Preparation of non-hazardous brominating reagents

Details Preparation of non-hazardous brominating reagents Preparation of non-hazardous brominating reagents

2002-01-23

2004-05-25

Davis, Brian (Department: 1621)

Compositions

Compositions containing a single chemical reactant or plural...

Organic reactant

C106S287270, C564S218000, C568S726000, C568S776000, C568S779000, C570S235000, C570S246000, C570S261000

Reexamination Certificate

active

06740253

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to the preparation of non-hazardous brominating reagents.
The invention particularly relates to suitable mixtures of alkali bromide and alkali bromate salts that can be prepared in stable form from inexpensive raw material and can be used as a substitute for liquid bromine in aromatic bromination reactions and also bromine addition in unsaturated compounds.
BACKGROUND OF THE INVENTION
Liquid bromine is used to prepare a variety of brominated compounds through addition or substitution reactions. The latter includes commercially important products such as: tetrabromobisphenol-A (TBBPA)—a flame retardant, eosin—a pigment used in personal care products, bromoacetanilide—an analgesic and antipyretic agent, tribromophenol—an intermediate used in the manufacture of antiseptic, germicide, fungicide, fire extinguishing fluids, and fire retardant, and 2-bromo-4-nitro acetanilide—a drug intermediate used in the preparation of nimenslide. Likewise, there are a number of addition compounds of bromine that have utility as intermediates or products. However, liquid bromine is hazardous by nature and requires extreme care in its production, transportation, and utilization. Moreover, for substitution reactions depicted by equation 1, half of the bromine atoms end up in the effluent as hydrobromic acid.
R—H+Br
2
→RBr+HBr  (1)
Bromine atom efficiency of liquid bromine can be 100% for addition across olefins (equation 2) but the need to handle the hazardous liquid bromine remains.
 R—CH═CH
2
+Br
2
→RCHBrCH
2
Br  (2)
Z. E. Jolles (Bromine and its compounds, Ernest Benn Limited London 1966, p352) describe the preparation of a number of dibromo compounds through addition of liquid bromine across unsaturated organic compounds. Such products are obtained in high yields but an important disadvantage is the hazards of handling liquid bromine.
C. A. Buechler and D. E. Pearson, (
Survey of organic syntheses
Wiley-Inter science, New York 1970 Chapter7) have reported the preparation of tribromophenol using liquid bromine as brominating agent. The drawbacks of this method are that it requires special devices for handling corrosive liquid bromine and at least half of the bromine atoms in the reagent end up in the effluent in the form of hydrobromic acid.
Reference may be made to S. Armstrong in U.S. Pat. No. 5,475,153, Dec. 12, 1995 who brominated Bisphenol-A with liquid bromine to get 98% pure tetrabromobisphenol-A (m.p, 180° C.) and where hydrogen peroxide was combined with the reactants to reuse the HBr produced as in equation 1 and thereby reduce the amount of bromine required. However, the principal difficulty of the hazardous nature of liquid bromine remains.
Brominating agents that are easy to handle are known but are used mainly for more selective transformations or those where bromine is less effective. A. Groweiss in
Organic Process
&
Development
2000, 4, 30-33, described the use of sodium bromate for bromination of aromatic compounds that contain deactivating substituents such as nitrobenzene, benzoic acid, benzaldehyde, 4-nitrofluorobenzene and 4-fluorobenzoic acid. In this process, the addition of a strong acid such as sulfuric acid into a stirred aqueous solution or slurry of the substrate and stoichiometric quantity of bromate salt at 40-100° C., leads to the decomposition of the bromate ions and production of active brominating species. The drawback of sodium bromate is that it is costly and its use cannot be justified in more conventional bromination reactions that can be effected by liquid bromine as such.
