Chitosan Capped Copper Oxide Nanocomposite: Efficient, Recyclable, Heterogeneous Base Catalyst for Synthesis of Nitroolefins

Round 1

Reviewer 1 Report

This article is devoted to the preparation and study of a nanocomposite based on copper oxide coated with chitosan. The article is written in understandable language. It contains a large amount of experimental data. The advantage is the practical application of the obtained catalyst, as well as various research methods. There are some fixes to consider:

1. Increase the quality of your drawings. On some, numbers and text are completely unreadable.

2. Unify the drawings.

3. Has the IR spectra been normalized?

4.XRD. mark the main peaks in the figure. This will help readers understand the content better.

5. Table 1. In the column "EtOH-H2O" it is desirable to indicate the ratio in brackets.

6. "Nature of Solvent" is described modestly. It is desirable to add more comparison with data from the literature in the description.

7. In principle, in most descriptions of experimental results, it is desirable to add more comparisons with literature data. This will allow us to trace the dynamics and draw more fundamental conclusions.

8. It is also desirable to cite: 10.1016/j.molstruc.2021.131083.

Author Response

Responses to the reviewer comments

Authors would like to thank the reviewer for his valuable comments.

Please see the following table of our responses, corrections and explanation based on the reviewer comments.

	Reviewer 1 Comments	Our Reply
1	Increase the quality of your drawings. On some, numbers and text are completely unreadable.	Ok, drawings with better resolution are added.
2	Unify the drawings.	Ok, the drawings are unified
3	Has the IR spectra been normalized?	Ok, IR spectra are revised and it is used only for comparison.
4	XRD. mark the main peaks in the figure. This will help readers understand the content better.	Ok, the main peaks are marked in the figure.
5	Table 1. In the column "EtOH-H2O" it is desirable to indicate the ratio in brackets.	Has been addressed
6	"Nature of Solvent" is described modestly. It is desirable to add more comparison with data from the literature in the description.	Effect of solvent was described in detail in table 1
7	In principle, in most descriptions of experimental results, it is desirable to add more comparisons with literature data. This will allow us to trace the dynamics and draw more fundamental conclusions.	Actually, the use of CuO as heterogenous catalyst in organic synthesis is very limited, and the available reported articles are mentioned in the introduction part. Herein, the novelty is to use the chitosan-CuO as an efficient catalyst in the selected organic reactions.
8	It is also desirable to cite: 10.1016/j.molstruc.2021.131083.	Unfortunately, the suggested article is not related to our interest in this article.

 

Reviewer 2 Report

The article numbered 1874820 and submitted for the publication in the journal Catalysts, describes the preparation of chitosan copper oxide nanocomposites to be used as heterogeneous base catalysts for the synthesis of nitroolefins. Previously, this type of hybrid nanocomposites has already been largely investigated by the corresponding author, and therefore the novelty of the topic is tiny, although the catalytic application appears to be slightly more original.  

Anyway, the topic fits well with the type of journal and this article, downstream of a number of major critical points to be resolved, hereafter highlighted, may be published in Catalysts:

 

_ It is unclear why the authors used a microwaves reactor for the preparation of the catalysts, but they are silent about the role this technique played in their synthesis...!!!

In other words, what are the effects due to the different irradiation powers and reaction times used on the chemical and physical nature of their samples? This point needs to be clarified in the revised work.

 

_ Authors describe two different methods for the synthesis of nitroolefin (A and B, paragraph 2.3) but in the text they never make a comparison between method A (the blank test?) and method B (the catalytic reaction) in terms of yield and selectivity of the process.

 

_ In the 3.1.1 paragraph (FTIR study), authors should better clarify the wavenumber assignments of the different peaks, and don’t generally state.... “.... is strong evidence for structural changes caused by the incorporation of copper oxide nanoparticles”. In fact, this technique proves to be very relevant for the confirmation of the expected experimental data.

 

_ In figure 3B, the magnification of the SEM figure does not allow one to verify the claim made by authors that “... the image of CS-CuO nanocomposite (B) exhibited distinct modifications due to coordination with CuO molecules that are uniformly dispersed over the chitosan surface.” Maybe a greater magnification would allow it.

 

_ One most important point: as known, the energy dispersive spectroscopy (EDS) technique is mostly used for qualitative analysis of materials, even if can provide semi-quantitative results as well. In order to measure in a quantitative way, the amount of active metal like Cu contained in the catalysts, authors need to use either ICP-MS (inductively coupled plasma mass spectrometry) or ICP-OES (Optical Emission spectroscopy) techniques: these data should be added in the revised version. After this, the authors should report the loading factor (LF), defined as mmol of active species immobilized per gram of support, in order to define the stoichiometric ratio of the catalyst with respect to the substrate, really employed in all the catalytic experiments: this crucial point need to be explicited in the revised version.

 

_ In the 3.2.1.1 paragraph, authors stated that toluene gave the lowest catalytic results. From results showed in Table 1, it seems instead that THF was the worst solvent...: wasn't it?

 

_ there is a discrepancy between the percentages of the ethanol-water mixture, used as solvent, cited in different parts of the manuscript: please check it.

 

_ Concerning the scope of the reaction (Table 2), the authors should discuss more deeply the results obtained in consequence of the different types of reagents used. For example, the results obtained in the entry 3 of Table 2, should be compared with those observed using nitroethane instead of nitropropane, for detect the role, if any, exerted by steric factors.

