Formation rate of benzyl cations in various aqueous solutions containing different concentrations of acid but with a specific proton activity in lignin acidolysis

Hiroaki Ito; Tomoya Yokoyama

doi:10.1515/hf-2022-0053

Abstract

This study aimed to clarify the effect of different solvents, aqueous 1,4-dioxane, ethanol, or ethylene glycol at various mol%, on the formation rate of the benzyl cation, which forms via two steps, the protonation of the benzyl hydroxy or alkoxy group as a pre-equilibrium step and subsequent liberation of the water or corresponding alcohol molecule, respectively, in a model system of the lignin acidolysis, focusing on distinguishing the effects on both steps. For this aim, the acidolysis reactions were conducted in various aqueous solutions and organic solvents that showed a specific proton activity to establish the pre-equilibrium at a specific position. The formation rate of the benzyl cation showed minima in the intermediate mol% range. However, these rate differences were much smaller than those observed in the previous report where the aqueous solutions were prepared to contain a specific acid concentration and show different proton activities and thus the net effect of the solvent type on both steps was indistinguishable. These results clearly showed that the solvent type affects the first step (the proton activity) much more than the last step (the solvent-dissociating power). This paper also describes the preparation of the aqueous solutions to demonstrate a specific proton activity.

Keywords: acidity; delignification; Hammett acidity function; trifluoromethanesulfonic acid

Corresponding author: Tomoya Yokoyama, Laboratory of Wood Chemistry, Department of Biomaterial Sciences, Graduate School of Agricultural and Life Sciences, The University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-8657, Japan, E-mail: yokoyama@woodchem.fp.a.u-tokyo.ac.jp

Author contributions: All the authors have accepted responsibility for the entire content of this submitted manuscript and approved submission.
Research funding: None declared.
Conflict of interest statement: The authors declare no conflicts of interest regarding this article.

References

Adler, E. (1977). Lignin chemistry: past, present and future. Wood Sci. Technol. 11: 169–218.10.1007/BF00365615Search in Google Scholar

Adler, E. and Lundquist, K. (1963). Spectrochemical estimation of phenylcoumaran elements in lignin. Acta Chem. Scand. 17: 13–26.10.3891/acta.chem.scand.17-0013Search in Google Scholar

Adler, E., Pepper, J.M., and Eriksoo, E. (1957). Action of mineral acid on lignin and model substances of guaiacylglycerol-β-aryl ether type. Ind. Eng. Chem. 49: 1391–1392.10.1021/ie50573a037Search in Google Scholar

Braude, E.A. (1948). Acidity functions part I: dissociation of hydrogen chloride in, and proton affinities of, some oxygen-containing solvents. J. Chem. Soc. 1948: 1971–1975.10.1039/jr9480001971Search in Google Scholar

Braude, E.A. and Stern, E.S. (1948). Acidity functions part II: the nature of hydrogen ion in some aqueous and non-aqueous solvents. The exceptional solvating properties of water. J. Chem. Soc. 1948: 1976–1981.10.1039/jr9480001976Search in Google Scholar

Brickman, L., Hawkins, W.L., and Hibbert, H. (1940). Studies on lignin and related compounds XLVIII: identification of vanillin and vanilloyl methyl ketone as ethanolysis products from spruce wood. J. Am. Chem. Soc. 62: 2149–2154.10.1021/ja01865a063Search in Google Scholar

Cramer, A.B., Hunter, M.J., and Hibbert, H. (1939). Studies on lignin and related compounds XXXV: the ethanolysis of spruce wood. J. Am. Chem. Soc. 61: 509–516.10.1021/ja01871a081Search in Google Scholar

De Ligny, C.L., Loriaux, H., and Ruiter, A. (1961). The applicability of Hammett’s acidity functions H0 to solutions in methanol-water mixtures. Rec. Trav. Chim. Pay-B 80: 725–739.10.1002/recl.19610800706Search in Google Scholar

Dence, C.W. (1992). 2.2. The determination of lignin. In: Lin, S.Y., and Dence, C.W. (Eds.). Methods in lignin chemistry. Springer-Verlag, Berlin/Heidelberg, Germany, pp. 33–61.10.1007/978-3-642-74065-7_3Search in Google Scholar

