9
THE OXIDATION OF TETRALIN INDUCED BY 6oCo y-RADIATION BY D. VERDIN Wantage Research Laboratory, Atomic Energy Research Establishment, Wantage, Berks Received 29th August, 1960 The oxidation of tetralin initiated by 6OCo y-rays has been studied at dose rates up to 3-66 x 1018 eV 1.-1 sec-1. The kinetics of oxygen absorption in the temperature range 25°C to 70"C, are consistent with a hydroperoxy-chain mechanism having an overall activation energy of 7.7 kcal/mole. The radical yield from tetralin was G = 1.52 radicals per 100 eV of energy absorbed. Small amounts of H202 (G = 0.47) result from the initiation step, and a molecular yield of H2 (G = 0.26) was observed. At 25"C, the 02 absorbed is almost quantitatively converted to hydroperoxide and H202 in the initial stages of the reaction. More extensive oxidation results in decomposition of the hydro- peroxide so that its concentration becomes less than the amount of 02 absorbed. The oxidation of hydrocarbons in the liquid phase initiated by ionizing radiation exhibits under certain conditions the kinetic characteristics of radical-chain oxidations, such as observed in the low-temperature photochemical oxidation of tetralin by Bamford and Dewar.1 The validity of this generalization at low radi- ation intensities (dose rates up to 4X 1018 eV L-1 sec-1) has been established by studies of the oxidation of cumene2 and cyclohexene 3 initiated by 6OCo y-rays and 200 kV X-rays respectively. In both cases, oxygen absorption was propor- tional to radiation dose, and all the oxygen absorbed was found in the form of hydroperoxide at temperatures up to 63°C. The reaction rates were proportional to the square roots of the dose rates. At higher temperatures the effect of irradi- ation is complicated by the thermal decomposition of the peroxidic products. This causes the reaction to be autocatalytic and results in a discrepancy between the oxygen absorbed and the yield of peroxides due to the formation of secondary products as observed for the oxidation of cetane 49 5 and di-isobutylene.4 The oxidation of oleic acid 6 at 20°C initiated by 6OCo y-rays resulted in the formation of peroxides whose measured rate of formation decreased at higher doses because of their radiolytic decomposition to secondary products, the extent of oxidation in this case exceeding 20 %. At very high dose rates, chain lengths should be reduced to the order of unity, so that a high proportion of the reaction products should be those resulting from the chain termination step. Bakh and Popov 7 studied the radiolytic oxidation of several hydrocarbons using dose rates up to 6x 1020 eV 1.-1 sec-1. They observed the simultaneous formation of peroxides (ROOR, ROOH and H202), carbonyl compounds and acids as primary products with individual G-values up to 2.0. These low values indicate a non-chain mechanism and were explained in terms of the reactions of Re and R02. radicals.8 At even higher dose rates (1.1 x 1022 eV 1.-1 sec-I), Dewhurst 9 found that the major products of the radio- lysis of cyclohexane in the presence of oxygen were cyclohexanol and cyclohexanone with G values of 3.7 and 3.5 respectively. The work reported here examines the 6OCo y-ray initiated oxidation of tetralin under conditions where long kinetic chains are expected. The detailed kinetics of the system are investigated by measurement of oxygen absorption and product formation. 484 Similar results were obtained with methyl oleate.6 Published on 01 January 1961. Downloaded on 29/08/2013 20:23:08. View Article Online / Journal Homepage / Table of Contents for this issue

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Page 1: The oxidation of tetralin induced by 60Co ?-radiation

THE OXIDATION OF TETRALIN INDUCED BY 6oCo y-RADIATION

BY D. VERDIN Wantage Research Laboratory, Atomic Energy Research Establishment,

Wantage, Berks

Received 29th August, 1960

The oxidation of tetralin initiated by 6OCo y-rays has been studied at dose rates up to 3-66 x 1018 eV 1.-1 sec-1. The kinetics of oxygen absorption in the temperature range 25°C to 70"C, are consistent with a hydroperoxy-chain mechanism having an overall activation energy of 7.7 kcal/mole. The radical yield from tetralin was G = 1.52 radicals per 100 eV of energy absorbed. Small amounts of H202 (G = 0.47) result from the initiation step, and a molecular yield of H2 (G = 0.26) was observed. At 25"C, the 0 2 absorbed is almost quantitatively converted to hydroperoxide and H202 in the initial stages of the reaction. More extensive oxidation results in decomposition of the hydro- peroxide so that its concentration becomes less than the amount of 0 2 absorbed.

