Tertiary amines reaction with, phosgene

Tertiary amines react with phosgene to give symmetrical tetrasubstituted ureas (Eq. 28). (See Table II.) This reaction probably involves the intermediate... 

Diphenyl carbonate, an alternative source of the carbonate group to phosgene, may be obtained by reacting phenol with phosgene in acqueous caustic soda solution, the reaction being accelerated by tertiary amines. The diphenyl carbonate can be purified by redistillation. 

Reaction of Tertiary Amines with Phosgene to Give Symmetrical Tetrasubstituted Ureas... 

Simple isocyanates containing up to twelve carbon atoms are best prepared by a vapor-phase reaction of phosgene and a primary amine reported in 1950. The reaction occurs without a catalyst at 240-350° to form carbamyl chlorides from which the isocyanates are obtained by refluxing in an inert solvent or by treating with a tertiary amine. Over-all yields range from 58% to 88%. Secondary amines are converted to disubstituted carbamyl chlorides, RjNCOCl. ... 

Scheme 117 Reaction of phosgene with tertiary alky amines.

The kinetics of the reactions of phosgene with tertiary amines (NEt3, NPtj, NPhEt or NEtjCHjPh) have been examined at between 6 and 40 C [1968], The rate of 1 1 salt formation is much greater than the rate of its ensuing decomposition. The rate-determining step of the reaction is thus that of the decomposition of the ionic intermediate ... 

Although the most extensively recorded aspect of phosgene chemistry is its interaction with compounds at a nitrogen centre, only three reactions of carbonyl chloride fluoride with amines have been reported. No reports have appeared concerning the reactions of COCIF with tertiary amines, amino acids, hydrazine derivatives, imino compounds or nitrogen-containing heterocycles, to name but a few unstudied reagents. 

Reactions. As with other tertiary alcohols, esterification with carboxylic acids is difficult and esters are prepared with anhydrides (181), acid chlorides (182), or ketene (183). Ca.rba.mic esters may be prepared by treatment with an isocyanate (184) or with phosgene followed by ammonia or an amine (185). 

Interfacial polymerization process. The interfacial polymerization process is the oldest and most widely used of the commercial processes. Although different companies and even different manufacturing plants may have variations of the interfacial process, overall they are quite similar. Both batch and continuous interfacial processes have been practiced. The overall reaction (shown below in Fig. 14.1) involves the condensation of BPA with phosgene. A base, typically caustic, is used to scavenge the hydrochloric acid generated. The condensation is catalyzed with a tertiary amine and/or a phase transfer catalyst or both. The condensation is done in a two-phase medium such as methylene chloride and water. For a more in-depth discussion of the reaction mechanism, the reader is referred to the following sources [50—58]. 

Carbonyldiimidazoles (e.g. GDI) are prepared in high yield with little by-product formation by the reaction of imidazoles [(un)substituted in the 4- and/or 5-positions] (e.g. imidazole) with phosgene in the presence of a tertiary amine (e.g. tributylamine), which acts as an HCl scavenger. This amine has a lower pKb value than the imidazole. The reaction is performed in an aromatic hydrocarbon solvent (e.g. xylene), from which the product is crystallized. The tertiary amine hydrochloride salt is extracted into water, neutralized with an aqueous solution of an inorganic base (e.g. NaOH), and the free amine is re-extracted into an organic solvent (EtOAc). 

The two reactive chlorine atoms at the opposite ends of the phosgene molecule determine the use of phosgene for addition reactions, polymerization reactions and for chain-enlargements. Other uses of phosgene are reactions with secondary amines to give imidoyl chlorides, with tertiary amines to form cationic complexes, with nitriles to produce heterocycles and with metal oxides to produce metal chlorides. 

In the industrial production of this PC, interfacial polycondensation is used. The bisphenol A is first dissolved in the aqueous phase as sodium salt, and the phosgene in the organic phase, which is not miscible with water, e.g. dichloromethane. The reaction occurs at the interface of the two phases to produce oligomers, which enter the organic phase. The hydrolysis product NaCl enters the aqueous phase. The addition of catalysts (tertiary amines) accelerates the polycondensation process. The chlorine leaves the process as sodium chloride, see Fig. 96. 

In the interfacial process, bisphenol A is dissolved in the aqueous sodium hydroxide phase of a two-phase system with methylene chloride. As phosgene is pumped into the mixture, the sodium chloride condensation by-product dissolves in the aqueous phase, and the growing polymer dissolves in the organic phase. A tertiary amine is used as the catalyst. When the reaction is complete, the methylene chloride solution is extracted with acid to remove basic components and then washed with water. The solvent is then flashed off and recycled, leaving the solid. 

The use of azides in the Curtius reaction is hazardous and the utility of the Hoffman and Lossen rearrangements is limited to preparation of aliphatic isocyanates, as aqueous media are employed (aromatic isocyanates react readily with water to form substituted ureas). Tertiary butyl hypochlorite can be used for non-aqueous Hoffman rearrangements but is costly. In practice mostly phosgenation of a primary amine is commercially important ... 

Thus, the early process of choice for one of the major producers was the reaction of BPA, phosgene, and monohydric phenols in a methylene-chloride solution in contact with an aqueous solution of sodium hydroxide [41]. For this reaction, a tertiary alkyl amine was the preferred catalyst. Lime was used extensively as the acid acceptor in an alternative process preferred at the time by another major producer [42]. 

Novel functionalized peroxides which may be used as UPR curing agents as well as initiators for polymerization reactions and as monomers for polymerizations to form peroxy-containing polymers were elaborated [162]. Initiators may be prepared by reacting hydroxy-containing tertiary hydroperoxides with diacid halides, dichloroformates, phosgene, diisocyanates, acid anhydrides and lactones to form the functionalized peroxides. These reaction products may be further reacted, if desired, with dialcohols, diamines, aminoalcohols, epoxides, epoxy alcohols, epoxy amines, diacid halides, dichloroformates and diisocyanates to form additional fimctionalized peroxides. The use of monoperoxyoxalates of the structure (Scheme 24) as initiators... 

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