Benzyl Ether Linkages Research Articles

Synthesis, Characterization, and Derivatization of Hyperbranched Polyfluorinated Polymers

A hyperbranched polyfluorinated benzyl ether polymer was prepared from the A2B monomer 3,5-bis[(pentafluorobenzyl)oxy]benzyl alcohol. The polymerization was based upon deprotonation of the benzylic alcohol (B), followed by nucleophilic substitution of the p-fluorines of the two pentafluorophenyl (A) groups to form tetrafluorophenyl benzyl ether linkages. Optimized reaction conditions for the polymerization involved the addition of sodium metal (<0.1 mm particle size, 30 wt % suspension in toluene) to a solution of monomer (0.3 M) in THF heated at reflux. The molecular weight and molecular-weight distribution of the resulting polymer were affected by the surface area of the sodium particles, the concentration of the monomer, and the polymerization temperature. An average of one pentafluorophenyl chain end per repeat unit plus one pentafluorophenyl end group was present within the hyperbranched polymer, which allowed for chemical modification by nucleophilic displacement reactions upon the p-fluorines, to a...

Photoinduced molecular transformations. Part 153. Long-range intramolecular hydroxylation of C(25) of the cholestane side chain

Alkoxyl radicals generated by photolysis of the hypoiodites of 5α-cholestan-7α-yl 4-(α-hydroxyphenylmethyl)phenylacetate and 5α-cholestan-7α-yl 3-[4-(α- hydroxyphenylmethyl)phenyl]-propanoate, respectively, abstracted hydrogen from C(25) of their cholestane side chain to give novel macrocyclic lactones. A reductive cleavage of the benzyl ether linkage of these lactones with sodium and liquid ammonia gave 5α-cholestane-7α,25-diol in good yields.

Cinnamic acid bridges between cell wall polymers in wheat and phalaris internodes

A method has been devised for the quantitative determination of cinnamic acids participating in ester—ether bridges between cell wall polymers based on the different reactivities of free carboxylic acids and their esters towards borohydride reductants and the different susceptibilities of cinnamic acid ester and benzyl ether linkages to alkaline treatments. Lignin—polysaccharide containing fractions extracted with dioxane—H 2O from cell walls of wheat ( Triticum aestivum) and phalaris ( Phalaris aquatica) internodes are hydrogenated using a Pd/C catalyst at room temperature to convert cinnamic acids to their corresponding dihydrocinnamic acids. The sample is subsequently reduced with LiBH 4 in ether—toluene to convert ester-linked dihydrocinnamates to their corresponding alcohols, hydrolysed with 4 M NaOH at 170°, and the dihydrocinnamic acid derivatives released from their etherified forms determined by GC. Using model compounds it was shown that these reactions proceeded quantitatively. The results indicate that all of the etherified ferulic acid in the dioxane—H 2O-soluble fractions of walls of wheat and phalaris internodes is also ester-linked. It has been calculated that there are nine to 10 ferulic acid ester—ether bridges for every 100 C 6—C 6 lignin monomers. p-Coumaric acid is not involved in ester-ether bridges.

Lignanes. 15. Première Synthèse Totale de la (−)-α-Conidendrine Naturelle

(−)-α-Conidendrin 1 was synthesized according to a general reactionscheme that could be applied to other retrolignans as well. Thus, treatment of the optically active β-benzyl-γ-butyrolactone (R)-(+)- 4 with NBS, followed with benzyl alcohol, selectively introduced a benzyloxy group in the benzylic position and afforded the mixture of epimers 7. α-Alkylation of the lithium enolate of the corresponding silyl ethers 10, with O-benzylvanillyl bromide 11, gave the trans disubstituted lactones 13 (2 epimers). Catalytic hydrogenolysis (Pd-C) of 13 selectively split the aryl benzyl ether linkage, and gave the compounds 14. Intramolecular Friedel-Crafts cyclization of the latter, using the benzyloxy group as the leaving group, was induced with BF3-Et2O and afforded (−)-α-conidendrin 1 in 36% overall yield from methyl α-vanillylhemis uccinate (R)-(+)-17.

Insoluble Lignin Models (3): Preparation of a Polymer-Bound Guaiacylpropanol Model

Abstract Guaiacylpropanol (4), has been attached at the gamma carbon through a benzyl ether linkage to a macroreticular polystyrene resin. The phenolic site of 4 was protected as an allyl ether when coupled to the resin. The amount of lignin model 4 which was attached to the polymer was determined by cleaving the benzyl ether linkage with iodotrimethlsilane (ITS) and quantifying the amount of released guaiacylpropanol. The ITS method was reproducible but not quantitative due to a high model loading (1.29 mmol/g). Both FTIR and 13C-NMR were used to characterize the insoluble model.

ChemInform Abstract: First Total Synthesis of (‐)‐α‐Conidendrin.