The oxidation of hydrocarbons in the liquid phase initiated by ionizing radiation exhibits under certain conditions the kinetic characteristics of radical-chain oxidations, such as observed in the low-temperature photochemical oxidation of tetralin by Bamford and Dewar.1 The validity of this generalization at low radi- ation intensities (dose rates up to 4X 1018 eV L-1 sec-1) has been established by studies of the oxidation of cumene2 and cyclohexene 3 initiated by 6OCo y-rays and 200 kV X-rays respectively. In both cases, oxygen absorption was propor- tional to radiation dose, and all the oxygen absorbed was found in the form of hydroperoxide at temperatures up to 63°C. The reaction rates were proportional to the square roots of the dose rates. At higher temperatures the effect of irradi- ation is complicated by the thermal decomposition of the peroxidic products. This causes the reaction to be autocatalytic and results in a discrepancy between the oxygen absorbed and the yield of peroxides due to the formation of secondary products as observed for the oxidation of cetane 49 5 and di-isobutylene.4 The oxidation of oleic acid 6 at 20°C initiated by 6OCo y-rays resulted in the formation of peroxides whose measured rate of formation decreased at higher doses because of their radiolytic decomposition to secondary products, the extent of oxidation in this case exceeding 20 %.

At very high dose rates, chain lengths should be reduced to the order of unity, so that a high proportion of the reaction products should be those resulting from the chain termination step. Bakh and Popov 7 studied the radiolytic oxidation of several hydrocarbons using dose rates up to 6 x 1020 eV 1.-1 sec-1. They observed the simultaneous formation of peroxides (ROOR, ROOH and H202), carbonyl compounds and acids as primary products with individual G-values up to 2.0. These low values indicate a non-chain mechanism and were explained in terms of the reactions of Re and R02. radicals.8 At even higher dose rates (1.1 x 1022 eV 1.-1 sec-I), Dewhurst 9 found that the major products of the radio- lysis of cyclohexane in the presence of oxygen were cyclohexanol and cyclohexanone with G values of 3.7 and 3.5 respectively.

The work reported here examines the 6OCo y-ray initiated oxidation of tetralin under conditions where long kinetic chains are expected. The detailed kinetics of the system are investigated by measurement of oxygen absorption and product formation.

484

Similar results were obtained with methyl oleate.6

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Page 2: The oxidation of tetralin induced by 60Co ?-radiation

D . VERDIN 485

EXPERIMENTAL MATERIALS

Tetralin (Hopkin and Williams redistilled) was repeatedly shaken with concentrated H2SO4 until the acid layer was pale yellow. It was then washed with 10 % Na2C03 solution and several times with distilled water. After drying over anhydrous CaS04 it was fractionally distilled in a nitrogen atmosphere through a 35-plate column. The main fraction was passed through a 15 cm column of chromatographic alumina, collected in a blackened flask, and stored under nitrogen. The boiling point was 207.1 to 207.5"C at 766 mm, n3 = 1-5415.

Oxygen from a cylinder was passed through columns of silica gel and KOH and then through a trap at -78°C.

2 : 6-di-t-butyl-p-cresol (Schuchardt, Munich) was twice recrystallized from methanol : m.p. = 69*3&0*4"C. The absorption spectrum of a methanol solution had a peak at 278 mp with E = 1 . 8 5 7 ~ 103.

Tetralin hydroperoxide was prepared by the method of Wibaut et al. ; 10 m.p. = 55-2& 0.2"C. Benzoyl peroxide (B.D.H.) was precipitated three times from a solution in chloro- form by adding methanol 10 and cooling to 5°C ; m.p. = 105-5&0.4"C.

