Synthesis of Fatty Alcohol based Sterically Hindered Esters as Potential Antioxidants for Bioadditives
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thesis of Fatty Alcohol based Sterically Hindered Esters as Potential Antioxidants for Bioadditives Venkateshwarlu Konthama, b, Korlipara V. Padmajaa, b, *, and Devarapaga Madhua, c, ** aCentre
for Lipid Science and Technology, CSIR-Indian Institute of Chemical Technology, Hyderabad, Telangana, 500007 India b Academy of Scientific and Innovative Research, New Delhi, India c Department of Chemistry, Indian Institute of Technology (BHU) Varanasi, Varanasi, 221005 India *e-mail: [email protected] **e-mail: [email protected] Received March 3, 2020; revised June 30, 2020; accepted July 10, 2020
Abstract—Four hindered phenolic esters were prepared by esterification between 3-(3,5-Di-tert-butylhydroxyphenyl)propionic acid and fatty alcohols. The synthesized esters were characterised by NMR, IR and ESI-MS and analysed for their antioxidant properties and thermal stability. Differential scanning calorimetry (DSC) and Rancimat studies were conducted to explore the effect of synthesized compounds on oxidation stability of base oil. The results from both the studies were correlated well. Thermogravimetric analysis indicates that all the esters have significantly high thermal stability. Among all the prepared compounds myristyl alcohol ester showed better antioxidant properties whereas, stearyl alcohol ester exhibited higher thermal stability. The synthesized antioxidants can be potential bio additives for lubricant formulations. Keywords: differential scanning calorimetry, thermal stability, oxidation induction time, rancimat, surfacevolume ratio DOI: 10.1134/S0965544120110110
INTRODUCTION Lubricating fluids are widely used in industrial and automobile applications to improve the service life of machineries by providing protection against wear and friction [1, 2]. Despite their many advantages, lubricating oils possess poor oxidation and thermal stabilities. The continuous exposure to elevated temperatures and environmental oxygen leads to the formation of free radicals [3, 4]. Additives are introduced to improve the lubricant performance and increase the shelf life by improving anti corrosion, antioxidant properties and also to enhance the tribological properties such as antiwear and antifriction [5, 6]. As per the environmental regulations low levels of sulfur, phosphate ash and metal free additives have been encouraged in lubrication applications [7–9]. In this regard, researchers synthesized some metal free additives and successfully characterised their tribological properties and their performance is comparable to conventional multifunctional additive Zinc dialkyldithiophosphates (ZDDP). Oxidative breakdown of lubricants usually results in the formation of primary and secondary oxidation products (peroxides, carboxylic acids, alcohols, aldehydes and ketones) which alter the physical and chemical properties of lubricant basestock [10]. Therefore, antioxidants are needed to delay or prevent
the oxidation process of lubricant by inhibiting the formation of free radicals [11–13]. Hindered phenols and arylamines
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