Borate esters are organic compounds of the type B(OR)3 where R is an organic residue (for example alkyl or aryl). They are conveniently prepared by a reaction such as
- B(OH)3 + 3 ROH → B(OR)3 +3 H2O
in the presence of a dehydrating agent, such as concentrated sulfuric acid. The borate ester is volatile and can be removed from the reaction mixture by distillation. This procedure is used for analysis of trace amounts of borate and for analysis of boron in steel. Alkyl borates burn with a characteristic green flame. This property is used to determine the presence of boron in qualitative analysis.
Trimethyl borate, B(OCH3)3, is used as a precursor to boronic esters for Suzuki couplings. Borate esters were shown to serve as effective coupling agents in the synthesis of amides from either carboxylic acids or primary amides.
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