A.R. acetic anhydride was distilled in a nitrogen atmosphere from cobalt acetate through a 35-plate column, and stored under nitrogen ; b.p. = 138-1 to 138.4 at 758 mm.

Sodium iodide (Hopkin and Williams) was incompletely soluble in the distilled acetic anhydride. It was therefore dissolved in acetone, filtered, and cooled to -20°C and the resulting yellow crystals filtered off and heated in a vacuum oven at 70°C for 6 h to remove the acetone. The sodium iodide was then recrystallized from very dilute NaOH solution, dried under vacuum and stored in a vacuum desiccator. The purified iodide was com- pletely soluble in the distilled acetic anhydride.

a-Tetralone (Light & Co.) and a-tetra101 (Sherman Chemicals) were each distilled three times under vacuum.

All other materials were of A.R. grade.

MEASUREMENT OF OXYGEN ABSORPTION

The rates of oxygen absorption in tetralin samples were measured at selected pressures in a constant pressure apparatus similar to that described by Bolland,ll but using a faster relay circuit and modified to enable the oxygen absorption to be automatically recorded. The gas burette consisted of two 50 ml calibrated tubes, one of which had a nichrome wire (8.8 ohms per yard) down the centre of the mercury column. This formed one arm of a d.c. bridge similar to that of Svec and Gibbs,12 but having variable resistors in both ratio arms so that the sensitivity and zero setting could be varied easily. The out-of-balance potential was recorded on a Sunvic RSP 2 recording potentiometer (10 mV). Calibration plots of the mercury height in one arm of the gas burette against recorder deflection were linear. The gas burette and manostat system were immersed in a thermostat maintained at 2040iO-01 "C.

The cylindrical reaction vessel 8 mm thick and of 5.5 ml capacity, had a 7 mm diam. side-tube incorporating a diaphragm break-seal and a narrow bore side-arm. Measured volumes of tetralin were distilled into the reaction vessel under vacuum through the side- arm which was then sealed off. Solids were introduced into the reaction vessel in the form of solutions from which the solvent was evaporated, and tetralin then distilled in. The reaction vessel was immersed in a thermostat controlled to &0.OS0C, and clamped in reproducible positions with respect to the 150-curie 6OCo source which was also immersed in the thermostat. The construction of the 6OCo source had been described elsewhere.13 To keep the hydrocarbon saturated with oxygen the reaction vessel was continuously shaken at measured rates up to 850c/min. The reaction vessel was connected to the manostat system via a flexible glass spiral and 5 m of thermally insulated 4 mm bore tubing passing through the radiation shield, so that the system within the shield was of all-glass construction. After evacuating and filling with oxygen to the required pressure, the break- seal was fractured by a glass-covered magnet.

The apparatus was calibrated for 5 , 15 or 50 ml absorption of oxygen to give full-scale recorder deflection. There was negligible drift at all settings over periods up to 50 h, and the measured oxygen absorption rates were reproducible to f 2 %. The reaction rate was independent of the shaking speed above 120 c/min, measurements normally being made at a rate of about 550. The reaction rate did not depend o n the volume of tetralin i n the reaction vessel.

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486 R A D I O L Y T I C OXIDATION O F T E T R A L I N

ANALYSES

The formation of reaction products was investigated in reaction vessels similar to those used for 0 2 absorption runs, but having a stoppered side-arm for sample with- drawal, the oxygen pressure in the vessels being maintained at about 800 mm.

Hydroperoxides were measured by reaction with NaI (0.60 g) in acetic anhydride (10 ml) solution 14 at room temperature 10 under an atmosphere of C02. The sample (if necessary, diluted with acetic anhydride to give a maximum sample of 5 x 10-7 moles peroxide) was added by micropipette, and the reaction mixture stirred in the dark for 20 min. The iodine produced was measured spectrometrically at 365 mp in stoppered cells relative to a blank solution similarly prepared, and the hydroperoxide concentration determined from a linear calibration plot obtained using tetralin hydroperoxide. A similar plot for benzoyl peroxide showed that the purity of the tetralin hydroperoxide was 97.6 % relative to that of the benzoyl peroxide. a-Tetralone and a-tetralol are possible reaction products, and it was shown that amounts up to 2-1 x 10-6 mole a-tetralone or 6.8 x 10-6 mole a-tetialol in the analytical sample had no effect on the analyses for hydroperoxides.

