Chloroacetic Acid (79-11-8) Physical and Chemical Properties
Chloroacetic Acid
A chlorinated carboxylic acid used industrially as an alkylating intermediate and building block for agrochemicals, pharmaceuticals and specialty chemicals.
| CAS Number | 79-11-8 |
| Family | Haloacetic acids |
| Typical Form | Crystalline solid or concentrated aqueous solution |
| Common Grades | ACS Grade, BP, EP, JP, Technical Grade, USP |
Chloroacetic acid is a low-molecular-weight chlorinated carboxylic acid of the haloacetic-acid structural class; it is formally 2‑chloro substituted acetic acid and conforms to the molecular formula \(\ce{C2H3ClO2}\). Structurally it comprises a carboxyl functional group adjacent to an electron‑withdrawing chlorine atom on the α‑carbon. The chlorine substituent increases the acidity relative to acetic acid, withdraws electron density from the carboxylate, and makes the α‑carbon more electrophilic; these electronic features underpin its reactivity as an alkylating agent and as a substrate for nucleophilic displacement or dehalogenation reactions.
In condensed phases chloroacetic acid is a polar, hydrogen‑bonding solid that is hygroscopic and deliquescent; it melts to a relatively dense liquid and is readily soluble in protic and many polar aprotic organic solvents. The acid dissociation constant is relatively low (\(\mathrm{p}K_a = 2.87\)), so aqueous solutions are predominantly in the anionic form at neutral pH. The compound has low-to-moderate lipophilicity (log P ≈ 0.2–0.34) and a small topological polar surface area (TPSA ≈ 37.3 Å^2), consistent with good aqueous solubility and modest membrane permeability. Under thermal stress the material decomposes to release acid and halogenated fragments (hydrogen chloride and oxidized chlorine species); it is corrosive to metals and biological tissues and will undergo neutralization reactions with bases, often releasing substantial heat.
Chloroacetic acid is an important industrial intermediate used to produce carboxymethyl celluloses, herbicide precursors, and a range of fine‑chemical and pharmaceutical intermediates; it is also encountered as a disinfection by‑product in chlorinated waters and as a reagent in laboratory and process chemistry. Common commercial grades reported for this substance include: ACS Grade, BP, EP, JP, Technical Grade, USP.
Basic Physical Properties
Density
Reported experimental densities vary with phase and temperature. Representative values include:
- 1.58 at 20 °C/20 °C (solid) — reported as "1.58 g/cm³".
- 1.3703 at 65 °C/4 °C (liquid).
- 1.4043 at 40 °C (reported as "1.4043 g/cu cm at 40 °C").
- 1.328 (reported without temperature annotation).
These values indicate the solid and molten liquid are denser than water; molten or liquid material will typically sink in water. Reported units are \(\mathrm{g\,cm^{-3}}\).
Melting Point
Multiple crystalline forms (polymorphs) are reported. Experimental values include:
- Exists in alpha, beta, and gamma forms having mp 63 °C (α), 55–56 °C (β), and 50 °C (γ). MP for acid of commerce: 61–63 °C.
- 52.5 °C (single reported value).
- 50–63 °C (range).
- 145 °F (alternative unit; corresponds to the same approximate range).
Polymorphism affects the observed melting point; industrial material is typically specified by the commercial mp range noted above.
Boiling Point
Reported boiling data at ambient pressure:
- 187.00 to 190.00 °C at 760.00 mm Hg.
- 189.1 °C (typical single value).
- 372 °F at 760 mmHg (alternative unit).
The relatively high normal‑pressure boiling point reflects the strong intermolecular hydrogen bonding and low volatility of the acid in its neutral form at ambient temperatures.
Vapor Pressure
Representative experimental values reported:
- 1 mmHg at 109.4 °F.
- 0.06 mmHg (unspecified conditions).
- \(6.5\times10^{-2}\ \mathrm{mmHg}\) (\(8.68\times10^{-3}\ \mathrm{kPa}\)) at \(25\,^\circ\mathrm{C}\).
Vapor pressures are low at ambient temperature and vapour is heavier than air; volatilization under ambient aqueous conditions is limited because the compound is predominantly ionized at typical environmental pH values.
Flash Point
Reported flash point values (closed and open cup reports):
- 126 °C (reported as 126 °C closed cup).
- 259 °F (reported, corresponding to 126 °C).
- 302 °F (alternative reported value).
Chloroacetic acid is classified as combustible; vapors at elevated temperatures can form flammable mixtures and care is required when heating or handling molten material.
Chemical Properties
Solubility and Phase Behavior
Chloroacetic acid is highly water‑soluble and miscible with many polar organic solvents. Representative experimental solubility data:
- "greater than or equal to 100 mg/mL at 68 °F" (solubility given in mg/mL).
