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Selective cyclization of 6‐aminocaproic acid adsorbed on silica gel to ϵ‐caprolactam: IR analysis of adsorbed state
Author(s) -
Ogawa Haruo,
Fujigaki Tamiki,
Ohwada Yoshiko,
Chihara Teiji
Publication year - 2001
Publication title -
journal of physical organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.325
H-Index - 66
eISSN - 1099-1395
pISSN - 0894-3230
DOI - 10.1002/1099-1395(200101)14:1<52::aid-poc339>3.0.co;2-#
Subject(s) - chemistry , caprolactam , adsorption , silica gel , polymer chemistry , organic chemistry
When 6‐aminocaproic acid (6‐ACA) was adsorbed on silica gel and the suspension of the adsorbed sample was treated in refluxing toluene, 6‐ACA was selectively converted to ϵ‐caprolactam (ϵ‐CL) in the absence of catalysts. The relationship between adsorption of 6‐ACA and its reactivity to give ϵ‐CL was investigated by IR spectrometry with the diffuse reflection technique. The smaller the amount of 6‐ACA adsorbed on silica gel, the higher both the yield and selectivity for ϵ‐CL became. When the loading amount of 6‐ACA on silica gel was lower than θ = 0.043 (θ = surface coverage), the amounts of chemical species having NH 2 , and CO groups increased and a high selectivity for ϵ‐CL was obtained. When the loading amount was higher than θ = 0.40, 6‐ACA was adsorbed as an amphoteric ion having NH + 3and CO 2 −groups as in the solid state and gave a low yield and selectivity for ϵ‐CL. Thus 6‐ACA activated by adsorption, which concomitantly hinders intermolecular interactions by suppressing the translational movement, facilitated intramolecular dehydration to yield ϵ‐CL. Copyright © 2000 John Wiley & Sons, Ltd.