Chlorine siting

Replacement of Labile Chlorines. When PVC is manufactured, competing reactions to the normal head-to-tail free-radical polymerization can sometimes take place. These side reactions are few ia number yet their presence ia the finished resin can be devastating. These abnormal stmctures have weakened carbon—chlorine bonds and are more susceptible to certain displacement reactions than are the normal PVC carbon—chlorine bonds. Carboxylate and mercaptide salts of certain metals, particularly organotin, zinc, cadmium, and antimony, attack these labile chlorine sites and replace them with a more thermally stable C—O or C—S bound ligand. These electrophilic metal centers can readily coordinate with the electronegative polarized chlorine atoms found at sites similar to stmctures (3—6). 

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. 

Zheng L, Settle M, Brubaker G, Schmitt D, Hazen SL, Smith JD, Kinter M (2005) Localization of Nitration and Chlorination Sites on Apolipoprotein A-I Catalyzed by Myeloperoxidase in Human Atheroma and Associated Oxidative Impairment in ABCA1-Dependent Cholesterol Efflux from Macrophages. J Biol Chem 280 38... 

Figure 5. Formation of tertiary chlorine sites in the polymerization...

Preparation of resin-hound amine 19 A 1 m tBuOK/THF solution (300 mo was added to a solution of diol 17 (300 mol%) in dry THF (2.5 mL/mmol) at 0 °C. The solution was stirred at 0 °C for 45 min and for 3 h at rt Merrifield resin (100 mol% of chlorine sites, loading 1.35 mmol g ) was added, and the suspension was shaken for 3.5 days at rt. After filtration, the resin-hound tert-aUcyl alcohol 18 was washed with THF (four times), 1 1 DMF/water (twice), DMF (twice), THF (twice), and CH2CI2 (twice), and dried. 

Chlorine SSNMR parameters have been reported for other selected anhydrous alkaline earth chlorides. Stebbins and Du ° acquired a Cl NMR spectrum of BaCl2 in their study of chlorine-containing glasses, and reported two chlorine sites with chemical shifts of 124 and 219 ppm (w.r.t. 1 M NaCl(aq)) and Cq values of 3.5 and 3.95 MHz, respectively. In a similar glass study, Stebbins and co-workers analysed CaCl2, reporting a chemical shift of 122 ppm (w.r.t. 1 M NaCl(aq)) and a Cq of 2.1 MHz. On the basis of the chemical shifts now known for chloride ions, it seems likely that the chemical shift of 2880 ppm reported for AICI3 is erroneous. 

Polymerization occurs in heterogeneous phase, and the catalytic activity strongly depends on the structure and the quality of the microcrystals of titanium chloride which are used. In titanium chloride, the valence of titanium is six (see Fig. 1.10) and, on the edges of the crystal, there are empty chlorine sites which play the role of active centres. Titanium behaves like an electron attractor with respect to the double bond of the monomer. The polymerization process is rather complex we shall sum it up by saying simply that the end of a growing chain is attached to an empty site of a titanium atom and in this way may react upon monomers attached to other empty sites, with formation of a longer chain. 

The mechanism proposed by Kennedy requires that allylic or tertiary chlorines be attached to the first polymer chain. Chlorobutyl rubber, PVC, and other chlorine-containing polymers usually have 1-2% of mers with chlorines in the required reactive positions. The halogen-containing polymer is dissolved in an inert but polar solvent in the presence of an organoaluminum catalyst and a cationically polymerizable monomer, such as styrene, and polymerization is effected, usually at about — 50 C. The major point is that the second component chains can be initiated only at an active chlorine site on the first polymer. 

The block copolymerization involving 3-pinene has also been investigated [37]. This strategy involved the synthesis of a poly(pPIN) bearing tertiary chloride end groups and the attachment of poly(THF) blocks by their activation, as shown in Fig. 2.9 for chains with a single chlorinated site, thus giving a di-block structure. 

Epoxy compounds. Epoxy compounds function both as plasticizers and stabilizers in flexible and semirigid PVC. As stabilizers, epoxies react with liberated HCl. In addition, they react with the polymer chain at labile-chlorine sites—either directly or catalytically by increasing the reactivity of the labile-chlorine site with metal salt stabilizers. Most epoxy stabilizers are derived from unsaturated fatty oils and fatty acid esters. Epoxidized soybean and linseed oils and epoxy tallate are commonly used products. Epoxy tallate also increases light stability. Epoxy compovmds can be formulated with metallic liquid stearates and, thus, can be sold to compounders as a one-package system if a constant ratio of stabilizer-to-epoxy is acceptable. However, since these epoxy compounds are also plasticizers, the balance of the formulation must be adjusted for this effect. 

Cationic grafting from PVC often occurs at structural irregularities on the backbone. A similar uncertainty regarding the nature and concentration of the active centres in the grafting reaction surrounds the use of chlorinated and brominated butyl rubber backbones, chlorinated polycyclopentadiene, and chlorinated st rene-butadiene copolymers." The graft reaction of st3o ene into chlorosulphonated polyethylene appears to occur at tertiary chlorine sites and not at the sulphonyl chlorides. ... 

Triazines. The application of sulfone as a safety-catch linker has also been demonstrated by Chang and coworkers in their orthogonal synthesis of highly pure trisubstituted triazines 37 (Scheme 12.9). Polystyrene thiophenol resin was hrst coupled with the triazine 33 to yield the polymer-bound resin 34. The chlorinated site... 

Titaniiun atoms on the lateral faces or edges of the a-TiCL crystals may be adjaeent to vacant chlorine sites within the crystal stracture. The active site is then formed when the titanium chloride bond is alkylated by the reaction with the alkylaluminium co-catalyst. This results in the formation of a titanium-... 

---