Oxidation accelerated

There are available standard accelerated oxidation tests that consist of passing air or oxygen through an oil at elevated temperature. The test is conducted with or without the presence of catalysts or water. 

Heat. As expected, heat accelerates oxidation (33). Therefore, the effects described previously are observed sooner and are more severe as temperature is increased. Because oxidation is a chemical reaction, an increase of 10°C in temperature almost doubles the rate of oxidation. 

The properties of 1,1-dichloroethane are Hsted ia Table 1. 1,1-Dichloroethane decomposes at 356—453°C by a homogeneous first-order dehydrochlofination, giving vinyl chloride and hydrogen chloride (1,2). Dehydrochlofination can also occur on activated alumina (3,4), magnesium sulfate, or potassium carbonate (5). Dehydrochlofination ia the presence of anhydrous aluminum chloride (6) proceeds readily. The 48-h accelerated oxidation test with 1,1-dichloroethane at reflux temperatures gives a 0.025% yield of hydrogen chloride as compared to 0.4% HCl for trichloroethylene and 0.6% HCl for tetrachloroethylene. Reaction with an amine gives low yields of chloride ion and the dimer 2,3-dichlorobutane, CH CHCICHCICH. 2-Methyl-l,3-dioxaindan [14046-39-0] can be prepared by a reaction of catechol [120-80-9] with 1,1-dichloroethane (7). 

Oxidation. Atmospheric oxidation of 1,2-dichloroethane at room or reflux temperatures generates some hydrogen chloride and results in solvent discoloration. A 48-h accelerated oxidation test at reflux temperatures gives only 0.006% hydrogen chloride (22). Addition of 0.1—0.2 wt. % of an amine, eg, diisopropylamine, protects the 1,2-dichloroethane against oxidative breakdown. Photooxidation in the presence of chlorine produces monochloroacetic acid and 1,1,2-trichloroethane (23). 

Oxidation. 1,1,1-Trichloroethane is stable to oxidation when compared to olefinic chlorinated solvents like trichloroethylene and tetrachloroethylene. Use of a 48-h accelerated oxidation test gave no hydrogen chloride, whereas trichloroethylene gave 0.4 wt % HCl and tetrachloroethylene gave 0.6 wt % HCl (22). 

Corrosion is described as hot corrosion and sulfidation processes. Hot corrosion is an accelerated oxidation of alloys caused by the deposition of Na2S04. Oxidation results from the ingestion of salts in the engine and sulfur from the combustion of fuel. Sulfidation corrosion is considered a form of hot corrosion in which the residue that contains alkaline sulfates. Corrosion causes deterioration of blade materials and reduces component life. 

The extent of the corrosion depends on the amount of nickel and chromium in the alloy. The oxide films become porous and nonprotective, which increases the oxidation rate (accelerated oxidation). 

Not all sulphates are as readily reduced as sodium sulphate, for instance, calcium sulphate does not usually lead to sulphide penetration, although the presence of other substances with calcium sulphate may lead to accelerated oxidation for other reasons. The results for laboratory tests on a series of metals and alloys in sodium sulphate -F sodium chloride and calcium sulphate + calcium chloride mixtures are shown in Table 7.12 . In many cases sulphide peneration could be noted with the sodium salts but not with the calcium salts. 

Rancimat is an accelerated method to assess oxidative stability of fats and oils. In this test, the sample is subjected to an accelerated oxidative process (by heat in presence of oxygen), where short-chain volatile acids are produced. The acids formed are measured by conductivity. 

Oxidation of organic compounds by dioxygen is a phenomenon of exceptional importance in nature, technology, and life. The liquid-phase oxidation of hydrocarbons forms the basis of several efficient technological synthetic processes such as the production of phenol via cumene oxidation, cyclohexanone from cyclohexane, styrene oxide from ethylbenzene, etc. The intensive development of oxidative petrochemical processes was observed in 1950-1970. Free radicals participate in the oxidation of organic compounds. Oxidation occurs very often as a chain reaction. Hydroperoxides are formed as intermediates and accelerate oxidation. The chemistry of the liquid-phase oxidation of organic compounds is closely interwoven with free radical chemistry, chemistry of peroxides, kinetics of chain reactions, and polymer chemistry. 

Initiation by light accelerates oxidation due to the photochemical generation of free radicals, which was noticed by Backstrom [16] and repeated by many others [9,11 — 13], The quantum yield (photooxidation products is sufficiently higher than unity. Here are several examples [12]. 

