Ammonium-catalyzed reactions

The heterocyclic rings in quinoline (116) and isoquinoline are selectively reduced by Pd on carbon-catalyzed reaction of ammonium formatc[107]. Some benzene rings are also reduced. For example, nitrobenzene is reduced to cyclohexylamine (117) with formic acid. It is important to use a sevenfold excess of formic acid[108]. 

The alkyl azide 118 is reduced to a primary amine by the Pd on carbon-catalyzed reaction of ammonium formate in MeOH at room temperature. No racemization takes place with chiral azides[l 11,112]. 

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. 

Microwave chemistry has been found to be a useful method for accelerating reactions or catalyzing reactions that are difficult to carry out by other methods. A modification of the Hantzsch method to directly obtain pyridines has been communicated. A dry medium using ammonium nitrate bentonitic clay system with microwave irradiation affords pyridines 96 in a single pot within 5 minutes. When the pyridine is not the major product (> 75% yield), the dealkylated pyridine 97 becomes an... 

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... 

Aryl and vinyl nitriles have been prepared very efficiently from the corresponding bromides by palladium-catalyzed reactions under microwaves. This energy source has been employed for the conversion of these nitriles into aryl and vinyl tetrazoles by cycloaddition reactions with sodium azide (Scheme 9.66). The direct transformation of aryl halides to the aryl tetrazoles in a one pot procedure could be accomplished both in solution and on a solid support [115], The reactions were complete in a few minutes, a reaction time considerably shorter than those previously reported for the thermal reactions. The cydoadditions were performed with sodium azide and ammonium chloride in DMF and, although no explosion occurred in the development of this work, the authors point out the necessity of taking adequate precautions against this eventuality. 

Several conclusions can be reached from these data. The first is that on a per mole basis, the quaternary ammonium salt is the most favorable catalyst for this reaction. Among the other compounds, the catalytic activity of 1.5 mole-% of crown, PEG, or PEG-MME are similar. If equal weights of PEG-400 and PEG-3400 are used, quite different reaction rates are observed. This is because each polymer chain is capable of transporting one cation across the phase boundary at a time. The ratio of molecular weights is 8.5, so there are 8.5 more catalysts available in the PEG-400 catalyzed reaction than in the one involving the higher molecular weight compound. The actual ratio of rates for these two processes is 12.5, or nearly the expected value. 

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... 

More recently, Menendez et al. reported a closely related four-component access to tetrahydropyridines, the amino alcohol being replaced by a primary amine and an alcohol. Thus, the cerium(IV) ammonium nitrate (CAN)-catalyzed reaction between primary aliphatic amines, 1,3-dicarbonyls, cx,p-unsaturated aldehydes, and alcohols resulted in the formation of 6-aUcoxy-2-methyl-l,4,5,6-tetrahydropyridines with... 

Materials. Chemically pure solvents and reagent grade ceric ammonium nitrate were used as received. Cumene hydroperoxide was purified via the sodium salt. Lucidol tert-butyl hydroperoxide was purified by low temperature crystallization. Tetralin hydroperoxide, cyclohexenyl hydroperoxide, and 2-phenylbutyl-2-hydroperoxide were prepared by hydrocarbon oxidation and purified by the usual means. 1,1-Diphenyl-ethyl hydroperoxide and triphenylmethyl hydroperoxide were prepared from the alcohols by the acid-catalyzed reaction with hydrogen peroxide (10). 

There are three common approaches to the displacement of amine substituents from purines. First, diazotization and dediazoniation have been used to replace amine substituents, primarily with hydrogen or hydroxyl, carboxyl, and halide functionalities. Second, the S Ar reactions of quaternary ammonium substituents have provided useful synthetic adjuncts to the displacement reactions of halopurines. Finally, of increasing importance has been the conversion of aminopurines (or oxopurines) to N-linked 1,2,4-triazoles (and other azoles), which function as pseudohalogens and can be displaced by nucleophiles or take part in transition metal-catalyzed reactions. 

R NCIO system also makes the medium acidic, however the strength of the EGA is much weaker than that of a CH Clj—LiClO system due to neutralization of EGA with trialkyl amine produced by cathodic reduction of the ammonium cation Therefore, an EGA-catalyzed reaction can be performed even in a CH Cl — —R NCIO or MeCN—R NCIO system when a divided cell is employed. Presumably, amines generated in the cathode compartment diffuse slowly into the anode compartment where the EGA reaction occurs. 

The observed high anti selectivity may reflect the acyclic extended transition-state mechanism postulated in the fluoride-catalyzed reactions (Figure 9.1) [27]. Judging from the product configuration, chiral ammonium cation should effectively cover the si- face of the nitronate and the selective approach of aldehyde from the re-face should result. 

In a study involving the superacid-catalyzed reaction of amino-alcohols, a chiral, dicationic electrophile was observed by low temperature 13C NMR.31 Ionization of benzylic alcohols in superacids can generate stable carbocations, such as the trityl cation. Because of the resonance stabilization of the carbocationic centers, they are fairly weak electrophiles, incapable of reacting with benzene (eq 31). However, it was shown that adjacent ammonium groups can increase the electrophilic reactivities of the diphenylethyl cations (eq 32). 

The activating effects of ammonium groups on carboxonium electrophiles has also been exploited in the Friedel-Crafts acylations with amides.50 For example, in comparing the superacid-catalyzed reactions of acetanilide, the monoprotonated species (198) is found to be unreac-tive towards benzene (eq 67), while the diprotonated, superelectrophilic species (199) reacts with benzene to give the acyl transfer product in reasonably good yield (eq 68). 

For example, the work by Emery and Schroeder (24) indicates that wood can be chemically oxidized with an iron catalyzed reaction under acidic conditions. It is conceivable that this type of treatment could degrade the pit membrane and increase the permeability. Furthermore, Tschernitz (25) has shown that treatment of Rocky Mountain Douglas fir sapwood with hot ammonium oxalate improved the treatability of this material. In this latter case, the ammonium oxalate probably solubilized the pectins in the pit membrane. 

What is especially intriguing is the reverse behavior exhibited by the use of ruthenium carbonyl as the metal carbonyl. This reaction, which is catalytic in both Ru3(CO)2 and quaternary ammonium halide (which accelerates the rate of formation of the hydride intermediate), occurs in much higher yield under a carbon monoxide than a nitrogen atmosphere (22). The reaction conditions used for the Ru3(CO)12-catalyzed reaction are much milder than those reported using the water gas shift reaction [100°C, 500 psi] (25). 

Dicarbonyl compounds can be prepared by the reactitxi of ketones with 3-butenyl halide as a CU component, following oxidation of the terminal double bond. A modified method for 3-butenylation of ketones by the palladium-catalyzed reaction of 4-acetoxy-2-butenylmethyl carbonate with ketones, followed by the palladium-catalyzed reaction of ammonium formate was reported (Scheme 15)." ... 

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