Oxalyl chloride (79-37-8) Physical and Chemical Properties
Oxalyl chloride
Reactive acyl chloride used as a chlorinating reagent and intermediate for pharmaceutical and fine-chemical synthesis, typically handled under anhydrous conditions in process chemistry and R&D.
| CAS Number | 79-37-8 |
| Family | Acid halides (acyl chlorides) |
| Typical Form | Colorless fuming liquid |
| Common Grades | BP, EP, Reagent Grade |
Oxalyl chloride is a small, aliphatic di-acyl chloride (functional formula (COCl)2) belonging to the acid chloride class. Structurally it contains two electrophilic carbonyl groups bridged directly by the oxalyl linkage; each carbonyl is activated by an adjacent chloride substituent, giving two highly electrophilic C=O centers that are strong acylating and chlorinating sites. The molecule is low in conformational flexibility (one rotatable bond) and lacks hydrogen-bond donors; its topological polar surface area and two oxygen acceptors indicate moderate polarity despite the presence of lipophilic chlorine atoms.
Electronically the carbonyl carbons are strongly electron-deficient and readily undergo nucleophilic attack, acyl substitution, and hydrolysis. These properties drive common laboratory and industrial behavior: vigorous hydrolysis on contact with water (with evolution of corrosive decomposition products and gases), strong corrosivity to skin and mucosa, and pronounced reactivity with nucleophilic or basic substrates. The compound typically appears as a colorless fuming liquid with a penetrating odor and significant vapor pressure at ambient temperature; it is handled as a reactive reagent rather than a bulk solvent.
In chemical manufacturing and research it is widely used as a chlorinating/activating reagent and as an intermediate in pharmaceutical and fine-chemical production owing to its capacity to convert carboxylic acids to more reactive derivatives and to generate reactive electrophilic species in situ. Common commercial grades reported for this substance include: BP, EP, Reagent Grade.
Basic Physical Properties
Density
No experimentally established value for this property is available in the current data context.
Melting Point
No experimentally established value for this property is available in the current data context.
Boiling Point
No experimentally established value for this property is available in the current data context.
Vapor Pressure
Experimental data report a vapor pressure of \(150.0\,\mathrm{mmHg}\). This relatively high vapor pressure for a low-molecular-weight liquid is consistent with the fuming character and the need to control vapors during handling (ventilated enclosures or fume hoods recommended).
Flash Point
No experimentally established value for this property is available in the current data context.
Chemical Properties
Solubility and Phase Behavior
Oxalyl chloride is a colorless, fuming liquid that does not behave as a conventional stable aqueous solute: it hydrolyzes vigorously on contact with water and aqueous media, producing corrosive decomposition products and gaseous/volatile by-products (see hazard classifications). Because hydrolysis is rapid and exothermic, aqueous solubility should not be considered a meaningful descriptor for practical handling; the substance is typically handled in dry organic solvents and as prepared solutions (commercial solutions in dichloromethane are commonly supplied).
Reactivity and Stability
Oxalyl chloride is chemically reactive and sensitive to nucleophiles, bases, water, and certain inorganic salts. It undergoes rapid hydrolysis with water (violent decomposition noted), is strongly corrosive to skin and eyes, and will react with alcohols, amines, and other nucleophiles to give acylated products. Specific reactivity alerts include hazardous reactions with N,N-dimethylformamide (formation of toxic chlorinated by-products such as dimethylcarbamoyl chloride) and potentially explosive behavior when mixed with sodium azide. Because of the high electrophilicity of the carbonyl carbons, thermal or uncontrolled contact with nucleophiles can be vigorous; material should be kept dry and away from incompatible reagents.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
No experimentally established value for this property is available in the current data context.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula: C2Cl2O2
- Molecular weight: \(126.92\,\mathrm{g}\,\mathrm{mol}^{-1}\)
- Exact (monoisotopic) mass: \(125.9275346\,\mathrm{u}\)
LogP and Polarity
- Computed XLogP3-AA: \(1.7\) (moderate lipophilicity for a small, polar electrophile)
- Topological polar surface area (TPSA): \(34.1\,\text{Å}^2\)
- Hydrogen-bond donors: 0; hydrogen-bond acceptors: 2; rotatable bonds: 1.
