Photocatalyzed Oxygenation Reactions with Organic Dyes: State of the Art and Future Perspectives
Round 1
Reviewer 1 Report
This review “Organic dyes promoted photooxygenations: prospectives and perspectives” summarizes the most recent literatures on organo-photocatalysis applications to promote selective oxygenation of organic substrates. In recent years, organic dyes have been emerging as powerful metal-free photocatalysts. Compared with metal photocatalysts, organo-photocatalysts proved to be highly efficient in catalytic terms, with similar or even superior performances, while maintaining a low environmental impact. Therefore, organo-photocatalysis is a significant and timely subject, which will be of great value to the readers of Catalysts. The literature review/citations are appropriate and comprehensive. overall, this review can be accepted for publication after a few minor revisions.
1. Although the authors provide a nice summary of organo-photocatalysis, the future directions and challenges that must be overcome should be proposed.
2. What’s the advantages of organo-photocatalysis compared to other metal-free photocatalysts? Such as C3N4.
3. There are some grammatical errors and formatting issues in the manuscript. I advise the authors check it carefully and revise them.
Author Response
Reviewer 1
- Although the authors provide a nice summary of organo-photocatalysis, the future directions and challenges that must be overcome should be proposed.
We thank the referee for the interesting suggestion. We added in the conclusions the future perspectives of organic photocatalysis, with the challenges to be addressed (lines 512-529).
- What’s the advantages of organo-photocatalysis compared to other metal-free photocatalysts? Such as C3N4.
We implemented the introduction part discussing about the advantages of using organic dyes photocatalysts with respect to graphitic carbon nitride, as suggested by the referee (lines 51-58). Refs. 22-24 have been added in the text.
- There are some grammatical errors and formatting issues in the manuscript. I advise the authors check it carefully and revise them.
We rechecked the text, and we corrected some typos, as indicated by the referee.
Reviewer 2 Report
Reviewer’s Comments:
The manuscript “Organic dyes promoted photooxygenations: prospectives and perspectives” is very interesting work. This paper investigates the oxygen atom incorporation into organic molecules is one of the most powerful strategies to increase their pharmacological activity and to obtain valuable intermediates in organic synthesis. Traditional oxidizing agents are very performing but their environmental impact and their low selectivity constitute significant limitations. On the contrary, visible light-promoted oxygenations represent a sustainable method for oxidizing organic compounds, since only molecular oxygen and a photocatalyst are required. Therefore, photocatalytic oxygenation reactions exhibit very high atom-economy and eco-compatibility. This mini-review aims to collect and analyze the most recent literature on organo-photocatalysis applications to promote selective oxygenation of organic substrates. However, the following issues should be carefully treated before publication.
1. The title of the manuscript is not impressive so rewrite the title.
2. In the abstract, the author should add more scientific findings.
3. Keywords: the synthesized system is missing in the keywords. So, modify the keywords.
4. In the introduction part, the introduction part is not well organized and cited references should cite recently published articles such as 10.1016/j.jece.2021.105534, 10.3389/fchem.2022.975355
5. Introduction part is not impressive and systematic. In the introduction part, the authors should elaborate on the scientific issues in Organic dyes research.
6. Organic dyes promoted photooxygenation processes…, The author should provide reason about this statement “Remarkably, no over-oxidation to benzoic acid occurred, demonstrating the high selectivity of the reaction”.
7. The authors should explain regarding the recent literature why “However, 365 nm UV irradiation and tetrabutylammonium borohydride (TBABH) additive were required to promote oxygenation reaction”.
8. Alkynes Oxygenation to 1,2-Diketones. The author should explain the latest literature “Reactions were performed in DCM:DMF (2:1 v/v), in presence of 0.5 equivalents of trifluoroacetic acid (TFA), and 2 equivalents of biphenyl co-sensitizer (BP)”.
9. The author should provide reason about this statement, “Molecular oxygen and visible light were the required reagents to afford aliphatic, cyclic, diaryl and heteroaromatic sulfoxides with high yields (91 - >99%), in short reaction times (1-2 hours), using 0.5% KuQ photocatalyst”.
10. Comparison of the present results with other similar findings in the literature should be discussed in more detail. This is necessary in order to place this work together with other work in the field and to give more credibility to the present results.
11. The conclusion part is very week. Improve by adding the results of your studies.
Author Response
- The title of the manuscript is not impressive so rewrite the title.
We changed the title accordingly.
- In the abstract, the author should add more scientific findings.
We modified the abstract according to referee’s suggestions. In particular, we mentioned the photocatalysts analyzed in the review, together with the oxygenation reactions under study (lines 16-18). In addition, the general findings are briefly summarized in the final part of the abstract (lines 18-23).
- Keywords: the synthesized system is missing in the keywords. So, modify the keywords.
