الفهرس 
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Abstract
Evaluation of the prepared compounds as lube oil additives a) As Antioxidants to verify the effectiveness of the prepared compounds as antioxidants, 0.01 g was added to the one liter of the used lube oil free from any additives, then the lube oil with and without the additives was Subjected to severe oxidation at 155°C with air at a rate of 10 litres/hour for 36 hours. Samples were taken at regular six hours intervals and tested for their oxidation stability expressed in terms of the total acid number according to ASTM D3242, carbonyl number, hydroxyl number, and saponification values and compared with the lube oil sample free from additives. The results are given in Tables (2a-d) and Figs. (1-6). It is obvious from the obtained results that, in the absence of additives, the oxidation products increase with time. When the additives I-XIV were added to the used oil at a concentration of 0.01 gm/litre, the oxidation increases with time but at a rate much less than when no additive was added. Thus, Table (2) and Fig. (3) reveal that the total acid number (T.A.N.) of the oil samples containing the prepared compounds after 36 hours oxidation showed good oxidation resistant properties to the used lube oil compared with the undoped oil and that compounds V(a,b), VII(a,b) ,XII and XIV exhibit the highest antioxidant activity. It could be concluded that the presence of both imidazolone and pyrazole moieties in compounds V(a,b) may be responsible for their antioxidant activity (acid number, 1.5 and 1.6 mg KOH/g oil, respectively) . It is also clear that the phenothiazine derivatives VII(a,b) were the highest effective antioxidant additives for the used oil (acid number 1.2 and 1.25 mg KOH/g oil). This could be attributed to the presence of the highly effective antioxidant groups, e.g., thione C=S, thioether linkage -S- and -NH- groups in their structure. This result agrees with that reported by Field et al who found that phenothiazine derivatives showed high antioxidant activity.