Ionic decompositions

Acid-catalyzed, ionic decompositions have been reported for peroxyesters, RC(0)—OOR, in which the R group can form a particularly stable carbonium ion, eg, tropybum ion (213). 

The chemistry of the di-/-butyl and cumyl peroxides is relatively uncomplicated by induced or ionic decomposition mechanisms. However, induced decomposition of di-/-butyl peroxide has been observed in primary or secondary alcohols31" "14 (Scheme 3.37) and primary or secondary amines.312 The reaction... 

Therefore one pair of ions produces one OH and one HO2 radicals. The total amount of radicals, which are produced in flue gas by electron beam irradiation, is possible to calculate using reported G-values. The main radicals produced initially through direct and ionic decomposition processes are OH, N, HO2, O, and H. 

Scheme 2), which acts as a catalyst for the ionic decomposition of hydroperoxides (B-80MI11504, B-81MI11502). Other sulfur compounds known to be active peroxide decomposers are the nickel dialkyldithiocarbamates (3) (B-80MI11505) and the thiol (4) (B-81MI11502). 

Ionic Decomposition of Rearrangement of Acetolysis of Lossen Rearrangement of... 

It is interesting that the ratio of ionic to non-ionic decomposition is not significantly dependent on temperature. The effect of applied electric field on the y-radiolysis of hydrocarbon gases has also been investigated18. 

An organic ester (an organic salt) was decomposed inside a mass spectrometer. An ionic decomposition product had the nuclidic molecular mass 117.090. What is the molecular formula of this product if it is known in advance that the only possible constituent elements are C, O, and H, and that no more than 4 oxygen atoms are present in the molecule ... 

Mathematical formulae for determining approximately numbers and densities of states have been used extensively in the calculations of rates of ionic decompositions. The classical approximation, which was employed in the pioneering studies [500, 720], is now recognised as giving serious errors in the calculated rates [883]. Some of the more accurate formulae have been evaluated by comparing their results with those obtained by direct or exact counting of states [306, 308]. It was found [306, 308] that a particular formula used most commonly in mass... 

Even with PI, theoretically one of the simplest ionization processes, the internal energy distribution, P(E), of the molecular ion cannot be predicted on the basis of Franck—Condon factors alone. Autoionization is well-known as being important [15, 177, 637, 640, 800], as is the more recently recognised effect of shape resonance [220, 803, 906]. It has also been shown that the onset of a decomposition can affect the energy distribution, P(E), [801, 802]. The latter effect is possibly a consequence of competition between neutral and ionic decompositions. 

The field ionization kinetics (FIK) technique allows rates of ionic decompositions to be determined over a continuous range of time extending from picoseconds to microseconds [38, 41, 223]. The applications of the technique have been reviewed [45, 226, 745]. 

Rate coefficients k(E) have been obtained in this way for decompositions of benzene, thiophene and benzonitrile over an energy range of some electron volts. These were the first direct experimental determinations of rate coefficients, k(E), for ionic decompositions. Moreover, a range of energies was accessible, since the times at which rates were measured extended over the 3 orders of magnitude, which contrasts with the later PIPECO experiments in which rates have been measured only in the microsecond time-frame. 

The k(E) vs. E curve obtained for bromobenzene using variable residence time [717] also differed from that for bromobenzene of the earlier study [22]. As before, the rate coefficients based on varying the residence time were lower than those from the earlier study of metastable ions. The critical energy was found to be 2.76 0.02 eV and the transition state was loose . Comparison was made with the corresponding neutral decomposition and it was concluded that the ionic decomposition had a marginally lower frequency factor and the lower critical energy (2.76 eV compared with 3.5 eV). The kinetic shift with the bromobenzene ion was about 0.2 eV on lengthening the residence time from 1.13 ps to 5.03 ps. 

The dependence of rates of ionic decomposition upon emitter temperature can be attributed to changes in the internal energy of the molecular ion, i.e. vibrational excitation is temperature dependent. The temperature of the sample molecules is governed, to some extent, by the emitter temperature (vide infra) and increasing the vibrational energy of the neutral molecule results in increased vibrational energy within the molecular ion [519]. 

