Redistribution reactions reaction

Alkyltin Intermedia.tes, For the most part, organotin stabilizers are produced commercially from the respective alkyl tin chloride intermediates. There are several processes used to manufacture these intermediates. The desired ratio of monoalkyl tin trichloride to dialkyltin dichloride is generally achieved by a redistribution reaction involving a second-step reaction with stannic chloride (tin(IV) chloride). By far, the most easily synthesized alkyltin chloride intermediates are the methyltin chlorides because methyl chloride reacts directiy with tin metal in the presence of a catalyst to form dimethyl tin dichloride cleanly in high yields (21). Coaddition of stannic chloride to the reactor leads directiy to almost any desired mixture of mono- and dimethyl tin chloride intermediates ... 

The other commercially important routes to alkyltin chloride intermediates utilize an indirect method having a tetraalkjitin intermediate. Tetraalkyltins are made by transmetaHation of stannic chloride with a metal alkyl where the metal is typicaHy magnesium or aluminum. Subsequent redistribution reactions with additional stannic chloride yield the desired mixture of monoalkyl tin trichloride and dialkyltin dichloride. Both / -butjitin and / -octjitin intermediates are manufactured by one of these schemes. 

Tetrasubstituted and some hindered trisubstituted alkenes react rapidly only to the monoalkylborane stage. Rarely, when the tetrasubstituted double bond is incorporated in a cycHc stmcture, does hydroboration under normal conditions fail (25—27). However, such double bonds may react under conditions of greater force (25,28—31). Generally, trialkylboranes are stable at normal temperatures, undergoing thermal dissociation at temperatures above 100°C (32—34). In the presence of B—H bonds, trialkylboranes undergo a redistribution reaction (35—38). 

Monohalogenoboranes are conveniendy prepared from borane—dimethyl sulfide and boron trihahdes (BX where X = Cl, Br, I) by redistribution reaction, eg, for monochloroborane—dimethyl sulfide [63348-81-2] (9) (81—83). Other methods are also known (84—87). 

In equation 7, ttimer radical (4) is produced when (3) dissociates. Whenever (4) couples with the other product of equation 7, ie, the 2,6-dimethylphenoxy radical, the tetramer is produced as described. These redistribution reactions of oligomers that proceed by ketal formation and subsequent dissociation ultimately generate terminal quinol ethers which enolize to the more stable terminal phenol (eq. 8). 

The most widely utilized reaction of tetraorganotins is the Kocheshkov redistribution reaction, by which the tri-, di-, and in some cases the monoorganotin hahdes can be readily prepared ... 

With tetraaryltins, the redistribution reaction can be made to proceed to the monoorganotin stage with the proper stoichiometry of reactants ... 

The production of triphenyl tin hydroxide [76-87-9] and triphenyl tin acetate [900-95-8] start with triphenyl tin chloride, which is prepared by the Kocheshkov redistribution reaction from tetraphenyltin and tin tetrachloride. The hydroxide is prepared from the chloride by hydrolysis with aqueous sodium hydroxide. The acetate can be made directiy from the chloride using sodium acetate or from the hydroxide by neutrali2ation with a stoichiometric quantity of acetic acid. 

By contrast to the selenium systems, tert-butylimidotellurium dihalides ( BuNTeX2)n (X = Cl, Br) are thermally stable in the solid state. They are obtained in good yields in THE solution by the redistribution reaction depicted in Eq. 8.19. ... 

Simple BX3 undergo rapid scrambling or redistribution reactions on being mixed and... 

In many cases, these cyclic siloxanes have to be removed from the system by distillation or fractionation, in order to obtain pure products. On the other hand, cyclic siloxanes where n = 3 and n = 4 are the two most important monomers used in the commercial production of various siloxane polymers or oligomers via the so-called equilibration or redistribution reactions which will be discussed in detail in Sect. 2.4. Therefore, in modern silicone technology, aqueous hydrolysis of chloro-silanes is usually employed for the preparation of cyclic siloxane monomers 122> more than for the direct synthesis of the (Si—X) functional oligomers. Equilibration reactions are the method of choice for the synthesis of functionally terminated siloxane oligomers. 

