Halide aromatic

Acid halides are among the most reactive carboxylic acid derivatives and can be converted into many kinds of substance, for example, to aldehydes by hydrogenolysis on Pd/BaS04 (Rosenmund reduction)[94-96]. The catalysts usually contain additives to moderate their activity and prevent over-reduction [97]. Tetra-methylthiourea was the most effective additive [98]. These additives probably do not block active sites but rearrange the surface structure of the catalysts [99]. Undec-lO-enoyl chloride was hydrogenolyzed, however, to undec-lO-enal on Pd/C without any inhibitor [100]. 

Greene, P. G, M. Writs, Protective Groups in Organic Synthesis, 2 ed, Wiley, New York, 1991. 

Mokubo, N. Kobayashi, J. Nagasawa, Y. Ishido, Tetrahedron Lett. 1989, 30, 115. 

Gondos, L. Gera, M. Bartok, in Stereochemistry of Heterogeneous Metal Catalysis, (ed. M. Bartok), Wiley, Chichester, 1985, pp. 414, 497 

Partyka, J. E. Hengeveld, in Chemical Industries (Catalysis of Organic Reactions), 1990, 40, 197, (ed. D.W. Blackburn), Marcel Dekker, New York. 

6 Aromatic Halides. The molecular ion peak of an aryl halide is readily apparent. The M — X peak is large for all compounds in which X is attached directly to the ring. 

3 Aliphatic Iodides. Aliphatic iodides give the strongest molecular ion peak of the aliphatic halides. Since iodine is monoisotopic, there is no distinctive isotope peak. The presence of an iodine atom can sometimes be deduced from isotope peaks that are suspiciously low in relation to the molecular ion peaks, and from several distinctive peaks in polyiodo compounds, the large interval between major peaks is characteristic. 

Iodides cleave much as do chlorides and bromides, but the C4H8I+ ion is not as evident as the corresponding chloride and bromide ions. 

Cl Br NaOCl, cat Ni tetraphenyl-porphyrin, cat (n-Bu3NCH2Ph)Br CuCl Mg / Ph3pa2 

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Ullman reaction The synthesis of diaryls by the condensation of aromatic halides with themselves or other aromatic halides, with the concomitant removal of halogens by a metal, e.g. copper powder thus bromobenzene gives diphenyl. The reaction may be extended to the preparation of diaryl ethers and diaryl thio-ethers by coupling a metal phenolate with an aryl halide. 

The iodine atom in iodobenzene (unlike that in the corresponding aliphatic compounds) is very resistant to the action of alkalis, potassium cyanide, silver nitrite, etc. This firm attachment of the iodine atom to the benzene ring is typical of aromatic halides generally, although in suitably substituted nitio-compounds, such as chloro-2,4-dinitrobenzene, the halogen atom does possess an increased reactivity (p. 262). 

Aromatic halides can, in virtue of their aromatic character, be nitrated, etc. 

Cu catalyzed arsonylation by substitution ol aromatic halides See also Bart-Schellet... 

ULLMANN GOLDBERG Aromatic substitution Cu catalyzed substitution of aromatic halides in the synthesis of disryls, diaiyl ethers, diaryl amines, phenols... 

Cheaper sources of tnfluoromelhyl groups have been the goal of several groups The use of sodium tnfluoroacetate and copper (1) iodide in dipolar aprotic solvents gave regiospecific trifluoromethylation of aromatic halides [202] (equation 136)... 

The activation energy of substitution of an unactivated aromatic halide (e.g., fiuorobenzene and 2-chloronaphthalene ) is over 30 kcal while that of activated compounds is 5-20 kcal. For the tabulated reactions (Tables II-VIII) with alkoxide and with primary, secondary, or tertiary amines, resonance activation (cf. 278 and 279) by ortho or para nitrogens is found to be greater than inductive activation (cf. 251). This relation is qualitatively demonstrated in... 

The authors describe a stabilizing effect of the ionic liquid on the palladium catalyst. In almost all reactions no precipitation of elemental palladium was observed, even at complete conversion of the aromatic halide. The reaction products were isolated by distillation from the nonvolatile ionic liquid. 

In small-scale experiments, overnight reaction of lithium dipropenylcuprate with lodobpnzene m ether containing 20 equivalents of pyridine at 25° gave 1-propenyl-benzene in 60 % yield. For couplmg with aromatic halides, this solvent system is superior either to ether-tetrahydrofuran or to ether containing 4 equivalents of hexamethylphosphonc triamide. 

The Ullman reaction has long been known as a method for the synthesis of aromatic ethers by the reaction of a phenol with an aromatic halide in the presence of a copper compound as a catalyst. It is a variation on the nucleophilic substitution reaction since a phenolic salt reacts with the halide. Nonactivated aromatic halides can be used in the synthesis of poly(arylene edier)s, dius providing a way of obtaining structures not available by the conventional nucleophilic route. The ease of halogen displacement was found to be the reverse of that observed for activated nucleophilic substitution reaction, that is, I > Br > Cl F. The polymerizations are conducted in benzophenone with a cuprous chloride-pyridine complex as a catalyst. Bromine compounds are the favored reactants.53,124 127 Poly(arylene ether)s have been prepared by Ullman coupling of bisphenols and... 

