For halogenation

Now grind up the mixture of solution and glass in the mortar to ensure extraction of the sodium salts, and then filter. Divide the filtrate into three portions, reserving two portions for testing for halogens and sulphur. 

Halogens. Test the second portion of the filtrate for halogens in the usual way, as described under the Lassaigne halogen test (p. 324). Note that cyanides if present must first be eliminated as usual. 

Another factor potentially affecting the market for halogenated fire retardants is the waste disposal of plastics (see Wastes, industrial). As landfiU availabihty declines or becomes less popular, two alternatives are incineration and recycling (qv). The nature of the combustion products from halogenated products requires carefiil constmction and maintenance of incinerators (qv) to avoid damage to the incinerator itself and a pubHc health problem from the exhaust. The ease of recycling used products also has a potential effect on fire retardants. 

Potassium fluoride [7789-23-3], KF, is the most frequently used of the alkaU metal fluorides, although reactivity of the alkaU fluorides is in the order CsF > RbF > KF > NaF > LiF (6). The preference for KF is based on cost and availabiUty traded off against relative reactivity. In its anhydrous form it can be used to convert alkyl haUdes and sulfonyl haUdes to the fluorides. The versatility makes it suitable for halogen exchange in various functional organic compounds like alcohols, acids and esters (7). For example, 2,2-difluoroethanol [359-13-7] can be made as shown in equation 9 and methyl difluoroacetate [433-53 ] as in equation 10. 

Ha/ogenation. Heats of reaction are highly exothermic for halogens, particularly fluorine (qv), and chain reactions can result in explosions over broad concentration ranges. Halogens also present severely challenging corrosion problems (see Corrosion and corrosion control). 

Glass-lined reactor systems ate used occasionally for halogenated resins to prevent corrosion of the reactor components. Copper and brass fitting should be avoided due to the significant induence on resin cute characteristics. 

Oxidation of aHoocimene in the presence of a catalyst produces a polymeric peroxide, which can be thermally isomerized to produce aHoocimene diepoxide [3765-28 ] (56) in 70—75% yield (99). The diepoxide has been used in the manufacture of resins and as an acid scavenger for halogenated solvents (100). 

However, as HOX is consumed, hydrolysis is retarded because of build-up of free amine. Consumption of hypohalous acid through reaction with HX can result in formation of elemental halogen HOX + + X X2 + H2 O (1—3). The tendency for halogen formation is much greater for HOBr and... 

EC Decision on import quotas for halogenated chlorofluorocarbons, halons, carbon tetrachlonde,... 

Applicability/Limitations Liquid injection incineration can be applied to all pumpable organic wastes including wastes with high moisture content. Care must be taken in matching waste (especially viscosity and solids content) to specific nozzle design. Particle size is a relevant consideration so that the wastes do not clog the nozzle. Emission control systems will probably be required for wastes with ash content above 0.5 percent (particulate control) or for halogenated wastes (acid gas scrubbers). 

Polymer-supported tetraphenylphosphonium bromide is a recyclable catalyst for halogen-exchange reactions. The reaction of 1 equivalent of chloro-2,4-dinitrobenzene with 1 5 equivalents of spray-dned potassium fluoride and 0.1 equivalent of this catalyst in acetonitnle at 80 C for 12 h gives 2,4-dinitro-fluorobenzene m 98% yield An 11% yield is obtained without the catalyst [3 /]. 

As an example of enolate-ion reactivity, aldehydes and ketones undergo base-promoted o halogenation. Even relatively weak bases such as hydroxide ion are effective for halogenation because it s not necessary to convert the ketone completely into its enolate ion. As soon as a small amount of enolate is generated, it reacts immediately with the halogen, removing it from the reaction and driving the equilibrium for further enolate ion formation. 

Problem 22.9 Why do you suppose ketone halogenations in acidic media referred to as being ackl-calalyzed, whereas halogenations in basic media are base-promoted In other words, why is a full equivalent of base required for halogenation ... 

One would certainly think that the above assumption concerning HX is valid if X = F, or even if X = Cl. However, published values of OB for halogen-containing expls (Refs 1 10) have been calculated via Eq 1, ie, the halogen is ignored... 

An important source of reference is another excellent review by Stern [844] this one is concerned with the high temperature properties of oxy-halides. The following general trends are found in salts containing an XO anion (X = Cl, Br and I) there are variations in stabilities in the sequences (i) (X =) Cl > Br > I for halogens in the same oxidation state, and (ii) XO4 > XOJ > XO2 > XCT for the different oxidation states of a particular halogen. 

Simple combustion at 700 °C in a stream of oxygen over platinum or silver has also been used for the sulphone sulphate oxidation219. However, this method does not work well for halogen- and nitrogen-containing sulphones. 

TABLE 4. Absolute kinetic data for halogen abstraction by some radicals from sulfonyl halides... 

Such reactions appear to be rather general in scope, since an aryl example, the substitution for bromine in bromobenzene, and for halogen in a normal alkyl halide has also been observed (21). 

Operationally, however, the vast majority of the metal-containing products are those expected from the reactions already presented, namely, successive exchange of trifluoromethyl for halogen. Equations (7) and (8), for example, represent the last two steps of the formation of (CF3)4Ge. 

We may ask How does Y know which side will give the more stable carbocation As in the similar case of electrophilic aromatic substitution (p. 681), we invoke the Hanunond postulate and say that the lower energy carbocation is preceded by the lower energy transition state. Markovnikov s rule also applies for halogen substituents because the halogen stabilizes the carbocation by resonance ... 

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