1-Butyl-3-methylimidazolium Bromide (BMIM Br): A Versatile Imidazolium Ionic Liquid for Biomass Processing
What Is BMIM Br and Why Is It a Key Ionic Liquid for Biomass Processing?
1-Butyl-3-methylimidazolium bromide (BMIM Br, CAS 85100-77-2) is a halide-based imidazolium ionic liquid with exceptional ability to dissolve cellulose, lignin, and other biopolymers. With the formula C8H15BrN2 and a molecular weight of 219.12 g/mol (as the anhydrous bromide salt), this white to pale yellow crystalline solid (mp 65-75 °C) represents one of the most studied ionic liquids for biomass pretreatment and green chemistry applications [001][002].
The global ionic liquids market was valued at approximately USD 55 million in 2024, with a projected CAGR of 18.3% through 2032. Imidazolium-based ionic liquids (BMIM, EMIM families) account for roughly 65% of total market volume, driven by cellulose dissolution, electrochemistry, and CO₂ capture applications [003].
How Does BMIM Br Dissolve Cellulose When Conventional Solvents Cannot?
The mechanism of cellulose dissolution by BMIM Br hinges on the unique properties of the bromide anion [001]:
- Hydrogen bond disruption: The Br⁻ anion is a strong hydrogen bond acceptor (β parameter = 0.87 on the Kamlet-Taft scale). It competes with and disrupts the inter-chain hydrogen bonding network that makes cellulose insoluble in water and most organic solvents.
- Coordination to hydroxyl groups: Br⁻ coordinates to the OH protons of cellulose (OH···Br⁻), while the BMIM cation interacts with the hydrophobic faces of the glucose rings through dispersion forces and weak C-H···π interactions.
- Concentration threshold: Effective dissolution requires a critical Br⁻ concentration. At 5–10 wt% cellulose loading in BMIM Br at 80–100°C, complete dissolution is achieved within 30–120 minutes.
- Lignin extraction from biomass: Treatment of lignocellulosic biomass (wood chips, corn stover, sugarcane bagasse) with BMIM Br at 120-150°C for 4-8 hours extracts 60-80% of the lignin fraction while leaving the cellulose-rich pulp intact. The bromide anion disrupts the hydrogen bonding between lignin and carbohydrate polymers (lignin-carbohydrate complexes, LCCs), facilitating lignin solubilization [002].
- Catalytic lignin depolymerization: BMIM Br serves as both solvent and acid catalyst for the hydrolytic cleavage of β-O-4 linkages — the most common inter-unit bond in lignin (45-60% of all linkages). At 150-180°C with 5-10 wt% water, BMIM Br achieves 40-60% depolymerization to monomeric phenolic compounds (guaiacol, syringol, vanillin precursors) within 2-4 hours [001].
This dissolution ability is not merely academic — it enables [002]:
- Cellulose regeneration: Dissolved cellulose can be precipitated by adding water or ethanol, yielding regenerated cellulose fibers and films with controlled crystallinity
- Enzymatic hydrolysis enhancement: Pretreatment with BMIM Br reduces cellulose crystallinity index from 60–80% to 20–40%, increasing enzymatic hydrolysis yields by 3–5×
- Chemical derivatization: Homogeneous acetylation, tosylation, and carboxymethylation of cellulose dissolved in BMIM Br
How Does BMIM Br Compare to BMIM Cl and Other Imidazolium Ionic Liquids?
| Property | BMIM Br | BMIM Cl | EMIM Cl | BMIM BF₄ | BMIM PF₆ |
|---|---|---|---|---|---|
| Anion | Br⁻ | Cl⁻ | Cl⁻ | BF₄⁻ | PF₆⁻ |
| MW (g/mol) | 219.12 | 174.67 | 146.62 | 226.02 | 284.18 |
| mp (°C) | 65–75 | ~70 | ~87 | ~15 (liquid) | 10–12 |
| H-bond acceptor (β) | 0.87 | 0.95 | 0.95 | 0.38 | 0.21 |
| Cellulose solubility | ★★★★ | ★★★★★ | ★★★★★ | ★ | ★ |
| Water miscibility | Yes | Yes | Yes | Yes | No |
| Relative cost | ★★★ | ★★★★ | ★★★★ | ★★★★ | ★★ |
BMIM Br offers a practical balance: excellent cellulose solubility (approaching that of EMIM Cl), lower melting point than the chloride analog, and competitive cost. The bromide anion is a slightly weaker hydrogen bond acceptor than chloride (β = 0.87 vs. 0.95), which marginally reduces cellulose solubility but improves chemical stability — BMIM Br is less hygroscopic and less corrosive than BMIM Cl [001][002].
Expanding Applications Beyond Biomass
Organic Synthesis Solvent
BMIM Br serves as a recyclable reaction medium for Diels-Alder cycloadditions, Heck couplings, and nucleophilic substitutions. The ionic environment can enhance reaction rates by 10–100× compared to molecular solvents due to increased local reactant concentration and stabilization of charged transition states [001].
CO₂ Capture
Imidazolium bromide ionic liquids show moderate CO₂ solubility (0.1–0.3 mol CO₂/mol IL at 1 bar, 25°C) through physical absorption. While less effective than amine-functionalized ionic liquids, BMIM Br is being investigated as a component in supported ionic liquid membranes for post-combustion CO₂ separation [002].
