Carbon Tetrachloride
Properties
| State | Liquid |
| Color | Colorless |
| Solubility | Practically insoluble in water (0.8 g/L at 20°C); miscible with organic solvents |
| Melting Point | -22.9°C |
| Boiling Point | 76.7°C |
About Carbon Tetrachloride
Carbon tetrachloride is the canonical example of how molecular symmetry can erase the macroscopic dipole of a molecule built from polar bonds. Each C–Cl bond carries a dipole of about 1.46 D, but the four bonds point to the corners of a perfect tetrahedron and the vector sum is exactly zero. The molecule belongs to the Td point group — the same symmetry as methane — which is why CCl4 is the textbook teaching molecule for tetrahedral geometry and the cancellation of bond dipoles. The practical consequence is a colorless liquid that dissolves fats, oils, greases, sulfur, iodine, and bromine handsomely while being immiscible with water, and that has no C–H bonds whatsoever. That last point is what kept it on the IR spectroscopy bench long after its other uses were banned: CCl4 has no fundamental absorptions in the C–H stretching region (2800 to 3000 cm⁻¹), the C–H bending region near 1450 cm⁻¹, or the C–H out-of-plane bands below 1000 cm⁻¹, so it is a clean window for IR work on hydrocarbons. From the 1920s through the 1970s, CCl4 was the dominant dry-cleaning solvent, the propellant in handheld 'Pyrene' fire extinguishers (which produced phosgene when sprayed on hot fires — a worse outcome than the original fire), and the first-generation refrigerant before CFCs. The Montreal Protocol classified it as an ozone-depleting substance with an ODP of 1.1 (more destructive per kilogram than CFC-11), and production for emissive uses was phased out globally by 2010. It also causes hepatic centrilobular necrosis through CYP2E1-mediated cleavage to the trichloromethyl radical (•CCl3), which initiates lipid peroxidation in hepatocytes — the textbook mechanism of free-radical liver injury, taught in every pharmacology course as the example of a CYP-bioactivated hepatotoxin.
Where you'll encounter it
If you have ever picked up a 1970s textbook and seen a beautifully clean IR spectrum of an alkane in CCl4, you are looking at the last gasp of carbon tet's most defensible use. Today the molecule shows up in the lab as the carbon source in the Appel reaction (PPh3 + CCl4 + ROH → RCl + Ph3PO + CHCl3) for converting alcohols to alkyl chlorides under mild conditions, and as a chlorinating agent in the Hunsdiecker reaction. Older fire-extinguisher cylinders labeled 'Pyrene' or 'Carbon Tet' still turn up at estate sales and need to be disposed of as hazardous waste rather than discharged. In a teaching lab the molecule is now a chalkboard exercise on Td symmetry rather than a bottle on the shelf — its acquisition is restricted in most jurisdictions to laboratory-quantity research use under Montreal Protocol rules.
Common Uses
- Solvent for IR spectroscopy in the C–H stretching window (no interfering C–H bands)
- Carbon source in the Appel reaction (PPh3 / CCl4) for converting alcohols to alkyl chlorides
- Chlorinating agent in the Hunsdiecker decarboxylation
- Teaching example of Td symmetry and bond-dipole cancellation
- Historical dry-cleaning, fire-extinguishing, and refrigerant uses (phased out under the Montreal Protocol)
Safety Information
Severe hepatotoxin via CYP2E1-mediated formation of the •CCl3 radical, which initiates lipid peroxidation and causes centrilobular necrosis — the textbook mechanism of CYP-bioactivated liver injury. IARC Group 2B (possibly carcinogenic to humans). GHS: H301 (toxic if swallowed), H311 (toxic in skin contact), H331 (toxic if inhaled), H351 (suspected carcinogen), H372 (organ damage from repeated exposure), H420 (ozone layer damage). OSHA PEL 10 ppm (8-hour TWA), 25 ppm ceiling; ACGIH TLV 5 ppm. Production restricted under the Montreal Protocol with ODP 1.1. Decomposes on hot surfaces or in fires to phosgene — historically the lethal failure mode of Pyrene-style fire extinguishers. Handle in a hood with nitrile gloves and dispose as halogenated waste.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.