Types of Oxides

Sahcylaldehyde is readily oxidized, however, to sahcyhc acid by reaction with solutions of potassium permanganate, or aqueous silver oxide suspension. 4-Hydroxybenzaldehyde can be oxidized to 4-hydroxybenzoic acid with aqueous silver nitrate (44). Organic peracids, in basic organic solvents, can also be used for these transformations into benzoic acids (45). Another type of oxidation is the reaction of sahcylaldehyde with alkaline potassium persulfate, which yields 2,5-dihydroxybenzaldehyde (46). 

Oxidation. There are 10 types of oxidative reactions in use industriaHy (80). Safe reactions depend on limiting the concentration of oxidi2ing agents or oxidants, or on low temperature. The foUowing should be used with extreme caution salts of permanganic acid hypochlorous acid and salts sodium... 

The selectivity of the oxidation of 2,6-disubstituted phenols depends on the type of oxidizing agent. For example, with a series of cobalt-containing catalysts of the salcomine type, oxidation of 2,6-dimethylphenol produces three products the poly(phenylene oxide), the diphenoquinone, and... 

The second type of oxidation behaviour is parabolic oxidation, with... 

The concentration of oxidizing agents is essential for the course of reactions involving Eq. (2-9). These can be divided into two groups according to the type of oxidizing agent ... 

Tetraazafulvalenes bearing two pyrazole subunits could be prepared by an original way. Tlius, treatment of benzylidene acetophenone with iso-pentylnitrite leads to an A, A -dihydroxy-bipyrazolyl-A, A -oxide, which in turn can be oxidized to TAF of type 100 (72CC961, 79JOC3211). Another type of oxidative dimerization was observed by the reaction of the electron-rich l-methyl-2,4-bis(dimethylamino)imidazole with silver salts (83TL3563). A bis-cation was isolated in 30% yield in the presence of sodium tetrafluo-roborate an unsymmetrical structure 101 was predicted from its NMR data (Scheme 40). 

Br R" = R" = Br, R" = H R" = R" = R" = Br). This type of oxidative addition has also been studied for a series of thienyl ligands formed from 2-bromothiophene or 2-bromo-3-methylthiophene [80JOM(188)121]. 

Ignition can take place for any flammable mixture within the concentration ranges for the respective LEL and UEL. The conditions for ignition may vary with the specific mixture, the type of oxidant (usually air or pure oxygen), the temperature, and pressure of the system. Ignition may result from electrical spark, static spark, contact with hot surfaces (autoignition) (see Figures 7-48,... 

As an example of a different type of oxide, we may consider ZnO. This oxide evolves oxygen and forms cations in interstitial positions (Zn O) or (Zn O), and free electrons (eo). If the interstitial zinc ions are only singly charged, the reaction describing the non-stoichiometry may be written... 

Fig. 7.38 Diagram. showing the type of oxide scales formed as continuous layers upon a number of superalloys at temperatures of about 1 100°C (after Pettit and Meier...

There are many transition metal ion oxidants used in organic chemistry for the interconversion of functional groups. Those which have been used for the preparation of sulphones from sulphoxides will be discussed below. It is very interesting to note that this type of oxidant often reacts more rapidly with sulphoxides than with sulphides and so sulphoxides may be selectively oxidized with transition metal ion oxidants in the presence of sulphides. This is in direct contrast to the oxidation of sulphides and sulphoxides with peracids and periodate, for example, where the rate of reaction of the sulphide is more than 100 times that for the corresponding sulphoxide. 

In another type of oxidative decarboxylation, arylacetic acids can be oxidized to aldehydes with one less carbon (ArCH2COOH ArCHO) by tetrabutylammonium... 

A special type of oxidative addition takes place between cobaltocene and boron halides (MeBBr2, PhBCl2, BCI3, BBr3) . Treatment of cobaltocene in hexane or... 

