Peroxides tartrates

TiO " (in a less acidic medium). At pH 1 basic salts precipitate, followed by the hydroxide, which displays very weak amphoteric properties. Titanium(IV) forms stable fluoride, peroxide, tartrate, oxalate, and EDTA complexes, and weak sulphate, thiocyanate and... 

Figure 6C.1. Proposed preferred transition state for the asymmetric oxidation of phenyl methyl sulfide with binudear titanium(peroxide)-tartrate complex.

Fenton s reagent. To a solution of tartaric acid or a tartrate add 1 drop of freshly prepared ferrous sulphate solution, i drop of hydrogen peroxide solution and then excess of NaOH solution an intense violet coloration is produced, due to the ferric salt of dihydroxyfumaric acid, HOOC C(OH) C(OH)COOH. 

Destruction of the masking ligand by chemical reaction may be possible, as in the oxidation of EDTA in acid solutions by permanganate or another strong oxidizing agent. Hydrogen peroxide and Cu(II) ion destroy the tartrate complex of aluminum. 

Copolymers of diallyl itaconate [2767-99-9] with AJ-vinylpyrrolidinone and styrene have been proposed as oxygen-permeable contact lenses (qv) (77). Reactivity ratios have been studied ia the copolymerization of diallyl tartrate (78). A lens of a high refractive iadex n- = 1.63) and a heat distortion above 280°C has been reported for diallyl 2,6-naphthalene dicarboxylate [51223-57-5] (79). Diallyl chlorendate [3232-62-0] polymerized ia the presence of di-/-butyl peroxide gives a lens with a refractive iadex of n = 1.57 (80). Hardness as high as Rockwell 150 is obtained by polymerization of triaHyl trimeUitate [2694-54-4] initiated by benzoyl peroxide (81). 

Transition metal-catalyzed epoxidations, by peracids or peroxides, are complex and diverse in their reaction mechanisms (Section 5.05.4.2.2) (77MI50300). However, most advantageous conversions are possible using metal complexes. The use of t-butyl hydroperoxide with titanium tetraisopropoxide in the presence of tartrates gave asymmetric epoxides of 90-95% optical purity (80JA5974). 

A great deal of kinetie information on the AE reaetion has been obtained. The rate of reaetion is first order in allylie aleohol, Ti(0-iPr)2(tartrate), and TBHP. In addition, the rate is inversely-square dependent on isopropoxide. This refleets the required replaeement of two isopropoxide ligands on Ti(0-iPr)2(tartrate) with TBHP and the allylie aleohol. The rate-determining step is oxygen transfer from the peroxide to the olefin. 

The mechanism for such a process was explained in terms of a structure as depicted in Figure 6.5. The allylic alcohol and the alkyl hydroperoxide are incorporated into the vanadium coordination sphere and the oxygen transfer from the peroxide to the olefin takes place in an intramolecular fashion (as described above for titanium tartrate catalyst) [30, 32]. 

The orientation of the reactants is governed by the chirality of the tartrate ligand. In the TS an oxygen atom from the peroxide is transferred to the double bond. The enantioselectivity is consistent with a TS such as that shown below.58... 

MnP is the most commonly widespread of the class II peroxidases [72, 73], It catalyzes a PLC -dependent oxidation of Mn2+ to Mn3+. The catalytic cycle is initiated by binding of H2O2 or an organic peroxide to the native ferric enzyme and formation of an iron-peroxide complex the Mn3+ ions finally produced after subsequent electron transfers are stabilized via chelation with organic acids like oxalate, malonate, malate, tartrate or lactate [74], The chelates of Mn3+ with carboxylic acids cause one-electron oxidation of various substrates thus, chelates and carboxylic acids can react with each other to form alkyl radicals, which after several reactions result in the production of other radicals. These final radicals are the source of autocataly tic ally produced peroxides and are used by MnP in the absence of H2O2. The versatile oxidative capacity of MnP is apparently due to the chelated Mn3+ ions, which act as diffusible redox-mediator and attacking, non-specifically, phenolic compounds such as biopolymers, milled wood, humic substances and several xenobiotics [72, 75, 76]. 

