Abstract: Gamma radiation induced formation of ICl in aerated and deaerated solutions of iodine in some aromatic chlorinated solvents has been studied for different concentrations and γ dosages. G values for formation of ICl and decomposition of I 2 were determined in gamma radiolysis of aerated and deaerated solutions of I 2 in 1,2-dichlorobenzene(1,2-DCB), 1,3-dichlorobenzene(1,3-DCB), 2-chlorotoluene, 3-chlorotoluene and benzotrichloride. G(ICl) values have been found to decrease in the following order 2-chlorotoluene &lt; 3-chlorotoluene &lt; 1,2-DCB &lt; 1,3-DCB &lt; benzotrichloride. G(ICl) is slightly higher in aerated solutions than in deaerated solutions and is found to be dependent on the structure of the parent organic molecule

D V Parwate

P S Kolte

S A Bhange

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http://www.e-journals.in                             Chemical Science Transactions  
DOI:10.7598/cst2014.694                          2014, 3(1), 424-430 
Gamma Radiation Induced Formation of  
Iodine Monochloride in Iodine in Some  
Aromatic Chlorinated Solvents 
P. S. KOLTE*, D.V. PARWATE and S. A. BHANGE 
Department of Chemistry, Rashtrasant Tukadoji Maharaj Nagpur University, 
Nagpur-440 033, India 
prernakolte@gmail.com  
Received 28 July 2013 / Accepted 30 August 2013 
Abstract: Gamma radiation induced formation of ICl in aerated and deaerated solutions of iodine in 
some aromatic chlorinated solvents has been studied for different concentrations and γ dosages. G 
values for formation of ICl and decomposition of I2 were determined in gamma radiolysis of aerated 
and deaerated solutions of I2 in 1,2-dichlorobenzene(1,2-DCB), 1,3-dichlorobenzene(1,3-DCB),   
2-chlorotoluene, 3-chlorotoluene and benzotrichloride. G(ICl) values have been found to decrease in 
the following order 2-chlorotoluene < 3-chlorotoluene < 1,2-DCB < 1,3-DCB < benzotrichloride.  
G(ICl) is slightly higher in aerated solutions than in deaerated solutions and is found to be dependent 
on the structure of the parent organic molecule. 
Keywords: Aromatic chlorinated solvents, Iodine monochloride, G-value 
Introduction 
In recent years, the addition of reactive solutes to liquids being irradiated has been extensively 
applied as a technique for scavenging free radicals intermediates. The radical scavenging using 
I2 in various chlorinated organic solvents has been a subject of detailed investigations
1-5 in the 
past. However, no detailed study has been studied in aromatic chlorinated solvents.  
 In the present work, we have investigated gamma radiation induced formation of ICl in 
1,2-DCB, 1,3-DCB, 2-chlorotoluene, 3-chlorotoluene and benzotrichloride at different 
concentrations of I2 in presence and absence of oxygen. 
Experimental 
All the chemicals used were of AR grade. Freshly prepared solutions of I2 of 0.4 mM, 0.8 mM 
and 1.2 mM in aromatic chlorinated solvents as mentioned above were air saturated for 
15 min prior to irradiation.  
 The steady-state irradiations were carried out with Cobalt-60 Gamma Chamber - 900 
housed in Nuclear  Chemistry  laboratory,  Department of  Chemistry, Rashtrasant Tukadoji  
 RESEARCH ARTICLE 
Chem Sci Trans., 2014, 3(1), 424-430                  425            
Maharaj Nagpur University, Nagpur. The dose rate of the Co-60 source during the course of 
work was ~ 0.5kGy/h. The dose rate was measured using Fricke dosimetry with G (Fe3+) = 
15.6. Dose correction for aromatic chlorinated solvents was applied using expression: 
D
M
DM AZ
AZ
DD
)/(
)/(
                                                                 (1) 
 Where Z/A is the mean ratio of sum of atomic numbers and molecular weight of the 
medium and the dosimeter solution respectively. An aliquot of each solution was exposed to 
successively increasing dosages depending on the appearance of ICl. Stoppered irradiation 
cells made of corning glass and standard B-19 joints were used to minimize solvent 
evaporation. Post irradiation absorbance spectra were recorded on Elico SL 210 Double 
beam UV-Visible spectrophotometer. The spectra of unirradiated sample solutions were 
recorded simultaneously. The same method was carried out for solutions of I2 (0.8mM) 
through which N2 was passed for 15 minutes prior to irradiation. 
Results and Discussion 
The visible spectra of non-irradiated solutions of I2 in aromatic chlorinated solvents 
mentioned above  exhibit characteristic maxima at ~515 nm showing presence of I2. 
However, after irradiation, I2 starts disappearing with subsequent appearance of new 
characteristic maxima indicating the formation of ICl. These spectra cross with each other at 
the isobestic point indicating the presence of two species I2 and ICl simultaneously. Typical 
absorption spectra for different concentrations of I2 at various dosages are shown in Figure 1. 
 