Consequently, the antioxidant activity of GA in biological systems is still an unresolved issue, and therefore it requires a more direct knowledge of the antioxidant capacity of GA that can be obtained by in vitro experiments against different types of oxidant species. The total antioxidant activity of a compound or substance is associated with several processes that include the scavenging of free radical species (eg. HO, ROO ), ability to quench reactive excited states (triplet excited states and/ or oxygen singlet molecular 1O2), and/or sequester of metal ions (Fe2+, Cu2+) to avoid the formation of HO by Fenton type reactions. In the following sections, we will discuss the in vitro antioxidant capacity of GA for some of these processes. 

Within the sulfur sub-group, there are two main types of oxides, the dioxides X 02 (X = S, Se, Te, Po) and the trioxides X Os (X = S, Se, Te). In addition, sulfur also forms disulfur monoxide, S2O. Transient XO species are known in the gaseous phase for S, Se, and Te. Polonium forms a black monoxide PoO. 

These oxidations have attracted wide interest and both specialised and comparative studies have been published. The rate laws which are summarised in Table 14 are not distinctive although the acidity dependence of the V(V) oxidations of some substrates suggests by analogy that a pinacol-type of oxidation may occur cf. V(V)-pinacol complexes, p. 388), viz. 

Laccase (PCL) as well as peroxidases (HRP and SBP) induced a new type of oxidative polymerization of the 4-hydroxybenzoic acid derivatives, 3,5-dimethoxy-4-hydroxybenzoic acid (syringic acid) and 3,5-dimethyl-4-hydroxybenzoic acid. The polymerization involved elimination of carbon dioxide and hydrogen from the monomer to give PPO derivatives with molecular weight up to 1.8 x lO (Scheme 22). - ... 

As mentioned in the introductory part, stereochemical course of the conversion of isocitric acid to a-ketoglutaric acid in TCA cycle is completely enantiose-lective although the reaction does not form an asymmetric carbon in the usual metabolic path. If such type of oxidative decarboxylation can be applied to synthetic compounds, it is expected that an entirely new type of asymmetric biotransformation will be developed. 

As a rule, different types of oxide film will form simultaneously on metal electrodes for instance, porous phase layers on top of adsorbed layers. Often, aging processes occur in the oxide layers, which produce time-dependent changes in the properties or even transitions between different forms. 

Many types of oxide layers have a certain, not very high electrical conductivity of up to 10 to 10 S/cm. Conduction may be cationic (by ions) or anionic (by or OH ions), or of the mixed ionic and electronic type. Often, charge transport occurs by a semiconductor hole-type mechanism, hence, oxides with ionic and ionic-hole conduction are distinguished (in the same sense as p-type and n-type conduction in the case of semiconductors, but here with anions or cations instead of the electrons, and the corresponding ionic vacancies instead of the electron holes). Electronic conduction is found for the oxide layers on iron group metals and on chromium. 

It is interesting to note that according to photoelectrochemical measurements, the a-oxide of platinum exhibits a photoeflect that is typical for n-type semiconductors, while for the P-type oxide the sign of the photoeflect is opposite, and typical for a p-type semiconductor. This is an indication for important dilferences in the properties of these two types of oxide layer. 

The oxidising properties of these salts were described previously. It is not surprising to find a table of dangerous reactions for this type of oxidant. The problem may be aggravated by the frequency of these accidents since these salts are used in pyrotechnics. Indeed, they are the raw materials of all fireworks which produce green colours. 

Thus, mercaptans are converted into disulfides. A large quantity of acid is used in this type of oxidation. 

The y-initiated oxidation of polyolefins produces a product mix which is less complex than that resulting from photo-or thermally initiated degradation. This results from the mild conditions in the Y-cell, where the major initial oxidation product, the -OOH group, is stable. Although the derivatization methods are applicable to all types of oxidation, for simplicity only the y-irradiated systems will be considered here. 

While the above comparison (or similar comparisons for other oxidants) of the amount of oxidant required for different oxidants may hold under controlled laboratory conditions, the actual amount and type of oxidant that is necessary for the treatment of MTBE or other oxygenates at a given site will depend on numerous factors beyond the amount of contaminant present including... 

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