Stearic Acid

Stearic acid 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 (156.9 °F) °C and a pKa of 4.50.

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Stearic acid^[1]
Names



Preferred IUPAC name Octadecanoic acid
Other names Stearic acid C18:0 (Lipid numbers)
Identifiers
CAS Number	57-11-4
3D model (JSmol)	Interactive image
ChEMBL	ChEMBL46403
ChemSpider	5091
DrugBank	DB03193
ECHA InfoCard	100.000.285
EC Number	200-313-4
IUPHAR/BPS	3377
KEGG	C01530
PubChem CID	5281
RTECS number	WI2800000
UNII	4ELV7Z65AP
CompTox Dashboard (EPA)	DTXSID8021642
SMILES
Properties
Chemical formula	C₁₈H₃₆O₂
Molar mass	284.484 g·mol⁻¹
Appearance	White solid
Odor	Pungent, oily
Density	0.9408 g/cm³ (20 °C)^[2] 0.847 g/cm³ (70 °C)
Melting point	69.3 °C (156.7 °F; 342.4 K)^[2]
Boiling point	361 °C (682 °F; 634 K) decomposes 232 °C (450 °F; 505 K) at 15 mmHg^[2]
Solubility in water	0.0018 g/100 g (0 °C) 0.0029 g/100 g (20 °C) 0.0034 g/100 g (30 °C) 0.0042 g/100 g (45 °C) 0.0050 g/100 g (60 °C)^[3]
Solubility	Soluble in alkyl acetates alcohols methyl formate phenyls carbon disulfide carbon tetrachloride ^[4]
Solubility in dichloromethane	3.58 g/100 g (25 °C) 8.85 g/100 g (30 °C) 18.3 g/100 g (35 °C)^[4]
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)^[4]
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)^[3]
Solubility in acetone	4.73 g/100 g^[5]
Solubility in chloroform	15.54 g/100 g^[5]
Solubility in toluene	13.61 g/100 g^[5]
Vapor pressure	0.01 kPa (158 °C)^[2] 0.46 kPa (200 °C) 16.9 kPa (300 °C)^[6]
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)^[7]
Refractive index (n_D)	1.4299 (80 °C)^[2]
Structure
Crystal structure	B-form = Monoclinic^[8]
Space group	B-form = P2₁/a^[8]
Point group	B-form = C^s _2h^[8]
Lattice constant	a = 5.591 Å, b = 7.404 Å, c = 49.38 Å (B-form)^[8] α = 90°, β = 117.37°, γ = 90°
Thermochemistry
Heat capacity (C)	501.5 J/mol·K^[2]^[6]
Std molar entropy (S^⦵₂₉₈)	435.6 J/mol·K^[2]
Std enthalpy of formation (Δ_fH^⦵₂₉₈)	−947.7 kJ/mol^[2]
Std enthalpy of combustion (Δ_cH^⦵₂₉₈)	−11342.4 kJ/mol^[9]
Hazards
NFPA 704 (fire diamond)	1 1 0
Flash point	205 °C (401 °F; 478 K)
Lethal dose or concentration (LD, LC):
LD₅₀ (median dose)	4640 mg/kg (rats, oral)^[10] 21.5 mg/kg (rats, intravenous)^[4]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references