Alcohols from hydroperoxide decomposition

Hydroperoxide formation is characteristic of alkenes possessing tertiary allylic hydrogen. Allylic rearrangement resulting in the formation of isomeric products is common. Secondary products (alcohols, carbonyl compounds, carboxylic acids) may arise from the decomposition of alkenyl hydroperoxide at higher temperature. 

The thermal or photochemical homolysis of the hydroperoxide leads to the formation of an alkoxy radical. The alkoxy radical is the precursor of unsaturated alcohols, acids and ketones. The decrease in intensity of the band at 807 cm-1 indicated saturation of the double bond, which could result from a radical addition to the double bond (for example, by reaction with the hydroxyl radicals resulting from the decomposition of hydroperoxides). Saturation reactions result in the formation of saturated alcohols, acids and ketones. 

The products from cumene hydroperoxide decomposition induced by organic sulfur compounds were determined by quantitative NMR except for phenol by high-pressure liquid chromatography and cumene hydroperoxide by iodometric titration (16). Cumyl alcohol is produced in the initial oxidation of sulfenic acid to sulfonic acid, and subsequently most of it is converted to a-methylstyrene as shown in Table II. The major products (40-45%) are phenol and acetone consistent with an acid-catalyzed decomposition of cumene hydroperoxide. Considerable... 

A variety of compounds such as hydrocarbons, alcohols, furans, aldehydes, ketones, and acid compounds are formed as secondary oxidation products and are responsible for the undesirable flavors and odors associated with rancid fat. The off-flavor properties of these compounds depend on the structure, concentration, threshold values, and the tested system. Aliphatic aldehydes are the most important volatile breakdown products because they are major contributors to unpleasant odors and flavors in food products. The peroxidation pathway from linoleic acid to various volatiles is determined in several researchs, - by using various techniques (Gas chromatography mass spectrometry, GC-MS, and electron spin resonance spectroscopy, ESR), identified the volatile aldehydes that are produced during the oxidation of sunflower oil. In both cases, hexanal was the major aldehyde product of hydroperoxide decomposition, whereas pentanal, 2-heptenal, 2-octenal, 2-nonenal, 2,4-nonadienal, and 2,4-decadienal were also identified. 

The autoxidation of isobutane is now mainly carried out to obtain terf-butyl hydroperoxide [36]. Halogenated metalloporphyrin complexes are reported to be efficient catalysts for the aerobic oxidation of isobutane [18,37]. It was found that the oxidation of isobutane by air (lOatm) catalyzed by NHPI and Co(OAc)2 in benzoni-trile at 100 °C produced tert-butyl alcohol in high yield (81%) along with acetone (14%) (Eq. (6.3)) [38]. 2-Methylbutane was converted into the carbonacetic acid, rather than the alcohols, as prindpal products. These cleaved products seem to be formed via P-sdssion of an alkoxy radical derived from the decomposition of a hydroperoxide by Co ions. The extent of the P Scission is known to depend on the stability of the radicals released from the alkoxy radicals [39]. It is thought that the 3-scission of a terf-butoxy radical to acetone and a methyl radical occurs with more difficulty than that of a 2-methylbutoxy radical to acetone and an ethyl radical. As a result, isobutane produces terf-butyl alcohol as the principal product, while 2-methylbutane affords mainly acetone and acetic acid. 

The oxidation of alkanes by r-butyl hydroperoxide (TBHP) has been catalysed by titanium alkoxides, producing the corresponding alcohols and ketones. A radical mechanism is proposed in which r-butoxyl radical formed from TBHP and titanium alkoxide initiates the reaction. The evolution of oxygen (from the decomposition of peroxide) and the abstraction of hydrogen from alkane to form alkyl radical occur competitively. A method for the determination of both the primary and secondary KIEs at a reactive centre based on starting-material reactivities allows the determination of the separate KIEs in reactions for which neither product analysis nor absolute rate measurements are applicable. It has been applied to the FeCls-catalysed oxidation of ethylbenzene with TBHP, which exhibits both a primary KIE and a substantial secondary KIE the findings are in accordance with previous mechanistic studies of this reaction. The oxidation of two l-arylazo-2-hydroxynaphthalene-6-sulfonate dyes by peroxy-acids and TBHP catalysed by iron(III) 5,10,15,20-tetra(2,6-dichloro-2-sulfonatophenyl)porphyrin [Fe(ni)P] is a two-step process. In single turnover reactions, dye and Fe(in)P compete for the initially formed OFe(IV)P+ in a fast reaction and OFe(IV)P is produced the peroxy acid dye stoichiometry is 1 1. This is followed by a slow phase with 2 1 peroxy acid dye stoichiometry [equivalent to a... 

Post-irradiation oxidation of UHMWPE at room temperature results in the formation of ketones as main products of the oxidation cycle, together with hydroperoxides and variable amounts of acids, alcohols, esters, and lactones [21]. It has been shown [21] that hydroperoxides in UHMWPE are stable at room temperature and start to decompose at temperature higher than 70°C, therefore ketones and the other oxidized species observed during post-irradiation oxidation cannot result only from the decomposition of hydroperoxides. Considering these results, it can be supposed that ketones are also formed during the first step of oxidation of UHMWPE as a consequence of a direct reaction between macroalkyl radicals and oxygen. A modified Bolland s cycle is proposed in Scheme 9 [21]. 

