Understanding CO_2 capture mechanisms in aqueous hydrazine via combined NMR and first-principles studies

Aqueous amines are currently the most promising solution for large-scale CO_2 capture from industrial sources. However, molecular design and optimization of amine-based solvents have proceeded slowly due to a lack of understanding of the underlying reaction mechanisms. Unique and unexpected reaction mechanisms involved in CO_2 absorption into aqueous hydrazine are identified using ^1H, ^(13)C, and ^(15)N NMR spectroscopy combined with first-principles quantum-mechanical simulations. We find production of both hydrazine mono-carbamate (NH_2-NH-COO^−) and hydrazine di-carbamate (^−OOC-NH-NH-COO^−), with the latter becoming more populated with increasing CO_2 loading. Exchange NMR spectroscopy also demonstrates that the reaction products are in dynamic equilibrium under ambient conditions due to CO_2 exchange between mono-carbamate and di-carbamate as well as fast proton transfer between un-protonated free hydrazine and mono-carbamate. The exchange rate rises steeply at high CO_2 loadings, enhancing CO_2 release, which appears to be a unique property of hydrazine in aqueous solution. The underlying mechanisms of these processes are further evaluated using quantum mechanical calculations. We also analyze and discuss reversible precipitation of carbamate and conversion of bicarbonate to carbamates. The comprehensive mechanistic study provides useful guidance for optimal design of amine-based solvents and processes to reduce the cost of carbon capture. Moreover, this work demonstrates the value of a combined experimental and computational approach for exploring the complex reaction dynamics of CO_2 in aqueous amines

Understanding CO_2 capture mechanisms in aqueous hydrazine via combined NMR and first-principles studies

Aqueous amines are currently the most promising solution for large-scale CO_2 capture from industrial sources. However, molecular design and optimization of amine-based solvents have proceeded slowly due to a lack of understanding of the underlying reaction mechanisms. Unique and unexpected reaction mechanisms involved in CO_2 absorption into aqueous hydrazine are identified using ^1H, ^(13)C, and ^(15)N NMR spectroscopy combined with first-principles quantum-mechanical simulations. We find production of both hydrazine mono-carbamate (NH_2-NH-COO^−) and hydrazine di-carbamate (^−OOC-NH-NH-COO^−), with the latter becoming more populated with increasing CO_2 loading. Exchange NMR spectroscopy also demonstrates that the reaction products are in dynamic equilibrium under ambient conditions due to CO_2 exchange between mono-carbamate and di-carbamate as well as fast proton transfer between un-protonated free hydrazine and mono-carbamate. The exchange rate rises steeply at high CO_2 loadings, enhancing CO_2 release, which appears to be a unique property of hydrazine in aqueous solution. The underlying mechanisms of these processes are further evaluated using quantum mechanical calculations. We also analyze and discuss reversible precipitation of carbamate and conversion of bicarbonate to carbamates. The comprehensive mechanistic study provides useful guidance for optimal design of amine-based solvents and processes to reduce the cost of carbon capture. Moreover, this work demonstrates the value of a combined experimental and computational approach for exploring the complex reaction dynamics of CO_2 in aqueous amines

Synthesis of Azines in Solid State: Reactivity of Solid Hydrazine with Aldehydes and Ketones

Highly conjugated azines were prepared by solid state grinding of solid hydrazine and carbonyl compounds such as aldehydes and ketones, using a mortar and a pestle. Complete conversion to the azine product is generally achieved at room temperature within 24 h, without using solvents or additives. The solid-state reactions afford azines as the sole products with greater than 97% yield, producing only water and carbon dioxide as waste

A novel method of CCl4 disposal by disproportionation with CH4 over Pt on various supports

In disproportionation of CCl4 with CH4 into CH3Cl and CHCl3, platinum supported on SrCO3, SiO2, MgO and MgAl2O4 showed stable activity and high selectivities around 700 K, providing a novel disposal method of ozone-depleting CCl4close2

One-pot solvent-free reductive amination with a solid ammonium carbamate salt from CO2 and amine

Many amines are liquid and their handling is inconvenient compared with the corresponding solids. We transformed a liquid (S)-(-)-1-phenylethylamine 1 to the corresponding neutral solid form 2 by reacting with carbon dioxide. We performed reductive amination of 2 with various aldehydes 3 under solvent-free conditions to provide secondary amines 5 in high yields

Synthesis and Anti-Inflammatory Activity of <i>N</i>(2)-Arylindazol-3(2<i>H</i>)-One Derivatives: Copper-Promoted Direct <i>N</i>-Arylation via Chan–Evans–Lam Coupling

Inflammatory-related diseases are becoming increasingly prevalent, leading to a growing focus on the development of anti-inflammatory agents, with a particular emphasis on creating novel structural compounds. In this study, we present a highly efficient synthetic method for direct N-arylation to produce a variety of N(2)-arylindazol-3(2H)-ones 3, which exhibit anti-inflammatory activity. The Chan–Evans–Lam (CEL) coupling of N(1)-benzyl-indazol-3-(2H)-ones 1 with arylboronic acids 2 in the presence of a copper complex provided the corresponding N(2)-arylindazol-3(2H)-ones 3 in good-to-excellent yields, as identified with NMR, MS, and X-ray crystallography techniques. The cell viability and anti-inflammatory effects of the synthesized compounds (3 and 5) were briefly assessed using the MTT method and Griess assay. Among them, compounds 5 exhibited significant anti-inflammatory effects with negligible cell toxicity

Large scale production of highly conductive reduced graphene oxide sheets by a solvent-free low temperature reduction

A novel one-pot process that can produce freestanding reduced graphene oxide (RGO) sheets in large scale through a mechanochemical method is presented, which is based on a 1:1 adduct of hydrazine and carbon dioxide (H_3N^+NHCO_2^−, solid hydrazine). We were able to synthesize RGO sheets by grinding solid hydrazine with graphene oxide (GO), followed by storing the mixed powder at 50 °C for 10 min. No solvents, nor large vessels, nor post-annealing at high temperatures are required. The resulting RGO sample was characterized by elemental analysis, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Brunauer–Emmett–Teller measurement, thermo gravimetric analysis, Fourier transform infrared spectroscopy, solid state nuclear magnetic resonance spectroscopy, and conductivity measurement. It exhibits excellent conductivity and possesses a high specific surface area. This reduction method was successfully applied for the fabrication of inkjet-printed RGO devices on a flexible substrate

Isolation and structural characterization of the elusive 1:1 adduct of hydrazine and carbon dioxide

A solid hydrazine was isolated as a crystalline powder by reacting aqueous hydrazine with supercritical CO2. Its structure determined by single crystal X-ray diffraction shows a zwitterionic form of NH3+NHCO2-. The solid hydrazine is remarkably stable but is as reactive as liquid hydrazine even in the absence of solvents

Solid-state and solvent-free synthesis of azines, pyrazoles, and pyridazinones using solid hydrazine

Azines, pyrazoles, and pyridazinones were isolated as the sole products in high yields (&gt;97%) by grinding solid hydrazine (H3N+NHCO2-) with di-carbonyl compounds or by their reaction in the absence of solvent. Neither catalysts nor additives were needed to promote the reactions. The solid-state and solvent-free reactions proceeded under ambient conditions and did not produce any wastes other than water and carbon dioxide. They are operationally easy, environmentally safe, and readily scalable, allowing for highly selective synthesis of compounds containing the hydrazine motif