Atom halogenated solvent

The selectivity of chlorination is influenced by solvents. For example, the chlorination of 2,3-dimethylbutane shows increased preference for the tertiary position in benzene. " The complexation with solvent attenuates the reactivity of chlorine atoms. Halogenated solvents also give evidence of complex formation. Brominated solvents lead to greater selectivity. " ... 

Besides the effect of solvent polarity, the C=C rotation in many push-pull ethylenes is sensitive to acid catalysis (143). This is probably explained by protonation of the acceptor groups, for example, the oxygen atoms in C=0 groups (16), which increases their acceptor capacity. Small amounts of acids in halogenated solvents, or acidic impurities, may have drastic effects on the barriers, and it is advisable to add a small quantity of a base such as 2,4-lutidine to obtain reliable rate constants (81). Basic catalysis is also possible, but it has only been observed in compounds containing secondary amino groups (38). 

Lithium hydride and sodium hydride are the only alkali metal hydrides of much practical importance. They are useful when it is desirable for proton (or hydrogen atom) transfers to accompany electron-transfer events. Because these hydrides react quickly with water to form alkali metal hydroxides and hydrogen gas, they are frequently used as drying agents, particularly for hydrocarbons and ethers. Care should be exercised in using them to dry solvents that are not predried, and they should not be used to dry alcohols or halogenated solvents. 

The primary act for other halogenated solvents may also be considered as Cl atom abstraction through the intermediate formation of a complex in the excited state between the excited anthracene and C1CX. 

It is evident that the values of the transfer constants are dependent on the nature both of the attacking radicals and of the transfer agent itself, and that similar effects should be expected during the synthesis of graft copolymers by chain transfer methods. For example, with respect to toluene the chain transfer constant is a little greater for methyl methacrylate radicals than for styrene radicals on the contrary, with respect to halogenated solvents (CC14) the polystyrene radical is much more effective in the removal of a chlorine atom. Vinyl acetate chains are far more effective than either of the other two polymer radicals. 

Treatment of tethered alkyne-allyl halides with indium metal in halogenated solvents affords carbocyclic vinyl halides via a novel atom-transfer reaction. The reactions are operationally facile and proceed smoothly at room temperature even with sub-stoichiometric quantities of indium. Use of a halogenated solvent containing a different... 

Treatment of the tris(dialkyldithiocarbamato)iron(III) complexes in benzene with a controlled amount of concentrated hydrohalic acid affords the black bis(ligand) complexes [FeX(S2CNR2)2] (X = Cl, Br or I).306 For X = Cl the complexes may also be prepared by irradiation of the tris-(ligand) complex in a halogenated solvent. This free radical reaction is believed to proceed via excited-state labilization of one ligand followed by attack of solvent.307 Analogous complexes of pseudohalide ions (X = NCO, NCS- or NCSe ) have been obtained from reaction of the parent tris complex with the appropriate Ag+ salt.380 Representative complexes of this class have been shown by X-ray diffraction methods to have square pyramidal structures (71) in which the sulfur atoms of the two bidentate ligands comprise the basal plane (Fe—S 2.228 2.30 A) with the halide ion in the apical position (Fe—Cl 2.26-2.28 A).309 310 In the cases examined the metal atom sits 0.6 A out of the mean S4 plane in the direction of the apical halide ion. 

To study the effects of water and other solvents on titanocene(III)-mediated processes we used the transannular cychzation of epoxygerma-crolides as a model reaction [47]. Thus, we found that in anhydrous, non-halogenated solvents such as THF the reaction led selectively to decalins with an exocyclic double bond (Scheme 5). In an aqueous medium (THF/H2O), however, the characteristic lime green color of Cp2TiCl turned deep blue and the main product was a reduced decalin (Scheme 5). Under these conditions, water (either H2O or D2O) proved to be more effective than the toxic and expensive hydrogen-atom donor 1,4-cyclohexadiene for the reduction of tertiary radicals [47]. This is an unusual phenomenon in free-radical chemistry [48-50], subsequently exploited by us for the selective reduction of aromatic ketones as we shall see later [51,52]. 

For the lanthanide metals, Sm, Eu, and Yb, which have a readily accessible ( + 2) oxidation state, oxidative addition reactions of M(1I) complexes with halogens and organic halides are dominated by the atom transfer or free radical mechanism (cf. 5.S.2.9.1.) in which two metal ions are each oxidized to the -I- 3 state. Numerous examples illustrate the ability of cyclopentadienyl or indenyl Ln(II) complexes (Ln = Sm, Eu, Yb) to abstract halogen atoms from molecular halogens ", halogenated solvents sueh as CH2CI2 and and alkyl halides . An archetypieal example is ... 

Fluorine and fluoroxytrifluoromethane were found to fluorinate tertiary carbon atoms in the liquid phase in halogenated solvents (CH2CI2, CHCI3,... 

Halogenated Solvents - Organic liquids containing at least one atom of a halogen (Cl, F, I, Br) are called halogenated solvents. 

The lifetime of incarcerated biacetyl is unaffected by the solvent as long as it doesn t contain heavy atoms. Interestingly, halogenated solvents enhance intersystem crossing via a remote external heavy atom effect. This was demonstrated by Romanova et al. for hemicarceplex 120biacetyl (Figure 9.35). ... 

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