Typical initiators for living anionic polymerization of siloxanes include conventional organoalkali compounds and lithium siloxanolates22). Initiators containing lithium counterions are preferable to sodium or potassium counterions due to the lower catalytic activity of lithium in siloxane redistribution reactions. Living anionic polymeriza-... 

Redistribution reactions in chemistry, Ann. N.Y. Acad. Sci. 159,1-334(1969). Transition metal compounds feature in one paper only. 

Van Wazer (19) has described the use of a redistribution reaction, illustrated in (5), to form linear oligomers from cyclic species ... 

In the past five years, researchers at Dow Corning have made a concentrated effort to explore and develop the use of Si-Cl/Si-N redistribution reactions as a means of preparing tractable, polysila-zane precursors to SijN (3A-A2). Initial work focussed on the reaction of chlorosilanes and chlorodisilanes with hexamethyl-disilazane ... 

The sequence of redistribution reactions leading to the polymer shown in reaction (18) is illustrated by the following ... 

The first step for the synthesis of a melt spinnable polysilane is the alkoxylation and distillation of the residue (Figure 1). 1,2-dimethyltetramethoxydisilane and 1,1,2-trimethyltrimethoxydisilane are mixed in a special ratio and a poly silane will be obtained by a catalytic redistribution reaction. Catalysts for this reaction are alkali alkoxides like sodium methoxylate. Phenylmethoxydisilanes [22] or phenylchloride are used as additives. A mixture of methyltrimethoxysilane and dimethyldimethoxy-silane distils off as a byproduct of the redistribution reaction. Figure 2 shows the mechanism of the catalytic redistribution. 

Jain, V. K. In Synthesis, Reactivity and Redistribution Reactions of Homo- and Heterobinuclear Palladium(II) and Platinum(II) Complexes. Adv. Organomet. Proceedings Indo-Sov. Symp. Organomet. Chem., 1st. ed. Jain, D. V. S., Ed. Indian Natl. Sci. Acad New Delhi, India 1989, 143-162. 

The combination of equimolar amounts of tris(trimethylsilyl)methyllithium and zinc bromide in a THF/diethyl ether mixture, Scheme 27, furnished tris(trimethylsilyl)methylzinc bromide, as a lithium bromide/ether adduct.43 The compound, which may also be formulated as a lithium alkyldibromozincate, showed no ligand redistribution reactions. It is monomeric in solution and can be treated with 1 equiv. of an organolithium reagent to afford heteroleptic diorganozinc compounds. 

Redistribution Reactions between Tetraalkyl- or Tetraarylgermanes and Germanium Tetrahalides... 

These redistribution reactions are possible at atmospheric pressure under the action of MW irradiation is performed for a few minutes in the presence of the same catalysts [57]. These reactions with the less volatile germanium tetrabromide (44b) (b.p. 184 °C) have also been performed by use of the GS/MW process, without added catalyst (Tab. 7.4, entries 1 and 3) [15, 16]. In this instance, despite the use of weaker incident power, the temperature reached 420 °C, very much higher than that obtained under the action of MW irradiation of a reaction mixture containing AlBr3 (200 °C to 250 °C) (Tab. 7.4, entries 2 and 4). The presence of this catalyst considerably favors redistribution towards the dibrominated products (46b) (84% for R = nBu, 85% for R = Ph) relative to the monobrominated compounds (46a), which are the major products of the GS/MW process (78% and 43% respectively). The tri-brominated products (46c), the most difficult to prepare, have been obtained with a rather high selectivity (73 to 80%) by use of the catalytic process under the action of MW [57]. In this reaction, therefore, the GS/MW process seems less effective than the MW-assisted and AlX3-catalyzed process. 

Tab. 7.4 Redistribution reactions between germanium tetrabromide (44b) and tetrabutyl- or tetra-phenylgermanes (45) under the action of MW irradiation [15, 16].

The redistribution reaction of Eq. (50) is not restricted to systems containing vinylsiloxanes. It was also observed with 2-pentene as follows ... 

Redistribution reactions are considered as quite important for the preparation of alkyltin halides having mainly identical alkyl groups. Actually, the redistribution reactions are halogenation reactions of organotin halides by SnX4 (X = F, Cl, Br, I). 

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 ... 

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