Coniferyl alcohol and coniferaldehyde

Dehydrodiconiferaldehyde (XVIII) 25) is an unsaturated aldehyde corresponding to XVII and is formed partly by condensation of free radicals derived from coniferyl alcohol and coniferaldehyde. 

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... 

The three glucosides (IV-VI) are present in the cambial sap of spruce, V being by far the most abundant (49). Furthermore, spruce cambial sap contains very small amounts of coniferyl alcohol (I), coniferaldehyde (VII), the dilignols (XVII), (XIX), (XXII), and the trilignol (XXXVI) (19). Other lignols are present but in amounts too small for convenient identification. Extensive work has been done to examine the pathway of lignin formation in vivo and in vitro. 

It has also been proposed that under the acidic conditions found ia whiskeys, ethanol reacts with lignin (qv) to reduce an alcohol-soluble form of lignin (ethanol lignin). This can be converted into coniferyl alcohol, which can be oxidized to coniferaldehyde. The partial oxidation of ethanol lignin can produce siaapic and coniferyl alcohols that can be converted to syfingaldehyde and vanillin, respectively (8). 

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... 

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

---