Abstract
Beckmann rearrangements of oximes to lactams often require harsh conditions and/or the use of large amounts of acid catalyst. To reduce the amount of Bronsted acid required, and to avoid the formation of a large amount of undesirable byproducts under mild reaction conditions, a low environmental load process was developed. Beckmann rearrangements of cyclohexanone oxime and cyclooctanone oxime were achieved using a combination of a Bronsted acid and cobalt tetra-fluoroborate hexahydrate. Various Bronsted acid catalysts (10 - 20 mol%) were used to obtain the corresponding lactams in high yields at 80℃.
Highlights
The Beckmann rearrangement is commonly used in organic chemistry to transform ketoximes into amides [1][9]
We developed catalysts combining cobalt salts and Lewis acids which were highly effective for the Beckmann rearrangement of cycloalkanone oximes [18]
We focus on the use of more traditional acids, and report that combinations of cobalt salts and Brønsted acids are highly effective for the Beckmann rearrangement of cycloalkanone oximes under mild conditions, assuring more economical and environmentally-friendly process
Summary
The Beckmann rearrangement is commonly used in organic chemistry to transform ketoximes into amides [1][9]. Cyclohexanone oxime (1) is widely-used to manufacture ε-caprolactam (2) which is used industrially as the raw material for nylon-6. One proposed Beckmann rearrangement method for 1 involves an acidcatalyzed reaction. The lactam formed typically forms salts with acids, inactivating the acid catalyst. An excessive amount of acid is necessary to accomplish the reaction in a practical way.
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