Figure 1. Absorption spectra of I2 solution in 2-chlorotoluene at different dosages for 0.4 mM 
initial I2 concentration 
 Spectral characteristic of solutions of I2 in chlorinated solvents are given in Table 1. 
Table 1. Spectral characteristic of I2 solutions in various aromatic chlorinated solvents 
Solvents 
Absorption 
maxima of I2 
λmax nm 
Absorption 
maxima of ICl  
λmax nm 
Isobestic point of 
I2 and ICl nm 
1,2-DCB 
1,3- DCB 
2-Chlorotoluene 
3-Chlorotoluene 
Benzotrichloride 
510 
510 
505 
505 
510 
425 
420 
400 
395 
440 
450 
440 
445 
440 
450 
426                   Chem Sci Trans., 2014, 3(1), 424-430            
 The formation of ICl and disappearance of I2 at increasing dosages were calculated from 
two simultaneous equations5,6.  
[Abs]
430
 = 40.6 [I2] + 128 [ICl]                                                   (2) 
[Abs]
515
 = 918  [I2]  + 59.8 [ICl]                                                 (3) 
 Where, absorbance values were directly obtained from spectra. The amount of ICl 
formed and I2 decomposed at different irradiation dosages were calculated using equations 
(2) and (3) and plotted to give yield dose curves. It was observed that as the concentration of 
I2 in chlorinated solvents increases, the dose required to convert iodine into ICl also 
increases. Figure 2 shows a plot of absorbed dose required for formation of ICl from I2 in 
1,2-DCB, 1,3-DCB, 2-chlorotoluene, 3-chlorotoluene and benzotrichloride. 
 
