Allyl bromide (106-95-6) Physical and Chemical Properties
Allyl bromide
A halogenated allylic reagent commonly used as a reactive intermediate in industrial organic synthesis and specialty chemical manufacture.
| CAS Number | 106-95-6 |
| Family | Allylic halide (halogenated aliphatic) |
| Typical Form | Colorless to light yellow liquid |
| Common Grades | BP, EP, JP, Reagent Grade, USP |
Allyl bromide is a low-molecular-weight unsaturated alkyl bromide of the allylic class. Structurally it is an allylic halide with molecular formula \( \ce{C3H5Br} \); the substituent pattern places a bromine atom at the primary allylic carbon of a propenyl fragment. The pi system of the C=C double bond conjugated with the benzylic-like (allylic) position stabilizes carbocation and radical intermediates, enhancing reactivity in nucleophilic substitution, radical addition and polymerization pathways compared with saturated primary bromides. Electronically the bromine atom withdraws electron density inductively while the allylic resonance delocalizes positive charge in intermediates; topological polar surface area is 0 and the compound lacks hydrogen-bond donor/acceptor functionality, consistent with low polarity and moderate lipophilicity.
As a halogenated unsaturated hydrocarbon, allyl bromide behaves as a volatile, flammable, and electrophilic alkylating agent. It is slightly soluble in water but miscible with many organic solvents; volatility and vapor density greater than air make inhalation a significant exposure route. It is chemically reactive toward nucleophiles, oxidizers and radical initiators and may undergo exothermic polymerization under initiation. Industrially and in laboratory practice it is principally used as an allylating intermediate and chemical building block for polymers, fragrances, pharmaceuticals and agrochemicals; it has also been used historically as a fumigant. Common commercial grades reported for this substance include: BP, EP, JP, Reagent Grade, USP.
Basic Physical Properties
Density
- Reported values: \(1.4161\) at \(68\ ^\circ\mathrm{F}\) (USCG, 1999) — denser than water; will sink. Alternative value: \(1.398\) at \(20\ ^\circ\mathrm{C}/4\ ^\circ\mathrm{C}\).
Qualitatively, the density significantly exceeds that of water, so bulk releases will form a liquid phase that can sink and collect in low areas or sewers; this influences spill containment and drainage control measures.
Melting Point
- Reported values: \(-182\ ^\circ\mathrm{F}\) (USCG, 1999); \(-119\ ^\circ\mathrm{C}\).
No additional experimentally established melting-point ensemble data are provided here beyond the reported values.
Boiling Point
- Reported values: \(158\ ^\circ\mathrm{F}\) at \(760\ \mathrm{mmHg}\) (USCG, 1999); \(71.3\ ^\circ\mathrm{C}\) at \(760\ \mathrm{mmHg}\).
The boiling point is consistent with a volatile organic liquid at ambient temperatures; closed-system vapor pressure and adequate ventilation are therefore relevant for process controls.
Vapor Pressure
- Reported value: \(136.0\ \mathrm{mmHg}\).
This relatively high vapor pressure at ambient temperature indicates substantial vapor formation and the potential for rapid volatilization from liquid surfaces; vapors are heavier than air (reported vapor density \(4.17\) relative to air).
Flash Point
- Reported values: \(28\ ^\circ\mathrm{F}\) (USCG, 1999); \(-1\ ^\circ\mathrm{C}\); summarized as \(30\ ^\circ\mathrm{F}\) (\(-1\ ^\circ\mathrm{C}\)).
The low flash point classifies the material as readily flammable; vapors can form explosive mixtures in air (see flammable limits below).
Chemical Properties
Solubility and Phase Behavior
- Miscible with alcohol, chloroform, ether, carbon disulfide and carbon tetrachloride.
- Water solubility: \(3,835\ \mathrm{mg\,L^{-1}}\) at \(25\ ^\circ\mathrm{C}\).
Allyl bromide is sparingly soluble in water but readily solvated by a broad range of organic media; this supports its use as an organic-phase reagent. Given its volatility and vapor density > 1, it will form a vapor phase above pools and can accumulate in low-lying, poorly ventilated areas.
Reactivity and Stability
- Polymerization may be caused by elevated temperature, oxidizers, peroxides.
- Decomposition produces toxic hydrogen bromide and related bromine-containing species when heated.
- Reactive/incompatibility profile: reacts violently with oxidizing materials and alkalies; reactive group membership includes halogenated organics and unsaturated aliphatic compounds.
Allyl bromide is an electrophilic alkylating agent at the allylic carbon and readily undergoes nucleophilic substitution (including rapid SN2-type reactions at the allylic position), radical addition and initiation of polymerization under appropriate conditions. It decomposes on heating and can release HBr — process designs should account for corrosive and toxic decomposition products and include peroxidation/polymerization inhibition measures when storing or distilling.
Thermodynamic Data
Standard Enthalpies and Heat Capacity
No experimentally established value for this property is available in the current data context.
Qualitatively, like other low-molecular-weight alkyl bromides, combustion and decomposition are exothermic and generate corrosive bromine-containing combustion products; thermal runaway risks during distillation or reactive processing should be mitigated by temperature control and inerting.
Molecular Parameters
Molecular Weight and Formula
- Molecular formula: \( \ce{C3H5Br} \).
- Molecular weight: \(120.98\ \mathrm{g\,mol^{-1}}\) (reported value: 120.98).
- Exact/monoisotopic mass: \(119.95746\).
