Functionalizations silver oxide

The benzyl group has been widely used for the protection of hydroxyl functions in carbohydrate and nucleotide chemistry (C.M. McCloskey, 1957 C.B. Reese, 1965 B.E. Griffin, 1966). A common benzylation procedure involves heating with neat benzyl chloride and strong bases. A milder procedure is the reaction in DMF solution at room temperatiue with the aid of silver oxide (E. Reinefeld, 1971). Benzyl ethers are not affected by hydroxides and are stable towards oxidants (e.g. periodate, lead tetraacetate), LiAIH, amd weak acids. They are, however, readily cleaved in neutral solution at room temperature by palladium-catalyzed bydrogenolysis (S. Tejima, 1963) or by sodium in liquid ammonia or alcohols (E.J. Rcist, 1964). 

Epoxides such as ethylene oxide and higher olefin oxides may be produced by the catalytic oxidation of olefins in gas-liquid-particle operations of the slurry type (S7). The finely divided catalyst (for example, silver oxide on silica gel carrier) is suspended in a chemically inactive liquid, such as dibutyl-phthalate. The liquid functions as a heat sink and a heat-transfer medium, as in the three-phase Fischer-Tropsch processes. It is claimed that the process, because of the superior heat-transfer properties of the slurry reactor, may be operated at high olefin concentrations in the gaseous process stream without loss with respect to yield and selectivity, and that propylene oxide and higher... 

The fact that pentacarbonyl carbene complexes react with enynes in a chemo-selective and regiospecific way at the alkyne functionality was successfully applied in the total synthesis of vitamins of the Kj and K2 series [58]. Oxidation of the intermediate tricarbonyl(dihydrovitamin K) chromium complexes with silver oxide afforded the desired naphthoquinone-based vitamin K compounds 65. Compared to customary strategies, the benzannulation reaction proved to be superior as it avoids conditions favouring (E)/(Z)-isomerisation within the allylic side chain. The basic representative vitamin K3 (menadione) 66 was synthesised in a straightforward manner from pentacarbonyl carbene complex 1 and propyne (Scheme 38). 

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... 

Temporary protection of the aldehyde function and reduction with aluminum hydride gave ( )-3-epigeissoschizal (275), from which silver oxide oxidation, followed by esterification, resulted in methyl ( )-epigeissoschizoate (277). 

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. 

Ag/Si02 composites prepared by the one-step method and two-step methods were characterized by TGA/DTA, FTIR, XRD, and TEM. The results showed that Ag or silver oxide nanoparticles in 20 to30 nm were dispersed on the surface of the carrier Si02. The calcination temperature and prepared method affect the crystal phase of the functional component. 

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). 

The primary objective of miniature battery design is to maximize the energy density in a small container. A compromise must be reached, however, since volumetric energy density decreases as cell volume decreases and the dead volume due to containers, seals, etc. becomes increasingly significant. A plot of energy density as a function of total volume is given in Fig. 3.28 for the zinc-mercuric oxide and zinc-silver oxide systems. 

The separator assembly is the most critical component of zinc-silver oxide secondary cells. In addition to its normal function of preventing contact and short circuit between electrodes of different polarity, a separator in this system must also ... 

Epoxides 72 may also act as starting materials for hybrid structures 77 containing an isohexide and a glyceryl moiety, with nitric ester functions at different positions.172 Additional monoethers of isosorbide 2- and 5-nitrate 78 were synthesized by reaction of the free hydroxyl group with any of several alkyl iodides in the presence of freshly prepared silver oxide. The yields were low, as usual.146 Amongst a larger series of different alcohol... 

Other active methylene compounds also react with both palladium(ll) <2002POL2653> and gold(m) <1997JOM243> to produce metallacyclobutane complexes (Scheme 34). The gold complex is not sufficiently stable for isolation. In these reactions, the silver oxide functions both as a base and a reagent for halide abstraction. In the gold series, 1,1,3,3-tetracyanopropane is also a competent pro-nucleophile <1999JOM219>. 

More functionalized boranes have also been coupled in the presence of silver oxide, but the reaction proved more efficient when chromous chloride was added as catalyst (Scheme 10.5).19... 

When functionalities such as esters are present, neutral or acidic conditions are required for benzylation. The combination of Ag20 and benzyl bromide in DMF effects benzylation under virtually neutral conditions (Scheme 2.1b).4 In this reaction, silver oxide complexes with the bromide of benzyl bromide to generate an electrophilic benzyl cation, which then alkylates hydroxyls, In some cases, (7-acetyl migration or cleavage occurs. Generally, these reactions require anhydrous conditions and freshly prepared silver oxide. 

The classical Hunsdiecker reaction (equation 18), involving the reaction of silver caiboxylates widi halogens, and the various associated side reactions, has been reviewed several tunes. Optimum yields are obtain widi bromine, followed by chlorine. Iodine gives acceptable yields provid diat the correct stoichiometry of 1 1 is used. The reaction is most frequently carried out in tetrachloromediane at reflux. From a practical pmnt of view, one drawback is the difficulty encountered in the preparation of dry silver caiboxylates the reaction of silver oxide on the acyl chloride in tetrachloromediane at reflux has been employed to circumvent diis problem. Evidendy the use of molecular bromine limits die range of functional groups compatible widi die reaction the different reaction pathways followed by the silver salts of electron poor (equation 19) and electron rich (equation 20) aryl carboxyl s illustrate this point well. 

Silver oxide functions by excbaitging hydroxide ion for iodide lon in the quaternary salt, thus providing the base nceeosary to cause elimination. The actual elimination step is an EZ reaction < eciion 11.11) in which hydroxide ion removes a proton at the same time that the positively chai gcd nitrogen atom acts as the leaving group. 

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