Cyclic halogenated carbonate

Halogenated flame-retardants may be either additive or reactive. The additive ones are aliphatic/aromatic or otherwise cyclic halogenated hydrocarbons. Generally their efficiency is inversely related to their thermal stability. The flame-retardant effect of the halogen atom (X) is increased by hydrogens on a vicinal carbon atom (as in aliphatic halogenated compounds) due to the ready scission of HX from the carbon chain. It is obvious, however, that these compounds are poor in thermal stability. The same is true for brominated flame-retardants they are more effective but less stable than chlorinated ones. For this reason, chlorinated paraffins and brominated aromatics are more commonly used as flame-retardants rather than aliphatic bromine compounds. 

Practicality has been an issue since many of the solvents referred to prior to 1994 have been quite expensive and the few others available have not had sufficient thermal stability to make them useful commercially. This chapter reviews our recent discovery of several commercially available cyclic perfluoro-carbons as well as other halogenated fluids (and even carbon dioxide) as solvents for tetrafluoroethylene-containing polymers. We will describe solvation at atmospheric pressure, under autogenous conditions and under superautogenous... 

The isomerization of primary halides generally involves an mechanism, whereas that of secondary halides follows the 5jjl mechanism. This type of intramolecular attack of the co-nitrogen atom on the halogenated carbon to form 3-, 4- and 5-membered cyclic ammonium ions, is shown in reaction (13). 

HFP can be synthesized from hexachloropropyl-ene via a multistep process beginning with fluorination [21]. Later steps convert the initial products to CFj—CFCl—CFj, which is dehalogenated to HFP. Other techniques report on the synthesis of HFP from the mixture of a variety of linear and cyclic three-carbon hydrocarbons with a partially halogenated three-carbon acyclic hydrocarbon. 

More recently other methods have been reported for the synthesis of hexafluoropropylene. One technique involves the pyrolysis of a mixture of tetrafluoroethylene and carbon dioxide at atmospheric pressure at 700-900°C.P ] Conversions of 20-80% and HFP yields of better than 80% were obtained. The unreacted tetrafluoroethylene and carbon dioxide were distilled from the product and recycled. HFP can be synthesized from hexachloropropylene via a multistep process beginning with fluorination.t ] Later steps convert the initial products to CF3-CFCI-CF3 which is dehalogenated to HFP. Other techniques report on the synthesis of hexafluoropropylene from the mixture of a variety of linear and cyclic three-carbon hydrocarbons with a partially halogenated three-carbon acyclic hydrocarbon.t " ]... 

Hydroxyl groups take precedence over ( outrank ) alkyl groups and halogen substituents m determining the direction m which a carbon chain is numbered The OH group is assumed to be attached to C 1 of a cyclic alcohol and is not numbered... 

In still other cases, the product of reaction of an electrophile with an aminoazole is from electrophilic attack at a ring carbon. This is electrophilic substitution and is the general result of nitration and halogenation (see Section 4.02.1.4). In such cases, reactions at both cyclic nitrogen and at an amino group are reversible. 

Addition is initiated by the positively polarised end (the less electronegative halogen atom) of the unsymmetrical molecule, and a cyclic halonium ion intermediate probably results. Addition of I—Cl is particularly stereoselective (ANTI) because of the ease of formation (and relative stability compared with carbocations) of cyclic iodonium ions. With an unsymmetrical alkene, e.g. 2-methylpropene (32), the more heavily alkyl-substituted carbon will be the more carbocationic (i.e. the less bonded to Br in 33), and will therefore be attacked preferentially by the residual nucleophile, Cle. The overall orientation of addition will thus be Markownikov to yield (34) ... 

Trialkyl phosphites undergo reaction with molecular halogen via a mechanism reminiscent of the Michaelis-Arbuzov reaction to form the dialkyl phosphorochloridate in good yield (Equation 4.4).7 With cyclic esters, the halogen performing the displacement reaction at carbon remains attached within the molecule. 

With the exception of chlorobenzene and 1,2-dichloroethane, halocarbon solvents are unsuitable diluents, as carbon tetrachloride and chloroform may react violently with alkylalumimum derivatives. The hazards of individually mixing 7 alkyla-luminiums with 7 chlorinated solvents have been assessed comparatively. Most of a series of cyclic coordination complexes between triethylaluminium and a-iminoketones decomposed violently when dissolved in halogenated solvents. 

As assumed, the small and positive valne of H/D kinetic isotope effect may be used as a criterion for an electron-transfer pathway. For example, anion-radicals of a-benzoyl-co-haloalkanes can react in two routes (Kimura and Takamnkn 1994). The first ronte is the common one—an electron is transferred from the oxygen anion of the carbonyl gronp to a terminal halogen. The transfer provokes fission of the carbon-halogen bond. The second ronte is the S 2 reaction, leading to a cyclic product as shown in Scheme 2.37. 

Acylpalladium intermediates can be involved in intramolecular processes leading to the formation of carbo- or heterocycles. In this chapter we discuss the cyclizations via the attack of acylpalladium intemediates at carbon centers and formation of new G-G bonds. The basic scheme (Scheme 7) of such processes includes the oxidative addition of Pd(0) to G(j )-X bonds (X = halogen or triflate), migratory insertion of GO, and subsequent intramolecular addition of acylpalladium intermediate to double or triple bonds to yield cyclic ketones. 

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