One-Pot Solvent-Free Synthesis of N,N-Bis(2-Hydroxyethyl) Alkylamide from Triglycerides Using Zinc-Doped Calcium Oxide Nanospheroids as a Heterogeneous Catalyst
Round 1
Reviewer 1 Report
In the manuscript titled, “One-pot solvent-free synthesis of N,N-Bis(2-hydroxyethyl) alkylamide from triglycerides using transition metal-doped CaO, MgO and ZnO nanospheroids as a heterogeneous catalyst”, the authors reported the solvent free synthesis of fatty acid amides from triglycerides using zinc doped calcium oxide nanospheroids as heterogenous catalysts. The authors did a detailed study about the catalytic activity that includes kinetic study and structural analysis of the catalyst by XRD. Though similar transformations such as transesterification by the same catalytic system and aminolysis using sodium doped calcium oxide nanoparticles were reported by the authors earlier, this is a new study with the known catalytic system. This work is novel enough to be published in the journal catalysts. However, there are certain concerns that were listed below and need to be addressed by authors before getting accepted for publication.
In the title, it was mentioned that transition metal doped CaO, MgO and ZnO nanospheroids as heterogeneous catalysts were used for the aminolysis. But the study is all about the aminolysis using zinc doped calcium oxide nanoparticles as catalysts. Hence the title is misleading and please change it to zinc doped calcium oxide nanospheroids as heterogenous catalysts.
It was mentioned in the structural analysis of catalyst, that at 400 ˚C calcium oxide exists in both cubic and hexagonal phases and that might be the reason for the enhancement of basic strength. Please justify this conclusion. Also, make a comment on how it is responsible for high catalytic activity when compared to other calcination temperatures.
3. There are several grammatical mistakes and typos throughout the manuscript. Please go through the entire manuscript and address them.
Author Response
Response to Reviewer 1 Comments
In the manuscript titled, “One-pot solvent-free synthesis of N,N-Bis(2-hydroxyethyl) alkylamide from triglycerides using transition metal-doped CaO, MgO and ZnO nanospheroids as a heterogeneous catalyst”, the authors reported the solvent-free synthesis of fatty acid amides from triglycerides using zinc doped calcium oxide nanospheroids as heterogeneous catalysts. The authors did a detailed study about the catalytic activity that includes kinetic study and structural analysis of the catalyst by XRD. Though similar transformations such as transesterification by the same catalytic system and aminolysis using sodium doped calcium oxide nanoparticles were reported by the authors earlier, this is a new study with the known catalytic system. This work is novel enough to be published in the journal catalysts. However, there are certain concerns that were listed below and need to be addressed by authors before getting accepted for publication.
We thank the reviewer for giving the perceptive review and positive feedback for the reported work.
Point 1: In the title, it was mentioned that transition metal-doped CaO, MgO and ZnO nanospheroids as heterogeneous catalysts were used for the aminolysis. But the study is all about the aminolysis using zinc doped calcium oxide nanoparticles as catalysts. Hence the title is misleading and please change it to zinc doped calcium oxide nanospheroids as heterogeneous catalysts.
Response 1: Though we have prepared catalysts with other transition metals but agree with the reviewer that the title should be changed to zinc doped calcium oxide nanospheroids as heterogeneous catalysts. Now the title of the revised manuscript has been changed to “One-pot solvent-free synthesis of N,N-Bis(2-hydroxyethyl) alkylamide from triglycerides using zinc doped calcium oxide nanospheroids as a heterogeneous catalyst”.
Point 2: It was mentioned in the structural analysis of catalyst, that at 400 ˚C calcium oxide exists in both cubic and hexagonal phases and that might be the reason for the enhancement of basic strength. Please justify this conclusion. Also, make a comment on how it is responsible for high catalytic activity when compared to other calcination temperatures.
Response 2: As point it out by a reviewer, at 400 °C we have found that the Zn doped CaO exists in both cubic and hexagonal phases. Here, the existence of hexagonal phase related to the appearance of hydroxide groups (-OH groups) and the formation of Ca(OH)2. Because of the emergence of hydroxide groups, there was an increase in the basic strength and which in turn was one of the reasons for higher catalytic activity.
Point 3: There are several grammatical mistakes and typos throughout the manuscript. Please go through the entire manuscript and address them.
Response 3: We thank the reviewer for pointing out important mistake. We have checked the revised manuscript for typos and grammatical mistakes with the help of native speaker and also with online software ‘spellchecker’ and ‘Grammarly’. We hope now it will meet the journal standards.
