Hot tritium reaction

M. Henchman R. Wolfgang USA Kinetic theory analysis of hot tritium reaction (impact model)... 

T. Miyazaki et al. Japan Quantum mechanical tunneling effect for hot tritium reaction... 

After the hot tritium reaction studies, Rowland also shifted his interests to atmospheric chemical reactions. He pointed out the danger of the possible destruction of the ozone layer... 

These fragmentation paths were confirmed by Wexler (1961b) by means of mass spectroscopy. Hot tritium reactions in a gaseous phase are most interesting because they are relatively simple. 

It is interesting to see the pressure dependence of hot tritium reaction in cyclobutane C4H8. Recoil tritium attacks this molecule to give tritiated cyclobutane (substitution reaction) in an excited state, which either stabilizes by collision with a third body or decomposes into two molecules of ethylene. This is shown in the following scheme ... 

Reactivity integral / and shadowing parameter K in hot tritium reaction with hydrocarbons... 

Hot atom reactions have also been used to label organic compounds with T. Irradiation of helium-3 with neutrons according to the nuclear reaction produces very energetic tritium atoms that can displace ordinary hydrogen in organic compounds. This procedure is not very selective, and the labeling pattern must be determined to enable the tritiated product to be used effectively as a tracer (34). 

In the first mechanism most of the reaction energy transforms into rotation-vibration energy of KI, while in the second mechanism the energy distribution between the products is more random. A third example of organic reaction studied dynamically is that of a hot tritium atom on a methane molecule (studied by Polanyiand collaborators on the one hand and by Bunker and collaborators "... 

The reaction of hot tritium atoms with substituted cyclopropanes... 

This reaction was studied thermally and found to have relatively low activation energy. In the case of thermal deuterium atoms, they did not show any exchange of D for H in the cyclopropane molecules ", indicating that reaction 51 has high activation energy. The kinetic energy of the hot tritium atom was found to overcome this activation energy, as 16 % of the hot tritium produced in the presence of c-CaH is incorporated in T-cyclopropane (equation 56) ... 

Both T-substituted 1-pentene and 3-methyl-1-butene were observed in yields comparable to the other T-pentene isomers. This observation clearly indicates that the primary source of T-pentene in these systems is through the loss of H atoms from the excited radicals formed by hot tritium addition with opening of the cyclopropane ring. The almost lack of isomerization of the T-substituted parent molecule set an upper limit for the energy left in the T-substituted parent molecule due to the reaction with energetic tritium the upper limit is equal to the activation energy for isomerization (65 kcal mol for cyclopropane and methylcyclopropane and about 62 kcal mol for ethylcyclopropane and dimethyl-cyclopropane. ... 

Besides the T-cyclopropanes, T-butenes and T-pentenes, several highly unsaturated tritium-labeled products, including acetylene, allene, propyne and 1,3-butadiene were observed in the hot T reaction with EC and DMC. Except for T-acetylene, whose yield is about 10 % of the substituted parent molecule, the yields of the other products are very low. 

Davanloo and Wai studied the reaction of hot tritium from the He(n, p)T reaction with gaseous cyclopropyl bromide. Table 6 gives the ratio of the yields in the presence of I2 as a scavenger. Due to the low vapor pressure of c-CjHsBr at room temperature, the effect of stabilization was observed by the addition of CHjBr. It acts both as a stabilizer and as a moderator, thus reducing the yields of all hot products, and the important results are the ratios of the yields of the various organic products. 

Hot atom reactions can be used for synthesis of labeled compounds. So far this technique has been used primarily for and labeling. For example, an organic gaseous conqx)und is mixed with He and the sample is irradiated with neutrons. The reaction He(n,p) H produces tritium as hot atoms (indicated by the small arrow) with kinetic ergies of approximately 0.2 MeV. These hot atoms react with the organic molecules to produce labeled compounds. An example is the formation of labeled butanol... 

Here M is any component of the reaction mixture that stabilizes vibra-tionally excited products on one or more collisions. Thermodynamic energy limits for each process were estabhshed. Thus, the integral of the CF4 excitation function could be estimated and used to obtain the initial internal energy distribution of the CFa F formed in Equation 1. The qualitative features of both results (5,21) are the same, and, as expected, the total energy deposited by hot fluorine atoms (22) is somewhat greater than by hot tritium in these replacement reactions. 

The overall reaction scheme for hydrogen replacement by hot tritium atoms in spiropentane is illustrated in Equations 5, 6, and 7. 

The recoil chemistry of tritium is perhaps one of the best understood in terms of a clear idea of the product spectrum under various conditions. Realistic models have been tested and correlations with theoretical approaches have been made. Thermal-neutron absorption reactions of lithium-6 and helium-3 have been used to produce hot tritium atoms. Some physical parameters are listed in Table 2. 

The charge state of the tritium while it is undergoing reactive collisions has been thoroughly discussed by El-Sayed et al. (1958). While the reactions of hot tritium are considered to be those of the neutral atom, the reader s attention is directed to the comments of Rowland et al. (1961). The tritium atom is also assumed to be in its electronic ground state at the time of reaction. 

The radiolytically produced atoms, radicals, ions and molecular fragments form the third and unwanted class of reactants in the system. They serve only to confuse and obscure the reactions of the hot tritium atom with the substrate. 

Results with inert moderators also support the view that some of the abstraction and all of the substitution reactions are hot . Helium is an effective non-reactive moderator for tritium since its mass is close to that of tritium (cf. Section II, E). As the concentration of helium in an organic system being subjected to tritium recoils is increased, the probability of a reactive encounter between a hot tritium atom and the substrate is decreased. Product distributions should shift in the direction of what might be expected from thermal tritium atoms. In the presence of helium the yield of HT (Eq. (8)) goes up and the yield of RT (eqs. (9) and (13)) goes down (cf. Estrup and Wolfgang, 1960b) in accordance with what one would predict. 

The reaction of hot tritium with methane has been the subject of several theoretical studies. These include compute simulation using a hard-sphere model, an examination of the nuclear displacements on the reaction co-ordinate in terms of the potential energy gradient, as evaluated from the electron density, and computations of the potential energy surface." " Several investigations of the reaction by trajectory analysis have also been carried out. ... 

Physico-chemical studies of hot tritium atom reactions. 842... 

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