The Ethanolysis of 3-Hydroxy-1-(4-Hydroxy-3-Methoxyphenyl)-2-Propanone in Relation to Lignin Chemistry

Abstract

The Icetol, 3-11ydrox~-l-(-l--hydroxy-3-n~eihoxypI~e11yl)-2-propanone, was s~t bjected t o ethanolysis and found to yield the four propylphenols which can be isolated from t h e etharlolysis products of isolated conifer lignin and of conifer lignin i n silz~. The sipnilicance of this finding is briefly disc~~ssed.I11 the period 1939-1943, a careful investigation of the water sol~tble phenolic products from the ethanolysis of extractive-free spruce-wood by Hibbert and co-workers (5,7,18,26) resulted in the isolatio~l and identification of four propylpl~enols, 2-ethoxy-1-(4-hydroxy-3-n1etl1oxyphen~~l)-l-propanone (I), 1-(4-hyclroxy-3-methoxyphenyl)-1,2-propa~~edione (I I), 1-ethoxy-1-(4-hydroxy-3-methoxyphe11~~l)-2-propanone (I1 I), and 1 -(4-h ydroxy-3-methoxyp11enyl)-2-propanone (IV). R-CH (OC?Hs)-CO-CHI R-CH 2-CO-CH,Frorn maple-wood, in addition to these, the syringyl (R = 4-hydroxy-3, 5-din~ethoxyphenyl) analogues were isolated. T h e total yielcl of pure identified products based upon the original I<lason lignin of the wood was approximately 5 per cent for spruce-wood and approximately 10 per cent for maple-wood. In spite of the low yields, these findings were of considerable significance in that they proviclecl some direct eviclence for the theory that lignin is derived from propylpl~enol monomers. In view of the absence of primary alcoholic or terminal ethel-groups in these products and the eviclence for the presence of such groups in lignin provided by analytical results (4) and by the isolation of 3-cyclohexyl-lpropanols from the products of high pressure llydrogenation (3, 12, 15), Hibbert (16) suggested that the propylphenols I-IV were derived from a more reactive P-hydroxyconiferyl alcohol (VI) type of structur-a1 elenlent by means of a series of in tercorlversio~ls :

Advanced Model Compounds for Understanding Acid-Catalyzed Lignin Depolymerization: Identification of Renewable Aromatics and a Lignin-Derived Solvent

“…When no ethylene glycol was added G was still obtained in good yield (69%), but the C2-aldehyde was not observed due to its conversion to a complex mixture of products, as seen for AB1 under these conditions (Supporting Information section S9.0). During these reactions, ketal P4 , the ethylene glycol ketal of the Hibbert ketone, , was also identified (UPLC-MS, Supporting Information section S10.2). Its formation provided evidence for the functioning of the C3 cleavage pathway in these reactions.…”

Soluble Native Lignin, Milled Wood Lignin, Synthetic Lignin, and the Structure of Lignin

“…When heated with dilute sodium hydroxide it yields vanillin and acetaldehyde (5); further heating with strong alkali yields more acetaldehyde. On alcoholysis with ethanol containing i% hydrogen chloride, soluble native lignin yields about 10% of "Hibbert's ketones" -a reaction considered typical for lignin and frequently used for a test to determine whether or not a radioactive lignin precursor has been incorporated into the lignin molecule (8,9). The oxidation of soluble native spruce lignin with nitrobenzene in an alkaline solution gives a high yield of vanillin (7).…”