Separation and characterisation of caprolactam–formaldehyde reaction products

Abstract

Methylolation and condensation products formed in caprolactam-formaldehyde reaction mixtures have been identified using nuclear magnetic resonance (NMR) and mass spectrometry (MS). Previously unreported side-products were also detected. All of the reaction products were separated by micellar electrokinetic chromatography (MEKC) and high performance liquid chromatography (HPLC), and the separation parameters, such as efficiency and distribution constants, obtained in the two techniques were compared. For quantification, the response factors for the monomers were determined using standard calibration and hydrolysis, whilst those for the condensation products were deduced from the values of the monomers. The accurate determination of the response factors was confirmed by checking the mass balance of a known mixture.

Separation and characterisation of products of the reaction between propionamide and formaldehyde

“…Firstly, the separation of amide-formaldehyde monomers is a critical factor in the optimisation of the MEKC separations. Knowing that PMEKC values are in the range 33 40 for the caprolactam monomers [12], and in the range 7 8 for the propionamide monomers, it can be seen that the ratio of the SDS concentrations used for the separations of propionamide-formaldehyde and caprolactam-formaldehyde reaction products, 4.6, is very similar to the ratio of the respective PMEKC values, -4 5. Knowing that PMEKC values are in the range 33 40 for the caprolactam monomers [12], and in the range 7 8 for the propionamide monomers, it can be seen that the ratio of the SDS concentrations used for the separations of propionamide-formaldehyde and caprolactam-formaldehyde reaction products, 4.6, is very similar to the ratio of the respective PMEKC values, -4 5.…”

“…From the work presented in this paper and in reference [12], generic conclusions can be drawn about the identification and quantification of amide-formaldehyde re-action systems. Firstly, the separation of amide-formaldehyde monomers is a critical factor in the optimisation of the MEKC separations.…”

“…A comparison is possible with distribution constants for corresponding caprolactam-formaldehyde reaction products [12]. N-methylol-caprolactam (CF), caprolactam (C), N,N'-methylene-bis(caprolactam) (CFC) and N,N'-oxy-bis(methylene)-bis(caprolactam) (CFFC) were found to have PMEKC values of 33 • 1, 40 • 1,223 • 11 and 356 • 25 respectively.…”

“…In a separate paper, we have successfully identified and quantified all reaction products and side products formed in caprolactam-formaldehyde reaction mixtures using NMR, MS, HPLC-UV-MS and micellar electrokinetic chromatography (MEKC) [12]. Caprolactam was chosen as the first model amide compound to study, as it has only one site for reaction with formaldehyde.…”