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 waxy solid and its chemical formula is C₁₇H₃₅CO₂H. 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 following palmitic acid. The triglyceride derived from three molecules of stearic acid is called stearin.

Stearic acid

Names
Preferred IUPAC name Octadecanoic acid
Other names Stearic acid C18:0 (Lipid numbers)
Identifiers
CAS Number	57-11-4 Y
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL46403 Y
ChemSpider	5091 Y
DrugBank	DB03193 Y
ECHA InfoCard	100.000.285
EC Number	200-313-4
IUPHAR/BPS	3377
KEGG	C01530
PubChem CID	5281
RTECS number	WI2800000
UNII	4ELV7Z65AP Y
CompTox Dashboard (EPA)	DTXSID8021642
SMILES CCCCCCCCCCCCCCCCCC(=O)O
Properties
Chemical formula	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
Solubility in water	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 alkyl acetates, alcohols, HCOOCH3, phenyls, CS2, CCl4
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)
Magnetic susceptibility (χ)	−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
Crystal structure	B-form = Monoclinic
Space group	B-form = P21/a
Point group	B-form = Cs 2h
Lattice constant	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)	1 1 0
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