Z. E. Jolles (Bromine and its compounds, Ernest Benn Limited London 1966, p394) has added a mixture of 356 g (2 moles) of N-bromosuccinimide and 4 g (0.0165 moles) of benzoyl peroxide over 20 min to a solution of 220 g (2.24 moles) of 3-methyl thiophene and 4 g (0.0165 moles) benzoyl peroxide in 700 ml of dry benzene under stirring at reflux conditions. After all the succinimide is added, the reaction mixture is cooled to below 5° C. The benzene is distilled at 75-78° C. under reduced pressure to give 280 g of 3-bromomethyl-thiophene. Although N-bromosuccinimide is a useful reagent for specific bromination reactions, it is a costly brominating agent and its use cannot be justified in those bromination reactions where liquid bromine would suffice; even more so since its preparation involves use of liquid bromine in any case (N-bromosuccinimide is prepared by reacting succinimide with bromine liquid below 0° C. in potassium hydroxide solution).
P. C. Merker and J. A. Vona (
J Chem. Ed.
1949, 26, 613) prepared p-bromoacetanilide by reacting 31.5 g (0.232 mole) of acetanilide in 50 ml of glacial acetic acid with 38 g (0.119 mole) of pyridinium bromideperbromide in hot 40 ml glacial acetic acid. The mixture was allowed to stand at room temperature for 30 min. To it, 2 ml of saturated sodium bisulfite solution was added. The resulting mass was filtered, washed with water and finally recrystallized from hot 95% aqueous ethanol to yield 13 g of p-bromoacetanilide having m.p. 168° C. The drawbacks of this method are that the brominating agent requires liquid bromine and hydrobromic acid in its preparation (L. F. Fieser and M. Fieser,
Reagents for Organic Chemistry
Vol. 1, John Wiley, New York, 1967, p967) and the reagent is costlier than liquid bromine.
G. Rothenberg and J. H. Clark (Organic Process & Development 2000, 4, 270-274) have claimed the catalytic bromination of various aromatic compounds using an alkali bromide or hydrobromic acid and hydrogen peroxide in the presence of 1-2 mol % vanadium pentoxide catalyst. The drawbacks of this method are that more than stoichiometric quantities of hydrogen peroxide are required and the reaction needs a catalyst.
G. Ramachandraiah, P. K. Ghosh, A. S. Mehta, R. P. Pandya, A. D. Jethva, S. S. Vaghela, S. N. Misra (pending U.S. pat. appln. Ser. No. 09/767,667 [2001]) have prepared tetrabromobisphenol-A from bisphenol-A using 2:1 molar ratio of bromide and bromate salts as brominating agent. To 0.50 kg (2.19 moles) of bisphenol-A in 1.50 liters of methylene chloride, a solution of 0.63 kg (6.14 moles) of sodium bromide, 0.44 kg (2.93 moles) of sodium bromate and 1 g of sodium lauryl sulfate in 2.5 liters of water was added. The flask was cooled to 10° C. by placing it in a cold water bath. To it, 0.90 liters (10.8 moles) of 12 N hydrochloric acid was added over 3 h under stirring. The contents were stirred for another 0.5 h and the separated solid product was filtered, washed twice with deionized water and dried in oven at 100° C. to give a yield of 0.85 kg of TBBPA. The organic layer was recycled in subsequent batches. The isolated yield of TBBPA (m.p. 178-180° C.) over three batches was 85.4%. Although the method has several advantages in that the brominating reagent is easy to handle, no catalyst is required, the bromine atom efficiency for the aromatic substitution reaction studied is as high as 95-100%, the main drawback of this method is that alkali bromide and bromate salts are individually much costlier than liquid bromine. Moreover the 4:2 stoichiometry of bromide:bromate is suitable for substitution reactions but not for addition of bromine across double bonds.
According to the present invention, the main drawback of U.S. Pat. No. 6,365,786 has been overcome by using a mixture of alkali bromide and alkali bromate salts of the desired ratios that can be prepared inexpensively from the intermediate of bromine recovery plants, the said mixture being easy to handle and stable under storage while, under the conditions of bromination reaction, the bromide and bromate salts self annihilate one another to create reactive species of bromine that are useful in the safe preparation of several organo bromine compounds as demonstrated through working examples.
OBJECTS OF THE INVENTION
The main object of the present invention is the preparation of suitable mixtures of alkali bromide and alkali bromate salts that are easy to handle, st

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