Hydrogen peroxide was determined by a modification of the titanium sulphate method of Eisenberg.15 To dissolve the oxidized tetralin samples an acetone+ water solvent was employed, the yellow complex having an absorption pack at 415 mp with &415 = 820.4. Tetralin hydroperoxide interferes with the analysis by slowly generating the yellow colour, whereas H202 initially present reacts instantaneously. Blank experiments showed that the effect of tetralin hydroperoxide was eliminated by making measurements over a short period, and extrapolating back to the time of adding the sample,

DOSIMETRY

The rates of energy absorption in tetralin were measured in the reaction vessels by means of the ferrous sulphate dosimeter, taking G F ~ ~ + = 15.45.16

RESULTS

The absorption of oxygen as a function of radiation dose (proportional to irradi- ation time) took the form shown in fig. 1, the short initial retardation period, during which the rate of oxygen uptake accelerates, being due to trace impurities in the tetralin. The oxygen absorption then reached a maximum rate, the extent of the linear portion of the graph depending on the dose rate. The turnover point A occurred after 9-15 mole % of the tetralin had been oxidized at a dose rate of 3.13 x lOl8eV 1.-1 sec-1, and after 12.1 mole % oxidation at a dose rate of 1975 x 1017 eV 1.-1 sec-1. Removal of the radiation source at stage B of a similar experiment resulted in immediate cessation of oxidation, indicating the absence of any post- irradiation effects. On replacing the source after 23% h the reaction rate was immediately restored to its previous value, so that there is no induction period when the traces of impurity have reacted. After point A the rate of oxygen absorption gradually decreases. For the majority of the kinetic work the reaction was only followed until the extent of oxidation was 2.1 mole %.

The rate of oxidation, measured as the slope of the linear part of the 0 2 ab- sorption curve, was independent of the 0 2 pressure above the tetralin over the range 25 to 1032 mm, the rates being measured at 25°C at a dose rate of 1 . 0 4 ~ 1018 eV 1.-1 sec-1.

The rate of oxygen absorption was found to be proportional to the square root of the dose rate (fig. 2) over the range 8.03 x 1015 to 2 . 8 0 ~ 1018 eV 1.-1 sec-1 at 25°C. The graph passed through the origin, the thermal rate being 4 % of the minimum radiation induced rate. G-values for oxygen absorption (molecules of 0 2 absorbed per 100 eV of energy absorbed in the tetralin) ranged from 1716 to 102.2 at the dose rates quoted above.

The rate of initiation of the oxidation was determined by introducing known amounts of 2 : 6-di-t-butyl -p-cresol and measuring the resulting induction periods. These were well defined and the subsequent rate of oxygen absorption was identical to that in the absence of the inhibitor, indicating that the peroxy radicals formed r c x t with 2 : 6-di-t-butyl-p-c~esol to give a product which does not affect the

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Page 4: The oxidation of tetralin induced by 60Co ?-radiation

D. VERDIN 487

time (h) FIG. 1.-A typical recorder trace of 0 2 absorption at 250°C.

Dose rate = 9 . 9 0 ~ 1017 eV 1.-1 sec-1; point A = 10.7 mole % of tetralin oxidized; 0 total peroxide concentration moles/l.

W 2 X

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488 R A D I O L Y T I C O X I D A T I O N O F T E T R A L I N

reaction rate. At each dose rate plots of the induction periods against the amounts of inhibitor used were linear, and the initiation rates were calculated from the slopes of these lines assuming that each inhibitor molecule reacts with two peroxy radicals.17 Fig. 3 shows the linear relationship found between initiation rate and dose rate at 25"C, and the point measured at 40°C falls on this line so that the initiation reaction has no activation energy. The G-value for production of peroxy radicals calculated from the slope of the line in fig. 3 is 1.52.

