Sustainable Catalytic Synthesis of 2,5-Diformylfuran from Various Carbohydrates
, Kihyuk Sung 1, June Young Jang 2, Sohee Bang 2, Seung Uk Son 2,* and Hye-Young Jang 1,*Round 1
Reviewer 1 Report
The manuscript "Sustainable Catalytic Synthesis of 2,5-Diformylfuran from 2
Various Carbohydrates" reports an interesting catalytic pathway for the obtention of DFF from several carbohydrates. I recommend its acceptance after minor revision, since all data and results are well-explained and represents a good scientific contribution to Catalysts journal.
Please find bellow some comments to improve the manuscript overall quality:
- The authors should carefully read the manuscript and insert all the abbreviations used in the whole text, e.g. PhSSPh should present firstly the chemical name of this compound and then its abbreviation;
- line 42 I suggest to change the word "formation" to isomerization.
- A brief scheme with the reaction pathway of all substrates conversion to DFF should be included in the introduction section.
- The authors should insert a catalytic cycle of a typical substrate conversion to DFF, such as glucose conversion into DFF.
- The authors should clearly state the advantages of using a heterogeneous instead the homogeneous (considering a green chemistry point of view).
- The authors should provide NMR spectra of the raw reaction product and assign the different products formed.
Author Response
1) The authors should carefully read the manuscript and insert all the abbreviations used in the whole text, e.g. PhSSPh should present firstly the chemical name of this compound and then its abbreviations
Response: Thank you for the comment. As pointed out, we inserted all the abbreviations.
2) line 42 I suggest to change the word “formation” to isomerization
Response: The indicated word has been changed.
3) A brief scheme with the reaction pathway of all substrates conversion to DFF should be included in the introduction section.
Response: A brief scheme was inserted in Scheme 1.
4) The authors should insert a catalytic cycle of a typical substrate conversion to DFF, such as glucose conversion into DFF.
Response: We have modified Scheme 5 as suggested.
5) The authors should clearly state the advantages of using a heterogeneous instead of the homogeneous (considering a green chemistry point of view)
Response: We have inserted the following sentences on page 8.
“Our recyclable heterogeneous catalysts maintaining good catalytic activities can be applied to a continuous operation. This protocol, including recyclable catalysts, accords to develop sustainable catalytic processes.”
6) The authors should provide NMR spectra of the raw reaction product and assign the different products formed.
Response: We inserted the NMR spectrum of the reaction mixture in Figure S9. Other by-products derived from fructose were not observed.
Reviewer 2 Report
The manuscript entitled Sustainable Catalytic Synthesis of 2,5-Diformylfuran from Various Carbohydrates by Si Ae Kim et al. describes the study aiming to optimize conditions leading to transform carbohydrates to 2,5-diformylfuran, an important building block for the chemical industry. The study is important as it touches the subject of biomass recycling and reuse of its components. The article fits the scope of the journal Catalysts.
The manuscript is well written and the experiments are well designed. My comments to the manuscript are:
- It would be beneficial if you also tested the synthetic method on mixture of cellulose and fructose, just to assess whether the water released in the process of fructose transformation would enable to simultaneous hydrolysis of cellulose.
- Why did you change the conditions for the experiments with heterogenous catalyst? Both the reaction time and temperature are different than in the homogenous processes. There is also double amount of the solvent used. This should be explained in-text.
- Did you optimize the catalytic reaction by means of temperature applied?
Author Response
1) It would be beneficial if you also tested the synthetic method on mixture of cellulose and fructose, just to assess whether the water released in the process of fructose transformation would enable to simultaneous hydrolysis of cellulose.
Response: We conducted the reactions using cellulose with water and without water. As suggested by reviewer 2, we thought that the addition of water might induce the hydrolysis of cellulose. However, the reactions with water or without water gave no product.
2) Why did you change the conditions for the experiments with heterogeneous catalyst? Both the reaction time and temperature are different than in the homogeneous processes. There is also double amount of the solvent used. This should be explained in the text.
Response: The temperature was not changed and kept at 120 oC. The reaction time was shortened in the heterogeneous catalyzed reactions for the convenience of recycling experiments. To provide enough solvent volume, we used more solvent in the heterogeneous reaction. We inserted the comment in the text (page 7-8)
“The reaction conditions (the reaction time and the concentration) of heterogeneous reactions were modified from the homogeneous reactions for the convenience of operation).”
3) Did you optimize the catalytic reaction by means of temperature applied?
Response: The temperature was changed. The results were inserted in Table S1. The following sentence was added in the main text.
“The temperature was varied from 100 to 150 °C, showing the best yield at 120 °C (see Supporting Information, Table S1).”
