Halogen formation

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... 

Oxidation of chloride and bromide has been studied , and reaction with iodide found very fast. In all cases reaction may be limited to halogen formation. Simple second-order rate laws... 

Attack by Halogen Formation of Sulfonyl Halides S-Halo-de-hydroxylation... 

One further point. We have encountered the two-step addition of unsym-metrical reagents in which the first step is attack by positive halogen formation of halohydrins (Sec. 6.14), and ionic addition of IN3 and BrN3 (Problem 7, p. 247). The orientation is what would be expected if a carbonium ion were the intermediate. Propylene chlorohydrin, for example, is CH3CHOHCH2CI IN3 adds to terminal alkenes to yield RCH(N3)CH2l. Yet the exclusively anti stereochemistry... 

Physical Properties of the Halogens, Formation of Sodium Chloride... 

Roberts TJ, Braban CF, Martin RS, Oppenheimer C, Adams JW, Cox RA, Jones RL, Griffiths PT (2009) Modelling reactive halogen formation and ozone depletion in volcanic plumes. Chem Geol 263(1-4) 151-163. doi 10.1016/j.chemgeo.2008.11.012... 

The above Born-Haber cycle represents the enthalpy changes in the formation of an alkali metal halide MX from an alkali metal (Li. Na, K, Rb. Cs) and a halogen (Fj. CI2. Br2 or I2). 

Nitrogen trifluoride and trichloride can both be prepared as pure substances by the action of excess halogen on ammonia, a copper catalyst being necessary for the formation of nitrogen trifluoride. 

Numerous ionic compounds with halogens are known but a noble gas configuration can also be achieved by the formation of a covalent bond, for example in halogen molecules, X2, and hydrogen halides, HX. When the fluorine atom acquires one additional electron the second quantum level is completed, and further gain of electrons is not energetically possible under normal circumstances, i.e... 

The formation of halatefV) and halide ions by reaction (11.4) is favoured by the use of hot concentrated solutions of alkali and an excess of the halogen. 

Halides of non-metals are usually prepared by the direct combination of the elements. If the element exhibits more than one oxidation state, excess of the halogen favours the formation of the higher halide whilst excess of the element favours the formation of the lower halide (e.g. PCI5 and PCI3). 

The following data ( fable 1) for niolcctilcs, including hydrocarbon s, strained ring system s. molecn les with heieroatom s, radicals, and ions conies from a review by Stewart. For most organic molecules,, YM 1 reports heals of formation accurate to within a few kilocalories per rn ol. bor soni e molecules (particularly inorgari ic compoun ds wdth several halogens, such as perch loryl fluoride, even the best sem i-em pineal method fails completely. 

It has been stated that many halogen-free compounds, e.g., certain derivatives of pyridine and quinoline, purines, acid amides and cyano compounds, when ignited on copper oxide impart a green colour to the dame, presumably owing to the formation of volatile cuprous cyanide. The test is therefore not always trustworthy. The test is not given by duorides. 

Strictly speaking the alkyl halides are esters of the halogen acids, but since they enter into many reactions (t.g., formation of Grignard reagents, reaction with potassium cyanide to yield nitriles, etc.) which cannot be brought about by the other eaters, the alkyl halides are usually distinguished from the esters of the other inorganic acids. The preparation of a number of these is described below. 

The conversion of an aliphatic carboxylic acid into the a-bromo- (or a-chloro ) acid by treatment with bromine (or chlorine) in the presence of a catal3rtic amount of phosphorus tribromide (or trichloride) or of red phosphorus is known as the Hell-Volhard-Zelinsky reaction. The procedure probably involves the intermediate formation of the acyl halide, since it is known that halogens react more rapidly with acyl haUdes than with the acids themselves ... 

Category Ic cyclizations involve formation of the C3-C3a bond and require aniline derivatives with a nitrogen substituent appropriate for such reaction. Some, but not all, such cyclizations also require an o-substituent, frequently halogen. The rctrosynthetic transformations corresponding to the most important of this group of syntheses are shown in Scheme 4.1... 

Thus a second method was envisaged, the reaction of a nitrile, hydrogen selenide, and an a-halogenated ketone in the presence of a condensation catalyst, which can be POCl, or POCI3 with a Lewis acid such as PCI3 or anhydrous ZnCl. The use of fresh AICI3 leads to the formation of tarry side-products. 

The formation of a sulfur-containing ring was justified by the attack of the halogenated carbon of the cMoroacetyl derivative by the sulfur atom of thiourea, a fact in accordance with the results just discussed by Wallach (49,50) and Claus (51). The new formula (37) of thiohydantoine explained why, contrary to thiourea, its desulfuration was difficult. 

Table 6 3 shows that the effect of substituents on the rate of addition of bromine to alkenes is substantial and consistent with a rate determining step m which electrons flow from the alkene to the halogen Alkyl groups on the carbon-carbon double bond release electrons stabilize the transition state for bromonium ion formation and increase the reaction rate... 

Both parts of the Lapworth mechanism enol formation and enol halogenation are new to us Let s examine them m reverse order We can understand enol halogenation by analogy to halogen addition to alkenes An enol is a very reactive kind of alkene Its carbon-carbon double bond bears an electron releasing hydroxyl group which makes it electron rich and activates it toward attack by electrophiles... 

As m the acid catalyzed halogenation of aldehydes and ketones the reaction rate is mde pendent of the concentration of the halogen chlorination brommation and lodmation all occur at the same rate Formation of the enolate is rate determining and once formed the enolate ion reacts rapidly with the halogen... 

Adipic acid undergoes the usual reactions of carboxyflc acids, including esterification, amidation, reduction, halogenation, salt formation, and dehydration. Because of its biflmctional nature, it also undergoes several industrially significant polymerization reactions. 

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