Chemical Properties and Application of Trans-1,4-diaminocyclohexane

Trans-1,4-diaminocyclohexane is a chiral cyclohexanediamine in which the two amino groups are in a trans configuration. Possessing notable basicity, trans-1,4-diaminocyclohexane readily undergoes acid–base neutralization reactions with common acidic substances. It is primarily employed as an organic synthetic intermediate, capable of efficiently undergoing condensation reactions with various aldehydes, and is widely used in fundamental chemical research on supramolecular self-assembly.

Figure1: Picture of Trans-1,4-diaminocyclohexane

Chemical Properties

Trans-1,4-diaminocyclohexane (DACH) is a primary diamine with properties that render it suitable as a CO₂ absorbent. Beckman et al. utilized DACH to synthesize a polymer for capturing CO₂ and other acid gases via the amine groups present in the DACH molecule. Similarly, Leclaire et al. employed DACH to capture p-block metal elements, subsequently releasing them by bubbling CO₂. However, aside from the work by Puxty et al., there has been limited research investigating the direct use of DACH in aqueous solution as a CO₂ absorbent. In their study, a micro-scale isothermal gravimetric analysis method was employed to measure the CO₂ absorption capacity and initial absorption rates of various aqueous amines. Trans-1,4-diaminocyclohexane was found to exhibit a higher initial absorption rate compared to MEA and DAB. Nevertheless, there remains a lack of detailed studies on the properties of DACH for CO₂ capture, including aspects such as mass transfer measurements, chemical speciation, or corrosion properties. [1]

Supramolecular Self-Assembly

The dinuclear phenylboronic ester derived from pentaerythritol and the trinuclear triphenylboroxine were combined with three different diamine tectons—namely, 1,4-diazacyclohexane (pz), trans-1,4-diaminocyclohexane, and 4-aminopyridine (4-apy)—to construct supramolecular assemblies via N→B coordination bonds and to advance understanding of the factors governing the formation of such aggregates. From these reactions, three novel complexes with the compositions {(PhBO)₃(pz)}ₙ·nDMF (2), {[(PhBO)₃]₂(trans-1,4-diaminocyclohexane)}·trans-1,4-diaminocyclohexane (3), and {[(PhBO₂)₂(C₅H₈)][4-apy]₂}·CHCl₃·1.25H₂O (4) were obtained and characterized by elemental analysis, IR and NMR spectroscopy, and single-crystal X-ray diffraction. Solid-state structural analyses revealed that all three products feature N→B bonds but differ in the stoichiometric ratios between the boron and nitrogen tectons, resulting in a 1:1 adduct for 2, a 2:1 adduct for 3, and a 1:2 adduct for 4. In the solid state, compound 2 forms a one-dimensional coordination polymer, whereas compounds 3 and 4 exhibit discrete molecular structures. Due to the presence of N–H hydrogen-bonding donors, extended two- or three-dimensional hydrogen-bonding networks are formed in each case. In solution, the N→B coordinated aggregates are largely dissociated at room temperature, as evidenced by ¹¹B NMR spectroscopy. [2]

Application

CO2 capture

To investigate the enhancement of CO₂ absorption capacity in tertiary amine systems, a sterically hindered diamine, trans-1,4-diaminocyclohexane (DACH), was examined as a promoter for bicarbonate formation in combination with N-methyldiethanolamine (MDEA). Comparative evaluations were conducted using monoethanolamine (MEA) and 1,4-diaminobutane (DAB) to assess how amine structure influences the CO₂ absorption rate. Among the three amines studied, trans-1,4-diaminocyclohexane, owing to its cyclic configuration, exhibited the highest initial CO₂ absorption rate (1.904×10⁻² mol CO₂/L/min) as well as the highest initial bicarbonate formation rate, with detailed mechanistic explanations provided. Furthermore, three mixed amine blends—MEA-MDEA, piperazine (PZ)-MDEA, and DACH-MDEA—were prepared to further evaluate the promotional role of trans-1,4-diaminocyclohexane in bicarbonate formation. Key performance indicators including CO₂ absorption capacity, mass transfer coefficients, and equilibrium CO₂ loading were systematically examined. While the overall CO₂ absorption rate followed the order PZ-MDEA > DACH-MDEA > MEA-MDEA, the DACH-MDEA blend demonstrated a higher bicarbonate concentration and a lower carbamate concentration relative to the PZ-MDEA system. This pronounced bicarbonate-forming capability of trans-1,4-diaminocyclohexane contributes to lower energy demand during solvent regeneration. Additionally, the DACH-MDEA blend achieved the highest CO₂ loading (0.576 mol CO₂/mol amine) under low CO₂ partial pressure conditions. Corrosion behavior analysis of the CO₂-loaded amine solutions revealed that the corrosion rates followed the trend: PZ-MDEA ≈ DACH-MDEA ≪ MEA-MDEA. Collectively, these findings underscore that trans-1,4-diaminocyclohexane, with its distinctive cyclic structure, represents a highly promising promoter for CO₂ capture processes. This study elucidates the influence of amine structural characteristics on CO₂ absorption performance, thereby contributing valuable insights for the design of efficient amine-based solvents for carbon capture applications. [1]

Reference

[1] Li X, Yang Q, Pearson P, et al. The application of trans-1, 4-diaminocyclohexane as a bicarbonate formation rate promoter in CO2 capture[J]. Fuel, 2018, 226: 479-489.

[2] Cruz‐Huerta J, et al. Self‐assembly of triphenylboroxine and the phenylboronic ester of pentaerythritol with piperazine, trans‐1, 4‐diaminocyclohexane, and 4‐aminopyridine[J]. European Journal of Inorganic Chemistry, 2016, 2016(3): 355-365.

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