FIG. 3.-Dependence of initiation rate on dose rate. 0 25°C; V 40°C.

The maximum concentration of inhibitor employed in the above experiments was 9.3 x 10-4 M and the induction periods were proportional to inhibitor con- centration. However, for the dose rate of 9.35 X 1017 eV 1.-1 sec-1, induction periods caused by 1-64 and 2 . 3 4 ~ 10-3 M inhibitor were respectively 10.8 % and 19.7 % larger than linearly extrapolated values and were unchanged when the O2 pressure was increased from 775mm to 98Omm. Hammond17 reported no complications in the use of 2 : 6-di-t-butyl-p-cresol at concentrations up to 3x 10-3 M. The present discrepancies may be due to energy transfer effects such as observed at similar scavenger concentrations in the radiolysis of cyclohexane.l8

The variation of the rate of reaction with temperature was determined from measurements of the rate of 0 2 absorption at three dose rates at each temperature. The square-root dependence on dose rate persisted to the highest temperature used. The rate constants obtained are summarized in table 1 and an Arrhenius plot of these data lead to an overall activation energy of 7.7 kcal/mole.

TABLE 1 .-TEMPERATURE DEPENDENCE OF RATE CONSTANT FOR 0 2 ABSORPTION

TOC

25-0 40.0 5 5.0 70.0

kObs. x 1015

mole ev-f 1.4 sec-4

2.83 5.54 9.47

15.1

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Page 6: The oxidation of tetralin induced by 60Co ?-radiation

D . V E R D I N 489

Tetralin hydroperoxide is the major primary product of the reaction, conse- quently its effect on the rate of 0 2 absorption was studied. The data obtained are given in table 2 and show that added tetralin hydroperoxide has no marked effect on the reaction rate even when added at concentrations exceeding twice that (0.13 M) obtained a t the end of normal kinetic runs.

TABLE 2.-INFLUENCE OF TETRALIN HYDROPEROXIDE ON RATE OF 0 2 ABSORPTION AT 25~0°C

Dose rate = 1-01 x 1018 eV 1.-1 sec-1 tetralin hydroperoxide d[Oz]/dt mole. 1.-1

moles/l. x 102 sec-1 X 106

0.00 2-97 4-26

1 1 -04 2 9 . 8 6

2.86 2.92 3-13 3.14 3-25

THE FORMATION OF REACTION PRODUCTS

Total peroxide (ROOH+ H202) formation during the oxidation was estimated iodometrically. The curve of peroxide formation (fig. 1) was almost coincident with the oxygen absorption plot, but the deviation from linearity occurred about 50 % lower than for 0 2 absorption. This behaviour was confirmed by graphs of peroxide formation at the other two dose rates at which the extensive oxygen absorption was followed. The titanium sulphate method was used to measure H202, which was produced linearly with the absorbed dose at a rate directly proportional to the dose rate (fig. 4) over the range 1.73 to 3 . 6 6 ~ 1018 eV 1.-1 sec-1 at 25°C. The yield was G H ~ o ~ = 0.47.

dose rate, eV 1.-1 sec-1 x 10-18 FIG. 4.-Formation of hydrogen peroxide at 2 5 . 0 " C .

The gaseous products were examined by oxidizing samples of tetralin in the presence of excess oxygen in closed vessels. The products volatile at -197°C were separated by means of a Toepler pump, their volume measured, and a sample analyzed mass-spectrometrically. Small amounts of Ha were found and traces of CH4 and C2H6 which never exceeded 3 % of the H2 yield. The hydrogen forma- tion was proportional to the dose with no induction period, arid was independent of dose rate over the range 8 . 2 ~ 1015 to 2 . 2 ~ 1018 eV 1.-1 sec-1 as shown in fig. 5. The yield was G H ~ = 0.26.

