TBHP decomposition

Primary alcohols are selectively oxidized to aldehydes by the RuCl2(TPP)3/ tert-butylhydroperoxide (TBHP) system. The reaction takes place at room temperature using catalytic amounts of the mthenium complex. Specific conditions are found leading to improved efficiency in the TBHP decomposition and in reduction of the level of secondary products originating from the aldehyde post-reactions. The effect of some free-radical scavengers and the stracture of the mthenium conplex will also be presented. 

The formation of the complex is expected to decrease the free energy of activation for the homolysis of the peroxide bond, and the decomposition of TBHP would occur at a lower temperature. It was further observed that at a higher concentration of mineral acid, the decomposition of TBHP occurs via an ionic pathway, as reported by Turner [27]. 

MMA onto cellulose was carried out by Hecker de Carvalho and Alfred using ammonium and potassium persulfates as radical initiators [30]. Radical initiators such as H2O2, BPO dicumylperoxide, TBHP, etc. have also been used successfully for grafting vinyl monomers onto hydrocarbon backbones, such as polypropylene and polyethylene. The general mechanism seems to be that when the polymer is exposed to vinyl monomers in the presence of peroxide under conditions that permit decomposition of the peroxide to free radicals, the monomer becomes attached to the backbone of the polymer and pendant chains of vinyl monomers are grown on the active sites. The basic mechanism involves abstraction of a hydrogen from the polymer to form a free radical to which monomer adds ... 

Chromium complexes in general are poor catalysts for the epoxidation of alkenes with TBHP due to the decomposition of the oxygen donor with formation of molecnlar oxygen . Epoxidation reactions with this metal are known with other oxygen transfer agents than peroxides (e.g. iodosylbenzene) and will not be discnssed here. 

Another advantage of mesoporous catalysts was the possibility to use bulky peroxides like TBHP as oxidant. As expected, no conversion was observed with TBHP over medium pore zeolites like Ti ZSM-48 or TS-1. Over Ti-Beta or Ti-HMS, the product di.stribution was similar to that obtained with H2O2, i.e. AZY was the major product formed. However, relatively large amounts of azobenzene (AZO) were also detected. AZO is usually formed by reaction of nitrosobenzene with aniline. Nevertheless, the presence of AZO when TBHP was used as the oxidant might be explained by the metal-catalyzed decomposition of the peroxide to give radicals. Indeed, similar observations were made during the oxidation of toluene with TBHP over VAPO-.5 [10]. 

To investigate the mechanism of the reaction, a decomposition experiment was carried out in the presence of cyclohexanol to see if cyclohexanone, which is the intermolecular oxidation product of cyclohexanol and cyclohexene hydroperoxide, was formed (Table 2). To compare the oxidizability of cyclohexanol and 2-cyclohexen-l-ol, oxidation of both substrates were carried out with CrAPO-5 as catalyst and tert-butyl hydroperoxide (TBHP) as oxidant (Table 2). 

Oxidation of cyclohexanol and 2-cyclohexen-l-ol with TBHP over CrAPO-5 and the decomposition of cyclohexenyl hydroperoxide in the presence of cyclohexanol. 

Isobutane oxidation is performed in the liquid phase at 130-160 °C and elevated pressures. Since this exceeds the critical temperature of isobutane (134 °C), products (TBA, t-butyl hydroperoxide (TBHP)) must be present to maintain a liquid phase. The epoxidation step is performed at 100-130 °C using 10-300 ppm of Mo. Since propene is a rather unreactive olefin, a high propene/TBHP molar ratio is used to suppress nonproductive decomposition of TBHP. The high propene concentration leads to very high operating pressures and high recycle costs. The PO and TBA products are purified by a combination of direct and extractive distillation. TBHP conversion and PO selectivity are in excess of 90 %. 

For example, a series of alkylaromatics afforded the corresponding aralkyl ketones in high selectivities with TBHP in the presence of CrAPO-5 (3 m %) at 80 °C (Table 5). TBHP could be replaced by Oj but this required neutralization of Bronsted acid sites on the CrAPO-5, by ion-exchange, in order to avoid acid-catalyzed decomposition of the benzylic hydroperoxide to the eorresponding phenol, which inhibits the autoxidation. The addition of a small amount of TBHP to initiate the reaction also had a beneficial effect. 

The oxidation of hydrocarbons and alcohols with TBHP is presumed to involve oxidation of the substrate by oxochromium(VI) followed by reoxidation of Cr by TBHP, i.e. an oxometal pathway. When O, is the oxidant the substrate undergoes initial chromium-catalyzed autoxidation to the corresponding hydroperoxide. The latter undergoes catalytic decomposition and/or functions as the oxidant. The observation that the bulky triphenylmethyl hydroperoxide, which cannot be accommodated in the micropores, gave no reaction was construed as evidence for the reactions taking place in the micropores. This subsequently proved to be a misinterpretation of the results (see later). 

A case in point is "dilution study". When using hazardous reactants such as benzoyl peroxide (BPO) or t-butyl hydroperoxide (TBHP) which are both labelled as hazardous by CHETAH, one can perform hazard evaluations at different concentrations in a stable (non-hazardous) solvent. This allows for selection of a safe concentration for initial scale-up studies in process development. The effect of dilution with xylene on the maximum enthalpy of decomposition of the above peroxides is shown below ... 

Several solvents have been tested in the epoxidation of a- isophorone with t-butyl hydroperoxide (TBHP). The best performance of the aerogel was observed in low polarity solvents such as ethylbenzene or cumene (Table 1). In these solvents 99 % selectivity related to the olefin converted was obtained at 50 % peroxide conversion, independent of the temperature. Rasing temperature resulted in increasing initial rate and decreasing selectivity related to the peroxide. The low peroxide efficiency is explained by the homol5d ic peroxide decomposition. Protic polar solvents were detrimental to the reaction due to their strong coordination to the active sites. There was no epoxide formation in water. 

Trace amounts of n-propanol ( 1%) were also formed(GC). As well, trace amounts of acetone were also found however, a control experiment verified its formation from the Mn cluster-catalyzed decomposition of TBHP. Additionally, small amounts of isopropanol can also be oxidized to acetone under the reaction conditions. 

Tertiary alkylhydroperoxides are used most often as oxidizing agents with alkenes since primary or secondary alkylhydroperoxides are susceptible to rearrangement and decomposition. Alkylhydroperoxides are relatively soluble in organic solvents, are more stable, and are easier to handle than hydrogen peroxide.256 Both TBHP and cumyl hydroperoxide are commercially available and widely used. As with hydrogen peroxide, reaction of alkenes with hydroperoxides usually requires transition metal catalysts in order to form... 

Selectivity of TBHP to both propylene oxide and rer/-butyl alcohol in the epoxidation reactor is 83%. The balance of the TBHP decomposes to hydrocarbon by-products and oxygen. For simplification, it is assumed that the decomposition is entirely to butane and oxygen. 

While the detailed mechanism of H2O2 decomposition by 1 is not known yet, we are interested if related organic hydroperoxides can be decomposed. The surprising results, shown in Figure 4, is that 1, which contains the Mn(II)Mn(III)3 core, does not decompose significantly either cumene hydroperoxide (CHP) or t-butyl hydroperoxide (TBHP). In contrast, Mn(II) and Mn(III) acetates decompose CHP. The lack of decomposition of ROOH by 1 combined with its catalytic activity reconmiend Mn4 complexes as candidates for oxidation catalysts. 

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