Ethers peroxide-forming

Low molecular weight ether hydroperoxides are similarly dangerous and therefore ethers should be tested for peroxides and any peroxidic products removed from them before ethers are distilled or evaporated to dryness. Many ethers autoxidize so readily that peroxidic compounds form at dangerous levels when stored in containers that are not airtight (133). Used ether containers should be handled cautiously and if they are found to contain hazardous soHd ether peroxides, bomb-squad assisted disposal may be required (134). ZeoHtes have been used for removal of peroxide impurities from ethers (135). 

The nature of the initiation step, which may occur in a variety of ways, is not known in all cases. Commonly used ethers such as ethyl ether, isopropyl ether, tetrahydrofuran, and i)-dioxane are particulady prone to form explosive peroxides on prolonged storage and exposure to air and light (see Peroxides AND PEROXY COMPOUNDS, ORGANIC), and should contain antioxidants (qv) to prevent their build-up. One of the exceptions to the peroxide forming tendency of ethers is methyl fert-alkyl ethers such as methyl fert-butyl ether [1634-04-4] (MTBE) and fert-amyl methyl ether [994-05-8] (TAME). Both have shown htde tendency if any to form peroxides (2,8). 

Explosions due to the presence of peroxides formed by aerial oxidation of ethers and tetrahydrofuran, decahydronaphthalene, acrylonitrile, styrene and related compounds. 

This reaction is the cause of a widely recognized laboratory hazard. The peroxides formed from several commonly used ethers, such as diethyl ether and tetrahydrofuran, are explosive. Appreciable amounts of such peroxides can build up in ether samples that have been exposed to the atmosphere. Because the hydroperoxides are less volatile than the ethers, they are concentrated by evaporation or distillation, and the concentrated peroxide solutions may explode. For this reason, extended storage of ethers that have been exposed to oxygen is extremely hazardous. 

List C deals with butadiene and unsaturated compounds, but does not include any ethers. Peroxides that are formed with the compounds in this list catalyse their polymerisation. This is the dangerous reaction. 

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. 

Examples 1,3-Butadiene 1,1-Dichloro-ethylene Isopropyl ether Other ethers Alkali metals Examples Most organic and inorganic materials are not peroxide forming... 

The very sensitive ether peroxide test strips (Merckoquant, Art. No. 10011), available from E. Merck, Darmstadt, are used. If the test is still positive at this point, an additional 0.2 ml. of N-methyl morpholine is added. Stirring and heating at 75° are continued for another 5 hours. Remaining peroxide renders the work-up and drying of the product potentially hazardous. N-Methylmorpholine N-oxide (1) and hydrogen peroxide form a strong 1 1 complex. In the reaction with osmium tetroxide, this complex produces conditions similar to those of the Milas reaction,7 and some ketol formation may result. 

Isopropyl ether readily forms explosive peroxides. It should be tested for peroxides, and contact with air should be minimized. 

The powder turns dark blue if it contains a large quantity of solvent and if it is exposed to the action of hot air, e.g. on drying at a temperature of 50-60°C. The investigations of Desmaroux [68), Marqueyrol and Muraour [69] and of Mar-queyrol and Loriette [70] showed that this is due to the oxidation of diphenylamine produced by peroxides formed from residual ether and atmospheric oxygen. 

Much research has been devoted to finding the mechanism of the changes which diphenylamine undergoes in powder. Marqueyrol and Loriette [70] report that under the action of oxidizing agents, particularly of peroxide formed from ether, diphenylamine undergoes the following reactions to produce tetraphenylhydrazine (I) and diphenylphenazine (II) ... 

It must be remembered that purified Ether again forms Peroxides on standing in contact with air. No inhibitor is completely successful, and the presence of Peroxides should always be detd before distilling Ether Refs 1) Beil 1, 320, [321] 2) L. Brandt,... 

