Ammonium-salt-catalyzed reactions

In 2000, Benaglia and coworkers reported preparation of MeO-PEG supported quaternary ammonium salt (10) and examined the catalytic efficiency in a series of phase-transfer reactions (Fig. 5.3) [69]. The reactions occurred at lower temperatures and with shorter reaction times than with comparable insoluble 2% cross-linked polystyrene-supported quaternary ammonium salts, although yields varied with respect to classical solution phase quaternary ammonium salt catalyzed reactions. It was observed that yields dropped with a shorter linker, and that PEG alone was not responsible for the extent of phase-transfer catalysis. While the catalyst was recovered in good yield by precipitation, it contained an undetermined amount of sodium hydroxide, although the presence of this byproduct was found to have no effect on the recyclability of the catalyst... 

Phase Transfer and Ammonium Salt Catalyzed Reactions... 

The literature on the basic study of the non-catalyzed epoxy-carboxy reaction is, surprisingly, rather abundant in number and volume, coming just after the amine-or the ammonium salt-catalyzed reaction. This is, in fact, surprising since the non-catalyzed reaction is generally very slow and of little interest for applications. 

Quaternary ammonium salts catalyze reactions between species dissolved in two immiscible phases, a phenomenon called phase-transfer catalysis (see also Real Life 26-2). For example, heating a mixture of 1-chlorooctane dissolved in decane with aqueous sodium cyanide shows no sign of the Sn2 product, nonanenitrile. On the other hand, addition of a small amount of (phenylmethyl)triethylammonium chloride results in a rapid, quantitative reaction. 

Quaternary ammonium salts catalyze the reaction between an anion and an organic substrate by transfemng the anion from the aqueous phase where it cannot contact the substrate to the organic phase In the example just cited the first step occurs m the... 

The nature of the ammonium-salt-catalyzed deamination and cross-linking of silazanes and aminosilanes is not well understood. Experiments indicate clearly that NH3 is evolved when [CH3(R)SiNH] -type silazanes participate in the reaction and that CH3NH2 is evolved when methylami-nosilanes or -silazanes are used. Such eliminations would lead to some cross-linking through conversion of Si2N units to Si3N, as shown in equation 6. 

Xu LW, Li JW, Zhou SL, Xia CG (2004) A green, ionic liquid and quaternary ammonium salt-catalyzed aza-Michael reaction of a,p-ethylenic compounds with amines in water. New J Chem 28 183-184... 

Scheme 28.21 Quaternary ammonium salt-catalyzed aldol reactions.

Quaternary Ammonium Salt-Catalyzed Mannich Reactions... 

Scheme 28.23 Quaternary ammonium salt-catalyzed Mannich reactions...

The reactions are catalyzed by tertiary amines, quaternary ammonium salts, metal salts, and basic ion-exchange resins. The products are difficult to purify and generally contain low concentrations of acryhc acid and some diester which should be kept to a minimum since its presence leads to product instabihty and to polymer cross-linking. 

It is known that Selenium catalyzes reaction of some dye reduction by Sulphide. On this basis spectrophotometric and test-techniques for Selenium determination are developed. Inefficient reproducibility and low sensitivity are their deficiencies. In the present work, solid-phase reagent on silica gel modified first with quaternary ammonium salt and then by Indigocarmine was proposed for Selenium(IV) test-determination. Optimal conditions for the Selenium determination by method of fixed concentration were found. The detection limit of Se(IV) is 10 ftg/L = 2 ng/sample). Calibration curve is linear in the range 50-400 ftg/L of Se(IV). The proposed method is successfully applied to the Selenium determination in multivitamins and bioadditions. 

Other nitrogen compounds, among them hydroxylamine, hydrazines, and amides (15-9), also add to alkenes. Even with amines, basic catalysts are sometimes used, so that RNH or R2N is the actual nucleophile. Tertiary amines (except those that are too bulky) add to Michael-type substrates in a reaction that is catalyzed by acids like HCl or HNO3 to give the corresponding quaternary ammonium salts. " ... 

Imidazolium PFg or BF4 salts were frequently used as solvent for the present lipase-catalyzed reaction. However, these salts are very expensive, and we should develop cheaper ILs. Imidazolium alkyl sulfates might be good candidates because various types of alkyl sulfates can be easily prepared. The imidazolium alkyl sulfate was prepared starting from the corresponding ammonium alkyl sulfate as follows ammonium alkyl sulfates ([NH4][RS04]) are easily prepared by the reaction of... 

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