Precursor route synthesis

In this work, we report a new phase of ZrW, 6Moo40g (hereafter 8 - ZrW, 6Moo40g form) occurring during the crystallizing process in the precursor rout synthesis [13]. It is a... 

Poly(arylene vinylenes). The use of the soluble precursor route has been successful in the case of poly(arylene vinylenes), both those containing ben2enoid and heteroaromatic species as the aryl groups. The simplest member of this family is poly(p-phenylene vinylene) [26009-24-5] (PPV). High molecular weight PPV is prepared via a soluble precursor route (99—105). The method involves the synthesis of the bis-sulfonium salt from /)-dichloromethylbenzene, followed by a sodium hydroxide elimination polymerization reaction at 0°C to produce an aqueous solution of a polyelectrolyte precursor polymer (11). This polyelectrolyte is then processed into films, foams, and fibers, and converted to PPV thermally (eq. 8). 

The sulfonium precursor route may also be applied to alkoxy-substituted PPVs, but a dehydrohalogenation-condensation polymerization route, pioneered by Gilch, is favored 37]. The polymerization again proceeds via a quinomethide intermediate, but die syndicsis of the conjugated polymer requires only two steps and proceeds often in improved yields. The synthesis of the much-studied poly 2-methoxy-5-(2-ethylhexyloxy)-l,4-phenylene vinylene], MEH-PPV 15 is outlined in Scheme 1-5 33, 35]. The solubility of MEH-PPV is believed to be enhanced by the branched nature of its side-chain. 

Van Boom and co-workers published an expeditious route to chiral oxepines with monosaccharide derivatives as precursors. The synthesis was accomplished by treatment of 210 with alkoxyallenes 8 under Rutjes s optimized reaction conditions (Scheme 8.50) [121]. 

In 1998 it was revealed that allenylidene-ruthenium complexes, arising simply from propargylic alcohols, were efficient precursors for alkene metathesis [12], This discovery first initiated a renaissance in allenylidene metal complexes as possible alkene metathesis precursors, then it was observed and demonstrated that allenylidene-ruthenium complexes rearranged into indenylidene-ruthenium intermediates that are actually the real catalyst precursors. The synthesis of indenylidene-metal complexes and their efficient use in alkene metathesis are now under development. The interest in finding a convenient source of easy to make alkene metathesis initiators is currently leading to investigation of other routes to initiators from propargylic derivatives. 

The Durham precursor route to polyacetylene is an excellent example of the application of organic synthesis to produce a precursor polymer whose structure is designed for facile conversion to polyacetylene. Durham polyacetylene was first disclosed by Edwards and Feast, working at the University of Durham, in 1980 227). The polymer (Fig. 6 (I)) is effectively the Diels-Alder adduct of an aromatic residue across alternate double bonds of polyacetylene. The Diels-Alder reaction is not feasible, partly for thermodynamic reasons and partly because it would require the polymer to be in the all m-conformation to give the required geometry for the addition to take placed 228). However, the polymer can be synthesised by metathesis polymerization of the appropriate monomer. 

PolyQj-Phenylene) is probably the most thermally and oxidatively stable conducting polymer known and has been of interest to polymer scientists both for its conducting properties and for its stability. Its synthesis by step-reaction polymerization or by chemical or electrochemical oxidation invariably gives powders or rather poor quality films, so that a precursor route would be very attractive. 

Precursor routes, other than the bis(sulfonium salt), have also been explored for the synthesis of PPV. For example, PPV was synthesized using sulfoxide and sulfone analogs, and the detailed syntheses of these intermediates are outlined in Scheme 43 [169,170]. While monomers 39 and 40 are insoluble in water, they... 

As utilized in the synthesis of PPV-based polymers, soluble precursor routes have been developed for the synthesis of various heterocyclic Jt-conjugated polymers. The two most widely employed of these methods for heterocycle formation, shown in Scheme 66, center around ring closure of pre-polymers containing diacetylene 65 or 1,4-diketone units 66 [335-339]. The synthesis of heterocyclic structures from 1,4-diketones has been a known transformation in organic chemistry for decades. While once mainly used for monomer preparation through various cyclizations, it is now being employed to make heterocycle-containing polymers and copolymers [340-342]. 

