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NMR study on residual lignins isolated from chemical pulps of beech wood by enzymatic hydrolysis
최준원,Oskar Faix 한국공업화학회 2011 Journal of Industrial and Engineering Chemistry Vol.17 No.1
Two residual lignins isolated from kraft and ASAMpulps of beech wood (Fagus sylvatica L.) were analyzed by 1H and 13C NMR spectra to confirm the structural features previously obtained from wet chemical degradation methods. 1H NMR spectra revealed that the most distinct features of ASAM lignin was the signal at dH 5.9 ppm and dH 6.6 ppm for Ha in b-O-4 linkage and protons for syringyl units. The abundance of syringyl units in ASAM lignin was also evidenced by the signals at dC 154 ppm and dC 104 ppm in the 13C NMR spectra, responsible for aromatic C3/C5 and C2/C6 of syringyl units. The important functional groups, such as phenolic OH, aliphatic OH and methoxyl groups, were indirectly evaluated by 13C NMR spectra of acetylated residual lignin. In particularly, the increment of phenolic OH,one of the parameter for cleavage of b-O-4 linkages,was determined to relative low in of b-O-4 linkages in ASAM residual lignin as compared to kraft residual lignin, indicating that ASAM procedures may run by quite different pathway for delignification unlike the fragmentation of b-O-4 linkages and cleavage of side chain in the general alkaline pulpings.
Choi, J.-W.,Faix, O. 한국목재공학회 2003 목재공학 Vol.31 No.6
The enzymatic isolation of residual lignins obtained from spruce and beech pulps (obtained by sulfite, kraft, ASAM and soda/AQ/MeOH pulping processes) and their characterization was described in previous publications. Here, the residual lignins have been submitted to potassium permanganate oxidation (KMnO₄degradation), and 9 aromatic carboxylic acids (3 of them are dimeric) were identified after methylation with diazomethane by GC/MS. The analytical challenge during qantification by the internal standard methods was the partly high protein content of the samples, which resulted in elevated anisic acid yields in the degradation mixture of sulfite residual lignins. The results are compared with the KMnO₄ degradation of the corresponding MWLs and discussed in terms of S/G ratios and degrees of condensation. The latter was calculated as a quotient between the aromatic carboxylic acids derived from condensed and non-condensed lignin structures. Typical degradation patterns for the various processes have been observed. Among other parameter, the relative compositions between iso-hemipinic acid (which is for condensation in pos. 5 of the aromatic ring) and meta-hemipinic acid and 3,4,5-trimethoxyphthalic acid (both are for condensation in pos. 6 of the aromatic ring) was found to be process specific. Kraft and soda/AQ/MeOH residual lignins yielded higher amounts of iso-hemipinic acid. In contrast, the relative yields of meta-hemipinic acid and 3,4,5-trimethoxyphthalic acid (the latter in beech lignins) are higher in sulfite and particularly in ASAM residual lignin. In case of beech residual lignins the amount of acids originated from non-condensed syringyl type lignin units was surprisingly high. The condensation degree of residual lignins was shown to be generally higher than that of MWLs. This was especially true for the G units. ASAM residual lignin exhibited very high S/G ratios and degrees of polymerization. Causality between condensation degree and total yield of degradation products was demonstrated.