Brominating solvents

TBPA is prepared in high yield by the bromination of phthalic anhydride in 60% oleum (51). The use of oleum as the bromination solvent results in some sulfonation of the aromatic ring (52). Sulfonated material is removed by hydrolyzing the anhydride with dilute NaOH, filtering and acidifying with dilute HCl. The precipitated acid is washed several times with hot water and reconverted to the anhydride by heating at 150°C for several hours. 

Organic compounds of bromine usually resemble their chlorine analogues but have higher densities and lower vapor pressures. The bromo compounds are more reactive toward alkaUes and metals brominated solvents should generally be kept from contact with active metals such as aluminum. On the other hand, they present less fire hazard one bromine atom per molecule reduces flammabiUty about as much as two chlorine atoms. 

This procedure, in contrast to previous methods, comprises only one step and is readily adapted to large-scale preparative work. Furthermore dibromination is very slow in methanol and hence the crude reaction products contain only traces of dibromo ketones. This contrasts with the behavior in other solvents such as ether or carbon tetrachloride, where larger amounts of dibromo ketones are always present, even when one equivalent of bromine is used. Methanol is thus recommended as a brominating solvent even when no orientation problem is involved. It should be noted that a-bromomethyl ketals are formed along with x-bromoketones and must be hydrolyzed during the workup (Note 8).7... 

Addition of bromine to quinolizinium bromide results in formation of the perbromide salt (13). The formation of this salt is reversible, for treatment with an easily brominated solvent like acetone regenerates the original bromide. Van der Plas and coworkers (81H(15)213) have shown that if the perbromide salt (13) is heated at 200 °C it is converted into 1-bromoquinolizinium bromide (Scheme 3). While the high temperature suggests that this may be a radical reaction, the orientation (at a carbon atom of lower positive charge, although not the 3-position predicted above) is consistent with an electrophilic mechanism. 

Recent field evidence indicates that the occurrence of these reaction products may be relatively common in hypoxic groundwaters which have been contaminated by bromoaliphatic compounds. Schwarzenbach et al. (1) reported the presence of a complex mixture of alkyl and chloroalkyl sulfides in a hypoxic groundwater polluted by a variety of bromo- and chloroaliphatic compounds. Ethanethiol (at a concentration of approximately 2 pM) was detected by Jackson et al. (5Q) in groundwater contaminated by a variety of chlorinated and brominated solvents beneath a municipal/industrial landfill. In addition, Watts and Brown (51 cited in 2) have reported the presence of ethanethiol, diethyl disulfide and triethyl disulfide in Florida groundwaters contaminated by 1,2-dibromoethane. 

Acetamide is useful in the bromination of acid-sensitive compounds since it forms a stable complex with hydrogen bromide, CH3CONH2 HBr, which is insoluble in common bromination solvents. ... 

The selectivity of chlorination is influenced by solvents. For example, the chlorination of 2,3-dimethylbutane shows increased preference for the tertiary position in benzene. " The complexation with solvent attenuates the reactivity of chlorine atoms. Halogenated solvents also give evidence of complex formation. Brominated solvents lead to greater selectivity. " ... 

But a hydrolysis reaction between tramp water and the solvents used in Class II cosolvent machines doesn t occur, because there are no chlorinated or brominated solvents present. In these machines, water is not a reactant, but a diluent. Water simply accumulates unless it is removed. 

N-Bromosuccinimidel azodiisobutyronitrilef irradiation Benzylic bromination Solvent effect s. 20, 648 suppl. 32... 

Huntingdon Life Sciences (Huntingdon). 1999. A Range-Finding Developmental/ Reproductive Study of 1-Bromopropane in Rats via Whole Body Inhalation Exposure. Final. Study No. 98-4140. West Lafayette, IN. Prepared for Brominated Solvents Consortium, Washington, D.C. June 7. 

WIL Research Laboratories, Inc. 2001. An Inhalation Two-Generation Reproductive Toxicity Study of 1-Bromopropane in Rats. Study No. WIL-380001. Ashland, OH. May 24. Sponsored by Brominated Solvents Consortium, Washington D.C. 

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