Triethylamine hydrochloride, initiation

Carbodiimides react with dicarbonyl compounds (or their sulfur analogues) to give imidazoles [48, 49]. When diimmonium salts (19) are treated with guanidines or O-methylisoureas the initial products are 4,5-dihydroimidazoles, but these are readily aromatized by heating in the presence of triethylamine hydrochloride (Scheme 4.3.10). The mildly acidic conditions result in the loss of one of the amino functions from the intermediate [50]. Yields of 2,5-diaminoimidazoles are usually 60-80% overall. 

Fig. 21. Maximum rate of cationic polymerization of caprolactam with different initiators [193]. Caprolactam hydrochloride (1), benzylamine hydrochloride (2) and triethylamine hydrochloride (3) at 256°C.

This method may be developed to the reaction between phenols and phosphorus-chlorine compounds. Selecting of a suitable solvent, which triethylamine hydrochloride or the other salt is low-soluble, develops the synthesis of some initial phosphorus-chlorine compounds such as [(CH3)(QHii)N]P(0)Cl2 [67], [4-CH3C6H4NH P(0)a2 [68], [C6HsO][4-... 

The results of the polymerization are listed in Table 20. In the case of adenine derivative, more triethylamine is consumed for initiating polymerization than the equimolar amount corresponding to the adenine derivative. This fact suggests that the NCA of adenine derivative 58a was present as a hydrochloride. The degree of polymerization was determined by the trinitrobenzene sulfonate method67. ... 

An insight into the mechanistic details of this transformation has been gained from the extensive studies of Takamizawa and co-workers. Initially, the reaction of thiamine hydrochloride (96) with diethyl benzoyl-phosphonate in the presence of sodium hydroxide was shown to give the dihydrothiazinone 97. When the reaction was carried out in AT,JV-dimethyl-formamide containing triethylamine, compound 84 (R = H) was obtained ... 

Chlorosulfonation of 2-ethoxybenzoic acid was found to be very regioselective a mole of thionyl chloride needs to be added to ensure the intermediate sulfonic acid is converted to the sulfonyl chloride (see Scheme 16.3). The sulfonyl chloride was converted to sulfonamide 9 by reaction with A-methylpiperazine. Initially triethylamine was used as a base, and compound 9 could only be isolated as its hydrochloride-triethylamine double salt, which was very insoluble and difficult to use in subsequent steps. A key breakthrough was obtained when it was discovered that sulfonamide 9 also could be isolated as its highly crystalline zwitterion. 

In the reaction of N-substituted carboxylic acid amides with phosphorus pentachloride generally the corresponding free imidoyl chlorides (I) or their hydrochlorides (II) (iminium chlorides) are formed. If the iminium chlorides are obtained initially, dehydrochlorination can be achieved by simply heating or using a stronger base, such as triethylamine, as the hydrogen chloride scavenger. 

An advance received too late to include in the table of this chapter concerned the preparation of four polydepsipeptides by the Rydon group. In this work, L-2-hydroxy-4-methylpentanoic acid was prepared from Leu, depside coupling was induced by DCCI in Py, and polymer formation was initiated by treating an acid chloride hydrochloride with triethylamine. By this means, for e.xample, was prepared poly-(0-Tri-Leu-L-2-hydroxy-4-methylpentanoic acid) which corresponded to a number average molecular weight of 46,000. 

A/-Methacryloyl-D,L-phenylalanine Methyl Ester. The enantiodiscrim-inating influence of cyclodextrin in the free-radical polymerization of the racemic monomer iV-methacryloyl-D,L-phenylalanine methyl ester (2e) (41) was investigated for the first time. 2e was synthesized in 99% yield by the reaction of phenylalanine methyl ester hydrochlorides with methacryloyl chloride in the presence of triethylamine. The racemic monomer was subsequently added to an aqueous solution of RAMEB yielding a clear colorless solution of complexed monomer. Homopolymerizations were carried out in the presence of redox initiator at various temperatures. It was showed that the L-enantiomer is enriched in the residual monomer mixture. This observation confirms that complexed D-enantiomer polymerizes faster than the complexed L-enantiomer. No polymerization of 2e was observed without cyclodextrin under the same conditions. 

Typically, DCC (1.1 equiv) is added to a concentrated solution (0.1-1.0 M) of the carboxylic acid (1.0 equiv), amine (1.0 equiv), and catalyst (when used) in methylene chloride or acetonitrile at 0 °C. The hydrated DCC adduct, dicyclohexylurea (DCU), quickly precipitates and the reaction is generally complete within 1 h at rt. The solvents THF and DMF can be used, but are reported to reduce reaction rates and encourage the formation of the A -acylurea side product, as well as increasing racemization in chiral carboxylic acids.If the amine is initially present as the salt (i.e. amine hydrochloride), it may be neutralized by adding 1 equiv of Diisopropylethylamine prior to adding DCC however, the addition of tertiary amines (particularly Triethylamine) can facilitate A -acylurea formation and racemization. Racemization occurs via the formation of an oxazalone intermediate. The addition of coupling agents (acylation catalysts) such as 1-Hydroxybenzotriazole (HOBt), l-hydroxy-7-azabenzotriazole... 

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