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The Short Chain Alcohol Esters (SCAE C2-C8) category covers esters from a fatty acid (C8-C29) and a C2-C8 alcohol (ethanol, isopropanol, butanol, isobutanol, pentanol, iso-pentanol, hexanol, 2-ethylhexanol or octanol). This category includes both well-defined mono-constituent substances as well as related UVCB substances with varying fatty acid chain lengths.

Fatty acid esters are generally produced by chemical reaction of an alcohol (e.g. isopropanol) with an organic acid (e.g. stearic acid) in the presence of an acid catalyst (Radzi et al., 2005). The esterification reaction is started by a transfer of a proton from the acid catalyst to the acid to form an alkyloxonium ion. The carboxylic acid is protonated on its carbonyl oxygen followed by a nucleophilic addition of a molecule of the alcohol to a carbonyl carbon of acid. An intermediate product is formed. This intermediate product loses a water molecule and proton to give an ester (Liu et al, 2006; Lilja et al., 2005; Gubicza et al., 2000; Zhao, 2000). Monoesters are the final product of esterification.  

The rationale for grouping the substances in the SCAE C2-C8 category is based on similarities in physicochemical, ecotoxicological and toxicological properties.


In accordance with Article 13 (1) of Regulation (EC) No 1907/2006, "information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI are met. In particular, information shall be generated whenever possible by means other than vertebrate animal tests, which includes the use of information from structurally related substances (grouping or read-across).


In this particular case, the similarity of the SCAE C2-C8 category members is justified, in accordance with the specifications listed in Regulation (EC) No. 1907/2006 Annex XI, 1.5

Grouping of substances and read across, based on representative molecular structure, physico-chemical properties, tox-, ecotoxicological profiles, supported by a robust set of experimental data and QSAR calculations. There is no convincing evidence that any one of these chemicals might lie out of the overall profile of this category, respectively.


Grouping of substances into this category is based on:


• Similar/overlapping structural features or functional groups: All category members are esters of primary alcohols (C2-C8) and fatty acids (C8-C29), with 13 to 32 carbons in total.

• Common precursors and the likelihood of common breakdown products via biological

processes: All category members are subject to enzymatic hydrolysis by pancreatic lipases (Mattson and Volpenhein, 1972; and references therein). The resulting free fatty acids and alcohols are absorbed from the intestine into the blood stream. Fatty acids are either metabolised via the beta-oxidation pathway in order to generate energy for the cell or reconstituted into glyceride esters and stored in the fat depots in the body. The alcohols are metabolised primarily in the liver through a series of oxidative steps, finally yielding carbon dioxide (Berg et al., 2002).

• Similar physico-chemical properties: The log Kow and log Koc values of all category members are high (log Kow > 4, log Koc > 3), increasing with the size of the molecule. The substances are poorly soluble in water and have low vapour pressure. 

• Common properties for environmental fate & eco-toxicological: Based on experimental data , all substances are readily biodegradable and do not show toxic effects up to the limit of water solubility.

• Common levels and mode of human health related effects:All available experimental data indicate that the members of the SCAE C2-C18 category are not acutely toxic, are not irritating to the skin or to the eyes and do not have sensitizing properties. Repeated dose toxicity was shown to be low for all substances. None of the substances showed mutagenic effects, and toxicity to reproduction was low throughout the category.


Having regard to the general rules for grouping of substances and read-across approach laid down in Annex XI, Item 1.5, of Regulation (EC) No 1907/2006, whereby substances may be considered as a category provided that their physicochemical, toxicological and ecotoxicological properties are likely to be similar or follow a regular pattern as a result of structural similarity, the substances listed below are allocated to the category of SCAE C2-C8.



Table 1: Members of the SCAE C2-C8 Category

EC No.


Chemical name

Alcohol Carbon No.

Fatty acid Carbon No.

