5-((4-(-Phenyldiazenyl)phenyl)diazenyl)quinolin-8-ol

Round 1

Reviewer 1 Report

molbank-2509124

In this manuscript, the authors report the synthesis of a new diazo-quinolin dye that has potential applications in metal-complexations.

Comments:

(1)    It will be clear for the audience that the yield for each reaction is included in the scheme.

(2)    The authors need to elaborate more on how the acid protonation affects the absorption properties of the azo dyes, especially the target compound has two azo groups.

(3)    The 1H NMR shows some impurities peaks in the aromatic regions. The authors need to comment on whether it’s due to cis/trans isomerization or impurities.

(4)    Some references are needed for the claim that “..8-Hq moiety, which is a well-known ligand in coordination chemistry…”

Summary, the manuscript is recommended for publication in Molbank after all the issues are addressed.

English needs some attentions. Many sentences need to be rephrased in a more scientific way.

Author Response

Comments:

• It will be clear for the audience that the yield for each reaction is included in the scheme.

The reaction yield was added on the reaction scheme. Yield could be calculated only for final product after purification because no isolation of diazonium salt was performed.

• The authors need to elaborate more on how the acid protonation affects the absorption properties of the azo dyes, especially the target compound has two azo groups.

By acidulation of the compound’s (3) methanolic solution using trifluoroacetic acid (TFA), the protonation occurs at the quinolinic nitrogen atom’s lone pair, which does not take part in the aromatic conjugation. As a result of protonation, a hypsochromic shift can be observed (maximum absorption wavelength changes as follows: λ_max = 409 nm → λ_max = 397 nm. In addition, a hyperchromic effect can be observed as a consequence of solution acidulation, manifested by increasing the molar absorption coefficient’s value (ε = 15487 M^-1 cm^-1 → ε = 24000 M^-1 cm^-1). The hyperchromic effect is probably caused by the increased HOMO-LUMO gap of the protonated compound (3) compared to unprotonated compound (3).

The above explanation was added also in the manuscript.

• The 1H NMR shows some impurities peaks in the aromatic regions. The authors need to comment on whether it’s due to cis/trans isomerization or impurities.

Compound (3) has a very low solubility in all known deuterated solvents. The only suitable solvent found is the trifluoroacetic acid (TFA) (10 mg of compound were dissolved in 0.7 mL of TFA). As a consequence, the carboxylic proton’s signal is very intense compared to the signals of compound’s protons. An amplification of the aromatic protons’ signals zone was done so they could be analyzed. Together with compound’s protons signals, the signals corresponding to impurities and carbon satellites were also amplified. By calculating the integral value ratio between the aromatic protons signals and those corresponding to impurities and carbon satellites, we found that percentage of impurities and carbon satellites signals is below 1%.

• Some references are needed for the claim that “..8-Hq moiety, which is a well-known ligand in coordination chemistry…”

3 new references ([17], [18] and [19]) were added to support the above statement.

Summary, the manuscript is recommended for publication in Molbank after all the issues are addressed.

Comments on the Quality of English Language

English needs some attentions. Many sentences need to be rephrased in a more scientific way.

Authors performed rephrasing of some sentences. If there are necessary additional text changes, please highlight the sentences which need attention.