All melting points for the prepared compounds were determined using Gallenkamp electric melting point apparatus. The compounds I, II and III were identified and confirmed by microanalysis of carbon, hydrogen, oxygen and nitrogen. The IR spectra were recorded on Perkin-Elmer infrared spectrophotometer model 157, Grating. Also, the 1H NMR spectra were recorded on a Varian Spectrophotometer at 200 MHz using TMS as an internal reference and DMSO-das solvent. The mass spectra (EI) were recorded on 70 ev with Kratos MS equipment and/or a Varian MAT 311 Spectrometer.

The prepared grease under investigation was prepared, according to the procedure previously described [11] ; Table 1 presented the composition of G1, G2, G3 and G4. The Compound I, II and III with concentration 0.3 wt% were added to grease G2, G3 and G4, respectively. The physicochemical properties of the prepared greases were determined according National lubricating grease institute (NLGI) and Egyptian standard. The oxidation stability of the lithium greases with and without prepared quinolone derivatives was determined using oxygen pressure drop test ASTM D-942 and Total acid number ASTM D-664.

The micro analysis of carbon, hydrogen, nitrogen and oxygen of prepared compound I, II and III are shown in Table 1. It can be seen from Table 2 that the calculated data given agree to a large extent with the found data. The molecular weight, melting point and yield for compounds I, II and III are given in Table 3. The obtained data from Infrared and Mass spectra of Compounds I, II and III are Tabulated in Table 4. These data are confirmed the chemical structure of the prepared compounds. It was well known that the efficiency of quinolinone derivatives is increased by the presence of hydroxyl and alkyl groups in such system. Also, the presence of an extended conjugated system in the skeleton of quinolinones facilitates the delocalization of free radicals throughout the compound. For these reasons, the Compounds I, II and III were prepared and used as antioxidant for lubricating grease.

Table 5 shows the physicochemical properties for prepared greases such as consistency, dropping point, penetration and oil separation. These data indicate good interaction between Li-soap and oils to form good three dimensional networks and good texture. The prepared grease had satisfactory performance in most automotive applications and they have standard code NLGI 2. It was concluded that the weight percent of the ingre-

dients that’s needed to prepare obtained greases (G1, G2, G3 and G4) is a good selection.

The prepared compounds ( I, II and III) were evaluated as antioxidants for lubricating greases using ASTM D-942 and ASTM d 664 to determine the oxygen pressure drop and total acid number, respectively (Figure 1 & Figure 2). The obtained result in these figures showed that the oxygen pressure drop and total acid number with time remarkable increased with increasing time in case G1 (blank grease). While this trend is reduced with compounds I, II and III when added to blank grease to give G2, G3 and G4 respectively. The experimental data obtained are shown graphically in Figure 1 & Figure 2 which gives an overview on the efficiency of the 4-hydroxy quinolinones derivatives in controlling the oxidized components compared with the blank grease. It can be seen, from Figure 1 and Figure 2, that the total acid number and oxygen pressure drop for grease G1, without quinolinones increases considerably with time compared with slight increase after addition of the quinolinones (I, II and III). Comparatively, compound III possess the lowest overall acid number and oxygen drop. Based on these results, the prepared quinolinones investigated proved to be successful in controlling the oxidative deterioration of lubricating greases.

Comparison of the antioxidant activity of the compounds I, II and III reveals the following order Comp. III. < Comp. I < Comp. II. This indicates that the oxidation inhibition efficiency is dependent on the structure of the quinolinone compound. It appears, therefore, that the introduction of hydroxyl group with butyl group in quinolinones (compound III) leads to increasing the efficiency of inhibiting the oxidation chain reactions.

Quantum chemical calculations were performed to investigate the relationships between the molecular structure of the prepared compounds and their oxidation stabilities. Quantitative structure activity relationship (QSAR) has been performed on the activity of antioxidants [12] .

The full geometry-optimized structures with Mulliken charges of three prepared quinolone derivatives are shown in Figures 3-8. Also, the theoretical value of the prepared compounds was tabulated in Table 6 using the Gaussian 05 (HF/3-21G). These data demonstrated that neither E HOMO, nor ΔE (E LUMO - E HOMO) are correlated to data in Figure 9 & Figure 10.

E HOMO (the highest occupied molecular orbital) and E LUMO (the lowest unoccupied molecular orbital) values were calculated. The charges representative atoms and other relevant quantum parameters were listed in Table 6. The optimized structure of

the molecules and the electric/orbital density distributions of HOMO and LUMO illustrated in Figures 3-8. Mulliken population analysis is mostly used for the calculation of the charge distribution in a molecule. These numerical quantities are easy to obtain and they provide at least a qualitative understanding of the structure and reactivity of molecules [13] .

Highest occupied molecular orbital energy (E HOMO) and lowest unoccupied molecular orbital energy ( E LUMO ) are very popular quantum chemical parameters. These orbitals, also called the frontier orbitals, determine the way the molecule interacts with other species.

The HOMO is the orbital that could act as an electron donor, since it is the outermost (highest energy) orbital containing electrons. The LUMO is the orbital that could act as the electron acceptor, since it is the innermost (lowest energy) orbital that has room to accept electrons. According to the frontier molecular orbital theory, the formation of a transition state is due to an interaction between the frontier orbitals (HOMO and LUMO) of reactants [14] .

From Table 6, it was found that the E HOMO and the E LUMO changed, while the energy gap E LUMO E HOMO and E LUMO-E HOMO (the difference in energy between the) decreased with increasing the inhibition efficiency. The energy gap (ΔE) is an important stability index. A large E HOMO ? E LUMO gap implies high stability for the molecule in chemical reactions [15] , which means less inhibition efficiency. The values of (ΔE) indicate remarkably that the smaller energy gap results in a high oxidation inhibition efficiency, reflecting the stronger interaction between the inhibitors and grease ingredients. The interactions are probably physical adsorption [16] . These theoretical data adapted with obvious experimental data.