Wurtz condensation reaction

At present, the only synthetic method leading to high molecular weight polysilanes is based on the Wurtz condensation reaction between dichlorodisubstituted silanes and alkali metals (low molecular weight oligomers were also prepared by dehydrogenation of secondary... 

For maximum yield, care must be taken to ensure that the rate of addition of the reagents is not excessive. If this occurs then the alkyllithium is generated in the presence of significant amounts of unchanged alkyl halide and the Wurtz condensation reaction may be favored. The rate of formation of the alkyllithium is proportional to the surface area of the lithium metal and so at a constant rate of addition the Wurtz condensation is reduced by an increase in the lithium surface available for reaction. 

In both cases Wurtz condensation reactions do not allow high chain end functionality to be obtained. 

The transformation of anionic living chain ends into a Grignard less reactive chain end allows the Wurtz condensation reaction to be completely eliminated (75). Yields as high as 95% were obtained by using this procedure. 

Organic bromides seem to give the best results. The lower yields with iodides are almost certainly due to increased probability of a Wurtz condensation reaction taking place between the organolithium species and the iodide. 

Another condensation method was investigated by Carothers and co-workers and reported in 1930. They reacted decamethylene dibromide with sodium in a Wurtz-type reaction but found it difficult to obtain polymers with molecular weights above 1300. 

Poly-p-phenylene has been prepared in the laboratory by a variety of methods, including the condensation of p-dichlorobenzene using the Wurtz-Fittig reaction. Although the polymer has a good heat resistance, with decomposition... 

Initially, PPV was synthesized by condensation reactions that can be found in most introductory organic textbooks. Most commonly, reactions such as the Wittig, Knoevenagel, Wurtz-Wittig, or McMurray, as well various dehydrohalo-genation reactions, were employed that yielded oligomers or low molecular weight PPV. 

For poly silanes made by Wurtz reaction, the presence of functional groups in polysilane polymers is limited by the vigorous conditions of the sodium condensation reaction. Any substituents that react with molten sodium metal must therefore be introduced after the polymer is synthesized. Halogen atoms can be introduced into alkenylpolysilanes by HBr or HC1 addition reactions, as shown for the 3-cyclohexenyl-ethyl polymers in equation (21).37 Chlorine atoms have also been introduced into arylpolysilanes by chloromethylation, in which -CH2C1 groups are substituted onto phenyl rings in the polymer.38... 

Wurtz synthesis. The condensation reaction between two halides brought about by the action of metallic sodium, as in... 

The trivial name of the reaction was applied by Wurtz in 1872, and stems from the trivial name of the dimer resulting from the acid-catalyzed self-reaction of acetaldehyde (equation 1). In time, the term came to be applied to the analogous self-condensation reactions of ketones, the first known example of which was the acid-mediated dimerization of acetone, discovered in 1838. The first use of a base as a catalyst for the aldol reaction was in the reaction of furfural with acetaldehyde or acetone (equation 2). This example also illustrates the first example of a mixed aldol reaction, a process that came to be known as the Claisen-Schmidt condensation. ... 

Condensation of arsenic trihalides with alkyl or aryl halides in the presence of metallic sodium, analogous to a Wurtz-Fittig reaction, leads to trialkyl- and triaryl-arsines. E.g., tribenzylarsine is obtained by prolonged boiling of benzyl chloride and arsenic trichloride in ether containing sodium and a little ethyl acetate 501 tripropylarsine is obtained similarly from propyl chloride, arsenic... 

Riccitiello et al. have synthesized preceramic polymers with Si—B bonds in their backbones by a Wurtz analogous reaction of dialkyldichlorosilanes and boron halides, either with or without adding methyl iodide for the control of molar masses of the condensation products. Most of the polymers obtained are solid, and soluble in hydrocarbons. Even though the Wurtz reaction is not specific, the IR spectra of the polymer clearly indicate that Si—B bonds have formed preferentially, but do not provide any evidence for the presence of Si—Si or B—B bonds. Based on these results the authors suggest that the backbones generated mainly consist of an alternating sequence of Si and B [55-59]. 

Multiblock polysilane copolymers can be made by modified Wurtz-type condensation reactions of dichlorosilanes [34] however, it is difficult to obtain simple di-block polysilane copolymers. The electroreductive method in this study provides a new procedure to synthesize well-controlled di-block polysilane copolymers. It is possible to control the sequence length of each block by tuning supplied electricity and monomer concentrations. 

Triphenylphosphine, the indispensable auxiliary for Wittig olefmations, is mass-produced by direct condensation of phosphorus trichloride with phenylsodium. The latter is generated in situ from chlorobenzene and sodium in a kind of Wurtz-Fittig reaction. Congeners such as the methoxymethoxy-armed phosphine 49 or tri-2-furylphosphine (50) can be conveniently prepared by metalation of the (het)aromatic precursor and its subsequent condensation with phosphorus trichloride or a trialkyl phosphite (Scheme 1 0). " ... 

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