Naphthenic acid

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Example of a naphthenic acid

Naphthenic acid (CAS: 1338-24-5 ) (NAs)is the name for an unspecific mixture of several cyclopentyl and cyclohexyl carboxylic acids with molecular weight of 120 to well over 700 atomic mass units. The main fraction are carboxylic acids with a carbon backbone of 9 to 20 carbons. McKee et al. claim that "naphthenic acids (NAs) are primarily cycloaliphatic carboxylic acids with 10 to 16 carbons."[1] Salts of naphthenic acids, which are naphthenates, are widely used as hydrophobic sources of metal ions in diverse applications.[2]

Preparation and occurrence[edit]

They are obtained by oxidation of the naphtha fraction of the crude oil refining. The composition varies with the crude oil composition and the conditions during refining and oxidation.[3] Naphthenic acids are present in crude oil. Fractions that are rich in naphthenic acids can cause corrosion damage to oil refinery equipment; the phenomenon of naphthenic acid corrosion (NAC) has therefore been well researched.[4][5] Crude oils with a high content of naphthenic acids are often referred to as high total acid number (TAN) crude oils or high acid crude oil (HAC). Naphthenic acids are the major contaminant in water produced from the extraction of oil from Athabasca oil sands (AOL).[6] Naphthenic acids have both acute and chronic toxicity to fish and other organisms.[6]

They can be extracted from aqueous solution.[7]

Metal naphthenates[edit]

Naphthenates are the salts of naphthenic acids. Analogous to the corresponding acetates, which are better defined but less lipophilic. Metal naphthenates are coordination complexes. They have the formula M(naphthenate)2 or are basic oxides with the formula M3O(naphthenate)6. The naphthenates are highly soluble in organic media. They have industrial applications including synthetic detergents, lubricants, corrosion inhibitors, fuel and lubricating oil additives, wood preservatives, insecticides, fungicides, acaricides, wetting agents, thickening agent of napalm and oil drying agents used in painting and wood surface treatment. Industrially useful naphthenates include those of aluminium, magnesium, calcium, barium, cobalt, copper, lead, manganese, nickel, vanadium, and zinc.[2]


One oft-cited study stated that "naphthenic acids are the most significant environmental contaminants resulting from petroleum extraction from oil sands deposits." However "under worst-case exposure conditions, acute toxicity is unlikely in wild mammals exposed to naphthenic acids in AOS tailings pond water, but repeated exposure may have adverse health effects."[8] Naphthenic acids are present in Athabasca oil sands (AOL) tailings pond water (TPW) at an estimated concentration of 81 mg/l.[7]

Using Organization for Economic Cooperation and Development [OECD] protocols for testing toxicity, McKee et al. (2014) argued that based on their studies refined NAs when consumed orally were not acutely genotoxic to mammals.[1] However, damage induced by NAs while transient in acute or discontinuous exposure, may be cumulative in repeated exposure.[8]

See also[edit]


  1. ^ a b Richard H. McKee; Colin M. North; Paula Podhasky; Jeffrey H. Charlap; Adam Kuhl (February 2014). "Acute and Subchronic Mammalian Toxicity of Naphthenic Acids from Oil Sands Tailings". International Journal of Toxicology. 33 (1): 347–355. doi:10.1177/1091581813504229. 
  2. ^ a b Angelo Nora, Alfred Szczepanek, Gunther Koenen, "Metallic Soaps" in Ullmann’s Encyclopedia of Industrial Chemistry, 2005, Wiley-VCH, Weinheim. doi:10.1002/14356007.a16_361
  3. ^ Walter E. Rudzinski; Leon Oehlers & Yi Zhang (2002). "Tandem Mass Spectrometric Characterization of Commercial Naphthenic Acids and a Maya Crude Oil". Energy Fuels. 16 (5): 1178–1185. doi:10.1021/ef020013t. 
  4. ^ Slavcheva E.; Shone B.; Turnbull A. (1999). "Review of naphthenic acid corrosion in oil refining". British Corrosion Journal. 34 (2): 125–131. doi:10.1179/000705999101500761. 
  5. ^ "Article with details concerning naphthenic acid corrosion" (PDF). 
  6. ^ a b Allen, E. W. (2008). "Process water treatment in Canada’s oil sands industry: I. Target pollutants and treatment objectives" (PDF). Journal of Environmental Engineering and Science. 7 (2): 123–138. doi:10.1139/S07-038. 
  7. ^ a b Vincent V. Rogers; Karsten Liber & Michael D. MacKinnon (August 2002). "Isolation and characterization of naphthenic acids from Athabasca oil sands tailings pond water". Chemosphere. 48 (5): 519–527. doi:10.1016/S0045-6535(02)00133-9. 
  8. ^ a b Vincent V. Rogers; Mark Wickstrom; Karsten Liber; Michael D. MacKinnon (2001). "Acute and Subchronic Mammalian Toxicity of Naphthenic Acids from Oil Sands Tailings". Toxicological Sciences. 66 (2): 347–355. doi:10.1093/toxsci/66.2.347. 

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