Chloroform
Chloroform (trichloromethane) is a colorless, volatile liquid organic compound with the chemical formula CHCl3, known for its sweet odor and historical significance as an anesthetic.[1] It has a molecular weight of 119.38 g/mol, a boiling point of 61.2 °C, a melting point of -63.5 °C, and a density of 1.489 g/cm³ at 25 °C, making it denser than water and only slightly soluble (about 8 g/L at 20 °C).[2][1] First synthesized in 1831 by German chemist Samuel Guthrie through the reaction of chloride of lime with alcohol, chloroform's anesthetic properties were discovered in 1847 by Scottish obstetrician James Young Simpson, who demonstrated its use during childbirth and surgery, revolutionizing medical practice despite early reports of toxicity.[3][4] By the mid-19th century, it became a preferred alternative to ether due to its lack of flammability and unpleasant smell, though its use as an inhalational anesthetic was largely discontinued by the early 20th century following recognition of severe side effects, including liver and kidney damage, and it was banned for such purposes in many countries before World War II.[1][5] Today, chloroform is primarily produced industrially (approximately 760,000 tonnes annually worldwide as of 2024)[6] as an intermediate in the synthesis of refrigerants like HCFC-22 and pharmaceuticals, with limited applications as a solvent in laboratories (e.g., for NMR spectroscopy using deuterated forms), extraction agent in organic chemistry, and in the production of dyes, pesticides, and polymers; its direct use in consumer products is restricted due to health concerns.[7][8][1] Chloroform is formed as a byproduct during water chlorination for disinfection, contributing to environmental exposure, and it readily volatilizes into air where it can persist for months.[9][10] Toxicity arises from all exposure routes—inhalation, ingestion, and skin absorption—with acute effects including central nervous system depression, dizziness, and unconsciousness, while chronic exposure is linked to liver toxicity (hepatitis, jaundice), kidney damage, and reproductive issues; it is classified as likely to be carcinogenic to humans (EPA).[11][9][12][13]Chemical Identity
Molecular Structure and Nomenclature
Chloroform, with the chemical formula CHCl₃, features a central carbon atom covalently bonded to one hydrogen atom and three chlorine atoms via single bonds. This arrangement results in a tetrahedral molecular geometry, characteristic of sp³ hybridization at the carbon center, with bond angles of approximately 109.5° for both Cl–C–Cl and H–C–Cl. The C–H bond length measures about 1.07 Å, while each C–Cl bond is approximately 1.77 Å long.[14][15] The systematic IUPAC name for CHCl₃ is trichloromethane, reflecting its composition as methane with three chlorine substituents. The retained common name "chloroform" was coined in 1834 by French chemist Jean-Baptiste Dumas, derived as a portmanteau of "chloro-" (indicating chlorine) and "formyl" (an obsolete term for the CH radical related to formic acid), owing to its initial preparation via alkaline cleavage of chloral (trichloroacetaldehyde).[16] Due to the significant electronegativity difference between carbon (2.55) and chlorine (3.16), the three C–Cl bonds are polar, with partial positive charge on carbon and partial negative charges on the chlorines. The single C–H bond is relatively nonpolar, as hydrogen (2.20) and carbon have closer electronegativities. This asymmetry imparts a net dipole moment to the molecule of 1.15 D (3.84 × 10⁻³⁰ C·m), making chloroform a polar solvent.[15] In nuclear magnetic resonance (NMR) spectroscopy, chloroform exhibits a characteristic ¹H NMR signal for its single hydrogen atom at approximately 7.26 ppm when measured in deuterated chloroform (CDCl₃) solvent at 90 MHz, downfield due to the deshielding effect of the adjacent chlorines.[17]Physical and Chemical Properties
Chloroform is a colorless liquid at room temperature, characterized by a sweet, ethereal odor and a slightly sweet taste.[1] Its pleasant, nonirritating aroma was historically noted in early descriptions of the compound.[1] Key physical constants of chloroform include a density of 1.489 g/cm³ at 20 °C, a boiling point of 61.2 °C, and a melting point of -63.5 °C.[1] It exhibits limited solubility in water, approximately 8 g/L at 20 °C, but is miscible with most organic solvents such as alcohols, ethers, and benzene.[1]| Property | Value | Conditions |
|---|---|---|
| Density | 1.489 g/cm³ | 20 °C |
| Boiling point | 61.2 °C | - |
| Melting point | -63.5 °C | - |
| Water solubility | 8 g/L | 20 °C |