{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,18]],"date-time":"2026-01-18T21:09:11Z","timestamp":1768770551367,"version":"3.49.0"},"reference-count":27,"publisher":"MDPI AG","issue":"22","license":[{"start":{"date-parts":[[2021,11,13]],"date-time":"2021-11-13T00:00:00Z","timestamp":1636761600000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Polymers"],"abstract":"<jats:p>Esterification of caprylic acid with methanol was performed over chitosan with sulfonic acid groups, as a catalyst, at 60 \u00b0C. The sulfonic acid groups were introduced into chitosan (CH) by using chlorosulfonic acid. Catalysts were characterized by scanning electron microscopy (SEM), elemental analysis, thermogravimetric analysis (TGA), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and acid\u2013base titration. Catalytic activity increased with the amount of sulfonic acid groups present on chitosan. The 4\u2013CH\u2013SO3H catalyst (chitosan with sulfonic acid groups\u2014sample 4 prepared) showed the highest activity of all materials. The esterification of caprylic acid with methanol was optimized using a 4\u2013CH\u2013SO3H catalyst. Under optimized reaction conditions, it was found that, at 60 \u00b0C, with 0.2 g of catalyst loading and with a molar ratio methanol to caprylic acid equal 1:95, a caprylic acid conversion of about 83%, after 4 h could be obtained. Catalytic stability of the 4\u2013CH\u2013SO3H material was evaluated through consecutive batch runs. After the second batch, the catalytic activity stabilized.<\/jats:p>","DOI":"10.3390\/polym13223924","type":"journal-article","created":{"date-parts":[[2021,11,14]],"date-time":"2021-11-14T20:51:53Z","timestamp":1636923113000},"page":"3924","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":8,"title":["Chitosan with Sulfonic Groups: A Catalyst for the Esterification of Caprylic Acid with Methanol"],"prefix":"10.3390","volume":"13","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2990-6394","authenticated-orcid":false,"given":"Jos\u00e9","family":"Castanheiro","sequence":"first","affiliation":[{"name":"MED-Instituto Mediterr\u00e2neo para a Agricultura, Ambiente e Desenvolvimento, Departamento de Qu\u00edmica, Escola de Ci\u00eancias e Tecnologia, Universidade de \u00c9vora, 7000-671 \u00c9vora, Portugal"}]}],"member":"1968","published-online":{"date-parts":[[2021,11,13]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"696","DOI":"10.1016\/j.rser.2015.05.038","article-title":"A review on recent advancement in catalytic materials for biodiesel production","volume":"50","author":"Avhad","year":"2015","journal-title":"Renew. 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