This experiment was performed on XAD-4 quaternary resin in the OH- form, and desorption was by ethyl ether only (i.e., HC1 saturated ether not used). Calcium hypochlorite [Ca(OCl)2] was used to provide the required 2-ppm chlorine concentration. Millipore Super-Q water was salted according to the general procedure and passed over a 10-mL bed volume of resin (approximate dry weight = 6 g at 150 bed volumes/h. The resins were blown with nitrogen (3 lb/in2) for 10 s to remove residual water and eluted with 3 X 50-mL portions of ethyl ether. Peroxide formation was suppressed by the addition of 2% (v/v) ethanol. 

The activity of the primary peroxides formed in hexane-air or ether-air mixtures is also demonstrated by the autoxidation of benzene and aniline, which occurs readily in the presence of hexane or ether, but cannot be induced at equally low temperatures in their absence. 

Air. Like all other ethers, dioxane forms explosive peroxides on exposure to air and these may be hazardous if the dioxane is distilled. Since dioxane is miscible with water, peroxides should be removed by passing the liquid through a column of activated alumina. The alumina should be washed with water or methanol before being discarded.4 Nickel. Dioxane reacts almost explosively with Raney nickel above 210°C.5 Sulfur Trioxide. The addition complex with sulfur trioxide decomposes violently on storage.6... 

An ether consists of two hydrocarbon moieties linked by an oxygen atom, as shown in Figure 14.7. Although diethyl ether is highly flammable, ethers are generally not very reactive. This property enables their uses in applications where an unreactive organic solvent is required. Some ethers form explosive peroxides when exposed to air, as shown by the example of diethyl ether peroxide in Figure 14.7. 

The carbonyl oxide, a valence-unsaturated species, is not the final product of an ozonolysis. Rather, it will react further in one of two ways. Carrying out the ozonol-ysis in methanol leads to the capture of the carbonyl oxide by methanol under formation of a hydroperoxide, which is structurally identical to the ether peroxide of isopropyl methyl ether. However, if the same carbonyl oxide is formed in the absence of methanol (e.g., if the ozonolysis is carried out in dichloromethane) the carbonyl oxide undergoes a cycloaddition. If the carbonyl oxide is formed along with a... 

When primary alkyl phenyl tellurium or secondary alkyl phenyl tellurium compounds in methanol were treated with an excess of 3-chloroperoxybenzoic acid at 20, the phenyltelluro group was eliminated and replaced by a methoxy group. This reaction, which converts alkyl halides used in the synthesis of alkyl phenyl telluriums to alkyl methyl ethers, produced the ethers in yields as high as 90%3-4 Olefins are by-products in these reactions4 With ethanol as the solvent, ethyl ethers were formed. Other oxidizing agents (hydrogen peroxide, ozone, (ert.-butyl hydroperoxide, sodium periodate) did not produce alkyl methyl ethers. 

Ammonium peroxides.—At —10° C. dry ammonia reacts with a solution of 98 per cent, hydrogen peroxide in absolute ether to form a crystalline precipitate of the formula NH OaH or (NH4)202)H202. It melts at 14° C., and is converted by the prolonged action of ammonia into an oil, (NH4)202, which solidifies at —40° C., begins to decompose about —10° C., and melts at —2° C. It readily loses ammonia, regenerating the parent substance, NB C H.1 A crystalline, hydrated form of the composition (NH4)2O2,2H2O2,]0H2O, has been prepared. Potassium hydroxide decomposes it, with formation of ammonia and potassium peroxide. 

Oxygen is readily soluble in organic solvents, and merely pouring such liquids in air serves to saturate them with oxygen. This should be kept in mind when determining the reactivity of air-sensitive materials in solution in organic solvents. Note that many organic substances such as ethers readily form peroxides or hydroperoxides in air. 

Autoxidation of ethers to ether peroxides also involves the formation of free radicals. THF forms the corresponding hydroperoxide 2.63 at the a-position. 

Cleavage reactions following Fmoc syntheses are typically worked up by precipitating the peptide in Et20 or MTBE. The latter is preferred because of its higher boding point and lower risk of causing a fire or explosion. Ethers readily form peroxides which can oxidize Met or Cys residues in peptides. For this reason, test ethers for the presence of peroxides with KI soln before use, and purify as described in Section 4.3.5.1.12.1 1... 

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