4-(4-(2-Bromoethyl)phenoxy)-2,3,5,6-tetrafluoropyridine

Round 1

Reviewer 1 Report

In this manuscript the synthesis of new ionic liquid bearing perfluorinated pyridine (PFP) unit is reported. The preparation of title compound is based on regioselective nucleophilic substitution of F atom in PFP followed by ‘quaternization’ with triphenylphosphine and ion metathesis. The final compound is indicated as potentially useful precursor of ionic liquids. Unfortunately, neither the first formed bromide (compd 2) nor final bistriflimide (compd 3) are available in pure form, hence, their usefulness are highly questionable. Also, to my opinion the performed TGA and DSC measurements for both compounds (which are accompanied by unknown impurities) are useless in the context of material analysis. Furthermore, the experimental part is full of some minor errors and misleadings (see detailed comments below).

First of all I suggest to optimize reaction conditions or to develop purification method to access analytically pure samples. For example, recrystallization in acetone bath might help; alternatively, chromatographic techniques by using neutral alumina and polar solvents are conceivable (simple filtration through short alumina plug should enable removal of non-ionic impurities). In addition, the paper is missing summary; perspective functionalizations of the target salt also deserve a brief comment.

Overall, I do not recommend publication in the present form.

Further comments:

a) The name of title compound: Why the authors use sophisticated ‘azane’ term for counterion of the title salt? The commonly used name for the Tf2N anion is ‘bistriflimide’.

b) abstract: the authors claimed that the title compound was prepared in ‘near quantitative yield’. this simply not true as there is 60% overall yield reported for this 3-step procedure.

c) line 68: remove ‘i’ to read ‘phosphine’

d) scheme 2: yields for each individual synthetic step should be added to this scheme.

e) the chemical shift of the signal of residual chloroform is d = 77.16 (see: J. Org. Chem. 1997, 62, 7512 or Organometallics 2010, 29, 2176)

f) line 118: what the 7.44-7.20 (m, 4H) refer to? There is no such absorption in 1H NMR spectrum of cmpd 1 depicted in Figure S1.

g) line 119 (13C NMR): there are absorptions of the PFP unit missing in the list. This problem of low intensity due to F-coupling should at least be mentioned in the text. Preferably, simultaneous 1H & 19F-decoupled 13C NMR should be taken for such systems. Same applies for 13C NMR of cpmd 2 and 3.

h) line 120: there are 4 extra F atoms listed in 19F NMR. Same for 19F NMR of cmpd 2 (line 134)

i) line 121: the relative % intensities are incorrect; for example, if the highest peak is 2.6 x 10^6, the intensity of peak at M = 349 (0.4 x 10^6) is 15, but not 40. Same applies to the others.

j) line 131: absorptions of para-substituted aromatic unit should not be interpreted as two doublets; these are always multiplets (AA’XX’ spin system!). correction is strongly suggested. (same for cmpd 3; line 144).

k) please supplement the SI file with 19F NMR of cmpd 2.

l) the experimental data should be supplemented either with elemental analyses or high resolution MS results.

Author Response

We thank the reviewer for providing the comments and we agree with them. However, the necessary revisions for re-submission (in 10 days) requires extensive laboratory work with the current personnel in our lab. Therefore, we are re-submitting the work by removing the IL salts 2 and 3 and focusing only on 1 as a precursor to ILs.  We plan to submit IL salts 2 and 3 at a later time.

With the revised manuscript, we have re-edited and corrected all all the reviewer's concerns with the exception of the performing HRMS. Per Molbank journal's of required supporting information, GC provides the proof of purity (in absence of combustion analysis) and MS is optional (see https://res.mdpi.com/data/molbank-checklist-for-authors.pdf). Therefore, we have kept the GCMS portion of the experimental and SI. For precedence, we have also published in Molbank (https://www.mdpi.com/1422-8599/2023/2/M1644) reporting with GCMS as well. 

We hope that the manuscript is suitable for publication after this revision and improvement per suggestions of the reviewer. 

Round 2

Reviewer 1 Report

In the revised version of this manuscript the authors report on the synthesis of title compound as promising building block for preparation of new ILs. I recommend publication after the following corrections:

abstract, lines 13/14: there are no metathesis reactions presented in this version; please correct.

experimental part, line 92: there is one chemical shift missing in descritpion of 13C NMR (next to the first dm absorption a value of chemical shift of the second dm should be provided).

Author Response

We have made the corrections per the reviewer's comments.