IINVESTigation of the catalytic and isomerization activity of multi-component skeletal nickel catalysts in the hydrogenation of hexene-1

In this work, the effect of the amount of catalyst, modifying additives, and the phase composition of the alloys on the catalytic and isomerizing activity of skeletal in the hydrogenation reaction of hexane-1 is investigated. It has been shown that for all studied catalysts, the yield of products in the processes of migration and isomerization depends very strongly on the weighed portion of the catalyst introduced into the reaction medium. So, for example, the yield of hexane-2 with an increase in the catalyst weight increases linearly to 0.5g of nickel, while at the initial stage of the reaction the yield of hexane-2 reaches 62%. With a further increase in the catalyst weight (up to 1 g of Ni), the yield of hexane-2 decreases. The results of chromatographic analysis indicate a high activity of modified skeletal nickel catalysts in the reaction of migration of -C = C- bonds during hydrogenation of hexene-1. Modification of Fe, Pd, Sn and Ag increases the migration coefficient (Kmigr) from 0.66 to 0.70-0.77, while additions of Ti, Mo, Ti-Mo and Zr practically do not change it. The activity of the catalyst increases with the introduction of the metals Cu, Zn, Pb, Ti-Mo, Mo, Bi, Ag, and Mo-Cu (W=120-290 cm3/min·g Ni) into the initial alloy, while the addition of Fe, Pd and Mn (W=56-80 cm3/min·g Ni), while the influence of the components Ti, Zr and Sn is insignificant (W=115-117 cm3/min·g Ni).

LIQUID-PHASE HYDROGENATION OF CYCLOPENTADIENE ON MODIFIED SKELETAL NICKEL CATALYSTS

This paper presents the results of a study on the hydrogenation of cyclopentadiene on modified skeletal nickel catalysts. It is shown that the activity of multicomponent skeletal nickel catalysts in the hydrogenation of cyclopentadiene is largely due to the nature of the additives introduced into the initial alloy. The introduction of Cu, Pb, Ta, Zn, Mo-Cu, Bi and Mo into the alloy leads to an increase in the activity (W = 14-280 cm3/min g Ni) and selectivity (Ks = 0.93-0.99) of cyclopentadiene hydrogenation, additions of Cr, Ti, Sn and Cr-Cu have no significant effect. As a result, when cyclopentadiene is hydrogenated, an intermediate alkene, cyclopentene, is formed. This is due to the cyclic structure of cyclopentadiene, which causes the formation of identical cycloalkene molecules when hydrogen is added to any position. The saturation of cyclopentadiene is completely completed upon absorption of 1 mole of hydrogen, and cyclopentene can be obtained in high yield.

INFLUENCE OF ADDITIVES OF ACID ON STAGE OF TRANSFORMATIONS OF 4-NITRO-2'-HYDROXY-5'-METHYLASOBENZENE ON SKELETONIC NICKEL IN WATER SOLUTION OF 2-PROPANOL

