Sulfur heterocyclic polymerization

Sulfur-containing heterocycles have rarely been used in ROP even though they are interesting for a variety of biomedical applications. Heterocycles higher than four membered cannot be polymerized by an anionic mechanism. While the cationic polymerization of thietanes leads to branched polymers or crosslinked networks, higher sulfur heterocycles were never used in the synthesis of hyperbranched polymers by ROP, since the synthesis of linear polymers is already... 

Nitroaniline reacts almost explosively [1], and 4-nitroaniline, 4-nitroacetanilide, aminonitrobiphenyls, aminonitronaphthalenes and their various derivatives [2], as well as some nitro-N-heterocycles [1,2], also react vigorously. 4-Nitroanilinium sulfate and 4-nitroaniline-2-sulfonic acid and its salts also generate foams when heated without sulfuric acid. The mechanism is not clear, but involves generation of a polymeric matrix foamed by sulfur dioxide and water eliminated during the reaction [1]... 

Naphthenic acids and sulfur- and nitrogen-containing heterocycles and naphthenoaromatic compounds can all be found in distillate fuel fractions. Degradation through condensation type reactions rather than through free-radical-initiated polymerization can be more common in distillate fuel. Because of this, degradation products are often quite complex in nature and structurally diverse. 

Comparable to thiophene, pyrrole is a five-membered heterocycle, yet the ring nitrogen results in a molecule with distinctly different behavior and a far greater tendency to polymerize oxidatively. The first report of the synthesis of polypyrrole (PPy) 62 that alluded to its electrically conductive nature was published in 1968 [263]. This early material was obtained via electrochemical polymerization and was carried out in 0.1 N sulfuric acid to produce a black film. Since then, a number of improvements, which have resulted from in-depth solvent and electrolyte studies, have made the electrochemical synthesis of PPy the most widely employed method [264-266]. The properties of electrosynthesized PPy are quite sensitive to the electrochemical environment in which it is obtained. The use of various electrolytes yield materials with pronounced differences in conductivity, film morphology, and overall performance [267-270]. Furthermore, the water solubility of pyrrole allows aqueous electrochemistry [271], which is of prime importance for biological applications [272]. 

As discussed in Chapter 3, some other inorganic polymers also contain phosphorus atoms.47 They are derived from the basic phosphazene structure described in Chapter 3, and are obtained by the ring-opening polymerization of heterocyclic compounds in which one of the disubstituted phosphorus atoms is replaced by another moiety. Specifically, introduction of a carbon atom can yield poly(carbophosphazenes), with the repeat unit shown in 6.49. Alternatively, replacement with a sulfur atom can yield a poly(thiophosphazene) (6.50). Relatively little is known about these polymers at the present time 47... 

Many sulfur-containing heterocycles have potential as materials for inducing electrical conductivity, for example materials based on polymeric thiophenes have been examined for possibilities in electrical conductivity <90SM327>, and cyclopenta- and benzobis-1,3-dithioles and benzothiadiazoles... 

The work of Nazarov on vinyl ethynyl carbinols involves condensation of vinylacetylene with ketones in the presence of caustic potash and also their conversions, many of which are catalytic in nature. A review of his work involving polymerization, isomerization, hydrogenation, and other conversions was published by him (252). Hydration of divinylacetylenes in methanol solution in the presence of mercuric sulfate and sulfuric acid gave vinyl alkyl ketones. These can be reacted with hydrogen sulfide, amines, etc., to yield heterocyclic compounds. Substituted vinyl alkyl ketones underwent spontaneous cyclization to cyclopentenones. Nazarov summarized a decade of this research in this field in 1951 (253). His general review of organic syntheses based on acetylene is also of interest in this connection (254). 

The reaction of sulfur-containing heterocyclic compounds such as thiophenes and thiazoles (Eq. 68) is specifically enhanced by addition of Cul, while the role is not yet definitive [135]. The use of a bulky phosphine ligand such as P(f-Bu)3 also promotes the arylation [141]. 2-Iodothiophenes are polymerized to produce polythiophenes (Eq. 69) [142]. 

Gates DP (1997) The synthesis, structure, reactivity and polymerization behavior of boron- and sulfur-nitrogen-phosphorus heterocycles and highly strained chalcogen- and boron-bridged [1], ferrocenophanes. PhD thesis, University of Toronto... 

A further potential concern in gas processing is the presence of carbon disulfide (CS2) or carbonyl sulfide (COS) in the natural gas. These may be from natural sources or are occasionally contributed from the use of carbon disulfide to remove sulfur blockages from sour gas wells or components of the Girbotol plant. These sulfur compounds react with monoethanolamine to yield complex thiazolidine and oxazolidine heterocycles and polymerization products of these which are not dissociated in the regeneration step of the gas cleaning plant [28] (Eq. 9.15). 

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