Phenol And Para-Substituted Phenols Electrochemical Oxidation Pathways

TLDR: The electrochemical behavior of phenol, catechol, hydroquinone, resorcinol, dopamine, and para-substituted phenolic compounds, 4-ethylphenol, tyrosine, and tyramine, was studied over a wide pH range using a glassy carbon electrode as discussed by the authors.

About: This article is published in Journal of Electroanalytical Chemistry.The article was published on 2011-05-15 and is currently open access. It has received 357 citations till now. The article focuses on the topics: Hydroquinone & Benzenediol.

Figures

Figure 2. DP voltammograms of (▬) supporting electrolyte pH 7.0 0.2 M phosphate buffer and 25 μM phenol: (▬) first and (▬) second scan, and DP voltammograms baseline-corrected, ( ) first and ( ) second scan.

Figure 8. SW voltammograms in pH 7.0 0.2 M phosphate buffer 25 μM: (A) first and (B) second scans of tyramine, and (C) first scan dopamine; f = 25 Hz, ΔEs = 2 mV, νeff = 50 mV s-1, pulse amplitude 50 mV; It – total current, If – forward current, Ib – backward current.

Table 1. Supporting electrolytes, 0.1 M ionic strength.

Figure 1. CVs with baseline subtracted in pH 7.0 0.1 M phosphate buffer 30 μM phenol: (▬) first scan and ( ) second scan, ν = 50 mV s-1.

Figure 4. (A) 3D plot of second DP voltammograms in 25 μM phenol and (B) Plot of phenol oxidation products Ep2 ( ), Ep3 ( ), Ip2 ( ) and Ip3 ( ) vs. pH.

Figure 3. (A) 3D plot of DP voltammograms in 25 μM phenol and (B) Plot of phenol Ep1 ( ) and Ip1 ( ) vs. pH.

Frequently asked questions

Q1. What are the contributions mentioned in the paper "Phenol and para-substituted phenols electrochemical oxidation pathways" ?

In this paper, the electron transfer properties of phenol derivatives have been investigated using voltammetric techniques at glassy carbon electrodes. 

Q2. How many voltammograms were recorded for each compound?

For each compound, twoconsecutive DP voltammograms were recorded between +0.0 V and + 1.0 V in a fresh solution at a clean GCE surface. 

Q3. Why have voltammetric methods been used to study the redox behavior of various biological?

Due to their high sensitivity, voltammetric methods have been successfully used to study the redox behavior of various biological compounds. 

Q4. What is the oxidation of the first peak of dopamine?

The oxidation ofthe first peak 1a, at Ep = + 0.18V, is attributed to the oxidation of the catechol group of dopamine in dopaminoquinone. 

Q5. What was the procedure used to obtain the voltammograms?

All the voltammograms presented were background-subtracted and baseline-corrected using the moving average with a step window of 3 mV included in GPES version 4.9 software. 

Q6. What is the reversibility of the peaks?

The second CV scanning in the positive direction, in the same solution and without cleaning the GCE surface, showed two anodic peaks: peak 2a at Ep2a = + 0.33 V, and peak 3a, at Ep3a = + 0.43 V, indicating the reversibility of peaks 2c and 3c. 

Q7. What is the oxidation potential of dopamine?

The first DP voltammograms recorded for all three para-substituted phenols,4-ethylphenol, tyramine and tyrosine, between +0.0 V and + 1.0 V at a clean GCEpresented one peak 1a, at Ep1a ~ + 0.65V, at the same potential of the oxidation of peak 1a of phenol. 

Q8. What is the significance of the CV study?

The CV study, although not so sensitive as DP voltammetry, was very important as it enabled rapid screening of the reversibility of electron transfer processes occurring and of the formation of electroactive products. 

Q9. What is the slope of the dotted lines?

In both cases, the slope of the dotted lines was 60 mV per pH unit, meaning that the number of protons transferred during the oxidation of phenol oxidation product is equal with the number of electrons [25]. 

Q10. What is the mechanism of phenol oxidation products?

the oxidation mechanism of phenol oxidation products involves the transfer of two electrons and two protons, and the current of the oxidation peaks of phenol oxidation products has a maximum in neutral electrolytes, Figure 4B. 

Q11. What is the reversibility of the phenol oxidation peak?

On the second SW voltammogram in resorcinol solution, without cleaning the GCE, a new peak 2a appeared at a lower potential, Ep = + 0.08 V, Figure 7F, corresponding to the oxidation of resorcinol oxidation product. 

Q12. What is the reversible peak of the phenol oxidation peak?

The first SW voltammograms recorded in a solution of 25 μM dopamine in pH7.0 0.1 M phosphate buffer, Figure 8C, showed a reversible peak 1a, at Ep = + 0.20 V, which corresponds to the oxidation of the catechol group in this quinone species. 

Q13. What is the oxidation of the second peak of dopaminoquinone?

the oxidation of the second peak 2a, at Ep2a = + 0.88V, corresponds to the oxidation of the leucodopaminochrome species formed in electrolytes with pH > 5.0. 

Q14. What is the meta position of phenol?

the meta position is not favored for any kind of chemical reaction and is followed by stabilisation of the phenoxyl radical by hydrolysis at a high potential, phenol oxidation peak 1a, resulting in the formation of two electroactive products, ortho-quinone and para-quinone.