Substituent effects on the rate and selectivity of the hydrogenation of 2-nitroazobenzenes on raney nickel in alkaline and acid media

The scheme of chemical transformations of 2-nitroazobenzene derivatives during catalytic hydrogenation on Raney nickel was found to be common to compounds containing electron donor and electron acceptor substituents. A qualitative correlation between solvation interaction parameters and the solubility of substituted 2-nitroazobenzenes was observed. The selectivity of the reaction with respect to intermediate products was determined by the composition of the solvent and weakly depended on the nature of the substituent. The introduction of sodium hydroxide and acetic acid into solvents ensured high selectivity of the hydrogenation of substituted 2-nitroazobenzene derivatives with respect to the corresponding N-oxides and nitrohydrazo derivatives, respectively.     

Hydrogenation of Substituted Benzenes Containing Nitro and Azo Groups over Skeletal Nickel in Aqueous Solutions of 2-Propanol

Russian Journal of Physical Chemistry A - An analysis is made of the kinetic characteristics of the hydrogenation of 4-nitro- and 2-nitro-2'-hydroxy-5'-methylazobenzenes, 4-nitroaniline and...     

Kinetic description of the hydrogenation of nitrobenzene and nitrosobenzene on skeletal nickel in aqueous solutions of propan-2-ol of different compositions

The kinetics of the hydrogenation of nitrosobenzene and nitrobenzene is simulated taking into account accompanying processes and specific features of the conversion of reactive groups. The constants of the hypothetical reaction steps are calculated. The influence of sodium hydroxide and acetic acid on the kinetic parameters of the reactions is discussed.     

The influence of the nature of substituents on adsorbability and the rate of liquid-phase hydrogenation of nitrobenzenes

The influence of the nature of substituents on the rate of liquid-phase hydrogenation of nitrobenzenes on Raney nickel was studied in an aqueous solution of 2-propanol. Interrelation between the rate of the reaction on the equiaccessible surface of the catalyst and solvation parameters, reactivity indices, and adsorption values of hydrogenated compounds containing electron acceptor (4-nitrobenzoic acid) and electron donor (4-nitroaniline) substituents was considered.     

Kinetics of catalytic hydrogenation of 4-nitroaniline in aqueous solutions of propan-2-ol with acid or base additives

The effect of addition of acetic acid and sodium hydroxide to an aqueous azeotropic solution of propan-2-ol on the rate of 4-nitroaniline hydrogenation is studied. The base additive accelerates the apparent rate of nitro group reduction, while the presence of acetic acid slows the reaction rate. It is experimentally established that the rate of nitro group conversion calculated from the amount of reacted 4-nitroaniline exceeds the rate of hydrogen uptake from the gas phase in all of the studied solvents. Hydrogen bound by active sites of the catalyst surface is found to participate notably in the reactions. It is proved both experimentally and theoretically that strongly bound atomic forms of adsorbed hydrogen are most active in the reduction of the nitro group.     

Peculiarities of azobenzene catalytic hydrogenation in 2-propanol aqueous solutions with acid or base additives

It is shown experimentally that the hydrogenation of azobenzenes over a nickel skeleton catalyst in 2-propanol aqueous solutions proceeds selectively with the formation of aniline. It is pointed out that during the reaction, considerable participation of hydrogen bonded with active centers of a catalyst surface was observed. The competitive character of adsorption between the initial azo compound and aniline formed as a result of reaction is established. It is concluded that purposeful change of the azo group hydrogenation rate is possible by introducing acid or base additives into 2-propanol aqueous solution.     

Kinetics of hydrogen absorption by porous nickel in an aqueous sodium hydroxide solution

Kinetic studies of hydrogen absorption by porous nickel catalyst establish that there are three regions on kinetic curves of the process differing in their regularities of adsorption. The dependence of the observed rate of hydrogen absorption on the adsorbate amount is formally described by a first order kinetic equation, and the absorption rate constants corresponding to distinct parts of the kinetic curve differ by 1–2 orders of magnitude. The obtained data are explained using the concept that hydrogen adsorption on nickel active centers proceeds with three forms of adsorption.     

Concentration Effects in the Hydrogenation of 4-Nitro-2′-Hydroxy-5′-Methylazobenzene over Skeletal Nickel in an Aqueous 2-Propanol Solution

The kinetics of hydrogenation of 4-nitro-2′-hydroxy-5′-methylazobenzene in aqueous 2-propanol solution over the skeletal nickel is investigated at different initial concentrations. It is established that the hydrogenation of 4-nitro-2′-hydroxy-5′-methylazobenzene over a skeletal nickel in azeotropic aqueous 2-propanol solution proceeds via two parallel pathways at both low and high initial concentrations. It is shown that increasing the initial concentration of the hydrogenated compound above its level of solubility raises the rate of azo group transformation in 4-nitro-2′-hydroxy-5′-methylazobenzene, while the content of 4-amino-2′- hydroxy-5′-methylazobenzene does not change in the hydrogenate and is not accumulated in the bulk of solution.     

Kinetics of the hydrogenation of 2-chloro-4-nitroaniline over skeletal nickel and supported palladium catalysts in an aqueous solution of 2-propanol

The kinetics of the liquid-phase hydrogenation of 2-chloro-4-nitroaniline in an aqueous solution of 2-propanol over skeletal nickel and supported palladium catalysts is studied. The selectivity of the reaction with respect to 2-chloro-1,4-phenylenediamine is determined. It is found that samples of supported palladium catalysts differ with respect to the amount of the active component and the nature of the support. Some of their structural characteristics are provided.