Petroleum benzine

Petroleum benzine is a hydrocarbon based solvent mixture that is classified by its physical properties (e.g. boiling point, vapor pressure) rather than a specific chemical composition, often obfuscating distinction within the long list of petroleum distillate solvent mixtures: mineral spirits, naphtha, white spirits, petroleum spirits, turps substitute, mineral turpentine, petroleum benzine, petroleum ether, ligroin, and Stoddard Solvent. The chemical composition of a petroleum distillate can also be modified to afford a solvent with reduced concentration of unsaturated hydrocarbons, i.e. alkenes, by hydrotreating and/or reduced aromatics, e.g. benzene, toluene xylene, by several dearomatization methods. In a document that attempts to draw more concise distinctions between hydrocarbon solvents, conservator Alan Phenix explains that the most important distinction amongst the various hydrocarbon solvents are their boiling/distillation ranges (and, by association, volatility, flash point etc.) and aromatic content.^[1] Given the toxicity/carcinogenicity of some aromatic hydrocarbons, most notably benzene, the aromatic content of petroleum distillate solvents, which would normally be in the 10-25% (w/w) range for most petroleum fractions, can be advantageously reduced when their special solvation properties are not required and a less odorous, lower toxicity solvent is desired, especially when present in consumer products. Phenix further points out that "To all intents and purposes petroleum benzine appears synonymous with petroleum spirit." Petroleum spirit is generally considered to be the fractions between the very lightest hydrocarbons, petroleum ether, and the heavier distillates, mineral spirits. For example, petroleum benzine with a boiling range of 36 - 83 °C sold by EMD Millipore under CAS-No. 64742-49-0 is identified in the product MSDS as hydrotreated light petroleum distillates comprising ≥ 90% C5-C7 hydrocarbons, n-alkanes, isoalkanes, and < 5% n-hexane, while Santa Cruz Biotechnology sells a petroleum ether product under the same CAS-No. Fisher Scientific offers a product ‘Benzine (Petroleum Naphtha)' that retails for a high price that would suggest it is a speciality product but in fact conforms to Marathon Petroleum's 'VM&P Naphtha' (Varnish Makers & Painters’ Naphtha) found widely distributed in many hardware stores in North America.^[2]

According to their corresponding MSDS, most commercially offered petroleum benzine solvents consist of parrafins (alkanes) with chain lengths of C5 to C9 (i.e. n-pentane to n-nonane and their isomers), cycloparaffins (cyclopentane, cyclohexane, ethylcyclopentane, etc.) and aromatic hydrocarbons (benzene, toluene, xylene, etc.). The TSCA Definition 2008 describes petroleum benzine as "a complex combination of hydrocarbons obtained by treating a petroleum fraction with hydrogen in the presence of a catalyst. It consists of hydrocarbons having carbon numbers predominantly in the range of C4 through C11 and boiling in the range of approximately -20°C to 190°C."

Health concerns

Beginning in the 1960s and 70's, the high incidence rate of polyneuropathy amongst industrial workers chronically exposed to petroleum benzine and other hydrocarbon solvents prompted investigations into the safety of chronic exposure to petroleum distillates.^[3][4][5] Many of the cases of polyneuropathy amongst workers chronically exposed to vapors of petroleum benzine and similar solvents have been attributed to the n-hexane component of these mixtures. Using an animal model (Wistar-strain male rats), Ono and coworkers^[6] reported that chronic exposure (12 h a day for 24 weeks) to hydrocarbon solvent vapors conspicuously impaired peripheral nerve function in the 500 ppm n-hexane group, slightly impaired in the 200 ppm n-hexane group and petroleum benzine II group (containing 500 ppm n-hexane), and barely impaired in the petroleum benzine I group (containing 200 ppm n-hexane). These results suggest that some components in petroleum benzine are likely to antagonize the neurotoxic effects of n-hexane to the peripheral nerves, possibly by inhibiting the oxidation of n-hexane to its more toxic metabolites 2-hexanone and 2,5-hexanedione. Ono and coworkers also observed depressed body weight gains amongst the exposed groups compared to the control group in the order: petroleum benzine II > petroleum benzine I (ccontaining 200 ppm n-hexane) >> 500 ppm n-hexane > 200 ppm n-hexane. These results suggest that other components found in petroleum benzine may have an additive, syngeristic or potentiative effects on the biological effects of n-hexane.^[7] Namely, 1000 ppm n-hexane, 3000 ppm n-heptane and 1000 ppm toluene were reported to have the effect of depressing the body weight gain of rats.^[8]

References

1. Phenix, A. Generic Hydrocarbon Solvents: a Guide to Nomenclature. WAAC Newsletter Volume 29 Number 2 May 2007. http://cool.conservation-us.org/waac/wn/wn29/wn29-2/wn29-204.pdf
2. Phenix, A. Generic Hydrocarbon Solvents: a Guide to Nomenclature. WAAC Newsletter Volume 29 Number 2 May 2007. http://cool.conservation-us.org/waac/wn/wn29/wn29-2/wn29-204.pdf
3. Patty, F.A.: Industrial hygiene and toxicology, Vol. II, 2nd revised ed., pp. 1198-1201. New York: Interscience Publisher 1962
4. ACGIH: Documentation of the threshold limit values for substances in workroom air, pp.121, 124, 126, 191 and 200 (1971)
5. Browning, E.: Toxicity and metabolism of industrial solvents, pp.145-171. London: Elsevier 1965
6. Ono, Yuichiro; Takeuchi, Yasuhiro; Hisanaga, Naomi; Iwata, Masamitsu; Kitoh, Junzoh; Sugiura, Yasuo (1982-08-01). "Neurotoxicity of petroleum benzine compared with n-hexane". International Archives of Occupational and Environmental Health. 50 (3): 219–229. doi:10.1007/BF00378084. ISSN 0340-0131.
7. Takeuchi Y, Mabuchi C, Takagi S ( 1975) Polyneuropathy caused by petroleum benzine. Int Arch Arbeitsmed 34:185-197
8. Takeuchi Y, Ono Y, Hisanaga N ( 1981) An experimental study on the combined effects of n-hexane and toluene on the peripheral nerve of the rat Br J Ind Med 38:14-19