Bromination of arenes

Halogenation (Section 12 5) Chlorination and bromination of arenes are carried out by treatment with the appropriate halogen in the presence of a Lewis acid catalyst Very reactive arenes undergo halogenation in the absence of a catalyst... 

Our recent studies on effective bromination and oxidation using benzyltrimethylammonium tribromide (BTMA Br3), stable solid, are described. Those involve electrophilic bromination of aromatic compounds such as phenols, aromatic amines, aromatic ethers, acetanilides, arenes, and thiophene, a-bromination of arenes and acetophenones, and also bromo-addition to alkenes by the use of BTMA Br3. Furthermore, oxidation of alcohols, ethers, 1,4-benzenediols, hindered phenols, primary amines, hydrazo compounds, sulfides, and thiols, haloform reaction of methylketones, N-bromination of amides, Hofmann degradation of amides, and preparation of acylureas and carbamates by the use of BTMA Br3 are also presented. 

Fig. 12. Bromination of acetanilides with BTMA Br3 Bromination of arenes...

Fig. 13. Bromination of arenes with BTMA Bt3 Bromination of thiophene derivatives...

SIDE-CHAIN BROMINATION OF AROMATIC COMPOUNDS Benzylic bromination of arenes... 

PV2M010O40 has usually been used in the acid form. H5PV2M010O40 catalyzes aerobic oxidative cleavage of cycloalkanes, 1-phenylalkanes, and ketones. For example, the oxidation of 2,4-dimethyl cyclopentanone and 2-methylcyclo-hexanone gives 5-oxo-3-methylhexanoic acid and 6-oxoheptanoic acid, respectively, in yields higher than 90% [285, 286). Bromination of arenes with HBr [287), oxidative dehydrogenation of cyclohexadiene [288, 289) and a-terpinene [290), oxidation of 2,4-dimethylphenol [291) and sulfides [292) are other examples. 

Bromination of arenes. The selective bromination using ZnEr /SiOj is environmentally more benign. 

Prepared by reaction of DBU with Br2 in HOAc in the presence of HBr. Bromination of arenes.1 This reagent brominates activated arencs at room temperature in DMF/H20 (phenol — tribromophenol, 89% yield). Less reactive aromatics are brominated by 1 in the presence of HgCI2 as catalyst (mesitylene — 2-bromomesitylene, 76% yield). Polycyclic arenes arc brominated by 1 in refluxing acetic acid (naphthalene — I-bromonaphthalcne, 65% yield). 

Bromination. Bromination of arenes (such as anisole) can use HBr or KBr as the bromine soin-ce in the presence of H Oj and sodium tungstate or molybdate. ... 

Oxidative bromination of arenes can be achieved by the reaction with a source of bromide anion and an appropriate oxidant, possibly via intermediate formation of electrophilic bromoiodanes. In particular, an efficient and regioselective monobromination of electron-rich aromatic compounds has been developed, in which iodobenzene is used as the catalyst in combination with wCPBA as the terminal oxidant. The bromination of arenes 35 with lithium bromide is fast in THF at room temperature, providing regioselective monobrominated products 36 in good yields (Scheme 4.18) [46]. 

The proposed catalytic cycle for this reaction includes initial formation of [hydroxyl(tosyloxy)iodo]benzene 37 by oxidation of iodobenzene in the presence of toluenesulfonic acid followed by its conversion into the bromoiodane 38 via ligand exchange and then the bromination of arene to form the aryl bromide (Scheme 4.19). The reduced by-product, iodobenzene, is again transformed into the hypervalent iodine reagent by oxidation with mCPBA [46]. 

A catalytic oxidative bromination of arenes, alkenes, and alkynes in aqueous media was achieved by using NH4VO3 catalyst combined with H2O2, HBr, and KBr [14]. Dodecyltrimethylammonium bromide was found to serve as an efficient surfactant to facilitate the NH4V03-catalyzed bromination in aqueous media. A scheme of the oxidative bromination of stilbenes in water in the presence of an additive is shown in Figure 2.2. 

MoUnari, A., Varani, G., Polo, E., et al. (2007). Photocatalytic and Catalytic Activity of Hetero-genized W loO in the Bromide-Assisted Bromination of Arenes and Alkenes in the Presence of Oxygen, J. Mol. Catal. A Chem., 262, pp. 156-163. 

Table 2.1 Oxidative bromination of arenes, alkenes, and alkynes by using cat. NRiVOj/AlBryOi system...

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