Methyl site, chlorination

Although the 13C NMR provides quantitative information on the chlorination at the methyl site, it is less definitive for the backbone carbons. The multiplet centered at 44.3 ppm attributed to the methylene carbon in the main chain decreases at high chlorine contents as does the a-carbon peak. At the same time a close examination of the 13C NMR reveals the appearance of broad weak signals at about 54 and 68 ppm. These peaks may be due to chlorine substitution of the protons on the polymer main chain but this assignment is not definitive since the shift in peak position relative to the unchlorinated carbon is not as great as it would be expected for chlorine substitution. 

FTIR are accurate to about 5 and 10% respectively. Values obtained from 13C NMR are accurate to 10% at low values of chlorination and probably only 20% at higher degrees of chlorination. The average of the relative reactivities of the methyl, methylene and methine carbons to chlorination are 56%, 21% and 23% respectively in the case of chlorination with t-BuOCl, and 58%, 23% and 19% in the case of chlorination with S02C12. The reactivities of the different chlorination sites are therefore similar, although the distribution of chlorines on the methyl site differs, particularly at high chlorine contents. 

In another oudine, cellulose was complexed with cuprammonium ions (Nicoll and Conaway, 1943). Lately, laboratory-scale isolation has relied on polar aprotic solvents and solvent systems, e.g., dimethylsulfoxide, pyridine, Af,7V-dimethylacetamide-lithium chloride, and l-methyl-2-pyrrolidinone-lithium chloride (Baker et al., 1978 McCormick and Shen, 1982 Seymour et al., 1982 Arnold et al., 1994). These solvents have enabled such homogeneous17 reactions as O- and N-derivatization of cellulose and chitin (Williamson and McCormick, 1994) and selective site chlorination (Ball et al., 1994). Dimethylsulfoxide was the solvent in a homogeneous reaction of cellulose and paraformaldehyde, prior to isolation of purified cellulose (Johnson et al., 1975). In yet another outline, paraformaldehyde enabled superior quality extracts when the parent tissues were presoaked in this solution (Fasihuddin et al., 1988). 

The apparatus can theoretically sample to any depth. However, at depths greater than 100 m, it is logistically diflBcult to anchor and to retrieve. The apparatus could be used to monitor baseline trace metal levels, sewage and industrial metal outfalls, offshore dumping sites, and diffusion of heavy metals from polluted sediments. The concentration apparatus could also be adapted to monitor other compoimds such as methylated mercury, chlorinated hydrocarbons, amino acids, etc. by replacing the Chelex-100 in the columns with other resins specific for the compounds to be monitored. 

In general, if condensation polymers are prepared with methylated aryl repeat units, free radical halogenatlon can be used to introduce halomethyl active sites and the limitations of electrophilic aromatic substitution can be avoided. The halogenatlon technique recently described by Ford11, involving the use of a mixture of hypohalite and phase transfer catalyst to chlorinate poly(vinyl toluene) can be applied to suitably substituted condensation polymers. 

There are also certain disubstituted quinacridones which are used commercially. The two peripheral rings in such quinacridone systems (53) are partially chlorinated or methylated. In the sequence 57 - 58 - 53 (p. 455), possible substitution sites on the peripheral rings are indicated by dashes (see also tables of chemical structures in the appendix). 

This includes bioremediation cases of contaminated sites with several toxic and carcinogenic pollutants, such as petroleum hydrocarbons, PAHs, dichlorobenzene, chlorinated hydrocarbons, carbon tetrachloride, Dicamba, methyl bromide, trinitrotoluene, silicon-based organic compounds, dioxins, alkyl-phenol polyethoxylates, nonylphenol ethoxylates, and polychlorinated biphenyls. The following is a brief summary of each case. 

Kinetic results on the chlorination of aniline by A-chloro-3-methyl-2,6-diphenylpiperi-din-4-one (3) suggest that the protonated reagent is reactive and that the initial site of attack is at the amino nitrogen. The effects of substituents in the aniline have been analysed but product studies were not reported. Zinc bromide supported on acid-activated montmorillonite K-10 or mesoporous silica (100 A) has been demonstrated to be a fast, selective catalyst for the regioselective para-bromination of activated and mildly deactivated aromatics in hydrocarbon solvents at 25 °C. For example, bromobenzene yields around 90% of dibromobenzenes with an ortholpara ratio of 0.12. 

Selective radical bromination of the p-methyl group by elemental bromine is performed in solution either thermally, photolytically, or in the presence of radical initiators. The reaction does not lead to any change in molar mass or distribution, and the only potential side reaction, which has to be controlled by adjusting the reaction conditions, is debromination between two p-bromobenzyl moieties. Under similar conditions radical chlorination leads to substitution on the benzylic site as well as on the methylene and methyl groups of isobutene units, with changes in molar mass. 

---