Abstract Regioselective introduction of a benzoxy group, in the benzylic position of the β-benzyl-γ-butyrolactone (R)-(+)-8, was achieved by tretment with NBS followed with benzyl alcohol. α-Alkylation of the lithium enolate of the resulting intermediate 11, with O -benzylvanillyl bromide 5, gave the trans disubstituted lactone 13. Catalytic hydrogenolysis (PdC) of 13 selectively split the aryl benzyl ether linkage, thus giving the compound 14. Intramolecular Friedel-Crafts cyclisation of the latter, using the benzoxy group as the leaving group, was induced with BF3. Et2O and afforded high yields of (−)-α-conidendrin 2.

Binding-site Analysis of the Ether Linkages between Lignin and Hemicelluloses in Lignin–Carbohydrate Complexes by DDQ-Oxidation

Lignin-carbohydrate complexes (LCC; nor-C-1-M, com-C-1-A) isolated from normal and compression woods of Pinus densiflora were hydrolyzed with two types of cellulase preparations, and the hydrolyzates formed were fractionated by adsorption chromatography on polyvinyl gel into water-soluble materials and LCC fragments. To elucidate the binding sites between the lignin and carbohydrate, the cellulase-degraded LCC fragments were subjected to acetylation, and then oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), which was confirmed to oxidatively cleave the benzyl ether linkages between the lignin and carbohydrate. The DDQ-oxidized fraction was then methylated by the method of Prehm, hydrolyzed, reduced and acetylated. A GC-MS analysis of the methylated sugar revealed that alditol acetates from 6-O-methyl mannose, 6-O-methyl galactose, 6-O-methyl glucose and a small amount of their 2-O- or 3-O-methyl isomers existed in both methylated fractions. 2-O-Methyl xylose and 3-O-methyl xylose were also identified in the fraction from the acidic LCC (com-C-1-A). These results led to the conclusion that acetylglucomannan and β-1,4-galactan were preferably bound to the lignin at C-6 position of the hexoses, and that arabinoglucuronoxylan did likewise at the C-2 and C-3 positions of xylose units.

The case for induced bond scission during coal pyrolysis

Bond scissions during coal pyrolysis are generally considered to result solely from the thermolysis of weak bonds in coal structures. Evidence is presented from published data showing that a significant amount of bond scission under pyrolysis cannot be due to simple thermolysis and must be induced by some other means. The evidence includes the following observations: 1, polymeric models consisting of no weak linkages are volatilized in the 450 to 550 °C range; 2, polymeric coal models designed specifically to degrade by thermolysis of weak bibenzylic linkages show nonetheless a significant fraction of the cleavage of strong C arC al linkage; 3, under pyrolysis conditions bibenzyl type structures immobilized on silica yield benzene and ethylbenzene in addition to the expected toluene; 4, pyrolysis of O-benzylated coals shows besides the expected cleavage of the benzyl ether linkage products from the scission of the strong phenyl-C bond. By analogy with coal liquefaction, the scission of strong bonds results from β-scission of radical intermediates, and from hydrogenolysis engendered by either free H-atoms or cyclohexadienyl radicals. These reactive cyclohexadienyl radicals themselves may be formed from the scavenging of radicals (produced by weak-bond thermolysis) by dihydroaromatic structures or from reverse radical-disproportionation between aromatic and hydroaromatic structures. Finally, the importance of induced bond scissions was illustrated by showing how they help rationalize the observed selective production of oils as opposed to gas in the hydropyrolysis of coals when the pyrolysis temperature is maintained below a certain threshold.

First total synthesis of (−)-α-conidendrin

Regioselective introduction of a benzoxy group, in the benzylic position of the β-benzyl-γ-butyrolactone (R)-(+)- 8, was achieved by tretment with NBS followed with benzyl alcohol. α-Alkylation of the lithium enolate of the resulting intermediate 11, with O -benzylvanillyl bromide 5, gave the trans disubstituted lactone 13. Catalytic hydrogenolysis (PdC) of 13 selectively split the aryl benzyl ether linkage, thus giving the compound 14. Intramolecular Friedel-Crafts cyclisation of the latter, using the benzoxy group as the leaving group, was induced with BF 3. Et 2O and afforded high yields of (−)-α-conidendrin 2.

Binding-site analysis of the ether linkages between lignin and hemicelluloses in lignin-carbohydrate complexes by DDQ-oxidation.

Lignin-carbohydrate complexes (LCC; nor-C-1-M, com-C-1-A) isolated from normal and compression woods of Pinus densiflora were hydrolyzed with two types of cellulase preparations, and the hydrolyzates formed were fractionated by adsorption chromatography on polyvinyl gel into water-soluble materials and LCC fragments. To elucidate the binding sites between the lignin and carbohydrate, the cellulase-degraded LCC fragments were subjected to acetylation, and then oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), which was confirmed to oxidatively cleave the benzyl ether linkages between the lignin and carbohydrate. The DDQ-oxidized fraction was then methylated by the method of Prehm, hydrolyzed, reduced and acetylated. A GC-MS analysis of the methylated sugar revealed that alditol acetates from 6-O-methyl mannose, 6-O-methyl galactose, 6-O-methyl glucose and a small amount of their 2-O- or 3-O-methyl isomers existed in both methylated fractions. 2-O-Methyl xylose and 3-O-methyl xylose were also ...

