n-Butanol occurs naturally as a minor product of the fermentation of sugars and other carbohydrates, and is present in many foods and beverages. It is also a permitted artificial flavorant in the United States, used in butter, cream, fruit, rum, whiskey, ice cream and ices, candy, baked goods and cordials. It is also used in a wide range of consumer products.
The largest use of n-butanol is as an industrial intermediate, particularly for the manufacture of butyl acetate (itself an artificial flavorant and industrial solvent). It is a petrochemical, manufactured from propylene and usually used close to the point of manufacture. Estimated production figures for 1997 are: United States 784,000 tonnes; Western Europe 575,000 tonnes; Japan 225,000 tonnes.
The unmodified term butanol usually refers to the straight chain isomer with the alcohol functional group at the terminal carbon, which is also known as n-butanol or 1-butanol. The straight chain isomer with the alcohol at an internal carbon is sec-butanol or 2-butanol. The branched isomer with the alcohol at a terminal carbon is isobutanol or 2-methyl-1-propanol, and the branched isomer with the alcohol at the internal carbon is tert-butanol or 2-methyl-2-propanol.
The butanol isomers have different melting and boiling points. n-butanol and isobutanol have limited solubility, sec-butanol has substantially greater solubility, while tert-butanol is fully miscible with water above tert-butanol's melting point. The hydroxyl group makes the molecule polar, promoting solubility in water, while the longer hydrocarbon chain mitigates the polarity and reduces solubility. The shorter chain molecules of methanol, ethanol, propanol, and tert-butanol are fully miscible with water, while n-butanol is only moderately soluble because of the diminishing polarity in the longer hydrocarbon group.
Butanol is used as a solvent for a wide variety of chemical and textile processes, in organic synthesis, and as a chemical intermediate. It is also used as a paint thinner and a solvent in other coating applications where a relatively slow evaporating latent solvent is preferable, as with lacquers and ambient-cured enamels. It is also used as a component of hydraulic and brake fluids.
It is also used as a base for perfumes, but on its own has a highly alcoholic aroma.
Salts of butanol are chemical intermediates; for example, alkali metal salts of tert-butanol are tert-butoxides.
n-Butanol is used as an ingredient in perfumes and as a solvent for the extraction of essential oils.n-Butanol is also used as an extractant in the manufacture of antibiotics, hormones, and vitamins; a solvent for paints, coatings, natural resins, gums, synthetic resins, dyes, alkaloids, and camphor. Other miscellaneous applications of n-butanol are as a swelling agent in textiles, as a component of hydraulic brake fluids, cleaning formulations, degreasers, and repellents; and as a component of ore floation agents, and of wood-treating systems.
Butanol is considered as a potential biofuel (butanol fuel). Butanol at 85 percent strength can be used in cars designed for gasoline (petrol) without any change to the engine (unlike 85% ethanol), and it contains more energy for a given volume than ethanol and almost as much as gasoline, and a vehicle using butanol would return fuel consumption more comparable to gasoline than ethanol. Butanol can also be added to diesel fuel to reduce soot emissions.
n-Butanol occurs naturally as a result of carbohydrate fermentation in a number of alcoholic beverages, including beer, grape brandies, wine, and whisky. It has been detected in the volatiles of hops, jack fruit, heat-treated milks, musk melon, cheese, southern pea seed, and cooked rice.n-Butanol is also formed during deep frying of corn oil, cottonseed oil, trilinolein, and triolein.
n-Butanol is used as an ingredient in processed and artificial flavourings, and for the extraction of lipid-free protein from egg yolk, natural flavouring materials and vegetable oils, the manufacture of hop extract for beermaking, and as a solvent in removing pigments from moist curd leaf protein concentrate.