These values reflect a molecule that is modestly polar but dominated in reactivity by electrophilic carbonyl centers rather than by extensive hydrogen-bonding capability.
Structural Features
SMILES: C(=O)(C(=O)Cl)Cl
InChI: InChI=1S/C2Cl2O2/c3-1(5)2(4)6
InChIKey: CTSLXHKWHWQRSH-UHFFFAOYSA-N
Structurally, oxalyl chloride is the dichloride derivative of oxalic acid (di-acyl chloride). The two acyl chloride moieties are adjacent, producing two strongly electron-withdrawing environments and rendering both carbonyl carbons highly susceptible to nucleophilic attack. The presence of chlorine directly bonded to the carbonyl carbon enhances electrophilicity relative to unhalogenated acyl derivatives; this underlies its utility as a chlorinating and activating reagent but also explains its corrosivity and instability toward moisture.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS Number: 79-37-8
- European Community (EC) Number: 201-200-2
- UNII: R4Y96317DW
- DSSTox Substance ID: DTXSID3058822
Synonyms and Structural Names
Common names and synonyms found in supplied identifiers include: oxalyl chloride; oxalyl dichloride; ethanedioyl dichloride; oxalic dichloride; oxaloyl chloride; oxalic acid dichloride; (COCl)2. SMILES and InChI strings are provided above for unambiguous structural representation.
Industrial and Commercial Applications
Representative Uses and Industry Sectors
Oxalyl chloride is used industrially and in research as a chlorinating and activating reagent. It is listed for use as an intermediate in pharmaceutical and fine-chemical manufacturing. Reported commercial formulations include concentrated reagent-grade material and preprepared solutions (for example, solutions in dichloromethane at commonly used molarities for convenience and safer metering during synthesis).
Role in Synthesis or Formulations
Functionally, oxalyl chloride is employed to convert carboxylic acids into more reactive acyl chloride derivatives and to generate reactive electrophilic species in situ for acylation, chlorination, and certain formylation activations when combined with polar nucleophilic catalysts or solvents. Its high electrophilicity makes it valuable for small-scale synthetic transformations where rapid activation is required; however, attendant hazards (vigorous hydrolysis, generation of corrosive gases, and reactive by-products with some solvents/reagents) require controlled procedures and appropriate engineering controls.
Safety and Handling Overview
Acute and Occupational Toxicity
Oxalyl chloride is acutely toxic by inhalation and ingestion and is corrosive to skin and eyes. Reported acute inhalation toxicity: LC50 (rat) = 1,840 ppm/1 hr. Aggregated hazard classifications indicate serious skin corrosion/irritation and serious eye damage potential. GHS hazard statements reported in safety summaries include: H260 (60%): In contact with water releases flammable gases which may ignite spontaneously; H301 (24.3%): Toxic if swallowed; H314 (100%): Causes severe skin burns and eye damage; H318 (67.7%): Causes serious eye damage; H331 (94.7%): Toxic if inhaled; H335 (52.3%): May cause respiratory irritation. Acute exposure can produce severe respiratory tract injury, corrosive burns, and systemic toxicity; appropriate respiratory protection and local exhaust are mandatory where vapors may be present.
Storage and Handling Considerations
Handle oxalyl chloride under an inert, dry atmosphere in corrosion-resistant equipment. Storage should be in tightly closed containers away from water and incompatible materials (alcohols, amines, strong bases, azides, etc.). Keep containers cool and well ventilated; avoid sources of ignition and minimize vapor release. Use appropriate personal protective equipment (chemical-resistant gloves, eye/face protection, protective clothing) and engineering controls (chemical fume hood, scrubbers, secondary containment). Specific reactivity alerts include formation of toxic chlorinated by-products when mixed with N,N-dimethylformamide and a risk of explosive reactions with sodium azide; vulnerable operations (mixing, quenching, solvent exchanges) require written procedures and emergency planning. For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
