Pyridine, as condensing agent

Jikei et al. have described the synthesis of aromatic HBPA copolymers by direct polycondensation of 3-(4-aminophenoxy)benzoic acid (AB monomer) and 3,5-bis(4-aminophenoxy)benzoic acid (AB monomer) in the presence of TPP and pyridine as condensation agents [69]. The structure of resulting polymers was confirmed... 

Both the monomers [2] and [5] were prepared either by reaction of acryloyl chloride with the steroids in the presence of an acid acceptor (Method A) or by the reaction of the steroids with acrylic acid, using N,N-dicyclohexylcarbodiimide and a catalytic amount of N N-dimethylamino-pyridine as condensing agents (Method B). 

More recendy, aramids have been obtained by direct polycondensation of aromatic dicarboxylic adds and aromatic diamines in amide solvents using triphenyl phosphite and pyridine as condensing agents. This method uses dicarboxylic acids which are easier to handle than acid chlorides and eliminates the additional step of converting the dicarboxylic adds into add chlorides. Lithium chloride and calcium chloride have also been added to these polymerization mixtures to increase polymer solubility. This method has been used to synthesize both flexible and rodlike polyamides with high inherent viscosity values (ie, up to 6.2 dL/g). It has also been shown that additional triphenyl phosphite ensures complete polymerization with... 

The preparation of aramids by direct polycondensation of aromatic diamines with aromatic dicarboxylic acids using triphenyl phosphite and pyridine as condensing agents has been well documented. This method was used here to polymerize the commercially available diamines, 4,4 -oxydianiline (ODA) and 1,4-phenylenediamine (PDA), with 10,11,15, and 16. Polymers obtained with this method formed fibrous precipitates on pouring the reaction mixtures into stirring methanol. Essentially quantitative yields were obtained for all systems evaluated. High molecular weight... 

Of the examples given above, pyridine and quinoline may serve both as condensing agents and as the solvent. 

Mono- or diacyl derivatives that undergo cyclization to benzoxazoles on heating or under the influence of dehydrating agents are formed as intermediates in this reaction [134, 452, 453, 459, 461 173], Phosphorus oxychloride [453, 457], boric anhydride [455, 461, 462], or polyphosphoric acid [134, 471] are used as condensing agents. In particular, 2-hydroxy-5-nitrobenzoxazole, used for the synthesis of antivirus medicines, has been obtained by the reaction of condensation of 4-nitro-2-aminophenol with (NH2)2CO in pyridine [474],... 

A variety of aldehydes—aliphatic, aromatic, and heterocyclic—have been condensed with hydantoin. Sodium acetate in a mixture of acetic acid and acetic anhydride as well as pyridine containing traces of piperidine serves as condensing agent. Reduction of the double bond is accomplished with phosphorus and hydriodic acid, ammonium sulfide, or stannous chloride, In a more recent modification, the hydantoins are synthesized from aldehyde or ketone cyanohydrins and ammonium... 

The reagent is used for the synthesis of phosphomonoesters of alcohols, particularly of nucleotides. It is coupled to the alcoholic component in pyridine using dicyclo hexylcarbodiimide (DCC) as condensing agent, as illustrated for the case of 5 -0-tritylthymidine. Acid hydrolysis eliminates the protective trityl group, and very mild... 

Feist-Benary synthesis. Formation of furans from a-halogeno ketones or ethers and 1,3-dicarbo-nyl compounds in the presence of pyridine. With ammonia as condensing agent, pyrrole derivatives are always formed as secondary products. 

The synthesis of a poly(etherimide) from BPTA was conveniently carried out in dimethylacetamide by condensing equimolar amounts (0.01 mol) of BPTA and l,12-bis(aminophenoxy)dodecane at 100 °C for 4 h. Imidisation was completed by adding 1 1 mix of acetic anhydride in pyridine as dehydrating agent... 

Triethylammonium salts of aryl H-phosphonates have been coupled to the 3 -OH of deoxynucleosides using pivaloyl chloride as condensing agent subsequent hydrolysis by aqueous pyridine gives nucleoside H-phosphonate building blocks... 

Bis(pentafluorophenyl) sulfite added to a soln. of N-r rFbutyloxycarbonylglycine in DMF containing 1 eq. pyridine, and stirred for 0.1-1 h at 20° - product. Y 96% (70% from pentafluorophenol with DCCI as condensing agent). There was no racemization with a-subst. derivs. F.e.s. A.V. Hina et al., Izv. Akad. Nauk SSSR Ser. Khim. 1988, 2816-8 with methyl pentafluorophenyl carbonate cf. Izv. Akad. Nauk LatvSSR Ser. Khim. 1988, 624. 

In a similar way, the synthesis of aromatic polyamides from aromatic diamines m-phenylenediamine, p-phenylenediamine, bis(4-aminophenyl)methane, and bis(4-aminophenyl)ether and dicarboxylic acids such as isophthalic and tereph-thalic acid was performed in a household microwave oven [72]. The polycondensation was carried out in an JV-methyl-2-pyrrolidone (NMP) solution in the presence of triphenyl phosphite (TPP), pyridine, and lithium chloride as condensing agents to produce a series of polyamides with moderate inherent viscosities of 0.21-0.92 dL/g within 30-50 s. However, no marked differences in molecular weight distribution and inherent viscosities between the polyamides produced by conventional (60 s, 220 °C) and microwave methods were found [72]. 

A variety of condensing agents, such as triphenylphosphite/pyridine [4,5] and DBOP/triethylamine [6], which are used in amounts equivalent to functional groups on monomers, had been developed by the 1980s, whereas new catalysts that promote condensation polymerization exactly with a catalytic amount were developed in the last decade. 

The yield is increased to 86 per cent using pyridine as the condensing agent. Sekera and Marvel, J. Am. Chem. Soc. 55, 345 (i933)-... 

R C(NHj) =CHCOjC2H5/ The synthesis of furans by this method has been improved and extended by substituting pyridine for ammonia as the condensing agent and by using a,/3-dichloroethyl ether as a source of chloroacetaldehyde/ ... 

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