The acute toxicity of n-butanol is relatively low, with oral LD50 values of 790–4,360 mg/kg (rat; comparable values for ethanol are 7,000–15,000 mg/kg). No deaths were reported at an inhaled concentration of 8,000 ppm (4-hour exposure, rats). At sub-lethal doses, n-butanol acts as a depressant of the central nervous system, similar to ethanol: one study in rats indicated that the intoxicating potency of n-butanol is some six times higher than that of ethanol, possibly because of its slower transformation by alcohol dehydrogenase.
n-Butanol is a natural component of many alcoholic beverages, albeit in low (but variable) concentrations. It (along with similar fusel alcohols) is reputed to be responsible for severe "hangovers", although experiments in animal models show no evidence for this. An unknown dose n-Butanol was consumed by a 47-year-old male with no previous medical history, leading to a range of adverse health effects.[clarification needed]
Like many alcohols, butanol is considered toxic. It has shown low order of toxicity in single dose experiments to laboratory animals. and is considered safe enough for use in cosmetics. Brief, repeated overexposure with the skin can result in depression of the central nervous system, as with other short-chain alcohols. Exposure may also cause severe eye irritation and moderate skin irritation. The main dangers are from prolonged exposure to fumes. In extreme cases this includes suppression of the central nervous system and even death. Under most circumstances, butanol is quickly metabolized to carbon dioxide. It has not been shown to damage DNA or cause cancer.
Liquid n-butanol, as is common with most organic solvents, is extremely irritating to the eyes; repeated contact with the skin can also cause irritation. This is believed to be a generic effect of "defatting". No skin sensitization has been observed. Irritation of the respiratory pathways occurs only at very high concentrations (>2,400 ppm).
With a flash point of 35 °C, n-butanol presents a moderate fire hazard: it is slightly more flammable than kerosene or diesel fuel but less flammable than many other common organic solvents. The depressant effect on the central nervous system (similar to ethanol intoxication) is a potential hazard when working with n-butanol in enclosed spaces, although the odour threshold (0.2–30 ppm) is far below the concentration which would have any neurological effect.
n-Butanol is of low toxicity to aquatic vertebrates and invertebrates. It is rapidly biodegraded in water, although an estimated 83% partitions to air where it is degraded by hydroxyl radicals with a half-life of 1.2–2.3 days. It has low potential to bioaccumulate. A potential hazard of significant discharges to watercourses is the rise in chemical oxygen demand (C.O.D.) associated with its biodegradation.
^Dubey, Gyan (2008). "Study of densities, viscosities, and speeds of sound of binary liquid mixtures of butan-1-ol with n-alkanes (C6, C8, and C10) at T = (298.15, 303.15, and 308.15) K". The Journal of Chemical Thermodynamics. 40 (2): 309–320. doi:10.1016/j.jct.2007.05.016.
^ abcdefgn-Butanol(PDF), SIDS Initial Assessment Report, Geneva: United Nations Environment Programme, April 2005.
^21 C.F.R. § 172.515; 42 FR 14491, Mar. 15, 1977, as amended.
^Hall, R. L.; Oser, B. L. (1965), "Recent progress in the consideration of flavouring ingredients under the food additives amendment. III. Gras substances", Food Technol.: 151, cited in Butanols: four isomers, Environmental Health Criteria monograph No. 65, Geneva: World Health Organization, 1987, ISBN92-4-154265-9.
^ abcdeMellan, I. (1950), Industrial Solvents, New York: Van Nostrand Reinhold, pp. 482–88, cited in Butanols: four isomers, Environmental Health Criteria monograph No. 65, Geneva: World Health Organization, 1987, ISBN92-4-154265-9.
^ abcDoolittle, A. K. (1954), The Technology of Solvents and Plasticizers, New York: Wiley, pp. 644–45, cited in Butanols: four isomers, Environmental Health Criteria monograph No. 65, Geneva: World Health Organization, 1987, ISBN92-4-154265-9.
^ abMonich, J. A. (1968), Alcohols: Their Chemistry, Properties, and Manufacture, New York: Chapman and Reinhold, cited in Butanols: four isomers, Environmental Health Criteria monograph No. 65, Geneva: World Health Organization, 1987, ISBN92-4-154265-9.
^Harris O.; et al. (August 1998). Toxicological Profile for 2-Butoxyethanol and 2-butoxyethanol acetate. U.S. Dept of Health and Human Services.
^ZA 7801031, Amundsen, J.; R. J. Goodwin & W. H. Wetzel, "Water-soluble pentachlorophenol and tetrachlorophenol wood-treating systems", published 28 Feb. 1979.
^Antoni, D; Zverlov, V. & Schwarz, W H. (2007). "Biofuels from Microbes". Applied Microbiology and Biotechnology. 77: 23–35. doi:10.1007/s00253-007-1163-x.
