Testing oxidizing properties

The first aim of a thermal stability screening test (e.g., DSC/DTA) is to obtain data on the potential for exothermic decomposition and on the enthalpy of decomposition (AHd). These data, together with the initial theoretical hazard evaluation, are used in reviewing the energetic properties of the substance (Box 4) and the detonation and deflagration hazards of the substance (Boxes 7 and 8). The screening tests also provide data on the thermal stability of the substance or mixture, on the runaway potential, on the oxidation properties, and to a lesser extent, on the kinetics of the reaction (Box 10). 

Several tests have been developed to identify the hazards of reactive substances [10]. Test methods for determining pyrophoric properties, water reactivity, and oxidizing properties (Box 17) are discussed in Section 2.3.4. 

All of the tests to investigate the oxidizing properties of substances involve a conical pile or a horizontal strip type of burning procedure and apparatus [134, 136, 157, 158]. The substance is mixed with a known dried combustible material such as sawdust, cellulose, or sugar, in various ratios. The burning velocity of a horizontal strip or the burning time of a conical pile of the mixture... 

The database for health effects related to dermal exposure to chlorine dioxide or chlorite is extremely limited. No reports were located regarding adverse effects in humans following dermal exposure to chlorine dioxide or chlorite. Available information in animals is restricted to a report that a solution containing chlorine dioxide concentrations of approximately 9.7-11.4 mg/L was nonirritating to the skin of mice in a 48-hour test. Dermal exposure to high concentrations would be expected to result in irritation, due to the oxidizing properties of chlorine dioxide and chlorite. Sodium chlorite was not carcinogenic in mice treated dermally for 51 weeks. Nor did sodium chlorite appear to be a cancer promoter in mice... 

Activity Measurements. To test catalytic properties of various samples partial oxidation of methanol to formaldehyde was studied in a flow micro-reactor operating under normal atmospheric pressure (10). For each run about 0.2 g of catalyst sample was used and the activities were measured at 173 C in the absence of any diffusional effects. The feed gas consisted of 72, 2 and by volume of nitrogen, oxygen and methanol vapor respectively. Reaction products were analysed with a 10% Carbowax 20 M column (2m long) maintained at 60 C oven temperature. 

As copper dissolves in the nitric acid, add new portions of copper shavings to it. When the entire selenium is oxidized, disconnect the flask with nitric acid, and suck a stream of dry air through the apparatus. Extract the prepared selenium(lV) oxide from the tube, put it into a weighing bottle, and weigh it. Determine the yield ip per cent. Write the equations of the reactions. Test the properties of selenium(IV) oxide (see p. 116). Hand in the preparation to your instructor. 

Reducing Action of Phosphorous Acid Non-Oxidizing Property of Phosphoric Acid. Review the discussion of Preparation 52, and the test employed for phosphorous acid. Phosphorous acid reduces silver nitrate to metallic silver, it itself being oxidized to phosphoric acid. 

It seemed of some interest to test the ability of a series of REY zeolites to ionize polynuclear aromatics since the oxidizing properties of zeolites were pointed out (8, 16), but the nature of the electron acceptor site is still under discussion. Hall et al. (5), studying dehydroxylated HY zeolites, presumed it to be molecular oxygen trapped in an anion vacancy, while Hirschler (7) asserted that the protons may be the oxidative centers. In a previous work, as stated by Turkevich et al. (16), we concluded that the active sites are Lewis centers, while the chemisorbed oxygen increases their electron affinity (27). In a recent work, Richardson (14) related spin concentration to the electron affinity of the cation, presuming that the electron transfer took place from the anthracene to the cupric ion, but he could not observe any variation of the Cu peak intensities. 

Nowadays, there is a growing interest in the pro-oxidant effects of flavonoids. It is of great importance to understand that a compound cannot just be classified as an antioxidant on the basis of one antioxidant experiment, because it can act as a pro-oxidant in another system. For example, diethylstilboestrol is an inhibitor of lipid peroxidation in vitro [144], but can accelerate oxidative DNA damage in vivo [145]. It is therefore recommended to use a battery of test systems involving DNA, lipids, proteins, and carbohydrates to determine both the antioxidant and pro-oxidant properties [146]. 

