increased by about 30%. This suggests phase with methane to give CH,CN or, on neutralthat the ireaction between NIB carriers to give the ization, it gives the cyanogen radical which can final product does not involve the free radicals from radiation-damage but the reaction apparently occurs with the target gas or the materials on the surface of the reaction vessel. The increase in HCN yield in the presence of BrZprobably results from thermalization and charge-transfer processes. Although one cannot as a result of this study outline a complete mechanism by which the radioactive prloducts are formed, one can make some pertinent conclusions as to the nature of the mechanism. The fact that CH,, CHsOH, and C2H60H give HCN and CHsCN, and in addition, the ethanol gives C2H[&N, suggests that the cyanogen ion or radical is 1,heIYl3 carrier as far as the observed radiocyanides are concerned. The fact that neither ammonia nor amines are observed suggests that neither NH nor NHZ are the N13 carriers. The question then arises-how is the C-Pi bond formed? A possibility is that N13 ion can react to form ions such as CH4N+ when methane is the target gas, for example, and this ion on decomposition gives
abstract hydrogen mostly from materials deposited on the walls of the vessel to give HCN. It also can replace hydrogen on the wall-adsorbed molecules to form cyanides which remain on the walls of the vessel. Such activity has been found on the walls; however, the material has not been identified as yet. activity The fact that a significant amount of is present in one or more unidentified forms on the walls of the vessel is of some concern since it may have an important influence on the mechanisms of the reactions occurring. It also has prevented the realization of a satisfactory radioactivity balance and this point should be taken into consideration when comparisons are being made between the changes in yields of radioactive products as in Fig. 2. Such comparisons cannot be made in the present data; however, it is expected that this complication will be overcome in future work.
THE EFFECT OF TH:E EXPONENTIAL DISTRIBUTION FUNCTION ON THE E.LECTROPHORETIC CONTRIBUTION TO THE CONDUCTANCE OF 1-1 ELECTROLYTES' BY DAVIDJ. KARLAND JAMESL. DYE Kedzie Chemical Laboratory, Michigan State University, East Lansing, Michigan Received September 66, 1061
The use of the exponential ionic distribution function rather than the linear or quadratic expansion of it is demonstrated to have a large effect upon the electrophoretic contribution to conductance. Calculations by digital computer were made for a number of salts in dioxane-water and in ethanol-water mixtures, and it was found that much of the deviation from conductance theory usually attributed to ion-pair formation could arise from neglect of the higher terms in the distribution funct>ion.
Introduction The theoretical calculation of the conductance of electrolytes has attracted attention for many years and has been beset by many problems. Not the least of these has been the calculation of the degree of association of the ions to form ion-pairs. Before one can calculate the association constant, it is necessary i o know the proper conductance function for the ionic species. When association is marked, as for a weak acid or a salt in a medium of low dielectric constant, the Onsager limiting law can be used successfully. For cases of slight association, however, the constant is very sensitive to the theoretical conductance function used. A number of extensions of the limiting law have been propc~sed~-~ and Fuoss has used the Fuoss(1) This paper is based in part on a thesis presented by David J. Karl to the School for Advanced Graduate Studies of Michigan State University in partial fulfillment of the requirements for the degree of Doctor of Philosophy, 1960. (2) E. Pitte, Proc. Roy. SOC.(London), ASl7, 43 (1953). (3) H. Falkeohagen, M. Leist, and G. Kelbg, Ann. Physik, (61 11, 61 (1953). (4) R. M. Fuoss and L. Onsager, Proc. Natl. Acad. Sei. U. S., 41, 274 1010 (1955): J . Phg8. Chem.. 61, 608 (1957); 62, 1339 (1958).
Onsager extension to calculate the association coiistant for ion-pair formation in mixed solvent systems.6s6 Since this treatment has been very successful in fitting conductance data and in correlating ion-size parameters, limiting mobilities, and association constants over a wide range of dielectric constants, the basic equations for the conductance of unassociated electrolytes appear to be sound, a t least for the case of large ions. This paper shows that terms which were dropped in the treatment of the electrophoretic effect are not small for those.cases requiring the introduction of an association constant. In fact, simply retaining these terms yields a surprisingly good fit of the data for reasonable and constant ion-size parameters in many cases, without requiring consideration of ionpair formation. It is suggested that the association constant calculated from conductance data is forced to include ionic interaction effects in addition to effects attributable to the formation of a distinct neutral species. The Distribution Function.-The terminology R. M. Fuoss, J . A m . Chem. Soc., 79, 3301 (1957). (6) R. M. Fuoss and C. A. Kraus, W d . , 79, 3304 (1957). (5)
