Silver oxides, structure

The structure of compound A was established in part by converting it to known compounds Treat ment of A with excess methyl iodide in the presence of silver oxide followed by hydrolysis with dilute hydrochlonc acid gave a tnmethyl ether of D galactose Companng this trimethyl ether with known trimethyl ethers of D galactose allowed the structure of compound A to be deduced... 

Ahl and Reichstein have pointed out that though it is certain that the structure of emetine includes one, and possibly two, 6 7-dimethoxy-tetrahydroisoquinoline nuclei, the suggestions so far made as to the nature of the rest of the molecule are speculative. They investigated the Hofmann degradation of A-acetylemetine, m.p. 97-9°. This forms a monomethiodide, m.p. 2ia-6°, from which, by the action of silver oxide and potassium hydroxide, followed by eautious tbermal deeomposition and reacetylation,... 

Battery systems of complex design and structure using—at least for one electrode—expensive materials are (for economic reasons) mainly conceived as storage batteries. Primary (and "reserve") versions of the zinc/silver oxide battery [(-) Zn/KOH/AgO (+)] — as a first example—are only used in particular cases where the question of cost is not crucial, e.g., for marine [26-28] and space applications [29]. 

This group showed that isolable silver(I) diaminocarbene complexes can be use in situ instead of free carbenes, to generate the copper carbene complex. The silver salts that precipitates during the formation of the copper complex have not any negative effect on the conversion. This method is advantageous since most of the silver complexes are isolable, air-stable and easily obtained by treatment of the corresponding imidazohnium salt by 0.5 equiv of silver oxide (Scheme 53). The solid structure of 78 was analyzed by X-ray diffraction. 

Chemisorption of oxygen at Ag(110) at 300 K forms added rows of-Ag-O-extending along the [001] direction much like those observed with Cu(110). At saturation the monolayer, as with Cu(110), has a (2 x 1)0 structure.16 On exposure to ammonia at 300 K, Guo and Madix established17 that this oxide structure undergoes extensive restructuring where the added silver atoms in the monolayer are released to form nanoscale islands with the formation of... 

The pyranose structure of D-galacturonic acid, which lactonizes with great difficulty, has been confirmed by Levene and Kreider66 from a study of the methylated ester of the uronoside. Methyl a-D-galacturonoside (XXXIII) was methylated with silver oxide and methyl iodide and there was obtained methyl 2,3,4-trimethyl-a-D-galacturonoside methyl ester (XXXVI) which on oxidation was converted to d,l(2,3,4-trimethylmucic) acid (XXXVII) and h-arabo-trimethoxyglutaric acid (XXXVIII). 

An extension of the research on silver complexes with Lewis base-functionalized mono(A-heterocyclic carbene) ligands has been made toward the better-studied and stronger coordinating phosphine systems. The reaction of a diphenylphosphine-functionalized imidazolium salt with silver oxide in dichloromethane affords a trinuclear silver carbene complex 50, as confirmed by electrospray-ionization mass spectrometry.96,97 Metathesis reaction of 50 in methanol using silver nitrate gives 51 in 33% yield. The crystal structures of 51 were found to be different when different solvents were used during crystallization (Scheme 12).97 One NO3- anion was found to be chelated to... 

The value of methylation studies in structural determination of carbohydrates is well known. Methylation of sucrose has generally been achieved by the use of dimethyl sulfate-sodium hydroxide,34,35 methyl iodide-silver oxide-acetone,20 sodium hydride-methyl io-dide-N,N-dimethylformamide,35 or diazomethane-boron trifluoride etherate.36,37 The last method (already applied to monosaccharides38,39) has been found particularly useful for sucrose, because it proceeds without concomitant migration of acyl groups. The reaction of 2,3,6,T,3, 4, 6 -hepta-0-acetylsucrose (21) and 2,3,4,6,1, 3, 4 -hepta-O-acetylsucrose (22) with diazomethane in dichloromethane in the presence of a catalytic proportion of boron trifluoride etherate for 0.5 h at —5° gave the corresponding 4-methyl (23) and 6 -methyl (24)... 

Most structural work on xylan has been done on that from esparto grass and the principal attack made by way of the methyl ether. Xylan can be methylated by heating with methyl iodide and silver oxide,92-93 but complete etherification is difficult and considerable degradation probably occurs. On the other hand, complete etherification is attained by methylation in two operations with potassium hydroxide and dimethyl sulfate to give a dimethylxylan in almost quantitative yield70 showing [< ]22d — 92° in chloroform. Methylation with potassium hydroxide appears to proceed more readily than with sodium hydroxide.70-92... 

