Thermal Stability of Ionic Liquids: Current Status and Prospects for Future Development
Round 1
Reviewer 1 Report
The review proposed by the Authors deals with a literature survey on the thermal stability of ionic liquids (ILs) focusing on the different kinetics analysis methods for the determination of the maximum operating temperature and the different structural feature (anion versus cation, cation functionalization or side chain length, mono cation versus dication) effects on the overall thermal stability. The topic is of the highest interest in the IL field and the manuscript would be of interest for the broad community of researchers involved in using ILs in diverse applications. However, some parts, listed below, need to be improved before recommending this review for publication.
Line 28: the definition of ILs as designer solvents derives from the possibility to adapt their physicochemical properties by changing the constituting ions. Therefore, this sentence should be changed accordingly and appropriate references should be added.
Line 64: some examples should be added: 10.1016/j.molliq.2019.111155, 10.1080/10402004.2012.701000
Line 65: the following reference should be added: 10.1007/978-981-10-6739-6_103-1 and ref 42
Line 74: the Authors should comment which effects has the heating rate on the thermograms shape (not only mention that differences are noticeable). This would help not experts to not underestimate this parameter and compare ILs thermal stabilities obtained under different conditions.
Line 84: in the cited work (reference 64) T10% is also reported and should be added to the text.
Lines 94-96: please delete or rephrase this sentence. It is not true that if two peaks are present in the DTG then one refers to the cation and the other to the anion. Please also double check the cited references.
Line 134: is Parajo’s method referring to equation 2? Please specify this in brackets.
Line 135: what exactly the Authors mean by standard value? Also could the Authors clarify why the Seeberger’s method would be better to determine the long thermal stability?
Line 146: the word “standard” is not appropriate.
Line 151: please remove the word always (often?) as it is confusing giving the following sentences.
Line 163: is there any explanation for the observed different thermal stabilities on account of the diverse atmosphere?
Line 184: please replace the word “proton” with “protic”.
Figure 8: please replace the word “pure ILs” with “neat ILs”.
Lines 192-201: the Authors should rephrase this part. By impurities, one should consider only traces of solvents/water/reagents/salts deriving from the ILs synthesis not added external compounds/materials. It is fine to highlight that the thermal stability of an IL changes depending on the presence of XXX, but please do not call them impurities!
Line 286: a table is present by mistake, is the same table 2 at line 293.
Line 290: the acronym ICTAC is not defined.
Lines 412-418: this part should be rephrased. Several studies have been performed on structurally related series of ILs. More data should be provided before drawing conclusions (and the Authors already showed that exceptions from the general trend are possible).
Lines 437-439: point 1) is this true only for imidazolium ILs?
Lines 440-442: point 2) from the presented data, it is not always true.
Line 467: this section would benefit by adding a discussion of the effect of the presence of hydroxyl groups on the thermal stability.
Line 477: please add the following reference: 10.1039/C3CP53648C
Line 478: please change “C2H” with “C-2H”
Line 499: the section about anions would benefit with a discussion about bio-based anions (eg fatty acid anions, levulinate ecc). Giving the increasing importance of bio-based ILs, improvements of this section are strongly encouraged. 10.1039/c9nj00191c, 10.1039/C5RA25001C, 10.1016/j.molliq.2018.06.096
Line 534: it is not clear what the Authors mean with “ideal values”.
Line 544: please add the following references. 10.1007/s10973-019-08951-w, 10.1021/je2000183.
Line 557: the same consideration holds true for monocationic ILs, this should be added.
Line 576: do the Authors refer to linear chain with straight chain?
Line 627-629: should be rephrased.
Please correct some minor typos and minor incorrectness (eg Tonset, onset should be subscript).
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
This review is comprehensive and well-written. It would be useful as a good reference material in the subject. I point out only a couple of correction and addition.
- Correction: pp. 2, line # 46, #67, #82, Tonset --> Tonset
- Addition to a reference concerning the use of ionic liquids as catalyst:
1. Y.-H. Oh, H. B. Jang, S. Im, M. J. Song, S.-Y. Kim, S.-W. Park, D. Y. Chi, C. E. Song, S. Lee, SN2 reactions in ionic liquids: A mechanistic study toward solvent engineering, Org. Biomol. Chem. 9, 418 (2011).
2. Solvent free nucleophilic introduction of fluorine with [bmim][F] Sébastien Bouvet, Bruce Pégot, Jérome Marrot, Emmanuel Magnier, Tetrahedron Letters 55, 826–829, 2014.
3. Ionic Liquids as Designer Solvents for Nucleophilic Aromatic Substitutions, Ian Newington, Juan M. Perez-Arlandis, Tom Welton, Org. Lett., Vol. 9, No. 25, 2007.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 1 Report
The Authors improved the manuscript substantially. Therefore, I recommend it for publication.
