Spectrophotometric study of reactions of substituted phenols with MBTH in alkaline medium: The effect of phenol structure on the formation of analytically useful coloured products

Abstract

The oxidative coupling reactions of unsubstituted phenol, 4-cresol, 2,6-xylenol and another fourteen substituted phenols with MBTH in alkaline medium containing potassium hexacyanoferrate (Ill) as the oxidant were examined by spectrophotometry. The maximum yield and stability of coloured species was attained at optimum pH 9.0-t-0.5. Stoichiometry of the reactions involving a four-electron transfer was confirmed. The coloured products were stable in an aqueous alkaline medium containing 50% (V/V) of a water-miscible organic solvent and they could be quantitatively extracted into chloroform. Absorption maxima Amax of the reaction products ranged between 495 nm and 610 nm depending on the phenol structure and their molar absorptivities fell within the range 2,500-47,000L mol-lcm -1 in aq. 50% ethanol. The calibration graphs were rectilinear for 2 to 20 gM phenol or 2,6-xylenol (r=0.9994-0.9997; n=6) and the RSD values were ~1.8% (n = 10) when determining 10 gmolL -1 of the analytes. The reactivity of the phenols with MBTH (and hence the yield of the coloured species in alkaline medium) depending on the analyte structure decreased in the order: 2,6-dialkylphenols or 4-halogenated 2,6-dialkylphenols>2-alkyl, 2-alkoxy or 2-arylphenols and 1-naphthol>unsubstituted phenol or 2-naphthol=2-halogenated phenols>4alkylphenols and 4-halogenated phenols>2-nitrophe-no1>2,4-or 3,4-dialkylphenols. For some 4-halogenated phenols the elimination of halogen upon coupling with the MBTH was observed.

Optical biosensor for catechol determination based on laccase‐immobilized anionic polyamide 6 microparticles

“…It has been described that, in general, phenols with blocked 4-position, that is, hydroquinone, exhibit very poor or decreased reactivity with MBTH chromophore in the presence of an oxidant. [65] 3.7 | Biosensor application to natural water samples analysis Biosensor applicability was tested in natural water samples from diverse origin (spring and river). They were preliminary analyzed confirming the absence of catechol.…”

Electrochemical oxidation of synthetic tannery wastewater in chloride-free aqueous media

“…The following reagent concentrations were used: (a) natural and synthetic tannins: 293.6 mg L −1 acácia extract (Seta Natur N), 4. Total phenols were measured by the 2-hydrazono-3-methylbenzothiazoline (MBTH) method [17] using Spectroquant ® phenol cell tests (Merck) and a Spectroquant ® Nova 60 spectrophotometer (Merck). TOC was determined using a Shimadzu TOC-V CPN analyzer.…”

Ultrasound assisted cold-induced aggregation: an improved method for trace determination of volatile phenol

“…They are introduced in industrial wastewater, domestic water, soil and sediments [17][18][19][20]. Up until now, several analytical methods such as, high performance liquid chromatography (HPLC), gas chromatography (GC), capillary electrophoresis (CE) [21][22][23], or spectrophotometry [24] have been developed for quantitation of phenolic compounds in different samples.…”