Oxidizing properties of CCl3O.2 radicals studied by pulse radiolysis

0146-5724/90 $3.00+ 0.00 Copyright © 1990 Pergamon Press plc

Radiat. Phys. Chem. Vol. 36, No. 2, pp. 177-179, 1990 Int. J. Radiat. Appl. Instrum., Part C

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OXIDIZING PROPERTIES OF CC130 ~ RADICALS STUDIED BY PULSE RADIOLYSIS J. GRODKOWSKI,1 Z. STUGLIK1 and W. CZAJKOWSKI2 tDepartment of Radiation Chemistry and Technology, Institute of Nuclear Chemistry and Technology, Dorodna 16, 03-195 Warszawa and 2Institute of Dyes, Technical University of LodL Wroblewskiego 15, 93-590 L6d4,, Poland Abstraet--CCl30~ radicals were produced by reactions of solvated electrons with CC14 in the presence of 02 in the solutions. The reducing species e~o~vwere thus converted into oxidizing radicals. There are presented examples of organic radical-cations prodution by reactions of appropriate solutes with CC130~ in methanol and 2-propanol solutions, which are rather typical media for reduction processes. The solvents, methanol and 2-propanol, analytical grade were kept over molecular sieves 12h and fractionated. CCI4, analytical grade, was used as received. All 4"-substituted derivatives of 4,4'-bis (N,N-dimethylamino)triphenylmethane were synthesized by the method in which appropriate 4-substituted benzaldehyde was condensed with the excess of N,N-dimethylaniline in the presence of hydrochloric acid, The same procedure was reported in the literature.(14)

INTRODUCTION

Peroxyl radicals derived from halogenated hydrocarbon are reactive intermediates which attack many chemical and biological systems, tl) The most frequently investigated is CC130~, which is thought to play an important role in toxicity of CC14. (1-11) The primary step of its formation is reduction of CC14 by electron (or other strongly reducing radical): CC14 + eLiv --* CCI; + CI-.

(1)

In the presence of oxygen CCI; is easily converted into CCI3 02: CC13 + 02 --' CC13O1

RESULTS AND DISCUSSION

(2)

(k] = 3.0 x 101° M -] s -l, k: = 3.3 x 109 M -l s-l). (s) CC130~ is an effective one-electron oxidant and a number of its reactions has been reported. "-11) Because of the solubility, it is also very convenient to study oxidation reaction in different organic solvent where reactions (1) and (2) can take place. Recently, we have observed formation of "aniline" type cation-radicals as products of one electron oxidation of cyanide of 4,4'-bis(N,N-dimethylamino) triphenyimethane (ieucocyanide of Malachite Green d y e - - M G C N ) in several halogenated solvents and acetone.l12'z31 Therefore, we decided to use CC1302 as oneelectron oxidant of derivatives of amino-substituted tripbenylmethane in alcoholic solutions, where CC130~ formation has been already reported, is'7)

(~H2OH+CC14~ CC1;+ H + +C1 + H2CO,

(3)

(CH3)2(~OH + CC14 --* CCI~ + H + + CI+ (CH3)2CO ,

EXPERIMENTAL

(4)

and next step is again reaction (2) ( k 4 - - ( 1 - 7 ) x 108 M - ] s-1).c7) It was suggested that in 2-propanol the chain process could be initiated via the reaction

The linear electron accelerator LAE 13/9 was used as a source of 2.5 and 5.5 #s, 10 MeV electron pulses. The pulse radiolysis experiments have been done on the modified setup described previously. (12) The digital oscilloscope TS-8123 IWATSU was used for recording and digitizing of the experimental data. The calculation have been made on microcomputer M E R A 60. Dosimetry was performed with aqueous potassium tiocyanate (10 -2 M). RPC 36/2--H

The main radiolysis products of alcohols, which has to be considered in microsecond time resolution are solvated electrons and hydroxyalkyl radicals:05) (~H2OH in methanol and (CH3)~OH in 2-propanol. In methanol solution also alkoxy-radical can be taken into account. Its half-life in neat methanol is estimated as T = 1.1 x 10-7s and for the concentration of solute S > 10 -3 M products of their reactions could be observed. °5) In the presence of CC14 (c = 0 . 2 M ) and 02 (c =0.01 M, oxygen saturated solutions) electrons react predominantly according to reaction (1), which is followed by reaction (2). Hydroxyalkyl radicals react with CC14:

CC13 O~ + (CH3)2CHOH --* CC1302H + (CH3)2~OH,

(5)

followed by reactions (4) and (2)34`7) The competition to the reactions (3) and (4) are the 177

178

J. GRODKOWSKIet al.

formation of peroxyl radicals:C~5) (~H:OH + O2 ~ 02CH2OH,

(6)

(CH3)2(~OH + 02 ~ (CH3)2C(OH)02,

(7)

which are not very reactive. {~6~ In the presence of appropriate solute we could expect the oxidation reaction: CCI302 + S ~ CCI30 2 + S +'.

