Trifluoroacetic Acid Hydroxylamine System as Organocatalyst Reagent in a One-Pot Salt Free Process for the Synthesis of Caprolactam and Amides of Industrial Interest

F Manente,A Vavasori,L Pietrobon,L Ronchin

doi:10.1007/s10562-021-03590-z

Abstract

In this work we studied the reactivity of the Trifluoroacetic acid hydroxylamine system in the one step salt free synthesis of amides from ketones. A particular regards was paid to the caprolactam synthesis because of its industrial relevance. Synthesis, reactivity and characterization of the hydroxylamine trifluoroacetate is given. Fast oximation reaction of several ketones was gained at room temperature (1 h of reaction quantitative conversion for several ketones). In the same reactor, by raising the temperature at 383 K, the Beckmann rearrangement of the so obtained oximes is easily accomplished in the presence of three equivalent of TFA. The possibility of obtaining the trifluoroacetate of the hydroxylamine with a modified nitric acid hydrogenation reactions was verified, too. Reuse of solvent and trifluoroacetic acid is easily achieved by distillation.Graphical abstractSalt free one-pot caprolactam and amides process catalyzed by CF3COOH, in the presence of NH2OH TFA as the oximation agent.

Highlights

Caprolactam is a chemical whose importance raises continuously from the beginning of its industrial production being the monomer of the important polyamide nylon 6
The reaction with Cl–H has reached 78% of conversion after 20 h of reaction. It is noteworthy the presence of Trifluoroacetic acid 98% (TFA) is mandatory to have in the second step, that is the Beckmann rearrangement of the oxime, high conversion and selectivity in CPL, for this reason we tested the reactivity of the various oximation agent in the presence of TFA in the optimal concentration for the Beckmann rearrangement [15,16,17,18]
The presence of TFA causes the reduction of the selectivity in cyclohexanone oxime (COX) especially at longer reaction time, because of the increases of the condensation products of cyclohexanone 99% (CON) catalyzed by TFA

Summary

Introduction

Caprolactam is a chemical whose importance raises continuously from the beginning of its industrial production being the monomer of the important polyamide nylon 6. The existing processes are based on several type of reactions, one of the most employed is the Hoechst-Celanese process where 4-hydroxy acetophenone reacts with hydroxylamine giving the corresponding oxime, which rearranges to the N-acetyl-4-aminophenol in the presence of thionyl chloride [22] In this case, two steps are necessary to carry out the synthesis: an oximation stage and the Beckmann rearrangement [22]. The reaction occurs in an aqueous solution of isopropyl alcohol, which reduces the risk of decomposition and explosion of the hydroxylamine eventually in solution [1] The use of such a solvent, in the amoximation process does not allow a further Beckmann rearrangement, by using the trifluoroacetic acid (as organocatalyst) in a onepot process [15,16,17,18]. Nitric acid conversion and hydroxyl amine formation are measured by spectrophotometric analysis [28]

Results and Discussions

Reactivity of TAH Towards Different Ketones

Conclusions