Oxidation spontaneous

Between 10 and 20% of raw individual-cow milk samples undergo oxidation rapidly while others are more stable. Milks have been classified into three categories, based on their propensity to lipid oxidation  

It has been proposed that spontaneous milks have a high content (10 times normal) of xanthine oxidase (XO). Although addition of exogenous XO to non-susceptible milk induces oxidative rancidity, no correlation has been found between the level of indigenous XO and susceptibility to oxidative rancidity. The Cu-ascorbate system appears to be the principal pro-oxidant in susceptible milk. A balance between the principal antioxidant in milk, a-tocopherol (Chapter 6), and XO may determine the oxidative stability of milk. The level of superoxide dismutase (SOD) in milk might also be a factor but there is no correlation between the level of SOD and the propensity to oxidative rancidity. 

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Silver difluoride [7783-95-1], AgF2, is a black crystalline powder. It has been classified as a hard fluorinating agent (3) which Hberates iodine from KI solutions and o2one from dilute aqueous acid solutions on heating. It spontaneously oxidizes xenon gas to Xe(II) in anhydrous hydrogen fluoride solutions (20). 

Xe is comparable to, that of molecular oxygen (1175kJmol for O2 -> 02 + e )- He quickly proceeded to show that deep-red PtFe vapour spontaneously oxidized Xe to produce an orange-yellow solid and announced this in a brief note/ Within a few months Xep4 and Xep2 had been synthesized in other laboratories/ Noble-gas chemistry had begun. 

Odontosyllis luciferin is colorless and shows an absorption maximum at about 330 nm in aqueous ethanol (Figs. 7.2.1 and 7.2.2), and it undergoes various spectrum changes upon spontaneous oxidation... 

The drying of negative plates is not possible without precautions, because of the tendency to spontaneous oxidation. This oxidation reaction is much ac-celerated by water, and the active material of a moist negative electrode is spon-taneously converted into lead oxide when exposed to air. When, on the other hand, the charged plate is dry, a thin layer of oxide covers the surface of the active material, and prevents... 

A number of alkylated and ring-annelated derivatives of cyclopentadienyl-thallium(I) have been reported. All were prepared by the same procedure used for the parent compound, and relevant experimental data are listed in Table I. None of these compounds is as stable as cyclopentadienylthallium-(I) the methyl-substituted derivative, for example, undergoes essentially spontaneous oxidation on exposure to the atmosphere (25), and, qualitatively, the order of stability has been assessed (105) as... 

Fig. 5.2 The n-Cd(Se,Te)/aqueous Cs2Sx/SnS solar cell. P, S, and L indicate the direction of electron flow through the photoelectrode, tin electrode, and external load, respectively (a) in an illuminated cell and (b) in the dark. For electrolytes, m represents molal. Electron transfer is driven both through an external load and also into electrochemical storage by reduction of SnS to metaUic tin. In the dark, the potential drop below that of tin sulfide reduction induces spontaneous oxidation of tin and electron flow through the external load. Independent of illumination conditions, electrons are driven through the load in the same direction, ensuring continuous power output. (Reproduced with permission from Macmillan Publishers Ltd [Nature] [60], Copyright 2009)...

In addition to the QM structure of the natural terpene QMs, the reactive oxygen species (ROS) may also play a significant role in the observed biological activities. In the synthesis of taxodione and taxodone, QMs were formed from the catechol precursors through the spontaneous oxidation in the presence of silica gel.7, 8,49-51... 

This is very prone to spontaneous oxidative heating. A mixture with absorbent cotton attained a temperature of 230°C 4 min after exposure to air. 

A colour mixture containing the 3 components ignited spontaneously. Oxidation products in the air-blown oil may have reacted exothermally with the complex cyanide, a reducant. 

The same starting compound 112 showed a totally different behavior when treated with trifluoroacetic acid (TFA), giving a rearrangement to 114 followed by spontaneous oxidation that afforded an equilibrium mixture of tautomeric compounds 115 and 116 (Scheme 15) <1999EJ03429>. 

