Hydrogen bonding alkyl hydroperoxides

Much of what is understood today about the influence of solvent on rates of oxidation reactions with hydrogen peroxide, alkyl hydroperoxides and peroxyacids can be attributed to the seminal studies by Edwards and his collaborators over thirty years ago " . They provided convincing experimental data that showed that a hydroxylic solvent (e.g. ROH) can participate in a cyclic transition state where a proton relay can in principle afford a neutral leaving group attending heterolytic 0-0 bond cleavage (equation 13). 

The largest number of hydrogen bonds in crystal structures of alkyl hydroperoxides refer to intermolecular bonds between the hydroperoxide proton and functionalities of the type 0=X, where X denotes a sulfur (e.g. 27), carbon (e.g. 30) or a phosphorous atom (e.g. 32, Figure 14, Table 7)93,108,115 geometry of [l,2-bis(diphenylphosphinoyl)ethane] bis(2,2-dihydroperoxypropane) (32) in the solid state is a rare example of a bifurcated hydrogen bond between an OOH donor and an 0=X proton acceptor. 

The second largest number of hydrogen bonds in crystal structures of alkyl hydroperoxides refers to interactions of the type OO—H OR R, where R is an alkyl group and R denotes H, alkyl or R O. The OO OR R distances vary between 2.67-2.91 A and the associated O—H O angles range from 152 to 177°. In some compounds, formation of intramolecular hydrogen bonds of the type OO—H 0=X would in principle have been feasible. The number of examples documented in the literature so far is clearly in favor of the intermolecular type of H bonding. 

In cA-3,4a,5,7a-tetrahydro-6,7a-diphenylcyclopenta[l,2-e]-l,2,4-trioxin-5/ -yl hydroperoxide (24) (P2i/c, O - O = 2.87 A, 0- - -H=1.99A, O- - - H-O = 172°), hydrogen bonding occurs between the OOH proton and the ether O (Figure 15). On the basis of pXhb data alone, an association via the endoperoxide entity of the molecule would have been expected . The affinity for H-bond formation toward ether O atoms is documented in the number of cocrystaUization adducts between ether molecules and alkyl... 

Disproportionation reaction 7 might be expected to be thermoneutral in the gas phase and perhaps less so in the liquid phase where there is the possibility of hydrogen-bonding. Only for gas phase dimethyl peroxide is the prediction true, where the reaction enthalpy is —0.2 kJmoD. The liquid phase enthalpy of reaction is the incredible —61.5 kJmoD. Of course, we have expressed some doubt about the accuracy of the enthalpy of formation of methyl hydroperoxide. For teri-butyl cumyl peroxide, the prediction for thermoneutrality is in error by about 6 kJmor in the gas phase and by ca 9 kJmoD for the liquid. The enthalpy of reaction deviation from prediction increases slightly for tert-butyl peroxide — 14kJmol for the gas phase, which is virtually the same result as in the liquid phase, — 19kJmol . The reaction enthalpy is calculated to be far from neutrality for 2-fert-butylperoxy-2-methylhex-5-en-3-yne. The enthalpies of reaction are —86.1 kJmoD (g) and —91.5 kJmol (Iq). This same species showed discrepant behavior for reaction 6. Nevertheless, still assuming thermoneutrality for conversion of diethyl peroxide to ethyl hydroperoxide in reaction 7, the derived enthalpies of formation for ethyl hydroperoxide are —206 kJmoD (Iq) and —164 kJmoD (g). The liquid phase estimated value for ethyl hydroperoxide is much more reasonable than the experimentally determined value and is consistent with the other n-alkyl hydroperoxide values, either derived or accurately determined experimentally. 

Alkyl halides, hydroperoxide synthesis, 327-8 Alkyl hydroperoxides anion ligands, 114-19 covalent radii, 114, 118-19 dihedral angles, 119 geometric parameters, 115-8 tetrahedral distortion, 119 artemisinin formation, 133-4 chlorotriorganosilane reactions, 779-83 crystal structure, 105-14 anomeric effect, 110-11 geometric parameters, 106-9 hydrogen bonding, 103-5, 111-14 tetrahedral distortion, 110 determination, 674... 

Bifurcated hydrogen bonds, alkyl hydroperoxides. 111, 112 Bimetalbc complexes, molybdenum(Vl), 428 Bioassays... 

There are very few examples in the literature of electrophilic additions of hydrogen peroxide or alkyl hydroperoxides to C—C multiple bonds. The products of these additions, alkyl hydroperoxides or dialkyl peroxides respectively, can be explosively unstable363 and are more commonly obtained by peroxymer-curation-demercuration methods (vide infra). 

Early work on the electrophilic addition of hydrogen peroxide to alkenes was performed in the presence of an acid catalyst, usually sulfuric acid364 or p-toluenesulfonic acid.363 The reaction proceeds via Markovnikov-directed protonation of the double bond (Scheme 3). Subsequent nucleophilic attack of hydrogen peroxide on the carbocation, followed by loss of a proton, furnishes the alkyl hydroperoxide.366... 

An interesting feature of the Corey proposal is that it predicts that homoallylic alcohols should epoxidize from the opposite face compared with allylic alcohols. This arises because the stereoelectronically favorable conformation available for the hydrogen bond of homoallylic alcohols in 7 projects the alkyl chain of the homoallylic alcohol below the plane described by the titanium and the fm-butyl hydroperoxide ring. This is the only conformation that places the tt-bond of the allylic alcohol in a position to receive the peroxy oxygen of the hydroperoxide. In the initial report of enantioselective epoxidation32 it was indeed observed that homoallylic alcohols epoxidized from the opposite face compared to allylic alcohols. 

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