The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids

[AAE]X composed of amino acid ester cations is a sort of typically “bio-based” protic ionic liquids (PILs). They possess potential Brønsted acidity due to the active hydrogens on their cations. The Brønsted acidity of [AAE]X PILs in green solvents (water and ethanol) at room temperature was systemat...

Full description

Bibliographic Details
Main Authors: Ting He, Cheng-Bin Hong, Peng-Chong Jiao, Heng Xiang, Yan Zhang, Hua-Qiang Cai, Shuang-Long Wang, Guo-Hong Tao
Format: Article
Language:English
Published: MDPI AG 2021-12-01
Series:Molecules
Subjects:
Online Access:https://www.mdpi.com/1420-3049/26/1/62
id doaj-caae204fa6ae4b0fb228a58f89c021b1
record_format Article
spelling doaj-caae204fa6ae4b0fb228a58f89c021b12020-12-26T00:00:04ZengMDPI AGMolecules1420-30492021-12-0126626210.3390/molecules26010062The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic LiquidsTing He0Cheng-Bin Hong1Peng-Chong Jiao2Heng Xiang3Yan Zhang4Hua-Qiang Cai5Shuang-Long Wang6Guo-Hong Tao7Institute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, ChinaCollege of Chemistry, Sichuan University, Chengdu 610064, ChinaInstitute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, ChinaInstitute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, ChinaInstitute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, ChinaInstitute of Chemical Materials, China Academy of Engineering Physics, Mianyang 621900, ChinaCollege of Chemistry, Sichuan University, Chengdu 610064, ChinaCollege of Chemistry, Sichuan University, Chengdu 610064, China[AAE]X composed of amino acid ester cations is a sort of typically “bio-based” protic ionic liquids (PILs). They possess potential Brønsted acidity due to the active hydrogens on their cations. The Brønsted acidity of [AAE]X PILs in green solvents (water and ethanol) at room temperature was systematically studied. Various frameworks of amino acid ester cations and four anions were investigated in this work from the viewpoint of structure–property relationship. Four different ways were used to study the acidity. Acid dissociation constants (p<i>K</i><sub>a</sub>) of [AAE]X determined by the OIM (overlapping indicator method) were from 7.10 to 7.73 in water and from 8.54 to 9.05 in ethanol. The p<i>K</i><sub>a</sub> values determined by the PTM (potential titration method) were from 7.12 to 7.82 in water. Their Hammett acidity function (<i>H</i><sub>0</sub>) values (0.05 mol·L<sup>−1</sup>) were about 4.6 in water. In addition, the p<i>K</i><sub>a</sub> values obtained by the DFT (proton-transfer reactions) were from 7.11 to 7.83 in water and from 8.54 to 9.34 in ethanol, respectively. The data revealed that the cationic structures of [AAE]X had little effect and the anions had no effect on the acidity of [AAE]X. At the same time, the OIM, PTM, Hammett method and DFT method were reliable for determining the acidic strength of [AAE]X in this study.https://www.mdpi.com/1420-3049/26/1/62protic ionic liquidsBrønsted acidityamino acid ionic liquidsbio-based ionic liquids
collection DOAJ
language English
format Article
sources DOAJ
author Ting He
Cheng-Bin Hong
Peng-Chong Jiao
Heng Xiang
Yan Zhang
Hua-Qiang Cai
Shuang-Long Wang
Guo-Hong Tao
spellingShingle Ting He
Cheng-Bin Hong
Peng-Chong Jiao
Heng Xiang
Yan Zhang
Hua-Qiang Cai
Shuang-Long Wang
Guo-Hong Tao
The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids
Molecules
protic ionic liquids
Brønsted acidity
amino acid ionic liquids
bio-based ionic liquids
author_facet Ting He
Cheng-Bin Hong
Peng-Chong Jiao
Heng Xiang
Yan Zhang
Hua-Qiang Cai
Shuang-Long Wang
Guo-Hong Tao
author_sort Ting He
title The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids
title_short The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids
title_full The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids
title_fullStr The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids
title_full_unstemmed The Proton Dissociation of Bio-Protic Ionic Liquids: [AAE]X Amino Acid Ionic Liquids
title_sort proton dissociation of bio-protic ionic liquids: [aae]x amino acid ionic liquids
publisher MDPI AG
series Molecules
issn 1420-3049
publishDate 2021-12-01
description [AAE]X composed of amino acid ester cations is a sort of typically “bio-based” protic ionic liquids (PILs). They possess potential Brønsted acidity due to the active hydrogens on their cations. The Brønsted acidity of [AAE]X PILs in green solvents (water and ethanol) at room temperature was systematically studied. Various frameworks of amino acid ester cations and four anions were investigated in this work from the viewpoint of structure–property relationship. Four different ways were used to study the acidity. Acid dissociation constants (p<i>K</i><sub>a</sub>) of [AAE]X determined by the OIM (overlapping indicator method) were from 7.10 to 7.73 in water and from 8.54 to 9.05 in ethanol. The p<i>K</i><sub>a</sub> values determined by the PTM (potential titration method) were from 7.12 to 7.82 in water. Their Hammett acidity function (<i>H</i><sub>0</sub>) values (0.05 mol·L<sup>−1</sup>) were about 4.6 in water. In addition, the p<i>K</i><sub>a</sub> values obtained by the DFT (proton-transfer reactions) were from 7.11 to 7.83 in water and from 8.54 to 9.34 in ethanol, respectively. The data revealed that the cationic structures of [AAE]X had little effect and the anions had no effect on the acidity of [AAE]X. At the same time, the OIM, PTM, Hammett method and DFT method were reliable for determining the acidic strength of [AAE]X in this study.
topic protic ionic liquids
Brønsted acidity
amino acid ionic liquids
bio-based ionic liquids
url https://www.mdpi.com/1420-3049/26/1/62
work_keys_str_mv AT tinghe theprotondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT chengbinhong theprotondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT pengchongjiao theprotondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT hengxiang theprotondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT yanzhang theprotondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT huaqiangcai theprotondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT shuanglongwang theprotondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT guohongtao theprotondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT tinghe protondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT chengbinhong protondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT pengchongjiao protondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT hengxiang protondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT yanzhang protondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT huaqiangcai protondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT shuanglongwang protondissociationofbioproticionicliquidsaaexaminoacidionicliquids
AT guohongtao protondissociationofbioproticionicliquidsaaexaminoacidionicliquids
_version_ 1724370880305299456