Formation of Peroxides

Many cases are known in which the storage of a substance for a long period of time in contact with air causes explosive peroxides to form and accumulate. These peroxides may eventually explode and cause an accident 1 n.  

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CAUTION. Ethers that have been stored for long periods, particularly in partly-filled bottles, frequently contain small quantities of highly explosive peroxides. The presence of peroxides may be detected either by the per-chromic acid test of qualitative inorganic analysis (addition of an acidified solution of potassium dichromate) or by the liberation of iodine from acidified potassium iodide solution (compare Section 11,47,7). The peroxides are nonvolatile and may accumulate in the flask during the distillation of the ether the residue is explosive and may detonate, when distilled, with sufficient violence to shatter the apparatus and cause serious personal injury. If peroxides are found, they must first be removed by treatment with acidified ferrous sulphate solution (Section 11,47,7) or with sodium sulphite solution or with stannous chloride solution (Section VI, 12). The common extraction solvents diethyl ether and di-tso-propyl ether are particularly prone to the formation of peroxides. 

The effectiveness of phenoHc inhibitors is dependent on the presence of oxygen and the monomers must be stored under air rather than an inert atmosphere. Temperatures must be kept low to minimise formation of peroxides and other products. Moisture may cause mst-initiated polymerization. 

This reaction is favored by higher reaction temperatures and polar solvents. Another degradation reaction common to ethers is oxidation, especially when the a-carbon is branched (17). Polymeric ethers of all types must not be exposed to oxygen, especially in the presence of transition metals because formation of peroxides can become significant. 

Most ethers are potentially ha2ardous chemicals because, in the presence of atmospheric oxygen, a radical-chain process can occur, resulting in the formation of peroxides that are unstable, explosion-prone compounds (7). The reaction maybe generalized in terms of the following steps involving initiation, propagation, and termination. 

Peroxide Formation. Except for the methyl alkyl ethers, most ethers tend to absorb and react with oxygen from the air to form unstable peroxides that may detonate with extreme violence when concentrated by evaporation or distillation, when combined with other compounds that give a detonable mixture, or when disturbed by heat, shock, or friction. Appreciable quantities of crystalline soHds have been observed as gross evidence for the formation of peroxides, and peroxides may form a viscous Hquid in the bottom of ether-fiHed containers. If viscous Hquids or crystalline soHds are observed in ethers, no further tests for the detection of peroxides are recommended. Several chemical and physical methods for detecting and estimating peroxide concentrations have been described. Most of the quaHtative tests for peroxides are readily performed and strongly recommended when any doubt is present (20). 

Heat, sometimes ambient, accelerates the speed of formation of peroxide by oxidation in air. 

This rather low AIT was explained by the quick formation of peroxides. With acetaidehyde the reaction is the following ... 

Peracetic acid lowers the AIT in this case. Besides, it has been demonstrated that the AIT depends on the partial pressure of peracetic acid formed and which settled on the container s walls that contains aldehyde. Metal oxides (rust, alumina) catalyse the formation of peroxidic compounds. This explains the effect of corroded metals that is described above. It is interesting to note that ketones,... 

This last comment forces one to reconsider the interpretation given to the following accident. A mixture of acetone and isoprene gives rise to the formation of peroxides that detonated spontaneousiy. One can ask oneself what role acetone plays since the presence of acetone is hardly necessary to the formation of explosive peroxides by isoprene in the presence of oxygen (see Hydrocarbons on p.242). 

A 41 bottle of of methyl acrylate that had been stored for a long time detonated a few hours after being transported from the storage place to the laboratory. This explosion was explained by the formation of peroxides, which thanks to the stirring of the medium caused by the transport, gave rise to violent... 

The formation of peroxides and formaldehyde in the high-purity polyoxyethylene surfactants in toiletries has been shown to lead to contact dermatitis [31], Peroxides in hydrogenated castor oil can cause autoxidation of miconazole [32], Oxidative decomposition of the polyoxyethylene chains occurs at elevated temperature, leading to the formation of ethylene glycol, which may then be oxidized to formaldehyde. When polyethylene glycol and poloxamer were used to prepare solid dispersions of bendroflumethiazide, a potent, lipophilic diuretic drug, the drug reacted with the formaldehyde to produce hydroflumethiazide [33],... 

During preparation of hydrogen bromide by addition of bromine to a suspension of red phosphorus in water, the latter must be freshly prepared to avoid the possibility of explosion. This is due to formation of peroxides in the suspension on standing and subsequent thermal decomposition [1], In the earlier description of such an explosion, action of bromine on boiling tetralin was preferred to generate hydrogen bromide [2], which is now available in cylinders. 

