305 C . B . ALLSOPP AND MISS J . WILSON RADIATION CHEMISTRY OF ORGANIC SOLUTIONS BY W. MINDER AND H. HEYDRICH Radium Institute and X-Ray Dept. of the University of Berne Switzerland Received 21st January 1952 From halogenated hydrocarbons irradiated in organic solutions (alcohol acetone) halogen acids can be extracted with water. The amount of irradiation products rises proportionally to the dose of radiation and is dependent on (i) the concentration of the solution (ii) the number of halogen atoms in the compound and (iii) the type of binding The yields are about & to & that found in aqueous solutions but are not influenced at all by the addition of large amounts of water. The relation between yield and concentration is exponential in form rising to a saturation value.In compounds containing many halogen atoms a proportional increase is also found. These results are discussed and compared with theoretical conceptions. As has been previously demonstrated by many workers the biological actions of ionizing radiations are very complicated and difficult to understand ; because of this the radiation-chemical changes in aqueous systems of all types and range of concentrations are of fundamental interest. Almost all radiation-chemical investigations connected with medical or biological problems therefore started from this rather restricted aspect. It seems quite well established that the radiation- chemical behaviour of aqueous solutions can be understood in terms of the radical theory of Weiss.17~ 18 This theory is able to explain qualitatively not only the so-called dilution,s.16 protection 39 15 and saturation effects 2 but allows quantitative predictions about all these fundamental effects in aqueous systems.l.2.18 The theory however is probably restricted to aqueous solutions as it is unlikely that radiation effects in non-aqueous systems can be brought about qualitatively and quantitatively by radicals in the same manner as in aqueous systems. The radical theory has as yet not been confirmed by conclusive experiments and it is difficult to do so because it is necessary to obtain quantitative estimations of the number of radicals primarily formed their spatial distributions life-times and also quantitative agreement for all of the energy changes from the primary photon or particle to the final stable products.Nevertheless this theory is the best starting point for all radiation-chemical work and there are no known experi- mental facts which cast serious doubt on its validity.9~14 It seemed of interest to perform irradiation experiments with non-aqueous systems and to compare the results with those obtained with aqueous solutions. During the past 7 years we have studied the formation of halogen acids by irradi- ation of aqueous solutions of halogenated hydrocarbons. These experiments have given some results of general interest which we have explained in terms of existing or new theoretical conceptions.4- 6 7 9 9 10,129 15 It was found that the formation of halogen acids from aqueous solutions of halogenated hydro- carbons is a so-called indirect irradiation effect which is independent of con- centration over a rather wide range,49 12 and which shows the protection effect 12915 ORGANIC SOLUTIONS 306 when a new component is added and which is almost completely suppressed in frozen solutions.** 12914 The results have been expressed in terms of the ionic yield M/N which is the number of molecules of the measured compound formed by the radiation energy of 32.5 eV necessary for one ionization in air.We think that this figure is preferable to the figure G (corresponding to 100 eV) because the latter has to be calculated from the former which is more directly obtained in radiation dose measurements. We choose these halogenated compounds for our experiments first because it is not difficult to measure the most important effect the formation of halogen acids.with sufficient accuracy in very small amounts using the increase of the ionic solute. measurements is the high purity of the solvent (water) and the requirement solutions. specific yield conductivity of M/N - of 1 the radiation irradiated effects of 1000 The r can only be determined With with of such an an accuracy of at least 10 %. Unfortunately radiation-chemical products other than electrolytes are not detected by this method. Therefore our general results have to be restricted to these products and do not allow us to formulate the complete chemical reaction within our systems. Nevertheless these same general results (dilution effect protection effect suppression of radiation effects in solid state) were found with different solutions.It was only after the war that we had access to the results of other workers in the field of radiation chemistry. Consequently we did not explain our results on the radical theory but tried to formulate them in terms of general reaction kinetics,73 9 