Butoxy decomposition

The right-hand side of Table 6-13 shows relative rates for alkoxy radical reactions in the atmosphere for boundary layer conditions. Comparison of the rates makes it immediately clear that reactions with N02 (or NO) are of little importance. For the smaller alkoxy radicals the reaction with oxygen is preponderant, whereas for alkoxy radicals largerthan butoxy, decomposition and isomerization reactions become competitive. Tertiary butoxy radicals have no abstractable hydrogen atom and thus cannot react with oxygen. In this case, decomposition is dominant. 

Because di-/ fZ-alkyl peroxides are less susceptible to radical-induced decompositions, they are safer and more efficient radical generators than primary or secondary dialkyl peroxides. They are the preferred dialkyl peroxides for generating free radicals for commercial appHcations. Without reactive substrates present, di-/ fZ-alkyl peroxides decompose to generate alcohols, ketones, hydrocarbons, and minor amounts of ethers, epoxides, and carbon monoxide. Photolysis of di-/ fZ-butyl peroxide generates / fZ-butoxy radicals at low temperatures (75), whereas thermolysis at high temperatures generates methyl radicals by P-scission (44). 

Dw-butyl pcroxyoxalatc (DBPOX) is a clean, low temperature, source of t-butoxy radicals (Scheme 3.33).136 The decomposition is proposed to take place by concerted 3-bond cleavage to form two alkoxy radicals and two molecules of carbon dioxide. 

The reactions of /-butoxy radicals are amongst the most studied of all radical processes. These radicals are generated by thermal or photochemical decomposition of peroxides or hyponitrites (Scheme 3.75). 

The f-butoxy radical can be produced from the radical decomposition of f-butylhypochlorite using azobisisobutyronitrile (AIBN) as catalyst(33) ... 

Separate experiments in which tert.-butoxy radicals were produced thermally in benzene from di-tert.-butyl peroxyoxalate failed to reveal any direct reaction of these radicals with amine II. Even at higher temperatures (A/ 150°C, dichlorobenzene, +00+ decomposition), the +0 radicals attacked neither amine II nor nitroxide I. The earlier described experiments of ketone photooxidation showed additionally that amine II displays no specially marked reactivity towards peroxy radicals. 

The crucial step in self-alkylation is decomposition of the butoxy group into a free Brpnsted acid site and isobutylene (proton transfer from the Fbutyl cation to the zeolite). Isobutylene will react with another t-butyl cation to form an isooctyl cation. At the same time, a feed alkene repeats the initiation step to form a secondary alkyl cation, which after accepting a hydride gives the Fbutyl cation and an -alkane. The overall reaction with a linear alkene CnH2n as the feed is summarized in reaction (10) ... 

For the photolysis of ferf-butyl nitrite a possible reaction mechanism (Scheme 6) consists of the production of ferf-butoxy radicals (equation 3), followed by their decomposition to give acetone and methyl radicals (equation 4). The latter are trapped by the nitric oxide liberated in the first step (equation 5). However, the absence of ethane production in the actual experiments suggested that an intramolecular formation of nitrosomethane is unlikely ". ... 

AU the products resulting from acid-catalysed solvolysis of A-acetoxy-A-butoxybenz-amides in acetonitrile-water mixtures were derived from the A-butoxy-A-hydroxybenz-amide intermediate (103), which is itself an anomeric amide and is the amide equivalent of a hemi-acetal . Decomposition reactions of 103 under acidic conditions are presented in Scheme 20. 

Co and Cu exchanged X and Y zeolites catalyze the decomposition of t-butyl hydroperoxide with generation of t-butoxy and t-butylperoxy radicals. When this decomposition is performed in the presence of olefins, such as cyclohexene or 1-octene, the corresponding epoxides are formed with selectivities ranging from 10 to 50% based on decomposed t-butyl hydroperoxide... 

The energy of activation for the addition of trifluoroinethyl radical to the C=0 double bond of hexafluoroaeetone was calculated to be 9.7 0.26 kcal. mol.-1 and that for the decomposition of the perfluoro tert-butoxy radical was found to be 30.6 1.3 kcal. mol.-1, so that AH for the formation of the perfluoro ferf-butoxy radical is —20.9 kcal. mol.-1. Thus at high light intensities and elevated temperatures, the contributions of these reactions cannot be neglected. 

