Diethyl ether peroxide formation

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. 

To a solution of 279 g of o-chloroacetophenone in 2 liters of anhydrous diethyl ether were added about 3 g of dibenzoyl peroxide. 5 g of bromine were added to the resulting solution, and after 3 minutes, the color of bromine had been discharged, indicating that the formation of oj-bromo-o-chloroacetophenone had been initiated. A further amount of 288 g of bromine was added dropwise to the reaction mixture over a VA hour interval. After the addition of the bromine had been completed, the reaction mixture was stirred for one-half hour and poured over about 1 kg of crushed ice. 

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]. 

Many incidents involving explosions have been attributed, not always correctly, to peroxide formation and violent decomposition. Individually indexed incidents are 2-Acetyl-3-methyl-4,5-dihydrothiophen-4-one, 2807 Aluminium dichloride hydride diethyl etherate, Dibenzyl ether, 0061 f 1,3-Butadiene, 1480 f Diallyl ether, 2431 f Diisopropyl ether, 2542... 

Oglialoro modification of, 708 Perkin triangle, 108, 218f Kon modification of, 109 Peroxides, detection of, in ether, 163 removal from diethyl ether, 163 removal from isopropyl alcohol, 886 Petroleum ether, purification of, 174 Phenacetin, 996, 997 1 10-Phenanthroline, 991, 992 p-Phenetidine, 997, 998 Phenetole, 665,670 Phenobarbitone, 1003,1004,1005 Phenol, 595, 613 Phenol aldehyde polymers, 1016 formation of, 1022 Phenolphthalein, 984, 985 action as indicator, 984 ... 

For the determination of vitamin E in seed oils by HPLC, the oils can simply be dissolved in hexane and analyzed directly. Solid-food samples demand a more rigorous method of solvent extraction. In a modified Rose-Gottlieb method to extract vitamin E from infant formulas (86), dipotassium oxalate solution (35% w/v) was substituted for ammonia to avoid alkalizing the medium, and methyl tert-butyl ether was substituted for diethyl ether because of its stability against the formation of peroxides. 

The commercial grade of this solvent is obtainable in greater than 99.5 per cent purity, in which water and peroxides are the major impurities an inhibitor for peroxide formation may have been added by the manufacturers. Peroxide, if present, must be removed by passage through a column of alumina (see 1. Light petroleum for footnote on the disposal of used alumina), or by shaking with iron(n) sulphate solution as described under diethyl ether before drying and further purification is attempted. If the latter method is employed the solvent should then be dried initially over calcium sulphate or solid potassium... 

Diethyl Ether. Decomposes vigorously in ether, especially if peroxides are present.3 Dimethyl Sulfoxide. Reacts violently or explosively in dimethyl sulfoxide,4 probably due to the formation and polymerization of formaldehyde.5 Dinitrogen Pentoxide. Reacts explosively.6 Lead Dioxide. Reacts explosively.7 Phosphorus. Red phosphorus reacts vigorously on warming.8... 

Compared to other classes of organic compounds, ethers have relatively low toxicities. This characteristic can be attributed to the low reactivity of the C-O-C functional group arising from the high strength of the carbon-oxygen bond. Like diethyl ether, several of the more volatile ethers affect the central nervous system. Hazards other than their toxicities tend to be relatively more important for ethers. These hazards are flammability and formation of explosive peroxides (especially with di-isopropyl ether). 

The reaction is earned out in a two phase system w ith 30 % aqueous NaOH and MTBE. which allows trapping as well as removal of the HCl evolved. Anilide 4 is obtained directly by ciystallization from the reaction mixture, This reaction was carried out on a 1,000 g scale. Methyl erf-buty) ether (MTBE) (14) was used as solvent because it i.s not halogcnatcd (at industrial plant scale, the use of halogenated solvents is avoided because of their noxiousness) and its handling compared to that of diethyl ether is safer because of its low er volatility and lack of peroxide formation. 

Some of the most widely studied organic reactions at this time are palladium catalysed carbon-carbon cross coupling reactions, which have been extensively investigated in water. For example, palladium catalysed Suzuki reactions can be performed in water in the presence of poly (ethylene glycol) (PEG). It should be noted that the PEG may be playing the role of a surfactant (PTC) and/or a support for the metal catalyst in water. Interestingly, in this example, no phosphine is needed and the products are easily separated and the catalyst phase reused. Unfortunately, diethyl ether was used to extract the product and as this solvent is hazardous (low flash point and potential peroxide formation), the overall process would be greener if an alternative solvent could be used. 

Cyclopentyl methyl ether (CPME) is another alternative to typical ethereal solvents such as diethyl ether, THF, DME and dioxane. At present it is not bio-sourced but it is mentioned here as it has many advantageous properties as a direct replacement for ethers. Most importantly, the rate of peroxide formation is very slow and therefore, CPME is green in terms of risk avoidance and other criteria. Its use in a range of classical and modern synthetic procedures has been reported. ... 

Problems with peroxide formation are especially critical for ethers. Ethers form peroxides readily and, because they are frequently used as solvents, they are often used in quantity and then removed to leave reaction products. Cans of diethyl ether should be dated when opened and if not used within one month should be treated for peroxides or disposed of. 

Diethyl ether is extremely flammable. Its volatility and low ignition temperature make it one of the most dangerous fire hazards in the laboratory. Ether vapor forms explosive mixtures with air due to the formation of unstable peroxides. Diethyl ether may react violently with halogens or strong oxidizing agents. 

Purification of MTBE (b.p. 55°C) for general solvent use is by distillation. Its use in general solvent applications is still small. However, since MTBE has no secondary or tertiary hydrogens it is very resistant to oxidation and peroxide formation. This makes it an attractive replacement for the more traditional diethyl, and diisopropyl ethers. 

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