Reviewer 2 Report
Please see the file attached
Comments for author File: 
Comments.pdf
Author Response
Response to Reviewer 2 Comments
Point 1: After reading the manuscript entitled "One-pot solvent-free synthesis of N,N-Bis(2-hydroxyethyl) alkylamide from triglycerides using transition metal-doped CaO, MgO and ZnO nanospheroids as a heterogeneous catalyst" (authors: D. Kumar , C. H. Park and C. S. Kim), I consider the manuscript could be publishable after some important improvements to the manuscript.
Response 1: We thank the reviewer for giving insightful and positive feedback for presented work.
Point 2: I am really in doubt about correctness of the discussion on the "improvement of the basic strength of CaO ... with increase in calcination temperature to 400 °C ...due to appearance of strong basic (OH group) sites" (page 2, subsection 2.1). In Kumar's earlier paper authors state that "The main problem...commercially available CaO is its moisture sensitivity ...". OH groups are introduced by adsorption of water what converts CaO to Ca(OH)2. According to the described process of the catalyst preparation, it is expected that authors do have CaO in the form of hydroxide even at room temperature and that dehydration takes place at the elevated temperatures. Indeed, authors do refer to their previous findings [ref. 32] where they observed dehydration at 450 °C and above while having Ca(OH)2 structure at lower temperatures. Based on this, I believe that authors ment "due to presence of strong basic groups", but I would say that increase in activity is due to partial dehydration and strong increase in surface area of the catalyst upon calcination at 400 °C.
Response 2: As suggested by reviewer we have made the changes in the discussion in the revised manuscript. Now the modified sentence in the discussion is, “The improvement of the basic strength of CaO after zinc ion doping with the increase in calcination temperature up to 400 °C could be due to the partial dehydration and strong increase in the surface area”.
Point 3: Second issue is the claim that, besides surface area, basicity of X-Zn/CaO-T catalysts is responsible for higher reactivity. According to the Figure 4c, catalysts with 2, 3 and 4 % of Zn dopant leads to similar activity. The data in Table 1 imply somewhat higher pKa of 2-Zn/CaO-400 than 3-Zn and 4-Zn catalysts while having similar surface area. In my opinion, authors should refrain from basicity/activity relation unless they can measure pKa more precisely and confirm it by some correlation.
Response 3: As correctly suggested by the reviewer we have refrain basicity/activity relation in figure 4c in the revised manuscript.
Point 4: Third problem is the last paragraph on the page 5. Authors analyzed amidation process of waste cotton seed oil (WCSO) by diethanolamine (DEA) by 1H-NMR which is, indeed, the appropriate technique. This particularly relates to the last sentence about "absence of the proton signals at 5.32 ppm in the case of methyl laurate..." and its amide derivative. Laurate does not have double bond and the corresponding statement is meaningless. Authors also point out "disappearance of glycerydic proton signals at 4.13, 4.3 and 5.32 ppm...". The last-mentioned one comes from double bond and it does not disappear as reaction proceeds (see Fig.3b(ii)).
Response 4: We thank the reviewer for highlighting critical mistakes. We have omitted the said statement about methyl laurate. The reviewer is right that there was the disappearance of glyceridic proton signals only at 4.13 and 4.30 ppm and not at 5.32 ppm. We have made the changes accordingly in the revised manuscript.
Point 5: I am very surprised about temperature limit at 90 °C. That would mean diffusion control of the reaction rate. Figure 5b referred in the text does not prove anything related to the reaction kinetics. It only gives information related to the maximal yield. In other words, reaction is finished after given time period regardless whether the temperature is 90 °C or higher. It would be interesting to see this Figure created from the data obtained after 5, 15 and 30 min of the reaction.
Response 5: We agree with the reviewer that the data presented in said figure created some sort of confusion. We do perform reactions to optimize the reaction temperature with regular time intervals and found that 90 °C was the minimum temperature when the reaction rate was maximum at minimum time. We have added more description of the reaction temperature parameter.
Point 6: Kinetic study is done by FTIR analysis of the product. I am really concerned about accuracy of this approach since IR signals usually overlap what obscures accurate concentration measurements. Authors should prove the accuracy of the method by calibration over some known mixture of the compounds. NMR is much more convenient technique in this regard.
Response 6: We do analyze the samples used for the kinetic study with 1H-NMR and found no inaccuracy when compared to FTIR analysis data. Yes, we do agree with the reviewer that sometimes IR signals overlaps and mislead too. But in this case, there were no similar products so the chances of signal overlap are minimal. The FTIR and NMR data matched perfectly.