Figure 2. Correlation of dose absorbed and ICl formed from I2 in 1,2-DCB, 1, 3-DCB, 2-
chlorotoluene, 3-chlorotoluene and benzotrichloride 
 A linear relationship with good coefficient of correlation (R=0.991, 0.998, 0.988, 0.997 
and 0.996 for 1,2-DCB, 1,3-DCB, 2-chlorotoluene, 3-chlorotoluene and benzotrichloride 
respectively) was observed. Thus, it is inferred that ICl formation from I2 in aromatic 
chlorinated solvents varies directly as the function of absorbed dose. 
Variation of G(–I2) and G(ICl) with dose absorbed 
A summary of variation of G(-I2) and G(ICl) for different concentrations of I2 in aromatic 
chlorinated solvents is given in Table 2. 
Table 2. Variation of G(-I2) and G(ICl) values at various I2 concentrations in different 
aromatic chlorinated solvents 
Solvent 
Initial Conc. of 
I2 mM 
Absorbed 
dose (kGy) 
G(-I
2
) G(ICl) Δ ICl/Δ I2 
Aerated 
1,2-DCB 
0.4 
0.49 
0.98 
1.47 
1.95 
3.65 
2.42 
0.94 
0.82 
18.58 
9.29 
6.91 
6.07 
1.66 
0.8 
0.87 
1.31 
2.18 
3.48 
3.57 
0.90 
0.15 
0.22 
16.10 
14.92 
10.97 
8.58 
1.83 
Contd… 
Chem Sci Trans., 2014, 3(1), 424-430                  427 
 1.2 
0.87
2.18 
3.05 
3.92
3.37
0.90 
0.32 
0.20
15.38
11.73 
10.42 
8.98
1.91 
1,3-DCB 
0.4 
0.43
0.86 
1.30 
1.73
4.53
1.81 
0.45 
0.11
18.73
11.16 
8.16 
6.30
1.92 
0.8 
0.87
1.30 
2.17 
2.60
4.07
1.05 
0.63 
0.30
16.17
13.42 
10.49 
9.46
1.83 
1.2 
0.87
1.73 
2.60 
3.90
4.29
1.02 
1.43 
0.25
15.41
13.30 
11.26 
8.07
1.61 
2-Chlorotoluene 
0.4 
0.43
0.85 
1.28 
1.71
2.29
1.38 
0.31 
0.24
21.16
14.23 
10.46 
8.57
2.00 
0.8 
0.85 
1.28 
1.70 
2.98 
2.53 
1.53 
1.15 
0.13 
20.47 
18.52 
16.64 
11.60 
2.00 
1.2 
0.85
2.98 
3.40 
3.83
2.30
0.46 
0.23 
0.10
18.66
10.87 
10.15 
9.27
1.86 
 
3-Chlorotoluene 
 
 
 
 
 
0.4 
0.85
1.28 
1.70 
2.13
2.07
0.61 
0.46 
0.18
21.22
14.88 
12.07 
10.24
 
 
 
2.00 
0.8 
0.85
1.28 
2.55 
2.98
3.45
1.23 
0.46 
0.20
20.11
16.33 
10.60 
9.72
 
 
 
1.86 
1.2 
0.85 
1.28 
2.55 
3.40 
3.68 
2.30 
0.77 
0.23 
18.29 
17.56 
13.17 
10.70 
 
 
 
1.76 
Benzotrichloride
0.4 
0.07 
0.14 
0.21 
0.43 
5.40 
2.78 
2.75 
1.11 
24.49 
24.35 
23.37 
22.28 
 
 
 
1.76 
0.8 
0.11 
0.21 
0.74 
0.85 
6.41 
5.61 
1.19 
1.01 
23.95 
23.45 
21.64 
20.00 
1.85 
Contd… 
428                   Chem Sci Trans., 2014, 3(1), 424-430            
 1.2 
0.14 
0.28 
1.13 
1.27 
6.97 
6.86 
1.38 
0.92 
23.89 
22.97 
19.76 
19.30 
1.82 
Deaerated 
1,2-DCB 0.8 
0.85 
1.28 
1.70 
2.13 
1.84 
1.38 
0.92 
0.46 
13.90 
12.68 
12.25 
11.85 
1.57 
1,3-DCB 0.8 
0.84 
1.26 
2.10 
2.94 
2.33 
1.86 
0.37 
0.20 
14.43 
11.59 
8.29 
6.56 
1.50 
2-Chlorotoluene 0.8 
0.85 
2.11 
2.54 
3.38 
3.93 
0.74 
0.39 
0.12 
15.47 
10.31 
9.21 
7.27 
1.91 
Benzotrichloride 0.8 
0.21 
0.42 
0.85 
0.90 
9.23 
6.00 
0.69 
0.62 
16.16 
15.42 
14.69 
13.71 
1.63 
 The plots of radiation chemical yield (G-values) and dose absorbed in various aromatic 
chlorinated solvents has been compared as shown in Figure 3. 
     
