Ammonium carboxylates, quaternary

Initiation takes place by rapid reaction of an ammonium salt with the anhydride (Eq. (46)) whereby ammonium carboxylate is formed. In the propagation step, the carboxylate anion opens an epoxy ring and forms an ammonium alcoholate (Eq. (47)). The latter reacts with the anhydride to yield another ester bond, and ammonium carboxylate is recovered (Eq. (48)). Termination occurs through decomposition of the ammonium counter ion, the alkoxide anion abstracting a proton from the quaternary nitrogen with the formation of a deactivated tertiary amine. 

Modification of the poly(carbodiimide) foams, using polyols as comonomers, is possible, but the excellent thermal and flammability properties are reduced. Poly(carbodiimide isocyanurate) foams can also be continuously produced using 1,3,5-tris-(3-dimethylaminopropyl)-hexahydro-s-triazine as the cocatalyst. Other trimerization catalysts, such as potassium 2-ethylhexanoate and quaternary ammonium carboxylate (Dabco TMR 2) are also used as cocatalysts in the formation of poly(carbodiimide isocyanurate)... 

The selection of this reagent was based partly on the observation [209] that, because various quaternary ammonium carboxylates undergo thermal decomposition to methyl esters, such esters could be formed in situ in good yield by the simple injection of a methanolic solution of the quaternary ammonium carboxylate above 250°C. Thus, the use of the quaternary ammonium hydroxide in the transesterification scheme described above permits the simultaneous conversion of both glycerides and fatty acids to methyl esters. 

This kinetical behavior was not observed when the catalyst was an amine. In this case, a mechanism was suggested, which includes the formation of an intermediate quaternary ammonium carboxylate according to the following scheme ... 

Mukaiyama-Michael Reactions. 1,4-Addition of ketene alkyl silyl acetals to a./S-unsaturated carbonyl compounds (eq 10) is promoted by a variety of Lewis acids (for example, TiCU, Ti(OR)4, SnCU, trityl perchlorate, lanthanide salts, Al-montmo-rillonite clay), or Lewis bases such as fluoride ion (eq 11), or quaternary ammonium carboxylates. Lanthanide salts are particularly effective catalysts, and in the case of ytterbium(III) tri-fluoromethanesulfonate, the catalyst can be recovered (eq 10). ... 

There are several reports in the literature of tertiary amine catalysis of reactions which appear to be of the phase transfer type. The first such example is the reaction of potassium benzoate with benzyl chloride to give benzyl benzoate, reported in a German patent issued in 1913 to be catalyzed by triethylamine [26]. Merker and Scott in 1961 utilized in situ quaternary ammonium carboxylate formation to facilitate the same esterification reaction [27]. Hennis and coworkers rediscovered and clarified amine catalysis in the reaction of benzyl chloride with potassium acetate... 

Hennis and coworkers reported that the reaction of carboxylates with alkyl chlorides is catalyzed by tertiary amines, the combination of tertiary amines and sodium iodide or quaternary ammonium compounds [3, 4]. It was found that the ester formation was catalyzed by quaternary ammonium salts and that these were generated in situ from the amine and alkyl halide. Sodium iodide in 2-butanone converted the alkyl chloride to the more reactive iodide (the Finkelstein reaction) which in turn alkylated amine. Alkyl iodides added directly to the reaction mixture were even more active co-catalysts but the preformed quaternary ammonium salt was the most effective catalyst. It was suggested that the enhanced solubility of the quaternary ammonium carboxylate or the lack of tight ion pairing in this salt might account for the... 

The reaction of quaternary ammonium carboxylates with primary alkyl halides in DMF solution at room temperature results in good yields of esters [12]. (See Table 6.4). 

The alkylation of carboxylates to yield esters has also been catalyzed by quaternary ammonium groups bound to a macroreticular resin. Amberlite IRA-904 was converted to the hydroxyl form and then treated with the acid to form ammonium carboxylate ion pairs. The alkylation was carried out by a batch process in such solvents as ether, hexane, or ethanol, as illustrated in equation 6.11 [29]. The results are summarized in Table 6.10. 

Carboxylic acid esters from carboxylic acids via quaternary ammonium carboxylates Carboxylic acid benzyl esters... 

The water/polar solvent solubility is achieved for these compounds by the generation of an ammonium or quaternary ammonium salt, for example, triethyl-ammonium, via the carboxylate group within the mercaptide ligand (Equation 15.4). 

Class 2. Quaternary ammonium/carboxylic acids. These materials contain a permanent cationic site (-N Rs) as well as the carboxyl group. At low pH they will, of course, be cationic. At slightly alkaline pH they will become isoelectric and remain so. They can never become anionic in the way that the class 1 materials can. 

New efficient vulcanization systems have been introduced in the market based on quaternary ammonium salts initially developed in Italy (29—33) and later adopted in Japan (34) to vulcanize epoxy/carboxyl cure sites. They have been found effective in chlorine containing ACM dual cure site with carboxyl monomer (43). This accelerator system together with a retarder (or scorch inhibitor) based on stearic acid (43) and/or guanidine (29—33) can eliminate post-curing. More recently (47,48), in the United States a proprietary vulcanization package based on zinc diethyldithiocarbamate [14324-55-1]... 

The isocyanurate reaction occurs when three equivalents of isocyanate react to form a six-membered ring, as shown in the fifth item of Fig. 1. Isocyanurate linkages are usually more stable than urethane linkages. Model compound studies show no degradation of the trimer of phenyl isocyanate below 270°C [10,11]. Catalysts are usually needed to form the isocyanurate bond. Alkali metals of carboxylic acids, such as potassium acetate, various quaternary ammonium salts, and even potassium or sodium hydroxide, are most commonly used as catalysts for the isocyanurate reaction. However, many others will work as well [12]. 

At higher pH values the amide groups are unproton-ated [106], while the carboxylate groups [7,11] and quaternary ammonium groups [61] are ionized. Alternatively, the interaction can occur between these cations of the solution and the active groups of the polymer chains for floe formation. 

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