Heterocyclic Halogen Compounds

The removal of a halogen from an aromatic heterocycle takes place more readily than the hydrogenolysis of a phenyl halide of the same type (Eqn. 20.61). 45 The relative difference between the ease of dehalogenation of a phenyl and a heterocyclic halide is more pronounced over Raney nickel in basic medium than it is over palladium (Eqn. 20.62). 46 

The usual basic, palladium catalyzed dehalogenation conditions are, however, preferred over Raney nickel for nonselective halide hydrogenolysis. Dehalogenation over palladium occurs in preference to ring and cyano group 

The use of platinum catalysts in acetic acid is not recommended for the removal of halogens from heterocycles as ring hydrogenation also occurs under these conditions. 

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Many heterocyclic halogen compounds are capable of quatemizing nitrogen bases and, indeed, of self-condensation, which can occur with great ease (for example, on warming a solution of l-chloro-4-methyl-... 

Cathodic Reduction of Aromatic and Heterocyclic Halogen Compounds... 

Dinonyl phthalate 20 150 I Tol 83 183 147 231 159 For aromatics, heterocycles, halogen compounds... 

The electrode reactions of heterocyclic halogen compounds exhibit generally no special features, but some may be of preparative value. Anodic halogenation may be advantageous in fluorination and iodination reactions and in halogenations in which a low, easily measured concentration of halogen is desirable. 

Heterocyclic bases which readily form quaternary salts with the more usual reagents will also react with suitably activated aryl and heterocyclyl halogen compounds, the classic case being the salt formed from pyridine and l-chloro-2,4-dinitrobenzene. Reactions of this type have been studied by Chapman et Salt formation between... 

A mammal may emit many volatile compounds. Humans, for instance, give off hundreds of volatiles, many of them chemically identified (Ellin etal., 1974). The volatiles include many classes of compound such as acids (gerbil), ketones, lactones, sulfides (golden hamster), phenolics (beaver, elephant), acetates (mouse), terpenes (elephant), butyrate esters (tamarins), among others. The human samples mentioned before contained hydrocarbons, unsaturated hydrocarbons, alcohols, acids, ketones, aldehydes, esters, nitriles, aromatics, heterocyclics, sulfur compounds, ethers, and halogenated hydrocarbons. Sulfur compounds are found in carnivores, such as foxes, coyotes, or mustelids. The major volatile compound in urine of female coyotes, Canis latrans, is methyl 3-methylhut-3-enyl sulfide, which accounts for at least 50% of all urinary volatiles (Schultz etal, 1988). 

Types of compounds are arranged according to the following system hydrocarbons and basic heterocycles hydroxy compounds and their ethers mercapto compounds, sulfides, disulfides, sulfoxides and sulfones, sulfenic, sulfinic and sulfonic acids and their derivatives amines, hydroxylamines, hydrazines, hydrazo and azo compounds carbonyl compounds and their functional derivatives carboxylic acids and their functional derivatives and organometallics. In each chapter, halogen, nitroso, nitro, diazo and azido compounds follow the parent compounds as their substitution derivatives. More detail is indicated in the table of contents. In polyfunctional derivatives reduction of a particular function is mentioned in the place of the highest functionality. Reduction of acrylic acid, for example, is described in the chapter on acids rather than functionalized ethylene, and reduction of ethyl acetoacetate is discussed in the chapter on esters rather than in the chapter on ketones. 

The heterocyclic tellurium compounds can also be isolated from the reaction mixtures by extraction with dichloromethane and distillation3 or by precipitation of the telluracyclohcxane dihalides upon addition of elemental halogens to the extracts4. 

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