Table 2 Oxidation products of PPD

Monomeric compounds

 Semibenzoquinone diimine radical cation (SBQDIRC) 108.14

ox. ag.: ferricyanide, pH 8 (phosphate buffer)

UV–VIS spectroscopy, EPR spectroscopy

+

[35]

+ •

pH 4.8 (acetate buffer)

CVA, EPR spectroscopy

+

[34]

pH 2–8 (Britton-Robinson buffer)

Electrolysis at GCE- or Pt-electrode, EPR spectroscopy

+

[38]

solv.: CH₂Cl₂ and ACN

Electrochemical oxidation at GCE, UV–VIS spectra

−

[37]

pH 7.0 (phosphate buffer)

Oxidation at a GCE modified with MnO₂, UV–VIS spectroscopy, 415–425 nm

−

[36]

pH 7.0 (water), 30 min reaction time, drying until solid formation under vacuum

Adsorption on Au- and Cu- surfaces of nanoparticles, UV–VIS spectroscopy, surface enhanced Raman spectroscopy (SERS)

+

[46]

solv.: ACN

Oxidation at Pt electrode, EPR spectroscopy

+

[39]

ox. ag.: OH• and N₃•, pH 8 (buffer)

UV–VIS spectroscopy, 300, 370, 460, and 490 nm, Raman spectroscopy, 1430 and 1650 nm

+

[45]

solv.: ACN

CVA, Pt electrode, EPR spectroscopy

+

[40]

ox. ag.: Br₂ or photolysis, solv.: methanol, ethanol, pH 7 (water)

UV–VIS, IR, and Raman spectroscopy, 300, 460, 490, and 560 nm

○

[43]

ox. ag.: Br₂ pH 4.6 (20 % acetate buffer + 80 % methanol)

UV–VIS spectroscopy, 462 and 479 nm

−−

[41]

Photolysis, ox. ag.: Br₂, solv.: ethanol, −72 °C, −130 °C, −196 °C

UV–VIS spectroscopy, 465 and 500 nm

−−

[71]

ox. ag.: Br₂ solv.: ethanol

UV–VIS spectroscopy, 463 and 490 nm, resonance Raman and Raman spectroscopy

○

[42]

 Dimeric SBQDIRC 216.29

ox. ag.: Br₂, UV photolysis, pH 7 (water), ethanol (−72 °C); methanol

UV–VIS spectroscopy, 600 nm, Raman spectroscopy

−−

[43]

+ •

Photolysis, solv.: ethanol, −72 °C, −130 °C, −196 °C

UV–VIS spectroscopy, 600 nm

−−

[71]

solv.: ethanol −72 °C, 25 °C

Equilibrium, SBQDIRC and (SBQDIRC)₂, UV–VIS and resonance Raman spectroscopy, 448 nm (monomer), 600 nm, 670 nm (dimer)

−

[44]

  para-Benzoquinone diimine (BQDI) 106.13

ox. ag.: ferricyanide, pH 8 (buffer)

UV–VIS spectroscopy 257 and 265.5 nm

−−

[35]

ox. ag.: O₂, ferricyanide, pH 7 (water), 30 min

HPLC-MS/MS, m/z: 107 amu [M + H]⁺fragments: 80 and 53 amu

+

[49]

ox. ag.: MnO₂, pH 7 (phosphate buffer)

CVA, oxidation at an electrode modified with MnO₂, UV–VIS spectroscopy, 276, 319, and 465 nm

−−

[36]

pH 7.4 (30 % ACN/70 % ammonium acetate)

Electrochemical oxidation, EC-ESI-MS-TOF, m/z: 107 amu [M + H]⁺

++

[25]

  para-Benzoquinone (PBQ) 108.10

ox. ag.: MnO_2, solv.: benzene

UV and IR spectroscopy, melting point

○

[73]

  para-Nitroaniline138.13

ox. ag.: H₂O₂, ammoniacal solution, filtration of precipitates, dissolution in DMF, TLC separation

