Lactose is a disaccharide sugar synthesized by galactose and glucose subunits and has the molecular formula C₁₂H₂₂O₁₁. Lactose makes up around 2–8% of milk (by mass). The name comes from lac (gen. lactis), the Latin word for milk, plus the suffix -ose used to name sugars. The compound is a white, water-soluble, non-hygroscopic solid with a mildly sweet taste. It is used in the food industry.[5]

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Lactose
Names

IUPAC name β-D-Galactopyranosyl-(1→4)-D-glucose
Preferred IUPAC name (2R,3R,4S,5R,6S)-2-()-6-{[(2R,3S,4R,5R,6R)-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxy}oxane-3,4,5-triol
Other names Milk sugar Lactobiose 4-O-β-D-Galactopyranosyl-D-glucose
Identifiers
CAS Number	63-42-3^Y
3D model (JSmol)	Interactive image
Beilstein Reference	90841
ChEBI	CHEBI:36218^Y
ChEMBL	ChEMBL417016^Y
ChemSpider	5904^Y
ECHA InfoCard	100.000.509
EC Number	200-559-2
Gmelin Reference	342369
KEGG	C01970
PubChem CID	6134
UNII	3SY5LH9PMK^Y
CompTox Dashboard (EPA)	DTXSID2023193
InChI InChI=1S/C12H22O11/c13-1-3-5(15)6(16)9(19)12(22-3)23-10-4(2-14)21-11(20)8(18)7(10)17/h3-20H,1-2H2/t3-,4-,5+,6+,7-,8-,9-,10-,11-,12+/m1/s1^Y Key: GUBGYTABKSRVRQ-DCSYEGIMSA-N^Y InChI=1/C12H22O11/c13-1-3-5(15)6(16)9(19)12(22-3)23-10-4(2-14)21-11(20)8(18)7(10)17/h3-20H,1-2H2/t3-,4-,5+,6+,7-,8-,9-,10-,11-,12+/m1/s1 Key: GUBGYTABKSRVRQ-DCSYEGIMBP
SMILES C([C@@H]1[C@@H]([C@@H]([C@H]([C@@H](O1)O[C@@H]2[C@H](O[C@H]([C@@H]([C@H]2O)O)O)CO)O)O)O)O
Properties
Chemical formula	C₁₂H₂₂O₁₁
Molar mass	342.297 g·mol⁻¹
Appearance	White solid
Density	1.525 g/cm³
Melting point	252 °C (anhydrous)[1] 202 °C (monohydrate)[1]
Solubility in water	195 g/L[2][3]
Chiral rotation ([α]_D)	+55.4°(anhydrous) +52,3° (monohydrate)
Thermochemistry
Std enthalpy of combustion (Δ_cH^⦵₂₉₈)	5652 kJ/mol, 1351 kcal/mol, 16.5 kJ/g, 3.94 kcal/g
Hazards
NFPA 704 (fire diamond)	0 0 0
Flash point	357.8 °C (676.0 °F; 631.0 K)[4]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). N verify (what is ^YN ?) Infobox references