In this part, we prepared and studied the Ag/Si02 catalyst by one-step and two-step sol-gel methods. The results show that the Ag/Si02 catalyst prepared here is one kind of bulk material which has a high surface area. The Ag/Si02 catalyst is made up with functional component of Ag or silver oxide in 20 to 30 nm and carrier Si02. Moreover, we found that the different preparation methods have great effect on crystal structure of the samples. The structure of the sample prepared by the one-step method is always a single crystal structure. And the structure of the sample prepared by the two-step method is always a mixed crystal structure. 

The diacetamide compounds were regularly obtained in all degradations employing ammonia with or without silver oxide until Hockett and Chandler applied the method to hexaacetyl-D-gluco-D-flruZo-heptono-nitrile (XLIX) and obtained a monoacetamide derivative that was identified as iV-acetyl-D-glucofuranosylamine (L). The furanose structure of L was established by lead tetraacetate oxidation. They... 

Oxidation of the acetyl group in 2-acetyl-3,S-dialkyl derivatiyes of 1 and 2 with iodine in pyridine, and of the formyl group in 5-ethyl-2-formyl- and 2-formylthieno[2,3-6]thiophene, and 4-formyl- and 6-formylthieno[3,4-6]thiophene (194 and 195) with silver oxide, was performed to verify the structures of the acetylation and formylation products. 

Fig. 5 Montage image combining an STM image of the Ag oxide structure (from bottom left) superimposed over the proposed oxide structure (from top right). The numbers, n = 1-5, correspond to the symmetrically different positions within the middle silver layer sandwiched between two O layers. Agi and Ag2 have metallic character, as they are exclusively bonded to silver atoms in the substrate below, whereas Ags, Ag4, and Ags are directly bonded to oxygen inside the oxide rings and are ionic in nature. Both Ag4 and Ags sites sit above threefold sites of the underlying (111) lattice atoms, whereas Ags occupies a top site. Reprinted with permission from Bocquet et at.. Journal of the American Chemical Society, 2003, 125, 3119. 2003, American Chemical Society.

Levene15 reported that heating of 2-amino-2-deoxy-D-mannose (8) in the presence of silver oxide leads to a crystalline, nitrogen-free compound to which he attributed the structure of 2,5-anhydro-D-glucose on the basis of its elemental analysis. The possibility of interconversion between the two chair forms Cl (d) — 1C (d), which would bring the amino group at C-2 into equatorial orientation, has been postulated.22 Without excluding this possibility, it remains to be proved that the deamination by silver oxide does, indeed, proceed by... 

Azacyclols arising from amide-amide interaction have been extensively investigated. The p-nitrophenyl ester (60) of the linear tripeptide N-benzyloxycarbonyl-L-alanyl-L-phenylalanyl-L-proline undergoes a double cyclization when left in an aqueous buffer-dioxane (1 1) solution for 1 h, to produce cyclol (61) (7 ICC 1605). The hydroxyl group of the cyclol could be converted to the methyl ether by treatment with methyl iodide-silver oxide. The structure of the cyclol (61) could be confirmed by X-ray crystallography of the corresponding p-bromobenzyloxycarbonyl derivative (7 ICC 1607). 

In model experiments with silver oxide and TTC (triphenyltetrazolium chloride) it could be shown that the 2-a-methylene function in 47 undergoes oxidation, resulting in structures 49-51 (75AP331) (Scheme 11). 

A simple example of a catalytic solid is metallic silver. It is the best known catalyst for oxidizing ethylene to ethylene oxide. Under the conditions of use, oxidizing silver to silver oxide is not thermodynamically possible, but oxygen is rapidly and strongly adsorbed to form up to a monolayer on the surface. There is considerable evidence of both adsorbed oxygen atoms and oxygen molecules. Thus, some of the conceivable simple structures on the three low-index planes are as shown in Table I, where M denotes a silver (or metal) atom in a surface plane. 

Hayward produced eyidence that the pentanitrate so obtained has the structure of D-mannitol-l,2,3,5,6-pentanitrate. Methylation of the pentanitrate with silver oxide and methyl iodide gave 4-methyl-D-mannitol pentanitrate (m.p. 111—112°C). 

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