Peroxide Content

Polyols may contain small amounts of peroxides formed during manufacture or by heating during processing operations. These can give rise to discoloration and perhaps to some reduction in physical properties due to molecular weight reduction by chain scission. 

When potassium iodide solution reacts with peroxides, free iodine is liberated. The amount liberated is directly proportional to the amount of peroxides present. The free iodine can be titrated with sodium thiosulphate solution. The peroxide content is then calculated as ppm H2O2. 

100 ml of glacial acetic acid is transferred to each of two 250 ml iodine flasks and one of the flasks reserved as a blank. Into the second flask is introduced 25 g of sample, weighed to the nearest 0 lg, and mixed thoroughly. To each flask is added 2 ml of 10% KI solution by means of a pipette. This is mixed thoroughly and allowed to stand in the dark for 15 min. It is then titrated with standard 0 01m sodium thiosulphate to a colourless end-point. No indicator is used. The blank should be titrated first and then the sample titrated to the same end-point. 

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To determine the exact peroxide content of benzoyl peroxide (and of other organic peroxides) the following procedure may be employed. Place about 0 05 g. of the sample of peroxide in a glass-stoppered conical flask add 5-10 ml. of acetic anhydride (A.R. or other pure grade) and 1 g. of powdered sodium iodide. Swirl the mixture to dissolve the sodium iodide and allow the solution to stand for 5-20 minutes. Add 50-75 ml. of water, shake the mixture vigorously for about 30 seconds, and titrate the liberated iodine with standard sodium thiosulphate solution using starch as indicator. 

Industrial specifications for aHphatic tertiary amine oxides generally requite an amine oxide content of 20—50%. These products may contain as much as 5% unreacted amine, although normally less than 2% is present. Residual hydrogen peroxide content is usually less than 0.5%. The most common solvent systems employed are water and aqueous isopropyl alcohol, although some amine oxides are available ia aoapolar solveats. Specificatioas for iadividual products are available from the producers. 

Sorbic acid and its salts are highly refined to obtain the necessary purity for use in foods. The quaUty requirements are defined by the Food Chemicals Codex (Table 3). Codistillation or recrystaUization from water, alcohoHc solutions, or acetone is used to obtain sorbic acid and potassium sorbate of a purity that passes not only the Codex requirements but is sufficient for long-term storage. Measurement of the peroxide content and heat stabiUty can further determine the presence of low amounts of impurities. The presence of isomers, other than the trans,trans form, causes instabiUty and affects the melting point. 

The reactive extrusion of polypropylene-natural rubber blends in the presence of a peroxide (1,3-bis(/-butyl per-oxy benzene) and a coagent (trimethylol propane triacrylate) was reported by Yoon et al. [64]. The effect of the concentration of the peroxide and the coagent was evaiuated in terms of thermal, morphological, melt, and mechanical properties. The low shear viscosity of the blends increased with the increase in peroxide content initially, and beyond 0.02 phr the viscosity decreased with peroxide content (Fig. 9). The melt viscosity increased with coagent concentration at a fixed peroxide content. The morphology of the samples indicated a decrease in domain size of the dispersed NR phase with a lower content of the peroxide, while at a higher content the domain size increases. The reduction in domain size... 

Figure 9 Complex viscosity of PP-NR blends vs. peroxide content of PP-NR blends at 220°C. Source Ref. 64.

Lubricating oils Bearings do not normally fail due to corrosion, but where this has occurred it has been associated with the acidity of white oils, the peroxide content and the presence of air. Peroxides are the controlling factor, but corrosion is reduced in the absence of air. The corrosion product consists of a basic lead salt of two or more organic acids " see Section 2.11). 

Of the many tests which have been submitted, the determination of active oxygen or peroxide content seems to give rather good correlation of data. During the oxidation of fat, certain oxygen-containing compounds are formed which are active in the sense that they are capable of liberating iodine from potassium iodide (19). The liberated iodine may be determined quantitatively and it thus becomes a measure of rancidity. 

A common method for determining the stability of pastry, potato chips, and the like is to place a number of broken pieces of the product in 4-ounce mayonnaise jars with screw tops and store them at room temperature or in the Schaal oven in the absence of light. At regular intervals samples are removed and tested for peroxide content and organoleptic rancidity. 