without regard to the detailed chemical reaction phenomena and it was possible to show that all the slopes of the reaction curves with respect to the radiation energy could be calculated from simple kinetic conceptions. The radical theory of the effects of radiations on aqueous solutions involves the reaction of free radicals primarily formed from water with the solute.We thought it interesting to perform irradiation experiments with our substances dissolved in solvents other than water. Many simple halogenated hydrocarbons are easily soluble in alcohol. Very pure alcoholic solutions of our compounds were irradiated with X-rays (31.5 kV beryllium window tube) with doses up to 106 r integrated over the whole sample. After irradiation the samples were diluted with very pure water and the irradiation product the halogen acid was estimated quantitatively from the specific conductivity of this solution and determined qualitatively by precipitation as the silver salt. Such experiments were made with 3 D.D.T. products viz. p-methyldiphenyl- trichlorethane (CH3 . C6H4)2 . CH . CCl3 1 2 dimethyldiphenyltrichlorethane [(CH3)2C6H3]2 .CH . CC13 p-chlordiphenylchlorethylene (p-C1 . C6H4)2 . C= CHCI y-hexachlorocyclohexane y-C6H&16 p-dichlorbenzene p-C6H&12 hexachlor- ethane C2C16 and chloroform CHC13 at different known concentrations in the range of M/5-M/10 down to M/1000.11*12~13 In every case the increase of conductivity in the aqueous extract was due to the formation of electrolytes by irradiation the greatest part of these being halogen acids. Other experiments were made with acetone solutions. In this solvent the formation of electrolytes has also been found but in smaller amounts than in alcohol. In fig. 1 the results with hexachlorethane in alcohol and acetone are shown. that The other investigations show the same general behaviour. It is clear (i) The amount of the irradiation product (hydrochloric acid) increases pro- portionally with the amount of radiation at all concentrations.(ii) The yield of the radiation-chemical product depends on the concentra- tion of the solute but a simple proportionality is found only with very small concentrations. (iii) In acetone as solvent the yield is not proportional to the concentration. Taking other experiments 11’ 12913 into account W . MINDER A N D H . HEYDRICH (iv) If water is added to the solvent in concentrations corresponding to 12.5 or 25 vol. % no change in the yield is found. FIG. 1.-Formation of HCl from C2Cl6 by irradiation of alcoholic solutions at differen concentrations. Dotted lines c2c16 diluted in acetone. Indications in % (g/lOO ml).I i f i 6 r 10 I t5 FIG. 2.-Formation of electrolytes by irradiation of pure alcohol and alcohol containing water. (1) Pure alcohol and alcohol containing up to 50 % H20. (2) Alcohol diluted in 90 vol. % H20. Dotted line 1 pure acetone. (v) In pure alcohol and pure acetone electrolytes are formed in small quanti- ties by irradiation. The yield is about 20 % smaller in acetone. (vi) Relatively large concentrations of water up to 50 vol. % do not change the yield of electrolytes in irradiated alcohol. Only at water concentrations greater than 75 % can a fall in yield be detected this fall being only about 30 % at water concentrations of 90 vol. % (fig. 2). 307 p [Z,] = ORGANIC SOLUTIONS cc13 concentrations and slowly at higher concentrations.It has been shown that the slope of all these curves can be expressed with a high precision by the following equation 11- 13 2 = Zo(1 - e-OC) + kc where 2 is the ionic yield and 20 u and k are constants having the following dimensions molecules of reaction product 32-5 eV [kl = [ cm3 x molecules of reaction product- I molecules of solute x 32.5 eV - ’ The above equation contains two terms one rising exponentially with con- Therefore and the other increasing linearly. 308 (vii) The ionic yield of all solutions investigated depends on concentration but is found to be between 0.2 and 2 in concentrations of about M/lO. The results of the irradiations of the above compounds dissolved in alcohol have been plotted in fig.3. This graph shows the ionic yield ( i s . the number of HCl molecules formed in the solution by a radiation energy of 32.5 eV equal to one ionization in air) as a function of the concentrations c of the solute. All the curves shown are of the same general form. The yield rises sharply at small FIG. 3.-Relation between ionic yield M/N and concentration of different compounds irradiated in alcoholic solutioc. centration to a constant value &) 309 TABLE 1 .