Alkylperoxy compounds

Insertion of O2 into element-carbon bonds is not well understood. Most examples of this reaction appear to involve radical intermediates that form metal alkylperoxy compounds [e.g., reactions (a)-(g)]. 

The reaction between hydroperoxides and trans-[IrX(CO)L2] (X = Cl or Br) has yielded stable alkylperoxy-compounds, as shown, with the evolution of... 

The selectivity to alcohol in LPO may be significantly increased when boric acid, meta-hotic acid, or boric anhydride is present in stoichiometric amounts (2). The boron compounds appear to convert alkyUiydroperoxides to alkyl borates and may also intercept alkylperoxy radicals, converting them to alkylperoxyboron compounds these are later converted to alkyl borates. The alkyl borates are resistant to further oxidation they are hydrolyzed to recover alcohols. 

The aromatic core or framework of many aromatic compounds is relatively resistant to alkylperoxy radicals and inert under the usual autoxidation conditions (2). Consequentiy, even somewhat exotic aromatic acids are resistant to further oxidation this makes it possible to consider alkylaromatic LPO as a selective means of producing fine chemicals (206). Such products may include multifimctional aromatic acids, acids with fused rings, acids with rings linked by carbon—carbon bonds, or through ether, carbonyl, or other linkages (279—287). The products may even be phenoUc if the phenoUc hydroxyl is first esterified (288,289). 

By way of example, tert-huty peroxyacetate [107-71-1] is more thermally stable than 3-hydroxy-1,1-dimethylbutyl peroxyneoheptanoate [110972-57-1]. Although other factors affect thermal stabiUty, the trends shown can be used to quaUtatively predict peroxyester reactivity trends. The order of activity of the R group ia peroxyesters is also observed ia other / fZ-aLkylperoxy-containing compounds. 

Symmetrical diaLkyl peroxides are commonly named as such, eg, dimethyl peroxide. For unsymmetrical diaLkyl peroxides, the two radicals usually are hsted ia alphabetical order, eg, ethyl methyl peroxide. For organomineral peroxides or complex stmctures, ie, where R and R are difficult to name as radicals, the peroxide is named as an aLkyldioxy derivative, although alkylperoxy is stUl used by many authors. CycHc peroxides are normally named as heterocychc compounds, eg, 1,2-dioxane, or by substitutive oxa nomenclature, eg, 1,2-dioxacyclohexane however, when the two oxygens form a bridge between two carbon atoms of a ring, the terms epidioxy or epiperoxy are frequendy used. The resulting polycycHc stmcture has been called an endoperoxide, epiperoxide, or transaimular peroxide. 

Alkylperoxy (RO2) and peroxyacyi (RC(O)OO) radicals react with NO to form NO2. The alkylperoxy radicals (RO2) react with NO2 to form pemitric acid-type compounds, which decompose thermally as the temperature increases. The peroxyacyi radical reacts with NO2 to form PAN-type compounds, which also decompose thermally. 

Y. Kamiya illustrates the influence on catalytic activity of the form of the catalyst. Thus, in the cobalt-catalyzed oxidation of hydrocarbons in acetic acid solution, introduction of bromide ions increases the activity of the catalyst, especially when the metal ion concentration is fairly high. The presence of bromides also results in a marked increase in the proportion of carbonyl compounds among the products and it is believed that these are formed as a result of a propagation step in which bromine-containing cobaltous ions react with alkylperoxy radicals. 

Since the metal-alkene association preceding the peroxymetalation reaction in mechanism (B) is a pure Lewis acid/Lewis base interaction, it would be expected that compounds having alkylperoxy groups bonded to a Lewis acid center should be active for the epoxidation of alkenes. This is indeed found for boron compounds, which are active as catalysts for the epoxidation of alkenes by alkyl hydroperoxides.246,247 Isolated boron tris(alkyl peroxides), B(OOR)3, have been shown to epoxidize alkenes stoichiometrically, presumably through alkylperoxyboration of the double bond (equation 76).248... 