Dasler, W. et al., Ind. Eng. Chem. (Anal. Ed.), 1946,18, 52 Like other monofunctional ethers but more so because of the four susceptible hydrogen atoms, dioxane exposed to air is susceptible to autoxidation with formation of peroxides which may be hazardous if distillation (causing concentration) is attempted. Because it is water-miscible, treatment by shaking with aqueous reducants (iron(II) sulfate, sodium sulfide, etc.) is impracticable. Peroxides may be removed, however, under anhydrous conditions by passing dioxane (or any other ether) down a column of activated alumina. The peroxides (and any water) are removed by adsorption onto the alumina, which must then be washed with methanol or water to remove them before the column material is discarded [1], The heat of decomposition of dioxane has been determined (130-200°C) as 0.165 kJ/g. 

Fig. 8. Gel formation of peroxide crosslinked poly(HAMCL), based on coconut fatty acids (COFA), oleic acid (OA), tall oil fatty acids (TOFA) or linseed oil fatty acids (LOFA)...

Such compounds with conugated ir-bonds are excited by light to the triplet state, and then such a triplet molecule reacts with dioxygen with the formation of peroxide. 

In the absence of an initiator, alcohols are oxidized with self-acceleration [7-9]. As in the oxidation of hydrocarbons, the increase in the reaction rate is due to the formation of peroxides initiating the chains. The kinetics of radical formation from peroxides was studied for the oxidation of isopropyl alcohol [58] and cyclohexanol [59,60]. 

The mechanism of PIP degradation appeared to be principally different. PIP has double bonds and oxidizes through intramolecular peroxyl radical addition to the double bond with formation of peroxide bridges. 

As ethers age, especially isopropyl ether, they form peroxides. The peroxides react further to form additional hazardous by-products, such as triacetone peroxide. These materials are unstable. Light, air, and heat accelerate the formation of peroxides. 

A final issue that faces this class of catalysts is stability in the fuel cell environment. Deactivation of materials in a fuel cell environment has been shown to be minimal in some studies,31,137 and severe in others.128,142 More active catalysts seem more susceptible to deactivation. Deactivation has been linked to the formation of peroxide and the loss of metal from the catalyst.128 On the other hand, demetallization has also been observed in pyrolyzed samples that did not lose activity with time.84 Another possible mode of deactivation could be due to the oxidation of the carbon surface. However, it seems reasonable that a complete understanding of the deactivation mechanism would first require a well-developed understanding of the active site. 

Also autooxidation or auto-oxidation. A slow, easily initiated, self-catalyzed reaction, generally by a free-radical mechanism, between a substance and atmospheric oxygen. Initiators of autoxidation include heat, light, catalysts such as metals, and free-radical generators. Davies (1961) defines autoxidation as interaction of a substance with molecular oxygen below 120°C without flame. Possible consequences of autoxidation include pressure buildup by gas evolution, autoignition by heat generation with inadequate heat dissipation, and the formation of peroxides. 

Much research into radiation effects on polymers is done with samples sealed under vacuum. However, polymer materials may, in practical applications, be subjected to irradiation in air. The effect of irradiation is usually substantially different in air, with increased scission at the expense of crosslinking, and the formation of peroxides and other oxygen-containing structures. Diffusion rates control the access of oxygen to radicals produced by the radiation, and at high dose rates, as in electron beams, and with thick samples, the behaviour may be similar to irradiation in vacuum. Surface changes may be quite different from bulk due to the relative availability of oxygen. 

The quantity of hydrogen peroxide found was not equivalent to the acid sorption. Catalytic decomposition might be responsible for this. The formation of peroxide-like substances when moist air and acid reacted on carbon was deducted by Lamb and Elder (114), Kolthoff (20), and King (33) from the positive potassium iodide-starch test and, in my laboratory, from the reaction with titanyl ions. 

The slow spontaneous oxidation of compounds in the presence of oxygen is termed autoxidation (autooxidation). This radical process is responsible for a variety of transformations, such as the drying of paints and varnishes, the development of rancidity in foodstuff fats and oils, the perishing of rabber, air oxidation of aldehydes to acids, and the formation of peroxides in ethers. 

Formation of peroxides by exposure to air and their involvement in polymerization processes is important for surface coating formulations containing polyunsaturated lipids called drying oils. Also nondrying oils, such as soybean oil, are under development as renewable sources for plastics and resins " . ... 

Various attempts have been made to measure the formation of peroxides in isolated proteins and low density lipoproteins upon exposure to various oxidizing agents including ionizing radiation, transition metals involved in Fenton reaction, peroxyl radicals, photosensitizers and enzymatic oxidative systems (for reviews see References 195, 234 and 241). 

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