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Peer-Review Record

3,5-Dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol

Molbank 2020, 2020(3), M1152; https://doi.org/10.3390/M1152
Reviewer 1: Anonymous
Reviewer 2: Anonymous
Reviewer 3: Anonymous
Molbank 2020, 2020(3), M1152; https://doi.org/10.3390/M1152
Received: 16 July 2020 / Revised: 4 August 2020 / Accepted: 6 August 2020 / Published: 11 August 2020

Round 1

Reviewer 1 Report

The manuscript described the synthesis and characterization of 3,5-dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol via the standard azo coupling reaction. Although no new chemistry, nor physico-chemical properties, were presented, the compound has not been reported in the literature. Analytical characteriztion of the compound appears to be sufficient. 

A few points to consider. 

Lines 39/40 "The lack of signals belonging to the BF4– ion in the 19F NMR spectrum makes possible to exclude that the product is in salt form." It really isn't necessary to conduct a 19F NMR to reach such a conclusion: mechanistically, the product cannot be charged. The fact that the product migrates on TLC with a Rf of 0.53 in dichloromethane also clearly supports a non-charged species. On the other hand, the lack of a siganal in 19F NMR can not be used as proof for the absence of fluorine.

Lines 56/57, explaination of difference in fluorescence between compounds 3 and 4 is not convincing. Most likely hydrogen bond is involved, but how does isomerization promote fluorescence process in compound 4? one would think otherwise, if anything.

Experimental procedures should present measurement with appropriate significant figures. For example, "3,5-dimethoxyphenol (0.2 mmol, 30.8 mg)", the sig. fig. for mass and mols are inconsistant.

Presentation in English is in general reasonable, but would benefit from a little polishing.

Author Response

We thank the Referee for his comments and suggestions.

The manuscript described the synthesis and characterization of 3,5-dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol via the standard azo coupling reaction. Although no new chemistry, nor physico-chemical properties, were presented, the compound has not been reported in the literature. Analytical characteriztion of the compound appears to be sufficient. 

A few points to consider. 

Lines 39/40 "The lack of signals belonging to the BF4– ion in the 19F NMR spectrum makes possible to exclude that the product is in salt form." It really isn't necessary to conduct a 19F NMR to reach such a conclusion: mechanistically, the product cannot be charged. The fact that the product migrates on TLC with a Rf of 0.53 in dichloromethane also clearly supports a non-charged species. On the other hand, the lack of a siganal in 19F NMR can not be used as proof for the absence of fluorine.

Answer: We have deleted the 19F-NMR from the text

 

Lines 56/57, explaination of difference in fluorescence between compounds 3 and 4 is not convincing. Most likely hydrogen bond is involved, but how does isomerization promote fluorescence process in compound 4? one would think otherwise, if anything.

Answer: There was an error on our part, in fact compound 4 does not present fluorescence. we have added “doesn’t”

 

Experimental procedures should present measurement with appropriate significant figures. For example, "3,5-dimethoxyphenol (0.2 mmol, 30.8 mg)", the sig. fig. for mass and mols are inconsistant.

Answer: We adjust the value

 

Presentation in English is in general reasonable, but would benefit from a little polishing.

Answer: We have revised the language

Reviewer 2 Report

In this submission, the authors detail the methods for the synthesis and characterization of the title compound. The solid-state fluorescence caused by the presence of the hydroxy group to restrict the conformation of the compound is of interest. The provided information is believed to enough reproduce the methods by others, and thus the manuscript is provisionally acceptable for publication in Molbank. On the other hand, there is a room for improvement about the contents of the manuscript; somehow the interesting UV-vis and emission properties are transferred to SI, and these pieces of important information should be described as a main context of this manuscript. In addition, the description about a parent 1-(4-methoxyphenyl)-2-(2,4,6-trimethoxyphenyl)diazene 4 is very brief, and detailed discussion is required to highlight the unique properties of the present new compound.