Total Carbon




ethyl linoleate or ethyl octadeca-9,12-dienoate







Ethyl oleate







Fatty acids, essential, ethyl esters


14 - 22

16 - 24




Isopropyl laurate







Isopropyl Myristate







Isopropyl palmitate







Isopropyl isostearate







Isopropyl oleate







Fatty acids, C16-18, isopropyl esters


16 - 18

19 - 21




Fatty acids, lanolin, isopropyl esters


10 - 29

13 - 32




butyl stearate







Fatty acids, tall-oil, butyl esters







Fatty acids, C16-18, Bu esters


16 - 18

20 - 22




Fatty acids, C16-18 and C18-unsatd., Bu esters


16 - 18

20 - 22

312.53- 340.58



Fatty acids, C16-18 and C18 unsatd. branched and linear, butyl esters


16 - 18

20 - 22

312.54- 340.58



Isobutyl stearate







Fatty acids, C16-18, iso-Bu esters


16 - 18

20 - 22

312.54- 340.60



Fatty acids, C16-18 and C18-unsatd., iso-Bu esters


16 - 18

20 - 22

312.54- 340.60



Isopentyl laurate







Fatty acids, C8-10, 3-methylbutyl esters


8 - 10

13 - 15

214.344- 242.40



Dodecanoic acid, hexyl ester







octyl octanoate







Dodecanoic acid, isooctyl ester







2-Ethylhexyl laurate







Fatty acids, C8-10, 2-ethylhexyl esters


8 - 10

16 - 18




Fatty acids, C8-16, 2-ethylhexyl esters


12 - 14

20 - 22




Hexadecanoic acid, 2-ethylhexyl ester







2-Ethyl hexyl Stearate







Fatty acids, coco, 2-ethylhexyl esters


12 - 18

20 - 26




Fatty acids, C16-18, 2-ethylhexyl esters


16 - 18

24 - 26




Fatty acids, C16-18 and C18-unsatd., 2-ethylhexyl esters


16 - 18

24 - 26




2-Ethylhexyl oleate






In order to avoid the need to test every substance for every endpoint, the category concept is applied for the assessment of environmental fate and environmental and human health hazards. Thus where applicable, environmental and human health effects are predicted from adequate and reliable data for source substance(s) within the group by interpolation to the target substances in the group (read-across approach) applying the group concept in accordance with Annex XI, Item 1.5, of Regulation (EC) No 1907/2006. In particular, for each specific endpoint the source substance(s) structurally closest to the target substance is/are chosen for read-across, with due regard to the requirements of adequacy and reliability of the available data. Structural similarities and similarities in properties and/or activities of the source and target substance are the basis of read-across.

A detailed justification for the grouping of chemicals and read-across is provided in the technical dossier (see IUCLID Section 13).



Basic toxicokinetics


There are no studies available in which the toxicokinetic behaviour of Fatty acids, C16-18, butyl esters (CAS No. 85408-76-0) has been investigated.

Therefore, in accordance with Annex VIII, Column 1, Item 8.8.1, of Regulation (EC) No 1907/2006 and with Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA, 2008), assessment of the toxicokinetic behaviour of the substance Fatty acids, C16-18, butyl esters is conducted to the extent that can be derived from the relevant available information. This comprises a qualitative assessment of the available substance specific data on physico-chemical and toxicological properties according to Guidance on information requirements and chemical safety assessment Chapter R.7c: Endpoint specific guidance (ECHA, 2008) and taking into account further available information on the SCAE C2-8 category.

The substance Fatty acids, C16-18, butyl esters consists of esters of butanol and fatty acids with a chain length of C16-18 and meets the definition of an UVCB substance.

The substance Fatty acids, C16-18, butyl esters can be solid or liquid at room temperature as the melting point is between 18 and 23 °C (Herzog, 2011). The substance has a molecular weight in the range of 312.53 and 340.58 g/mol. The log Pow is calculated to be in the range of 8.72 to 9.70 (Ozolins, 2011). The vapour pressure for the single components is calculated to be between 9.9E-6 and 2.31E-4 Pa at 20 °C (Nagel, 2011) and the water solubility of Fatty acids, C16-18, butyl esters is determined to be < 0.05 mg/L (Frischmann, 2012).


Absorption is a function of the potential for a substance to diffuse across biological membranes. The most useful parameters providing information on this potential are the molecular weight, the octanol/water partition coefficient (log Pow) value and the water solubility. The log Pow value provides information on the relative solubility of the substance in water and lipids (ECHA, 2008).


The smaller the molecule, the more easily it will be taken up. In general, molecular weights below 500 are favourable for oral absorption (ECHA, 2008). As the molecular weight of Fatty acids, C16-18, butyl esters is 312.53 and 340.58 g/mol, absorption of the molecule in the gastrointestinal tract is in general anticipated.

