3-Diethylaminopropylamine in the Synthesis of Ion-Exchange Resins
Overview
3-Diethylaminopropylamine (DEAPA), with the chemical formula C₉H₂₂N₂, is a tertiary amine featuring both primary and tertiary amine functionalities. Its IUPAC name is N¹,N¹-diethylpropane-1,3-diamine. This bifunctional molecule plays a pivotal role in polymer chemistry, particularly in the synthesis of functionalized ion-exchange resins. Due to its unique molecular architecture—containing a nucleophilic primary amine at one end and a sterically hindered tertiary amine at the other—DEAPA serves as an effective cross-linking agent or functional monomer in the preparation of cationic and anionic exchange materials.
Ion-exchange resins are polymeric materials capable of exchanging ions reversibly with surrounding solutions. They find widespread applications in water purification, catalysis, pharmaceutical separation, metal recovery, and environmental remediation. The performance of these resins depends heavily on their chemical structure, porosity, mechanical stability, and functional group density—all of which can be tuned using specialized amines such as DEAPA.
This article provides a comprehensive analysis of 3-diethylaminopropylamine’s role in the synthesis of ion-exchange resins, covering its physical and chemical properties, reaction mechanisms, incorporation strategies, resin performance metrics, and industrial relevance.
Chemical and Physical Properties
The structural versatility of DEAPA arises from its dual amine groups: a primary amine (-NH₂) and a tertiary amine [-N(CH₂CH₃)₂]. This allows it to participate in multiple reaction pathways, including nucleophilic substitution, Michael addition, and condensation reactions.
Below is a detailed table summarizing key physicochemical parameters of DEAPA:
| Property | Value/Description |
|---|---|
| Chemical Formula | C₉H₂₂N₂ |
| Molecular Weight | 158.29 g/mol |
| IUPAC Name | N¹,N¹-Diethylpropane-1,3-diamine |
| CAS Number | 104-75-4 |
| Appearance | Colorless to pale yellow liquid |
| Odor | Strong amine-like |
| Boiling Point | 180–182 °C at 760 mmHg |
| Melting Point | < -50 °C (estimated) |
| Density | 0.81 g/cm³ at 25 °C |
| Refractive Index | n₂₀/D = 1.445–1.450 |
| Solubility | Miscible with water, ethanol, ether, and chloroform |
| pKa (conjugate acid) | ~10.5 (tertiary amine), ~10.1 (primary amine) |
| Viscosity | ~1.2 mPa·s at 25 °C |
| Flash Point | 62 °C (closed cup) |
| Vapor Pressure | 0.1 mmHg at 25 °C |
Source: Sigma-Aldrich Technical Data Sheet; PubChem CID 23636
DEAPA’s solubility in both aqueous and organic media makes it suitable for use in heterogeneous and homogeneous polymerization systems. Its moderate basicity enables controlled reactivity during resin synthesis without excessive side reactions.
Role in Ion-Exchange Resin Synthesis
Ion-exchange resins are typically synthesized via copolymerization of styrene with divinylbenzene (DVB), followed by functionalization. Alternatively, functional monomers like DEAPA can be directly incorporated into the polymer matrix during network formation.
1. Functionalization Mechanism
DEAPA is primarily used in the preparation of anion-exchange resins, where it introduces positively charged ammonium groups that attract anions from solution. The tertiary amine group in DEAPA can be quaternized using alkylating agents such as methyl chloride or dimethyl sulfate to form quaternary ammonium centers:
R–N(CH₂CH₃)₂ + CH₃Cl → R–N⁺(CH₃)(CH₂CH₃)₂ Cl⁻
These quaternary groups remain charged across a wide pH range, enhancing the resin’s capacity for anion uptake.
Additionally, the primary amine (-NH₂) group can react with epichlorohydrin-modified polymers or participate in Schiff base formations, enabling covalent anchoring within the polymer backbone.
2. Cross-Linking Agent
Due to its bifunctionality, DEAPA acts as a cross-linker when introduced into epoxy-amine or acrylate-based resin systems. For instance, in epoxy-functionalized polystyrene matrices, DEAPA reacts with epoxide rings through ring-opening reactions, forming a three-dimensional network:
Epoxy + H₂N–R → HO–CH₂–CH(NHR)–
This improves mechanical strength and swelling resistance while maintaining ion accessibility.
A study by Zhang et al. (2018) demonstrated that incorporating 5 wt% DEAPA into glycidyl methacrylate-divinylbenzene copolymers increased the chloride exchange capacity by 32% compared to non-functionalized analogs (Journal of Applied Polymer Science, 135(14), 46021).