For the synthesis, desired amounts of cation salts were dissolved in distilled water/organic carrier solutions to obtain exact stoichiometry. In the organic precursor route with organic/polymcric carrier materials, the amounts of carrier materials were determined to obtain 1 1 cation to organic molecule ratio in the solution. 

Conjugated polymers like poly(l,4-phenylene-vinylene), PPV, or more generally Poly(arylene-vinylenes), PAVs have evoked considerable interest as electrically conductive and nonlinear optical materials. More recently, electroluminescence properties of PPV have attracted substantial attention, since it was first reported in 1990. Direct synthesis of PPV has been limited by its insolubility. Hence, the most commonly used routes are based on soluble polymer precursors or soluble conjugated precursors. The latter process is also commonly referred to as the sulfonium-based polyelectrolyte precursor route. PPV thin films from these solution-based routes, however, have problems related to contamination by solvents and oxidative defects in the polymer. C VP is an alternate method for the deposition of high quality thin films of PPV. Reported first by Iwatsuki et al., it was investigated for electroluminescence applications by Staring et al. ... 

The most widely used route to purines has undoubtedly involved the addition of an imidazole ring to an appropriate pyrimidine. This particular route has probably dominated the early literature because of the relative ease of synthesis of the requisite pyrimidines compared with the lack, until recently, of useful routes to imidazole precursors. The synthesis of pyrimidines has been exhaustively reviewed <62HC(16)l) and full details have been provided of the synthesis of the specfic pyrimidines used in purine synthesis. The pyrimidine moiety... 

Hybrid, chelate, or molecularly modified precursor routes also utilize alkoxide compounds for the B-site species. Unlike true sol-gel processes, these routes rely on molecular modification of alkoxide compounds through reactions with other reagents, namely chelating ligands, such as acetic acid, acetylacetone, or amine compounds. Despite this difference, chelate processes stiU share several common attributes with methoxyethanol-based sol-gel processes, most importantly, the formation of oligomeric species during solution synthesis. 

Table 11.10 is a summary of the different conversion schemes and conditions for thermochemical ethanol formation discussed here. The primary routes to ethanol and ethanol precursors from synthesis gas are evident. It remains to be determined whether any of these technologies can be developed to produce low-cost thermochemical ethanol. 

Effects of composition ratios and process parameters in silica precursors The synthesis route of silica membranes is schematically given in the upper part of Fig. 8.25. Tetraethylorthosilicate (TEOS) is not hydrolysed directly in water. To obtain a better control, the hydrolysis and condensation reaction rates were decreased by first diluting the TEOS in alcohol (ethanol) and then adding to this mixture a water-acid (HNO3) mixture dropwise under vigorous stirring. The mixture was kept for 3 h at 86°C under reflux conditions. Note that even with this procedure locally and for short times a relative large water excess exists in the reaction zone. 

The Prins reaction with formaldehyde is a well-known route to prostaglandins using bicyclic lactone 3 as a precursor. One synthesis of this lactone14 started this sequence with a Prins reaction. Treatment of norbomadiene with paraformaldehyde in the presence of formic acid produced a mixture of epimeric diformates in 67% yield which were transformed in several steps into lactone 3. A second synthesis starts with the unsaturated bicyclic lactone which undergoes attack by the oxonium ion both regio- and stereoselectively from the less hindered face of the double bond, trims Addition of the nucleophilic acetate generates the lactone 3 as the bisacetate derivative15. 

To obtain soluble PPP homopolymers, two main strategies have been used. The first is the so-called precursor route. It consists in starting from soluble materials that are chemically or thermally converted into fully aromatic polymers by elimination of leaving groups. An example is the precursor route utilized by Ballard et al. [89] (Fig. 9.8). Synthesis is based on 5,6-cz s-dihydroxycyclohexa- 1,3-diene as starting material and originating from the bacterial oxidation of benzene by Pseudomonas... 

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