Hydroperoxides formed due to the oxidation of amides are decomposed into free radicals and accelerate oxidation. Hydroperoxides form hydrogen bonds with amides. The enthalpies, entropies, and equilibrium constants of hydrogen bonding are presented in Table 9.7. 

During this process, the metal catalyst transforms the slow self-accelerated oxidation into the fast accelerated chain process. One can lower the temperature of oxidation and decrease undesirable side reactions and products. 

This leads to chain termination in the absence of hydroperoxide. There are experimental examples when the introduction of transition metal salt does not accelerate oxidation but... 

Compounds of transition metals (Mn, Cu, Fe, Co, Ce) are well known as catalysts for the oxidation of hydrocarbons and aldehydes (see Chapter 10). They accelerate oxidation by destroying hydroperoxides and initiating the formation of free radicals. Salts and complexes containing transition metals in a lower-valence state react rapidly with peroxyl radicals and so when these compounds are added to a hydrocarbon prior to its oxidation an induction period arises [48]. Chain termination occurs stoichiometrically (f 1) and stops when the metal passes to a higher-valence state due to oxidation. On the addition of an initiator or hydroperoxide, the induction period disappears. 

The resulting products, such as sulfenic acid or sulfur dioxide, are reactive and induce an acid-catalyzed breakdown of hydroperoxides. The important role of intermediate molecular sulfur has been reported [68-72]. Zinc (or other metal) forms a precipitate composed of ZnO and ZnS04. The decomposition of ROOH by dialkyl thiophosphates is an autocata-lytic process. The interaction of ROOH with zinc dialkyl thiophosphate gives rise to free radicals, due to which this reaction accelerates oxidation of hydrocarbons, excites CL during oxidation of ethylbenzene, and intensifies the consumption of acceptors, e.g., stable nitroxyl radicals [68], The induction period is often absent because of the rapid formation of intermediates, and the kinetics of decomposition is described by a simple bimolecular kinetic equation... 

A widespread method for determining the induction period for autoxidation of oils and fats consists of passing a continuous stream of air through the heated sample and collecting the volatile acids evolved in a water trap, where they are determined on a real time basis. The time plot usually presents a flat appearance for a certain period and then takes off in an accelerated manner. This test is the basis of several national and international standards (e.g. AOCS Cd 12b-92—oil stability index" ISO 6886—accelerated oxidation test for oxidative stability of fats and oils ) and the design of the Rancimat equipment, where the end determination is based on conductivity measurements . In addition to oxidation stability as determined by the Rancimat method and POV, which negatively affects virgin olive oil stability, other nonstandard properties were proposed for better assessment of the quality of this oil, namely LC determination of Vitamin E (21), colorimetric determination of total polar phenols and UVD of total chlorophyll. ... 

A study was carried out on the correlation between ANV determined by the lUPAC 2504 method and the corresponding FTIR spectra of various oils (safflower, sunflower, rapeseed and olive) exposed to accelerated oxidation (10 g of oil in an 80 mm Petri dish in an oven at 70 °C, in darkness). All ANV vs. time curves show a typical sigmoid shape however, the induction period for olive oil is 10 days, after which a moderate growth takes place for two days before the beginning of stabilization by day 13 the ANV of other oils starts to rise after 1 to 4 days and begins stabilization by the 6th day. This points to ANV being a measure of secondary oxidation processes, after the primary ones, as determined by the POV, have taken place to some extent. The correlation of these findings with the spectral ones is summarized in Section IV.B.4. 

ISO 6886 1996, Animal and vegetable fats and oils—Determination of oxidation stability (Accelerated oxidation test), International Organization for Standardization, Geneva, Switzerland (http //www.iso.ch/iso/en/CatalogueListPage.CatalogueList7ICSl =67 ICS2= 200 ICS3=10). 

Earp and Hill (99) find that the addition of salts to graphite usually accelerates oxidation markedly the notable exceptions being most of the borates and phosphates. 

Some of recent papers by Ratner et al. [63, 64] revealed that there are significant differences in the surface chemistry of Biomer lots. The surface of some lots was dominated by poly(diisopropylaminoethyl methacrylate) (DPAEMA or DIPAM), a high molecular weight UV stabilizer, which was absent from some older lots [65]. Ratner et al. carried out comparative studies on in vitro enzymatic and oxidative degradation of two lots of Biomer, BSU 001 and BSP 067. Lot BSU 001 contains both DPAEMA and an antioxidant, Santowhite powder, while BSP 067 contains only the antioxidant. It was found that DPAEMA retarded the enzymatic degradation process, but accelerated oxidative degradation. 

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