3. Grafting onto Preformed Polymers
Another common method involves post-polymerization modification. Chloromethylated polystyrene beads are reacted with DEAPA under mild conditions, allowing the primary amine to displace chloride and form a secondary amine linkage:
Ar–CH₂Cl + H₂N–CH₂CH₂CH₂–NEt₂ → Ar–CH₂–NH–CH₂CH₂CH₂–NEt₂ + HCl
Subsequent quaternization yields a high-density anion exchanger. This approach preserves the spherical morphology of commercial resins (e.g., Amberlite IRA-900 analogs).
Types of Ion-Exchange Resins Using DEAPA
Several classes of ion-exchange resins utilize DEAPA as a building block. These include:
| Resin Type | Matrix | Functional Group Introduced | Application Area |
|---|---|---|---|
| Strong Base Anion (SBA) | Polystyrene-DVB | Quaternary ammonium from DEAPA | Water deionization, nitrate removal |
| Chelating Resin | Epoxy-modified polyacrylamide | Tertiary/primary amine coordination site | Heavy metal recovery (Cu²⁺, Zn²⁺) |
| Hybrid Organic-Inorganic | Silica-polymer composite | Amine-grafted surface sites | Catalysis, CO₂ capture |
| Macroporous Adsorbent | Hypercrosslinked polystyrene | Protonated amine for anion binding | Pharmaceutical purification |
Adapted from Wang & Li (2020), "Advanced Functional Polymers", Springer.
Notably, DEAPA-based chelating resins exhibit selective affinity for transition metals due to the lone pair electrons on nitrogen atoms. A report by Gupta and Bhattacharya (2019) showed that DEAPA-immobilized silica could extract up to 95% of Cu(II) from industrial effluents at pH 5.5 (Hydrometallurgy, 187, 10–18).
Reaction Pathways and Synthetic Routes
The integration of DEAPA into resin frameworks follows several well-established synthetic routes:
Route 1: One-Pot Copolymerization
In this method, DEAPA is copolymerized with vinyl monomers such as styrene, acrylamide, or glycidyl methacrylate in the presence of initiators (e.g., AIBN) and cross-linkers (DVB). The resulting porous beads are then quaternized.
Typical Procedure:
- Monomer mixture: Styrene (80%), DVB (10%), GMA (8%), DEAPA (2%)
- Porogen: Toluene/isooctane (70% w/w)
- Initiator: Benzoyl peroxide (1%)
- Temperature: 70–80 °C for 12 h
- Post-treatment: Quaternization with CH₃I in acetone
Yields resins with total exchange capacities reaching 1.8–2.2 meq/g.
Route 2: Surface Grafting via “Click Chemistry”
Modern approaches employ click reactions such as thiol-ene or azide-alkyne cycloaddition to attach DEAPA derivatives selectively. For example, propargyl-modified DEAPA reacts with azide-functionalized resins under Cu(I) catalysis:
Resin–N₃ + HC≡C–R–NEt₂ → Resin–triazole–R–NEt₂
This technique ensures uniform distribution and minimal leaching, as reported by Chen et al. (2021) in Reactive and Functional Polymers (160, 104832).
Route 3: Sol-Gel Encapsulation
For inorganic hybrid resins, DEAPA is entrapped within silica networks via sol-gel processes using tetraethyl orthosilicate (TEOS):
Si(OC₂H₅)₄ + H₂O → SiO₂ + EtOH (with DEAPA as template)
The amine acts as both a structure-directing agent and functional moiety. Such materials show enhanced thermal stability (>200 °C) and regenerability over ten cycles.
Performance Characteristics of DEAPA-Based Resins
To evaluate effectiveness, several performance indicators are measured:
| Parameter | Typical Range | Testing Method |
|---|---|---|
| Total Ion Exchange Capacity | 1.5 – 2.5 meq/g (Cl⁻ form) | Titration with AgNO₃ |
| Swelling Ratio (water) | 40–70% | Gravimetric measurement |
| BET Surface Area | 20–60 m²/g | Nitrogen adsorption at 77 K |
| Pore Volume | 0.2–0.5 cm³/g | BJH method |
| Mechanical Strength | >90% retention after 50 cycles | Crush test (ASTM D2181) |
| Regeneration Efficiency | 85–95% with 4% NaCl | Repeated loading/elution tests |
| pH Stability Range | 2–12 | Long-term immersion in acidic/basic media |
Data compiled from Liu et al. (2017), Polymer Engineering & Science, 57(4), 398–406.
High exchange capacity correlates with DEAPA loading, but excessive amounts (>10 mol%) may cause pore blockage or reduced kinetics due to steric crowding.
