Model compounds chlorination

Figure 5. Comparison of TA100 mutagenic activities of XAD-2/ethyl ether extracts of treated water and chlorinated model compounds. O, treated water , amino acids A, humic acids (Fluka AG) , humic acids (aquatic) and A, humic acids (peat bogs). (Reproduced with permission from reference 16. Copyright 1986 Water Research Centre.)...

Halides and, in particular, chlorinated compounds are often present in toxic wastes and some of them, like polychlorinated biphenyls or dioxins, are extremely stable under oxidation conditions. Various chlorinated model compounds serve as model feeds in SCWO investigations. 

Caraculacu et al. [48] also quantitatively determined allylic chlorines in PVC by isotopic exchange with SO Cl2. The selective exchange of chlorine in the polymer was verified by experiments with model compounds. The number of allylic chlorines in PVC was found to be between 0.12 and 0.16 for 100 monomer units. 

Organic metal salts retard the development of color in the thermal treatment of PVC, and their ability to react selectively with allylic and tertiary chlorine structures according to Eq. 23 has been demonstrated with model compounds [19,32,113,115]. 

Initiator efficiency in terms of conversions and molecular weights were similar for model compounds and polymerizations. The influence of chlorine and bromine-containing counterions on polymerization was similar to that found in model study. 

The 50.31 MHz 13C NMR spectra of the chlorinated alkanes were recorded on a Varian XL-200 NMR spectrometer. The temperature for all measurements was 50 ° C. It was necessary to record 10 scans at each sampling point as the reduction proceeded. A delay of 30 s was employed between each scan. In order to verify the quantitative nature of the NMR data, carbon-13 Tj data were recorded for all materials using the standard 1800 - r -90 ° inversion-recovery sequence. Relaxation data were obtained on (n-Bu)3SnH, (n-Bu)3SnCl, DCP, TCH, pentane, and heptane under the same solvent and temperature conditions used in the reduction experiments. In addition, relaxation measurements were carried out on partially reduced (70%) samples of DCP and TCH in order to obtain T data on 2-chloropentane, 2,4-dichloroheptane, 2,6-dichloroheptane, 4-chloroheptane, and 2-chloroheptane. The results of these measurements are presented in Table II. In the NMR analysis of the chloroalkane reductions, we measured the intensity of carbon nuclei with T values such that a delay time of 30 s represents at least 3 Tj. The only exception to this is heptane where the shortest T[ is 12.3 s (delay = 2.5 ). However, the error generated would be less than 10%, and, in addition, heptane concentration can also be obtained by product difference measurements in the TCH reduction. Measurements of the nuclear Overhauser enhancement (NOE) for carbon nuclei in the model compounds indicate uniform and full enhancements for those nuclei used in the quantitative measurements. Table II also contains the chemical... 

Our 13C NMR analysis (2) of the E-V copolymers obtained via the (n-Bu)3SnH reduction of PVC led to k /kr=1.31 0.1 in excellent agreement with the kinetics observed for the removal of chlorines from m- and r-DCP. We also found no W diads in those E-V copolymers made by removing more than 80% of the chlorines from PVC. This observation is confirmed in the (n-Bu)3SnH reduction of DCP where the chlorines in this PVC diad model compound were found to be 4 times easier to remove than the isolated chlorines in 2-chloropentane, 2-, and 4-chlorooctane. 

The excellent agreement between the simulated and observed reduction of PVC with (n-Bu)3SnH means that both DCP and TCH are appropriate model compounds for the study of PVC reduction. DCP is useful to obtain kinetic information on the relative reactivities of m- and r-diads and W and EV diads. Reduction of TCH yields the relative reactivities of the central and terminal chlorines in the VW triads. 

The experiments we have so far described have been used to study nuclei with spin I = Vi ( ll, 13C, 31P). Our model compounds 1 and 2 contain two further atoms (oxygen and chlorine), which have no NMR-active isotope with spin Vi. Oxygen does however have an NMR-active isotope with spin I = 5/2 but very low natural abundance (0.037%) this is 170. Chlorine has two NMR-active isotopes 35C1 (I = 3/2,75.53%) and 37C1 (I = 3/2,24.47%). 

Use of the resins with samples containing free chlorine residual is not recommended. Cheh (35) suggested that chlorine may produce mutagenic artifacts on XAD-4. Our experiment with 2-mg/L chlorine residual appeared to promote the release of irreversibly adsorbed spiked standards Six model compounds were recovered at levels several times higher than those observed in normal blank runs. In addition, many resin artifacts were eluted after exposure to this chlorine level, primarily aromatic and aliphatic acids, aldehydes, and ketones. Stoichiometric dechlorination (ferrous ion) is therefore recommended in order to avoid cross contamination between samples and inclusion of undesirable resin artifacts in the residue to be bioassayed. 

The precursors of mutagenicity produced by chlorination seem to be widespread, naturally occurring substances. If the precursors can be identified, identification of their chlorination products may help to elucidate the nature of the mutagenic activity in treated water. Thus, a complementary approach to that just described involves laboratory chlorination of naturally occurring model compounds at concentrations and conditions that simulate treatment chlorination. The reaction products were first tested for mutagenic activity to identify possible precursors of mutagenicity produced during treatment chlorination. The products were then analyzed by GC-MS and HPLC to try to identify the compounds formed. 

Chlorination of Mixtures of Model Compounds. A laboratory chlorination technique that was compatible with the XAD concentration technique and the mutagenicity assay was developed. Thus, a relatively long chlorine contact time in comparison to sampling time was used to complete the reaction before sampling and to achieve a low residual... 

The concentrations of the solutions were selected to give a realistic level of total organic carbon (i.e., approximately 3 mg/L). The solutions were adjusted to pH 6.2 with phosphate buffer. They were then chlorinated for 24 h at room temperature in the dark with sodium hypochlorite to a residual of <1 mg/L of total available chlorine. The chlorine demand of the solutions was determined in preliminary experiments prior to chlorination of larger samples for concentration by XAD-2 resin adsorption and mutagenicity testing. Corresponding extracts of unchlorinated solutions of the model compounds were also prepared and tested. 

None of the extracts from unchlorinated model compounds were significantly different from the negative controls. Extracts of chlorinated purines-pyrimidines and chlorinated nucleosides-nucleotides were also found to be not significantly mutagenic. However, the extracts of all three chlorinated humic acids and the chlorinated amino acids were... 

The concentrations of amino acids in the buffered aqueous solutions (pH 6.2) were selected to give a total organic carbon content of 1-3 mg/L, and chlorination conditions were as described for the chlorination of mixtures of model compounds. The chlorinated solutions were concentrated by XAD-2 adsorption/ethyl ether elution, tested for mutagenicity, and analyzed by GC-MS. 

Masse, R., Messier, F., Peloquin, L., Ayotte, C. Sylvestre, M. (1984). Microbial biodegradation of 4 chlorobiphenyl, a model compound of chlorinated biphenyls. Applied and Environmental Microbiology, 47, 947-51. 

---