Tert-Butyl hypobromite, bromination

In our previous studies on chlorination of toluene we had found that solvent had an important effect on the selectivity. In particular, the use of diethyl ether as a cosolvent was advantageous for the production of a high proportion of the para-isomer (ref. 9). An experiment in which the amount of ether in a tetrachloromethane/diethyl ether solvent mixture was varied under otherwise identical reaction conditions (Ih reaction at 18°C with 1.04 molar equivalent of tert-butyl hypobromite) demonstrated that diethyl ether also had a marked influence on the selectivity of the bromination reaction (Fig. 6). There was also an effect on the yield of the reaction as performed under these standard conditions. As the... 

This work is in its early stages, but it is already clear that a significant improvement in P-selectivity can be achieved by use of H zeolite Y as the catalyst for the bromination of naphthalene with tert-butyl hypobromite (Fig. 8) (ref. 11). It remains to be seen whether further improvements can be achieved by variation of the counterion or by variation of solvent. Such studies are currently in progress. 

Boron trifluoride and boron trifluoride-diethyl ether complex can be used as a source of fluoride ions in the presence of hypobromites and hypochlorites, e.g. methyl hypobromitc, tert-butyl hypobromite, methyl hypochlorite in carbon tetrachloride at 25 C. The addition of bromine monofluoride" and chlorine monofluoride" to various alkenes is accompanied by the formation of the corresponding alkoxybromides and alkoxychlorides which hinder the isolation of the halofluorinated products.57 jV-Bromo- and A -chloro-substiluted alkyl- and arylamines. -amides, and -imides, A -chloro-A,-methylamine, A -bromo-A -methylamine, A -chloro-A, /V-dimethylamine, A-bromo-A.A-dimethylamine, ACV-dichloro-A -methylamine, V,fV-dibromo-,V-mcthylaminc, A -bromosuccinimide, -V-chlorosuccinimide, Af-bromoacct-amide, A.A -dichlorourethane, can be used in the reaction instead of the hypohalites. The reactions with various alkenes conducted in dichloromethane at room temperature in the presence of boron trifluoride-diethyl ether complex produce bromofluoro and chlorofluoro addition products in 40-80 % yield. However, the reactions are complicated by the addition of A -halo-succinimides and Af.A-dichlorourcthane to the C = C bonds.58... 

The zeolite can easily be regenerated by heating. Similar high para selectivity can be achieved in the case of toluene by use of tert-butyl hypobromite as reagent with zeolite HX in a solvent mixture (CCI4 and ether). ZnBr2 supported on mesoporous silica or acid-activated montmorillonite is a fast, effective, reusable catalyst for the para-bromination of alkylbenzenes.257... 

Reaction of pentafluorophenol with rerf-butyl hypobromite starts as an electrophilic substitution in the benzene ring. The electrophile is formed by dissociation of tert-butyl hypobromite to tert-butoxy anion and bromine cation. The bromine cation attacks the para position and forms a positively charged Wheland complex, a nonaromatic species that is converted by ejection of proton from the phenolic hydroxyl to a quinon-oid compound, 4-bromopentafluorocyclohexa-2,5-dienone [39]. 

A mixture of N-tert-butyl-4-nitrobenzamide and a soln. of acetyl hypobromite prepared from Ag-acetate and bromine in CCI4 stirred 15 min. at room temp, protected from light by aluminum foil N-bromo-N-t rt-butyl-4-nitrobenzamide. Y 99%. - F. e., also N,N-dibromination, s. T. R. Beebe and J. W. Wolfe, J. Org. Chem. 35, 2056 (1970). 

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