-CALCULATION 0.008 0.180 0.327 0.545 0.794 0.957 0.990 ( y ~ w ~ l c 25.0 25.6 20.8 15.5 10.1 7.1 5.1 3% 0.20 0.42 0.67 1.00 1-30 1.80 2.60 0.016 0.032 0.064 0.128 0.255 0.510 W . MINDER AND H. HEYDRICH the yield against concentration curve can be represented by summing an ex- ponential curve and a straight line.We have suggested in earlier publications that the exponentially rising part may be caused by an indirect irradiation effect while the linear part which is only significant at higher concentrations is due to the direct action of radiation on the solute. In table 1 the calculated values of the ionic yield of C2C16 in alcohol are compared with the experimental results. OF THE IONIC YIELD FOR DIFFERENT CONCENTRATIONS OF c2c16 1N ALCOHOLIC SOLUTION ionic yield ionic yield kC 0.025 0.050 0.099 0.199 0.398 0.797 1-592 calc. Z = MIN 0-205 0.377 0.644 0.993 1-355 1.786 2.592 This table was calculated using the following values 1-00 20 = 1-00 HC1/32.5 eV k = 3-13 X 10-20 cm3 HCI/C2C&j .32.5 ev. cr = 25 x 10-20 cm3/C2C16 The agreement between calculation and experiment is as good as with other substances which have been investigated in the same manner. We therefore believe that the formulation is a possible manner of representing the behaviour of our compounds when irradiated in alcoholic solutions. What therefore is the physical significance of the constants used above? The constant 20 is the maximum number of molecules of the reaction product which can be formed by indirect action by the energy of 32.5 eV compared with one ionization in air and 2 is this number (the ionic yield) at different concentra- tions. On the other hand k is the factor by which the yield of the direct irradi- ation effect increases with concentration.It has the same dimension as Z/c indicated in table 1 i.e. the number of molecules of the reaction product formed by the energy of 32.5 eV per one molecule of the solute in 1 cm3 (ionic yield per unit concentration). For the direct irradiation effect k is constant while the corresponding term a(& - 2) decreases with increasing concentration for the indirect irradiation effect (maximum value 020). In fig. 4 the ionic yields 2 = M/N and the figures (M/N)/c are plotted against concentration of solute on a logarithmic scale. It can be seen from the graph that for small concentrations (M/N)/c is constant indicating that the yield is proportional to concentration. Between the concentration values 0.016 and 0.1 28 (M/N)/c falls exponentially.At higher concentrations the decrease is smaller because the direct irradiation effect is significant. Within a concentration range of 1-32 (M/N)/c decreases by 1-5. The terms [(M/N)/c] E [oZO] f [k] representing the mean number of molecules of the reaction product formed by the energy of 32.5 eV per one molecule of the solute in 1 cm3 of the irradiated solution and also the mean volume per molecule of solute to which the energy of 32.5 eV must be added for the production of 1 molecule of the reaction product. If such volumes are thought to have any reality (cp. absorption phenomena) they have molecular dimensions corresponding to about 2600 alcohol molecules at the lowest to about 500 alcohol molecules at the highest concentrations in- vestigated.The dimension of CT is that of a reciprocal concentration i.e. the volume per molecule of solute for an ionic yield of Z = M/N = 1 caused by the indirect irradiation effect. ORGANIC SOLUTIONS 3 10 It may be of interest to compare the results of experiments plotted in fig. 3 with each other. It can be seen that the yields of the substances investigated are different. Within the concentration range of the experiments a definite direct effect is found only with C2C16 and yC6H6C16 ; with all other compounds such an effect is not proved with certainty. The values of Zo and cr are very close to the product numbers 2 3 4 on the one hand and 6 and 7 on the other. If the yields are compared with each other it is necessary to do so at the same molec- ular concentrations of 0-2 x 1020 or 0.1 x 1020 molecules/cm3 for example.Table 2 shows the corresponding results. zot 2-0 yield/Cl 0.27 0.33 0.30 0.27 4 3 LO.008 0.016 0.032 0-064 O-QB 0255 05/0 yield 1 *oo 1.61 0.90 FIG. 4.-Ionic yield M/N and ionic yield per concentration (M/N)/c at different con- centrations for C2C16 irradiated in alcoholic solution. conc. 0.2 x 1020 no. - compound yield/Cl ~ 2 ~ 1 6 1 2 TABLE 2 conc. 0.1 x 1020 yield 1.20 0.70 0.64 0.20 0.23 0.21 (CH3C6H4)2CHCC13 CHClj ((CH3)2C6H3)2CHCC13 0.18 0.82 0.55 0.46 0.66 0.1 1 5 0.075 In the first four compounds the CI atoms are aliphatic in the last three aromatic in type.As far as the indirect radiation effect is concerned the yield per atom of C1 is practically constant for the aliphatic as well as for the aromatic binding. For the former these figures are about 3 times greater than for the latter. The yield therefore is dependent on the number of C1 atoms in the compound and the type of binding. If the curves of fig. 3 are plotted in terms of the concentrations of CI atoms they are close together for the aliphatic compounds on the one side and for the aromatic on the other. This rule is valid for the concentration range in which the indirect irradiation effect is far greater than the