Identifiers for structure specification: SMILES C=CCBr, InChI InChI=1S/C3H5Br/c1-2-3-4/h2H,1,3H2, InChIKey BHELZAPQIKSEDF-UHFFFAOYSA-N.
LogP and Polarity
- Reported XLogP / log Kow: XLogP = 1.8; log Kow = 1.79.
- Topological polar surface area (TPSA): 0.
- Hydrogen-bond donors: 0; hydrogen-bond acceptors: 0.
Moderate lipophilicity and absence of hydrogen-bonding functionality explain limited water solubility and moderate potential for membrane permeability and dermal absorption; measured occupational exposure limits are correspondingly low.
Structural Features
Allyl bromide contains a terminal C=C double bond adjacent to the bromomethyl substituent (an allylic bromide). The allylic position imparts: - Enhanced reactivity toward nucleophiles (stabilized carbocation/transition state); - Increased reactivity in radical chemistry and propensity to undergo addition or polymerization reactions; - Alkylating behavior that can modify thiol-containing biomolecules and nucleophilic centres in proteins and nucleic acids.
The combination of an electrophilic allylic centre and a good leaving group (Br) makes the molecule a widely used allylating reagent in organic synthesis but also a potent biological alkylator.
Identifiers and Synonyms
Registry Numbers and Codes
- CAS number: 106-95-6
- European Community (EC) Number: 203-446-6
- UN/NA shipping number reported: UN1099
- UNII: FXQ8X2F74Z
- Other registry identifiers appear in source annotations (e.g., ChEMBL, DSSTox) and may be used for cross-referencing in procurement and regulatory workflows.
Synonyms and Structural Names
Common synonyms and structural names reported include: allyl bromide; 3-bromoprop-1-ene; 3-Bromopropene; 3-Bromo-1-propene; 1-Propene, 3-bromo-; 2-Propenyl bromide; 1-Bromo-2-propene; CH2=CHCH2Br. These synonyms are widely used in specifications, procurement documentation and material safety literature.
Industrial and Commercial Applications
Representative Uses and Industry Sectors
Allyl bromide is primarily used as a chemical intermediate in organic synthesis and as a building block for: - Manufacture of polymers and resins (including copolymerization with sulfur dioxide); - Synthetic fragrances and perfumery intermediates; - Pharmaceuticals and agrochemical intermediates; - Specialty allylic derivatives used in further chemical transformations.
Occupational exposure can occur in chemical production and formulation, and in industries where allylation reactions are performed at scale.
Role in Synthesis or Formulations
Functionally, allyl bromide serves as a commercial allylating reagent for introduction of the allyl group into nucleophiles (oxygen, nitrogen, sulfur and carbon nucleophiles) and as a monomer/intermediate in polymer chemistry. It is handled and formulated as a reactive liquid reagent; process control typically includes inhibitors to prevent uncontrolled polymerization and stabilizers for shipping and storage.
If a concise application summary is not sufficient for a particular use case, selection is typically based on the compound's reactivity profile described above (allylic electrophile, volatility, flammability).
Safety and Handling Overview
Acute and Occupational Toxicity
- Reported acute toxicity metrics and exposure thresholds: RD50 (respiratory irritancy) = \(257.0\ \mathrm{ppm}\); TLV \(0.1\ \mathrm{ppm}\) with TLV-STEL \(0.2\ \mathrm{ppm}\).
- Toxicity data examples: LD50 (oral, guinea pig) = \(30\ \mathrm{mg/kg}\); LD50 (intraperitoneal, mouse) = \(108\ \mathrm{mg/kg}\); LC50 (rat, inhalation) entries reported (e.g., \(2020\ \mathrm{ppm}/30\ \mathrm{min}\) in one study and another tabled value of \(10{,}000\ \mathrm{mg/kg}\) inhalation rat/30 min).
- Reported health effects: severe eye and skin burns, respiratory irritation, mucous membrane irritation, and systemic toxicity including gastrointestinal and pulmonary injury. Allyl bromide is an alkylating agent capable of modifying thiol groups and DNA; mutagenicity signals are reported for allylic alkylators.
Given the low occupational exposure limits and established dermal and inhalation toxicity, engineering controls (local exhaust ventilation), process containment, and stringent personal protective equipment are required in manufacturing and handling environments. Emergency first-aid recommendations include immediate irrigation for eye or skin exposure and prompt medical attention for inhalation or ingestion.
Storage and Handling Considerations
- Storage conditions: Keep tightly closed; store in a cool, dry, well-ventilated location away from oxidizing materials and alkalies. Separate from heat and ignition sources.
- Fire/explosion: Highly flammable liquid and vapor; lower flammable limit \(4.4\%\) by volume, upper flammable limit \(7.3\%\) by volume. Autoignition temperature reported as \(563\ ^\circ\mathrm{F}\) (\(295\ ^\circ\mathrm{C}\)). Vapors are heavier than air and may travel to ignition sources and flash back.
- Emergency response: In fire scenarios, combustion releases toxic hydrogen bromide and bromine-containing species. Use dry chemical, CO2, alcohol-resistant foam or water spray for large fires (cooling of containers). Evacuate and isolate spill area; eliminate ignition sources and ground equipment during transfer.
- Personal protective equipment: Chemical-resistant gloves, splash goggles/face shield and appropriate protective clothing; respiratory protection (positive-pressure SCBA) for high vapor concentrations or emergency response.
For process design and procurement, consider stabilizer requirements and polymerization inhibition for storage and distillation operations. For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
