Silver phosphate catalyst

The transformation of ort/zo-alkynylaryl ketones (275) to isochromene derivatives (276) through a cyclisation/enantioselective-reduction sequence has been realised in the presence of a chiral silver phosphate catalyst (277). The reaction afforded the li -isochromene derivatives (276) in high yield with fairly good to high enantioselectivity (Scheme 75). ... 

Woerpel and Clark identified silver phosphate as the optimal catalyst to promote di-ferf-butylsilylene transfer from cyclohexene silacyclopropane to a variety of substituted alkynes (Scheme 7.25).95 While this silver salt exhibited attenuated reactivity as compared to silver triflate or silver trifluoroacetate, it exhibited greater functional group tolerance. Both di- and monosubstituted silacyclopropenes were easily accessed. Terminal alkynes are traditionally difficult substrates for silylene transfer and typically insert a second molecule of the starting acetylene.61,90 93 Consequently, the discovery of silver-mediated silylene transfer represents a significant advance as it enables further manipulation of monosubstituted silacyclopropenes. For enyne substrates, silylene transfer the alkynyl group was solely observed. The chemoselectivity of the formation of 99f was attributed to ring strain as theoretical calculations suggest that silacyclopropenes are less strained than silacyclopropanes.96 97... 

Preferred catalysts generally are silica/alumina compositions which may be impregnated with promoters, such as silver phosphate, cobalt sulfide, etc. 

Silver phosphate precipitated on silica gel is a very weak catalyst in the presence of oil and water vapor. 

The conversion of methanol and ammonia to methylamines is achieved over dehydration catalysts operated in the temperature range 300450°C and 0.12 MPa pressure. The reactions are exothermic, and excess ammonia is used to control the product distribution. The dehydration catalysts are generally promoted Si-Al composites. The promoters include molybdenum sulfide and silver phosphate [68]. In the commercial Leonard process, a gas-phase downflow catalytic reactor operating at about 350°C and 0.62 MPa is used [69]. Recovery of the desired product is achieved throu a series of four distillation and extractive distillation columns. Unwanted product is recycled, suppressing further formation of the undesired component in the reactor. A very small amount of methanol is lost to CO and H2, and yields from the commercial process based on methanol and anunonia are >97% [70]. 

Conventional catalysts consist of about 86 percent silica and 14 percent alumina and yield predominantly TMA, which is in the least commercial demand. The undesired TMA is separated and recycled to the reactor for disproportionation into other amines. U.S. patent 3,387,032 claimed that by adding 0.05 to 0.95 percent silver phosphate, rhenium heptasulfide, molysulfide, or cobalt sulfide to the conventional catalyst, with the proper steam treatment, the selectivity of the catalyst is shifted in favor of mono- and di- at the expense of tri-. The relative increases of MM A and DMA in the reactor effluent are 67 percent and 98 percent, respectively. The corresponding decrease in TMA is 63 percent. 

In 2009, the catalytic enantioselective semipinacol rearrangement of 2-oxo allylic alcohols 83 was detailed by Zhang et al., leading to enantioenriched spiro-ethers 84 in a single operation (Scheme 2.24). They found that both phosphoric acids 5b and silver phosphate 5i were optimal catalysts, while the latter probably underwent silver-proton exchange with hydroxyl group of subsnates in the catalytic procedure [35],... 

Electrochemical Process. Several patents claim that ethylene oxide is produced ia good yields ia addition to faradic quantities of substantially pure hydrogen when water and ethylene react ia an electrochemical cell to form ethylene oxide and hydrogen (206—208). The only raw materials that are utilized ia the ethylene oxide formation are ethylene, water, and electrical energy. The electrolyte is regenerated in situ ie, within the electrolytic cell. The addition of oxygen to the ethylene is activated by a catalyst such as elemental silver or its compounds at the anode or its vicinity (206). The common electrolytes used are water-soluble alkah metal phosphates, borates, sulfates, or chromates at ca 22—25°C (207). The process can be either batch or continuous (see Electrochemicalprocessing). 

In aqueous solution, manganous salts are oxidised to manganese dioxide,6 and if silver nitrate is present as catalyst, to permanganate 0 the latter change constitutes Marshall s reaction. Chromium solutions in a similar manner give rise to chromate,7 even without a catalyst. Ferrous and cerous salts are converted into ferric and ceric salts, respectively, and phosphites are oxidised to phosphates. 

Mn(II) can be oxidized quantitatively to permanganate in perchloric acid by the use of silver ion as a catalyst. In the presence of phosphate, Ce(III) is oxidized to Ce(lV) phosphate, which precipitates from a solution containing sulfuric and phosphoric acids. The precipitate can be dissolved in sulfuric acid. Other oxidations that can be performed quantitatively are V(IV) to V(V) in acid solution, hypophosphite and phosphite to phosphate, selenite to selenate, tellurite to tellurate, nitrite to nitrate, and in alkaline solution, iodide to periodate. 

US patent 5,763,630 claims silver catalysts supported on other alkaline earth metal compounds than carbonates, such as calcium titanate, tribasic calcium phosphate, calcium molybdate, or calcium fluoride, as well as the magnesium and strontium analogues. Such supports provide significantly higher selectivity to the desired epoxide than would be expected from the performance of related materials. Selectivities are lower than those reported in the original Union Carbide patent. 

Addition and cyclization reactions. Chiral propargylic amines are obtained from aUcynylation of imines by catalysis of the silver salt of IB. The enantiomer of phosphate ID also finds use in the addition of indole to a-acetaminostyrenes. One more catalyst for intramolecular hydroamination to form pyrrolidine derivatives is the silylated 3. The... 

Up to now, several groups have devoted their efforts to synthesize it. In 1957, Lesiak and Schittek synthesized anthranilic acid from o-nitroethylbenzene. Jan Bakke et al prepared it from o-nitrotoluene. With the help of the Ullrnan reaction. Cook also synthesized it. Srinivasan, in 1957, described the synthesis of anthranilic acid from Shikimic acid-5-phosphate and L-glutamine. " Jana et al. ° explored for the first time a facile approach for the catalytic reduction of o-nitrobenzoic acid (o-NB A) to anthranilic acid (o-aminobenzoic acid) over a resin-bound silver nanocomposite as catalyst in the presence of sodium borohydride. 

Besides the metal complexes based on Ni and Pd that were previously proved suitable for the asymmetric hydrovinylation reactions, Ru and Co complexes have also been employed in this type of transformation. The one sole example of Ru-catalyzed enantioselective hydrovinylation was reported by the List group in 2012. In their initial studies, they envisioned that Ni complexes with chiral counteranions might enable the desired reaction. However, it was found that these species either were unreactive or did not furnish enantioselective control in the hydrovinylation reactions. In this context, Jiang and List focused their attention on Ru catalysis (Table 9.6). Systematic evaluation on the effects of Ru complexes ligated by different phosphine ligands as well as various chiral phosphate anions introduced by the corresponding silver salts demonstrated that the combination of Ru complex Ru-3 and additive Ag-1 was the optimal catalyst, leading to acceptable results (entry 8). 

---