1,2-Dichloroethane, CAS 107-06-2, chemical formula C₂H₄Cl₂, molar mass 98.96 g mol⁻¹, is supplied as a clear, colourless liquid with a chlorinated odour. The compound is produced mainly by direct chlorination of ethylene and by oxychlorination of ethylene with hydrogen chloride and oxygen; both routes yield a crude ethylene dichloride stream that is washed, dried, and distilled. Direct chlorination is typically operated at 50–70 °C and 0.2–0.5 MPa, whereas oxychlorination commonly runs at 200–300 °C and 0.5–1.0 MPa over a supported copper chloride catalyst. The liquid has a boiling point of 83.5 °C at 101.325 kPa, density 1.253 g cm⁻³ at 20 °C, closed-cup flash point 13 °C, and vapour pressure 8.5 kPa at 20 °C. These values place the product between dichloromethane and trichloroethylene in volatility while retaining a flammable classification that excludes it from many open solvent-cleaning operations.

Commercial product models are differentiated by assay and impurity profile rather than by molecular structure. A general technical-grade model corresponds to purity ≥99.0 area%, while vinyl chloride monomer feedstock grades require purity ≥99.5 area% and lower water, iron, and acidity limits. Small-lot packaging may be in lined steel drums or ISO tank containers; bulk supply is normally handled by dedicated pipeline, rail, or pressurised tanker. The product is not manufactured to a single harmonised model code; purchase specifications normally reference the seller’s grade code, CAS number, and the impurity table that follows.

What Purity Boundaries Are Used for Technical and Vinyl Chloride Feedstock Grades?

Assay is determined by gas chromatography with flame ionisation detection; because no single ISO or ASTM designation is uniformly cited across major producers, supplier methods dominate. Water is measured by ASTM E203-16, acidity by ASTM D1613-17, colour by ASTM D1209-05(2019), nonvolatile residue by ASTM D1353-13, and distillation range by ASTM D1078-11. Low water is critical because wet EDC hydrolyses slowly to hydrogen chloride, accelerating corrosion in tanks and quench columns. The VCM-feedstock limit of ≤20 mg kg⁻¹ is typical for licensors that specify furnace inlet feed; some process packages require lower values, but published supplier-specific limits are not uniform. Acidity is measured as hydrogen chloride because free acid damages transfer piping and can shift cracker pH balance. Iron is often controlled at ≤0.5 mg kg⁻¹ in furnace-grade product even when not listed in generic tables; iron chloride deposition on radiant coil surfaces reduces heat transfer and may promote coke nucleation. Distillation range is a secondary check on chlorinated by-products and light ends. Published grade nomenclature varies among producers; a vendor model code may carry the same assay as another vendor but differ in stabiliser or inhibitor package, so the specification sheet rather than the trade model is the binding purchase document.

Because the dominant use is vinyl chloride monomer production, the performance requirement for 1,2-dichloroethane is often defined by its behaviour in a fired tubular reactor. Vaporised EDC is preheated to 350–420 °C, then mixed with recycled hydrogen chloride and unconverted EDC and passed through radiant coils at 480–540 °C. Typical outlet pressure is 0.6–1.2 MPa, with gas-phase residence time between 4 s and 12 s. Conversion per pass is maintained at 50–60%; pushing conversion higher increases recycle energy savings but raises the rate of condensation, oligomer, and coke deposition. Selectivity to vinyl chloride under well-controlled low-iron coil conditions is normally above 98 mol%. The primary side reactions include formation of chloroprene, acetylene, and heavy chlorinated hydrocarbons, and their distribution shifts with coil outlet temperature and feed impurities. Trace acetylene and chloroprene are controlled because they can polymerise and accelerate radiant-coil fouling. Some operators add chlorinated methanes at low mg kg⁻¹ levels to suppress coking; published data for optimal addition rate in a specific furnace geometry are limited because feed impurity profiles and heat-flux distributions vary across installations. The cracked gas is quenched, and hydrogen chloride is recovered by distillation or absorption; the water quench must be designed to handle chlorinated hydrocarbon condensation without excessive emulsion formation. Furnace tube metallurgy generally uses nickel-chromium alloys with controlled silicon and manganese content to reduce catalytic coking; low-iron surface treatment reduces filamentous coke formation in the radiant section.

In ethylenediamine and polyamine synthesis, 1,2-dichloroethane reacts with excess ammonia at elevated temperature and pressure. The process is liquid-phase or supercritical depending on the licensor, and the specification emphasis shifts from cracker impurities to water and acidity. Water hydrolyses the alkyl halide and reduces amine yield, while free hydrogen chloride consumes ammonia and forms ammonium chloride fouling. VCM-feedstock product is often acceptable, but additional drying or neutralisation may be required for sensitive catalyst packages.

Historically, 1,2-dichloroethane was blended with tetraethyllead as a lead scavenger in leaded motor gasoline. The addition ratio was tied to lead alkyl concentration and combustion chamber deposit control; this application has been eliminated in most jurisdictions under unleaded gasoline mandates and is no longer a meaningful volume driver.

When 1,2-Dichloroethane Is Evaluated Against Dichloromethane and Trichloroethylene in Cleaning and Extraction

The comparison shows the product is not a direct substitute for trichloroethylene in vapour degreasing because its flash point is 13 °C and its vapour can form flammable mixtures. Dichloromethane offers lower-temperature extraction and higher volatility but has a boiling point below 40 °C, which increases evaporative loss relative to 1,2-dichloroethane in closed immersion cells. Tetrachloroethylene provides non-flammability and higher density but requires more energy for distillation recovery. The vicinal chlorine arrangement of 1,2-dichloroethane permits intramolecular elimination of hydrogen chloride to vinyl chloride; this reaction pathway is absent in the C₁ chlorinated solvents and is the basis of its use as a vinyl chloride feedstock rather than as a formulated solvent. The 1,1-isomer has a boiling point of 57.3 °C and density 1.175 g cm⁻³ at 20 °C; it is not marketed as an integrated VCM feedstock because its production route and downstream value chain differ, even though the molecular formula is identical. Global production is dominated by integrated EDC/VCM plants, so merchant material is often a co-product from chlorination units; this differs from trichloroethylene and tetrachloroethylene, which are produced primarily as solvent or chemical intermediates. The technical specification of EDC is therefore tied to cracker tolerance, whereas solvent-grade chlorinated products normally carry stabiliser packages that are not present in VCM-grade ethylene dichloride.

During bulk storage in carbon steel tanks, the product is kept dry and blanketed with nitrogen because hydrolysis produces hydrogen chloride and accelerates pitting. Closed-loop transfer and low-temperature storage reduce vapour losses, but the vapour space remains flammable and must be inerted. Flammable limits in air are approximately 6.2 vol% to 15.9 vol%. The material is incompatible with strong bases, strong oxidisers, and reactive metals; contact with finely divided aluminium or zinc can generate heat and chlorinated decomposition products. Transport classification is UN 1184, Class 3, Packing group II. The CLP harmonised classification includes Flam. Liq. 2 H225, Acute Tox. 3 H301/H311/H331, Carc. 1B H350, and Muta. 1B H340. The American Conference of Governmental Industrial Hygienists threshold limit value for ethylene dichloride is 10 ppm per 8-hour time-weighted average, equivalent to 40 mg m⁻³. This regulatory profile excludes the product from consumer formulations and makes enclosed processing the normal industrial practice. VCM-grade EDC is not normally stabilised; solvent-grade EDC may contain acid acceptors or antioxidants if sold for laboratory or extraction use, but such grades are small volume and must be specified separately.