Co-N-Si/AC Catalyst for Aerobic Oxidation of Benzyl Alcohols to Esters under Mild Conditions
Round 1
Reviewer 1 Report
The new methods for the synthesis of esters are of interest to scientific society. Tandem process oxidation of benzylic alcohols to acids followed by esterification with alcohols used as a solvent seems to be very interesting. The substrate scope of alcohols is narrow and only benzyl alcohols reacts with high yield. Only for phenylpropanol respective ester was obtained in moderate yield and extended time. This phenomenon should be considered as a method limitation and in manuscript title instead of the world "alcohols" the sentence "benzyl alcohols" should be used. The scale of experiments regarding the use of 0.5 mmol of substrates is a series limitation of the proposed method. The authors should demonstrate the result of at least one experiment performed on preparative scale. The question of reaction mechanism remains to be solved. Since its two step process; oxidation of benzyl alcohols to acids followed by esterification the current limits of the method proposed can relay on either the first or second reaction. Additional experiments are required to present the results of esterification reaction only by new catalyst. The structures of products obtained are not supported by any data. Experimental part of manuscript should be extended by proper characterization of all compounds from Scheme 1. Product purification by preparative TLC is very expensive in relation to the simple structures of products. This issue remains to be limitation of proposed catalyst.
Author Response
25-Oct-2021
Manuscript ID: molecules-1438306
Title: Co-N-Si/AC catalyst for aerobic oxidation of benzyl alcohols to esters under mild conditions
Dear Reviewer:
Thank you for your valuable comments, your comments are quite helpful, and I revised my paper very carefully, thank you again for your help! If there is more question, we are willing to revise it again. We appreciate your warm work earnestly, and hope that the correction will meet with approval.
Given below is our specific point-by-point response to each of the specific comments.
Comments:
- The new methods for the synthesis of esters are of interest to scientific society. Tandem process oxidation of benzylic alcohols to acids followed by esterification with alcohols used as a solvent seems to be very interesting. The substrate scope of alcohols is narrow and only benzyl alcohols reacts with high yield. Only for phenylpropanol respective ester was obtained in moderate yield and extended time. This phenomenon should be considered as a method limitation and in manuscript title instead of the world "alcohols" the sentence "benzyl alcohols" should be used.
Response 1: Many thanks for your comments. According to your valuable advice, we have replaced the alcohols in the title with benzyl alcohols.
- The scale of experiments regarding the use of 0.5 mmol of substrates is a series limitation of the proposed method. The authors should demonstrate the result of at least one experiment performed on preparative scale.
Response 2: Thanks a lot for your constructive suggestions. In view of your valuable suggestions, we selected seven substrates, and enlarged the amount of substrates to 5 grams, and reacted with methanol, which also achieved better reaction results. The description of this paragraph has been added in the text.
- The question of reaction mechanism remains to be solved. Since its two step process; oxidation of benzyl alcohols to acids followed by esterification the current limits of the method proposed can rely on either the first or second reaction. Additional experiments are required to present the results of esterification reaction only by new catalyst.
Response 3: Many thanks for your advice. In the part of mechanism study, we carried out some control experiments and referred to relevant literatures to supplement the possible paths of our reactions into the text.
- The structures of products obtained are not supported by any data. Experimental part of manuscript should be extended by proper characterization of all compounds from Scheme 1.
Response 4: Many thanks for your comments. In fact, the characterization data about the product are put in the supporting information, including nuclear magnetic spectrum, infrared data, mass spectrum data, melting point. Please see pages 16-45 in the supporting information.
- Product purification by preparative TLC is very expensive in relation to the simple structures of products. This issue remains to be limitation of proposed catalyst.
Response 5: Many thanks for your comments. Regarding the purification of products, in fact, many of our products are obtained by direct filtration, that is, taking an appropriate amount of silica gel, putting it into the sand core funnel, then pouring the reaction liquid directly into the sand core funnel, rinsing it with ethyl acetate, and then sending samples for testing after concentration and drying.
Once again, thank you very much for your comments and suggestions.
Sincerely yours,
Changjian Zhou
2021-10-30
Reviewer 2 Report
The authors describe a stable, earth-abundant, reusable cobalt-based heterogeneous catalyst for the oxidative esterification of alcohols under ambient conditions, featuring broad substrate scope. The active sites of Co-N-Si/AC are proposed to be Co-N species.
The paper bears a strong resemblance to a previous report by Jagadeesh et al., (R. V. Jagadeesh, H. Junge, M. M. Pohl, J. Radnik, A. Bruckner, M. Beller, J. Am. Chem. Soc., 2013, 135, 236, 10776-10782 (cited in this manuscript 4f) in terms of the outline of the manuscript, and the problem identification in the introduction the papers are similar. I cannot see how the present work is significantly different. The authors need to explain how the present work provides additional novelty.
The current manuscript does differ with the addition of TEOS and the subsequent transformation and incorporation of Si clearly well dispersed (from mapping) and the authors stating a modification of the catalyst structure. But it is unclear if this results in a significant improvement to previous reports, or an improved recyclability of the catalyst. Jagadeesh et al., did report similar recyclability and conversion.
