{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,3,8]],"date-time":"2026-03-08T23:38:46Z","timestamp":1773013126406,"version":"3.50.1"},"reference-count":52,"publisher":"MDPI AG","issue":"23","license":[{"start":{"date-parts":[[2023,12,1]],"date-time":"2023-12-01T00:00:00Z","timestamp":1701388800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"name":"EaSI-CAT at the University of St Andrews"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Molecules"],"abstract":"<jats:p>Environmentally acceptable and renewably sourced flame retardants are in demand. Recent studies have shown that the incorporation of the biopolymer lignin into a polymer can improve its ability to form a char layer upon heating to a high temperature. Char layer formation is a central component of flame-retardant activity. The covalent modification of lignin is an established technique that is being applied to the development of potential flame retardants. In this study, four novel modified lignins were prepared, and their char-forming abilities were assessed using thermogravimetric analysis. The lignin was obtained from date palm wood using a butanosolv pretreatment. The removal of the majority of the ester groups from this heavily acylated lignin was achieved via alkaline hydrolysis. The subsequent modification of the lignin involved the incorporation of an azide functional group and copper-catalysed azide\u2013alkyne cycloaddition reactions. These reactions enabled novel organophosphorus heterocycles to be linked to the lignin. Our preliminary results suggest that the modified lignins had improved char-forming activity compared to the controls. 31P and HSQC NMR and small-molecule X-ray crystallography were used to analyse the prepared compounds and lignins.<\/jats:p>","DOI":"10.3390\/molecules28237885","type":"journal-article","created":{"date-parts":[[2023,12,1]],"date-time":"2023-12-01T04:12:56Z","timestamp":1701403976000},"page":"7885","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":13,"title":["The Covalent Linking of Organophosphorus Heterocycles to Date Palm Wood-Derived Lignin: Hunting for New Materials with Flame-Retardant Potential"],"prefix":"10.3390","volume":"28","author":[{"given":"Daniel J.","family":"Davidson","sequence":"first","affiliation":[{"name":"School of Chemistry, University of St Andrews and EaStCHEM, North Haugh, St Andrews KY16 9ST, UK"},{"name":"Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews KY16 9ST, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-8578-7054","authenticated-orcid":false,"given":"Aidan P.","family":"McKay","sequence":"additional","affiliation":[{"name":"School of Chemistry, University of St Andrews and EaStCHEM, North Haugh, St Andrews KY16 9ST, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5366-9168","authenticated-orcid":false,"given":"David B.","family":"Cordes","sequence":"additional","affiliation":[{"name":"School of Chemistry, University of St Andrews and EaStCHEM, North Haugh, St Andrews KY16 9ST, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-1498-9652","authenticated-orcid":false,"given":"J. Derek","family":"Woollins","sequence":"additional","affiliation":[{"name":"School of Chemistry, University of St Andrews and EaStCHEM, North Haugh, St Andrews KY16 9ST, UK"},{"name":"Department of Chemistry, Khalifa University, Abu Dhabi 127788, United Arab Emirates"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"ORCID":"https:\/\/orcid.org\/0000-0003-0630-0138","authenticated-orcid":false,"given":"Nicholas J.","family":"Westwood","sequence":"additional","affiliation":[{"name":"School of Chemistry, University of St Andrews and EaStCHEM, North Haugh, St Andrews KY16 9ST, UK"},{"name":"Biomedical Sciences Research Complex, University of St Andrews, North Haugh, St Andrews KY16 9ST, UK"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2023,12,1]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"105526","DOI":"10.1016\/j.envint.2020.105526","article-title":"Serum Concentrations of Polybrominated Biphenyls (PBBs), Polychlorinated Biphenyls (PCBs) and Polybrominated Diphenyl Ethers (PBDEs) in the Michigan PBB Registry 40 Years after the PBB Contamination Incident","volume":"137","author":"Chang","year":"2020","journal-title":"Environ. Int."