Derivatization of the kerogen backbone changes its chemical reactivity profile. In this study, kukersite kerogen was methylated with dimethyl carbonate. The substance was analyzed before and after processing by Fourier transform infrared spectroscopy, 13C cross-polarization/magic angle spinning nuclear magnetic resonance spectroscopy, and elemental analysis. It was observed that kukersite kerogen can be readily methylated with dimethyl carbonate. Based on mass balance and the Lille-Blokker model, an average of 19 methyl groups were added to the kerogen unit. It was concluded that about half of the hydroxyl groups in Estonian kukersite kerogen are “free” and accessible to methylation.
1. Lille, Ü. Current knowledge on the origin and structure of Estonian kukersite kerogen. Oil Shale, 2003, 20(3), 253–263.
https://doi.org/10.3176/oil.2003.3.03
2. Veiderma, M. Estonian oil shale – resources and usage. Oil Shale, 2003, 20(3S), 295–303.
https://doi.org/10.3176/oil.2003.3S.02
3. Oja, V., Suuberg, E. M. Oil shale processing, chemistry and technology. In Encyclopedia of Sustainability Science and Technology(Meyers, R. A., ed.). Springer, New York, NY, 2017, 1–38.
https://doi.org/10.1007/978-1-4939-2493-6_102-3
4. Hutton, A. C. Organic petrography of oil shales. In Composition, Geochemistry and Conversion of Oil Shales (Sanpe, C., ed.). Vol. 455. Springer Netherlands, NATO ASI Series, Dordrecht, 1995, 17–33.
https://doi.org/10.1007/978-94-011-0317-6_2
5. Lille, Ü. On the origin of 5-alkyl-1,3-benzenediols in the retort oil of Estonian kukersite. Oil Shale, 1999, 16(3), 231–237.
https://doi.org/10.3176/oil.1999.3.04
6. Blokker, P., van Bergen, P., Pancost, R., Collinson, M. E., de Leeuw, J. W., Sinninghe Damste, J. S. The chemical structure of Gloeocapsomorpha prisca microfossils: implications for their origin. Geochimica et Cosmochimica Acta, 2001, 65(6), 885–900.
https://doi.org/10.1016/S0016-7037(00)00582-2
7. Lille, Ü., Heinmaa, I., Pehk, T. Molecular model of Estonian kukersite kerogen evaluated by 13C MAS NMR spectra. Fuel, 2003, 82(7), 799–804.
https://doi.org/10.1016/S0016-2361(02)00358-7
8. Chu, W., Cao, X., Schmidt-Rohr, K., Birdwell, J. E., Mao, J. Investigation into the effect of heteroatom content on kerogen structure using advanced 13C solid-state nuclear magnetic resonance spectroscopy. Energy Fuels, 2019, 33(2), 645–653.
https://doi.org/10.1021/acs.energyfuels.8b01909
9. Mets, B., Kaldas, K., Uustalu, J. M., Lopp, M. The Lille-Blokker model – an excellent tool to describe the structure of kukersite. Oil Shale, 2023, 40(3), 234–243.
https://doi.org/10.3176/oil.2023.3.04
10. Lopp, M., Kaldas, K. Possibilities of the direct chemical transformation of kukersite kerogen: a critical review. ACS Omega, 2025, 10(36), 40740–40749.
https://doi.org/10.1021/acsomega.5c04675
11. Eraghi Kazzaz, A., Hosseinpour Feizi, Z., Fatehi, P. Grafting strategies for hydroxy groups of lignin for producing materials. Green Chemistry, 2019, 21, 5714–5752.
https://doi.org/10.1039/c9gc02598g
12. Laurichesse, S., Avérous, L. Chemical modification of lignins: towards biobased polymers. Progress in Polymer Science, 2014, 39(7), 1266–1290.
https://doi.org/10.1016/j.progpolymsci.2013.11.004
13. Suota, M. J., Kochepka, D. M., Ganter Moura, M. G., Pirich, C. L., Matos, M., Magalhães, W. L. E. et al. Lignin functionalization strategies and the potential applications of its derivatives – a review. BioResources, 2021, 16(3), 6471–6511.
https://doi.org/10.15376/biores.16.3.Suota
14. Elnaggar, E. M., Abusaif, M. S., Abdel-Baky, Y. M., Ragab, A., Omer, A. M., Ibrahim, I. et al. Insight into divergent chemical modifications of chitosan bio-polymer: review. International Journal of Biological Macromolecules, 2024, 277, 134347.
https://doi.org/10.1016/j.ijbiomac.2024.134347
15. Jahani, A., Jazayeri, M. H. Tailoring cellulose: from extraction and chemical modification to advanced industrial applications. International Journal of Biological Macromolecules, 2025, 309, 142950.
https://doi.org/10.1016/j.ijbiomac.2025.142950
16. Haq, F., Yu, H., Wang, L., Teng, L., Haroon, M., Khan, R. U. et al. Advances in chemical modifications of starches and their applications. Carbohydrate Research, 2019, 476, 12–35.
https://doi.org/10.1016/j.carres.2019.02.007
17. Wang, Z., Deuss, P. J. The isolation of lignin with native-like structure. Biotechnology Advances, 2023, 68, 108230.
https://doi.org/10.1016/j.biotechadv.2023.108230
18. Guo, L., Gao, Q., Ding, J., Xiong, Z., Chen, S., Li, X. et al. Lignin: dissolution, modification, and derived materials. International Journal Biological Macromolecules, 2025, 309, 142748.