 

_ If we consider the moderate yields of the nitroaldol reaction, showed in Table 2, it would be appropriate to indicate the nature of the main observed by-products.

 

_ In the scheme of Table 2, the products should be renumbered as 1b-i, instead of 1a, already used for the product of scheme 2.

 

_ For what concerns the recyclability, the authors should clearly indicate how the catalyst was recycled, after each run.

 

 

Minor typos:

 

Line 36: change “cos of” with “because of”;

Line 48: change “...due to its unique...” with “due to their unique”;

Line 51: capitalize the first letter in “copper”;

Line 225: change “without any loss” with “with minor loss”;

Line 235: change “that present” with “that are present”

 

Author Response

Responses to the reviewer comments

Authors would like to thank the reviewer for his valuable comments.

Please see the following table of our responses, corrections and explanation based on the reviewer comments.

	Reviewer 2 Comments	Our Reply
1	It is unclear why the authors used a microwaves reactor for the preparation of the catalysts, but they are silent about the role this technique played in their synthesis...!!! In other words, what are the effects due to the different irradiation powers and reaction times used on the chemical and physical nature of their samples? This point needs to be clarified in the revised work.	Actually, based on our previous preparation for this catalyst, we have noticed that the metal oxide incorporation within the polymer matrix was better under microwave irradiations.
2	Authors describe two different methods for the synthesis of nitroolefin (A and B, paragraph 2.3) but in the text they never make a comparison between method A (the blank test?) and method B (the catalytic reaction) in terms of yield and selectivity of the process.	Ok, the comparison between ammonium acetate and CS-CuO is mentioned in the Results and Discussion section 3.2.1
3	In the 3.1.1 paragraph (FTIR study), authors should better clarify the wavenumber assignments of the different peaks, and don’t generally state.... “.... is strong evidence for structural changes caused by the incorporation of copper oxide nanoparticles”. In fact, this technique proves to be very relevant for the confirmation of the expected experimental data.	Actually, the obtained IR peaks in the spectra are discussed and the main structural differences between chitosan, CuO, and the hybrid material are clarified. Anyhow, more explanation is added to clarify this point.
4	In figure 3B, the magnification of the SEM figure does not allow one to verify the claim made by authors that “... the image of CS-CuO nanocomposite (B) exhibited distinct modifications due to coordination with CuO molecules that are uniformly dispersed over the chitosan surface.” Maybe a greater magnification would allow it.	SEM images of greater magnification is added.
5	One most important point: as known, the energy dispersive spectroscopy (EDS) technique is mostly used for qualitative analysis of materials, even if can provide semi-quantitative results as well. In order to measure in a quantitative way, the amount of active metal like Cu contained in the catalysts, authors need to use either ICP-MS (inductively coupled plasma mass spectrometry) or ICP-OES (Optical Emission spectroscopy) techniques: these data should be added in the revised version. After this, the authors should report the loading factor (LF), defined as mmol of active species immobilized per gram of support, in order to define the stoichiometric ratio of the catalyst with respect to the substrate, really employed in all the catalytic experiments: this crucial point need to be explicated in the revised version.	Unfortunately, only EDS is available for semi-quantitative methodology to estimate the metal amount inside the polymer matrix. Thus, we rewrite the calculated amount as approximate value. Actually, the calculated amount should be 15% wt. and EDS gave approximate value.
6	In the 3.2.1.1 paragraph, authors stated that toluene gave the lowest catalytic results. From results showed in Table 1, it seems instead that THF was the worst solvent...: wasn't it?	The paragraph has been corrected
7	there is a discrepancy between the percentages of the ethanol-water mixture, used as solvent, cited in different parts of the manuscript: please check it.	The ethanol-water (70% solution) has been checked throughout the manuscript
8	Concerning the scope of the reaction (Table 2), the authors should discuss more deeply the results obtained in consequence of the different types of reagents used. For example, the results obtained in the entry 3 of Table 2, should be compared with those observed using nitroethane instead of nitropropane, for detect the role, if any, exerted by steric factors.	Thanks for suggestion. Actually, to do such comparison between nitroethane and nitropropane, they must be reacted to same aldehyde. Which is not done during the current work
9	If we consider the moderate yields of the nitroaldol reaction, showed in Table 2, it would be appropriate to indicate the nature of the main observed by-products.	Unfortunately, by products has not been investigated during this study
10	In the scheme of Table 2, the products should be renumbered as 1b-i, instead of 1a, already used for the product of scheme 2.	Has been addressed
11	For what concerns the recyclability, the authors should clearly indicate how the catalyst was recycled, after each run.	Ok, the way of recyclability is added. See the experimental part, method B
12	Minor typos: Line 36: change “cos of” with “because of”; Line 48: change “...due to its unique...” with “due to their unique”; Line 51: capitalize the first letter in “copper”; Line 225: change “without any loss” with “with minor loss”; Line 235: change “that present” with “that are present”	All the typos are corrected

 

Round 2

Reviewer 1 Report

Accepted 

Reviewer 2 Report

The authors' answers on several essential aspects of the research, outlined in the previous report, were evasive or completely unsatisfactory, thus compromising the overall quality of the work!