(8)

In the paper we present the intermediate spectra obtained according to reaction (8) in the pulse radiolysis of the methanol or 2-propanol solutions of the following solutes: C6 H4--N(CH3)2

of initial absorption band with maximum in the range 470-490nm. According to our previous observations (x2'~3)and taking into account the chemistry of the investigated systems, we described the "480 nm" band to the cation-radicals of the corresponding compounds. The cation-radicals of CVH, with absorption maximum at 480 nm were already postulated as intermediates in photochemical investigations.,7 ~9) Besides, the "480 nm" band is very similar to the absorption of N,N-dimethylaniline cation-radical.(2°'-m

C6H4--N(CH3)2

I

C6 H4--N(CH3)2

I

C6 H s - - C - - H

I

BrC 6H 4 - - C - - H

NO 2C 6H 4 - - C - - H

l

L

I

C6 H4--N(CH3)2

C6 H4--N(CH3)2 BrMGH

C 6H 4 - - N ( C H 3)2 NO2 M G H

MGH C6 H4--N(CH3 )2

C6H4--N(CH3)2

I

I

CH 30C 6H a - C - H

(CH3)2 N--C6 H 4 - - C - - H

I

I

C6 H4--N(CH3)2 CH3OMGH

CeH4--N(CH3)2 CVH

The results are presented in Figs 1-3. The common components in all data reported here is the presence

The "480 nm" band for all presented triphenylmethanes can be observed only when oxidizing conditions are fulfilled. The results are higher

0.12 0.11

0.08

0.10 0.09

0.06

0.08

0.07 OD

0.08

0.04

°°~ t

OD 0.04

/

i/

~/

\ o/ 0.02 F ~o" 0,01 01

0.0; Q~

ONQ

A

-,.A "~'A'A I 400

I 400 L 500

I 600

l 700

rim

Fig. 1. Optical absorption spectra of 10-3 M solution of MGH, 02 saturated, [CC14]=0.2M, in: solid line-methanol; (Q) immediately after the pulse, (C)) 180 #s after the pulse; and dashed line--2-propanol; (A) immediately after the pulse, (A) 180 #s after the pulse. Dose 48 Gy.

I 500

I 600

nm

Fig. 2. Optical absorption spectra in 2-propanol solutions 02 saturated, [CC14]=0,2M, 10-3M of: solid line-BrMGH; (O) immediately after the pulse, (C)) 180 ps after the pulse, dose 99Gy; and dashed line--NO2MGH; (A) immediately after the pulse, (A) 90 #s after the pulse. Dose 90 Gy.

Oxidizing properties of CC130½ radicals 0.4

O

179

derivatives of triphenylmethane cannot be simply summarized. Acknowledgements--We appreciate the technical support of Mrs M. Tomasik and Mrs B. Gawarska. This work has been supported by the program CPBP 01.19.02.07.

0.3

REFERENCES

OD0.2

j

o.~

~ +'%,/ ~* , r " % +(/, ,.,+.; I ]"~*++ +.-". .",

e. . . . •

O

I 400

I 500

I 600

nm

Fig. 3. Optical absorption spectra in 2-propanol solution, 02 saturated, [CC14] = 0.2 M, 10 3 M of." solid line---CVH; (O) immediately after the pulse, (O) 80/as after the pulse, dose I l l Gy; and dashed line---CH3OMGH; (A) immediately after the pulse, (A) 180/as after the pulse. Dose 99 Gy.

in methanol. Probably the oxidation reaction by alkoxyl radicals can take place, or peroxyl radicals derived from methanol are reactive enough to cause oxidation of the solute. In fact we observed the "'480 n m " band formation in the radiolysis of M G H solution in methanol without CC14 addition. All these facts support our assignment of "480 n m " band and indicate that CC130~ is very convenient oxidant of aminosubstituted triphenylmethanes. We do not intend to discuss here the mechanism of reactions of particular radical cations and the nature of the final spectra. Changing of the substituent in one aryl group have very strong effect on the subsequent reactions and this indicates that radiochemical processes observed in amino-substituted

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