De Santi, A., Galkin, M.V., Lahive, C.W., Deuss, P.J., and Barta, K. (2020). Lignin-first fractionation of softwood lignocellulose using a mild dimethyl carbonate and ethylene glycol organosolv process. ChemSusChem 13: 4468–4477.10.1002/cssc.201903526Search in Google Scholar PubMed

Fisher, H.E. and Hibbert, H. (1947). Studies on lignin and related compounds LXXXIII: synthesis of 3-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-2-propanone. J. Am. Chem. Soc. 69: 1208–1210.10.1021/ja01197a065Search in Google Scholar

Gellerstedt, G., Pranda, J., and Lindfors, E.-L. (1994). Structural and molecular properties of residual birch kraft lignins. J. Wood Chem. Technol. 14: 467–482.10.1080/02773819408003108Search in Google Scholar

Hammett, L.P. and Deyrup, A.J. (1932). A series of simple basic indicators I: the acidity functions of mixtures of sulfuric and perchloric acids with water. J. Am. Chem. Soc. 54: 2721–2739.10.1021/ja01346a015Search in Google Scholar

Hirata, M. and Yokoyama, T. (2022). Effect of solvent type on the formation rate of benzyl cation intermediate in acidolysis of lignin. Holzforschung 76: 223–234.10.1515/hf-2021-0193Search in Google Scholar

Hoo, L.H., Sarkanen, K.V., and Anderson, C.D. (1983). Formation of C6C2-enol ethers in the acid-catalyzed hydrolysis of erythro-veratrylglycerol-β-(2-methoxyphenyl) ether. J. Wood Chem. Technol. 3: 223–243.10.1080/02773818308085161Search in Google Scholar

Hunter, M.J., Cramer, A.B., and Hibbert, H. (1939). Studies on lignin and related compounds XXXVI: ethanolysis of maple wood. J. Am. Chem. Soc. 61: 516–520.10.1021/ja01871a082Search in Google Scholar

Imai, T., Yokoyama, T., and Matsumoto, Y. (2011). Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin IV: dependence of acidolysis reaction on the type of acid. J. Wood Sci. 57: 219–225.10.1007/s10086-010-1166-6Search in Google Scholar

Imai, T., Yokoyama, T., and Matsumoto, Y. (2012). Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin. Part 5: on the characteristics of acidolysis using hydrobromic acid. J. Wood Chem. Technol. 32: 165–174.10.1080/02773813.2011.624668Search in Google Scholar

Ito, H., Imai, T., Lundquist, K., Yokoyama, T., and Matsumoto, Y. (2011). Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin. Part 3: search for the rate-determining step of a non-phenolic C6-C3 type model compound. J. Wood Chem. Technol. 31: 172–182.10.1080/02773813.2010.515050Search in Google Scholar

Ito, T., Terashima, N., and Yasuda, S. (1981). Chemical structures of sulfuric acid lignin III: reaction of arylglycerol-β-aryl ether with five percent sulfuric acid. Mokuzai Gakkaishi 27: 484–490.Search in Google Scholar

Karlsson, O., Lundquist, K., Meuller, S., and Westlid, K. (1988). On the acidolysis cleavage of arylglycerol β-aryl ethers. Acta Chem. Scand. B42: 48–51.10.3891/acta.chem.scand.42b-0048Search in Google Scholar

Lowry, T.H. and Richardson, K.S. (1987). Influence of solvent, nucleophile, leaving group, and substrate structure. In: Lowry, T.H., and Richardson, K.S. (Eds.). Mechanisms and theory in organic chemistry, 3rd ed. HarperCollins Publishers, Inc., New York, pp. 361–367.Search in Google Scholar

Lundquist, K. (1973). Acid degradation of lignin part VIII: low molecular weight phenols from acidolysis of birch lignin. Acta Chem. Scand. 27: 2597–2606.10.3891/acta.chem.scand.27-2597Search in Google Scholar

Lundquist, K. and Lundgren, R. (1972). Acid degradation of lignin part VII: the cleavage of ether bonds. Acta Chem. Scand. 26: 2005–2023.10.3891/acta.chem.scand.26-2005Search in Google Scholar

Phan, H.D., Yokoyama, T., and Matsumoto, Y. (2012). Direct participation of counter anion in acid hydrolysis of glycoside. Org. Biomol. Chem. 10: 7382–7391.10.1039/c2ob25451dSearch in Google Scholar PubMed

