Int. J. Curr.Res.Chem.Pharma.Sci. 2(2): (2015):80–93 © 2015, IJCRCPS. All Rights Reserved 80 INTERNATIONAL JOURNAL OF CURRENT RESEARCH IN CHEMISTRY AND PHARMACEUTICAL SCIENCES (p-ISSN: 2348-5213: e-ISSN: 2348-5221) www.ijcrcps.com Research Article THE ROLE OF 5-(4-ALKOXYBENZYLIDENE)-2-THIOXO-4-OXO-1, 3-THIAZOLIDINE AS ANTIOXIDANTS FOR EGYPTIAN LUBE OIL BASE STOCK MAHER I.NESSIM *1 , DOAA I. OSMAN 1 , EL-SAYED K. ATTIA 1 EBTSAM A.AHME 2 AND HODA A. MOHAMMED 1 1 Egyptian Petroleum Research Institute, Analysis and Evaluation Department, Nasr City, Cairo, Egypt 2 Helwan University, Faculty of Science, Chemistry Department, Ain Helwan, Cairo, Egypt Corresponding Author: maherni@yahoo.com Abstract This work presents a study to the oxidation stability of local base stock, delivered from Co-operative Petroleum Company, in the presence of two prepared Rhodanine derivatives, namely 5-(4-hexyloxybenzylidene)-2-thioxo-4-oxo-1,3-thiazolidine, (I) and 5-(4- octyloxybenzylidene)-2-thioxo-4-oxo-1,3-thiazolidine, (II). The structures of the prepared compounds were elucidated using the traditional tools analyses including elemental analysis, I.R., 1 H-NMR and electron ionization mass spectroscopy (EI-MS). The oxidation reaction was tested using the change in total acid number (TAN) and viscosity. The data showed that compound (II) is more efficient than compound (I). The quantum chemical parameters such as the highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energy levels, the energy gap (EHOMO-ELUMO) and the dipole moment were calculated. The quantum chemical calculations were on the same line with the experimental results. Keywords: Base stocks, antioxidant, oxidation stability, total acid number, viscosity and quantum chemical calculations. 1.Introduction Mineral lubricating oils are usually used in presence of air whereby oxidative Chemical reactions can take place. The rate of these oxidative processes varies greatly with the nature of oils, the extent of processing in refining, the temperature, and the presence of a metallic catalyst [1,2]. Such oxidations have a drawback on the oil, thus leading to failures in lubrication that accompanied by damage of engines. Large degree of damage is due to the formation of viscous, solid bodies, or jelly-like emulsions which interfere with the regular distribution of the lubricant. Antioxidants can generally be considered as free radical inhibitors of peroxide decomposers, and may vary in their chemical structures. Three types of additives have been proved to be successful in controlling the oxidation of lubricating oils; radical scavengers, and hydro peroxides decomposers, as well as synergistic mixtures of both of them. Thus, various classes of compounds have been used as antioxidant additives, such as phenols [3-9], amines [10- 12] and heterocyclic compounds [13-16] as well as synergistic mixtures of them [17-22]. Quantum chemical methods have already proven to be very useful in determining the molecular structure as well as elucidating the electronic structure and reactivity. Recently, antioxidant publications contain substantial chemical calculations [23 - 24]. Such calculations are usually used to explore the relationship between the antioxidants molecular properties and their inhibition efficiency. In the present work, two rhodanine derivatives have been synthesized, characterized and evaluated as antioxidants for local base oil. Also we discussed the relationship between quantum chemical calculations and experimental results of the two synthesized antioxidants by determining the quantum chemical parameters such as the energies of the highest occupied molecular orbital (E HOMO ) and the lowest unoccupied molecular orbital (E LUMO ), the energy difference E (E HOMO -E LUMO ) and the dipole moment.