Absorption after oral administration is also expected when the “Lipinski Rule of Five” (Lipinski et al. (2001), refined by Ghose et al. (1999)) is applied to the substance Fatty acids, C16-18, butyl esters, as all rules are fulfilled except for the log Pow, which is above the given range of -0.4 to 5.6.

The log Pow of 8.72 to 9.70 suggests that Fatty acids, C16-18, butyl esters are favourable for absorption by micellar solubilisation, as this mechanism is of importance for highly lipophilic substances (log Pow > 4), which are poorly soluble in water (1 mg/L or less).

After oral ingestion, esters of short-chain (C2-8) alcohols and fatty acids undergo stepwise chemical changes in the gastro-intestinal fluids as a result of enzymatic hydrolysis. The respective alcohol as well as the fatty acid is formed, even though it was shown in-vitro that the hydrolysis rate of methyl oleate was lower when compared with the hydrolysis rate of the triglyceride Glycerol trioleate (Mattson and Volpenhein, 1972). The physico-chemical characteristics of the cleavage products (e.g. physical form, water solubility, molecular weight, log Pow, vapour pressure, etc.) are likely to be different from those of the parent substance before absorption into the blood takes place, and hence the predictions based upon the physico-chemical characteristics of the parent substance do no longer apply (ECHA, 2008). However, also for both cleavage products, it is anticipated that they are absorbed in the gastro-intestinal tract. The highly lipophilic fatty acid is absorbed by micellar solubilisation (Ramirez et al., 2001), whereas the alcohol is readily dissolved into the gastrointestinal fluids and absorbed from the gastrointestinal tract. 

Exemplarily, experimental data of the structurally similar Ethyl oleate (CAS No. 111-62-6) confirmed this assumption: The absorption, distribution, and excretion of 14C-labelled Ethyl oleate was studied in Sprague Dawley rats after a single, oral dose of 1.7 or 3.4 g/kg bw. It was shown that the test material was well (approximately 70–90%) absorbed (Bookstaff et al., 2003).

Overall, a systemic bioavailability of Fatty acids, C16-18, butyl esters and/or the respective cleavage products in humans is considered likely after oral uptake of the substance.


The smaller the molecule, the more easily it may be taken up. In general, a molecular weight below 100 favours dermal absorption, above 500 the molecule may be too large (ECHA, 2008). As the molecular weight of Fatty acids, C16-18, butyl esters is in the range 312.53 and 340.58 g/mol, dermal absorption of the molecule cannot be excluded.

If the substance is a skin irritant or corrosive, damage to the skin surface may enhance penetration (ECHA, 2008). As Fatty acids, C16-18, butyl esters is not skin irritating in humans, enhanced penetration of the substance due to local skin damage can be excluded.

Based on a QSAR calculated dermal absorption a value in the range of 1.22E-05 to 3.3-E05 mg/cm2/event (very low) was predicted for Fatty acids, C 16-18, butyl esters (Dermwin v.2.01, EPI Suite). Based on this value the substance has a low potential for dermal absorption.

For substances with a log Pow above 4, the rate of dermal penetration is limited by the rate of transfer between the stratum corneum and the epidermis, but uptake into the stratum corneum will be high. For substances with a log Pow above 6, the rate of transfer between the stratum corneum and the epidermis will be slow and will limit absorption across the skin, and the uptake into the stratum corneum itself is also slow. The substance must be sufficiently soluble in water to partition from the stratum corneum into the epidermis (ECHA, 2008). As the water solubility of Fatty acids, C16-18, butyl esters is estimated to be less than 0.05 g/L, dermal uptake is likely to be very low.

Overall, the calculated low dermal absorption potential, the low water solubility, the molecular weight (>100), the high log Pow value and the fact that the substance is not irritating to skin implies that dermal uptake of Fatty acids, C16-18, butyl esters in humans is considered as very limited.


Fatty acids, C16-18, butyl esters has a low vapour pressure in the range of 9.9E-6 to 2.31E-4 Pa at 20 °C thus being of low volatility. Therefore, under normal use and handling conditions, inhalation exposure and thus availability for respiratory absorption of the substance in the form of vapours, gases, or mists is not significant.

However, the substance may be available for respiratory absorption in the lung after inhalation of aerosols, if the substance is sprayed. In humans, particles with aerodynamic diameters below 100μm have the potential to be inhaled. Particles with aerodynamic diameters below 50μm may reach the thoracic region and those below 15μm the alveolar region of the respiratory tract (ECHA, 2008). Lipophilic compounds with a log Pow > 4, that are poorly soluble in water (1 mg/L or less) like Fatty acids, C16-18, butyl esters can be taken up by micellar solubilisation.