Electrochemistry
BMIM Br aqueous solutions have been explored as electrolytes for zinc-bromine redox flow batteries due to high bromide concentration and reduced bromine vapor pressure compared to conventional NaBr or ZnBr₂ electrolytes [001].
Handling and Practical Notes
- Hygroscopicity: BMIM Br is moderately hygroscopic. Store under inert atmosphere or in a desiccator. Water content >1% significantly reduces cellulose dissolution efficiency [001].
- Viscosity: The pure molten salt has viscosity ~500–1,000 cP at 80°C. Adding 5–10% co-solvent (DMSO, DMF) can reduce viscosity by 50–80% without significantly compromising cellulose solubility [002].
- Recovery and recycling: After cellulose regeneration, BMIM Br can be recovered by evaporating the aqueous anti-solvent and drying under vacuum at 60–80°C. Recovery yields of 92–97% are achievable over 5 cycles [002].
- Corrosivity: Halide-based ionic liquids are corrosive to stainless steel at elevated temperatures (>100°C). For process-scale applications, glass-lined or Hastelloy equipment is recommended [001].
FAQ
Q: Can BMIM Br dissolve chitin or chitosan?
A: BMIM Br shows limited chitin solubility (2–3 wt% at 100°C). For chitin dissolution, BMIM acetate (BMIM OAc) is significantly more effective (5–10 wt%), as the acetate anion is a superior hydrogen bond acceptor [001].
Q: What is the maximum cellulose concentration BMIM Br can dissolve?
A: Under optimized conditions (100–110°C, mechanical stirring, 2–4 hours), BMIM Br can dissolve 15–20 wt% microcrystalline cellulose. The practical working range is 5–10 wt% due to the dramatic viscosity increase above this concentration [002].
Q: Can BMIM Br be used with enzymes?
A: Not directly — the high ionic strength and bromide concentration denature most cellulases. The standard workflow is: (1) dissolve/pretreat cellulose in BMIM Br, (2) regenerate cellulose with water/ethanol, (3) wash thoroughly, (4) enzymatic hydrolysis of the regenerated cellulose. Residual BMIM Br at concentrations >1 mM inhibits cellulase activity [001].
Q: Is BMIM Br biodegradable?
A: Imidazolium-based ionic liquids with short alkyl chains (≤C₄) show limited but measurable biodegradability — typically 20–40% degradation in OECD 301D tests over 28 days. This is significantly better than PF₆⁻-based ionic liquids (<5%) but worse than choline-based or amino acid-based ionic liquids (60–80%) [002].
Key Statistics
| Metric | Value | Source |
|---|---|---|
| Molecular Weight | 219.12 g/mol | |
| Melting Point | 65-75 °C | |
| H-bond Acceptor (β) | 0.87 | |
| Max Cellulose Solubility | 15–20 wt% at 100°C | |
| Ionic Liquids Market (2024) | ~USD 55M | |
| IL Market CAGR (2024-2032) | 18.3% |
---
Availability at CoreyChem: ✅ This product is available in the CoreyChem catalog.
[View Product: 1-Butyl-3-methylimidazolium Bromide (BMIM Br) (CAS 85100-77-2) →](https://careerchemical.com/product/85100-77-2)
---
BMIM Br in Lignin Valorization
While cellulose dissolution dominates the BMIM Br literature, lignin processing represents an equally important emerging application [001][002]. Lignin — the second most abundant biopolymer on Earth after cellulose — is a complex, cross-linked aromatic polymer that is notoriously resistant to chemical depolymerization. BMIM Br addresses two key challenges:
The economic viability of BMIM Br-based lignin processing depends critically on ionic liquid recovery. After lignin depolymerization, BMIM Br is recovered by (a) extraction of organic products with ethyl acetate or methyl tert-butyl ether, (b) evaporation of the aqueous phase, (c) drying under vacuum at 80°C for 12 hours. Recovery yields of 90-95% per cycle are achievable, with a target of >99% for industrial deployment [002].
BMIM Br as a Reaction Medium for Organic Transformations
Beyond biomass processing, the unique solvation environment of BMIM Br accelerates several classes of organic reactions [001]:
- Nucleophilic aromatic substitution (SNAr): The rate of fluoride displacement from 1-fluoro-4-nitrobenzene by azide ion is accelerated 200-500× in BMIM Br compared to acetonitrile. The highly structured ionic liquid environment pre-organizes the charged nucleophile and electrophile, lowering the entropic barrier to reaction.
- Diels-Alder cycloaddition: The endo:exo selectivity of the cyclopentadiene + methyl acrylate Diels-Alder reaction increases from 3:1 in toluene to 8:1 in BMIM Br at 25°C. The ionic environment stabilizes the more polar endo transition state through favorable ion-dipole interactions.
- Heck coupling: Pd-catalyzed Heck coupling of iodobenzene with methyl acrylate proceeds in BMIM Br at 100°C without added phosphine ligand, using Pd(OAc)₂ (1 mol%) as the sole catalyst. The ionic liquid stabilizes Pd(0) nanoparticles formed in-situ, preventing aggregation and maintaining catalytic activity over 5-10 recycles [001].
Source Through CoreyChem
CoreyChem supplies research-grade this product (CAS 85100-77-2). Contact us for bulk quotations and technical documentation.