direct one. The compound (CI . C6H&C=CHCl merits special interest. It contains two aromatic C1 atoms and one aliphatic linked to a double-bonded C atom.compound 0.84 0-53 2-52 1.60 CHC13 CHBr3 As far as the dilution effect in aqueous solutions has been investigated i.e. at strictly comparable concentrations the yield from aliphatic compounds is 3 to 4 times greater than from aromatic compounds just as in alcoholic solutions. It is also about 3 to 4 times greater in aqueous solutions. We therefore believe that the reaction mechanisms cannot be fundamentally different in both cases. In table 4 the constants of the above theoretical equation for all substances investigated are calculated. compound no. TABLE 4 1020 20 molecules/ 325 eV 23.5 11.2 1.9 0.48 0.5 W . MINDER AND H. HEYDRICH The yield per Cl atom here is somewhat smaller in all concentrations than for the other aromatic compounds and on the basis of the aromatic C1 atoms only is somewhat greater.The aliphatic C1 atom is therefore bound somewhat more tightly than the aromatic and can only be detached in amounts which are only just detectable. The similarity of the yields per C1 atom of all aliphatic compounds on the one hand and the aromatic on the other cannot be fortuitous. It indicates that our measured irradiation effect (i.e. the increased specific conductivity of the aqueous extract of the irradiated alcoholic solutions) is almost entirely due to the formation of halogen acids if the effect on pure alcohol is subtracted. The yield of acid in more concentrated solutions is many times greater than the formation by irradiation of electrolytes in alcohol and acetone and it is improbable that the two simultaneous reactions are closely connected.The yield of acid is of the same order of magnitude as in aqueous solutions as shown by the values in table 3 which indicate the yields of some compounds in the same concentration range as in table 2. TABLE 3.-IONIC YIELDS OF ACID FORMED BY IRRADIATION OF HALOGEN COMPOUNDS IN WATER yield conc. MI100 yield/Cl 1.7 5 6 7 ?‘-c6H6c16 CI(C6H4)2C= CHCl P-C6H4C12 0.44 3.8 3.8 conc. M/1000 yield 1 *60 1.56 uzo diam. of uZo a;Cod& in A It may be seen from table 4 that the values of 20 are similar for all aliphatic and also for the aromatic compounds. The differences are about 1 2 to 1 3.The coefficients (volumes) cr of all compounds with the same number of C1 atoms are about the same (if only the two aromatically bound C1 atoms of compound 6 are taken into account). The product 020 indicating the increase of the ionic yield at very small concentrations with increasing concentration is more different from one compound to another because the maximum yields are also different. 59.8 33.2 32.0 yield/<=] 0.53 0.52 molecules 175 31 1 1150 196 GENERAL DISCUSSION c - t o ; z-to; -=az,; c r = - 1 I d Z d Z dc 312 The definition of 020 is given in the following expression for very small con- centrations 10 Minder Radiol. Clin. 1947 16 339. 11 Minder Radiol. Clin. 1950 19 277. 12 Minder Brit.J. Rad. 1951 24 435. 13 Minder J. Chim. Phys. 1951 48 423. 14 Minder and Liechti Experentia 1946 2 410. 16 Risse Ergebn. Physiol. 1930 42 228. 17 Weiss Nature 1944 153 748. 18 Weiss Nature 1946 157 584. 20 d c ' The dimension of OZO (see above) is the same as that of (M/N)/c and k and can be considered as a volume. For all substances investigated these virtual or perhaps real volumes have about the same linear dimensions between 30 and 80A and contain between 175 to 2600 molecules of alcohol as indicated in table 4. Their linear dimensions may be considered as the mean distances of " travel " of energy for the observed irradiation effect. With increasing concentration these dimensions decrease as the radiation energy is used for other effects which cannot be detected by the measurement of only one irradiation product.Therefore it is an urgent problem to perform irradiation experiments with the possibility of quantitative detection of all reaction products and with substances of which all molecular properties are quantitatively known; only then do we think that it will be possible to give a general theory of the phenomena governing the actions of ionizing radiations on all kinds of liquid systems. The results above were obtained by means of a special X-ray tube which was acquired through financial assistance given by the Foundation for Research at the University of Berne to which we are greatly obliged. 1 Dainton J. Physic. Chem. 1948 52 490. ZDale Phil. Trans. Roy. SOC. A 1949 242 33.3 Dale Meredith and Tweedie Nature 1943 151 295. 4 Feller Minder and Liechti Radiol. Clin. 1948 17 156. 5 Fricke and Morse Amer. J . Rontgen. 1927 28 426 430. 6 Meister and Minder Radiol. Clin. 1950 19 238. 7 Minder Radiol. Clin. 1946 15 30. 8 Minder Radiol. Clin. 1946 suppl. vol. 15 81. 9 Minder Radiol. Clin. 1947 16 73. 