Reactions of 2-Bromo-3-methoxy-1,4-naphthoquinone with Secondary Alkyl Amines: The Role of the Bromine Atom in the Stability of the Product
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Quinones are involved in many biological pathways.It is essential to understand their basic chemical properties.Substitution process is often involved in the reactions of quinones.Here we study the reactions of 2-bromo-3-methoxy-1,4-naphthoquinone with secondary alklylamines.Various alkylamines were chosen to react with 2-bromo-3-methoxy-1,4-naphthoquinone.Reactions of 2-methoxy-1,4-naphthoquinone with secondary alkylamines were also studied in order to understand the role of bromine atom.Since a methoxy group is not considered a good leaving group in nucleophilic substitution,it was expected that an alkylamine would replace the bromine atom.In reality, however,an alkylamine was found to replace the mothoxy group in 2-bromo-3-methoxy-1,4-naphthoquinone.By comparing the stability of the product of a secondary alkylamine with 2-methoxy-1,4-naphthoquionone,we found that the bromine would make the substitution product more readily decomposing.The product in the reaction of 2-bromo-3-methoxy-1,4-naphthoquinone with N-methylethylamine,for example,is 2-bromo-3-N-methylethylamino-1,4-naphthoquinone. This product was found to decompose through dealkylation,where one of the alkyl groups was lost. The major decomposition product was identified as 2-bromo-3-methylamino-1,4-naphthoquinone by losing ethyl group.On the other hand, no decomposition was detected in reaction product of 3-methoxy-1,4-naphthoquinone with N-methylethylamine,that is,2-N-methylethylamino-1,4-naphthoquinone.Our observation suggests the bromine plays a critical role in the stability of the product.