Shioya, T., Akiyama, T., Yokoyama, T., and Matsumoto, Y. (2017). Formation rate of benzyl cation intermediate from p-hydroxyphenyl, guaiacyl, or syringyl nucleus in acidolysis of lignin. J. Wood Chem. Technol. 37: 75–86.10.1080/02773813.2016.1235587Search in Google Scholar

Tickle, P., Briggs, A.G., and Wilson, J.M. (1970). The protonation of weak bases. A study of the protonation of some nitroaniline indicators and the determination of the H0 values of aqueous sulphuric acid. J. Chem. Soc. B 1970: 65–70.10.1039/j29700000065Search in Google Scholar

Yamauchi, F., Ito, T., Kawamoto, O., Komatsu, T., Akiyama, T., Yokoyama, T., and Matsumoto, Y. (2020). Effects of lignin structure and solvent on the formation rate of quinone methide under alkaline conditions. Holzforschung 74: 559–566.10.1515/hf-2019-0269Search in Google Scholar

Yasuda, S. and Terashima, N. (1982). Chemical structures of sulfuric acid lignin V: reaction of three arylglycerol-β-aryl ethers [α-, β-, γ-13C] with seventy-two percent sulfuric acid. Mokuzai Gakkaishi 28: 383–387.Search in Google Scholar

Yasuda, S., Adachi, K., Terashima, N., and Ota, K. (1985). Chemical structures of sulfuric acid lignin VIII: reactions of 1,2-diaryl-1,3-propanediol and pinoresinol with sulfuric acid. Mokuzai Gakkaishi 31: 125–131.Search in Google Scholar

Yasuda, S., Terashima, N., and Ito, T. (1981a). Chemical structures of sulfuric acid lignin II: chemical structures of condensation products from arylglycerol-β-aryl ether type structures. Mokuzai Gakkaishi 27: 216–222.Search in Google Scholar

Yasuda, S., Terashima, N., and Ito, T. (1981b). Chemical structures of sulfuric acid lignin IV: reaction of arylglycerol-β-aryl ether with seventy-two percent sulfuric acid. Mokuzai Gakkaishi 27: 879–884.Search in Google Scholar

Yasuda, S., Terashima, N., and Kaneko, H. (1982). Chemical structures of hydrochloric acid lignin II: reaction of arylglycerol-β-aryl ether with hydrochloric acid. Mokuzai Gakkaishi 28: 570–576.Search in Google Scholar

Ye, Q. and Yokoyama, T. (2020). Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin VII: acidolyses of non-phenolic C6-C2-type model compounds using HBr, HCl and H2SO4, and a proposal on the characteristic action of Br¯ and Cl¯. J. Wood Sci. 66: 80.10.1186/s10086-020-01928-6Search in Google Scholar

Ye, Q. and Yokoyama, T. (2021). Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin Part 8: comparison between phenolic and non-phenolic C6-C2-type model compounds. J. Wood Chem. Technol. 41: 294–306.10.1080/02773813.2021.1986072Search in Google Scholar

Yokoyama, T. (2015). Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin. Part 6: a review. J. Wood Chem. Technol. 35: 27–42.10.1080/02773813.2014.881375Search in Google Scholar

Yokoyama, T. and Matsumoto, Y. (2008). Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin. Part 1: kinetics of the formation of enol ether from non-phenolic C6-C2 type model compounds. Holzforschung 62: 164–168.10.1515/HF.2008.037Search in Google Scholar

Yokoyama, T. and Matsumoto, Y. (2010). Revisiting the mechanism of β-O-4 bond cleavage during acidolysis of lignin. Part 2: detailed reaction mechanism of a non-phenolic C6-C2 type model compound. J. Wood Chem. Technol. 30: 269–282.10.1080/02773811003675288Search in Google Scholar

Supplementary Material

The online version of this article offers supplementary material (https://doi.org/10.1515/hf-2022-0053).

Received: 2022-03-23

Accepted: 2022-05-08

Published Online: 2022-05-24

Published in Print: 2022-08-26

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Supplementary Material

Formation rate of benzyl cations in various aqueous solutions containing different concentrations of acid but with a specific proton activity in lignin acidolysis

Abstract

References

Supplementary Material

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