     
Figure 3. Variation of G(-I2) and G(ICl) with dose absorbed in aerated 1,2-DCB, 1,3-DCB, 
2-chlorotoluene and deaerated benzotrichloride 
Chem Sci Trans., 2014, 3(1), 424-430                  429       
 From Figure 3, it is observed that G(-I2) and G(ICl) values decrease with increase in 
concentration due to decrease in number of ICl molecules formed with increasing 
concentration of I2. As the number of Cl atoms available for formation of ICl at higher 
concentration of I2 becomes less, it is quite likely that less number of ICl molecules are 
formed at higher I2 concentrations. It is noticed that G values suddenly drop at higher 
dosages. Presumably, at higher dosages, a part of ICl is getting decomposed and it reaches to 
saturation value. 
 The formation of ICl and •Cl as one of the products was observed by Bibler8,9 in 
radiolysis of air-saturated solution of I2 in CCl4. In the present work, radiolysis of I2 
solutions in aromatic chlorinated solvents also results in ICl as the major product due to 
radical reaction.  
 In aromatic chlorinated solvents, very high dose is required to effect a colour change 
and for formation of ICl, a part of energy gets deposited on benzene ring which is resonance 
stabilized and hence, Ar-Cl bond is not broken easily. The dose required to effect colour 
change and for formation of ICl in C6H5CCl3 is less as compared to C6H4Cl2 and Cl 
C6H4CH3 as Cl in C6H5CCl3 is not directly attached to benzene ring. 
 In case of I2 in chlorobenzenes, ICl is the main product containing iodine although very 
small amounts of C6H6, C6H5C6H5, C6H5C6H5 Cl, C6H4ICl and C6H5I (G < 0.5) have also 
been detected10,11. The primary dissociation reaction may take place directly through 
dissociation of excited molecules or indirectly through ionic intermediates12. Radiolysis of 
chlorotoluenes possibly lead to ionization, excitation and electrons react by dissociative 
electron attachment13. 
 There may be formation of several other products like HCl, higher chlorohydrocarbons 
or oxides of chlorine but these were not identified. The possibility of chain reaction 
mechanism cannot be ruled out due to high G(ICl) values. Due to certain constraints of the 
experimental set up in our laboratory, the formation of other products could not be 
identified. 
 Thus, it is observed that in radiolysis of aromatic chlorinated compounds at one stage or 
the other, •Cl is one of the products formed as a result of carbon-halogen and carbon-
hydrogen bond rupture14. It seems that presence of aromatic ring does not stabilize the 
aromatic chlorinated compounds towards radiolysis. 
 Radiolysis of I2 in 1,2-DCB, 1,3-DCB, 2-chlorotoluene, 3-chlorotoluene and 
benzotrichloride solutions under aerated conditions gives significantly higher G(ICl) than in 
absence of oxygen. This additional yield possibly derives due to the addition of molecular 
oxygen to the radicals generated by the reactions of the primary radiation-induced radicals, 
e- with the respective aromatic chlorinated solvents15,16. 
Conclusion 
The concentration of ICl varies linearly with the dose absorbed at lower dosages with good 
coefficient of correlation. After a certain dose, a deviation in G(-I2) and G(ICl) values are 
observed for every solvent and each concentration. This could be due to C-Cl bond 
dissociation energy. 
 The observed values of G(ICl) in presence of oxygen were found to be slightly higher 
than those in absence of oxygen due to the addition of molecular oxygen to the radicals 
generated by the reactions of the primary radiation-induced radicals, e-, with the respective 
aromatic chlorinated solvents. 
430                   Chem Sci Trans., 2014, 3(1), 424-430            
 G(-I2) and G(ICl) are found to be almost constant for every solvent and each iodine 
concentration. Radiolytic decomposition of I2 in aromatic chlorinated solvents and formation 
of ICl is observed to be dependent on the structure of the parent organic molecule. 
Acknowledgement 
Thanks are due to the Head of the Department of Chemistry for providing laboratory and 
irradiation facilities.  
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Gamma Radiation Induced Formation of Iodine Monochloride in Iodine in Some Aromatic Chlorinated Solvents

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Gamma Radiation Induced Formation of Iodine Monochloride in Iodine in Some Aromatic Chlorinated Solvents

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