The current manuscript does point out Si plays a role in the modification of the structure of the catalyst, (line 105-108), however the importance of this modification is not emphasized or explained i.e. does this result show significant improvement to previous works?
Perhaps the authors should compare their improved reaction times to previous reports, which does seem to be significantly shorter than reference 4f. In Table 1 this is also apparent since the catalyst Co-N/AC (same prep as ref 4f) and Co-N-Si/AC (this work) shows a 28 % increase in yield at 3h.
However, in its current form the manuscript only provides a route to a catalyst which performs comparatively similar with a previous report. The authors could provide a comparison of their results with previous literature, which lacked throughout, this would improve the manuscript.
Figure 1 - The elemental mapping should have scale bars on all plots, without them, the distribution can be misleading.
Figure 2 - The XPS plots and data need to be improved for clarity. The data points displayed in the manuscript are not clear, and seem to have faded out. The assignment is therefore questionable.
Line 95 and 103 - Change the word 'owned'
Author Response
25-Oct-2021
Manuscript ID: molecules-1438306
Title: Co-N-Si/AC catalyst for aerobic oxidation of benzyl alcohols to esters under mild conditions
Dear Reviewer:
Thank you for your valuable comments, your comments are quite helpful, and I revised my paper very carefully, thank you again for your help! If there is more question, we are willing to revise it again. We appreciate your warm work earnestly, and hope that the correction will meet with approval.
Given below is our specific point-by-point response to each of the specific comments.
Comments:
- The paper bears a strong resemblance to a previous report by Jagadeesh et al., (R. V. Jagadeesh, H. Junge, M. M. Pohl, J. Radnik, A. Bruckner, M. Beller, J. Am. Chem. Soc., 2013, 135, 236, 10776-10782 (cited in this manuscript 4f) in terms of the outline of the manuscript, and the problem identification in the introduction the papers are similar. I cannot see how the present work is significantly different. The authors need to explain how the present work provides additional novelty.
The current manuscript does differ with the addition of TEOS and the subsequent transformation and incorporation of Si clearly well dispersed (from mapping) and the authors stating a modification of the catalyst structure. But it is unclear if this results in a significant improvement to previous reports, or an improved recyclability of the catalyst. Jagadeesh et al., did report similar recyclability and conversion.
The current manuscript does point out Si plays a role in the modification of the structure of the catalyst, (line 105-108), however the importance of this modification is not emphasized or explained i.e. does this result show significant improvement to previous works?
Perhaps the authors should compare their improved reaction times to previous reports, which does seem to be significantly shorter than reference 4f. In Table 1 this is also apparent since the catalyst Co-N/AC (same prep as ref 4f) and Co-N-Si/AC (this work) shows a 28 % increase in yield at 3 h.
However, in its current form the manuscript only provides a route to a catalyst which performs comparatively similar with a previous report. The authors could provide a comparison of their results with previous literature, which lacked throughout, this would improve the manuscript.
Response 1: Many thanks for your comments. What you said is very reasonable, indeed there are some similarities between our manuscript and Jagadeesh's paper, including the types of catalytic reactions and the preparation process of catalysts. At first, when we are in the preparation of catalyst, also tried a lot of kinds of preparation methods, including the replacement of different nitrogen ligand, different calcination temperature, different doses of the ligand, different metal, and different carriers, finally finding that among a lot of practice operation, the preparation of catalytic materials to the catalytic effect of esterification reaction reported in the article is the best. In addition, we also tried other types of various reactions and got good results.
Compared with the previously work reported by Jagadeesh, the catalytic material prepared by us has better catalytic performance, such as shorter reaction time and lower reaction temperature. The description of this feature has been added to line 57-59 of the manuscript. Moreover, the introduction of silicon promotes the catalytic activity of the catalyst. The text of this paragraph is described in lines 133-140 of the article.
- Figure 1 - The elemental mapping should have scale bars on all plots, without them, the distribution can be misleading.
Response 2: Thanks a lot for your constructive suggestions. Figure 1, we have changed the elemental mapping with scale bars on all plots and high resolution.
- Figure 2 - The XPS plots and data need to be improved for clarity. The data points displayed in the manuscript are not clear, and seem to have faded out. The assignment is therefore questionable.
Response 3: Many thanks for your comments. Figure 2, we have improved the clarity of the XPS plots and data. Thank you very much for your advice.
- Line 95 and 103 - Change the word 'owned'
Response 4: Many thanks for your comments. Line 95 and 103, we have changed the word ‘owned’ by ‘possessed’.
Once again, thank you very much for your comments and suggestions.
Sincerely yours,
Changjian Zhou
2021-10-30
Round 2
Reviewer 1 Report
The contents of manuscript was substantially improved. The mechanism of esterification reaction is well documented.
Reviewer 2 Report
I have read the revised version of the paper and found it much improved and that my comments have been satisfactorily addressed, hence I recommend the paper for publication.