Alkoxyall l Hydroperoxides. These compounds (1, X = OR , R = H) have been prepared by the ozonization of certain unsaturated compounds in alcohol solvents (10,125,126). 2-Methoxy-2-hydroperoxypropane [10027-74 ] (1, X = OR , R" = methyl), has been generated in methanol solution and spectral data obtained (127). A rapid exothermic decomposition upon concentration of this peroxide in a methylene chloride—methanol solution at 0°C has been reported (128). 2-Bromo-l-methoxy-l-methylethylhydroperoxide [98821-14-8]has been distilled (bp 60°C (bath temp.), 0.013 kPa) (129). Two cycHc alkoxyaLkyl hydroperoxides from cyclodecanone have been reported (1, where X = OR R, R = 5-oxo-l, 9-nonanediyl) with mp 94—95°C (R" = methyl) and mp 66—68°C (R" = ethyl) (130). Like other hydroperoxides, alkoxyaLkyl hydroperoxides can be acylated or alkylated (130,131). 

The traditional chain oxidation with chain propagation via the reaction RO/ + RH occurs at a sufficiently elevated temperature when chain propagation is more rapid than chain termination (see earlier discussion). The main molecular product of this reaction is hydroperoxide. When tertiary peroxyl radicals react more rapidly in the reaction R02 + R02 with formation of alkoxyl radicals than in the reaction R02 + RH, the mechanism of oxidation changes. Alkoxyl radicals are very reactive. They react with parent hydrocarbon and alcohols formed as primary products of hydrocarbon chain oxidation. As we see, alkoxyl radicals decompose with production of carbonyl compounds. The activation energy of their decomposition is higher than the reaction with hydrocarbons (see earlier discussion). As a result, heating of the system leads to conditions when the alkoxyl radical decomposition occurs more rapidly than the abstraction of the hydrogen atom from the hydrocarbon. The new chain mechanism of the hydrocarbon oxidation occurs under such conditions, with chain... 

MCBA enhances the solubility of the cobalt salts in MeCN solution, thereby ensuring better efficiency to a needed redox decomposition of the hydroperoxide intermediate of the substrate en route to the products". By using the HPI/Co(II)/MCBA/02 system in MeCN solution at 25 °C, competitive oxidations of p-X-substituted benzyl alcohols were run pairwise (Scheme 8). From the amount of the aldehydes produced, the relative reactivity (kx/ h) could be reckoned, and the acquired data provided a p = —0.68 in a Hammett plot vs. <7+. ... 

For the formal deoxygenation (decomposition) reaction 5, there is an enthalpy of formation value for every alcohol that matches a hydroperoxide . Using our exemplary groups, R = 1-hexyl, cyclohexyl and ferf-butyl, the liquid enthalpies of reaction are —77.9, —75.0 and —65.6 kJmoR, respectively (there is no liquid phase enthalpy of formation reported for f-butyl peroxide from Reference 4). The secondary hydroperoxides enthalpies of reaction average —77 7 kJmoR. For the three instances where there are also gas phase enthalpies of formation, the enthalpies of reaction are almost identical in the gas and liquid phases. The 1-heptyl (—60.3 kJmoR ) and 1-methylcyclohexyl (—50.6 kJmoR ) enthalpies of reaction are again disparate from the 1-hexyl and tert-butyl. If the enthalpy of reaction 5 for 1-hexyl hydroperoxide is used to calculate an enthalpy of formation of 1-heptyl hydroperoxide, it is —325 kJmoR, almost identical to values derived for it above. The enthalpies of reaction for the liquid and gaseous phases for the tertiary 2-hydroperoxy-2-methylhex-5-en-3-yne are —78.2 and —80.9 kJmoR, respectively. For gaseous cumyl hydroperoxide, the enthalpy of reaction is —84.5 kJmoR. ... 

In 1996, Hamann and Hoft were able to obtain 1,2,3,4-tetrahydronaphthyl hydroperoxide (THPO, 16b) in enantiomerically enriched form starting from the racemic mixture by selective decomposition of one enantiomer in the presence of Jacobsen s catalyst 21 . Besides the enantiomerically enriched hydroperoxide (5)-16b, also the corresponding alcohol (/f)-l-tetralol (19b) was isolated in enantiomerically enriched form (opposite... 

The cleanest product composition may be effected by decomposition of the pure hydroperoxide or solutions in the injection block of the gas chromatograph. In carbon tetrachloride solution only methyl vinyl ketone and methyl vinyl carbinol were produced, the ratio of ketone to alcohol being 2.9. No definite traces of products from isomerized hydroperoxide were observed. 

Results of product studies of three experiments in Table II are given in Table III. Hydroperoxide yields based on AOo vary from 7 to 92%, and the yields increase with increasing isobutane pressure, although there is some scatter that may be caused by wall decomposition. From the yields of methanol and tert-butyl alcohol after reduction, nearly all of the hydroperoxide formed at high isobutane pressures is tert-butyl hydroperoxide. The yields of hydroperoxide at high isobutane pressures are comparable to those found in the liquid phase at 50° and 100°C. (Table I) and those reported by Winkler and Heame for liquid-phase runs at 125°C. (34). 

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