15 Mullis Minder Liechti and Wegmuller Radiol. Clin. 1946 15 295. C . B . ALLSOPP AND MISS J . WILSON 305 RADIATION CHEMISTRY OF ORGANIC SOLUTIONS BY W. MINDER AND H. HEYDRICH Radium Institute and X-Ray Dept. of the University of Berne Switzerland Received 21st January 1952 From halogenated hydrocarbons irradiated in organic solutions (alcohol acetone) halogen acids can be extracted with water. The amount of irradiation products rises proportionally to the dose of radiation and is dependent on (i) the concentration of the solution (ii) the number of halogen atoms in the compound and (iii) the type of binding The yields are about & to & that found in aqueous solutions but are not influenced at all by the addition of large amounts of water.The relation between yield and concentration is exponential in form rising to a saturation value. In compounds containing many halogen atoms a proportional increase is also found. These results are discussed and compared with theoretical conceptions. As has been previously demonstrated by many workers the biological actions of ionizing radiations are very complicated and difficult to understand ; because of this the radiation-chemical changes in aqueous systems of all types and range of concentrations are of fundamental interest.Almost all radiation-chemical investigations connected with medical or biological problems therefore started from this rather restricted aspect. It seems quite well established that the radiation-chemical behaviour of aqueous solutions can be understood in terms of the radical theory of Weiss.17~ 18 This theory is able to explain qualitatively not only the so-called dilution,s. 16 protection 39 15 and saturation effects 2 but allows quantitative predictions about all these fundamental effects in aqueous systems.l.2.18 The theory however is probably restricted to aqueous solutions, as it is unlikely that radiation effects in non-aqueous systems can be brought about qualitatively and quantitatively by radicals in the same manner as in aqueous systems.The radical theory has as yet not been confirmed by conclusive experiments, and it is difficult to do so because it is necessary to obtain quantitative estimations of the number of radicals primarily formed their spatial distributions life-times and also quantitative agreement for all of the energy changes from the primary photon or particle to the final stable products. Nevertheless this theory is the best starting point for all radiation-chemical work and there are no known experi-mental facts which cast serious doubt on its validity.9~14 It seemed of interest to perform irradiation experiments with non-aqueous systems and to compare the results with those obtained with aqueous solutions.During the past 7 years we have studied the formation of halogen acids by irradi-ation of aqueous solutions of halogenated hydrocarbons. These experiments have given some results of general interest which we have explained in terms of existing or new theoretical conceptions.4- 6 7 9 9 10,129 15 It was found that the formation of halogen acids from aqueous solutions of halogenated hydro-carbons is a so-called indirect irradiation effect which is independent of con-centration over a rather wide range,49 12 and which shows the protection effect 1291 306 ORGANIC SOLUTIONS when a new component is added and which is almost completely suppressed in frozen solutions.** 12914 The results have been expressed in terms of the ionic yield M/N which is the number of molecules of the measured compound formed by the radiation energy of 32.5 eV necessary for one ionization in air.We think that this figure is preferable to the figure G (corresponding to 100 eV), because the latter has to be calculated from the former which is more directly obtained in radiation dose measurements. We choose these halogenated compounds for our experiments first because it is not difficult to measure the most important effect the formation of halogen acids. with sufficient accuracy in very small amounts using the increase of the specific conductivity of the irradiated solutions. The only requirement of such measurements is the high purity of the solvent (water) and the solute. With an ionic yield of M/N - 1 radiation effects of 1000 r can be determined with an accuracy of at least 10 %.Unfortunately radiation-chemical products other than electrolytes are not detected by this method. Therefore our general results have to be restricted to these products and do not allow us to formulate the complete chemical reaction within our systems. Nevertheless these same general results (dilution effect protection effect suppression of radiation effects in solid state) were found with different solutions. It was only after the war that we had access to the results of other workers in the field of radiation chemistry. Consequently we did not explain our results on the radical theory but tried to formulate them in terms of general reaction kinetics,73 9 without