Solution H2S can also be lowered by spontaneous oxidation catalyzed by a number of compounds in the presence of 02. Accordingly, calibration solutions should contain DTPA and should be sparged with nitrogen or argon to remove 02. 

Addition of 1,5-dithiacyclooctane to zeolite CaY in the presence of molecular oxygen results in spontaneous oxidation to mono- and bis-sulfoxides through formation of the corresponding radical cation characterized by ESR and diffuse reflectance of UV-Vis spectroscopy.51... 

An alternative method of synthesizing the pyrazine compounds was described by Ghosh et al, and the synthesis is shown is Scheme 32 [78]. Reaction of a 1,2-dione (124) with a 1,2-diamine (125) to form an imine intermediate followed by spontaneous oxidation of the dihydropyrazine intermediate, formed the protected pyrazine compound 126. The free phenol 127 was obtained by removal of the methyl-protecting groups with a boron trifluoride-dimethyl sulfide complex. Similar compounds were prepared via the same method by Simoni et al. [79]. 

The kinetic results reported by Jameson and Blackburn (11,12) for the copper catalyzed autoxidation of ascorbic acid are substantially different from those of Taqui Khan and Martell (6). The former could not reproduce the spontaneous oxidation in the absence of added catalysts when they used extremely pure reagents. These results imply that ascorbic acid is inert toward oxidation by dioxygen and earlier reports on spontaneous oxidation are artifacts due to catalytic impurities. In support of these considerations, it is worthwhile noting that trace amounts of transition metal ions, in particular Cu(II), may cause irreproducibilities in experimental work with ascorbic acid (13). While this problem can be eliminated by masking the metal ion(s), the masking agent needs to be selected carefully since it could become involved in side reactions in a given system. 

Surface Coordination of the Iodo Ligand. The chemisorption of iodine at Au, Pt and Ir surfaces has been demonstrated (15-9). Previous studies with single- and polycrystalline Pt (15-7) showed that aqueous iodide undergoes spontaneous oxidation upon chemisorption to form a monolayer of zerovalent iodine ... 

Surface Oraanometallic Chemistry of Hvdroauinone. Previous studies (2) have established that the interaction of aqueous HQ with smooth polycrystalline Pt is concentration-dependent. Below 0.1 m M, HQ undergoes spontaneous oxidation to form a chemisorbed monolayer of flat-oriented (ne) benzoquinone (BQ) similar to that in the homogeneous coordination of benzoquinone to tris (triethylphosphine) Pt (0) (2) ... 

In research work on the transformation of [l,2,4]triazolo[4,3-A][l,2,4]triazines, introduction of various moieties into position 7 of this ring system has been elaborated by Chupakhin and co-workers <2001IZV2084, 2002HC075, 2003ZOB862>, as illustrated in Scheme 12. Some of these transformations have been carried out under acidic conditions, and in several cases basic conditions have been applied. In most cases, a formal addition of a CH moiety of the reagent to the C(7) = N(8) bond of the triazine ring occurs to result in the formation of a partially saturated triazine stmcture, and this transformation was followed by spontaneous oxidation to yield heteroaromatic triazine rings. 

A Chinese research team found <1997PS299> that derivative 21 of the new [l,3,4]thiadiazolo[3,2-f][l,3,5,2,]thia-diazaphosphorine ring system undergoes spontaneous oxidation on air, as shown in Scheme 5. Thus, storage of the dichloromethane solution of 21 for 48 h at room temperature results in formation of a mixture of 22 and 23. 

Aluminum coating (for surface fluorescence quenching see Section 13.5.5) can be accomplished in a standard vacuum evaporator the amount of deposition can be made reproducible by completely evaporating a premeasured constant amount of aluminum. After deposition, the upper surface of the aluminum film spontaneously oxidizes in air very rapidly. This aluminum oxide layer appears to have some similar chemical properties to the silicon dioxide of a glass surface it can be derivatized by organosilanes in much the same manner. 

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