Silver oxide method

Weinstock and Boekelheide introduced Amberlite IRA-400 (OH ) for conversion of alkyltrimethylammonium iodides into the corresponding quaternary ammonium hydroxides. The procedure is simpler than the conventional silver oxide method and avoids undesirable side reactions sometimes encountered. In the case of a derivative of /3-erythroidine, this technique raised the yield in a Hofmann degradation from 40 to 78%. 

Scheme 3 3 Synthesis of [(NHQPd] and [(NHQAu] complexes using the silver oxide method.

Since the silver salts of the carboxylic acids are usually soluble in dilute nitric acid, they must be prepared by treating an aqueous solution of a neutral salt of the acid (and not the free acid itself) with silver nitrate solution. It is not practicable to attempt to neutralise the acid with sodium or potassium hydroxide solution, because the least excess of alkali would subsequently cause the white silver salt to be contaminated with brown silver oxide. The general method used therefore to obtain a neutral solution j to dissolve the acid in a small excess of ammonia solution, and then to boil the solution until all free... 

The exact amount of silver oxide required may be determined by titrating a sample of the solution with silver nitrate by the Volhard method. 

J.J. Lander, R. D. Weaver, A.J. Salkind, J.J. Kelley in Characteristics of Separators for Alkaline Silver Oxide Zinc Secondary Batteries. Screening Methods (Eds. J.E. Cooper, A. Fleischer), NASA Technical Report NAS 5-2860,1964. 

In the Koenigs-Knorr method and in the Helferich or Zemplen modifications thereof, a glycosyl halide (bromide or chloride iodides can be produced in situ by the addition of tetraalkylammonium iodide) is allowed to react with a hydrox-ylic compound in the presence of a heavy-metal promoter such as silver oxide, carbonate, perchlorate, or mercuric bromide and/or oxide,19-21 or by silver triflu-oromethanesulfonate22 (AgOTf). Related to this is the use of glycosyl fluoride donors,23 which normally are prepared from thioglycosides.24... 

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. 

Therefore, the use of several specific techniques while implementing the method of semiconductor sensors makes it feasible to detect and analyze emission of oxygen atoms at initial stage of metal oxidation although in case of silver it should be noted that there are no phase of silver oxide formed due to its instability at such conditions [57]. Rather, the absorption of oxygen by silver would be related to dissolution and internal oxidation. 

Olah, G. A. et al., J. Inorg. Nucl. Chem., 1960, 14, 295-296 Experimental directions must be followed exactly to prevent violent spontaneous explosions during preparation of the salt from silver oxide and boron trifluoride etherate in nitromethane, according to the earlier method [1], The later method [3] is generally safer than that in [2],... 

Two variants of this method have been devised in which milder oxidants can be employed. Lead dioxide or silver oxide convert the free base of 8a into the azetidinone in good yield, perhaps34 via intermediate radical cations... 

Other Methods of Preparation.—The ethyl 2-(D-oro6fno-tetrahydroxybutyl)-5-methyl-4-furoate may also be oxidized with hydrogen peroxide in alkaline medium, to give 5-methyl-2,4-furandicarboxylic acid, but the yield is lower.6 On the other hand, when 2-(4-carboxy-5-methylfuryl-2)-diglycolaldehyde (XXXVI) is oxidized with 6% hydrogen peroxide in alkaline solution at 0°, the acid III is obtained in a yield of 65% of the theoretical.60 The same acid is obtained when ethyl 2-formyl-5-methyl-4-furo-ate (V) is oxidized with silver oxide in alkaline medium.7... 

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)... 

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