Isotopic substitution affects rates of ionic decompositions and isomerisations in essentially the same ways as isotopic substitution affects rates of thermal reactions [360, 608, 654, 764, 905, 925]. Mass spectrometry does, however, own a few idiosyncracies in this area and it is important to distinguish clearly the different sorts of isotope effects involved. The term kinetic isotope effects in this review will be restricted to effects of isotopic substitution on the values of rate coefficients, k(E). Kinetic isotope effects on unimolecular gas-phase... 

Changes in moments of inertia have generally been neglected in studies of ionic decompositions, i.e. 7a(I) 7b(I) 7C(I) has been put equal to 7a(n) 7b(ii> 7c(Ii). They will probably receive more attention in the future as interest in rotational energy effects grows. If, however, the moments are cancelled, the Teller — Redlich product rule for competing decompositions of the same ion reduces to... 

From consideration of the mean translational energy release in a considerable number of ionic decompositions, the empirical relationship = /0.44n has been found [310]. [E is considered to be equivalent to (E — E0) (see Sect. 8.3.1).] The predictions of eqn. (39) are, therefore, only marginally greater than the experimental energy releases. The use of eqn. (39) has been advocated as a first approximation to the partition of excess energy, E — E0, in the case of a decomposition with a reverse critical energy ER [167, 603]. The partition of ER would be treated separately (see Sect. 8.1.3). 

A number of cases have been reported in which the thermal fragmentation and ionic decomposition of heterocycles proceed by unique paths. Most of these divergences appear to be specific heteroatomic effects. 

Jones and Paisley have reported the ionic and thermal fragmentation of 4,6-diphenyl-l,2,3,5-oxathiadiazine-2,2-dioxide, 26. Thermal decomposition of 26 in the solid state leads to formation of benzonitrile and a brown-colored intractable glass. The major ionic decomposition pathways for 26 are shown in Eq. (17). The failure of 26 to eliminate SO 2 on thermolysis lysis may reflect a heteroatom effect it may also be due to a medium effect with the SO 2 being trapped before it could escape the solid. It should be noted that the only volatile pyrolysis product, benzonitrile, appears as an intense ion, mfe 103, in the mass spectrum of 26. 

Swinehart and coworkers and Wilson and coworkers have investigated the pyrolysis of methyl and ethyl 46) cyclobutanes respectively. The primary path for thermal and ionic decomposition of these compounds are shown in Eq. (24) and (25) respectively. 

A considerable amount of kinetic data is available on the ionic decomposition of peresters. These reactions are beyond the scope of this review d . 

ZDDPs, and also metal dithiocarbonates, act as oxidation inhibitors by peroxide decomposition in a manner which does not produce radicals, thus removing a major initiation source. It seems likely that ZDDPs are sources of DDPAs (dialkyldithio-phosphonic acids) and it is this which is responsible for either ionic decomposition of the hydroperoxide or decomposition by electron transfer, Reaction (3.4) [56] ... 

Further reaction of acid XV with hydroperoxide leads to the formation of sul-phinic acid, Reaction (4.49). Sulphinic acids are the most important acid catalysts for ionic decompositions below 100°C. At higher temperatures, SO2 resulting from Reaction (4.50) is a most efficient catalyst [59, 60] ... 

The performance of ZnDTP as an antioxidant is a complex interaction pattern involving hydroperoxides and peroxy radicals. The performance matrix is additionally influenced by other additives present in industrial or engine oil formations. In a model system comprising cumene hydroperoxide and diverse ZnDTPs, it was demonstrated that the antioxidant mechanism proceeds by an acid-catalysed ionic decomposition of the hydroperoxide. The catalyst species is (9,0 -dialkyl-hydrogendithiophosphate, (RO)2PS2H, derived from the ZnDTP, Reaction (4.57) ... 

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