Chemically Reversible Organogels via “Latent” Gelators. Aliphatic Amines with Carbon Dioxide and Their Ammonium Carbamates

Abstract

Rapid and isothermal (at room temperature) uptake of CO2 by solutions or, in some cases, organogels comprised of a primary or secondary aliphatic amine (1) and an organic liquid leads to in situ chemical transformation to the corresponding alkylammonium alkylcarbamate (2) based gels. Chemical reversibility is demonstrated by removal of CO2 from 2-based gels upon gentle heating in the presence of nitrogen. This is a general strategy for reversible self-assembly or disassembly of molecular aggregates relying on the initiation or termination of ionic interactions. The dependence of the amine structure and the nature of the liquid component on the formation and stability of the 1 and 2 organogels are examined by differential scanning calorimetry, optical microscopy, and X-ray diffraction methods. In most cases, the 2 gelators are more effective (based on the minimum gelator concentration required at room temperature, the gelation temperature, and the duration of time a gel persists without bulk phase separation) and more diverse (based on the classes of liquids gelled) than their corresponding amines. The differences are attributed to the presence of ionic interactions between molecular segments of the alkylammonium alkylcarbamates that are stronger than the hydrogen-bonding interactions available between molecules of amines. The initial stages of aggregation in the gel assemblies (i.e., changes in the degree of aggregation of sols of some 2 gelators) have been examined as a function of concentration and temperature by NMR techniques.

A multiphase reaction medium including pressurized carbon dioxide and water for selective hydrogenation of benzonitrile with a Pd/Al2O3 catalyst

“…The formation of carbamate salt from BA and CO 2 was also reported by Chatterjee et al, who noted its importance for the high BA selectivity [29]. The carbamate salt is unstable and so the corresponding primary amine can easily be obtained by heating [40]. Compared to medium (a), this medium (d)…”

Structural Transcription of Organogels to Mesoporous Silicas: A Chain-length Dependent Morphology and Pore Texture

“…Recently, they are shown to form efficient gelators to various solvents. 26 For example, in our previous report, 27,28 we found that the formation of organogel is mainly driven by the interaction between alkylamines and ethylene glycol (solvent). The introduction of sodium oleate can alter the solubility of hexadecylamines in ethylene glycol leading to the morphology change from spheres to fibres, which is based on the nucleation-crystallization mechanism.…”

Development of mustard oil- and groundnut oil-based span 40 organogels as matrices for controlled drug delivery

“…Higher T m , ΔH, and lower ΔS values suggested that the GG organogels were more stable than the MG organogels. [37,38] Addition of drug did not cause any significant variation in the thermal properties of both the types of organogels.…”