IR spectroscopy, melting point

○

[55]

 4-Aminophenyl formamide 136.15

Culture medium

HPLC-MS; ¹³C-, UV-, MS-detection, m/z: 137 amu [M + H]⁺

−

[8]

Culture medium

HPLC-MS/MS, d⁴-PPD, m/z: 137/141 amu [M + H]⁺

○

[56]

Dimeric compounds

 4,4′-Diamino-azobenzene (DAB) 212.25

ox. ag.: MnO₂, solv.: benzene, 30 % yield

IR and UV spectroscopy of the isolated substance

○

[73]

ox. ag.: H₂O₂, ammoniacal solution, filtration of precipitates, dissolution in DMF, TLC separation

R_f-value (TLC), UV- and IR spectroscopy, elemental analysis, melting point

+

[55]

ox. ag.: O₂, ferricyanide, aqueous solution, 30 min

HPLC-MS/MS m/z: 198 amu [M + H]⁺

○

[49]

pH 7.4 (30 % ACN/70 % ammonium acetate)

Electrochemical oxidation, EC-ESI-MS-TOF, m/z: 213 amu [M + H]⁺

++

[25]

 2-(1′,4′-Benzoquinone diimine)-4-aminoaniline 212.25

pH 7.4 (30 % ACN/70 % NH₄Ac)

Electrochemical oxidation, EC-ESI-MS-TOF, m/z: 213 amu [M + H]⁺

○

[25]

 2-(1,4-Benzoquinone diimine)-1,4-benzoquinone diimine 210,24

pH 7.4 (30 % ACN/70 % NH₄Ac)

Electrochemical oxidation, EC-ESI-MS-TOF, m/z: 211 amu [M + H]⁺

○

[25]

 2-(4′-Aminoaniline)-5-hydroxy-1,4-benzoquinone diimine 228.25

ox. ag.: H₂O₂, ammoniacal solution, filtration of precipitates, dissolution in DMF, TLC separation

UV, NMR, and IR spectroscopy, 460 nm, 550 nm, melting point, elemental analysis

+

[55]

 2-(4′-Aminoaniline)-1,4-diaminobenzene 214.27

solv.: ACN

Electrochemical oxidation, coulometry at Pt electrode

−−

[58]

Trimeric product

 Bandrowski’s Base N’,N’-bis-(4-Aminophenyl)-2,5-diamino-1,4-benzoquinone diimine 318.38

ox. ag.: O₂, ferricyanide

Elemental analysis

−−

[24]

Culture medium

PPD transformation by dendritic cells, reaction time 16 h, HPLC-MS, HPLC radio detection, HPLC-UV (254 nm)

+

[2]

ox. ag.: H₂O₂ ammoniacal solution, filtration of precipitates, dissolution in DMF, TLC separation

NMR, IR, and UV–VIS spectroscopy (~460 nm)

+

[55]

ox. ag.: H₂O₂ pH 9.5 (sodium carbonate); filtration of precipitates

Elemental analysis, TLC, IR, and UV–VIS spectroscopy

○

[59]

pH 7.4 (30 % ACN/70 % NH₄Ac)

Electrochemical oxidation, EC-ESI-MS-TOF, m/z: 319 amu [M + H]⁺

○

[25]

ox. ag.: O₂, ferricyanide, pH 7 (water), 30-min reaction time, pH 4 (buffer), 1-h reaction time

HPLC-MS/MS, m/z: 319 amu [M + H]⁺, confirmation of substance identity by comparison with standard material

++

[49]

pH-dependency (pH 4, 5, 6, 7, and 9) of BB formation

HPLC-DAD (480 nm)

+

[49]

ox. ag.: H₂O₂ pH 2.2 (HCl), pH 9.9 (ammoniacal solution)

Ames Test, TLC separation, UV–VIS spectroscopy, comparison with standard

○

[63]

ox. ag.: photolysis, solv.: DMSO, reaction time 1–4 h

Ames Test, TLC separation, detection with UV and IR spectroscopy

−

[64]