HTML by Rhodium
It has recently been reported1 that a yield of 25% of vanillin based on Klason lignin can be obtained by treatment of spruce wood with alkali in the presence of nitrobenzene. Employing the same technique1, we have confirmed this result by digesting spruce woodmeal (35.0g, 28.6% Klason lignin), sodium hydroxide solution (400 mL, 2 N), and nitrobenzene (24 mL) in a stainless steel bomb with good agitation at 160°C for three hours. In duplicate experiments, 4.73g and 5.12g of crude vanillin m-nitrobenzoylhydrazones (mp 204-206°C) were finally isolated; after recrystallization, mp 210-211°C; mixed mp 210-211°C. Yields were 22.8% and 24.7%, respectively, calculated on the Klason lignin.
Application of this method to maple wood (38.5g, 22.0% Klason lignin) left 13.7g of insoluble woody residue containing 0.2% Klason lignin. Neutralization of the alkaline reaction liquors and continuous extraction with benzene removed 4.23g, of which 3.63g was extractable with sodium bisulfite solution. Acidification of the neutralized aqueous liquor to pH 3, and benzene extraction, yielded additional benzenesoluble substances (1.21g). The benzene-insoluble material precipitated by acidification of the alkaline aqueous reaction liquor weighed 4.1g.
Vanillin and syringaldehyde were isolated from the bisulfite solution by acidification and benzene extraction. Their separation was effected by solution of the crude extract in 250 mL of ethanol and fractional precipitation by gradual addition of increasing amounts of ammonia. In this way, by precipitation of the much more insoluble syringaldehyde addition product, crude syringaldehyde (2.7g) was isolated; mp 105-112°C; after recrystallization, mp 110.5-112°C; mixed mp gave no depression. The ammoniacal ethanol solution remaining after removal of the syringaldehyde component was evaporated to remove the ammonia and ethanol and the residue dissolved in about 125 mL of dry ether. Addition of ammonia precipitated the crude addition product from which 0.55g of crude vanillin-containing material was isolated. A preliminary purification by sublimation2 at 61°C/1mmHg yielded 0.29g crude vanillin (mp 75-80°C), recrystallized mp 80-82°C, mixed mp no depression. Vanillin was also isolated by direct fractional sublimation2 of the bisulfite soluble material (3.56 g) to yield 0.60g of crude vanillin (mp 77-81°C), Precipitation of the total aldehydes in 3.63 g. of the bisulfite soluble extract yielded 7.01 g. of mixed m-nitrobenzoylhydrazones.
Based on the Klason lignin content of maple wood, the yield of syringaldehyde isolated by treatment with ammoniacal ethanol amounted to 31.8%; that of vanillin 3.4%. By sublimation 7.1% vanillin was obtained. By weight, the total yield of bisulfite soluble material was 42.9%, while the yield of total carboxyl-containing constituents of the bisulfite soluble fraction was 43.0% (calculated from the mixed m-nitrobenzoylhydrazones on the assumption of a syringaldehyde-vanillin ratio of 3:1). A duplicate experiment gave very similar yields.