Kinetics and Mechanism of Oxidation of Fluorenone Hydrazone by Permanganate Ion in Different Acidic Media

Research Article

Austin Chem Eng. 2016; 3(4): 1040.

Kinetics and Mechanism of Oxidation of Fluorenone Hydrazone by Permanganate Ion in Different Acidic Media

Fawzy A1,2*, Ahmed SA1,2*, Altass HM1, Althagafi II1, Zaafarany IA1 and Khairou KS1

1Chemistry Department, Faculty of Applied Science, Umm Al-Qura University, Makkah, Saudi Arabia

2Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt

*Corresponding author: Ahmed Fawzy, Associate Professor, Chemistry Department, Faculty of Applied Science, Umm Al-Qura University, Makkah, Saudi Arabia; Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt Saleh A Ahmed, Professor, Chemistry Department, Faculty of Applied Science, Umm Al-Qura University, Makkah, Saudi Arabia; Chemistry Department, Faculty of Science, Assiut University, Assiut, Egypt

Received: August 23, 2016; Accepted: September 07, 2016; Published: September 09, 2016


The kinetics of permanganate oxidation of Fluorenone Hydrazone (FH) in both perchloric and sulfuric acid solutions was studied spectrophotometrically at a constant ionic strength of 1.5 mol dm-3 and at 20oC. In both acids, the reactions showed a first order dependence with respect to permanganate ion concentration, whereas the orders with respect to fluorenone hydrazone concentration were less than unity. The orders with respect to both perchloric and sulfuric acid concentrations were found to be fractional-second. Variation of either ionic strength or dielectric constant of the medium had no any significant effect on the oxidation rates. The reactions mechanism describing the kinetic data was proposed. In both acids, the main oxidation products of fluorenone hydrazone as confirmed by GC/MS analysis and FT-IR spectroscopy as the corresponding ketone (9H-fluorenone). Under comparable experimental conditions, the oxidation rate of fluorenone hydrazone in perchloric acid was slightly lower than that in sulfuric acid. The activation parameters of the second order rate constants have been evaluated and discussed.

Keywords: Fluorenone hydrazone; Oxidation; Permanganate; Kinetics; Mechanism


Oxidation reactions are very important in organic synthesis. Among the important oxidizing agents, permanganate ion is widely used in the oxidation of many organic compounds in neutral, alkaline and acidic media [1-11]. The mechanism of oxidation reactions by permanganate ion is governed by pH of the medium [12]. During oxidation by permanganate, it is evident that the Mn(VII) in permanganate is reduced to various oxidation states neutral, alkaline and acidic media. In acid media, permanganate ion (MnO4 -) can exist in several different forms, HMnO4, H2MnO4 +, HMnO3, and Mn2O7 depending on the nature of the reluctant. The oxidant has been assigned with an inner-sphere and an outer-sphere mechanism pathways in their redox reactions [13,14].

Fluorene and its derivatives (FLs) are a unique class of polycyclic aromatic hydrocarbons (PAHs) which exist in the fossil fuels, petrogenic sources burning of gasoline [15,16]. Recently, studies on the exhaust emitting of different types of reformulated diesel fuels showed presence of fluorene as a precedence compound and isomers of methyl fluorene as a hesitant compound in the exhaust [17]. The fluorene unit is regularly employed in the growth of an assortment of visual devices with latent application as dye-sensitized solar cells [18], polymer light-emitting diodes [19,20] and other electro emissive materials [21]. In addition, fluorene based systems possess sole photo physical properties such as high fluorescent quantum yield, huge photo stability, and excellent hole-transporting properties [22,23]. Furthermore, fluorene is one of the highest plentiful polycyclic aromatic hydrocarbons (PAHs) in the surroundings due to its high volatility. Established to be a neurotoxicant through mouthful of air, it was also recognized as a contributive PAH to food contagion. Fluorene compounds with intrinsic rigid structures have been attracting much consideration as organic functional materials because of their promising physical and chemicals properties such as glass transition temperatures, good solubility and their amorphous nature, which make them very talented as an move toward for optic electric materials [24,25]. In addition, hydrazone derivatives were found to be biologically important class of compounds [26]. Hydrazone derivatives were found in natural and synthetic products of biological interest [27]. Literature studies revealed that, hydrazones and the different substituted derivatives showed a broad spectrum of biological activities. Furthermore, fluorenone hydrazones are used as precursors for the synthesis of photochromic di and tetrahydroindolizines [28-30] and more recently as efficient corrosion inhibitors [31].

Although the kinetics of oxidation of fluorenone hydrazone by permanganate ion in alkaline medium has been studied previously [32], the present title studied the kinetics and mechanism of oxidation of this important organic compound with permanganate ion in two different acidic media, namely, perchloric and sulfuric acids. The objectives of the present work are to establish the most favorable conditions affecting oxidation of such compound, to investigate the effect of the acidic medium used on the oxidation kinetics and finally to elucidate a plausible oxidation mechanism.



The chemicals used in the present work were of Aldrich grades.

Fluorenone hydrazone was prepared according to the described procedures with some modifications [33,34]. The synthesized fluorenone hydrazone was confirmed by both spectroscopic and analytical tools. All solvents used were of spectroscopic grade and used without further purifications. The solvents used were checked for the absence of absorbing or any fluorescent impurities. A fresh solution of potassium permanganate was prepared and standardized as reported earlier [35]. Sodium perchlorate and sodium sulfate were used to vary the ionic strength of the reactions media in both perchloric and sulfuric acid solutions, respectively.

Kinetic measurements

All kinetic runs were followed under pseudo-first order conditions where fluorenone hydrazone was existed in a large excess over that of permanganate. Initiation of the reactions were done by mixing the previously thermostatted solutions of both permanganate and fluorenone hydrazone that also contained the required amounts of the acid, NaClO4 or Na2SO4. The courses of the reactions were followed by monitoring the decay in the absorbance of permanganate as a function of time at its absorption maximum (λ = 526 nm), whereas the other constituents of the reaction mixtures did not absorb considerably at this wavelength. The absorption measurements were done in a temperature-controlled Shimadzu UV-VIS-NIR-3600 double-beam spectrophotometer. Application of Beer’s law was verified for permanganate concentrations at λ = 526 nm, and the molar extinction coefficient was found to be e = 2234 ± 43 dm3 mol-1 cm-1. The orders of the reactions with respect to the reactants were determined from the slopes of the log kobs versus log (concentration) plots by varying the concentrations of the substrate and acids, in turn, while keeping other conditions constant.


Reaction stoichiometry and product analysis

Reaction mixtures containing various amounts of permanganate ion and fluorenone hydrazone at constant [H+], ionic strength, and temperature were allowed to react for 24 h for completion of the oxidation reactions. The unconsumed [permanganate] was determined spectrophotometrically at 526 nm. The results indicate expenditure of four permanganate ions for five molecule of fluorenone hydrazone substrate to yield the oxidation products as shown in the following equation,

The above stoichiometric equation is consistent with the results of products analysis as confirmed by the head-space GC/MS. Further assignment of the oxidation products was done by the help of FT-IR spectra as described elsewhere [32].

Spectral changes

The spectral scans during the oxidation of fluorenone hydrazone by permanganate ion in both perchloric and sulfuric acid solutions are shown in Figure 1 (a) and (b), respectively. In both acids, there was gradual disappearance of permanganate band at its absorption maximum (λ = 526nm).