^Bonte, W. (1979), "Congener substances in German and foreign beers", Blutalkohol, 16: 108–24, cited in Butanols: four isomers, Environmental Health Criteria monograph No. 65, Geneva: World Health Organization, 1987, ISBN92-4-154265-9.
^Schreier, Peter; Drawert, Friedrich; Winkler, Friedrich (1979), "Composition of neutral volatile constituents in grape brandies", J. Agric. Food Chem., 27 (2): 365–72, doi:10.1021/jf60222a031.
^Bonte, W. (1978), "Congener content of wine and similar beverages", Blutalkohol, 15: 392–404, cited in Butanols: four isomers, Environmental Health Criteria monograph No. 65, Geneva: World Health Organization, 1987, ISBN92-4-154265-9.
^Postel, W.; Adam, L. (1978), "Gas chromatographic characterization of whiskey. III. Irish whiskey", Branntweinwirtschaft, 118: 404–7, cited in Butanols: four isomers, Environmental Health Criteria monograph No. 65, Geneva: World Health Organization, 1987, ISBN92-4-154265-9.
^Tressl, Roland; Friese, Lothar; Fendesack, Friedrich; Koeppler, Hans (1978), "Studies of the volatile composition of hops during storage", J. Agric. Food Chem., 26 (6): 1426–30, doi:10.1021/jf60220a036.
^Jaddou, Haytham A.; Pavey, John A.; Manning, Donald J. (1978), "Chemical analysis of flavor volatiles in heat-treated milks", J. Dairy Res., 45 (3): 391–403, doi:10.1017/S0022029900016617.
^Yabumoto, K.; Yamaguchi, M.; Jennings, W. G. (1978), "Production of volatile compounds by Muskmelon, Cucumis melo", Food Chem., 3 (1): 7–16, doi:10.1016/0308-8146(78)90042-0.
^Dumont, Jean Pierre; Adda, Jacques (1978), "Occurrence of sesquiterpones in mountain cheese volatiles", J. Agric. Food Chem., 26 (2): 364–67, doi:10.1021/jf60216a037.
^Fisher, Gordon S.; Legendre, Michael G.; Lovgren, Norman V.; Schuller, Walter H.; Wells, John A. (1979), "Volatile constituents of southernpea seed [Vigna unguiculata (L.) Walp.]", J. Agric. Food Chem., 27 (1): 7–11, doi:10.1021/jf60221a040.
^Chang, S. S.; Peterson, K. J.; Ho, C. (1978), "Chemical reactions involved in the deep-fat frying of foods", J. Am. Oil Chem. Soc.: 718–27, cited in Butanols: four isomers, Environmental Health Criteria monograph No. 65, Geneva: World Health Organization, 1987, ISBN92-4-154265-9.
^Gaillard, D.; Derache, R. (1965), "Métabilisation de différents alcools présents dans les biossons alcooliques chez le rat", Trav. Soc. Pharmacol. Montpellier, 25: 541–62, cited in Butanols: four isomers, Environmental Health Criteria monograph No. 65, Geneva: World Health Organization, 1987, ISBN92-4-154265-9.
^Ethanol(PDF), SIDS Initial Assessment Report, Geneva: United Nations Environment Programme, August 2005.
^Woo, Kang-Lyung (2005), "Determination of low molecular weight alcohols including fusel oil in various samples by diethyl ether extraction and capillary gas chromatography", J. AOAC Int., 88 (5): 1419–27, doi:10.5555/jaoi.2005.88.5.1419, PMID16385992.
^ abWysocki, C. J.; Dalton, P. (1996), Odor and Irritation Thresholds for 1-Butanol in Humans, Philadelphia: Monell Chemical Senses Center, cited in n-Butanol(PDF), SIDS Initial Assessment Report, Geneva: United Nations Environment Programme, April 2005.
^Cometto-Muñiz, J. Enrique; Cain, William S. (1998), "Trigeminal and Olfactory Sensitivity: Comparison of Modalities and Methods of Measurement", Int. Arch. Occup. Environ. Health, 71 (2): 105–10, doi:10.1007/s004200050256, PMID9580447.