1. Field of the Invention
The present invention relates to methods for synthesizing tetrabromobenzoate esters and, more particularly, to a method for synthesizing tetrabromobenzoate esters from tetrabromophthalic anhydride using a process that provides high yields.
2. Description of the Related Art
Tetrabromobenzoate esters have been formed as minor by-products in the synthesis of tetrabromophthalate diesters from tetrabromophthalic anhydride. However, these by-products are considered undesirable in the synthesis of tetrabromophthalate diesters and, therefore, the process has been refined to avoid the production of tetrabromobenzoate esters.
Tetrabromobenzoate esters have also been synthesized directly through the esterification of tetrabromobenzoic acid using a metal or organometallic esterification catalyst. Unfortunately, tetrabromobenzoic acid is not readily available and, therefore, must be synthesized prior to esterification. In addition, the esterification of tetrabromobenzoic acid requires long reaction times and the metal or organometallic esterification catalyst is relatively expensive and often requires complicated, time-consuming removal and disposal procedures.
Alternatively, tetrabromobenzoate ester compounds have been prepared from tetrabromophthalic anhydride using a one-pot batch synthesis in which tetrabromophthalic anhydride is reacted in a single reactor with an appropriate alcohol in the presence of a decarboxylation catalyst to form the tetrabromobenzoate ester. More specifically, the tetrabromophthalic anhydride is reacted with the alcohol at low reactor temperatures to form a half-ester intermediate. The reactor is then heated to higher temperatures and the half-ester intermediate, in the presence of a decarboxylation catalyst, forms the tetrabromobenzoate ester. However, this reaction scheme yields a product containing the target compound tetrabromobenzoate ester and a significant amount of tetrabromophthalate diester. In addition, the reaction product often has an undesirable amber color.
Therefore, a need remains for a more efficient process for producing tetrabromobenzoate esters. More specifically, a need remains for a method for synthesizing tetrabromobenzoate esters at higher yield ratios of tetrabromobenzoate ester to tetrabromophthalate diester, and/or a more desirable lighter color.