Redistribution reactions Subject

The first redistribution reactions were introduced early by Kocheshkov334. They remain still the subject of extended interest in the field of organometallic syntheses of Ge(IV), Sn(IV) and Pb(IV) compounds291,335,336. For example, the redistribution reactions occurring between allyltrialkyltin or crotyltributyltin compounds and SnCU at — 50 °C were studied by NMR335 ... 

Redistribution in Polymer Coupling. Monomer-polymer redistribution occurs most easily when the monomeric phenol and the phenol of the polymer are identical or, at least, very similar in reactivity (2). The homopolymers of DMP and MPP obviously redistribute very rapidly with either of the two monomers, so that sequential oxidation of DMP and MPP can produce only random copolymer. The redistribution reaction and its relation to the overall polymerization mechanism have been the subject of many previous investigations (2, 10, 13, 14), but the extraordinary facility of redistribution in the DMP-MPP system leads to results that could not be observed in other systems examined. 

The mixed methyl-ethyl tetraalkyllead compounds have become quite important commercially in the past several years because of their excellent antiknock effects and volatilities (see Extent of Antiknock Effect). Sometimes tetramethyllead and tetraethyllead are simply mixed together in motor fuel, but usually the compounds are subjected to "redistribution of the methyl and ethyl groups. The redistribution reaction involves the exchange of the organic groups between the compounds, yielding practically a random equilibrium production of all the possible products in a statistical distribution, as shown in the equation ... 

The complexes [Tp ]MgR may be considered to be modifications of Grignard reagents. As such, these complexes may be expected to be subject to the facile ligand redistribution reactions of the Schlenk equilibrium. Indeed, although solutions of the tris(3,5-dimethylpyrazolyl)hydroborato derivatives [Tp ]MgR are stable at room temperature, heating to 80-120°C does result in ligand redistribution and the formation of the six-coordinate sandwich complex [Tp ]2Mg [Eq. (4), 21,22]... 

Compounds of type (p -Cp)2MX2 are usually subject to a redistribution reaction such as 24.51 unless sterically hindered as in (p -C5Me5)2ThCl2 and (p -C5Me5)2UCl2. 

The product mixture from a typical MCS reaction is subjected to several distillation and isolation steps. The product mixture can be roughly divided into monomers and residue. The monomers are separated from the residue stream by distillation the residue contains siloxanes and disilanes. Some monomers can be recovered by various redistribution reactions of the residue mixture (15). The individual monomers are separated by distillation where the separation of Di from Tri is difficult. With Di as an example, equation 3 shows the hydrolysis and condensation to form linear and cyclic polysiloxanes. Another useful material is hexamethyldisiloxane (MM) which forms from hydrolysis/condensation of Me3SiCl (mono), equation 4. 

Consider a micellar solution at equilibrium that is subject to a sudden temperature change (T-jump). At the new temperature the equilibrium aggregate size distribution will be somewhat different and a redistribution of micellar sizes will occur. Aniansson and Wall now made the important observation that when scheme (5.1) represents the kinetic elementary step, and when there is a strong minimum in the micelle size distribution as in Fig. 2.23(a) the redistribution of micelle sizes is a two-step process. In the first and faster step relaxation occurs to a quasi-equilibrium state which is formed under the constraint that the total number of micelles remains constant. Thus the fast process involves reactions in scheme (5.1) for aggregates of sizes close to the maximum in the distribution. This process is characterized by an exponential relaxation with a time constant Tj equal to... 

Once they enter the atmosphere, PAHs are redistributed between gas and particle phases and are subject to removal mechanisms such as oxidative and photolytic reactions and wet and dry deposition. 

Entropy production during chemical change has been interpreted [7] as the result of resistance, experienced by electrons, accelerated in the vacuum. The concept is illustrated by the initiation of chemical interaction in a sample of identical atoms subject to uniform compression. Reaction commences when the atoms, compacted into a symmetrical array, are further activated into the valence state as each atom releases an electron. The quantum potentials of individual atoms coalesce spontaneously into a common potential field of non-local intramolecular interaction. The redistribution of valence electrons from an atomic to a metallic stationary state lowers the potential energy, apparently without loss. However, the release of excess energy, amounting to Au = fivai — fimet per atom, into the environment, requires the acceleration of electronic charge from a state of rest, and is subject to radiation damping [99],... 

The hydrosilylation of alkenes and alkynes catalyzed by transition metal complexes is often accompanied by side reactions such as isomerization, polymerization, and hydrogenation of unsaturated compounds and/or redistribution and dehydrogenation of silicon hydrides as well as reactions in which both substrates take part, such as dehydrogenative silylation (4,13). The latter reaction, which in certain conditions permits direct production of unsaturated silyl compound, has been a subject of intense study over the last two decades. 

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