Attempted reaction of 1,3-pentadiene with the optically active diboron derived from dialkyl tartrate in the presence of a phosphine-free platinum catalyst gave poor diastereoselectivity (20% de).63 Better selectivity has been attained with a modified platinum catalyst bearing a PCy3 ligand (Scheme 6).64 The reaction of allylborane thus obtained with an aldehyde followed by oxidation with basic hydrogen peroxide affords the corresponding diol derivative with moderate ee. 

Scheme 17 Reagents and conditions i) Ti(0- -Pr)4 (+)-diethyl tartrate, t-butylhydro-peroxide, — 20 °C.

The reaction of Rochelles salt, sodium potassium tartrate, with hydrogen peroxide is catalyzed with C0CI2 at 70°C. Photograph A shows the reactants before mixing. 

An experiment you may have carried out in previous years Involves the reaction of a solution of potassium sodium tartrate (Rochelle salt) with hydrogen peroxide, which Is catalysed by cobalt(ll) chloride solution. 

Enantioselective epoxidation of allylic alcohols using t-butyl peroxide, titanium tetra-wo-propoxide, and optically pure diethyl tartrate. 

An alternative method for the epoxidation of enones was developed by Jackson and coworkers in 1997 , who utilized metal peroxides that are modified by chiral ligands such as diethyl tartrate (DET), (5,5)-diphenylethanediol, (—)-ephedrine, ( )-N-methylephedrine and various simple chiral alcohols. The best results were achieved with DET as chiral inductor in toluene. In the stoichiometric version, DET and lithium tert-butyl peroxide, which was generated in situ from TBHP and n-butyllithium, were used as catalyst for the epoxidation of enones. Use of 1.1 equivalent of (-l-)-DET in toluene as solvent afforded (2/f,35 )-chalcone epoxide in 71-75% yield and 62% ee. In the substo-ichiometric method n-butyllithium was replaced by dibutylmagnesium. With this system (10 mol% Bu2Mg and 11 mol% DET), a variety of chalcone-type enones could be oxidized in moderate to good yields (36-61%) and high asymmetric induction (81-94%), giving exactly the other enantiomeric epoxide than obtained with the stoichiometric system (equation 37). 

Indeed, several interesting procedures based on three families of active catalysts organometallic complexes, phase-transfer compounds and titanium silicalite (TS-1), and peroxides have been settled and used also in industrial processes in the last decades of the 20th century. The most impressive breakthrough in this field was achieved by Katsuki and Sharpless, who obtained the enantioselective oxidation of prochiral allylic alcohols with alkyl hydroperoxides catalyzed by titanium tetra-alkoxides in the presence of chiral nonracemic tartrates. In fact Sharpless was awarded the Nobel Prize in 2001. 

These species, and in particular the Ti derivative, have a fundamental significance, being related to the Sharpless epoxidation reaction. In fact, despite the many attempts made in order to isolate and characterize the titanium tartrate peroxide derivative involved in that enantioselective process, only indirect evidence in solution and theoretical calculation clues have been obtained so far . ... 

Diphenyl-1 -pyrenylphosphine hydroperoxide determination, 679-80 peroxide value, 659, 680 Diphenyl sulfide, peroxyacid reduction, 700-1 Dipolar intermediate, ene reaction, 853 Dipole moments, dioxiranes, 1132 DIPT (diisopropyl tartrate), 395 Dipyridamole, low-density hpoprotein antioxidant, 611 Di radicals... 

In plants, ascorbate is required as a substrate for the enzyme ascorbate peroxidase, which converts H202 to water. The peroxide is generated from the 02 produced in photosynthesis, an unavoidable consequence of generating 02 in a compartment laden with powerful oxidation-reduction systems (Chapter 19). Ascorbate is a also a precursor of oxalate and tartrate in plants, and is involved in the hydroxylation of Pro residues in cell wall proteins called extensins. Ascorbate is found in all subcellular compartments of plants, at concentrations of 2 to 25 mM—which is why plants are such good sources of vitamin C. 

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