},{"key":"ref_2","doi-asserted-by":"crossref","first-page":"25","DOI":"10.1080\/10426509908546173","article-title":"Design of New Organophosphorus Flame Retardants","volume":"144","author":"Woodward","year":"1999","journal-title":"Phosphorus Sulfur Silicon Relat. Elem."},{"key":"ref_3","doi-asserted-by":"crossref","first-page":"107027","DOI":"10.1016\/j.porgcoat.2022.107027","article-title":"Recent Developments in Phosphorus Based Flame Retardant Coatings for Textiles: Synthesis, Applications and Performance","volume":"171","author":"Gaan","year":"2022","journal-title":"Prog. Org. Coat."},{"key":"ref_4","doi-asserted-by":"crossref","unstructured":"Wendels, S., Chavez, T., Bonnet, M., Salmeia, K.A., and Gaan, S. (2017). Recent Developments in Organophosphorus Flame Retardants Containing P-C Bond and Their Applications. Materials, 10.","DOI":"10.3390\/ma10070784"},{"key":"ref_5","doi-asserted-by":"crossref","first-page":"47910","DOI":"10.1002\/app.47910","article-title":"Recent Developments in P(O\/S)\u2013N Containing Flame Retardants","volume":"137","author":"Nazir","year":"2020","journal-title":"J. Appl. Polym. Sci."},{"key":"ref_6","doi-asserted-by":"crossref","unstructured":"Yang, J., Zhao, Y., Li, M., Du, M., Li, X., and Li, Y. (2019). A Review of a Class of Emerging Contaminants: The Classification, Distribution, Intensity of Consumption, Synthesis Routes, Environmental Effects and Expectation of Pollution Abatement to Organophosphate Flame Retardants (OPFRs). Int. J. Mol. Sci., 20.","DOI":"10.3390\/ijms20122874"},{"key":"ref_7","doi-asserted-by":"crossref","first-page":"638","DOI":"10.1021\/acs.estlett.9b00582","article-title":"Organophosphate Ester Flame Retardants: Are They a Regrettable Substitution for Polybrominated Diphenyl Ethers?","volume":"6","author":"Blum","year":"2019","journal-title":"Environ. Sci. Technol. Lett."},{"key":"ref_8","doi-asserted-by":"crossref","unstructured":"Shen, J., Liang, J., Lin, X., Lin, H., Yu, J., and Wang, S. (2022). The Flame-Retardant Mechanisms and Preparation of Polymer Composites and Their Potential Application in Construction Engineering. Polymers, 14.","DOI":"10.3390\/polym14010082"},{"key":"ref_9","doi-asserted-by":"crossref","first-page":"271","DOI":"10.1016\/0141-3910(88)90073-0","article-title":"Performance and Mechanisms of Fire Retardants in Polymers\u2014A Review","volume":"20","author":"Camino","year":"1988","journal-title":"Polym. Degrad. Stab."},{"key":"ref_10","doi-asserted-by":"crossref","first-page":"109962","DOI":"10.1016\/j.polymdegradstab.2022.109962","article-title":"Recent Advances in Flame Retardant Epoxy Systems Containing Non-Reactive DOPO Based Phosphorus Additives","volume":"200","author":"Bifulco","year":"2022","journal-title":"Polym. Degrad. Stab."},{"key":"ref_11","doi-asserted-by":"crossref","first-page":"529","DOI":"10.1016\/j.jhazmat.2019.03.045","article-title":"Single Component Phosphamide-Based Intumescent Flame Retardant with Potential Reactivity towards Low Flammability and Smoke Epoxy Resins","volume":"371","author":"Jian","year":"2019","journal-title":"J. Hazard Mater."},{"key":"ref_12","doi-asserted-by":"crossref","first-page":"111263","DOI":"10.1016\/j.eurpolymj.2022.111263","article-title":"Review of Reversible Dynamic Bonds Containing Intrinsically Flame Retardant Biomass Thermosets","volume":"173","author":"Liu","year":"2022","journal-title":"Eur. Polym. J."},{"key":"ref_13","doi-asserted-by":"crossref","first-page":"1772","DOI":"10.1039\/c1gc00002k","article-title":"From Biomass to Feedstock: One-Step Fractionation of Lignocellulose Components by the Selective Organic Acid-Catalyzed Depolymerization of Hemicellulose in a Biphasic System","volume":"13","author":"Grande","year":"2011","journal-title":"Green Chem."