Exchange Involving Partial Dissociation

At least two possible mechanisms can be proposed that are compatible with these results. The first, originally proposed by Mole 34, 35), for systems containing two strong bridges, is given in Eq. (11) and has a S- 

The most recent work on these systems favors the mechanism described in Eq. (12). This mechanism also has been suggested for the intermolecular methyl exchange in the Me6Al2-p-tolyl-MesAl2 system (51). 

Unfortunately, it is not possible in the present studies with similar bridging and terminal groups to assign a mechanism unequivocally, but only to show that it is consistent with the observed kinetics for the system. Certainly additional work must be carried out in order to establish paths completely and to explore fully the influence of the bridging group on the mode of reaction. 

---

Aluminium.—A. review on the organometallic chemistry of aluminium contains some mechanistic work, particularly n.m.r. studies of exchange reactions. Kinetic studies of the exchange between bridging and terminal sites for alkyl aluminium dimers indicate that, for the methyl compound, reaction proceeds by a dissociative mechanism but that for meta- and para-to y alkyls the mechanism involves only partial dissociation of the brid. For the addition of (Bu 2AlH)3 to oct-4-yne, the kinetic order of i for the aluminium compound indicates that the monomer, Bu AlH, is the active species. Further studies on the Lewis acid behaviour of a range of species, including aluminium compounds, have been published. ... 

Thermal dissociation of 02 has a high activation energy and is usually quite slow. However, at the high temperatures in combustion systems where thermal NO is important, both O and 02 are involved in a number of reactions that are fast compared to the thermal NO formation. Due to the fast exchange between O and 02 in these reactions, the partial equilibrium assumption for (R12) is a reasonable approximation. Assuming partial equilibrium, we can relate the oxygen atom concentration to the 02 concentration and the equilibrium constant for the reaction,... 

Demineralization by ion exchange usually involves chemical regeneration of the resins with strong acid or alkali solutions. Weaker electrolyte regenerants are sometimes employed such as solutions of carbon dioxide, ammonia, or lime as demonstrated by various novel processes such as Desal and Carix for the partial demineralization, or desalination, of brackish waters. The increased dissociation of the salt forms of weakly functional cation and anion exchange resins at increased temperatures is the basis of the Sirotherm process which uses alternate... 

---