Overall, a systemic bioavailability of Fatty acids, C16-18, butyl esters in humans is considered likely after inhalation of aerosols with aerodynamic diameters below 15μm.


Highly lipophilic substances tend in general to concentrate in adipose tissue, and depending on the conditions of exposure may accumulate. Although there is no direct correlation between the lipophilicity of a substance and its biological half-life, it is generally the case that substances with high log Pow values have long biological half-lives. The high log Pow of > 5 implies that Fatty acids, C16-18, butyl esters may have the potential to accumulate in adipose tissue (ECHA, 2008).

However, as further described in the section metabolism below, esters of alcohols and fatty acids undergo esterase-catalysed hydrolysis, leading to the cleavage products butanol and the respective C16-18 fatty acid.

The log Pow of the first cleavage product butanol is 0.88, indicating a high solubility in water (HSDB). Consequently, there is no potential for butanol to accumulate in adipose tissue. The second cleavage product, the fatty acid, can be stored as triglycerides in adipose tissue depots or be incorporated into cell membranes. At the same time, fatty acids are also required as a source of energy. Thus, stored fatty acids underlie a continuous turnover as they are permanently metabolized and excreted. Bioaccumulation of fatty acids only takes place, if their intake exceeds the caloric requirements of the organism.

Overall, the available information indicates that no significant bioaccumulation of the parent substance in adipose tissue is anticipated.


Distribution within the body through the circulatory system depends on the molecular weight, the lipophilic character and water solubility of a substance. In general, the smaller the molecule, the wider is the distribution. If the molecule is lipophilic, it is likely to distribute into cells and the intracellular concentration may be higher than extracellular concentration particularly in fatty tissues (ECHA, 2008).

Fatty acids, C16-18, butyl esters undergo chemical changes as a result of enzymatic hydrolysis, leading to the cleavage products butanol and the respective fatty acid.

Butanol, a small, water-soluble substance, will be distributed in aqueous compartments of the organism. Fatty acids are also distributed in the organism and can be taken up by different tissues. They can be stored as triglycerides in adipose tissue depots or they can be incorporated into cell membranes (Masoro, 1977).

Overall, the available information indicates that the cleavage products, butanol and the fatty acid will be distributed in the organism.


Esters of fatty acids are hydrolysed to the corresponding alcohol (butanol) and fatty acid by esterases (Fukami and Yokoi, 2012). Depending on the route of exposure, esterase-catalysed hydrolysis takes place at different places in the organism: After oral ingestion, esters of alcohols and fatty acids undergo enzymatic hydrolysis already in the gastro-intestinal fluids. In contrast, substances that are absorbed through the pulmonary alveolar membrane or through the skin enter the systemic circulation directly before entering the liver where hydrolysis will basically take place.

The rate of hydrolysis of Fatty acids, C16-18, butyl esters was determined to be 242 µmol/g*min by in vitro analysis. After 4 h, 50% of the substance was hydrolysed in simulated intestinal fluid in the presence of pancreatin but no hydrolysis occurred in simulated saliva or simulated gastric fluid (Cognis, 1993a/b).

The first cleavage product, butanol, is oxidized by the non-specific alcohol dehydrogenase (ADH) to butyraldehyde, which is further oxidized to butyrate via mitochondrial aldehyde dehydrogenase. After activation to butyryl CoA it is also combusted to carbon dioxide via beta-oxidation (HSDB).

The second cleavage product, the fatty acid, is stepwise degraded byβ-oxidation based on enzymatic removal of C2 units in the matrix of the mitochondria in most vertebrate tissues. The C2 units are cleaved as acyl-CoA, the entry molecule for the citric acid cycle. The omega- and alpha-oxidation, alternative pathways for oxidation, can be found in the liver and the brain, respectively (CIR, 1987).


The main route of excretion of Fatty acids, C16-18, butyl esters is expected to be by expired air as CO2 after metabolic degradation. The second route of excretion is expected to be by biliary excretion with the faeces. For the cleavage products, the main route is renal excretion via the urine due to the low molecular weight and the high water solubility. A large proportion of butanol is excreted via exhalation and urinary excretion.