regard to the detailed chemical reaction phenomena and it was possible to show that all the slopes of the reaction curves with respect to the radiation energy could be calculated from simple kinetic conceptions.The radical theory of the effects of radiations on aqueous solutions involves the reaction of free radicals primarily formed from water with the solute. We thought it interesting to perform irradiation experiments with our substances dissolved in solvents other than water. Many simple halogenated hydrocarbons are easily soluble in alcohol. Very pure alcoholic solutions of our compounds were irradiated with X-rays (31.5 kV beryllium window tube) with doses up to 106 r integrated over the whole sample. After irradiation the samples were diluted with very pure water and the irradiation product the halogen acid, was estimated quantitatively from the specific conductivity of this solution and determined qualitatively by precipitation as the silver salt.Such experiments were made with 3 D.D.T. products viz. p-methyldiphenyl-trichlorethane (CH3 . C6H4)2 . CH . CCl3 1 2 dimethyldiphenyltrichlorethane [(CH3)2C6H3]2 . CH . CC13 p-chlordiphenylchlorethylene (p-C1 . C6H4)2 . C= CHCI, y-hexachlorocyclohexane y-C6H&16 p-dichlorbenzene p-C6H&12 hexachlor-ethane C2C16 and chloroform CHC13 at different known concentrations in the range of M/5-M/10 down to M/1000.11*12~13 In every case the increase of conductivity in the aqueous extract was due to the formation of electrolytes by irradiation the greatest part of these being halogen acids. Other experiments were made with acetone solutions.In this solvent the formation of electrolytes has also been found but in smaller amounts than in alcohol. In fig. 1 the results with hexachlorethane in alcohol and acetone are shown. It is clear that : (i) The amount of the irradiation product (hydrochloric acid) increases pro-portionally with the amount of radiation at all concentrations. (ii) The yield of the radiation-chemical product depends on the concentra-tion of the solute but a simple proportionality is found only with very small concentrations. (iii) In acetone as solvent the yield is not proportional to the concentration. Taking other experiments 11’ 12913 into account : The other investigations show the same general behaviour W . MINDER A N D H . HEYDRICH 307 (iv) If water is added to the solvent in concentrations corresponding to 12.5 or 25 vol.% no change in the yield is found. FIG. 1.-Formation of HCl from C2Cl6 by irradiation of alcoholic solutions at differen concentrations. Dotted lines c2c16 diluted in acetone. Indications in % (g/lOO ml). I f i 6 i r 10 I , t5 p FIG. 2.-Formation of electrolytes by irradiation of pure alcohol and alcohol containing water. (2) Alcohol diluted (v) In pure alcohol and pure acetone electrolytes are formed in small quanti-ties by irradiation. The yield is about 20 % smaller in acetone. (vi) Relatively large concentrations of water up to 50 vol. % do not change the yield of electrolytes in irradiated alcohol. Only at water concentrations greater than 75 % can a fall in yield be detected this fall being only about 30 % at water concentrations of 90 vol.% (fig. 2). (1) Pure alcohol and alcohol containing up to 50 % H20. in 90 vol. % H20. Dotted line 1 pure acetone 308 ORGANIC SOLUTIONS (vii) The ionic yield of all solutions investigated depends on concentration, but is found to be between 0.2 and 2 in concentrations of about M/lO. The results of the irradiations of the above compounds dissolved in alcohol, have been plotted in fig. 3. This graph shows the ionic yield ( i s . the number of HCl molecules formed in the solution by a radiation energy of 32.5 eV equal to one ionization in air) as a function of the concentrations c of the solute. All the curves shown are of the same general form. The yield rises sharply at small FIG. 3.-Relation between ionic yield M/N and concentration of different compounds irradiated in alcoholic solutioc.cc13 concentrations and slowly at higher concentrations. It has been shown that the slope of all these curves can be expressed with a high precision by the following equation 11- 13 where 2 is the ionic yield and 20 u and k are constants having the following dimensions : 2 = Zo(1 - e-OC) + kc, molecules of reaction product 32-5 eV [Z,] = I cm3 x molecules of reaction product-[kl = [ molecules of solute x 32.5 eV - ’ The above equation contains two terms one rising exponentially with con-Therefore centration to a constant value &) and the other increasing linearly W . MINDER AND H. HEYDRICH 309 the yield against concentration curve can be represented by summing an ex-ponential curve and a straight line.We have suggested in earlier publications that the exponentially rising part may be caused by an indirect irradiation effect, while the linear part which is only significant at higher concentrations is due to the direct action of radiation on the solute. In table 1 the calculated values of the ionic yield of C2C16 in alcohol are compared with the experimental results. TABLE 1 .