Hydroperoxide oxidation decomposition method

Particle size, morphology, and structure have strong influence on the activities of catalysts, so it is important to develop a simple but effective method to be capable of controlling the particle size and even the microstructure of nanoparticles. Several preparation methods, including impregnation-reduction method (formaldehyde was used as the reducing agent) [38], hydroperoxide oxidation decomposition method [39-41], and the modified polyol method [42-44], were attempted in our laboratory. 

The set of the rate constants k determined for experimental runs of Figure 15 and their comparison with the rate constants of hydroperoxide decomposition determined by other methods may be seen in Table 3. When we take into account that PPs of different origin were examined, the agreement seems quite satisfactory. This agreement is valid for faster decomposing peroxides, which are the species determining the resulting rate of oxidation [49]. 

Ketones play an important role in the decomposition of peroxides to form radicals in alcohols undergoing oxidation. The formed hydroxyhydroperoxide decomposes to form radicals more rapidly than hydrogen peroxide. With an increase in the ketone concentration, there is an increase in the proportion of peroxide in the form of hydroxyhydroperoxide, with the corresponding increase in the rate of formation of radicals. This was proved by the acceptor radical method in the cyclohexanol-cyclohexanone-hydrogen peroxide system [59], The equilibrium constant was found to be K — 0.10 L mol 1 (373 K), 0.11 L mol 1 (383 K), and 0.12 L mol 1 (393 K). The rate constant of free radical generation results in the formation of cyclohexylhydroxy hydroperoxide decomposition and was found to be ki = 2.2 x 104 exp(—67.8/7 7) s 1 [59]. 

By the CL method in the oxidation catalyzed by Fe203 decomposition of cumyl hydroperoxide [258]... 

A simple method for assessing lipid oxidation is measuring the headspace concentration of hexanal by capillary GLC. Also, the total volatiles appearing in the chromatogram up to hexanal can be taken as oxidation index. The method was applied to determine the amounts of lipid peroxides present in rat liver cells. Enhancement of the hexanal concentration can be achieved on adding ascorbic acid (22), that reduces Fe(ni) present in the matrix to Fe(II), which catalyzes decomposition of hydroperoxides to aldehydes. Significant correlations are found between hexanal concentrations and various oxidation indices, such as TBARS (Section IV.D.2)" . ... 

From the above description of a molecular species absorbing in the UV wavelength range, it appears that the UV test is not wholly specific for substances produced in lipid peroxidation. Therefore other methods are needed to detect and evaluate lipid oxidation. Among the variety of methods available in the literature, iodometry is the chosen official method, although it fails when hydroperoxides are present in low amounts. Note also that iodometry will measure the peroxides present in the oil, but not their decomposition products. 

As oxidation normally proceeds very slowly at the initial stage, the time to reach a sudden increase in oxidation rate is referred to as the induction period (6). Lipid hydroperoxides have been identified as primary products of autoxidation decomposition of hydroperoxides yields aldehydes, ketones, alcohols, hydrocarbons, volatile organic acids, and epoxy compounds, known as secondary oxidation products. These compounds, together with free radicals, constitute the bases for measurement of oxidative deterioration of food lipids. This chapter aims to explore current methods for measuring lipid oxidation in food lipids. 

The primary oxidation products (hydroperoxides) are unstable and susceptible to decomposistion. A complex mixture of volatile, nonvolatile, and polymeric secondary oxidation products is formed through decomposition reactions, providing various indices of lipid oxidation (5). Secondary oxidation products include aldehydes, ketones, alcohols, hydrocarbons, volatile organic acids, and epoxy compounds, among others. Methods for assessing lipid oxidation based on their formation are discussed in this section. 

Chemiluminescence has been used to assess phosphatidylcholine oxidation, and to measure the kinetics of decomposition of hydroperoxides formed during the oxidation of soya phosphatidylcholine. The direct chemiluminescence method correlated well with other methods of determining oxidation status (chemical, UV, HPLC, and microcalorimetry), and it was concluded that chemiluminescence was an ideal method for estimating the oxidation of phosphatidylcholine (and phospholipids in general). Kinetics measurements revealed that... 

Many references to kinetic measurements may have already been covered earlier with other physical methods. These include studies on pseudorotation of stereoisomers of a 10-P-5 spirophosphorane, on the formation rate of acylpho-sphonate hemiketals, on the rate of decomposition of hydroperoxides formed by the oxidation of soya phosphatidylcholine, on the kinetics of the reaction of trimethyl phosphite with benzylidene acetophenones, calorimetric studies on the reaction kinetics of dithiophosphoric acid 0,0 -dialkyl esters with zinc oxide, " and the kinetics of selective dephosphorylation of 2 -phosphorylated and 2 -thiophosphorylated dinucleotides. 

The reaction of tetraethyl pyrophosphite with perfluoroalkyl iodides in the presence of di-tert-butyl peroxide in l,l,2-trichloro-l,2,2-trifluoroethane (1-113) was described for the first time in 1981 Thermal decomposition of di-tert-butyl peroxide leads to the abstraction of an iodine atom and gives the reactive perfluoroalkyl radical, which reacts with tetraethyl pyrophosphite to produce the perfluoroalkyl phosphonite. Subsequent oxidation with tert-butyl hydroperoxide provides the desiied perfluoroalkylphosphonates in 40-71% yields (Scheme 3.40). 2 a photochemical variant, which avoids heating the reaction mixture with a peroxide, was reported later. This milder method allows the preparation of functionalized perfluoroalkylphosphonates in good yields... 

Phenol is a material of major commercial importance. One of its earliest uses was as a disinfectant (carbolic acid). Earlier in the twentieth century, it became important as a feedstock for resins such as Bakelite , and in the latter part of the century it also became very important as a precursor for caprolactone and caprolactam and hence polyester and polyamide manufacture. The two major methods for phenol production nowadays are by the catalytic oxidation of benzoic acid and catalytic decomposition of cumene hydroperoxide (Scheme 4.55). 

---