Biodegradable Naphthenic Acid Ionic Liquids: Synthesis, Characterization, and Quantitative Structure–Biodegradation Relationship

Authors

  • Yinghao Yu Dr.,

    1. Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 (PR China), Fax: (+86) 10-8262-7080
    2. Graduate University of Chinese Academy of Sciences, Beijing 100149 (PR China)
    Search for more papers by this author
  • Xingmei Lu Dr.,

    1. Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 (PR China), Fax: (+86) 10-8262-7080
    Search for more papers by this author
  • Qing Zhou Dr.,

    1. Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 (PR China), Fax: (+86) 10-8262-7080
    Search for more papers by this author
  • Kun Dong,

    1. Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 (PR China), Fax: (+86) 10-8262-7080
    Search for more papers by this author
  • Hongwei Yao,

    1. Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 (PR China), Fax: (+86) 10-8262-7080
    2. Graduate University of Chinese Academy of Sciences, Beijing 100149 (PR China)
    Search for more papers by this author
  • Suojiang Zhang Prof. Dr.

    1. Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190 (PR China), Fax: (+86) 10-8262-7080
    Search for more papers by this author

Abstract

It has been confirmed that commonly used ionic liquids are not easily biodegradable. When ultimately disposed of or accidentally released, they would accumulate in the environment, which strongly restricts large-scale industrial applications of ionic liquids. Herein, ten biodegradable ionic liquids were prepared by a single, one-pot neutralization of choline and surrogate naphthenic acids. The structures of these naphthenic acid ionic liquids (NAILs) were characterized and confirmed by 1H and 13C NMR spectroscopy, IR spectroscopy, and elemental analysis, and their physical properties, such as densities, viscosities, conductivities, melting points (Tm), glass transition points (Tg), and the onset temperatures of decomposition (Td), were determined. More importantly, studies showed that these NAILs would be rapidly and completely biodegraded in aquatic environments under aerobic conditions, which would make them attractive candidates to be utilized in industrial processes. To explore the underlying mechanism involved in the NAIL biodegradation reaction and seek prediction of their biodegradability under environmental conditions, four molecular descriptors were chosen: the logarithm of the n-octanol/water partition coefficient (log P), van der Waals volume (VvdW), energies of the highest occupied molecular orbital (EHOMO), and energies of the lowest unoccupied molecular orbital (ELUMO). Through multiple linear regression, a general and qualified model including the biodegradation percentage for NAILs after the 28-day OECD 301D test (%B28) and molecular descriptors was developed. Regression analysis showed that the model was statistically significant at the 99 % confidence interval, thus indicating that the %B28 of NAILs could be explained well by the quantum chemical descriptor EHOMO, which might give some important clues in the discovery of biodegradable ionic liquids of other kinds.

Ancillary