Preparation of polymer-supported amino acid

Insoluble polymer-supported amino acids have been synthesized by simple one-pot synthesis. Amino acids were solubilized in organic solvent by trimethylsilylation. Solubilized amino acids (L-Tyr, L-Ser, D-HPG, L-Cys) having functional groups such as OH or SH were easily attached to crosslinked polystyrene beads through benzyl ether or thioether linkage. Other amino acids without extra functional groups could be attached to the polymer through benzyl amine linkage.

Stability of α-Ether type Model Compounds During Chemical Pulping Processes

Abstract In order to examine the stability of lignin-carbohydrate complexes (LCC) during alkaline chemical pulping, benzyl ether type LCC model compounds containing different non-phenolic units were synthesized and cooked under chemical pulping conditions. At least 80% of the starting substance was recovered unchanged, from soda, kraft and acid sulfite reactions indicating the benzyl ether linkage in this compound is stable during pulping. Furthermore, by blocking the reactive benzylic hydroxyl group, the cleavage of adjacent β-ether linkages in lignin moiety is retarded. Thus it is concluded that non-phenolic α-ether linkages between lignin and carbohydrates are stable under alkaline pulping conditions and may be the cause for the residual lignin to resist a complete delignification.

Molecular Orbital Investigations on Lignin Model Compounds. XX. Conformational Analysis of Benzyl Ether and Benzyl Ester Linkages in Lignin-Carbohydrate Complexes

Molecular Orbital Investigations on Lignin Model Compounds. XX. Conformational Analysis of Benzyl Ether and Benzyl Ester Linkages in Lignin-Carbohydrate Complexes

Synthesis of some 4-pyranones and 4-pyridones structurally related to isoproterenol

The syntheses of 2-isopropylamino-1-(5-hydroxy-4H-pyran-4-on-2-yl)ethanol and the corresponding 4-pyridone and 1-methyl-4-pyridone analogues are described. The selective reduction of an aliphatic nitro group in the presence of a benzyl ether linkage was a key step in the reaction sequence.

Hydrogenolysis of lignocarbohydrate complex, isolated from spruce wood by the mechanical grinding method

1. On the basis of an analogous reactivity during the hydrogenolysis of the lignin component of the lignocarbohydrate complex, its low-molecular fraction and Bjorkman lignin it was concluded that they all have a structural similarity. 2. The destruction of the low-molecular fraction of the lignocarbohydrate complex occurs due to the cleavage of the linkages in the lignin portion of the complex. The lignocarbohydrate linkage is retained in the fragments that are formed as a result of this cleavage. 3. One of the most probable types of linkage in the investigated complex is the phenylglycoside linkage. The possibility of the existence of benzyl ether and benzylglycoside linkages is restricted to linkages that are difficultly accessible and quite unreactive under the hydrogenolysis conditions.

Behavior of dibenzyl ether linkage in model lignin compounds during nitration

1. When 1,1′-di(3,4-dimethoxyphenyl) diethyl ether (I) is nitrated in ether the NO2 group enters the 6 position of the aromatic rings. 2. Together with aromatic substitution, cleavage of the benzyl ether linkage occurs when (I) is nitrated in CCl4, with the formation of benzyl alcohol and nitro ester groups, electrophilic replacement of the side chain by the NO2 groups, and also the formation of the corresponding biphenyl nitro derivative.

Ionic polymerization of p‐vinylbenzyl methyl ether

AbstractIonic polymerizations of vinylbenzyl methyl ether initiated by either carbanions or Lewis acids has been found to lead to crosslinked polymers. By comparative studies of strong carbanionic bases and Lewis acids with benzyl ethers, it has been possible to define details of mechanisms which in conjunction with cationic or anionic propagation lead to crosslinks. The α‐hydrogens of benzyl ethers have been found to be sufficiently acidic to terminate anionic polymerization of styrene and displacement of alkoxide anion from the benzyl ether linkage by nucelophilic polymer anions is proposed as a mechanism leading to branching and eventual crosslinking in anionic polymerization of vinylbenzyl methyl ether. Cationic polymerization of vinylbenzyl methyl ether is quite complex. In addition to propagation, chain transfer, and spontaneous termination of cation chain carriers, there is evidence for complex formation between Lewis acid initiator and the benzyl ether substituent. A slow decomposition of ether–Lewis acid complexes produces benzylcarbonium ions which alkylate aromatic rings of polymer and thereby crosslink the polymer. Benzyl ether has been found to be an effective chain terminator for cationic styrene polymerization.