},{"key":"ref_14","doi-asserted-by":"crossref","first-page":"3533","DOI":"10.1039\/C4GC02534B","article-title":"Fractionation of Lignocellulosic Biomass Using the OrganoCat Process","volume":"17","author":"Grande","year":"2015","journal-title":"Green Chem."},{"key":"ref_15","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1007\/s12010-009-8786-6","article-title":"The Effect of Varying Organosolv Pretreatment Chemicals on the Physicochemical Properties and Cellulolytic Hydrolysis of Mountain Pine Beetle-Killed Lodgepole Pine","volume":"161","author":"Chandra","year":"2010","journal-title":"Appl. Biochem. Biotechnol."},{"key":"ref_16","doi-asserted-by":"crossref","first-page":"1157","DOI":"10.1016\/j.cej.2011.02.003","article-title":"The Effect of Organosolv Pretreatment Variables on Enzymatic Hydrolysis of Sugarcane Bagasse","volume":"168","author":"Mesa","year":"2011","journal-title":"Chem. Eng. J."},{"key":"ref_17","doi-asserted-by":"crossref","unstructured":"Teramura, H., Sasaki, K., Oshima, T., Matsuda, F., Okamoto, M., Shirai, T., Kawaguchi, H., Ogino, C., Hirano, K., and Sazuka, T. (2016). Organosolv Pretreatment of Sorghum Bagasse Using a Low Concentration of Hydrophobic Solvents Such as 1-Butanol or 1-Pentanol. Biotechnol. Biofuels, 9.","DOI":"10.1186\/s13068-016-0427-z"},{"key":"ref_18","doi-asserted-by":"crossref","first-page":"202","DOI":"10.1039\/C6GC02739C","article-title":"Pre-Treatment of Lignocellulosic Feedstocks Using Biorenewable Alcohols: Towards Complete Biomass Valorisation","volume":"19","author":"Lancefield","year":"2017","journal-title":"Green Chem."},{"key":"ref_19","doi-asserted-by":"crossref","first-page":"11069","DOI":"10.1021\/acssuschemeng.8b05841","article-title":"Versatility of a Dilute Acid\/Butanol Pretreatment Investigated on Various Lignocellulosic Biomasses to Produce Lignin, Monosaccharides and Cellulose in Distinct Phases","volume":"7","author":"Schmetz","year":"2019","journal-title":"ACS Sustain. Chem. Eng."},{"key":"ref_20","doi-asserted-by":"crossref","unstructured":"Zijlstra, D.S., Analbers, C.A., de Korte, J., Wilbers, E., and Deuss, P.J. (2019). Efficient Mild Organosolv Lignin Extraction in a Flow-Through Setup Yielding Lignin with High \u03b2-O-4 Content. Polymers, 11.","DOI":"10.3390\/polym11121913"},{"key":"ref_21","doi-asserted-by":"crossref","unstructured":"Viola, E., Zimbardi, F., Morgana, M., Cerone, N., Valerio, V., and Romanelli, A. (2021). Optimized Organosolv Pretreatment of Biomass Residues Using 2-Methyltetrahydrofuran and n-Butanol. Processes, 9.","DOI":"10.3390\/pr9112051"},{"key":"ref_22","doi-asserted-by":"crossref","first-page":"14323","DOI":"10.1021\/acssuschemeng.2c03670","article-title":"Organosolv Pretreatment of Cocoa Pod Husks: Isolation, Analysis, and Use of Lignin from an Abundant Waste Product","volume":"11","author":"Davidson","year":"2023","journal-title":"ACS Sustain. Chem. Eng."},{"key":"ref_23","doi-asserted-by":"crossref","first-page":"5972","DOI":"10.1039\/D1GC01109J","article-title":"Pristine Lignin as a Flame Retardant in Flexible PU Foam","volume":"23","author":"Zhang","year":"2021","journal-title":"Green Chem."},{"key":"ref_24","doi-asserted-by":"crossref","first-page":"32252","DOI":"10.1039\/C8RA05598J","article-title":"Synthesis of a Lignin-Based Phosphorus-Containing Flame Retardant and Its Application in Polyurethane","volume":"8","author":"Zhang","year":"2018","journal-title":"RSC Adv."},{"key":"ref_25","doi-asserted-by":"crossref","first-page":"2129","DOI":"10.1039\/D0GC00449A","article-title":"Lignin-Derived Bio-Based Flame Retardants toward High-Performance Sustainable Polymeric Materials","volume":"22","author":"Yang","year":"2020","journal-title":"Green Chem."},{"key":"ref_26","doi-asserted-by":"crossref","first-page":"10918","DOI":"10.1021\/acssuschemeng.7b02822","article-title":"Renewable Thiol-Ene Thermosets Based on Refined and Selectively Allylated Industrial Lignin","volume":"5","author":"Jawerth","year":"2017","journal-title":"ACS Sustain. Chem. Eng."