Tertiary hydroperoxide

The preparation of neopentyl alcohol from diisobutylene herein described represents an example of acid-catalyzed addition of hydrogen peroxide to a branched olefin, followed by an acid-catalyzed rearrangement of the tertiary hydroperoxide formed. In addition to neopentyl alcohol, there are formed acetone and also small amounts of methanol and methyl neopentyl ketone by an alternative rearrangement of the hydroperoxide. 

The yield of the formed hydroperoxide depends on the structure of the oxidized hydrocarbon. The tertiary hydroperoxides appeared to be the most stable. Hence they can be received by hydrocarbon oxidation in high yield (see Table 1.3). 

The hydrocarbon with a tertiary C—H bond is oxidized to stable tertiary hydroperoxide. This hydroperoxide is decomposed homolytically with the formation of alcohol [82] ... 

Under the catalytic action of acid, tertiary hydroperoxide is hydrolyzed to alcohol and hydrogen peroxide [46,83]. 

Tertiary hydroperoxide is decomposed to alkoxyl and peroxyl radicals, for example [67] ... 

The hydrogen bond formation decreases the frequency of the O—H bond valence vibration (see Section 4.2.3). Two configurations of tertiary hydroperoxides are known E- and Z-configurations. The activation barrier for transition from Z- to /i-configuration is found to be equal to 195 kJ mol 1 (quantum-chemical calculation [64]). 

Due to the ability of tertiary peroxyl radicals to disproportionate with the formation of alkoxyl radicals, the chain decomposition of tertiary hydroperoxides proceeds via the action of intermediate alkoxyl radicals [9,135]. 

The activity of secondary and tertiary peroxyl radicals is different due to different BDEs of the forming O—H bond D(O—H) = 365.5 kJ mol-1 for secondary hydroperoxide and D(O—H) = 358.6 kJmol-1 for tertiary hydroperoxide [57]. The comparison of the rate constants of secondary and tertiary R02 reactions with different hydrocarbons is given below (rate constants are given in L moR1 s 1 at 348 K) [9]. 

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. 

The important role of reaction enthalpy in the free radical abstraction reactions is well known and was discussed in Chapters 6 and 7. The BDE of the O—H bonds of alkyl hydroperoxides depends slightly on the structure of the alkyl radical D0 H = 365.5 kJ mol 1 for all primary and secondary hydroperoxides and P0—h = 358.6 kJ mol 1 for tertiary hydroperoxides (see Chapter 2). Therefore, the enthalpy of the reaction RjOO + RjH depends on the BDE of the attacked C—H bond of the hydrocarbon. But a different situation is encountered during oxidation and co-oxidation of aldehydes. As proved earlier, the BDE of peracids formed from acylperoxyl radicals is much higher than the BDE of the O—H bond of alkyl hydroperoxides and depends on the structure of the acyl substituent. Therefore, the BDEs of both the attacked C—H and O—H of the formed peracid are important factors that influence the chain propagation reaction. This is demonstrated in Table 8.9 where the calculated values of the enthalpy of the reaction RjCV + RjH for different RjHs including aldehydes and different peroxyl radicals are presented. One can see that the value A//( R02 + RH) is much lower in the reactions of the same compound with acylperoxyl radicals. 

For the formal reaction of replacing both oxygens in the hydroperoxide by methylene groups (equation 4), there are more comparison data available. Although there was seemingly no difference in the enthalpies of reaction 3 for a typical primary, secondary and tertiary hydroperoxide whose experimental enthalpies of formation we accepted, the situation changes with reaction 4. The enthalpies of reaction are quite different depending... 

TADOOH (60) (90%) SCHEME 27. Preparation of the tertiary hydroperoxide 60 from TADDOL... 

SCHEME 28. Stereoselective synthesis of camphor-derived tertiary hydroperoxides... 

Besides the chiral, secondary hydroperoxides employed by Adam and coworkers and the tertiary hydroperoxide used by Seebach, the optically active carbohydrate hydroperoxides 72, 93 and 94 have been tested by Taylor and coworkers in epoxidation reactions of the quinones 95 under basic conditions (Scheme 41). The yields of the corresponding epoxides 96 that were obtained with this type of oxidant varied from 33 to 83% and the enantioselectivities were moderate and in some cases good (23 to 82%), depending... 

Tertiary hydroperoxides derived from tetrasubstituted olefins containing allylic H atoms undergo scission on acid treatment at the site of the original double bond, yielding... 

Teeth whiteners, percarbamide, 623 Temperature, reaction rates, 903-12 Terminal olefins, selenide-catalyzed epoxidation, 384-5 a-Terpinene, peroxide synthesis, 706 a-Terpineol, preparation, 790 Terrorists, dialkyl peroxide explosives, 708 Tertiary amines, dioxirane oxidation, 1152 Tertiary hydroperoxides, structural characterization, 690-1... 

Addition of hydrogen peroxide to the triphenylimidazolyl (lophyl) radical (49), generated from its piezochromic dimer, yields 43 tertiary hydroperoxides likewise give 50 (R = Me, Ph). °... 

Dimethylcyclohexene (209) is converted to two tertiary hydroperoxides, 210 (12%) and 211 (88%).85,135 1-Methylcyclohexene (30) gives rise to 45% of the tertiary hydroperoxide 31 and to 55% of a non-resolved mixture of secondary hydroperoxides, 52.135 Since the ratio tertiary/secondary hydroperoxides is the same as with limonene (16) and carvomenthene (19), a similar product distribution among the secondary hydroperoxides 32 as was found for 16 and 19 has been assumed. No product distribution has been reported for the photosensitized oxygenation of 1-methylcyclopentene, 213.85,123... 

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