Fatty alcohol

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Fatty alcohol

Fatty alcohols (or long-chain alcohols) are usually high-molecular-weight, straight-chain primary alcohols, but can also range from as few as 4-6 carbons to as many as 22-26, derived from natural fats and oils. The precise chain length varies with the source.[1][2] Some commercially important fatty alcohols are lauryl, stearyl, and oleyl alcohols. They are colourless waxy solids, although impure samples may appear yellow. Fatty alcohols usually have an even number of carbon atoms and a single alcohol group (-OH) attached to the terminal carbon. Some are unsaturated and some are branched. They are widely used in industry.

Production and occurrence[edit]

Most fatty alcohols in nature are found as waxes which are esters with fatty acids and fatty alcohols.[1] They are produced by bacteria, plants and animals for purposes of buoyancy, as source of metabolic water and energy, biosonar lenses (marine mammals) and for thermal insulation in the form of waxes (in plants and insects).[3] Fatty alcohols were unavailable until the early 1900s. They were originally obtained by reduction of wax esters with sodium by the Bouveault–Blanc reduction process. In the 1930s catalytic hydrogenation was commercialized, which allowed the conversion of fatty acid esters, typically tallow, to the alcohols. In the 1940s and 1950s, petrochemicals became an important source of chemicals, and Karl Ziegler had discovered the polymerization of ethylene. These two developments opened the way to synthetic fatty alcohols.

From natural sources[edit]

The traditional and still important source of fatty alcohols are fatty acid esters. Wax esters were formerly extracted from sperm oil, obtained from whales. An alternative plant source is jojoba. Fatty acid triesters, known as triglycerides, are obtained from plant and animal sources. These triesters are subjected to transesterification to give methyl esters, which in turn are hydrogenated to the alcohols. Although tallow is prodominantly C16-C18, the chain length from plant sources are more variable (C6-C24). Higher alcohols (C20–C22) can be obtained from rapeseed or mustard seed. Midcut alcohols (C12-C14) are obtained from coconut or palm oil.

From petrochemical sources[edit]

Fatty alcohols are also prepared from petrochemical sources. In the Ziegler process, ethylene is oligomerized using triethylaluminium followed by air oxidation. This process affords even-numbered alcohols:

Al(C2H5)3 + 18 C2H4 → Al(C14H29)3
Al(C14H29)3 + 1.5 O2 + 1.5 H2O → 3 HOC14H29 + 0.5 Al2O3

Alternatively ethylene can be oligomerized to give mixtures of alkenes, which are subjected to hydroformylation, this process affording odd-numbered aldehyde, which is subsequently hydrogenated. For example, from 1-decene, hydroformylation gives the C11 alcohol:

C8H17CH=CH2 + H2 + CO → C8H17CH2CH2CHO
C8H17CH2CH2CHO + H2 → C8H17CH2CH2CH2OH

In the Shell higher olefin process, the chain-length distribution in the initial mixture of alkene oligomers is adjusted so as to more closely match market demand. Shell does this by means of an intermediate metathesis reaction.[4] The resultant mixture is fractionated and hydroformylated/hydrogenated in a subsequent step.

Applications[edit]

Fatty alcohols are mainly used in the production of detergents and surfactants. They are components also of cosmetics, foods, and as industrial solvents. Due to their amphipathic nature, fatty alcohols behave as nonionic surfactants. They find use as emulsifiers, emollients and thickeners in cosmetics and food industry. About 50% of fatty alcohols used commercially are of natural origin, the remainder being synthetic.[1]

Nutrition[edit]

Very long chain fatty alcohols (VLCFA), obtained from plant waxes and beeswax have been reported to lower plasma cholesterol in humans. They can be found in unrefined cereal grains, beeswax, and many plant-derived foods. Reports suggest that 5–20 mg per day of mixed C24–C34 alcohols, including octacosanol and triacontanol, lower low-density lipoprotein (LDL) cholesterol by 21%–29% and raise high-density lipoprotein cholesterol by 8%–15%.[citation needed] Wax esters are hydrolyzed by a bile salt–dependent pancreatic carboxyl esterase, releasing long chain alcohols and fatty acids that are absorbed in the gastrointestinal tract. Studies of fatty alcohol metabolism in fibroblasts suggest that very long chain fatty alcohols, fatty aldehydes, and fatty acids are reversibly inter-converted in a fatty alcohol cycle. The metabolism of these compounds is impaired in several inherited human peroxisomal disorders, including adrenoleukodystrophy and Sjögren-Larsson syndrome.[5]


