Electrochemical Conversion of the Lignin Model Veratryl Alcohol to Veratryl Aldehyde Using Manganese(III)-Schiff Base Homogeneous Catalysts
, M. Isabel Fernández-García 1, Ana M. González-Noya 2, Gustavo González-Riopedre 1,3, Alexei M. Tyryshkin 4 and Marcelino Maneiro 1,*Round 1
Reviewer 1 Report
An author should answer in the manuscript text about the following comment.
It should be mentioned in detail about electrochemistry measurement and the electrolytic reaction condition.
The turnover number of catalyst and the current efficiency of electrolytic reaction should be mentioned.
When these case of reaction time to more than 2 hours, is it possible to raise the conversion rate of VA to VAH?
Is an activity of a catalyst kept after the reaction?
Does a peak potential of a catalyst shift by pH?
Author Response
The authors are very much grateful to this reviewer for his/her valuable comments.
REVIEWER: It should be mentioned in detail about electrochemistry measurement and the electrolytic reaction condition.
ANSWER: As suggested by the reviewer we have incorporated details about:
Electrochemistry measurements. A new paragraph has been added in the Experimental details for materials and methods section of the Supplementary Materials:“Cyclic voltammetry was performed using an EG&G Princeton Applied Research model 273 potentiostat, controlled by EG&G PAR model 270 software. A Metrohm model 6.1204.000 graphite disc was used as working electrode. A saturated calomel electrode was used as reference and a platinum wire as an auxiliary electrode. Measurements were made with ca. 10-3 M solutions of complexes in DMF using 0.1 mol dm-3 tetraethylammonium perchlorate as a supporting electrolyte”.
Electrolytic reaction conditions. Section 2.5 has been rewritten (see the highlighted version of the revised manuscript) incorporating new details, and also Table 4 with details about the experimental conditions for the electrochemical conversion of VA to VAH has been incorporated at the main text of the manuscript.
REVIEWER: The turnover number of catalyst and the current efficiency of electrolytic reaction should be mentioned.
ANSWER: Table 4 now includes turnover numbers and also current efficiency data for all the complexes.
REVIEWER: When these case of reaction time to more than 2 hours, is it possible to raise the conversion rate of VA to VAH?
ANSWER: The conversion of VA to VAH continues after 2 h. A sentence has been added in order to explain this fact in section 3.3 of the manuscript:
“The catalysts seem to be stable for longer periods, in fact highest VA to VAH conversion rates can be gradually achieved for times up to 8 h although this causes a considerably loss of the electrochemical efficiency”.
REVIEWER: Is an activity of a catalyst kept after the reaction?
ANSWER: The activity of the catalyst continues after 2 hours. The TON numbers above 100 (for 0.25% of catalyst) also indicates the stability of the system. The catalysts were removed after electrochemical reaction by filtrating the solution through a short silica gel plug.
REVIEWER: Does a peak potential of a catalyst shift by pH?
ANSWER: It is expected slight shifting of the peak potential of the catalysts by pH. However, our results reveal that the redox potentials are not the determining factor in the obtained catalytic rates for this case. For instance, the active compound 4 shows the lowest E1/2 value (-196 mV), but the second lowest value (-186 mV) corresponds to the inactive complex 5. A parallel analysis can be done with the peak to peak separation, thus there is no trend in catalytic activity that can be attributed to the MnIII/MnII redox waves obtained in the electrochemical probes for 1-7. Unfortunately, the EG&G PAR model 273 potentiostat is unavailable for a period, until one of the electrodes is replaced. This fact prevents us for checking this peak shifting for now.
Reviewer 2 Report
The paper reports crystal structures, characterization, and catalytic activities of seven Mn(III) complexes with Schiff base ligands. Complex 1, 3, 5, and 6 are defined in the text but Complex 2, 4, and 7 are unclear. Though the references are given for them, all references contain several complexes. So, I can’t judge whether the discussions are appropriate or not. This paper is not recommended for publication in Applied Science. The document needs to be improved on the following points.
Line 99, 105: The chemical formula and calculated analytical values of Complex 3 and 5 are incorrect.
Line 112: The formula should be addressed by CAS format.
Line 201: The measurement conditions for CV are not described. The observed redox waves should be assigned.
Line 227,228: Distances should have standard deviations.
Table 2: O530-Mn1-N2 angle should be included.
Discussion section: To help the discussions the table which includes the activities, axial distances, redox potentials, and some other essential data should be prepared.
SI: NMR chart is missing from Figure S4.
Author Response
REVIEWER: The paper reports crystal structures, characterization, and catalytic activities of seven Mn(III) complexes with Schiff base ligands. Complex 1, 3, 5, and 6 are defined in the text but Complex 2, 4, and 7 are unclear. Though the references are given for them, all references contain several complexes. So, I can’t judge whether the discussions are appropriate or not.
REPLY: We would like to thank this reviewer for the careful reading of the manuscript and for his/her opinions and suggestions, which have certainly contributed to improve the quality of this article. We have modified the manuscript following the suggestions of this referee as outlined below. Table S1 has been incorporated to the Supplementary Materials Section in order to facilitate the recognition of each of the complexes.
REVIEWER: Line 99, 105: The chemical formula and calculated analytical values of Complex 3 and 5 are incorrect.
REPLY: Thank you for detecting this error. This has been corrected in the revised version of the manuscript.
REVIEWER: Line 112: The formula should be addressed by CAS format.
REPLY: Done as suggested by the reviewer.
REVIEWER: The measurement conditions for CV are not described. The observed redox waves should be assigned.
REPLY: A new paragraph describing the measurements conditions for CV has been added in the experimental details for materials and methods section of the supplementary materials:
“Cyclic voltammetry was performed using an EG&G Princeton Applied Research model 273 potentiostat, controlled by EG&G PAR model 270 software. A Metrohm model 6.1204.000 graphite disc was used as working electrode. A saturated calomel electrode was used as reference and a platinum wire as an auxiliary electrode. Measurements were made with ca. 10-3 M solutions of complexes in DMF using 0.1 mol dm-3 tetraethylammonium perchlorate as a supporting electrolyte”.
Redox waves has been assigned. Table 5 now collects the Eox(MnII →MnIII) and Ered(MnIII→MnII) potentials for the complexes.
REVIEWER: Line 227,228: Distances should have standard deviations.
REPLY: Standard deviations for these distances has been added.
REVIEWER: Table 2: O530-Mn1-N2 angle should be included.
REPLY: The O530-Mn1-N2 has been incorporated in table 2.
REVIEWER: Discussion section: To help the discussions the table which includes the activities, axial distances, redox potentials, and some other essential data should be prepared.
REPLY: Table 5, including the suggested data, has been incorporated to the main text of the manuscript. Part of discussion section has been rewritten in order to facilitate the discussion about the results. We think that these changes improve the understanding of this section and we would like to thank to the reviewer for this suggestion.
REVIEWER: SI: NMR chart is missing from Figure S4.
REPLY: The chart has been incorporated to Figure S4.
Round 2
Reviewer 2 Report
The revised version has bee improved. It can be accepted in its present form.