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490 R A D I O L Y T I C O X I D A T I O N OF T E T R A L I N

Infi-a-red spectra of extensively oxidized tetralin samples showed a weak -0-0- band at 835 cm-1, a band at 3500 cm-1 presumably due to hydrogen bonding in tetralin hydroperoxide,lg and a carbonyl band at 1680 cm-1. A calibra- tion plot was constructed for the carbonyl band using known amounts of cc- tetralone, and from this, carbonyl concentrat ions were estimated in extensively oxidized tetralin. For the oxidation shown in fig. 1 after 69-3 and 86.1 h irradiation, the carbonyl concentrations were 0.027 M and 0-050 M respectively, which account for the difference between 0 2 absorption and peroxide formation. Infra-red

total dose per 1. tetralin x 19-22 eV

FIG. 5.-Yield of H2 as a function of dose at various dose rates at 250°C. 0 3-23 X 1017 eV 1.-1 sec-1; 0 8.24 x 1015 eV L-1 sec-1; V 2-15 x 1018 eV 1.-1 set-1.

spectra confirmed that no appreciable yields of carbonyl compounds were formed in the early stages of the oxidation. It was confirmed that the carbonyl compound was a-tetralone by preparation of the 2 : 4dinitrophenylhydrazones of pure a- tetralone and the reaction product. Their absorption spectra in basic solution 20 were identical, having maxima at 467 mp with extinction coefficients of 2.95~ 104.

DISCUSSION

The high values of G(-02) compared with G (radical) indicate that the reaction occurs by a chain mechanism, and the near equivalence of 0 2 absorption and peroxide formation in the initial stages may be explained by the generally accepted oxidation chain 1 in which the initiation reaction is

(1) RH-+R- +H*, R* being a CloHll radical. The formation of H2 in the presence of the reactive scavenger 0 2 may be attributed to the molecular process,

c ~ ~ H ~ ~ being an unsaturated product. The occurrence of a reaction similar to (2) in the presence of 0 2 is also proposed by Dewhurst 9 who measured the yields

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Page 8: The oxidation of tetralin induced by 60Co ?-radiation

D . V E R D I N 49 1

of cyclohexene in the radiolysis of cyclohexane in the presence of 0 2 . The low yields of H2 do not interfere with the experimental measurement of the rates of 0 2 absorption.

Reaction (1) will be followed by the normal propagating sequence,

R* + 02+R02* (3) RO2* +RH-+ROOH+R*. (4)

The small increases in reaction rate with added tetralin hydroperoxide show that, in the early stages of the oxidation, induced decomposition of the peroxide does not significantly contribute to initiating oxidation chains.

The square-root dependence of the reaction rate on the radiation intensity indicates that termination is by radical combination or disproportionation. Moreover, since the rate of 0 2 absorption is independent of the oxygen pressure, all the primary radicals must immediately react with 0 2 to form peroxy radicals, so that the termination reaction may be written,

R02- + R02. +inert products + 02. (5 ) The formation of H202, which has not previously been reported for oxidation

at low dose rates, may result from the following reactions of H atoms formed in reaction (1) :

H* + O2+HO2* (6)

HOz*+RH+R* +H202 (7)

H02*+R02m-+ROOH+02 (81 2HO,m+H,O,+ 0 2 . (9)

The scavenger employed reacts with all the primary peroxy radicals formed so that the radical yield can be expressed by

Gradical = GROzm + GH02* = GR. GHm.

Since the chain lengths are high and G H ~ O ~ is low the overall reaction rate will be governed by reactions (I), (3), (4) and (5), for which, assuming stationary concentrations of R. and RO2. it follows that

where Ri is the rate of initiation, I is the dose rate, and N is Avogadro's number. The experimental data may be summarized in the equation,

- d[O,]/dt = kob,,If[O2]". Thus, if the above mechanism applies to the reaction,

From the measured values of kobs. and Gradical the values of k4/k& were calculated as 3.44 x 10-3 and 8.00 x 10-3 1.4 mole-* s e c t at 25°C and 45°C respectively. These are somewhat higher than the corresponding values of 2 . 8 7 ~ 10-3 and 4.50~ 10-3 reported by Bamford and Dewar.1

The stationary concentration of ROp radicals will greatly exceed that of H02. radicals so that reaction (9) may be neglected in comparison with reaction (8). Then from reactions (l), (6), (7) and (8) it follows to a first approximation that