Point 7: Besides that, some minor objections are as follows: Page 1: several exponents are not formatted correctly Page 2/3: Table 1, footnote contains "ND = not determined" while there is no ND in the Table 1.
Response 7: The exponents have been corrected in the revised manuscript. The typing mistake in the footnote of Table 1 (ND) has been also corrected now.
Point 8: Page 3, line 103: "its" should be "it is"
Response 8: The error has been corrected in the revised manuscript.
Point 9: Page 3, line 105: a reference or equation should be given.
Response 9: The reference has been inserted in the revised manuscript.
Point 10: Page 5, Scheme 1: temperatures are 110 °C while the 90 °C is the lowest temperature with the highest reaction rate, and the most of the reactions were conducted at 90 °C. I do not understand why this discrepancy is.
Response 10: We thank the reviewer for pointing out the crucial typing mistake. The discrepancy pointed out by the reviewer is corrected now in the revised manuscript.
Reviewer 3 Report
The work described in the present manuscript, by Kumar, Park and Kim, is a follow-up study of a previous work published at Energy Fuels 2013, 27, 3758−3768, where the preparation and structural analysis of a similar catalyst 1.5-Zn/CaO-550, was reported. At that time, Kumar and Ali used this catalyst for the complete transesterification reactions of triglycerides with methanol. They have studied the reaction kinetics and calculated the activation energy. The reusability of the catalyst was also investigated and it was found to be effective even for the transesterification of low quality feedstock. The same kind of studies are reported now in the present manuscript, were the catalyst 2-Zn/CaO-400 was used for the amidation of a variety of natural triglycerides. So in this sense, the originality/ novelty of the work is low.
The manuscript is well-written, however some mistakes/ inconsistencies need to be corrected before publication.
According to the template of Catalysts journal, the authors’ affiliation should be presented using italic style. Please change also in the Supplementary Information file. In the abstract, for the units min-1 (-1 should be superscript). The authors should define the abbreviation BET (Brunauer-Emmett-Teller…). Page 2, line 79: please change “The doing of Zn…” by “The doping of Zn…” Page 2, line 80: a numerical value is missing in the sentence, “…caused the increase in surface area from to 14.89 m2/g and … Page 2, in the title of Table 1, please replace “oxiedes” by “oxides”. Page 3, from lines 87-107: the peaks of XRD analysis should be indicated by increasing order (example: 32.27°, 47°, 53.89°, 67.39° instead of 37.47°, 53.89°, 32.27°, 67.39°). Ponctuation is missing at the end of the sentence at line 97. Use bold style for the words Figure 1, Figure 2, Figure 4 and Figure 5 in the caption of the corresponding figures. Page 3, line 114: Please change “2-Zn/CaO-40 was 115 nm …” by “2-Zn/CaO-400 was 115 nm …” Page 4: At line 117, change (Figure 1c) by (Figure 2c) and at line 119, change (Figure 1d) by (Figure 2d). The caption of Figure 2 seems to be uncorrect. Please check. Page 4, line 124: Please replace “The amidation of variety…” by “The amidation of a variety…” Page 5: The temperature value (110 °C) indicated in Scheme 1 is not in agreement with the reaction temperature referred at the end of page 4, line 129, which is 90°C. Please check and correct. Page 5: At line 141, please replace (Figure S2, supporting information) by (Figure S4, supporting information) and at line 143, replace (Figure 1A) by (Figure 3A). Page 5, line 147: to be in aggrement with the other values, which have two decimal points, please write 4.30 instead of 4.3 (ppm). Page 7, line 193: please change “1wt% to 4%” by “1wt% to 4wt%”. Page 7, line 208: please define FFAs. Please correct the legend of X axis of Figure 5c by replacing “Diethanoamine” by “Diethanolamine”. Page 9, line 271: please change “…make it most efficient heterogeneous for aminolysis…” by “…make it most efficient heterogeneous catalyst for aminolysis…” References section: please correct the volume and page numbers of reference 2; Check the authors’ names of reference 14; Correct the title of reference 15; Correct the chemical formula in the title of references 17 and 32; Check the publication year of reference 29; I think it is 2015 and not 2014.
