Stearic acid
Stearic acid (/ˈstɪərɪk/ STEER-ik, /stiˈærɪk/ stee-ARR-ik) is a saturated fatty acid with an 18-carbon chain. The IUPAC name is octadecanoic acid. It is a soft waxy solid with the formula CH3(CH2)16CO2H. The triglyceride derived from three molecules of stearic acid is called stearin. Stearic acid is a prevalent fatty-acid in nature, found in many animal and vegetable fats, but is usually higher in animal fat than vegetable fat. It has a melting point of 69.4 °C and a pKa of 4.50.
| Names | |
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| Preferred IUPAC name
Octadecanoic acid | |
| Other names
Stearic acid C18:0 (Lipid numbers) | |
| Identifiers | |
3D model (JSmol) |
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| ChemSpider | |
| DrugBank | |
| ECHA InfoCard | 100.000.285 |
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PubChem CID |
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| UNII | |
CompTox Dashboard (EPA) |
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| Properties | |
| C18H36O2 | |
| Molar mass | 284.484 g·mol−1 |
| Appearance | White solid |
| Odor | Pungent, oily |
| Density | 0.9408 g/cm3 (20 °C) 0.847 g/cm3 (70 °C) |
| Melting point | 69.3 °C (156.7 °F; 342.4 K) |
| Boiling point | 361 °C (682 °F; 634 K) decomposes 232 °C (450 °F; 505 K) at 15 mmHg |
| 0.00018 g/100 g (0 °C) 0.00029 g/100 g (20 °C) 0.00034 g/100 g (30 °C) 0.00042 g/100 g (45 °C) 0.00050 g/100 g (60 °C) | |
| Solubility | Soluble in |
| Solubility in dichloromethane | 3.58 g/100 g (25 °C) 8.85 g/100 g (30 °C) 18.3 g/100 g (35 °C) |
| Solubility in hexane | 0.5 g/100 g (20 °C) 4.3 g/100 g (30 °C) 19 g/100 g (40 °C) 79.2 g/100 g (50 °C) 303 g/100 g (60 °C) |
| Solubility in ethanol | 1.09 g/100 mL (10 °C) 2.25 g/100 g (20 °C) 5.42 g/100 g (30 °C) 22.7 g/100 g (40 °C) 105 g/100 g (50 °C) 400 g/100 g (60 °C) |
| Solubility in acetone | 4.73 g/100 g |
| Solubility in chloroform | 15.54 g/100 g |
| Solubility in toluene | 13.61 g/100 g |
| Vapor pressure | 0.01 kPa (158 °C) 0.46 kPa (200 °C) 16.9 kPa (300 °C) |
| −220.8·10−6 cm3/mol | |
| Thermal conductivity | 0.173 W/m·K (70 °C) 0.166 W/m·K (100 °C) |
Refractive index (nD) |
1.4299 (80 °C) |
| Structure | |
| B-form = Monoclinic | |
| B-form = P21/a | |
| B-form = Cs 2h | |
a = 5.591 Å, b = 7.404 Å, c = 49.38 Å (B-form) α = 90°, β = 117.37°, γ = 90° | |
| Thermochemistry | |
Heat capacity (C) |
501.5 J/mol·K |
Std molar entropy (S⦵298) |
435.6 J/mol·K |
Std enthalpy of formation (ΔfH⦵298) |
−947.7 kJ/mol |
Std enthalpy of combustion (ΔcH⦵298) |
−11342.4 kJ/mol |
| Hazards | |
| NFPA 704 (fire diamond) | |
| Flash point | 113 °C (235 °F; 386 K) |
| Lethal dose or concentration (LD, LC): | |
LD50 (median dose) |
4640 mg/kg (rats, oral) 21.5 mg/kg (rats, intravenous) |
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references | |
Its name comes from the Greek word στέαρ "stéar", which means tallow. The salts and esters of stearic acid are called stearates. As its ester, stearic acid is one of the most common saturated fatty acids found in nature and in the food supply, following palmitic acid. Dietary sources of stearic acid include meat, poultry, fish, eggs, dairy products, and foods prepared with fats; beef tallow, lard, butterfat, cocoa butter, and shea butter are rich fat sources of stearic acid.