In this review, we analyzed 10 classes of reactions, therefore it was not possible to include in the keywords all the mentioned systems. However, we have changed some keywords, thus including the most used organic-photocatalysts involved in the review.
- In the introduction part, the introduction part is not well organized and cited references should cite recently published articles such as 10.1016/j.jece.2021.105534, 10.3389/fchem.2022.975355
- Introduction part is not impressive and systematic. In the introduction part, the authors should elaborate on the scientific issues in Organic dyes research.
We thank the referee for the interesting suggestions in points 4 and 5. We have organized the introduction part starting with a general overview on photocatalysis, followed by limitations related with the use of the widely adopted metal-photocatalysts. Afterwards, a brief introduction to metal-free photocatalysts has been presented, highlighting the advantages of organic dyes in this field. To conclude, a focus on photooxygenation reactions, which is the topic of the review, has been reported.
However, we implemented the introduction as suggested also by Referee 1 (lines 51-58). We added one of the references suggested by referee 2 (ref. 21: Front. Chem. 2022, 10, 975355) but we preferred to not add the other one, because it is not related with organic transformations, but it deals with environmental remediation applications of modified carbon nitride photocatalyst.
- Organic dyes promoted photooxygenation processes…, The author should provide reason about this statement “Remarkably, no over-oxidation to benzoic acid occurred, demonstrating the high selectivity of the reaction”.
As indicated in the text, the mild reaction conditions adopted in such light-driven oxygenation allowed to afford remarkable selectivity to the carbonyl product and no over-oxidation was observed by the authors. More details can be found in the cited paper (ref. 40).
- The authors should explain regarding the recent literature why “However, 365 nm UV irradiation and tetrabutylammonium borohydride (TBABH) additive were required to promote oxygenation reaction”.
The role of TBABH (that acts as a phase-transfer catalyst) was added in the text (line 129). In the original paper (ref. 44) authors also demonstrate that reactions performed at different wavelengths led to low yields. Indeed, being a brief review, we decided to not include in the text the experimental details, that can be found in the cited paper(s).
- Alkynes Oxygenation to 1,2-Diketones. The author should explain the latest literature “Reactions were performed in DCM:DMF (2:1 v/v), in presence of 0.5 equivalents of trifluoroacetic acid (TFA), and 2 equivalents of biphenyl co-sensitizer (BP)”.
The role of the additives was added in the text (line 246). As underlined in point 7, we preferred to not add in the text the reaction conditions optimization and other experimental details, that can be easily found in the cited paper (ref. 63).
- The author should provide reason about this statement, “Molecular oxygen and visible light were the required reagents to afford aliphatic, cyclic, diaryl and heteroaromatic sulfoxides with high yields (91 - >99%), in short reaction times (1-2 hours), using 0.5% KuQ photocatalyst”.
See points 7 and 8.
- Comparison of the present results with other similar findings in the literature should be discussed in more detail. This is necessary in order to place this work together with other work in the field and to give more credibility to the present results.
In this review, the activity of different organic photocatalysts has been compared for each class of reactions; comparisons with other catalysts in the text, being the focus of the review organic photocatalysts, in our opinion is not appropriate.
Nonetheless, we added in the introduction part a comparison between organic dyes photocatalysts with other metal-free photocatalysts reported in the literature (as C3N4).
- The conclusion part is very week. Improve by adding the results of your studies.
The conclusion part has been implemented, following indications of all the reviewers.
Reviewer 3 Report
The review article “Organic dyes promoted photo oxygenations: prospectives and perspectives” by Federica Sabuzi et al. have very briefly elaborated the historical prospective and recent development in this field. The field is relatively new and very promising from atom economy and green chemistry perspective. The review article is indeed very nicely written and will be helpful to get a concise information to the readers as this topic has not been covered.
The authors have covered all important substrate specific oxygenation protocols promoted by specific organic dye under suitable light wavelength. The mechanistic detail, substrate scope, yield, specificity and other reaction parameters have been elaborated in an orderly manner with suitable reaction schemes and reaction flow charts. A total of 130 references have been reviewed in this mini review, which is quite good.
At the end, I would expect one subsection (before conclusion part) to elaborate a future perspective of this field where the authors may highlight the scope of further development sought in this field. Especially with respect to metal catalyst based oxygenations, what further developments are expected.
Overall, this review article is very informative and nicely written, so it may be accepted for publication after the required revision.
Author Response
At the end, I would expect one subsection (before conclusion part) to elaborate a future perspective of this field where the authors may highlight the scope of further development sought in this field. Especially with respect to metal catalyst based oxygenations, what further developments are expected.
We thank the referee for the suggestion. We added in the conclusions the future directions and challenges that must be overcome in organic dyes promoted photocatalytic processes.
