Triazinyl ammonium

Chloro-4,6-disubstituted-l,3,5-triazines 1 have been widely used in the activation of carboxylic acids in die formation of peptide bonds. The reaction requires the presence of a tertiary amine in the reaction medium and the participation of quaternary triazinyl ammonium salts 2 as intermediates of the reaction has been demonstrated. The role of fliese species in die activation of the carboxylic acid involves substitution of die amine-leaving group in 2 by the carboxylate ion, to afford triazine super active esters 3, the reagents employed in the peptide bond formation step (Scheme 26.1). 

The common trend of intermediates 2 is to decompose rapidly at room temperature. Nevertheless, triazinyl ammonium derivative 4, obtained from 2-chloro-4,6-dimedioxy-l,3,5-triazine 5 (CDMT) and iV-methylmorpholine 6, resulted to be sufficiently stable to be studied (Scheme 26.2). 

Mechanism 2 in turn, proposes that the triazinyl ammonium salt 4 is formed in one step (as in a Sn2 process), by simultaneous rupture of the triazine C-Cl bond and formation of the triazine-morpholine bond, as represented in the transition state 8 (Scheme 26.4). 

Apart from other considerations, the most striking feature in the formation of triazinyl ammonium salts 2 is the strong dependence of the reaction rate on the steric hindrance of the tertiary amine employed. In fact, two important conclusions could be deduced from this data First, the tertiary amine has to be necessarily involved in the slow step of the reaction. Second, the sensitivity to the steric hindrance suggests a sterically crowded transition state. 

Considering all these arguments, the more likely mechanism for the formation of triazinyl ammonium salts can be drawn as in Scheme 26.8. ... 

The activation of carboxylic acids by means of 2-chloro-l,3,5-triazines 1 proceeds via triazinyl ammonium salts 2 that are formed in situ in flie presence of flie appropriate tertiary amine. The formation of salts 2 occurs by an addition-elimination SNAr mechanism and the reaction rates strongly depend on the steric hindrance of the substituents in the amine employed. 

Ammonium ion, JV-(2-thenyl)-N-benzyldimethyl-Stevens and Sommelet rearrangement, 4, 800 Ammonium salts, diallyldialkyl-polymerization, 1, 293 Ammonium salts, 2-pyrrolylmethyl-nucleophilic substitution abnormal, 4, 244 Sommelet rearrangement, 4, 244 Ammonium salts, trimethyl(l,3,5-triazinyl)-applications, 3, 525 Amobarbital, 3, 150 Amodiaquine, 1, 145 Amolanone applications, 4, 708... 

Brighteners are applied to cotton by methods similar to direct dyes. By far the most common are triazinyl derivatives of diaminostilbenedisulphonic acid (DAS) of general formula 11.5, where M is an alkali metal, ammonium or alkylammonium cation. Examples of groups Ilj and R2 are shown in Table 11.1. Most suppliers of FBAs market such compounds, often called DAST brighteners. Products in this class have sometimes been marketed because the supplier needed to offer something different for commercial reasons, or to avoid infringing a competitor s patent, rather than for any real technological necessity. 

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