Synthesis of Eugenol Ethyl Ether by Ethylation of Eugenol with Diethyl Carbonate over KF/γ-Al2O3 Catalyst
Round 1
Reviewer 1 Report
In this manuscript, the authors prepared several heterogeneous catalysts using Lewis bases such as KF, CH3COOK, KOH, and K2CO3 loaded on γ-Al2O3 via wet impregnation. These catalysts were then applied to the O-ethylation reaction of DEC and Eugenol to produce Eugenol ethyl ether. The KF-γ-Al2O3 catalyst was found to be the most effective for the O-ethylation reaction. The catalyst was characterized using various techniques, and the catalyst preparation process was optimized by studying the impregnation temperature, impregnation concentration, impregnation time, and calcination temperature. Finally, the formed Eugenol ethyl ether was characterized using H-NMR, FTIR, and MS analysis, and a proposed mechanism for its formation was presented.
I have serious concerns about the scientific soundness and merit of the work, as well as the usefulness of the results obtained. In addition, I would like to point out the following issues:
1. The authors did not provide a clear rationale for choosing the Lewis bases that they used.
2. The experimental methods used to prepare and characterize the catalysts were not well-described.
3. In the first line of the introduction, write the chemical formula of Eugenol ethyl ether and isoeugenol ethyl ether.
4. In lines 33-35, the sentence "The traditional EEE......to......ethyl halide) [4]" is repeated. Remove the repeated sentence.
5. In line 38, write the chemical formula of Diethyl carbonate and show its chemical structure within the text.
6. In line 40, merge the number of references [6, 7].
7. In section 2.2.1, Catalysts Preparation, mention the idea behind drying the catalyst at 100 °C then at 150 °C.
8. In section 2.2.6, lines 121-129:
a. Give a number for each equation in the manuscript and cite it in the text.
b. In line 129, the authors mentioned that "n: theoretical molarity of eugenol ethyl ether, mol" which is wrong; the molarity should be mol/L.
c. Please revised equation 2 “ Eugenol ethyl ether yield (%)” I suppose it is a wrong equation.
d. Please provide a reference for these equations. The authors could cite a reference for the general equation for yield.
9. Line 127, the authors mentioned "w: content of eugenol ethyl ether in the product, %, detected by GS". It should be detected by GC not GS.
10. Which method was used to quantitate the amount of converted eugenol and the formed eugenol ethyl ether by GC, such as standard calibration curve, internal standard...? The authors should clarify which method they used.
11. Nothing mentioned in the experimental part regarding the section 3.1, a- did the authors prepared these materials (CH3COOK-γ-Al2O3, KOH-γ-Al2O3, and K2CO3-γ-Al2O3) under the same conditions as KF-γ-Al2O3. If yes, the preparation process especially the calcination temp. could affect the activity of these materials. As the authors mentioned that they optimized the reaction conditions with the KF-γ-Al2O3, in my opinion, similar comparison should be made for other materials.
b- The authors should explain why they used acetate and carbonate ions as Lewis bases, even though these ions are known to degrade at higher temperatures. The authors could also discuss how they chose the specific concentrations of acetate and carbonate ions that they used in their experiments.
12. The caption of figure 2 did not mention the reaction conditions. The authors should mention the reaction conditions in the text, such as the temperature, time, and catalyst loading.
13. The resolution of all the figures in the manuscript is very bad, all the figures are blurry.
14. The paragraph from line 161 to 170 needs to be rewritten. There are many repetitions and the author's meaning is not clear.
15. in section 3.2.1
a- The author concluded the catalyst impregnated at room temperature is poorly effective and recommended 50 °C. However, in the experimental part, the author stated that they prepared the KF-γ-Al2O3 catalyst at room temperature.
b- The calcination temperature in this section is 400 °C, but in the experimental part, the author used 800 °C.
16. In line 178, the author mentioned Figure 6. This should be Figure 4.
17. The author mentioned in lines 186-187 that “the more isomerization of the allyl groups in eugenol increases”. However, the author did not detect the formation of isomerization of the allyl groups during their investigation. Therefore, it is not appropriate to write in line 188 that this conclusion is similar to the work of other researchers. Additionally, according to Reference 14, isomerization takes place under neutral conditions, as mentioned in References 415 and 416 in the same reference.
18 In line 182, the author mentioned that increasing the percentage of KF reduces the surface area. However, the author did not provide any values for the surface area to support this hypothesis.
19. In Section 3.2.3, the author discussed the results of Figure 5, not Figure 7 as mentioned in line 193.
20. In Section 3.2.4, line 215, the author stated that "This is due to it is easy to bond KF with γ-Al2O3 since it melts at high temperature." This sentence is unclear. The melting point of KF is around 860 °C, and the author mentioned that they found that 450 °C is the best calcination temperature. Therefore, it is unclear what the author means by this explanation.
21. According to the presented data, the author found that the optimum conditions for preparing the KF-γ-Al2O3 catalyst are: 40% impregnation concentration, 50 °C impregnation temperature, 8 hours impregnation time, and 450 °C calcination temperature. However, the conditions in Section 2.2.1 of the experimental part are completely different. For which catalyst did the author use this procedure?
