Ferricyanide hydrolysis

The authors believe hydrolysis to be rate-determining but do not account for the presence of ferricyanide in the transition state. 

Also fifteen years of painstaking work and the gradual improvement of the system, the Sharpless team announced that asymmetric dihydroxylation (AD) of nearly every type of alkene can be accomplished using osmium tetraoxide, a co-oxidant such as potassium ferricyanide, the crucial chiral ligand based on a dihydroquinidine (DHQD) (21) or dihydroquinine (DHQ) (22) and metha-nesulfonamide to increase the rate of hydrolysis of intermediate osmate esters 1811. 

Marchand and co-workers reported a synthetic route to TNAZ (18) involving a novel electrophilic addition of NO+ NO2 across the highly strained C(3)-N bond of 3-(bromomethyl)-l-azabicyclo[1.1.0]butane (21), the latter prepared as a nonisolatable intermediate from the reaction of the bromide salt of tris(bromomethyl)methylamine (20) with aqueous sodium hydroxide under reduced pressure. The product of this reaction, A-nitroso-3-bromomethyl-3-nitroazetidine (22), is formed in 10% yield but is also accompanied by A-nitroso-3-bromomethyl-3-hydroxyazetidine as a by-product. Isolation of (22) from this mixture, followed by treatment with a solution of nitric acid in trifluoroacetic anhydride, leads to nitrolysis of the ferf-butyl group and yields (23). Treatment of (23) with sodium bicarbonate and sodium iodide in DMSO leads to hydrolysis of the bromomethyl group and the formation of (24). The synthesis of TNAZ (18) is completed by deformylation of (24), followed by oxidative nitration, both processes achieved in one pot with an alkaline solution of sodium nitrite, potassium ferricyanide and sodium persulfate. This route to TNAZ gives a low overall yield and is not suitable for large scale manufacture. 

Total thiamine Milk Enzymatic hydrolysis of protein with trypsin and thiamine phosphates to thiamine with claradiastase oxidation of thiamine to thiochrome using ferricyanide (derivatization stopped with sodium sulphite) thiochrome extracted with 1-butanol Analytical Nucleosil Phenyl (150 mm, 5 fi Macherey-Nagel). Isocratic methanol + acetonitrile + isobutanol + water (80 +10+10+5 v/v/v/v). 0.7 ml/min. Fluorescence 375/430 nm (ex/em). External standardization. 76 Recoveries 95% thiamine as thiochrome from milk. 

When the secondary reaction cycle shown in Scheme 6D.3 was discovered, it became clear that an increase in the rate of hydrolysis of trioxogly colate 10 should reduce the role played by this cycle. The addition of nucleophiles such as acetate (tetraethylammonium acetate is used) to osmylations is known to facilitate hydrolysis of osmate esters. Addition of acetate ion to catalytic ADs by using NMO as cooxidant was found to improve the enantiomeric purity for some diols, presumably as a result of accelerated osmate ester hydrolysis [16]. The subsequent change to potassium ferricyanide as cooxidant appears to result in nearly complete avoidance of the secondary cycle (see Section 4.4.2.2.), but the turnover rate of the new catalytic cycle may still depend on the rate of hydrolysis of the osmate ester 9. The addition of a sulfonamide (usually methanesulfonamide) has been found to enhance the rate of hydrolysis for osmate esters derived from 1,2-disubstituted and trisubstituted olefins [29]. However, for reasons that are not yet understood, addition of a sulfon-amide to the catalytic AD of terminal olefins (i.e., monosubstituted and 1,1-disubstituted olefins) actually slows the overall rate of the reaction. Therefore, when called for, the sulfonamide is added to the reaction at the rate of one equivalent per equivalent of olefin. This enhancement in rate of osmate hydrolysis allows most sluggish dihydroxylation reactions to be mn at 0°C rather than at room temperature [29]. 

Reaction of the 3-substituted l,2,3-triazolo[4,5-d]pyrimidines (183) with one equivalent of a Grignard reagent in THF afforded the dihydro compounds 185 after hydrolysis of the intermediates 184. Aromatization of 185 by oxidation with potassium ferricyanide (79CPB3176) or with 2,3-dichloro-4,5-dicyanobenzoquinone (DDQ) (89CPB1731) gave the 3-substituted 7-alkyltriazolopyrimidines 186. Replacement of the methylsul-... 

Berberine has been converted into a mixture of a- and /3-hydrastines, in the proportions 1 2 oxidation with potassium ferricyanide produced dimeric oxy-bisberberine, which with methanolic hydrochloric acid yielded the betaine (91). Hydration of this, followed by N-methylation, yielded the keto-ester (92), which gave a- and /3-hydrastines on reduction with sodium borohydride and subsequent hydrolysis.100 The photo-oxidation of tetrahydroberberine methiodide to allo-cryptopine has been reported.101... 

Oxidation of anopteryl alcohol (74) with potassium ferricyanide gave an 8% yield of a compound with either structure (78) or (79). The major product of this reaction (following purification by acetylation and then alkaline hydrolysis of the acetylated product) was determined to be (80) by an X-ray crystallographic analysis. Acetylation of (80) gave (81). 

Application and Principle This procedure is used to determine the amylase activity of barley malt and other enzyme preparations. The assay is based on a 30-min hydrolysis of a starch substrate at pH 4.6 and 20°. The reducing sugar groups produced on hydrolysis are measured in a titrimetric procedure using alkaline ferricyanide. 

In neutral solution potassium ferricyanide undergoes hydrolysis to a small extent, ferric hydroxide being precipitated. Thus —5... 

Hiinig and Oette prepared azothiadiazoles (85) by oxidative coupling of 3-methyl-l,3,4-thiadiazolin-2(3)-one hydrazones (84) with phenols and diphenylamine. 84 was prepared by reaction of 2-methyl-thio-3-methyl-l,3,4-thiadiazolium ions (82) with benzhydrazide and hydrolysis of the first formed benzhydrazone (83). The coupling to 85 was performed with potassium ferricyanide in alkaline medium. 

Alkaline hydrolysis of the hexa- and tetrahydropyrrolo[2,1 -6]quinazolin-1-ones 308 and 310 afforded the respective tetra- and dihydroquinazoline-2-propionic acids (309 and 311 ). In the presence of potassium ferricyanide in aqueous potassium hydroxide, the tetrahydropyrrolo[2,l-6]quinazolin-1-one 310 gave the quinazoline-2-propionic acid 312. ... 

Ogino, Y., Chen, H., Kwong, H. L., Sharpless, K. B. The timing of hydrolysis-reoxidation in the osmium-catalyzed asymmetric dihydroxylation of olefins using potassium ferricyanide as the reoxidant. Tetrahedron Lett. 1991, 32, 3965-3968. 

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