Oxygen addition, rate constant

Foote reactivity indices (ft) have been measured for rubrene and 9,10-dimethyl-anthracene undergoing autophotoperoxidation in a range of solvents for which , has been measured. The variation in /3-values (about a factor of 40) is almost entirely due to the solvent dependence of t 0,. Thus = 1// t 0i varies by less than a factor of 2 ( is the singlet oxygen addition rate constant). However, for... 

TABLE 10.2 Addition Rate Constants kj of Various Radicals to Monomers Reaction Rate Constants kr of These Radicals with Oxygen, an Amine, a Stabilizer (HQME Hydroquinone-Methyl Ether) and a Spin Trap (TEMPO 2,2,6,6 Tetramethylpiperidine N-Oxyl). 

Various /-alkoxy radicals may be formed by processes analogous to those described for /-butoxy radicals. The data available suggest that their propensities for addition vs abstraction are similar.72 However, rate constants for [3-scission of /-alkoxy radicals show marked dependence on the nature of substituents a to oxygen (Figure 3.6).210 420,421 Polar, steric and thermodynamic factors are all thought to play a part in favoring this trend.393... 

Because of the importance of hydroperoxy radicals in autoxidation processes, their reactions with hydrocarbons arc well known. However, reactions with monomers have not been widely studied. Absolute rate constants for addition to common monomers are in the range 0.09-3 M"1 s"1 at 40 °C. These are substantially lower than kL for other oxygen-centered radicals (Table 3.7). 454... 

Steady state measurements of NO decomposition in the absence of CO under potentiostatic conditions gave the expected result, namely rapid self-poisoning of the system by chemisorbed oxygen addition of CO resulted immediately in a finite reaction rate which varied reversibly and reproducibly with changes in catalyst potential (Vwr) and reactant partial pressures. Figure 1 shows steady state (potentiostatic) rate data for CO2, N2 and N2O production as a function of Vwr at 621 K for a constant inlet pressures (P no, P co) of NO and CO of 0.75 k Pa. Also shown is the Vwr dependence of N2 selectivity where the latter quantity is defined as... 

An additional example of a cycloamylose-induced rate acceleration which may be reasonably attributed to a conformational effect is the facilitation of the transfer of the trimethylacetyl group from the phenolic oxygen of 9 to the aliphatic oxygen of the adjacent hydroxymethyl group to form 10. This intramolecular transesterification is remarkably enhanced relative to a comparable intermolecular reaction,6 and occurs, at pH 7.0 and 25.5°, with a rate constant of 0.0352 sec-1 (Griffiths and Bender, 1972). An even larger rate enhancement is achieved upon inclusion of this material within the cyclohexaamylose cavity—fc2 = 0.16 sec-1. This fivefold acceleration cannot be satisfactorily explained either by a microsolvent effect which would be expected to depress the rate of the reaction or, at this pH, by covalent... 

The reactivity of a carbonyl compound RjCOR2 is correlated with its rate constant with eh against (<3j + o ). The result was a fairly good straight line, with a slope of-0.74. The active center of reaction is known to be the carbonyl oxygen. 

At 373 K, the ratio of the rate constants is kis/kp = 8x 10 5 L-1 mol, where kis and kp refer to the reactions of isomerization and addition of oxygen. Isomerization competes with the reaction of the macroradical P with 02 therefore, intense hydroxylation during the oxidation of PP may imply that isomerization in the solid phase is slower than in the liquid phase. The experimentally measured ratio A[02]/[ROOH] at different partial pressure of oxygen helps to estimate the ratio k jkp in the oxidized polymer. Since the kinetics of chain PP oxidation are characterized by the rate v... 

Using basic pH leads to higher plateau rate constants, indicating that the ratedetermining step is reaction 18. Reaction 17 must be at least as fast as the rate of 02 addition in the highest 02 concentration used, kn 8 x 105 s 1, which is the limit of the instrument measurement. The G of benzene in pulse radiolysis was found to be equal to that of the nitroform anion (1.6 x 10-7 molJ-1) as can be expected from reactions 17-19. Since the yield of the cyclohexadienylperoxyl radical is 2.9 x 10-7 mol. 1 1 it means that only a fraction (ca 60%) of the cyclohexadienylperoxyl radicals eliminates HO2. The H02 elimination occurs by H-transfer of the allylic hydrogen to the oxygen... 

We have examined the competing isomerization and solvolysis reactions of 1-4-(methylphenyl)ethyl pentafluorobenzoate with two goals in mind (1) We wanted to use the increased sensitivity of modern analytical methods to extend oxygen-18 scrambling studies to mostly aqueous solutions, where we have obtained extensive data for nucleophilic substitution reactions of 1-phenylethyl derivatives. (2) We were interested in comparing the first-order rate constant for internal return of a carbocation-carboxylate anion pair with the corresponding second-order rate constant for the bimolecular combination of the same carbocation with a carboxylate anion, in order to examine the effect of aqueous solvation of free carboxylate anions on their reactivity toward addition to carbocations. 

Formic acid did not adsorb on clean Ag(llO) above 180 K. In order to obtain the adsorbed species, the surface was predosed with oxygen to produce adsorbed oxygen atoms. Surface species could then be stabilized by reacting formic acid with surface oxygen to produce water and the formate (102). Subsequent heating of the surface produced decomposition near 425 K. Only CO2 and H2 were observed as products from the HCOO intermediate. Additionally, some back reaction to reform HCOOH occurred between HCOO(a) and the H(a) liberated by the decomposition. The rate constant for the decomposition was... 

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