},{"key":"ref_27","doi-asserted-by":"crossref","first-page":"2100461","DOI":"10.1002\/macp.202100461","article-title":"Preparation of Renewable Thiol-Yne \u201cClick\u201d Networks Based on Fractionated Lignin for Anticorrosive Protective Film Applications","volume":"223","author":"Jedrzejczyk","year":"2022","journal-title":"Macromol. Chem. Phys."},{"key":"ref_28","doi-asserted-by":"crossref","first-page":"5949","DOI":"10.1016\/S0040-4039(01)01113-3","article-title":"Selenocarbonyl Synthesis Using Woollins Reagent","volume":"42","author":"Bhattacharyya","year":"2001","journal-title":"Tetrahedron Lett."},{"key":"ref_29","doi-asserted-by":"crossref","first-page":"6221","DOI":"10.1002\/chem.200500291","article-title":"A New Synthesis of (PhPSe2)2 (Woollins Reagent) and Its Use in the Synthesis of Novel P\u2013Se Heterocycles","volume":"11","author":"Gray","year":"2005","journal-title":"Chem. Eur. J."},{"key":"ref_30","doi-asserted-by":"crossref","first-page":"805","DOI":"10.1016\/j.poly.2010.12.018","article-title":"Formation of New Organoselenium Heterocycles and Ring Reduction of 10-Membered Heterocycles into Seven-Membered Heterocycles","volume":"30","author":"Hua","year":"2011","journal-title":"Polyhedron"},{"key":"ref_31","doi-asserted-by":"crossref","first-page":"1058","DOI":"10.1104\/pp.17.01172","article-title":"Highly Decorated Lignins in Leaf Tissues of the Canary Island Date Palm Phoenix Canariensis","volume":"175","author":"Karlen","year":"2017","journal-title":"Plant Physiol."},{"key":"ref_32","doi-asserted-by":"crossref","first-page":"12175","DOI":"10.3390\/molecules200712175","article-title":"Novel Fluorinated Phosphorus-Sulfur Heteroatom Compounds: Synthesis and Characterization of Ferrocenyl-and Aryl-Phosphonofluorodithioic Salts, Adducts, and Esters","volume":"20","author":"Hua","year":"2015","journal-title":"Molecules"},{"key":"ref_33","doi-asserted-by":"crossref","first-page":"106","DOI":"10.1016\/j.poly.2016.08.031","article-title":"Synthesis, Characterization and Structures of Cadmium(II) and Mercury(II) Complexes with Bis(Dipiperidinylphosphino)Methylamine Dichalcogenides","volume":"119","author":"Sanhoury","year":"2016","journal-title":"Polyhedron"},{"key":"ref_34","doi-asserted-by":"crossref","first-page":"119","DOI":"10.1016\/j.polymdegradstab.2014.12.014","article-title":"An Overview of Some Recent Advances in DOPO-Derivatives: Chemistry and Flame Retardant Applications","volume":"113","author":"Salmeia","year":"2015","journal-title":"Polym. Degrad. Stab."},{"key":"ref_35","doi-asserted-by":"crossref","first-page":"109151","DOI":"10.1016\/j.polymdegradstab.2020.109151","article-title":"A DOPO-Based Phosphorus-Nitrogen Flame Retardant Bio-Based Epoxy Resin from Diphenolic Acid: Synthesis, Flame-Retardant Behavior and Mechanism","volume":"176","author":"Chi","year":"2020","journal-title":"Polym. Degrad. Stab."},{"key":"ref_36","doi-asserted-by":"crossref","first-page":"100562","DOI":"10.1016\/j.mtchem.2021.100562","article-title":"Flame-Retardant Effect of a Functional DOPO-Based Compound on Lignin-Based Epoxy Resins","volume":"22","author":"Lu","year":"2021","journal-title":"Mater. Today Chem."},{"key":"ref_37","doi-asserted-by":"crossref","first-page":"171","DOI":"10.1007\/s13233-023-00129-6","article-title":"New Quinone-Based Electrode Additives Electrochemically Polymerized on Activated Carbon Electrodes for Improved Pseudocapacitance","volume":"31","author":"Lee","year":"2023","journal-title":"Macromol. Res."},{"key":"ref_38","doi-asserted-by":"crossref","first-page":"1153","DOI":"10.1002\/bkcs.12126","article-title":"Phosphonamidate Compounds for Butyrylcholinesterase Selective Inhibitors","volume":"41","author":"Oh","year":"2020","journal-title":"Bull. Korean Chem. Soc."},{"key":"ref_39","doi-asserted-by":"crossref","first-page":"1","DOI":"10.1016\/j.reactfunctpolym.2017.12.006","article-title":"Synthesis and Characterization of Phosphorus-Containing, Silicone Rubber Based Flame Retardant Coatings","volume":"123","author":"Januszewski","year":"2018","journal-title":"React. Funct. Polym."