- "In water, 8.58X10+5 mg/L at 25 °C" (equivalent to ≈858 mg/mL when converted).
- "858 mg/mL at 25 °C."
- Soluble in ethanol, diethyl ether, benzene, chloroform; slightly soluble in carbon tetrachloride.
- The substance is hygroscopic and absorbs water from air, often forming a syrup and deliquescent crystals. It is commercially handled as flakes, concentrated aqueous solutions (e.g., up to ~80%), or molten material for transport and processing.
Because the acid dissociates (\(\mathrm{p}K_a = 2.87\)), in aqueous media at neutral pH the chloroacetate anion predominates and solubility behavior is governed by ionization and salt formation.
Reactivity and Stability
Chloroacetic acid is a reactive halogenated carboxylic acid with several characteristic chemistries:
- Acid–base: behaves as a typical carboxylic acid; neutralization with bases is exothermic and produces salts (e.g., sodium chloroacetate).
- Nucleophilic displacement: the α‑chloro substituent is amenable to nucleophilic substitution (SN2) producing substituted acetates or undergoing dehalogenation under reductive conditions. This electrophilicity is the basis for its use as an alkylating intermediate.
- Corrosivity and compatibility: strongly corrosive to metals and tissues; can react with active metals to produce hydrogen gas and metal salts. Contact with cyanides, sulfites, nitrites and other reactive anions can generate hazardous gases.
- Thermal decomposition: on heating or combustion, generates corrosive and toxic gases including hydrogen chloride and oxidized chlorine species; phosgene formation has been reported under severe decomposition conditions.
- Oxidation/reduction: strong oxidizers and strong reducing agents can cause violent reactions. Stability is adequate under recommended storage conditions, but incompatibilities must be managed.
In biological and environmental contexts, dehalogenation and conjugation reactions (notably glutathione conjugation leading to S‑carboxymethyl derivatives) are important metabolic and detoxification pathways.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
Available energetic data reported for specific thermodynamic quantities include:
- Heat of combustion (reported): −715.9 kJ/mol (alpha‑chloroacetic acid).
- Heat of fusion at the melting point: "Heat of fusion at the melting point = 1.2285X10+7 J/kmol" (reported in J·kmol−1 units).
- Heat of vaporization: "250 Btu/Lb = 139 cal/g = 5.82X10+5 J/kg" (reported multiple unit expressions).
No comprehensive set of standard enthalpies of formation or temperature‑dependent heat capacity functions is given in the current data context for full thermochemical modelling. Where precise calorimetric data are required for process design, consult product‑specific technical literature or calorimetric determinations.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula (canonical): \(\ce{C2H3ClO2}\).
- Molecular weight (reported): 94.50 (units: \(\mathrm{g\,mol^{-1}}\)).
- Exact mass / Monoisotopic mass: 93.9821570 (reported).
Other computed descriptors from structure analysis:
- XLogP: 0.2 (computed).
- Topological polar surface area (TPSA): 37.3 Å^2.
- Heavy atom count: 5.
- Formal charge: 0.
LogP and Polarity
Reported lipophilicity and partitioning parameters:
- XLogP3 (computed): 0.2.
- Experimental/computed log Kow entries reported: "log Kow = 0.22", "0.22", and "0.34" in different measurements/estimations.
These low positive log P values indicate low-to-moderate hydrophobicity and support strong aqueous solubility and limited bioaccumulation potential.
Structural Features
Chloroacetic acid is 2‑chloro substituted acetic acid (IUPAC: 2‑chloroacetic acid). Key structural points:
- The α‑chloro substituent exerts a strong −I effect, stabilizing the conjugate base and lowering the \(\mathrm{p}K_a\).
- The molecule contains one hydrogen‑bond donor (carboxylic OH) and two hydrogen‑bond acceptors (carbonyl oxygen and hydroxyl oxygen counted separately in many descriptor schemes).
- Rotatable bond count: 1 (reported).
- The electrophilic α‑carbon enables displacement reactions (formation of esters, amides, thioethers) and underpins much of its utility as a chemical intermediate and as a herbicidal moiety.
Representative structural identifiers:
- SMILES: C(C(=O)O)Cl
- InChI: InChI=1S/C2H3ClO2/c3-1-2(4)5/h1H2,(H,4,5)
- InChIKey: FOCAUTSVDIKZOP-UHFFFAOYSA-N
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 79-11-8
- EC (European Community) number: 201-178-4 (reported)
- UN numbers for transport states (reported in transport contexts): various forms for solid, solution and molten material appear in regulatory listings.
- Other registry identifiers (reported): UNII 5GD84Y125G, multiple chemical registry IDs and internal catalog numbers appear in technical listings.
