Hydroperoxides in ethers

Hunsdiecker reaction, 341 Hybridization, 17 Hybrid orbital number, 17, 18, 32 Hybrid, resonance, 24 Hydration of cyclohexane derivatives, 191 Hydrazine, 4 Hydride shift, 93 Hydroboration, 95 Hydroboration-oxidation, 258, 270 Hydrocarbons, cyclic, 162 unsaturated, 87 Hydrogenation of alkenes, 57 Hydrogen bond, 22 Hydroperoxides in ethers, 284 Hydroquinone, 430 Hydroxy acids, 344... 

Hydroperoxides in ethers can be detected by shaking a small amount of the ether with an acidified 10% aqueous solution of potassium iodide, KI, or by using starch iodine paper with a drop of acetic acid. Peroxides oxidize iodide ion to iodine, I2, which gives a yellow color to the solution. Hydroperoxides can be removed by treating them with a reducing agent. One effective procedure is to shake the hydroperoxide-contaminated ether with a solution of iron(ll) sulfate in dilute aqueous sulfuric acid. You should never use ethers past their expiration date, and you should properly dispose of them before then. 

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. 

These hydroperoxides and peroxides, which often accumulate in ethers that have been left standing for long periods in contact with air, are dangerously explosive. 

Along with tertiary hydroperoxide of ether, the BDE of the O—H bonds of alkoxy hydroperoxides are higher than that of similar hydrocarbons. Very valuable data were obtained in experiments on ether oxidation (RiH) in the presence of hydroperoxide (RiOOH). Peroxyl radicals of oxidized ether exchange very rapidly to peroxyl radicals of added hydroperoxide ROOH and only R02 reacts with ether (see Chapter 5). The rate constants of alkylperoxyl radicals with several ethers are presented in Table 7.18. The reactivity of ethers in reactions with peroxyl radicals will be analyzed in next section. 

Calculation of O—H Bond Dissociation Energies in Ether Hydroperoxides from Kinetic Data (See Table 2.8 and Table 7.16)... 

The thermal decomposition of />-nitrotriphenylmethyl hydroperoxide in benzene gives -nitrophenol 32%, phenol 9%, >-nitro-triphenylcarbinol 23%, -nitrobenzophenone 14%, and no benzo-phenone the decomposition in ether plus sulfuric acid gives -nitro-benzophenone 94% and phenol 81%.817 The latter reaction is very probably ... 

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]. 

As was the case for the alkyl hydroperoxides in reaction 4, the enthalpies of the oxy-gen/hydrocarbon double exchange reaction 8 for dialkyl peroxides are different depending on the classification of the carbon bonded to oxygen. For R = Me, Et and f-Bu, the liquid phase values are —4, 24.6 and 52.7 kJmoR, respectively, and the gas phase values are 0.1, 25.7 and 56.5 kJmoR, respectively. For the formal deoxygenation reaction 9, the enthalpies of reaction are virtually the same for dimethyl and diethyl peroxide in the gas phase, —58.5 0.6 kJ moR. This value is the same as the enthalpy of reaction of diethyl peroxide in the liquid phase, —56.0 kJ moR (there is no directly determined liquid phase enthalpy of formation of dimethyl ether). Because of steric strain in the di-ferf-butyl ether, the enthalpy of reaction is much less negative, but still exothermic, —17.7 kJmol (Iq) and —19.6 kJmol (g). 

Silyl alkyl and silyl aryl peroxides 7 are prepared by reaction of alkyl, aryl or aralkyl hydroperoxides with halosilanes (equation 12). Such reactions are carried out in an inert solvent in the presence of an acid acceptor, such as pyridine, ammonia or a tertiary amine in ether or petroleum ether (Table 3) . ... 

The reaction of l,3-dichloro(tetramethyl)siloxane 12 with f-butyl hydroperoxide in the presence of pyridine in ether gave l-f-butylperoxy-3-chlorotetramethyldisiloxane 13 in 60% yield (equation 19). 

Peroxy esters 67 were prepared in situ by the reaction of phosphonochloridate and terf-butyl hydroperoxide in diethyl ether. The peroxy ester 67 (R = Ph) is stable for several days at 5 °C in diethyl ether. Most peroxyphosphates 67 with an RO group other than ferf-butylperoxy are unstable even for short periods . This synthetic method was successfully applied for synthesis of ring peroxyphosphates 70 and 71 as colorless oils. They are very unstable and decompose at 25 °C to yield polymeric products and volatile side products . ... 

The first synthesis of a peroxyphosphonate 68, i.e. ferf-butyl alkyl peroxyphospho-nate 72, was performed by the condensation of the corresponding alkyl alkylphospho-nochloridate with the sodium salt of ferf-butyl hydroperoxide in anhydrous diethyl ether (equation 99) . ... 

After filtration, the ether is removed by evaporation in an air stream. The final product is recovered by distillation under reduced pressure (behind a shield because possible hydroperoxides of ether have not been adequately removed) yield 3.8 gm (44%), b.p. 84°-86°C (150 mm Hg), n 5 1.4660. 

Uniperox 60. A proprietary mixt of cyclic hydrocarbon hydroperoxides contg 6 to 8 C atoms. Its avg mw is 130, which corresponds to the empirical formula C7H1302H. The commercial product, manufd by the R.T. Collier Corp, Los Angeles, Cal, is a water-white liq contg 60—65% by wt of hydroperoxide in admixt with ales and ketones of about the same boiling range. Its d is 0.96g/cc mp —80° bp (decompn at 110°) flash pt 80° sol in w 0.5% by wt and is completely miscible with ales, ethers, ketones, esters and petroleum fractions... 

Benzo[c]furans undergo very rapid photooxidation. 1,3-Diphenylbenzo[c ]furan yields the oxide (368) on sensitized photooxygenation in ether at -50 °C. Reduction of the oxide with potassium iodide in acetic acid affords 1,2-dibenzoylbenzene and reaction with methanol supplies the hydroperoxide (369). 

Peroxide and hydroperoxide ions. A patent disclosure h Barueoh and Payne101 has described addition of teri-bntylliydi- peroxide to ethylene oxide, propylene oxide, and isobutylene oxide in ether, in the presence of either basic or acidic catalysts. The <°rt-Imtylperoxide ion, like other nucleophiles, apparently prefers to uttar. c... 

The perester is obtained in 75% yield by reaction of 4-benzoylbenzoyl chloride with t-butyl hydroperoxide and N(C2H5)3 in ether.1... 

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