REV. CHIM. (Bucharest) ♦ 61♦ Nr.8 ♦ 2010 http://www.revistadechimie.ro 718 Partition Studies in Biphasic Systems of Nitrophenols IOANA DIACONU * , ELENA RUSE, EUGENIA EFTIMIE TOTU, GHEORGHE NECHIFOR University Politehnica Bucharest, Faculty of Applied Chemistry and Material Science, Department of Analytical Chemistry and Instrumental Analysis, 1-3 Polizu, 011061, Bucharest , Romania The paper presents experimental data obtained in the study of liquid-liquid partition equilibria in biphasic system in order to optimize the process of extraction of nitrophenols. The partition equilibria of some nitrophenols using chloroform as extraction solvent were studied. The influence of the pH on the partition equilibria was investigated. The extraction diagrams were realized and the repartition coefficient and the pK a values of the studied nitrophenols were calculated in the system water-chloroform. The studied compounds were: p-nitrophenol, o-nitrophenol and, 2,4-dinitrophenol. In optimum extraction conditions (pH=2 for the aqueous phase) extraction efficiencies of 62-65% were obtained. The analytical control of the process was realized using molecular absorption in the range ultraviolet-visible at their characteristic wavelengths. Keywords: nitrophenols, extraction, partition coefficients diaconuioana12@yahoo.com In the last years a special attention was given to the presence of nitroaromatic compounds in the environment [1-4]. Nitrophenols are contaminants frequently encountered in the environment as herbicides or degradation products of some organophosphorus insecticides [5-6]. Nitrophenols are encountered in wastewater from industries such as: pharmaceuticals - aspirin substitute acetaminophen-, the manufacture of pesticides such as parathion, paraoxon and methyl parathion, explosives, solvents and intermediates of dyes [7-10]. A review related to this point of view has been published [11]. Nitrophenols have a high toxic potential level with strong effects on health of the human beings, animals and plants. For example long exposure to high concentrations of para- nitrophenol can cause blood disorder, kidney and liver damage. It can also cause skin and eye irritation [12]. Nitrophenols are encountered in surface water as well as in groundwater or in deep soils. Due to the economic and environmental impact it is important to separate and develop efficient separation methods for nitrophenols. In order to realize the removal and recovery of phenols from the environment various researches were realized. For the treatment of wastewaters containing nitrophenols two main procedures were used: destructive procedures such as biodegradation, thermal decomposition and oxidation [13]; and recuperative procedures such as adsorption, liquid membrane separation [14-16], liquid– liquid extraction [18-19]. From the procedures mentioned methods solvent extraction and membranary methods are two modalities that are used to separate compounds in a mixture, being intensively promoted. The solvent extraction permits obtaining of efficient separations through simple experimental procedures. Consequently solvent extraction was the topic of several researches aimed to improve the experimental techniques. Improvement of the solvent extraction methods permitted the enrichment of the separation techniques with new techniques using the transport through membranes [20-22]. In the field of liquid- liquid extraction it can be pointed out the separation of orto-nitrophenol from para-nitrophenol in a triphasic extraction system [19]. The triphasic system in this case is formed from polyethylene glycol with different molecular weight and simulated wastewater-containing isomers of para-nitrophenol and orto-nitrophenol. The results showed a great effect of the solution pH, extractant type on the partition coefficient of the two isomers. At pH = 4.00, about 85% orto-nitrophenol and 90% para-nitrophenol partitioned into the top organic phase and middle polymer-rich phase, respectively. The separation factor decreased sharply with the increase of the pH solution from 6.5 to 8.5. The separation procedure based on liquid emulsion membranes [23-25] and supported liquid membranes techniques were applied [26-28]. The main objective of this study is to determine if the liquid-liquid extraction can be used as nitrophenol recuperative process. The extraction solvent used was chloroform based on the excellent results obtained for transport through bulk liquid membranes with chloroform membrane [14]. The liquid-liquid extraction, characterized by easiness to operate and convenience to scale up, has received much attention in recent years [19]. Experimental part Reagents All the reagents used are of analytical grade. p- nitrophenol, o-nitrophenol, 2,4-dinitrophenol were supplied by Merck (Germany). Chloroform, previously saturated with distilled water, is used as an organic solvent in the partition equilibria was purchased from Merck (Germany). Hydrochloric acid and sodium hydroxide were used for the variation of the pH between 2 and 12. The distilled water used in this study was also saturated with chloroform. Apparatus The pH was measured with a glass/AgCl, Ag combined electrode using SevenMulti Metler Toledo pH-meter. The nitrophenols content from the aqueous phases and in solvent, respectively, was determined by molecular spectrofotometry using a LAMBDA 750 spectrophotometer (Perkin Elmer Co).