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492 R A D I O L Y T I C O X I D A T I O N OF TETRALIN

The rate of H202 formation should thus depend on a power between JJ and 1 of the dose rate; however, the sensitivity of the analytical method for H202 neces- sitated the use of high doses and limited its estimation to a narrow range of dose rates, over which an apparent direct dependence of rate of H202 formation on dose rate was observed. The maximum rate of H202 should be +Ri so that G H ~ ~ ~ should have a maximum value of 3Gradical = 0.76, whereas the experimental value is 0.47. The discrepancy may reflect the contribution of the second term in the above equation, or may be due to radiation induced decomposition of H202.

The kinetic chain length is

The experimental values at 25°C ranged from 1129 at the minimum dose rate (8.03 x 1015 eV 1.-1 sec-1) to 67.2 at the maximum dose rate used (2-80 x 1018 eV 1.-1 SCC-1). They were inversely proportional to the square root of the radiation intensity, in accordance with the relationship deduced by substituting the ex- pressions for -d[02]/dt and Ri in the above equation.

It was verified that the initiation reaction has zero activation energy, so that the measured overall activation energy is EA = E4-3E5. The experimental value of 7.7 kcal/mole is comparable to that reported by Woodward and Mesrobian 21 (8.2 &0*6), but somewhat higher than that of Bamford and Dewar 1 (4-3) determined from rates measured at two temperatures.

The near-equivalence of 0 2 absorption and peroxide formation in the early stages of the reaction indicates that negligible amounts of carbonyl compounds are formed, the yields which should result from the chain-termination reaction 21 being undetectable by the infra-red method employed. After more extensive oxidation carbonyl compounds appear, presumably resulting from the radiolytic decomposition of tetralin hydroperoxide.

1 Bamford and Dewar, Proc. Roy. SOC. A, 1949, 198,252. ZDurup, Durup, Kuffer and Magat, Proc. 2nd U.N. Con$ Peaceful Uses Atomic

Energy (United Nations, Geneva, 1958), 29, p. 143. 3 Brun and Montarnal, Compt. rend., 1958, 247, 2361. 4 Montarnal, gnergie Nuclkaire, 1959, 1, 282. 5 Proskurnin, Khmel 'nitskii, Barelko, Slepneva and Melekhonova, Doklady Acad.

6 Dugan and Landis, J. Amer. Oil Chem. SOC., 1956, 33, 152. 7 Bakh and Popov, Symp. Radiation Chemistry (Acad. Sci. U.S.S.R., Moscow, 1955)

8 Bakh and Saraeva, Zhur. Fiz. Khim., 1958, 32, 209. 9 Dewhurst, J . Physic. Chem., 1959, 63, 813. 10 Wibaut, van Leeuwen and van der Wal, Rec. trav. chin?., 1954, 73, 1033. 11 Bolland, Proc. Roy. Soc. A , 1946, 186, 218. 12 Svec and Gibbs, Rev. Sci. Instr., 1953, 24, 202. 13 Murray, Roberts and Dove, Radioisotopes in Scientific Research (Proc. 1st UNESCO

14 Nozaki, Ind. Eng. Chem. (Anal.), 1946, 18, 583. 15 Eisenberg, Ind. Eng. Chem. (Anal.), 1943, 15, 327. 16 Schuler and Allen, J. Chem. Physics, 1956, 24, 56. 17 Boozer and Hammond, J. Amer. Chem. SOC., 1955, 77, 3233. 1 8 Schuler, J. Physic. Chem., 1957, 61, 1472. 19 Minkoff, Proc. Roy. SOC. A , 1954,224, 176. 20 Jones, Holmes and Seligman, Anal. Chem., 1956, 28, 191. 21 Woodward and Mesrobian, J. Amer. Chem. Soc., 1953,75, 6189.

Sci. U.S.S.R., 1957, 112, 886.

(Consultants Bureau Translation, New York, 1956), p. 119, 129.

Int. Conf. Paris 1957) (Pergamon, London, 1958), vol. 1, p. 139.

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