-CALCULATION OF THE IONIC YIELD FOR DIFFERENT CONCENTRATIONS OF c2c16 1N ALCOHOLIC SOLUTION kC ( y ~ w ~ l c ionic yield ionic yield calc. Z = MIN 3% 0.008 0.180 0.025 0-205 0.20 25.0 0.016 0.327 0.050 0.377 0.42 25.6 0.032 0.545 0.099 0.644 0.67 20.8 0.064 0.794 0.199 0.993 1.00 15.5 0.128 0.957 0.398 1-355 1-30 10.1 0.255 0.990 0.797 1.786 1.80 7.1 0.510 1-00 1-592 2.592 2.60 5.1 This table was calculated using the following values : 20 = 1-00 HC1/32.5 eV, cr = 25 x 10-20 cm3/C2C16, k = 3-13 X 10-20 cm3 HCI/C2C&j .32.5 ev. The agreement between calculation and experiment is as good as with other substances which have been investigated in the same manner. We therefore believe that the formulation is a possible manner of representing the behaviour of our compounds when irradiated in alcoholic solutions. What therefore is the physical significance of the constants used above? The constant 20 is the maximum number of molecules of the reaction product, which can be formed by indirect action by the energy of 32.5 eV compared with one ionization in air and 2 is this number (the ionic yield) at different concentra-tions.On the other hand k is the factor by which the yield of the direct irradi-ation effect increases with concentration. It has the same dimension as Z/c indicated in table 1 i.e. the number of molecules of the reaction product formed by the energy of 32.5 eV per one molecule of the solute in 1 cm3 (ionic yield per unit concentration). For the direct irradiation effect k is constant while the corresponding term a(& - 2) decreases with increasing concentration for the indirect irradiation effect (maximum value 020). In fig. 4 the ionic yields 2 = M/N and the figures (M/N)/c are plotted against concentration of solute on a logarithmic scale. It can be seen from the graph that for small concentrations (M/N)/c is constant indicating that the yield is proportional to concentration.Between the concentration values 0.016 and 0.1 28 (M/N)/c falls exponentially. At higher concentrations the decrease is smaller because the direct irradiation effect is significant. Within a concentration range of 1-32 (M/N)/c decreases by 1-5. The terms representing the mean number of molecules of the reaction product formed by the energy of 32.5 eV per one molecule of the solute in 1 cm3 of the irradiated solution and also the mean volume per molecule of solute to which the energy of 32.5 eV must be added for the production of 1 molecule of the reaction product. If such volumes are thought to have any reality (cp. absorption phenomena), they have molecular dimensions corresponding to about 2600 alcohol molecules at the lowest to about 500 alcohol molecules at the highest concentrations in-vestigated.The dimension of CT is that of a reciprocal concentration i.e. the volume per molecule of solute for an ionic yield of Z = M/N = 1 caused by the indirect irradiation effect. [(M/N)/c] E [oZO] f [k 3 10 ORGANIC SOLUTIONS It may be of interest to compare the results of experiments plotted in fig. 3 with each other. It can be seen that the yields of the substances investigated are different. Within the concentration range of the experiments a definite direct effect is found only with C2C16 and yC6H6C16 ; with all other compounds such an effect is not proved with certainty. The values of Zo and cr are very close to the product numbers 2 3 4 on the one hand and 6 and 7 on the other.If the yields are compared with each other it is necessary to do so at the same molec-ular concentrations of 0-2 x 1020 or 0.1 x 1020 molecules/cm3 for example. Table 2 shows the corresponding results. zot 2-0 LO.008 0.016 0.032 0-064 O-QB 0255 05/0 FIG. 4.-Ionic yield M/N and ionic yield per concentration (M/N)/c at different con-centrations for C2C16 irradiated in alcoholic solution. TABLE 2 conc. 0.1 x 1020 conc. 0.2 x 1020 no. compound -1 ~ 2 ~ 1 6 1.20 0.20 1.61 0.27 2 (CH3C6H4)2CHCC13 0.70 0.23 1 *oo 0.33 3 CHClj 0.64 0.21 0.90 0.30 4 ((CH3)2C6H3)2CHCC13 0.55 0.18 0.82 0.27 yield yield/Cl yield yield/Cl 5 0.46 0.075 0.66 0.1 1 In the first four compounds the CI atoms are aliphatic in the last three aromatic in type.As far as the indirect radiation effect is concerned the yield per atom of C1 is practically constant for the aliphatic as well as for the aromatic binding. For the former these figures are about 3 times greater than for the latter. The yield therefore is dependent on the number of C1 atoms in the compound and the type of binding. If the curves of fig. 3 are plotted in terms of the concentrations of CI atoms they are close together for the aliphatic compounds on the one side and for the aromatic on the other. This rule is valid for the concentration range in which the indirect irradiation effect is far greater than the