https://doi.org/10.1016/j.ijbiomac.2025.142748
19. Beaudoin, D., Palus, E., Konduri, M. K. R., Gagné, A. Methylation of softwood and hardwood kraft lignins with chloromethane. RSC Advances, 2024, 14(4), 2293–2299.
https://doi.org/10.1039/D3RA08404C
20. Sadeghifar, H., Cui, C., Argyropoulos, D. S. Toward thermoplastic lignin polymers. Part 1. Selective masking of phenolic hydroxyl groups in kraft lignins via methylation and oxypropylation chemistries. Industrial & Engineering Chemistry Research, 2012, 51(51), 16713–16720.
https://doi.org/10.1021/ie301848j
21. Duval, A., Avérous, L. Mild and controlled lignin methylation with trimethyl phosphate: towards a precise control of lignin functionality. Green Chemistry, 2020, 22(5), 1671–1680.
https://doi.org/10.1039/C9GC03890F
22. Sen, S., Patil, S., Argyropoulos, D. S. Methylation of softwood kraft lignin with dimethyl carbonate. Green Chemistry, 2015, 17(2), 1077–1087.
https://doi.org/10.1039/C4GC01759E
23. Xiong, S.-J., Pang, B., Zhou, S.-J., Li, M.-K., Yang, S., Wang, Y.-Y. et al. Economically competitive biodegradable PBAT/lignin composites: effect of lignin methylation and compatibilizer. ACS Sustainable Chemistry & Engineering, 2020, 8(13), 5338–5346.
https://doi.org/10.1021/acssuschemeng.0c00789
24. Aarna, A. J., Lippmaa, E. T. О структуре керогена прибалтийского горючего сланца (On the structure of the Baltic oil shale kerogen). Transactions of the Tallinn Polytechnic Institute, Series A, 1955, 63, 3–50.
25. Tundo, P., Selva, M. The chemistry of dimethyl carbonate. Accounts of Chemical Research, 2002, 35(9), 706–716.
https://doi.org/10.1021/ar010076f
26. Kaldas, K., Preegel, G., Muldma, K., Lopp, M. Wet air oxidation of oil shales: kerogen dissolution and dicarboxylic acid formation. ACS Omega, 2020, 5(35), 22021–22030.
https://doi.org/10.1021/acsomega.0c01466
27. Derenne, S., Largeau, C., Casadevall, E., Sinninghe Damsté, J. S., Tegelaar, E. W., de Leeuw, J. W. Characterization of Estonian kukersite by spectroscopy and pyrolysis: evidence for abundant alkyl phenolic moieties in an Ordovician, marine, type II/I kerogen. Organic Geochemistry, 1990, 16(4–6), 873–888.
https://doi.org/10.1016/0146-6380(90)90124-I
28. Derenne, S., Largeau, C., Landais, P., Rochdi, A. Spectroscopic features of Gloeocapsomorpha prisca colonies and of interstitial matrix in kukersite as revealed by transmission micro-FT-i.r.: location of phenolic moieties. Fuel, 1994, 73(4), 626–628.
https://doi.org/10.1016/0016-2361(94)90049-3
29. Smith, B. C. The C-O bond III: ethers by a knockout. Spectroscopy, 2017, 32(5).
https://www.spectroscopyonline.com/view/c-o-bond-iii-ethers-knockout (accessed 2025-10-24).
30. Kogerman, P., Luts, K., Hüsse, I. The Chemistry of Estonian Oil Shale. Goshimtexizdat, Moscow, Leningrad, 1934.
31. Tiikma, L., Zaidentsal, A., Tensorer, M. Formation of thermobitumen from oil shale by low-temperature pyrolysis in an autoclave. Oil Shale, 2007, 24(4), 535–546.
https://doi.org/10.3176/oil.2007.4.05
32. Shi, J., Ma, Y., Li, S., Wu, J., Zhu, Y., Teng, J. Characteristics of Estonian oil shale kerogen and its pyrolysates with thermal bitumen as a pyrolytic intermediate. Energy & Fuels, 2017, 31(5), 4808–4816.
https://doi.org/10.1021/acs.energyfuels.7b00054
33. Lille, Ü., Heinmaa, I., Müürisepp, A.-M., Pehk, T. Investigation of kukersite structure using NMR and oxidative cleavage: on the nature of phenolic precursors in the kerogen of Estonian kukersite. Oil Shale, 2002, 19(2), 101–116.
https://doi.org/10.3176/oil.2002.2.02
34. Smith, B. C. The C=O bond, part VI: esters and the rule of three. Spectroscopy, 2018, 33(7).
https://www.spectroscopyonline.com/view/co-bond-part-vi-esters-and-rule-three (accessed 2025-10-24).
35. Smith, B. C. The C=O bond, part VII: aromatic esters, organic carbonates, and more of the rule of three. Spectroscopy, 2018, 33(9).
https://www.spectroscopyonline.com/view/co-bond-part-vii-aromatic-esters-organic-carbonates-and-more-rule-three (accessed 2025-10-24).
36. Kogermann, P. N. On the Chemistry of the Estonian Oil Shale Kukersite. Tartu, 1931.