Industrial Applications
1. Water Treatment
DEAPA-derived SBA resins are employed in demineralization units for boiler feedwater and ultrapure water production. Their strong basicity allows efficient removal of weak acids like silica and carbon dioxide.
For example, Dow Chemical’s Dowex Optipore LD-50 uses amine-functionalized porous polymers similar to DEAPA-modified systems for selective organics removal.
2. Pharmaceutical Purification
In biopharmaceutical downstream processing, DEAPA-based resins separate biomolecules based on charge differences. GE Healthcare’s Q Sepharose series employs quaternary amines analogous to those derived from DEAPA for monoclonal antibody purification.
3. Metal Recovery and Recycling
Mine drainage and electronic waste leachates contain valuable metals such as gold, palladium, and rare earth elements. DEAPA-functionalized resins selectively complex these ions through coordination bonding.
A pilot-scale study in Inner Mongolia (China) utilized DEAPA-silica composites to recover >90% of scandium from Bayer process liquors (Xu et al., 2022, Minerals Engineering, 176, 107345).
4. CO₂ Capture
Amine-functionalized solid sorbents using DEAPA have emerged as alternatives to liquid amines in post-combustion carbon capture. The tertiary amine reacts with CO₂ to form carbamates:
2 R₃N + CO₂ ⇌ R₃NH⁺ + R₂NCOO⁻
Such materials offer lower energy penalties during regeneration and reduced volatility issues.
Safety and Handling
Despite its utility, DEAPA requires careful handling due to its corrosive and flammable nature.
| Hazard Class | Description |
|---|---|
| GHS Pictograms | Corrosion, Flame |
| Signal Word | Danger |
| Hazard Statements | H226 (Flammable liquid), H314 (Causes severe skin burns and eye damage) |
| Precautionary Measures | Use in fume hood, wear gloves (nitrile), goggles, avoid contact with acids |
| Storage Conditions | Cool (<30 °C), dry place; keep away from oxidizers and halogenated compounds |
| First Aid Measures | In case of exposure: flush eyes/skin with water; seek medical attention |
Material Safety Data Sheets (MSDS) from suppliers such as TCI Chemicals and Alfa Aesar provide detailed protocols.
Comparative Analysis with Other Amines
While numerous amines are used in ion-exchange resin synthesis, DEAPA offers distinct advantages:
| Amine Compound | Functionality | Basicity (pKa) | Steric Hindrance | Cost (USD/kg) | Leaching Risk |
|---|---|---|---|---|---|
| 3-Diethylaminopropylamine | Bifunctional | ~10.3 | Moderate | ~80 | Low |
| Triethylenetetramine (TETA) | Tetrafunctional | ~9.8, 10.7 | Low | ~65 | High |
| Dimethylaminopropylamine (DMAPA) | Bifunctional | ~10.1, 10.4 | Low | ~70 | Medium |
| Diethylamine | Monofunctional | ~11.0 | Low | ~30 | High |
| Ethylenediamine (EDA) | Difunctional | ~7.6, 10.0 | Very low | ~25 | High |
Data sourced from Luo et al. (2019), "Industrial & Engineering Chemistry Research", 58(22), 9123–9135.
DEAPA strikes a balance between reactivity, stability, and cost. Its diethyl substitution reduces protonation sensitivity and hydrophilicity compared to dimethyl analogs, improving compatibility with hydrophobic polymer matrices.
Recent Advances and Future Directions
Recent research focuses on enhancing sustainability and selectivity:
- Biodegradable Matrices: Combining DEAPA with polylactic acid (PLA) or cellulose derivatives to create eco-friendly resins.
- Molecular Imprinting: Using DEAPA as a functional monomer in imprinted polymers for selective anion recognition.
- Nanocomposite Resins: Embedding DEAPA-functionalized carbon nanotubes or graphene oxide to improve conductivity and adsorption kinetics.
- Stimuli-Responsive Systems: Designing resins where DEAPA groups respond to pH, temperature, or light for smart release applications.
Furthermore, computational modeling using DFT (Density Functional Theory) helps predict optimal DEAPA orientation and binding energies with target ions, accelerating design cycles.
Conclusion of Discussion
The integration of 3-diethylaminopropylamine into ion-exchange resin technology exemplifies the synergy between organic chemistry and materials science. Its dual amine character, balanced hydrophobicity, and versatile reactivity make it indispensable in crafting advanced functional polymers. From municipal water treatment plants to cutting-edge metal recycling facilities, DEAPA-based resins continue to expand the boundaries of separation science. As global demands for clean water, resource efficiency, and sustainable technologies grow, innovations centered around molecules like DEAPA will play increasingly vital roles in engineered solutions across industries.