Experimental data of the structurally similar Ethyl oleate (CAS No. 111-62-6, ethyl ester of oleic acid) are regarded exemplarily. The absorption, distribution, and excretion of 14C labelled Ethyl oleate was studied in Sprague Dawley rats after a single, oral dose of 1.7 or 3.4 g/kg bw. At sacrifice (72 h post-dose), mesenteric fat was the tissue with the highest concentration of radioactivity. The other organs and tissues had very low concentrations of test material-derived radioactivity. The main route of excretion of radioactivity in the groups was via expired air as CO2. Excretion of 14CO2 was rapid in the groups, thus 12 h after dosing 40-70% of the administered dose was excreted in expired air (consistent withβ-oxidation of fatty acids). The females had a higher percentage of radioactivity expired as CO2 than the corresponding males. A second route of elimination of radioactivity was via the faeces. Faecal elimination of Ethyl oleate appeared to be dose-dependent. At the dose of 1.7 g/kg bw, 7–8% of the administered dose was eliminated in the faeces. At the dose of 3.4 g/kg bw, approximately 20% of the administered dose was excreted in the faeces. Renal elimination was minimal, with approximately 2% of the radioactivity recovered in urine over 72 h post-dose for the groups (Bookstaff et al., 2003).


*Berg, J.M., Tymoczko, J.L. and Stryer, L., 2002, Biochemistry, 5thedition, W.H. Freeman and Company

* Bookstaff et al. (2003). The safety of the use of ethyl oleate in food is supported by metabolism data in rats and clinical safety data in humans. Regul Toxicol Pharm 37: 133-148.

* CIR (1987). Final report on the safety assessment of oleic acid, lauric acid, palmitic acid, myristic acid, stearic acid. J. of the Am. Coll. of Toxicol.6 (3): 321-401.

* Cognis (1993a). Determination of the enzymatic hydrolysis of fatty acid-alkyl esters.

* Cognis (1993b). Determination of the hydrolysis of fatty acid alkyl esters by simulated saliva, gastric fluid and intestinal fluid.

* ECHA (2008). Guidance on information requirements and chemical safety assessment, Chapter R.7c: Endpoint specific guidance.

* Fukami, T. and Yokoi, T. (2012). The Emerging Role of Human Esterases. Drug Metabolism and Pharmacokinetics, Advance publication July 17th, 2012.

* Ghose et al. (1999). A Knowledge-Based Approach in Designing Combinatorial or Medicinal Chemistry Libraries for Drug Discovery. J. Comb. Chem. 1 (1): 55-68.

* Gubicza, L. et al. (2000). Large-scale enzymatic production of natural flavour esters in organic solvent with continuous water removal. Journal of Biotechnology 84(2): 193-196

* HSDB – Hazardous Substances Data Bank, Toxnet Home, National Library of Medicine

* Lilja, J. et al. (2005). Esterification of propanoic acid with ethanol, 1-propanol and butanol over a heterogeneous fiber catalyst. Chemical Engineering Journal, 115(1-2): 1-12

* Lipinski et al. (2001). Experimental and computational approaches to estimate solubility and permeability in drug discovery and development settings. Adv. Drug Del. Rev. 46: 3-26.

* Liu, Y. et al. (2006). A comparison of the esterification of acetic acid with methanol using heterogeneous versus homogeneous acid catalysis. Journal of Catalysis 242: 278-286

* Masoro (1977). Lipids and lipid metabolism. Ann. Rev. Physiol.39: 301-321.

* Mattson, F.H. and Volpenhein, R.A. (1972). Hydrolysis of fully esterified alcohols containing from one to eight hydroxyl groups by the lipolytic enzymes of the rat pancreatic juice. Journal of lipid research 13: 325-328

* Radzi, S.M. et al. (2005). High performance enzymatic synthesis of oleyl oleate using immobilised lipase from Candida antartica. Electronic Journal of Biotechnology 8: 292-298

* Ramirez et al. (2001). Absorption and distribution of dietary fatty acids from different sources. Early Human Development 65 Suppl.: S95–S101.

*Tocher, D.R. (2003):Metabolism and function of lipids and fatty acids in teleost fish,Reviews of Fisheries Science, 11 (2), 197

* Zhao, Z. (2000). Synthesis of butyl propionate using novel aluminophosphate molecular sieve as catalyst.Journal of Molecular Catalysis 154(1-2): 131-135.