Alumina/ammonium formate

Keywords aldehyde, diethyl phosphite, alumina/ammonium formate, microwave irradiation, 1 -aminophosphonate... 

Other PK variations include microwave conditions, solid-phase synthesis, and the fixation of atmospheric nitrogen as the nitrogen source (27—>28). Hexamethyldisilazane (HMDS) is also an excellent ammonia equivalent in the PK synthesis. For example, 2,5-hexanedione and HMDS on alumina gives 2,5-dimethylpyrrole in 81% yield at room temperature. Ammonium formate can be used as a nitrogen source in the PK synthesis of pyrroles from l,4-diaryl-2-butene-l,4-diones under Pd-catalyzed transfer hydrogenation conditions. 

See also Ammonium compounds Anhydrous ammonia for activated alumina gel formation, 2 397... 

In an acetonitrile suspension, the intermediate a-cyanoalkoxide can be trapped by acyl chlorides to give cyanohydrin esters. In a preparation of synthetic pyrethroids, the comparison between the sonicated reaction and its PTC equivalent gave an advantage to the latter in terms of reaction time and yield. i A modest change in stereoselectivity is observed in some cases. The same reaction in the presence of ammonium chloride leads to a-amino nitriles, the first step of the Strecker amino acid synthesis.4 72 xhe procedure is more efficient in the presence of alumina. The formation of by-products, cyanohydrins or benzoins, is avoided. From an experimental viewpoint, the work-up is considerably easier than with conventional procedures, and consists mostly of a simple filtration. With ketones, and in the presence of ammonium carbonate, a hydantoin is formed (Eq. 21)7 ... 

A continuous process has been described (14) which can produce either the amide or the nitrile by adjusting the reaction conditions. Boric acid has been used as a catalyst in the amidation of fatty acid (15). Other catalysts employed include alumina (16), titanium, and 2inc alkoxides (17). The difficulty of complete reaction during synthesis has been explained by the formation of RCOOH NH RCOO , a stable intermediate acid ammonium salt (18). 

An interesting sequence, again overall an isomerization, is the stoichiometric formation of the manganese complexes 68, which, on basic alumina, isomerize to the allenyl complexes 69 from the latter the allenes 70 can be liberated with cerium(IV) ammonium nitrate (CAN) in good yields [128] (Scheme 1.30). 

Anionicallv Activated Alumina. At this time we had also developed an interest in anionically activated alumina. These basic reagents were active in promoting alkylation(42), condensation(43) and hydrolysis(44) reactions. Thus, we impregnated alumina with sodium hydroxide and used this combination both with and without a phase transfer catalyst (benzyltriethyl ammonium chloride). When BTEAC was added, the conversion to ether was decreased and the formation of ester was noted. In the absence of a phase transfer catalyst, the ether became a minor product and methyl phenylacetate became the major product with coproduction of phenylacetic acid. This ester does not result from esterification of the acid as simple stirring of phenylacetic acid with Na0H/A1203 in methanol does not produce methyl phenylacetate. 

Unlike divalent oxides, the solubility of alumina is low and hence some warm temperature treatment is required. In addition, rather than using lower solubility phosphate solutions such as ammonium and potassium phosphate solutions, phosphoric acid solution is directly used. Wagh et al. [ 17] employed a thermodynamic analysis to study the elfect of the temperature on the solubility of individual phases of alumina on the formation of its phosphate phases during heat treatment where solubility of hydrated aluminum oxide, viz., hydrargillite (A1203-3H20) is enhanced, and that contributes further to the formation of berlinite phase. They confirmed this by differential thermal analysis (DTA) and X-ray diffraction (XRD) analysis on samples heated beyond 118°C. 

Most interesting are the selectivity differences between an alumina phase and a strongly basic anion exchanger with quaternary ammonium groups. In comparison with a conventional anion exchanger, halide ions, for example, are eluted in reverse order I-< Br < Cl < F. This order corresponds to the formation constants of aluminum halide complexes [46], which suggests an interaction between aluminum and halide ions within the A1203 structure. 

It should be pointed out that the coprecipitation or cogelation of silica-alumina from sodium silicate and aluminum salts (sulfate, chloride, or sodium aluminate) results in the formation of a product having strong zeolitic properties. It is necessary to remove the sodium ion by exchanging with another ion such as H+, NH4+ or A10+, and this is usually done by treatment of the precipitate or hydrogel with a dilute solution of ammonium chloride (or sulfate) or of aluminum sulfate. After the sodium is exchanged out, the material is washed free of electrolytes, dried, and calcined (700°C.). 

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