Pyridine phosgene

A variation of this process involves the formation of a preformed pyridine-phosgene complex. Polymerisation will then be effected by adding a solution of bis-phenol A. 

Similarly, with 1,2-ethanedithiol in the presence of pyridine, phosgene gives 2-oxo-l, 3-dithiolane [1781a] ... 

The reaction may be carried out in the presence of pyridine that acts as a catalyst and as an HCl scavenger. Often, a chlorinated solvent is used as a diluent for the pyridine. Phosgene is bubbled through a solution of the diphenol at 25-35 The pyridine hydrochloride precipitates out and, after washing the pyridine solution with dilute HCl and water, the polymer is precipitated with a nonsolvent. 

Pyridine-phosgene adduct l-[2-(Chloroformyl) -2-azacyclohexa-3,5-dienyl] pyridinium chloride (2-DHPP)... 

Chloroethyl isocyanate 174 is the major product obtained when aziridine is allowed to react with an equivalent amount of 1 1 triethylamine-phosgene complex 175 [108] or 2 1 pyridine-phosgene complex 177 [109]. Aziridine carbamoyl chloride 176 was postulated as a transient intermediate in this reaction. Attempts to trap this elusive species as the triethylammonium or pyridinium salt have been unsuccessfiil [109]. 

The historical direct reaction route, which utilised phosgenation of a solution of BPA in pyridine, proved inefficient commercially because of the need for massive pyridine recycle. Calcium hydroxide was used as an HCl scavenger for a period of time. In the historical transesterification process, BPA and diphenyl carbonate are heated in the melt in the presence of a catalyst, driving off by-product phenol, which is recycled to diphenyl carbonate. Using a series of reactors providing higher heat and vacuum, the product polymer was eventually produced as a neat melt. 

In another method, phosgene is gradually passed into 1,2-propylene glycol (9). The chloroformate is washed, dried, and distilled at 266 Pa (2 mm Hg) and added slowly to a mixture of aHyl alcohol and pyridine below 15°C. The purified monomer 1,2-propylene glycol bis(aHyl carbonate) (C H O ) heated with lauroyl peroxide at 70°C gives a hard clear, polymer. 

Carbazole-9-carbonyl chloride [73500-82-0J M 300.0, m 100-103 , 103.5-104.5 . Recrystd from C6H6. If it is not very pure (presence of OH or NH bands in the IR) dissolve in pyridine, shake with phosgene in toluene, evaporate and recrystallise the residue. Carry out this experiment in a good fume cupboard as COCI2 is very TOXIC, and store the product in the dark. It is moisture sensitive. The amide has m 246.5-247 , and the dimethylaminoethylamide hydrochloride has m 197-198 . [Weston et al. J Am Chem Soc IS 4006 1953.]... 

Polycarbonates were first prepared by Einhom in 1898 by reacting the dihydroxybenzenes, hydroquinone and resorcinol, separately with phosgene in solution in pyridine. The hydroquinone polycarbonate was an infusible and insoluble crystalline power whereas the resorcinol polymer was an amorphous material melting at about 200°C. The third dihydroxybenzene, catechol, yields a cyclic carbonate only, which is not surprising bearing in mind the proximity of... 

Typically in such a process the bis-phenol A is dissolved in about ten times its weight of pyridine and vigorously stirred at 25-35°C. Phosgene is then bubbled into the solution and in a few minutes the pyridine hydrochloride starts to precipitate. As polymer is formed the viscosity of the solution increases and eventually becomes too great for stirring. The polymer is then recovered by the addition of a solvent such as methyl alcohol which dissolves the pyridine hydrochloride but precipitates the polymer. 

Because of the cost of pyridine the phosgenation process may be carried out with a mixture of pyridine and a non-hydrohalide-accepting solvent for the polymer and the growing complexes. Suitable solvents include methylene dichloride, tetrachlorethane and chloroform. Although unsubstituted aromatic hydrocarbons may dissolve the solvent they are not effective solvents for the acid chloride-pyridine complexes. 

Dichlorocarbene, generated in a variety of ways, was shown to deoxygenate pyridine iV-oxide, being itself oxidized to phosgene. 

One of a variety of syntheses of the antipsychotic agent bro-foxine (50) begins with a Grignard reaction on methyl anthra-nilate. The resulting product ( ) is reacted with phosgene in pyridine and the synthesis is completed by bromination in acetic acid to give brofoxine. 

In the formation of tert-butyl azidoformate by the addition of phosgene to alcohols followed by the addition of Na nitride or hydrazoic acid in the presence of pyridine, reaction of phosgene with the azide can cause the formation of expl carbazide (Ref 9)... 

With base (e.g., pyridine) the reaction rate is enhanced. No thioamides could be obtained starting with ketonitrones. If C-phenyl-TV-methylnitrone is treated with thio-phosgene instead of a thioazolide, only N-methylbenzamide (73%) is formed, but no thioamide. 170 ... 

A quite simple way to form the oxazolo[3,4- ]pyridine or thiazolo[3,4- ]pyridine ring system is to build the five-membered ring, respectively, starting from a 2-hydroxymethyl-piperidine or 2-thiomethyl-piperidine. The reaction of the latter compounds with aldehydes, acetals, phosgene, carbonates, or synthetic equivalents have been known for years and will therefore not be detailed here. Representative and typical examples are summarized in Table 10. 

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