Aryl Halogen Compounds

The hydrogenolysis of aryl halides proceeds more readily than the cleavage of alkyl-halogen bonds. Aryl chlorides are rather stable to hydrogenolysis in neutral medium and bromides are dehalogenated only to a moderate extent 24,132 but iodides are readily lost. Aryl fluorides, however, are hydrogenolyzed only under 

The presence of amino, hydroxy, alkoxy, or carboxy groups on the ring facilitates the dehalogenation of a phenyl halide (Eqn. 20.58). 36. 37 jhe relative position of the activating group to the departing halide has little effect on the amount of halogen lost. 2 d36 

Complete dechlorination of polychlorobenzenes has been accomplished using a palladium catalyst at room temperature and 3-4 atmospheres pressure. 41 The presence of a surfactant also facilitates this reaction. 34, M2 Very good yields of 3,5-dichloroaniline were obtained by the selective hydrodechlorination of poly-chloroanilines over palladium in acidic medium (Eqn. 20.60). 43,M4 Dehydrochlorination of polychlorophenols under these conditions gave good yields of 3,5-dichlorophenol. 44 

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Reaction XLIV. (b) Condensation of Alkyl and Aryl Halogen Compounds with the Sodio- and other Metallo-derivatives of Ethyl Aceto-acetate and its Homolognes. (A., 186, 214 201, 143 213, 143.)—Like malonic ester, acetoacetic ester contains two 1 3-carbonyl groups with a methylene group in position 2. It is only to be expected then that it yields with metallic sodium or sodium alcoholate sodio-derivatives from which mono- and di-, alkyl and aryl homologues can be obtained by treatment with a suitable halide, including halogen esters. Acetoacetic acid... 

This cyclization is a reaction developed by Mori, who carried out a series of investigations with tin reagent 33. Fluoride is a much more reactive anion for initiation than any of the other halides, although it often leads to decomposition of the starting materials. In the case of vinylic or aryl halogen compounds the iodides are easier to transform than the bromides, and chlorides are unrcactive. The carbonyl group can be derived from either an aldehyde or a ketone, and even esters are sufficiently electrophilic.22... 

From To — Akanes CycJoaikanes Akenes Akynes Aryls Halogen compounds Alcohols Phenols Ethers, Quinones B, 5 and Si compounds P and BI compounds Nttro. Nitroso, Azo. Azoxy, Hydrazo Azides Amines Organometahic compounds Adehydes Ketones Acids. AnHyd rides. Esters Amides, Amidines. Nitriles Hydroxy-aldehydes or -ketones. Sugars. Hydroxy acids Ammo acids. Peptides Heterocycles Nucleosides Miscellaneous, including heterocycles... 

The results have shown that in these reactions, also, the preliminary preparation of the magnesium compound is unnecessary, and that a good yield of the desired product is obtained by gradually adding a mixture of the alkyl or aryl halogen compound with the aldehyde, ketone or ester, to the theoretical quantity of magnesium, which is covered with a little ether. 

Notice that all the examples m Table 8 1 involve alkyl halides, that is compounds m which the halogen is attached to an sp hybridized carbon Alkenyl halides and aryl halides, compounds m which the halogen is attached to sp hybridized carbons are essentially unreactive under these conditions and the principles to be developed m this chapter do not apply to them... 

A key step in the reaction mechanism appears to be nucleophilic attack on the alkyl halide by the negatively charged copper atom but the details of the mechanism are not well understood Indeed there is probably more than one mechanism by which cuprates react with organic halogen compounds Vinyl halides and aryl halides are known to be very unreactive toward nucleophilic attack yet react with lithium dialkylcuprates... 

Contains Halogen.—Halogen compounds may be n/ly/em aryl or add haUdc tQ ha/oyru aethylene bromide, btomoben/ene, benzoyl cbloiide, oi rhloio-benzoic acid). 

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... 

In these compounds the following substituents can be present alkyl,alkenyl,aryl, halogen,sulfonic acid, amino, hydroxyalkyl, acyl, and carboxyl. The cleavages of 5,5 - (109) and 3,5 -diisoxazolyl (111) proceed similarly both isoxazole rings are cleaved in the former (109—> 110). ... 

Reaction of aryl organometallic compounds with halogens Aryl halide exchange halo-denitration halo-dehydroxylation Reaction between diazonium salts and iodide ion Heating of diazonium fluoroborates (Schiemann)... 

Phosphorinanes (1), R being H, alkyl, aryl, halogen, OR, NR2 and others, are known. Like open chained P compounds of CN = 3, most of these compounds are air sensitive and non-crystalline. The six-membered ring is nearly always in a chair conformation. Both structures (la) and (lb) are possible, R being axial (a) or equatorial (e). 

Aryl iodides are exceptional among the aromatic halogen compounds in that they form a series of derivatives in which the iodine exhibits a covalency greater than one. Some typical interconversions for which experimental conditions are given (Expts 6.31 to 6.36) are summarised below. 

Aryl ethers.1 Activated halogen compounds react with triaryl phosphates in the presence of KOH and DMF to form aryl ethers in 50-98% yield. 

Since the late 1990s, new multicomponent reactions based on a palladium/ copper-catalyzed coupling-isomerization sequence of 1-aryl prop-2-yn-l-ols and electron-deficient sp2-hybridized halogen compounds leading to the correspond-... 

Note Colorless, odorless (when pure), hygroscopic liquid, powerful aprotic solvent dissolves many inorganic salts, soluble in water combustible readily penetrates the skin incompatible with strong oxidizers and many halogenated compounds (e.g., alkyl halides, aryl halides), oxygen, peroxides, diborane, perchlorates. Synonyms DMSO, methyl sulfoxide, sulfinylbismethane. 

Structures of compounds in entries 16-20 are all based on the type (LXXXII), in which R1 and R2 can be alkyl, aryl, halogen, a metal carbonyl group, or part of a cyclic system. 

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