Peroxides, formation caused

Inhibited THF is problematic for semipreparative separations. Because small quantities of polymer are being collected along with larger volumes of solvent, more inhibitor, usually butylated hydroxytoluene (BHT), than sample is often collected in each fraction. Thus, one must carefully consider if the BHT will cause a problem in the subsequent analysis of the isolated fractions. If it does, uninhibited THF or other alternate solvents should be used. It must be remember that if uninhibited THF is used, the analyst must pay careful attention to the inevitable peroxide formation in the solvent/fractions. 

The chlorination of methyl chloroformate in sunlight was first reported by Hentschel, but without a detailed description of either the procedure or the results. The first step of the present procedure for the preparation of trichloromethyl chloroformate utilizes an ultraviolet light source and affords a simple and reproducible way to obtain this reagent. Although trichloromethyl chloroformate may also be synthesized by photochemical chlorination of methyl formate,the volatility of methyl formate causes losses during the reaction and increases the hazard of forming an explosive mixture of its vapor and chlorine gas. The preparation of trichloromethyl chloroformate by chlorination of methyl chloroformate in the dark with diacetyl peroxide as initiator has been reported. However, the procedure consists of several steps, and the overall yield is rather low. 

The solvent had been dried over the aluminate and then stored over calcium hydride for 2 years to prevent peroxide formation . Subsequent addition of more aluminate caused a strong exotherm and ignition of liberated hydrogen. Calcium hydride does not prevent peroxide formation in solvents. 

A 7 year old screw capped sample burst in storage. Peroxide formation seems a less likely cause than slow hydrolysis and carbon dioxide evolution, though both are possibilities. 

After storage for 16 years in a tin, a sealed bottle originally holding sodium dispersed in xylene was found to contain a yellow/white solid layer in place of the expected supernatant xylene. Scraping the solid out caused a violent explosion. The force of the explosion leads to a suspicion of peroxide formation, but there is no obvious explanation. Reactive materials like alkali-metal dispersions in volatile solvents should not be stored indefinitely, but clearly labeled after receipt or preparation to show the disposal date. Disposal of such dispersions by binning is recommended. Sodium dispersed in toluene might behave in the same way. 

Some chemicals are susceptible to peroxide formation in the presence of air [10, 56]. Table 2.15 shows a list of structures that can form peroxides. The peroxide formation is normally a slow process. However, highly unstable peroxide products can be formed which can cause an explosion. Some of the chemicals whose structures are shown form explosive peroxides even without a significant concentration (e.g., isopropyl ether, divinyl acetylene, vinylidene chloride, potassium metal, sodium amide). Other substances form a hazardous peroxide on concentration, such as diethyl ether, tetrahydrofuran, and vinyl ethers, or on initiation of a polymerization (e.g., methyl acrylate and styrene) [66]. 

The radiation decomposition in 10-3 M polonium solution ( 1 curic/ml) causes a visible evolution of gas (5, 34). The radiolysis products are strongly oxidizing, which adds difficulty to the study of the element in its lower, bipositive, state. Peroxide formation appears to be the factor which prevents a study of solutions of the element in the sexapositive state (13), at any rate on the milligram scale. 

It is assumed by some authors that hydroxyl radicals formed from hydrogen peroxide and ferrous ions react with cellulose in a similar manner to ethanol in reaction (XI) and that radical formation caused by such hydrogen abstraction leads to active sites from which graft polymerization can start ... 

Following fires in which endotracheal tubes became ignited by surgical lasers or electrocautery in atmospheres enriched by oxygen and/or nitrous oxide, the flammability of PVC, silicone rubber and red rubber tubes in enriched atmospheres was studied [1], Ozonised oxygen was reacted with hydrogen at low pressure to generate hydroxyl radicals. Pressure in the apparatus was maintained by a vacuum pump protected from ozone by a tube of heated silver foil. On two occasions there was an explosion in the plastic vent pipe from the vacuum pump. The vent gas should have been outside explosive limits and the exact cause is not clear the editor suspects peroxide formation. 

It is known that metals such as zinc and copper become more concentrated in the brain with increasing age and that these metals can induce Ab aggregation, thereby enhancing the deposition of senile plaques. In addition, the presence of these metals with Ab initiates the formation of hydrogen peroxide which causes oxidative damage to neurons. By using... 

Depletion of cellular GSH has been widely studied with hundreds of chemicals including APAP and bromobenzene. These studies demonstrated very clearly that bioactivation followed by GSH adduct formation causes depletion of cytosolic glutathione and oxidative stress as indicated by indicators including enhanced levels of GSSG, lipid peroxidation, and loss of membrane integrity. 

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