The rate constant for the decomposition of tert-butoxy radicals... 

Hoare and Wellington (22) produced CH3O radicals from the photochemical (50° and 100°C.) and thermal (135°C.) decompositions of di-terf-butyl peroxide in the presence of 02. The initially formed tert-butoxy radicals decomposed to acetone plus methyl radicals, and the methyl radicals oxidized to methoxy radicals. Formaldehyde and CH3OH were products of the reaction the formation of the former was inhibited, and the latter was enhanced as the reaction proceeded. If the sole fate of CH3O were either... 

A recent oommtiruo tion by Gritter and Wallace discloses initiation of a study of the free-radical chemistry of epoxides Under the influence of U t-butoxy radicals, formed by thermal decomposition of di-lerf-butyl peroxide, propylene oxide is believed to yield an epoxy radical as shown in Eq. (3). The latter undergoes Isomerization to CHsCOCH - and further reaction with unreaoted propylene oxide or other available substrates, such as 1-octene, toluene, oyolohexene, and ethanol,fl7a as shown in Eq. (3). 

The general trends of this oxidation are consistent with the mechanism depicted in Scheme 6. This involves the complexation of the alkene to the metal followed by its insertion into the palladium-oxygen bond, forming the five-membered pseudocyclic intermediate which decomposes to give the methyl ketone and the palladium- t-butoxy complex. The decomposition of (84a) is similar to that of the rhodium dioxametallacycles previously shown in Scheme 3.42... 

Large alkoxy groups also provide steric stabilization. For example, tri-ferf-butoxysilanol, obtained by hydrolysis of sodium tri-terf-butoxy-silanolate, can be vacuum distilled without decomposition (8). 

Batt L, Hisham WWM, Mackay M (1998) Decomposition of the f-butoxy radical. II. Studies over the temperature range 303-393 K. Int J Chem Kinet 21 535-546 Bausch R, Schuchmann H-P, von Sonntag C, Benn R, Dreeskamp H (1976) CIDNP detection of the transient 4-benzyl-cyclohexa-2,5-dienone in the photorearrangement of benzyl phenyl ether. J Chem Soc Chem Commun 418-419... 

Fittschen C, Hippier H, ViskoIczB (2000) The (1 C-C bond scission in alkoxy radicals thermal unimo-lecular decomposition of f-butoxy radicals. Phys Chem Chem Phys 2 1677-1683 Gajewski E, Dizdaroglu M (1990) Hydroxyl radical induced cross-linking of cytosine and tyrosine in nudeohistone. Biochemistry 29 977-980... 

Hiatt et a/.34a-d studied the decomposition of solutions of tert-butyl hydroperoxide in chlorobenzene at 25°C in the presence of catalytic amounts of cobalt, iron, cerium, vanadium, and lead complexes. The time required for complete decomposition of the hydroperoxide varied from a few minutes for cobalt carboxylates to several days for lead naphthenate. The products consisted of approximately 86% tert-butyl alcohol, 12% di-fe/T-butyl peroxide, and 93% oxygen, and were independent of the catalysts. A radical-induced chain decomposition of the usual type,135 initiated by a redox decomposition of the hydroperoxide, was postulated to explain these results. When reactions were carried out in alkane solvents (RH), shorter kinetic chain lengths and lower yields of oxygen and di-te/T-butyl peroxide were observed due to competing hydrogen transfer of rm-butoxy radicals with the solvent. 

The radical initially produced by homolytic decomposition of a dialkyl peroxide can undergo further scission. The rate of scission depends on the temperature and the stability of the resulting radical(s). For example, t-butoxy radicals decompose on heating to methyl radicals and acetone. 

Kinetics of thermal decomposition of dialkyl peroxides in solution as well as the gas phase have been reviewed by Molyneux and Frost and Pearson . The decomposition of dialkyl peroxides is moderately free from induced decomposition, compared to other types of peroxides. As seen from Table 65, the first-order rate coefficient increases by about 16 % when the initial peroxide concentration is increased about 5 fold at reasonably high peroxide concentrations. The increase in the rate coefficient is attributed to an induced decomposition where hydrogen atom abstraction generates the radical (I). Further reaction of (I) produces isobutylene oxide and the f-butoxy radical, viz. 

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