Minor corrections: aromatic 1H proton is somewhat missing from the spectrum data (probably, the authors’ careless mistake). The reaction time is better to be indicated in the reaction in Scheme 1.

Author Response

We thank the Referee for his comments and suggestions.

In this submission, the authors detail the methods for the synthesis and characterization of the title compound. The solid-state fluorescence caused by the presence of the hydroxy group to restrict the conformation of the compound is of interest. The provided information is believed to enough reproduce the methods by others, and thus the manuscript is provisionally acceptable for publication in Molbank. On the other hand, there is a room for improvement about the contents of the manuscript; somehow the interesting UV-vis and emission properties are transferred to SI, and these pieces of important information should be described as a main context of this manuscript. In addition, the description about a parent 1-(4-methoxyphenyl)-2-(2,4,6-trimethoxyphenyl)diazene 4 is very brief, and detailed discussion is required to highlight the unique properties of the present new compound.

Answer: We moved from SI to main text the UV/Vis and emission spectra, as suggested.

We also added the following sentence:

The reported synthesis was made starting from  1,3,5-trimethoxyphenyl lithium and 2 in THF at -78 °C under inert atmosphere; to the best of our knowledge, no information about fluorescence of it has been reported. We synthesized compound 4 under the experimental conditions currently reported for the preparation of 3, and no fluorescence was observed.

 

Minor corrections: aromatic 1H proton is somewhat missing from the spectrum data (probably, the authors’ careless mistake). The reaction time is better to be indicated in the reaction in Scheme 1.

Answer: We corrected the 1H NMR description and added reaction time in Scheme 1.

Reviewer 3 Report

C. Boga and her group described a synthetic method with detailed spectrum data for a red dye, 3,5-dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol.

The synthetic procedure is fine, and the structural analysis and the spectrum data are also well organized to show the products.  Overall, the manuscript is enough for publication on Molbank as Short Note after the following revisions.

  1. A hyphen between ‘nuclide’ and ‘NMR’ should be inserted and the authors should be check it out in all text – for example, ‘19F-NMR’ in Abstract, ‘1H-NMR’ in line 28 on page 1, ‘13C-NMR’ in line 85 on page 3, and so on.
  2. In line 24 on page 1, please correct the bold face of close parenthesis.
  3. The title of Figure 2 should begin with capital letters and add a period in the title end.
  4. Although representative UV/Vis and emission spectra for the title compound are depicted, some more information should be provided and discussed, e.g. molar extinction coefficients, Stokes shifts, quantum yields etc.
  5. The molar concentration should be added in UV/Vis and emission spectrum in the article and SI.

Author Response

We thank the Referee for his comments and suggestions.

Boga and her group described a synthetic method with detailed spectrum data for a red dye, 3,5-dimethoxy-2-[(4-methoxyphenyl)diazenyl]phenol.

The synthetic procedure is fine, and the structural analysis and the spectrum data are also well organized to show the products.  Overall, the manuscript is enough for publication on Molbank as Short Note after the following revisions.

1. A hyphen between ‘nuclide’ and ‘NMR’ should be inserted and the authors should be check it out in all text – for example, ‘19F-NMR’ in Abstract, ‘1H-NMR’ in line 28 on page 1, ‘13C-NMR’ in line 85 on page 3, and so on.

Answer: We have added the hyphen, as suggested.

 

2. In line 24 on page 1, please correct the bold face of close parenthesis.

Answer: We have removed the bold face, as suggested.

 

3. The title of Figure 2 should begin with capital letters and add a period in the title end.

Answer: We have corrected the caption, as suggested.

 

4. Although representative UV/Vis and emission spectra for the title compound are depicted, some more information should be provided and discussed, e.g. molar extinction coefficients, Stokes shifts, quantum yields etc.

Answer: Molar extinction coefficients is reported.

 

5. The molar concentration should be added in UV/Vis and emission spectrum in the article and SI.

Answer: We add the concentrations, as suggested.

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