Synonyms and Structural Names
Common synonyms reported in commerce and the technical literature include:
- 2‑chloroacetic acid
- monochloroacetic acid (MCA)
- chloroacetic acid
- chloroethanoic acid
- ClCH2COOH
- alpha‑chloroacetic acid
- monochloroethanoic acid
Additional vendor and grade descriptors (analytical, technical, medicinal grades) are used commercially; see the commercial grades listed above for common specification names.
Industrial and Commercial Applications
Representative Uses and Industry Sectors
Chloroacetic acid is produced and used at scale as an intermediate in chemical manufacture. Principal industrial roles include:
- Manufacture of carboxymethyl cellulose (a major large‑scale application).
- Production of herbicides and herbicide precursors (aryl‑hydroxyacetic derivatives).
- Intermediate for synthesis of glycine, thioglycolic acid, EDTA precursors, and other fine chemicals.
- Use in the preparation of dyes, surfactants, and pharmaceuticals.
- Sold as technical, reagent, or pharmaceutical grades for laboratory and process chemistry.
It also appears as a disinfection by‑product in chlorinated or chloraminated water treatment contexts and is monitored in drinking‑water and environmental matrices.
Role in Synthesis or Formulations
Chemically, chloroacetic acid functions as an activated acetic acid derivative: the α‑chloro substituent allows SN2 displacement to introduce diverse functional groups (e.g., nucleophilic substitution by amines, thiols, alcohols), enabling formation of carboxymethyl and related building blocks. It is used to introduce carboxymethyl functionality onto polymers (e.g., cellulose ether production) and to prepare esters, salts (e.g., sodium chloroacetate), and other intermediates in agrochemical and specialty chemical production. It is available in concentrated aqueous solutions, molten form for transport, and as solid flakes/powders depending on the manufacturing and downstream processing requirements.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS: 79-11-8
Synonyms and Structural Names
- 2‑chloroacetic acid; monochloroacetic acid; ClCH2COOH; chloroethanoic acid; alpha‑chloroacetic acid.
Safety and Handling Overview
Acute and Occupational Toxicity
Chloroacetic acid is a highly corrosive and systemically toxic halogenated organic acid. Key safety characteristics and exposure considerations:
- Routes of exposure: inhalation, dermal contact, and ingestion are all significant; the substance is readily absorbed through skin and can cause systemic toxicity following dermal exposure.
- Acute hazards: causes severe skin burns, ocular damage, and respiratory tract irritation. Systemic toxicity can include central nervous system depression, metabolic acidosis, cardiac and renal effects, and in severe exposures may be fatal. Reported probable oral lethal dose estimates appear in toxicological reports; occupational exposure limits are low.
- Occupational exposure guidelines reported include a recommended 8‑hr TWA of 0.5 ppm (inhalable fraction and vapor) and similar workplace exposure thresholds; short‑term exposure levels and AEGLs have been proposed for emergency planning. The vapour is heavier than air and can accumulate in low areas.
- Toxicology and emergency care: first aid emphasizes rapid decontamination (copious flushing of skin/eyes with water for at least 15 minutes), removal of contaminated clothing, avoidance of inducing vomiting after ingestion, and prompt medical evaluation. Supportive care and monitoring for delayed systemic effects (metabolic acidosis, cardiac arrhythmia, renal impairment) is essential.
Personal protective equipment for handling includes chemical‑resistant gloves (e.g., neoprene/viton as appropriate for the task), full face/eye protection, acid‑resistant clothing, and respiratory protection (air‑purifying or supplied‑air respirators) when engineering controls are not sufficient. For emergency response to large releases or fires, positive‑pressure self‑contained breathing apparatus and fully encapsulating chemical protective suits are recommended.
For detailed hazard, transport and regulatory information, users should refer to the product‑specific Safety Data Sheet (SDS) and local legislation.
Storage and Handling Considerations
Practical handling and storage guidance based on chemical class and reported industrial practice:
- Store in tightly closed containers in a cool, dry, well‑ventilated area away from incompatible materials (strong bases, strong oxidizers, strong reducing agents, and reactive metals). Use corrosion‑resistant containment (e.g., glass‑lined or PTFE‑lined vessels).
- Avoid sources of heat and ignition where molten or concentrated solutions are handled; molten material is used during transport at elevated temperatures in some supply chains. Use closed transfer systems and non‑sparking tools.
- Keep separate from food and feedstuffs; prevent environmental releases — containment and secondary containment are recommended for storage tanks and process units.
- For spills and leaks: isolate area, eliminate ignition sources, prevent entry to drains/waterways, use appropriate acid‑resistant absorbents or neutralizing agents only with care (neutralization can be exothermic), and collect waste for disposal by licensed hazardous‑waste contractors. Do not attempt clean‑up without appropriate PPE and trained personnel.
Note: this overview is descriptive and non‑exhaustive. For site‑specific handling, storage, emergency response and transport instructions consult the manufacturer's SDS and regulatory guidance applicable to the jurisdiction.