Safety[edit]

Human Health[edit]

Fatty alcohols are relatively benign materials, with LD50s (oral, rat) ranging from 3.1-r g/kg for hexanol to 6 -8 g/kg for octadecanol.[1] For a 50 kg person, these values translate to more than 100 g. Tests of acute and repeated exposures have revealed a low level of toxicity from inhalation, oral or dermal exposure of fatty alcohols. Fatty alcohols are not very volatile and the acute lethal concentration is greater than the saturated vapor pressure. Longer chain (C12-C16) fatty alcohols produce fewer health effects than short chain (< C12). Short chain fatty alcohols are considered eye irritants, while long chain alcohols are not.[6] Fatty alcohols exhibit no skin sensitization.[7]

Repeated exposure to fatty alcohols produce low level toxicity and certain compounds in this category can cause local irritation on contact or low-grade liver effects (essentially linear alcohols have a slightly higher rate of occurrence of these effects). No effects on the central nervous system have been seen with inhalation and oral exposure. Tests of repeated bolus dosages of 1-hexanol and 1-octanol showed potential for CNS depression and induced respiratory distress. No potential for peripheral neuropathy has been found. In rats, the no observable adverse effect level (NOAEL) ranges from 200 mg/kg/day to 1000 mg/kg/day by ingestion. There has been no evidence that fatty alcohols are carcinogenic, mutagenic, or cause reproductive toxicity or infertility. Fatty alcohols are effectively eliminated from the body when exposed, limiting possibility of retention or bioaccumulation.[7]

Margins of exposure resulting from consumer uses of these chemicals are adequate for the protection of human health as determined by the Organization for Economic Co-operation and Development (OECD) high production volume chemicals program.[6][8]

Environment[edit]

Fatty alcohols up to chain length C18 are biodegradable, with length up to C16 biodegrading within 10 days completely. Chains C16 to C18 were found to biodegrade from 62% to 76% in 10 days. Chains greater than C18 were found to degrade by 37% in 10 days. Field studies at waste-water treatment plants have shown that 99% of fatty alcohols lengths C12-C18 are removed.[7]

Fate prediction using fugacity modeling has shown that fatty alcohols with chain lengths of C10 and greater in water partition into sediment. Lengths C14 and above are predicted to stay in the air upon release. Modeling shows that each type of fatty alcohol will respond independently upon environmental release.[7]

Aquatic Organisms[edit]

Fish, invertebrates and algae experience similar levels of toxicity with fatty alcohols although it is dependent on chain length with the shorter chain having greater toxicity potential. Longer chain lengths show no toxicity to aquatic organisms.[7]

Chain Size Acute Toxicity for fish Chronic Toxicity for fish
< C11 1–100 mg/l 0.1-1.0 mg/l
C11-C13 0.1-1.0 mg/l 0.1 - <1.0 mg/l
C14-C15 NA 0.01 mg/l
>C16 NA NA

This category of chemicals was evaluated under the Organization for Economic Co-operation and Development (OECD) high production volume chemicals program. No unacceptable environmental risks were identified.[8]

Common names and related compounds[edit]