The deoxyribose assay is a simple test tube assay to determine the antioxidant or pro-oxidant properties of test compounds against carbohydrates [151-152]. In the deoxyribose assay, OH are produced from the reaction of H2O2 with Fe2+ (Fenton reaction), where the latter is formed by the ability of ascorbic acid to reduce ferric iron (Fe3+) to ferrous iron (Fe2+) (Eq. 27). 

The oxidizing properties of HNO3 can be shown by a very simple experiment. Place a drop of 3 M nitric acid, HNO3, solution on a strip of starch-potassium iodide test paper that has been placed in the concave dip of a watch glass. Describe what you observe in TABLE 38.lA. 

The physical and chemical characteristics of preparations via parameters (e.g., explosive properties, oxidizing properties, flashpoint and other indications of flammability, acidity/alkalinity and pH, surface tension, density, wettability, suspensi-bility, dilution stability, dry and wet sieve test, particle size distribution and other properties of the formulation) and the corresponding methods have to be determined and reported in detail [46]. 

The incorporation of LA and CLA isomers into cellular phospholipids has different effects on lipid peroxidation measured as oxygen consumption (Fig. 10.8—10.11). PC(SA LA) at a level of 5 mol% of total fatty acids reduced oxygen consumption in all of the tested PC liposome systems (Fig. 10.8—10.11), while 5 mol% PC(SA c9,rl 1-CLA) increased oxygen consumption in liposomes prepared with PC(soy) and PC(egg yolk), but reduced it in PC(rat heart) and PC(rat brain) liposomes. These data indicated that PC(SA cS,tl 1-CLA) may exhibit antioxidant or pro-oxidant properties in different phospholipids systems including membranes. Interestingly, PC(SA rlO,differed from both PC(SA LA) and PC(SA c9,t 1-CLA) in its influence on lipid peroxidation in liposome prepared with different PC. Incorporation of 5 mol% PC(SA rlO,cl2-CLA) decreased lipid oxidation in the soy PC liposomes (Fig. 10.8), but increased lipid oxidation in the liposomes prepared from all the other PC, egg, rat heart, and rat brain (Fig. 10.9—10.11). 

B.13.3.4 In cases where chemicals generate a pressure rise (too high or too low), caused by chemical reactions not characterizing the oxidizing properties of the chemical, the test described in Part III, sub-section 34.4.2 of the UN ST/SG/AC.10 (incorporated by reference See 1910.6) shall be repeated with an inert substance (e.g., diatomite (kieselguhr)) in place of the cellulose in order to clarify the nature of the reaction. 

Monteleone et al. [153] studied anaerobic H2S adsorption on activated carbons, with particular attention to the influence of thermal treatment on adsorption capacity, to feasibility of regeneration and the competitive adsorption of H2S and CO2. The selected materials were characterized before and after adsorption tests, nsing sorption of N, XRPD, TGA-DTA, SEM, and EDX. All tested carbons showed a better adsorption capacity before thermal treatment, confirming the andal role of H2O in absorption mechanism. Activated C impregnated with metal salts, revealed the highest adsorption capacity due to the combination of microporosity and oxidative properties. 

ASTM committees have dealt with standard test methods to determine the oxidative properties of materials (c/r. ASTM D 3350, 3895, 4565, 5483, 5885 and E 1858). ASTM E 1858-97 (DSC-OIT) can be used to determine the oxidative behaviour of polyolefins (HDPE) and hydrocarbon oils (diluted engine pass oil blend). This method is precise. There is a good correlation between DSC/TGA-OOT in air/02 (ASTM E 2009-99) and PDSC-OIT (ASTM E 1858-97) under high-pressure oxygen for polyolefins. The ASTM method D 3895-92 for DSC-OIT and DSC-OIT has recently been modified into a generalised technique with considerably expanded... 

---