Hydroperoxides enthalpies of reactions

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. ... 

The enthalpy of the R02 + RH reaction is determined by the strengths of disrupted and newly formed bonds AH= Z>R H—Droo—h- For the values of O—H BDEs in hydroperoxides, see the earlier discussion on page 41. The dissociation energies of the C—H bonds of hydrocarbons depend on their structure and vary in the range 300 - 440 kJ mol-1 (see Chapter 7). The approximate linear dependence (Polany-Semenov relationship) between activation energy E and enthalpy of reaction AH was observed with different E0 values for hydrogen atom abstraction from aliphatic (R1 ), olefinic (R2H), and alkylaromatic (R3H) hydrocarbons [119] ... 

For the comparison of hydroperoxides with methyl ethers (equation 2), we find there is enthalpy of formation data only for dimethyl ether, isopropyl methyl ether and t-butyl methyl ether (again ignoring the ethyl and propyl hydroperoxides). The enthalpies of formal reaction 2 for R = Me, i-Pr and f-Bu (two gas phase enthalpies of formation for f-BuOOH) are —53.1, —54.9 and —37.6 or —48.6 kJmoU, respectively, in the gas phase. In the liquid phase, the enthalpies of reaction are —7.4, —35 (from the estimated enthalpy of formation of isopropyl hydroperoxide) and —20.0 kJmoU, respectively. Because the enthalpy of formation deviations from linearity for dimethyl ether and methyl hydroperoxide might not be identical, the reaction enthalpy might not be consistent with those... 

For reaction 3 to replace an oxygen with a methylene group to form a primary alcohol, there are enthalpies of formation for only seven alcohols to compare with the nineteen hydroperoxides, almost all of them only for the liquid phase. The enthalpies of the formal reaction are nearly identical, —104.8 1.1 kJmol, for R= 1-hexyl, cyclohexyl and ferf-butyl, while we acknowledge the experimental uncertainties of 8.4 and 16.7 kJmol, respectively, for the enthalpies of formation of the secondary and tertiary alcohols. We accept this mean value as representative of the reaction. For R = 1- and 2-heptyl, the enthalpies of reaction are the disparate —83.5 and —86.0 kJmol, respectively. From the consensus enthalpy of reaction and the enthalpy of formation of 1-octanol, the enthalpy of formation of 1-heptyl hydroperoxide is calculated to be ca —322 kJ mol, nearly identical to that derived earlier from the linear regression equation. The similarly derived enthalpy of formation of 3-heptyl hydroperoxide is ca —328 kJmol. The enthalpy of reaction for R = i-Pr is only ca —91 kJmol, and also suggests that there might be some inaccuracy in its previously derived enthalpy of formation. Using the consensus enthalpy of reaction, a new estimate of the liquid enthalpy of formation of i-PrOOH is ca —230 kJmoU. ... 

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... 

The three solid phase tetralin and decalin hydroperoxides have enthalpies of reaction that are surprisingly comparable, —93.9 6.4 kJmoR, despite the sometimes large error bars associated with either the peroxide or corresponding alcohol and their differences in structure. Notably, the gas phase reaction enthalpy for the cumyl hydroperoxide is nearly identical to the solid phase reaction enthalpy for the 1-methyl-1-tetralin hydroperoxide, —87.0kJmoR, for these structurally similar compounds and supports the hypothesis that the gas and condensed phase formal reaction enthalpies are nearly the same for all compounds. Flowever, for 2,5-dimethylhexane-2,5-dihydroperoxide, the enthalpies of reaction 5 per hydroperoxy group for the solid and gaseous phase are not close —57 and —76 kJmoR, respectively. Compare them with the enthalpies of reaction for ferf-butyl hydroperoxide of —66 (Iq) and —67 or —78 (g) kJmoR. For the unsaturated counterpart, 2,5-dimethylhex-3-yne-2,5-dihydroperoxide, the solid and gas phase enthalpies of reaction per hydroperoxy group are —64.2 kJmoR and —74.6 kJmoR, respectively. 

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. 