},{"key":"ref_40","doi-asserted-by":"crossref","unstructured":"Denis, M., Coste, G., Sonnier, R., Caillol, S., and Negrell, C. (2023). Influence of Phosphorus Structures and Their Oxidation States on Flame-Retardant Properties of Polyhydroxyurethanes. Molecules, 28.","DOI":"10.3390\/molecules28020611"},{"key":"ref_41","doi-asserted-by":"crossref","first-page":"240","DOI":"10.1016\/j.copbio.2019.02.019","article-title":"Lignin Structure and Its Engineering","volume":"56","author":"Ralph","year":"2019","journal-title":"Curr. Opin. Biotechnol."},{"key":"ref_42","doi-asserted-by":"crossref","first-page":"4238","DOI":"10.1002\/cssc.202000989","article-title":"An Introduction to Model Compounds of Lignin Linking Motifs; Synthesis and Selection Considerations for Reactivity Studies","volume":"13","author":"Lahive","year":"2020","journal-title":"ChemSusChem"},{"key":"ref_43","doi-asserted-by":"crossref","first-page":"10640","DOI":"10.1021\/acssuschemeng.7b02575","article-title":"Grafting of Technical Lignins through Regioselective Triazole Formation on \u03b2-O-4 Linkages","volume":"5","author":"Panovic","year":"2017","journal-title":"ACS Sustain. Chem. Eng."},{"key":"ref_44","doi-asserted-by":"crossref","first-page":"1538","DOI":"10.1021\/jf00054a023","article-title":"2-Chloro-4,4,5,5-Tetramethyl-1,3,2-Dioxaphospholane, a Reagent for the Accurate Determination of the Uncondensed and Condensed Phenolic Moieties in Lignins","volume":"43","author":"Granata","year":"1995","journal-title":"J. Agric. Food Chem."},{"key":"ref_45","doi-asserted-by":"crossref","first-page":"375","DOI":"10.1002\/mrc.1260330509","article-title":"Correlation Analysis of 31P NMR Chemical Shifts with Substituent Effects of Phenols","volume":"33","author":"Jiang","year":"1995","journal-title":"Magn. Reason. Chem."},{"key":"ref_46","doi-asserted-by":"crossref","first-page":"267","DOI":"10.1038\/176267a0","article-title":"Ester Groups in Lignin","volume":"176","author":"Smith","year":"1955","journal-title":"Nature"},{"key":"ref_47","doi-asserted-by":"crossref","first-page":"655983","DOI":"10.3389\/fchem.2021.655983","article-title":"Highly Efficient Semi-Continuous Extraction and In-Line Purification of High \u03b2-O-4 Butanosolv Lignin","volume":"9","author":"Zijlstra","year":"2021","journal-title":"Front. Chem."},{"key":"ref_48","unstructured":"(CrystalClear-SM Expert, 2015). CrystalClear-SM Expert, v2.1."},{"key":"ref_49","unstructured":"(2023). CrysAlisPro, v1.171.42.94a Rigaku Oxford Diffraction, Rigaku Corporation."},{"key":"ref_50","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1107\/S2053273314026370","article-title":"SHELXT\u2014Integrated space-group and crystal structure determination","volume":"71","author":"Sheldrick","year":"2015","journal-title":"Acta Crystallogr. Sect. A Found. Adv."},{"key":"ref_51","doi-asserted-by":"crossref","first-page":"3","DOI":"10.1107\/S2053229614024218","article-title":"Crystal structure refinement with SHELXL","volume":"71","author":"Sheldrick","year":"2015","journal-title":"Acta Crystallogr. Sect. C Struct. Chem."},{"key":"ref_52","doi-asserted-by":"crossref","first-page":"339","DOI":"10.1107\/S0021889808042726","article-title":"OLEX2: A complete structure solution, refinement and analysis program","volume":"42","author":"Dolomanov","year":"2009","journal-title":"J. Appl. Crystallogr."}],"container-title":["Molecules"],"original-title":[],"language":"en","link":[{"URL":"https:\/\/www.mdpi.com\/1420-3049\/28\/23\/7885\/pdf","content-type":"unspecified","content-version":"vor","intended-application":"similarity-checking"}],"deposited":{"date-parts":[[2025,10,10]],"date-time":"2025-10-10T21:35:51Z","timestamp":1760132151000},"score":1,"resource":{"primary":{"URL":"https:\/\/www.mdpi.com\/1420-3049\/28\/23\/7885"}},"subtitle":[],"short-title":[],"issued":{"date-parts":[[2023,12,1]]},"references-count":52,"journal-issue":{"issue":"23","published-online":{"date-parts":[[2023,12]]}},"alternative-id":["molecules28237885"],"URL":"https:\/\/doi.org\/10.3390\/molecules28237885","relation":{},"ISSN":["1420-3049"],"issn-type":[{"value":"1420-3049","type":"electronic"}],"subject":[],"published":{"date-parts":[[2023,12,1]]}}}