Removal of peroxides from ethers

Detection and removal of peroxides from solvents Organic Solvents Physical Properties and Methods of Purification, 4th ed., ed. J. A. Riddick et al. (Chichester Wiley, 1986). Deperoxidation of ethers with molecular sieves Burfield, D. R., J. Org. Chem., Al, 3821-3824, 1982. 

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). 

Removal of peroxides.1 Self-indicating activated 4 A molecular sieve (J. T. Baker, Merck) effectively removes peroxides from various ethers. The effectiveness is not a result of adsorption but of interaction with the impregnated indicator. 

Tetrahydrofuranyl (THF) ethers are reported to be useful alternatives to tetrahydropyranyl (THP) ethers for the protection of alcohols (and thiols). THF ethers are easily formed, and are more sensitive to acidic hydrolysis than are THP ethers. We are warned that hydroboration-oxidation or peracid oxidation of simple unsaturated compounds containing a hydroxy-group protected as its THP ether has led to violent detonations. The danger comes from the ready formation of peroxides from THP ethers, and presumably also from THF ethers these peroxides, though very sensitive, are not easily removed by ordinary chemical methods. 

Some of the following material is taken from the second edition of this handbook from an article by Norman V. Steere, Control of Peroxides in Ethers. It has been edited to conform with the format of the current edition and has been added to from other sources. The sections on detection and estimation of peroxides and removal of peroxides have been substantially shortened, in line with the philosophy espoused elsewhere in this section to keep on hand only amormts that will be quickly used, and in order to reduce the risks in handling possibly contaminated materials. 

Appropriate action to prevent injuries from peroxides in ethers depends on knowledge about formation, detection, and removal of peroxides, adequate labeling and inventory procedures, personal protective equipment, suitable disposal methods, and knowledge about formation, detection, and removal of peroxides. 

CAUTION Upon standing, ethers may form peroxides. Peroxides are very explosive. To test for the presence of these substances, use starch-iodide paper that has been moistened with 6 M HQ. Peroxides cause the paper to turn blue. To remove peroxides from ethers, pass the material through a short column of highly activated alumina (Woelm basic alumina, activity grade 1). ° Always retest for peroxides before using the ether. 

Absolute diethyl ether. The chief impurities in commercial ether (sp. gr. 0- 720) are water, ethyl alcohol, and, in samples which have been exposed to the air and light for some time, ethyl peroxide. The presence of peroxides may be detected either by the liberation of iodine (brown colouration or blue colouration with starch solution) when a small sample is shaken with an equal volume of 2 per cent, potassium iodide solution and a few drops of dilute hydrochloric acid, or by carrying out the perchromio acid test of inorganic analysis with potassium dichromate solution acidified with dilute sulphuric acid. The peroxides may be removed by shaking with a concentrated solution of a ferrous salt, say, 6-10 g. of ferrous salt (s 10-20 ml. of the prepared concentrated solution) to 1 litre of ether. The concentrated solution of ferrous salt is prepared either from 60 g. of crystallised ferrous sulphate, 6 ml. of concentrated sulphuric acid and 110 ml. of water or from 100 g. of crystallised ferrous chloride, 42 ml. of concentrated hydiochloric acid and 85 ml. of water. Peroxides may also be removed by shaking with an aqueous solution of sodium sulphite (for the removal with stannous chloride, see Section VI,12). 

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 synthesis for each differs only in the relative proportion of monomer loaded into the reaction vessel. Commercial benzoyl peroxide (1 percent by weight based on the sum of TBTM and MMA) was employed as the initiator. 0.8 mol of TBTM freshly recrystallized from ether and 0.8 mol MMA were added to 860 g of benzene in a flask equipped with a thermometer and reflux condenser. To this mixture was added 4.3 g (0.018 mol) of benzoyl peroxide. The flask and contents were warmed at the reflux temperature of benzene (80.1°C) with stirring. After 24 hours reaction time the benzene was removed in vacuo at 50°C. 

Apart from the conversion of peroxides to useful products, it is sometimes necessary to reduce peroxides, and especially hydroperoxides formed by auto-oxidation. Such compounds are formed especially in hydrocarbons containing branched chains, double bonds or aromatic rings, and in ethers such as diethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, etc. Since most peroxidic compounds decompose violently at higher temperatures and could cause explosion and fire it is necessary to remove them from liquids they contaminate. Water-immiscible liquids can be stripped of peroxides by shaking with an aqueous solution of sodium sulfite or ferrous sulfate. A simple and efficient way of removing peroxides is treatment of the contaminated compounds with 0.4 nm molecular sieves [669]. 

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