Author Response
Response to Reviewer 3 Comments
Point 1: The work described in the present manuscript, by Kumar, Park and Kim, is a follow-up study of a previous work published at Energy Fuels 2013, 27, 3758−3768, where the preparation and structural analysis of a similar catalyst 1.5-Zn/CaO-550, was reported. At that time, Kumar and Ali used this catalyst for the complete transesterification reactions of triglycerides with methanol. They have studied the reaction kinetics and calculated the activation energy. The reusability of the catalyst was also investigated and it was found to be effective even for the transesterification of low quality feedstock. The same kind of studies are reported now in the present manuscript, were the catalyst 2-Zn/CaO-400 was used for the amidation of a variety of natural triglycerides. So in this sense, the originality/ novelty of the work is low.
Response 1: We thank the reviewer for reviewing the manuscript in detail. As pointed out by the reviewer, our previous published work (Energy Fuels 2013, 27, 3758−3768) does involve a similar catalyst for the transesterification studies. Though, in present work, we have modified the catalyst preparation method completely and improved the basic strength, surface area, and the catalytic activity of catalyst significantly. In previously reported work the catalyst took 45 min to complete the transesterification reaction whereas in the present case it took only 30 min for the same reaction. Also, the amount of the catalyst used in previous work was 5 wt% while in the present case it was 4 wt%. So, there was great improvement in the overall catalytic performance of Zn/CaO catalyst prepared in the present case.
Point 2: The manuscript is well-written, however some mistakes/ inconsistencies need to be corrected before publication.
According to the template of Catalysts journal, the authors’ affiliation should be presented using italic style. Please change also in the Supplementary Information file.
In the abstract, for the units min-1 (-1 should be superscript).
The authors should define the abbreviation BET (Brunauer-Emmett-Teller…).
Page 2, line 79: please change “The doing of Zn…” by “The doping of Zn…”
Page 2, line 80: a numerical value is missing in the sentence, “…caused the increase in surface area from to 14.89 m2/g and …
Page 2, in the title of Table 1, please replace “oxiedes” by “oxides”.
Page 3, from lines 87-107: the peaks of XRD analysis should be indicated by increasing order (example: 32.27°, 47°, 53.89°, 67.39° instead of 37.47°, 53.89°, 32.27°, 67.39°).
Ponctuation is missing at the end of the sentence at line 97.
Use bold style for the words Figure 1, Figure 2, Figure 4 and Figure 5 in the caption of the corresponding figures.
Page 3, line 114: Please change “2-Zn/CaO-40 was 115 nm …” by “2-Zn/CaO-400 was 115 nm …”
Page 4: At line 117, change (Figure 1c) by (Figure 2c) and at line 119, change (Figure 1d) by (Figure 2d).
The caption of Figure 2 seems to be uncorrect. Please check.
Page 4, line 124: Please replace “The amidation of variety…” by “The amidation of a variety…”
Page 5: The temperature value (110 °C) indicated in Scheme 1 is not in agreement with the reaction temperature referred at the end of page 4, line 129, which is 90°C. Please check and correct.
Page 5: At line 141, please replace (Figure S2, supporting information) by (Figure S4, supporting information) and at line 143, replace (Figure 1A) by (Figure 3A).
Page 5, line 147: to be in aggrement with the other values, which have two decimal points, please write 4.30 instead of 4.3 (ppm).
Page 7, line 193: please change “1wt% to 4%” by “1wt% to 4wt%”.
Page 7, line 208: please define FFAs.
Please correct the legend of X axis of Figure 5c by replacing “Diethanoamine” by “Diethanolamine”.
Page 9, line 271: please change “…make it most efficient heterogeneous for aminolysis…” by “…make it most efficient heterogeneous catalyst for aminolysis…”
References section: please correct the volume and page numbers of reference 2; Check the authors’ names of reference 14; Correct the title of reference 15; Correct the chemical formula in the title of references 17 and 32; Check the publication year of reference 29; I think it is 2015 and not 2014.
Response 2: We thank the reviewer for going through the manuscript thoroughly and highlighting important points. We have addressed all the issues as per suggested by the reviewer. Also, we have used native English speaker’s help and online software to correct the grammatical or typing errors.
Round 2
Reviewer 2 Report
Authors modified the manuscript in a proper way and did some additional corrections to the language. However, I still noticed some typos in the abstract:
Ea: E should be in italic
4.75x108 - 8 should be an exponent.
Nevertheless, I consider the manuscript - acceptable for publication.
Author Response
Point 1: Authors modified the manuscript in a proper way and did some additional corrections to the language. However, I still noticed some typos in the abstract:
Ea: E should be in italic
4.75x108 - 8 should be an exponent.
Nevertheless, I consider the manuscript - acceptable for publication.
Response 1: The typos in the abstract have been corrected now in the revised manuscript. We thank the reviewer for accepting a manuscript for publication.
