2,3-Dimethyl-1,3-butadiene (513-81-5) Physical and Chemical Properties
2,3-Dimethyl-1,3-butadiene
A branched conjugated diene (C6H10) used as a reactive monomer and synthetic intermediate in polymer chemistry and organic synthesis; typically handled as a stabilized, volatile feedstock in industrial and laboratory settings.
| CAS Number | 513-81-5 |
| Family | Conjugated dienes |
| Typical Form | Colorless liquid |
| Common Grades | EP, JP |
2,3-Dimethyl-1,3-butadiene is a small, nonpolar conjugated diene belonging to the 1,3-butadiene structural class. The molecule is a symmetrically substituted 1,3-diene with methyl groups at the C-2 and C-3 positions, giving the formula \(\ce{C6H10}\). Conjugation across the two double bonds produces a delocalized π-system that governs the compound's electronic reactivity (notably Diels–Alder cycloadditions and radical polymerizations) and UV/IR spectral features. The compound lacks polar functional groups (topological polar surface area = 0) and has no hydrogen-bond donors or acceptors, which strongly biases its phase behaviour toward immiscibility with water and good affinity for nonpolar media.
Electron-donating methyl substitution increases electron density of the diene relative to the parent 1,3-butadiene, which typically increases its dienophilic reactivity in normal-electron-demand cycloadditions and stabilizes allylic radical intermediates. The combination of modest molecular weight, low polarity, and significant vapour pressure makes the material volatile and readily flammable; industrial samples are commonly supplied with an antioxidant/stabilizer to suppress oxidative polymerization during storage and handling.
Common commercial grades reported for this substance include: EP, JP.
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
Measured vapour pressure: 152.0 \(\mathrm{mmHg}\). The high vapour pressure at ambient or modestly elevated temperatures is consistent with the compound's low molecular weight and liquid physical description; this contributes to significant volatility and flammability hazards in open systems.
Flash Point
No experimentally established value for this property is available in the current data context.
Chemical Properties
Solubility and Phase Behavior
2,3-Dimethyl-1,3-butadiene is a nonpolar hydrocarbon with computed topological polar surface area = 0 and no hydrogen-bonding functionality. It is therefore effectively insoluble in water and readily miscible with nonpolar organic solvents (e.g., aliphatic and aromatic hydrocarbons, chlorinated solvents). The compound is described as a liquid under ambient conditions; its volatility makes headspace and vapour-phase behaviour important for process and occupational controls.
Quantitative aqueous solubility values are not available in the current data context.
Reactivity and Stability
The molecule is a conjugated diene and is chemically reactive in pathways characteristic of this class: Diels–Alder cycloadditions with activated dienophiles, cationic and radical polymerization, and electrophilic addition across the double bonds. Alkyl substitution at C-2 and C-3 increases electron density in the diene and stabilizes allylic cations/radicals, influencing both rates and regioselectivity of additions and polymerization.
The material is prone to oxidative degradation and radical-initiated polymerization on exposure to air, light, heat, or trace peroxides; industrial samples are commonly stabilized with small amounts of antioxidants (e.g., butylated hydroxytoluene). The substance is flammable and should be handled under measures that exclude ignition sources. Chemical incompatibilities include strong oxidizers and radical initiators.
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: \(\ce{C6H10}\)
Molecular weight: 82.14
Exact/monoisotopic mass: 82.078250319
Structural identifiers and cheminformatic descriptors from computed data:
SMILES: CC(=C)C(=C)C
InChI: InChI=1S/C6H10/c1-5(2)6(3)4/h1,3H2,2,4H3
InChIKey: SDJHPPZKZZWAKF-UHFFFAOYSA-N
Other computed descriptors: XLogP = 3.1 (XLogP3-AA), topological polar surface area = 0, rotatable bond count = 1, heavy atom count = 6, formal charge = 0.
