The Dechlorination of Polychlorinated Biphenyls by UV-irradiation. IX. Reactions of Monochlorobiphenyls in a 2-Propanol Solution

Abstract

The multiplicity of the photo-excited state responsible for the dechlorination reaction of monochlorobiphenyls was determined in 2-propanol. Linear Stern-Volmer plots were obtained by the use of 1,3-cyclohexadiene for the dechlorination reactions of 2- and 3-chlorobiphenyl; the slopes were 35.7 and 11.0 dm3 mol−1 respectively. Fluorescence emissions were also quenched, and the quenching constants for 2- and 3-chlorobiphenyls were in accord with the respective values of the slope obtained from the Stern-Volmer plot for the reaction. The reaction of 4-chlorobiphenyl was quenched by cis-1,3-pentadiene, but was accelerated by 1,3-cyclohexadiene. Photosensitized dechlorinations of monochlorobiphenyls took place with several ketones, such as acetone and acetophenonc. These sensitized reactions were, however, very inefficient compared with the reactions in the direct excitations, except in the case of 4-chlorobiphenyl. It was, then, concluded that the dechlorinations of 2- and 3-chlorobiphenyl occurred only from the excited singlet state, while that of 4-chlorobiphenyl took place predominantly from the excited triplet state.

Polychlorobiphenyls: problems of the pollution of the environment and technological neutralisation methods

“…183 The most widely used procedure for the destruction of PCBcontaining solid and liquid waste is combustion in cyclone and cement furnaces and incinerators. By virtue of the high temperature and a fairly long contact time, the complete decomposition of PCB and the intermediate PCDD and PCDF is achieved in rotating cement furnaces, 54,77,174,176 while the limestone present in the initial charge binds quantitatively the acid gases formed on combustion (Cl 2 , HCl, etc.). The addition of PCB-containing materials to the initial charge improves the quality of the cement obtained.…”

“…77 The materials combusted served as an additional source of heat and this makes it possible to economise on the main fuel. 174 An interesting method involving the combination of the combustion of PCB-containing materials with a blast furnace process has been proposed. 174 As in the cement furnaces, here the problem of the recovery of the heat is solved successfully and the acid gases formed are bound by the limestone used as the flux.…”

Borohydride, micellar, and exciplex-enhanced dechlorination of chlorobiphenyls

“…In each case, the average of duplicate or triplicate injections was used in the quantitation of the percent reaction. Temperature programming allowed excellent separation of the many isomers and congeners involved in this work, as exemplified by Figure 1 which shows the separation of a mixture of 2-chlorobiphenyl (1), 4chlorobiphenyl (2), 2,4-dichlorobiphenyl (3), 2,4,6-trichlorobiphenyl (4), 2,2',4,6-tetrachlorqbiphenyl (5), 2,2',3',4,5-pentachlorobiphenyl ( 6), 2*2',3,4,5,6-hexachlorobiphenyl (7), 2,2,,3,4,4',5,,6-heptachlorobiphenyl (8), 2,2',3,3,,5,5',6,6/-octachlorobiphenyl (9), 2,2',3,3',4,4/,5,6,6'-nonachlorobiphenyl (10), and 2,2',3,3,,4,4/,5,5',6,6'-decachlorobiphenyl (11) to demonstrate the chromatographic separation.…”

“…However, the utility of photolysis for destruction of PCB's is limited by two major disadvantages. First, the "quantum efficiency" (the statistical number of molecules which react per photon of light absorbed) is extremely low for many congeners (6)(7)(8)(9)(10)(11). The quantum yield is usually particularly low in those compounds lacking an ortho chlorine but bearing meta or para substituents and also many of the highly chlorinated biphenyls.…”

“…Figure 1. Separation of a mixture of11 RGB's by capillary column gas chromatography. Initial column temperature of 50 °C for 3 min, followed by a temperature program at 3 °C min"1 to 250 °C.…”