It can be seen that the pseudocyclic intermediate (84a) strongly resembles the stable alkylperoxy-mercury compound (84b) prepared from the reaction of TBHP with an alkene in the presence of mercury(II) carboxylate.238 The X-ray structure of the similar BrHg CH(Ph)CH(Ph)(OOBu1) compound has clearly shown the pseudocyclic nature of this adduct by the interaction existing between mercury and the OBu1 group.259 The transmetalation of mercury by palladium in (84b) produces acetophenone in 95% yield, presumably via the formation of the pseudocyclic intermediate (85 equation 85).42... 

In regions of the atmosphere where the NO concentrations are low, reaction 28 of alkylperoxy radicals with H02 could be important40. If the halogenated compounds behave in the same manner as alkylperoxy, the resulting hydroperoxides may be expected to under-... 

In the presence of mineral acids, the hydroxyl groups in 44 can be replaced by alkoxy or alkylperoxy groups to give 45, 46, or 47. The monomethoxy compound (48) occurs as an intermediate in the formation of the dimethoxy compound (45). 48 was obtained by Bailey et al.i6 on ozonization of naphthalene, 2-methoxynaphthalene, and 2-ethoxynaphthalene in methanol. Ozonization of 2-ethoxynaph-thalene in ethanol leads to the diethoxy compound (46).46 The peroxides 44-46 and 48 can be converted into o-phthaldialdehyde (in 55% yield from 48) by hydrogenation in the presence of a Lindlar catalyst.45 The peroxide oxygen in 45-48 cannot be quantitatively determined by iodometry.45... 

The alkyl radical initially formed reacts readily with oxygen to give the corresponding alkylperoxy radical, which may abstract hydrogen from a fuel molecule to form the alkylhydroperoxide or alternatively decompose to yield an aldehyde and an alkoxy radical. Some workers thought that this decomposition was preceded by an isomerization of the alkylperoxy radical, the activation energy of which had been estimated by Semenov [3] to be ca. 20 kcal. mole. Shtern was of the opinion that the major, if not the only, fate of the alkylperoxy radical was decomposition, but in contrast to other workers he believed that it must involve scission of a C—C bond and could not lead to the formation of a carbonyl compound and hydroxyl radical. 

In contrast to the alkene theory the predominant mode of oxidation of the alkyl radicals is by oxygen addition and the alkylperoxy radical so formed then undergoes homogeneous intramolecular rearrangement (reaction (14)). Decomposition of the rearranged radical (reaction (16)) usually leads to a hydroxyl radical and stable products which include O-heterocycles, carbonyl compounds and alcohols with rearranged carbon skeletons relative to the fuel and alkenes. The chain-cycle is then completed by unselective attack on the fuel by the hydroxyl radical (reaction (12)). 

In view of the known extensive isomerization and subsequent decomposition of alkylperoxy radicals which occurs under the same reaction conditions it is not unreasonable to suppose that these unsaturated carbonyl compounds are also the result of hydroperoxyalkyl decomposition even though it requires the scission of three bonds. Fish et al. [78] have formally explained the formation of the above compounds from... 

In the presence of dioxygen, the carbon radical R- produced by reactions (201) and (202) ar transformed into alkylperoxy radicals ROO, reacts with Co or Mn species to regenerate th Co " or Mn " oxidants, and produce primary oxygenated products (alcohol, carbonyl compounds which can be further oxidized to carboxylic acids. This constitutes the basis of several Industrie processes such as the manganese-catalyzed oxidation of n-alkenes to fatty acids, and the cobal catalyzed oxidation of butane (or naphtha) to acetic acid, cyclohexane to cyclohexanol-on mixture, and methyl aromatic compounds (toluene, xylene) to the corresponding aromatic monc or di-carboxylic acids. ... 

This reaction consumes two alkylperoxy radicals and produces an alcohol and a carbonyl compound. At least one a-hydrogen atom must be present on one of the alkylperoxy radicals. If the peroxy radicals involved retain the carbon skeleton of the starting hydrocarbon, so will the products. 

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