22. The X-ray diffraction (XRD) results in Figure 8 are not clear. Additionally, the XRD diffraction for eugenol, EEE, Al2O3 before and after the preparation should be included in the figure.
23. The scanning electron microscope (SEM) image in Figure 9 is not clear. It is not possible to distinguish between the catalyst and the substrate. Therefore, it is not possible to conclude that the increased surface roughness of KF/γ-Al2O3 is related to the homogeneous coverage of KF on the surface of γ-Al2O3, as the author mentioned in lines 273-274. The surface of the catalyst in Reference 20, Hoo et al., is completely different from the author's catalyst.
24. What is the effect of calcining the catalyst at 800 °C on the phase of γ-Al2O3?
25. How did the author distinguish the formation of CO2?
Extensive editing of English language required
Author Response
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Reviewer 2 Report
In this paper, the authors reported the effects of catalyst active component, impregnation temperature, KF impregnation concentration, impregnation time, and calcination temperature on catalyst performance. The results showed that the KF/γ-Al2O3 catalyst can adequately facilitate the conversion of eugenol to EEE. The work is interesting and worth publications after following revisions:
1) The stabiltiy of the catalyst after reaction is important. is the structure stable?
2) Will KF affect the surface area of Al2O3? More discussions are needed.
3) What is the purity of the products?
4) Related references may be cited, such as DOI: 10.3866/PKU.WHXB202212060ï¼›DOI: 10.3866/PKU.WHXB202212065ï¼›
GOOD
Author Response
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Round 2
Reviewer 1 Report
After considering the revised manuscript of Zhang et al., it is clear that the authors did not enhance the manuscript according to the reviewers' comments. Several points of the reviewer's comments are not covered in an acceptable manner. In my opinion, the manuscript still needs many corrections before it can be accepted for publication in the Catalysts journal. A major revision is necessary for covering the following points.
1- Comment 1: The authors did not provide a clear rationale for choosing the Lewis bases that they used.
The authors’ response to this point is not logical, they mention the reaction conditions, why?
2- Comment 8:
a- I still convince that the equation should be numbered.
The authors can write the following :
2.2.6. Eugenol ethyl ether yield analysis
The conversion, yield, and selectivity of EEE were calculated according to equations (1-3), as follows:
c and d- Equation 2 (Eugenol ethyl ether yield (%)) is still wrong
According to the provided equation:
Eugenol ethyl ether yield (%) = (mass(g) * content in %)/ n (mol.L-1) *100%
The final unit will be ( g. mol-1. L) %2 ???!!
If the authors used this equation in their calculation, I recommend reviewing all the calculations in the manuscript.
The authors should note that it is not necessary to cite an article that used these equations to calculate the conversion, yield, and selectivity of the EEE, you can used another references that used these equations to perform these calculations.
I suggest the authors to check these equation in the following references and cite them in the text: 10.1021/acscatal.9b03322, and 10.1021/acscatal.0c01713.
3- Comment 11: the response of the authors for point (a) is very weak, this part is very confusing for the reader.
a. Did the authors prepare these catalysts?
b. If yes, mention the procedure!
c. At which calcination temperature did the authors prepared these materials (CH3COOK-γ-Al2O3, KOH-γ-Al2O3, and K2CO3-γ-Al2O3).
4- Comment 11 b- the reviewer did not understand the authors response, this answer is not a scientific answer?!!
5- Comment 12- in scientific writing, the experimental conditions should be written as a description after each experimental figure.
6- Comment 18- if the authors did not provide the surface area, they should modified the main text or provide a reference to support there hypothesis.
7- Comment 20: line 222 does not belong to this point!
8- Comment 21: the answer is not accepted.
9- Comment 23: what is the relation between the authors catalyst (KF/γ-Al2O3) and the cobalt–phosphorous catalysts?!
Extra comments:
10- The citation of many figures in the text is wrong, such as figure 4 and figure 8, figure 9, figure 11,…
11- If the authors, as they claim, that they prepare the catalyst (KF/γ-Al2O3) according to their previous procedure ( the one mentioned in the previous copy of the manuscript before the revision), why they did not present the data in the previous manuscript?
12- In the procedure (section 2.2.1), the calcination temperature of the first prepared catalyst or catalysts does not mentioned, why?
13- In section 3.1, at which calcination temperature these catalysts were prepared? And why the authors chose that temperature?
14- What is the added value behind section 3.1?
15- Added more space between the compounds in figure 1.
16- Why the Eugenol in Figure 1 has a (+) charge, it is not a cation.
I want to point out that the design of the manuscript is very confusing and the authors did not revise their manuscript in the right way. I suggest the authors revise the experimental part very well and mention the right procedures for preparing the catalysts that they used. Then in the results and discussion part, they should tell the readers what they do as a story starting from the prepared catalysts and then go to the optimization of the conditions of the reaction which leads to enhanced selectivity. Besides, in my opinion, section 3.1 does not add any value to this manuscript, the authors should just focus on presenting the first data that they collect after testing the activity of the KF/γ-Al2O3. Then present the data after each optimization process.
Moderate editing of English language required
Author Response
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Author Response File: 
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