LogP and Polarity
Reported XLogP3 value: 3.1, indicating moderate-to-high lipophilicity consistent with a nonpolar hydrocarbon. The absence of polar functionality (TPSA = 0; H-bond donors = 0; H-bond acceptors = 0) further supports strong partitioning into nonpolar phases and limited aqueous solubility. These properties imply rapid diffusion into organic matrices and membranes and favor use as an organic-phase reactant or solvent component rather than as an aqueous reagent.
Structural Features
The connectivity corresponds to a 1,3-butadiene core with methyl substituents at the internal carbons; a skeletal representation is \(\ce{CH2=C(CH3)-C(CH3)=CH2}\). Conjugation across the 1,3-diene motif controls frontier orbital energetics (HOMO–LUMO spacing), making the molecule a competent diene in [4+2] cycloadditions and a substrate for radical and cationic polymerizations. The substituted diene is sterically and electronically differentiated from unsubstituted 1,3-butadiene, which affects selectivity in pericyclic reactions and polymer growth kinetics.
Identifiers and Synonyms
Registry Numbers and Codes
CAS Registry Number: 513-81-5
European Community (EC) number: 208-172-0
UNII: 61TUU25HCO
DSSTox Substance ID: DTXSID2022046
SMILES, InChI, and InChIKey are shown above under Molecular Weight and Formula.
Synonyms and Structural Names
Reported synonyms and alternative names include (selection from supplier/depositor annotations):
- 2,3-dimethyl-1,3-butadiene
- 2,3-DM-B
- 2,3-Dimethylbuta-1,3-diene
- 2,3-Dimethylbutadiene
- Biisopropenyl / Diisopropenyl
- CH2=C(CH3)C(CH3)=CH2
(Additional depositor-supplied synonyms and trade descriptors exist in vendor specifications.)
Industrial and Commercial Applications
Representative Uses and Industry Sectors
2,3-Dimethyl-1,3-butadiene occurs in hydrocarbon fractions derived from shale oil and other petroleum distillates and is used industrially as a reactive hydrocarbon monomer. Primary application sectors include elastomer and polymer manufacture where conjugated dienes are used as comonomers or monomeric building blocks. Its volatility and reactivity also make it relevant in specialty chemical synthesis where substituted dienes serve as substrates in cycloaddition chemistry.
Role in Synthesis or Formulations
The compound functions as a reactive diene in synthetic organic chemistry (for example, as a partner in Diels–Alder cycloadditions) and as a monomer or comonomer in polymerization processes to produce hydrocarbon polymers with tailored properties. In commercial supply, material may be offered with small concentrations of antioxidant stabilizer to limit oxidative polymerization during storage and transit.
Safety and Handling Overview
Acute and Occupational Toxicity
GHS classification reported includes: Signal word "Danger" and hazard statement H225: "Highly flammable liquid and vapour." The substance is classified as a Flammable Liquid, Category 2 (Flam. Liq. 2) in the aggregated notifications. Product-specific safety information notes potential for irritation on contact; ingestion can be harmful and aspiration into the lungs may cause severe injury. As a volatile hydrocarbon, inhalation of vapours at high concentrations can produce central nervous system effects.
Industrial samples are commonly stabilized with antioxidants (e.g., BHT) to suppress auto-oxidation and polymerization; stabilizers do not eliminate flammability or the need for controls.
Storage and Handling Considerations
Handle in well-ventilated areas with elimination of ignition sources. Use closed handling systems where practical and implement vapour control (local exhaust, explosion-proof ventilation). Typical precautions for flammable volatile hydrocarbons apply: grounding/bonding during transfers, use of intrinsically safe equipment, and appropriate personal protective equipment (chemical-resistant gloves, eye protection, and respiratory protection if vapour exposure cannot be adequately controlled).
Store cool, in original tightly closed containers, away from oxidizing agents, strong acids/bases, and radical initiators. Use of inhibitor-stabilized material and nitrogen blanketing may be appropriate for bulk storage to minimize oxidative polymerization risk. For detailed hazard, transport and regulatory information, users should refer to the product-specific Safety Data Sheet (SDS) and local legislation.