As was the case for the alkyl hydroperoxides in reaction 4, the enthalpies of the oxy-gen/hydrocarbon double exchange reaction 8 for dialkyl peroxides are different depending on the classification of the carbon bonded to oxygen. For R = Me, Et and f-Bu, the liquid phase values are —4, 24.6 and 52.7 kJmoR, respectively, and the gas phase values are 0.1, 25.7 and 56.5 kJmoR, respectively. For the formal deoxygenation reaction 9, the enthalpies of reaction are virtually the same for dimethyl and diethyl peroxide in the gas phase, —58.5 0.6 kJ moR. This value is the same as the enthalpy of reaction of diethyl peroxide in the liquid phase, —56.0 kJ moR (there is no directly determined liquid phase enthalpy of formation of dimethyl ether). Because of steric strain in the di-ferf-butyl ether, the enthalpy of reaction is much less negative, but still exothermic, —17.7 kJmol (Iq) and —19.6 kJmol (g). 

Dimethyl-2-hydroperoxide-5-ierr-butylperoxyhexane contains both a peroxy and a hydroperoxy group. The enthalpy of reaction 5, to give 2,5-dimethyl-2-hydroxy-5-f-butylperoxyhexane, is —59.9kJmoR (Iq) and —58.8kJmol (g), comparable to those obtained from 1-methylcyclohexane hydroperoxide and f-butyl hydroperoxide. If the mixed peroxide were to undergo the formal reactions 5 and 6 simultaneously, the alcohol product would be 2,5-dimethylhexane-2,5-diol, for which there is only an enthalpy... 

The gas phase enthalpy of reaction 6 for bis(hydroxymethyl) peroxide is — 192 kJ mol , which deviates from the other hydrate-producing peroxides by nearly 89 kJ mol . The enthalpy of reaction 8, 145 kJmol, is likewise discrepant by some 120 kJmol from that for diethyl peroxide, ca 26 kJ mol. From the high-level calculations reported in Reference 28, the reaction enthalpy for the addition of H2O2 to formaldehyde is —59 kJ mol. A similar reaction is equation 10 for the gas phase addition of tert-butyl hydroperoxide to a carbonyl group. 

The value is from the liquid phase enthalpy of reaction between cyclohexanone and tert-butyl hydroperoxide from V. L. Antonovskii, E. V. Federova, N. E. Shrivel and V. D. Emelin, Kinet. Ratal., 30, 1235 (1989). 

Dialkyl peroxides (continued) colorimetry, 707-8 flame ionization detection, 708 NMR spectroscopy, 708 titration methods, 707 UV-visible spectrophotometry, 707-8 enthalpies of reactions, 153-4 graft polymerization initiation, 706 hydroperoxide determination, 685 peroxide transfer synthesis, 824-5 stmctural characterization, 708-16 electrochemical analysis, 715-16 electron diffraction, 713 mass spectrometry, 714 NMR spectroscopy, 709-11 thermal analysis, 714-15 vibrational spectra, 713-14 X-ray crystallography, 711-13 synthesis... 

Relatedly, despite the synthesis and structural characterization of numerous arsine and stibine oxides, bomb calorimetry measurements have only been reported on triphenylarsine oxide . While corresponding measurements have been made on triphenylarsine, it is clearly premature to make general observations as to E—O bond enthalpies in the absence of additional data. In principle, reaction calorimetry should prove useful. Indeed, we note a solution phase (benzene) enthalpy of reaction study of triphenylarsine and -butyl hydroperoxide according to the reaction... 

The oxidation of a hydrocarbon to hydroperoxide is an exothermic reaction. The values of the enthalpies of these reactions are collected in Table 1.4. The enthalpies of oxidation of different hydrocarbon groups by dioxygen to ROOH have the following values ... 

These data appeared to be very useful for the estimation of the relative O H bond dissociation energies in hydroperoxides formed from peroxyl radicals of oxidized ethers. All reactions of the type R02 + RH (RH is hydrocarbon) are reactions of the same class (see Chapter 6). All these reactions are divided into three groups RO + R (alkane, parameter bre = 13.62 (kJ moC1)172, R02 + R2H (olefin, bre = 15.21 (kJ mob1)1 2, and R02 + R3H (akylaromatic hydrocarbon), hrc 14.32 (kJ mol )12 [71], Only one factor, namely reaction enthalpy, determines the activation energy of the reaction inside one group of reactions. Also,... 

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. 

Enthalpies, Activation Energies, and Rate Constants of Reactions of 1,1-dimethylethyl Hydroperoxide with Phenols (AhOH) in Hydrocarbon Solutions ROOH + AriOH —> RO + H20 + AriO Calculated via IPM Method [114]... 

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