direct one. The compound (CI . C6H&C=CHCl merits special interest. It contains two aromatic C1 atoms and one aliphatic linked to a double-bonded C atom W .MINDER AND H. HEYDRICH 31 1 The yield per Cl atom here is somewhat smaller in all concentrations than for the other aromatic compounds and on the basis of the aromatic C1 atoms only is somewhat greater. The aliphatic C1 atom is therefore bound somewhat more tightly than the aromatic and can only be detached in amounts which are only just detectable. The similarity of the yields per C1 atom of all aliphatic compounds on the one hand and the aromatic on the other cannot be fortuitous. It indicates that our measured irradiation effect (i.e. the increased specific conductivity of the aqueous extract of the irradiated alcoholic solutions) is almost entirely due to the formation of halogen acids if the effect on pure alcohol is subtracted. The yield of acid in more concentrated solutions is many times greater than the formation by irradiation of electrolytes in alcohol and acetone and it is improbable that the two simultaneous reactions are closely connected.The yield of acid is of the same order of magnitude as in aqueous solutions as shown by the values in table 3, which indicate the yields of some compounds in the same concentration range as in table 2. TABLE 3.-IONIC YIELDS OF ACID FORMED BY IRRADIATION OF HALOGEN COMPOUNDS IN WATER conc. MI100 conc. M/1000 compound yield/<=] yield yield/Cl yield CHC13 2-52 0.84 1 *60 0.53 CHBr3 1.60 0-53 1.56 0.52 As far as the dilution effect in aqueous solutions has been investigated i.e. at strictly comparable concentrations the yield from aliphatic compounds is 3 to 4 times greater than from aromatic compounds just as in alcoholic solutions.It is also about 3 to 4 times greater in aqueous solutions. We therefore believe that the reaction mechanisms cannot be fundamentally different in both cases. In table 4 the constants of the above theoretical equation for all substances investigated are calculated. TABLE 4 no. compound 20 molecules/ 1020 uzo diam. of uZo a;Cod& 325 eV in A molecules 5 ?‘-c6H6c16 0.48 23.5 11.2 59.8 1150 6 CI(C6H4)2C= CHCl 0.5 3.8 1.9 33.2 196 7 P-C6H4C12 0.44 3.8 1.7 32.0 175 It may be seen from table 4 that the values of 20 are similar for all aliphatic and also for the aromatic compounds. The differences are about 1 2 to 1 3. The coefficients (volumes) cr of all compounds with the same number of C1 atoms are about the same (if only the two aromatically bound C1 atoms of compound 6 are taken into account).The product 020 indicating the increase of the ionic yield at very small concentrations with increasing concentration is more different from one compound to another because the maximum yields are also different 312 GENERAL DISCUSSION The definition of 020 is given in the following expression for very small con-centrations : d Z 1 d Z c - t o ; z-to; -=az,; c r = - I dc 20 d c ' The dimension of OZO (see above) is the same as that of (M/N)/c and k and can be considered as a volume. For all substances investigated these virtual or perhaps real volumes have about the same linear dimensions between 30 and 80A and contain between 175 to 2600 molecules of alcohol as indicated in table 4.Their linear dimensions may be considered as the mean distances of " travel " of energy for the observed irradiation effect. With increasing concentration these dimensions decrease as the radiation energy is used for other effects which cannot be detected by the measurement of only one irradiation product. Therefore it is an urgent problem to perform irradiation experiments with the possibility of quantitative detection of all reaction products and with substances of which all molecular properties are quantitatively known; only then do we think that it will be possible to give a general theory of the phenomena governing the actions of ionizing radiations on all kinds of liquid systems. The results above were obtained by means of a special X-ray tube which was acquired through financial assistance given by the Foundation for Research at the University of Berne to which we are greatly obliged. 1 Dainton J. Physic. Chem. 1948 52 490. ZDale Phil. Trans. Roy. SOC. A 1949 242 33. 3 Dale Meredith and Tweedie Nature 1943 151 295. 4 Feller Minder and Liechti Radiol. Clin. 1948 17 156. 5 Fricke and Morse Amer. J . Rontgen. 1927 28 426 430. 6 Meister and Minder Radiol. Clin. 1950 19 238. 7 Minder Radiol. Clin. 1946 15 30. 8 Minder Radiol. Clin. 1946 suppl. vol. 15 81. 9 Minder Radiol. Clin. 1947 16 73. 10 Minder Radiol. Clin. 1947 16 339. 11 Minder Radiol. Clin. 1950 19 277. 12 Minder Brit. J. Rad. 1951 24 435. 13 Minder J. Chim. Phys. 1951 48 423. 14 Minder and Liechti Experentia 1946 2 410. 15 Mullis Minder Liechti and Wegmuller Radiol. Clin. 1946 15 295. 16 Risse Ergebn. Physiol. 1930 42 228. 17 Weiss Nature 1944 153 748. 18 Weiss Nature 1946 157 584