Chain Dechlorination of Organic Chlorinated Compounds in Alcohol Solutions by 60Co γ-Rays, (II)

Abstract

Chlorinated benzenes dissolved in deoxygenated alkaline 2-propanol were dechlorinated by irradiating with 6°C o r-rays to produce the lower chlorinated benzenes and chloride ion. The yield of dechlorination was found to depend on the number of chlorine atoms on the benzene ring, the G(CI-)-values being, for instance, 6,500, 480 and 2.0 for 0.07 M pentachlorobenzene, I, 2, 4-trichlorobenzene, and monochlorobenzene, respectively, in 0.2 M KOH-2-propanol solution. In contrast, the values of G(CI-) differed little between the isomers of trichlorobenzene. The large difference in G(CI-) according to the number of chlorine atoms can be explained by considering the redox potential of the chlorinated benzenes and the ketyl radical ion. Trichlorobenzene is dechlorinated to dichlorobenzene and then to monochlorobenzene while producing potassium chloride and acetone, and consuming hydroxide ion. In the experiment, some chlorinated benzene derivatives were observed to be generated in the course of this process-probably dichlorophenyl-2-propanol and monochlorophenyl-2-propanol, judging from observation by gaschromatograph-mass spectrometer and from the pathway of formation. The observation also indicated the presence of dichlorophenyl-2-propanol in predominant amounts in 1, 3, 5-trichlorobenzene solution, but only in a small fraction in 1, 2, 3-trichlorobenzene.

Degradation pathways of PCB upon gamma irradiation.

“…These electrons react with PCB through dissociative attachment to generate a chloride anion and a PCB radical (3) that removes a hydrogen atom from the solvent to generate the dechlorinated congeners described in Table 1. Contrary to be results reported by Shimokawa et al (9) for chlorinated aromatics irradiated in hydroxylic solvents, PCB-solvent adducts, such as hydroxy or hydroxymethyl PCB, were not detected by GC/MS. These data also indicate that the relative amounts of the various degradation products generated upon irradiation of a specific congener are influenced by the solvent.…”

“…Petroleum ether was selected as a solvent because its hydrophobicity mimics, to a certain extent, the fatty tissues in which PCB tends to accumulate in living organism. A methanol solution containing 20% water was also used to study the potential formation of PCB solvent adducts as reported upon UV (7,8) and gamma irradiation of chlorinated aromatics (9). Although such adducts were not detected in our previous experiments performed with Aroclor 1260, they could have been produced in minute amounts, preventing their positive detection and characterization from this very complex mixture upon GC analysis.…”

Degradation pathways of PCB upon gamma irradiation

“…Petroleum ether was selected as a solvent because its hydrophobicity mimics, to a certain extent, the fatty tissues in which PCB tends to accumulate in living organism. A methanol solution containing 20% water was also used to study the potential formation of PCB solvent adducts as reported upon UV (7,8) and gamma irradiation of chlorinated aromatics (9). Although such adducts were not detected in our previous experiments performed with Aroclor 1260, they could have been produced in minute amounts, preventing their positive detection and characterization from this very complex mixture upon GC analysis.…”

Using electron-transfer reactions to propagate radical chain processes

“…Photolysis of a mixture of non-l-yne (0.1 M), isopropyl bromoacetate (0.5 M), collidine (0.5 M), and benzophenone (0.01 M) in methanol gave I-H (32%; reactions 1-5, R = ), II-H (30%; reactions 1, 2, 7, and 8), and II-Br (38%; reactions 1, 2, 7, and 9) at 14% conversion of isopropyl bromoacetate.18 I* + CH3(CH2)6C=CH -CH3(CH2)6C=CHCH2C(0)0Pr-t (7) II…”