Name Carbon atoms Branches/saturated? Formula
tert-Butyl alcohol 4 carbon atoms C4H10O
tert-Amyl alcohol 5 carbon atoms C5H12O
3-Methyl-3-pentanol 6 carbon atoms C6H14O
Ethchlorvynol 7 carbon atoms C7H9ClO
1-Octanol (capryl alcohol) 8 carbon atoms C8H18ClO
2-ethyl hexanol 8 carbon atoms branched
pelargonic alcohol (1-nonanol) 9 carbon atoms
1-Decanol (decyl alcohol, capric alcohol) 10 carbon atoms
Undecyl alcohol (1-undecanol, undecanol, Hendecanol) 11 carbon atoms
Lauryl alcohol (Dodecanol, 1-dodecanol) 12 carbon atoms
Tridecyl alcohol (1-tridecanol, tridecanol, isotridecanol) 13 carbon atoms
Myristyl alcohol (1-tetradecanol) 14 carbon atoms
Pentadecyl alcohol (1-pentadecanol, pentadecanol) 15 carbon atoms
cetyl alcohol (1-hexadecanol) 16 carbon atoms
palmitoleyl alcohol (cis-9-hexadecen-1-ol) 16 carbon atoms unsaturated
Heptadecyl alcohol (1-n-heptadecanol, heptadecanol) 17 carbon atoms
stearyl alcohol (1-octadecanol) 18 carbon atoms
Nonadecyl alcohol (1-nonadecanol) 19 carbon atoms
arachidyl alcohol (1-eicosanol) 20 carbon atoms
Heneicosyl alcohol (1-heneicosanol) 21 carbon atoms
behenyl alcohol (1-docosanol) 22 carbon atoms
erucyl alcohol (cis-13-docosen-1-ol) 22 carbon atoms unsaturated
lignoceryl alcohol (1-tetracosanol) 24 carbon atoms
ceryl alcohol (1-hexacosanol) 26 carbon atoms
1-heptacosanol 27 carbon atoms
montanyl alcohol, cluytyl alcohol, or 1-octacosanol 28 carbon atoms
1-nonacosanol 29 carbon atoms
myricyl alcohol, melissyl alcohol, or 1-triacontanol 30 carbon atoms
1-dotriacontanol 32 carbon atoms C32H66O
geddyl alcohol (1-tetratriacontanol) 34 carbon atoms
Cetearyl alcohol

References[edit]

  1. ^ a b c d Klaus Noweck, Wolfgang Grafahrend, "Fatty Alcohols" in Ullmann's Encyclopedia of Industrial Chemistry 2006, Wiley-VCH, Weinheim. doi:10.1002/14356007.a10_277.pub2
  2. ^ http://goldbook.iupac.org/F02330.html
  3. ^ Stephen Mudge; Wolfram Meier-Augenstein, Charles Eadsforth and Paul DeLeo (2010). "What contribution do detergent fatty alcohols make to sewage discharges and the maine environment?". Journal of Environmental Monitoring: 1846–1856. doi:10.1039/C0EM00079E. 
  4. ^ Ashford's Dictionary of Industrial Chemicals, Third edition, 2011, page 6706-6711
  5. ^ Nutritional Significance and Metabolism of Very Long Chain Fatty Alcohols and Acids from Dietary Waxes - Hargrove et al. 229 (3): 215 - Experimental Biology and Medicine
  6. ^ a b Veenstra, Gauke; Catherine Webb, Hans Sanderson, Scott E. Belanger, Peter Fisk, Allen Nielson, Yutaka Kasai, Andreas Willing, Scott Dyer, David Penney, Hans Certa, Kathleen Stanton, Richard Sedlak (2009). "Human health risk assessment of long chain alcohols". Ecotoxicology and Environmental Safety: 1016–1030. doi:10.1016/j.ecoenv.2008.07.012. 
  7. ^ a b c d e UK/ICCA (2006). "SIDS Initial Assessment Profile". OECD Existing Chemicals Database. 
  8. ^ a b Sanderson, Hans; Scott E. Belanger, Peter R. Fisk, Christoph Schäfers, Gauke Veenstra, Allen M. Nielsen, Yutaka Kasai, Andreas Willing, Scott D. Dyer, Kathleen Stanton, Richard Sedlak, (May 2009). "An overview of hazard and risk assessment of the OECD high production volume chemical category—Long chain alcohols [C6–C22] (LCOH)". Ecotoxicology and Environmental Safety 72 (4): 973–979. doi:10.1016/j.ecoenv.2008.10.006. 

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