In this reaction scheme, the steady-state concentration of peroxyl radicals will be a direa function of the concentration of the transition metal and lipid peroxide content of the LDL particle, and will increase as the reaction proceeds. Scheme 2.2 is a diagrammatic representation of the redox interactions between copper, lipid hydroperoxides and lipid in the presence of a chain-breaking antioxidant. For the sake of clarity, the reaction involving the regeneration of the oxidized form of copper (Reaction 2.9) has been omitted. The first step is the independent decomposition of the Upid hydroperoxide to form the peroxyl radical. This may be terminated by reaction with an antioxidant, AH, but the lipid peroxide formed will contribute to the peroxide pool. It is evident from this scheme that the efficacy of a chain-breaking antioxidant in this scheme will be highly dependent on the initial size of the peroxide pool. In the section describing the copper-dependent oxidation of LDL (Section 2.6.1), the implications of this idea will be pursued further. 

The potency of a chain-breaking antioxidant, which scavenges peroxyl radicals, will decrease as the concentration of lipid peroxides in the LDL particle increases (Scheme 2.2). This is illustrated in the experiment shown in Fig. 2.3 in which the antioxidant potency of a peroxyl radical scavenger (BHT) decreases as a function of added exogenous hpid hydroperoxide. If the endogenous lipid peroxide content of LDL were to vary between individuals, this could explain the observed diferences in the effectiveness of a-tocopherol in suppressing lipid peroxidation promoted by copper. 

Thus in mixtures with various model hydroperoxides (reaction (24)), neither amine II nor nitroxide I had any effect on the iodometrically determined peroxide content after standing for a few days at RT. 

The data presented above are based on the assumption that hydroxyl-mediated DNA damage must depend on iron ion and hydrogen peroxide contents. Itoh et al. [15] showed that... 

Fig. 4.7 Typical behavior of a solid detergent product during the first 20 minutes in a commercially available washing machine. Relevant parameters (pH value, conductivity A, surface tension y, peroxide content ) were detected by on-line sensorics.

Photooxidation reactions of fluoroolefins in the presence of oxygen is one commercial method used in the production of PFPEs, generally employing either TFE or HFP. Fluorolefin concentration, oxygen level, light intensity, and temperature are all variables that have substantial impact on reaction rates, product distributions, polymer microstructure, peroxide content, and molecular weight. While HFP photooxidations are often carried out in bulk at low temperatures, TFE photooxidation must be carried out in an inert solvent, historically chlorofluor-ocarbons. 

The phenyl modified polymers possess the optimum combination of high temperature and elastomeric properties and were used in the study of formulation parameters These variables can have an important effect on the thermal stability and property profile of vulcanized systems For example, the use of reinforcing silicas, peroxide content, and oxidative stabilizers have been shown to be important ( 3, 10, in However, polymer-silica interactions had the most pronounced effect on retaining properties during high temperature aging studies ... 

List A, giving examples of compounds which form explosive peroxides while in storage, include diisopropyl ether, divinylacetylene, vinylidene chloride, potassium and sodium amide. Review of stocks and testing for peroxide content by given tested procedures at 3-monthly intervals is recommended, together with safe disposal of any peroxidic samples. 

Tetrahydrofuran freshly distilled from lithium aluminum hydride should be used. A commercial product with a peroxide content giving a positive iodine test must be treated with about 0.3% of cuprous chloride (boiling for 30 minutes and distillation) before the addition of the hydride. 

At any pH, [HO2 ] will depend on the fraction of PB dissociated (a) and the fraction of the total peroxide content existing as H02 This latter number Is given by + H ). 

Jasmine lactone, preparation, 787 Jet fuel, autoxidation, 665 Jojoba oil, ozonized, 718 Juice, hydrogen peroxide content, 653... 

Seafood, hydroperoxide determination, 680 Seawater, hydrogen peroxide content, 606,... 

Tetralin hydroperoxide is a convenient model compound for many studies in peroxide chemistry. It remains colorless and does not decrease in peroxide content for months if stored in the dark at or below 0°. Storage under warm summer conditions for several months results in decomposition to a dark, viscous liquid. 

FIGURE 7 Influence of a lipid emulsion and daylight on peroxide levels in freshly prepared solutions of parenteral nutrition containing multivitamins (PN + MVI and PN + Lipid + MVI). (PN = parenteral nutrition MVI = multi vitamin preparation.) The data represent the mean SEM,n = 3 the variations are not depicted because of their small size relative to the symbols. The peroxide content rose significantly over time (P < 0.001), and exposure to daylight had a significant effect on peroxide generation (P < 0.001) [33]. 

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