Reviewer 3 Report
The authors presented an interesting work regarding the synthesis of DFF from carbohydrates, a very actual research topic. However, the work should be improved before being accepted according to the following comments:
1) In the Introduction the authors should specify if the reaction that they have investigated has been conducted in air or under oxygen pressure in the literature references that they reported.
2) At the moment it is not clear how the samples have been analysed for the quantification of yield and selectivity (HPLC, GC?). The selectivity, as carbohydrates conversion, is a parameter not reported in the work but it should be commented.
3) The authors reported that the DMSO was removed by evaporation but it is a high boiling point solvent (189 °C) and this procedure could led to the degradation of unconverted carbohydrates and HMF and the obtained results could be falsified by this procedure. Why authors have removed the solvent? This is not required if they analyze the sample by HPLC or GC.
4) Why Br- has a critical role and Cl- led to very low yield? Which are the main by-products in runs 6 and 7 Table 1?
5) Why PhSSPh has a critical role?
6) Line2 92-93: in order to show that the limit of DFF yield from glucose was the conversion of glucose the authors should report this value.
7) Why only Al(OTf)3 improved the DFF yield starting from glucose? Evidently this is due to both anion and cation effect because it performed better than the other OTf salts and also AlCl3. How anion and cation have an influence on the reaction?
8) The authors should add the column of carbohydrates conversion in Tables 1 and S1.
Author Response
1) In the introduction, the authors should specify if the reaction that they have investigated has been conducted in air or under oxygen pressure in the literature references that they reported.
Response: References 29 and 30, which are closely related to this work, do not state the use of air or oxygen pressure in the main text and the supporting information. Because DMSO functions as an oxidant, we speculate that air or oxygen was not applied.
2) At the moment it is not clear how the samples have been analysed for the qunatification of yield and selectivity (HPLC, GC?). The selectivity, as carbohydrates conversion, is a parameter not reported in the work but it should be commented.
Response: We inserted the annotation indicating the isolated yields of DFF at the bottom of Table 1. When we obtained the DFF as a major product, we isolated DFF and reported isolated yields. Before separating the product, we ran TLC (thin layered chromatography) experiments to check the presence of HMF. No HMF was observed in the results reporting the isolated yields. When DFF was not a major product, we measured NMR yields of DFF and HMF, which are stated as annotation b-e of Table 1.
3) The authors reported that the DMSO was removed by evaporation but it is a high boiling point solvent (189 oC) and this procedure could led to the degradation of unconverted carbohydrates and HMF and the obtained results could be fasified by this procedure. Why authors have removed the solvent? This is not required if they analyze the sample by HPLC or GC.
Response: When we wrote the experimental procedure in the supporting information, we made mistakes. Thank you for the comments. We did not evaporate DMSO. After the reaction, the column chromatography was conducted without evaporating DMSO. We removed the expression “the solvent was evaporated”.
4) Why Br- has a critical role and Cl- led to very low yield? Which are the main by-products in runs 6 and 7 Table 1?
Response: Br- may function a vital role in the oxidation of HMF to DFF. Other by-products were not observed in entry 6 of Table 1. The reaction involving Cl- forms DFF with a 1% yield and 65% yields of HMF (entry 7). Although fructose was completely consumed, the oxidation was not efficient with Cl-. We added the yield of HMF in entry 7 and modified the text as follows.
“When benzyltriphenylphosphonium chloride (BTPPCl) was used instead of BTPPBr, the DFF yield dropped to 1%, exhibiting the critical role of Br- in the oxidation (entries 6 and 7).”
5) Why PhSSPh has a critical role?
Response: As illustrated in Scheme 5, PhSSPh activates the DMSO, rendering an efficient reaction with HMF.
6) Line 292-93: in order to show the limit of DFF yield from glucose was the conversion of glucose the authors should report this value.
Response: The conversion of glucose was added in Table S1. No glucose was left.
7) Why only Al(OTf)3 improved the DFF yield starting from glucose? Evidently this is due to both anion and cation effect because it performed better than the other OTf salts and also AlCl3. How anion and cation have an influence on the reaction?
Response: As reviewer 3 pointed out, both anions and cations affect the isomerization of glucose to fructose. However, this reaction is composed of isomerization of glucose to fructose, dehydration of fructose to HMF, and oxidation of HMF to DFF. The Lewis acids yielding products with low yields or no DFF may affect the dehydration and oxidation steps, based on empirical results. It is difficult to determine the effect of cations and anions in this complicated reaction system.
8) The authors should add the column of carbohydrates conversion in Tables 1 and S1.
Response: Carbohydrates were all consumed. As suggested, the conversion of carbohydrates was inserted in Tables 1 and S1.
Round 2
Reviewer 3 Report
The manuscript has been improved according to the reviewer's comments, thus it is ready to be accepted.
