Coniferyl alcohol structures

Raman Spectroscopic Evidence for Coniferyl Alcohol Structures in Bleached and Sulfonated Mechanical Pulps... 

AGARWAL AND ATALLA Raman Evidence for Coniferyl Alcohol Structures 27... 

Other Structures. From the results on the pulps studied here, it appears that coniferyl alcohol structures survive bleaching and sulfonation treatments. As alternative causes of residual intensity at 1654 cm-1, we have considered quinone and stilbene structures. Stilbene structures (samples 25 and 26) give a Raman band around 1635 cm-1 (Table I, Fig. 61,J). Such structures have not been... 

Implications to Photoyellowing. On the basis of the Raman spectral results, survival of coniferyl alcohol structures (this includes both phenolics and those etherified at the para-position) in bleached and sulfite pulps would seem to be a major reason why pulps yellow in daylight. Such groups are expected to participate in the primary photochemical events that lead to yellowing. Thus, in pulps, coniferyl alcohol structures would act as leucochromophores. Photoyellowing of coniferyl alcohol structures has been evaluated [34], and it has been reported that the free phenolic structure contributes much more to yellowing than does the para-etherified unit. 

Characterization of lignin end groups. The compounds isolated (Figure 1), which are assumed to constitute lignin end groups, include coniferyl alcohol structures (4,8, 15 and 18), coniferaldehyde structures (3,7,12 and 17), detached pyruvaldehyde enol... 

Biphenyl structures and a-carbonyl-p-aryl ether structures, which are both assumed to be present in native lignin with a higher abundance than coniferyl alcohol structures (22,23) and both considered to be important leucochromophores, were not observed among die products, presumably because they are not present in spruce lignin as end groups. Both these types of structures are very stable and unlikely to be structurally changed during mild acid hydrolysis (24). 

Coniferyl alcohol and coniferaldehyde structures. It has been estimated that spruce lignin contains about 6% of coniferyl alcohol units as end groups (28). In previous work, the behaviour of coniferyl alcohol structures during a mild sulfite treatment simulating the chemical pretreatment in a CTMP process was studied (75). It was found that coniferyl alcohol is liberated from spruce wood more rapidly under acidic than under neutral or alkaline conditions. The treatment time needed for complete liberation of coniferyl alcohol structures from wood lignin was, however, found to be more than 100 minutes irrespective of treatment conditions. Considering the short treatment time (5-15 min.) employed in the commercial process, it can... 

Figure 6. Relative yields of coniferaldehyde and coniferyl alcohol structures...

UP Agarwal and RH Atalla. Raman Spectroscopic Evidence for Coniferyl Alcohol Structure in Bleached and Sulfonated Mechanical Pulps. In C Heitner and 1C Scaiano, eds. Photochemistry of Lignocellulosic Materials. ACS Symposium Series, 531. Washington, DC American Chemical Society, 1993, pp. 26-44. 

J Gierer, O Lindeberg. Reactions of Lignin during Sulfate Pulping. Part XV. The Behaviour of Intermediary Coniferyl Alcohol Structures. Acta Chem Scand 332 577-587, 1978. 

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