Condensation of an activated aromatic halide witli eitlier an alkali metal tliio-phenoxide or an alkali metal sulfide is performed under the same experimental condensations as used for polyetherification (Scheme 6.33).248... 

The principal mechanisms for the nucleophilic arylation by aromatic halides... 

The Heck-Cassar-Sonogashira-Hagihara system, which couples terminal alkynes and vinylic or aromatic halides in an amine solvent, typically piperi-... 

As noted in Section 11.2.2, nucleophilic substitution of aromatic halides lacking activating substituents is generally difficult. It has been known for a long time that the nucleophilic substitution of aromatic halides can be catalyzed by the presence of copper metal or copper salts.137 Synthetic procedures based on this observation are used to prepare aryl nitriles by reaction of aryl bromides with Cu(I)CN. The reactions are usually carried out at elevated temperature in DMF or a similar solvent. 

In aqueous DMF, the reaction can be applied to the formation of C-C bonds in a solid-phase synthesis with resin-bound iodobenzoates (Eq. 6.33).80 The reaction proceeds smoothly and leads to moderate to high yield of product under mild conditions. The optimal conditions involve the use of 9 1 mixture of DMF-water. Parsons investigated the viability of the aqueous Heck reactions under superheated conditions.81 A series of aromatic halides were coupled with styrenes under these conditions. The reaction proceeded to approximately the same degree at 400°C as at 260°C. Some 1,2-substituted alkanes can be used as alkene equivalents for the high-temperature Heck-type reaction in water.82... 

The relative inertness of unactivated aromatic halides towards nucleophiles, under normal conditions, is in sharp contrast to their marked reactivity towards nucleophiles that are also very strong bases. Thus chlorobenzene is readily converted into aniline by reaction with eNH2 (NaNH2) in liquid ammonia at — 33° ... 

SNAr substitutions of activated aromatic halides, especially aromatic fluorides, provide useful means for the construction of aromatic diethers or amines. Primary and secondary amines react with l, 2-dihalo-4,5-dinitrobenzene to give nitro group substitution at room temperature. The halogen substituents on the ring remain unsubstituted and can be used in further transformation (Eq. 9.5).8... 

There are many variants of such syntheses of heterocycles. Recent examples are presented in Eqs. 9.58 and 9.59.90 Because these transformations do not require aromatic halides or transition metals, they may provide a clean technology for production of biologically important materials. 

Low-valent nickel complexes of bpy are also efficient electrocatalysts in the reductive coupling reaction of aromatic halides.207 Detailed investigations are in agreement with a reaction mechanism involving the oxidative addition (Equation (40)) of the organic halide to a zero valent complex.208-210 Starting from [Nin(bpy)2(X)2]0 with excess bpy, or from [Nin(bpy)3]2 +, results in the [Ni°(bpy)2]° complex (Equations (37) and (38)). However, the reactive complex is the... 

Vinylic halides or vinyl-metal species couple with a very high degree of stereospecificity, cry-vinylic halides giving cis coupling products and tra/iy-vinylic halides trans coupling products (example 17, Table III). Aromatic halides give homo- or cross-coupling reactions (examples 18 and 19, Table III). 

Aromatic halides (example 21, Table VII) also react in the presence of Ni(0) complexes in alkaline media. Complex nickel carbonyl anions, such as Ni5(CO),22, Ni6(CO)122, Ni9(CO)182 (194) are formed which, being more nucleophilic, can attack aromatic halides. 

Examples of amination reactions of aromatic halides and of unsaturated compounds are presented in Table X (228, 232-240). 

I, Table X) requires tertiary phosphine-nickel halide or tertiary phosphine-nickel carbonyl complexes at 140-170°C. This implies oxidative addition of aromatic halides to nickel, replacement of the halide with amines, and reductive elimination. 

Replacement reactions of aromatic halides or other halides with SCN, NCO, or N02 can be easily carried out by oxidation of nickel complexes with copper salts (examples 8-11, Table XI). 

Simple reaction occurs with aryl halides only when the ring is sufficiently substituted with electron-withdrawing functions to allow attack by the nucleophilic phosphorus.53-56 Generally, reaction with aryl halides requires the presence of a Lewis acid catalyst or some other means of reaction initiation. These reactions will be considered in detail in Chapter 6 of this work. Interestingly, while reactions involving vinylic halides seem to correlate with those of aromatic halides (see Chapter 6), acetylenic halides undergo facile reaction with these phosphorus reagents.57 58... 

Aromatic halides such as chlorobenzene and p-fluorololuene were rapidly hy-drogenolyzed in 100% conversion by NaH of nanometric size in the presence of homogeneous catalysts. One- or two-component (e.g., Ni(OAc)2/TiCl4) systems were effective. The combination of ytterbium chloride and a transition-metal chloride showed a remarkable synergistic effect [37, 38]. 

Comput. Sci., 41, 692, 2001. With permission. a The 15 aromatic compounds are a mixture of 11 aromatic hydrocarbons and four aromatic halides. 

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