Dioxane, peroxides, removal

The acetal (b 82.5°) is removed during fractional distn. Traces of benzene, if present, can be removed as the benzene/MeOH azeotrope by distn in the presence of MeOH. Distn from LiAlHa removes aldehydes, peroxides and water. Dioxane can be dried using Linde type 4X molecular sieves. Other purification procedures include distn from excess C2H5MgBr, refluxing with Pb02 to remove peroxides, fractional crystn by partial freezing and the addition of KI to dioxane acidified with aq HCl. Dioxane should be stored out of contact with air, preferably under N2. 

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. 

If ether is not suitable for the oxidation reactions in which the peracid is to be used, the material can be dissolved in another solvent after removal of the ether. An excellent solvent for monoperphthalic acid oxidations is dioxane, and a solution of the peracid in dioxane is readily prepared by adding dioxane to the dried ether extract and then removing the ether under reduced pressure at 150. The dioxane must be peroxide-free.1... 

The amount of liberated carbon dioxide was equimolar to the HCl adsorption. Rivin confirmed also that hydrogen peroxide is formed by reaction of carbon black with formic acid in the presence of oxygen. Physically adsorbed hydrochloric acid was removed by washing with dioxane. The remaining chloride ions on the surface were replaced by hydroxide ions on treatment with sodium hydroxide. The reaction was formulated as production of a carbinol ... 

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]. 

The checkers found that removing peroxides by passing dioxane through an activated alumina column prior to distillation greatly reduced discoloration of the reaction solution which develops during reflux, f An excess of hydrogen chloride decreases the yield markedly. 

Peroxides in ether solvents. This is one of the commonest causes of explosions in organic chemistry laboratories. Simple dialkyl ethers such as diethyl ether and di-isopropyl ether, and cyclic ethers such as 1,4-dioxane and tetrahydrofuran, form less volatile peroxides on exposure to air and light. If therefore one of these solvents is purified by distillation, the peroxide content in the residue is progressively increased and eventually a violent explosion may occur. In view of this (i) such solvents should not be stored for long periods or in half empty bottles containers should be of dark glass (ii) before the solvents are distilled a peroxide test should be carried out, and, if positive, the peroxide must be removed (Section 4.1.11, p. 402 and Section 4.1.75, p. 404) and (iii) since purified ethers in contact with air rapidly peroxidise again (10 minutes in the case of tetrahydrofuran) they should be retested for peroxides and purified if necessary immediately before use. 

Distillation of the purified dioxane from calcium hydride or preferably passage through a column of basic activated alumina (1) before use, ensures the removal of any peroxide which may develop on storage. 

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... 

To remove peroxides, wear butyl rubber gloves, laboratory coat, and eye protection. Pour the dioxane (100 mL) into a separatory funnel and shake with a freshly prepared 50% aqueous solution of sodium metabisulfite (20 mL) for 3 minutes. Release the pressure in the funnel at 10-second intervals. Separate the aqueous layer. Retest the dioxane for the continued presence of small amounts of dialkyl peroxides that are not reduced by the metabisulfite treatment. If peroxides are absent, the dioxane can be dried for reuse or packaged for disposal by burning. If peroxides are still present, in the fume hood, place the ether in a 250-mL round-bottom flask equipped with a condenser, and add a solution of 100 mg of potassium iodide in 5 mL of glacial acetic acid and 1 drop of concentrated hydrochloric acid. Reflux gently for 1 hour. Package the ether for disposal by burning.13... 

Stannous chloride has been used to remove peroxides from dioxane and ether, Fisher and Baxter, Colo. School Mines Mag., 30, 447 (1940)[C. A., 84, 8111 (1940)1. 

A mixture of methyl xanthate (0.4 mmol) and Bu2POH (dibutylphosphine oxide, 2.0 mmol) in dry dioxane (3 ml) was refluxed under an argon atmosphere, and then a solution of benzoyl peroxide (0.4 mmol) in dioxane (3 ml) was added dropwise to the mixture. After 90 min, the solvent was removed and the residue was chromatographed on silica gel to give the reduction product [22]. 

Peroxides are removed from dioxane by passage through an alumina... 

Purification of Dioxane. Dioxane was purified (to remove unwanted peroxides) as follows (11) 300 mL water, 40 mL... 

Dioxane, refluxed over lithium aluminum hydride for 1 h (to decompose peroxides) and distilled, b.p. 100-102°C Methanol, refluxed over solid potassium hydroxide (pellet form) for 15min to remove residual acids and distilled, b.p. 64-65 °C... 

For cleavages involving iPrOH/dioxane (up to 1 1), the latter should first be tested for the presence of peroxides by mixing it with an equal volume of 4% KI soln. If any brown color is formed after 1 min, remove the peroxides by passing the dioxane through a column of activated alumina (AI2O3). Not all commercially available activated alumina is effective Baker No. 0537 is satisfactory. Do not use acid-washed alumina. The same procedure is used to purify THF.td... 

Dioxane, C4H8O2 101 A very good solvent, not too difficult to remove from crystals a mild carcinogen, forms peroxides. 

Dioxane (bp 101°) is another useful ether-type solvent and is particularly suitable for some reactions since it is completely miscible with water and can therefore be easily removed at the completion of the reaction. Commercial dioxane contains water, glycol acetal, and peroxides, all of which should be removed. Three liters of dioxane, 40 ml of concentrated hydrochloric acid, and 300 ml of water are heated to reflux in order to hydrolyze the acetal, and a stream of nitro-... 

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