The article is devoted to the analysis of the reaction kinetics of hydrogenation of 4-nitro-2'-hydroxy-5'-methylazobenzene in an aqueous solution of 2-propanol with acetic acid addition on skeletal nickel at different initial quantity of the starting compound. Clarification of the sequence of transformations of compounds containing several reactive groups, and the development of approaches to controlling the selectivity of processes with their participation is a practically significant task. According to the data obtained, at both low and high initial concentrations the hydrogenation of 4-nitro-2'-hydroxy-5'-methylazobenzene on skeletal nickel in a 2-propanol aqueous solution-0.01 M CH3COOH solvent proceeds in two parallel directions. The largest contribution in the first phase of the reaction is made by the azo group conversion of the starting compound, in contrast to the reaction in an aqueous solution of 2-propanol without acid addition. An increase in the initial quantity of the hydrogenated compound above its solubility limit leads to an increase in the rate of conversion of the azo group in 4-nitro- and 2-amino-2'-hydroxy-5'-methylazobenzene. Consequently, optimum quantity of 4-nitroaniline and 2-amino-2'-hydroxy-5'-methylazobenzene in the bulk solution during hydrogenation of the specified quantity of 4-nitro-2'-hydroxy-5'-methylazobenzene practically didn’t change, in contradiction to the hydrogenation on skeletal nickel in a neutral aqueous solution of 2-propanol. In a neutral aqueous solution of 2-propanol, when passing to high concentrations of the hydrogenated compound, the maximum yield of 4-nitroaniline increases twice as long the better, while as 4-amino-2'-hydroxy-5'-methylazobenzene, is reduced conversely. The results obtained do not contradict the concept of a parallel-sequential scheme for the conversion of 4-nitro-2'-hydroxy-5'-methylazobenzene. One of the directions involves the conversion of 4-nitro-2'-hydroxy-5'-methylazobenzene through 4-nitroaniline and 2-amino-4-methylphenol due to the hydrogenation of the azo group, and the second is the conversion of 4-nitro-2'-hydroxy-5'- methylazobenzene via 4-amino-2'-hydroxy-5'-methylazobenzene by reduction of the nitro group. At the end of the reaction, all the intermediate compounds are reduced to 2-amino-4-methylphenol and 1,4-phenylenediamine. When acetic acid is introduced into the composition of the neutral solvent 2-propanol-water, the contribution of the direction that ensures the formation of 4-nitroaniline and 2-amino-4-methylphenol to the overall reaction rate increases. An increase in the initial amount of 4-nitro-2′-hydroxy-5′-methyl-azobenzene leads to an increase in the rate of conversion of the azo group in the starting compound and to a decrease in the rate of conversion of 4-amino-2′-hydroxy-5′-methylazobenzene. The effect of the acid on the change in the conversion rates of nitro and azo groups to 4-nitro-2′-hydroxy-5′-methylazobenzene does not contradict the previously obtained results for the hydrogenation of its analogue, 2-nitro-2′-hydroxy-5-methylazobenzene, as well as individual compounds containing a nitro and azo group.

HYDROGEN ROLE IN SELECTIVITY OF SUBSTITUTED NITRO-AZOBENENES HYDROGENI-ZATION ON SKELETAL NICKEL IN 2-PROPANOL AQUEOUS SOLUTIONS

Elucidation of the substituted nitrobenzenes transformations sequence, in particular, containing several reactive groups and the development of approaches to the control of the selectivity of processes involving them is of interest from both theoretical and practical points of view. The article is devoted to the analysis of the hydrogenation kinetics of 2-nitro-2'-hydroxy-5'-methylazobenzene, 4-nitro-2'-hydroxy-5'-methyl-isobenzene, 4-nitroaniline, 4-amino-2'-hydroxy-5'-methylazobenzene on skeletal nickel in 2-propanol aqueous solutions of different composition, including with the addition of acetic acid or sodium hydroxide with various initial amounts of organic compound. The rise in the 4-nitro-2'-hydroxy-5'-methylazobenzene initial amount leads to increase in the nitro group transformation rate in the starting compound and to decrease in the azo-group transformation rate. The effect of sodium hydroxide additives in the 2-propanol aqueous solution on the nitro- and azo-groups conversion rate into 4-nitro-2'-hydroxy-5'-methyl-isobenzene is analogous to the change in the individual compounds hydrogenation rates (4-nitroaniline and 4-amino-2'-hydroxy-5'-methylazobenzene). Obtained results do not contradict the parallel-sequential scheme concept for the 4-nitro-2'-hydroxy-5'-methylazobenzene transformations. One of the directions is associated with the azo-group transformation into 4-nitro-2'-hydroxy-5'-methylazobenzene and 4-nitroaniline and 2-amino-4-methylphenol formation, and the second with the 4-nitro-2'-hydroxy-5'-methyl-isobenzene conversion through 4-amino-2'-hydroxy-5'-methyl-isobenzene by the nitro-group reducing. At the reaction end, all intermediate compounds are reduced to 2-amino-4-methylphenol and 1,4-phenylenediamine. When 2-nitro-2'-hydroxy-5'-methylazobenzene is hydrogenated, one of the directions leads to the 2-nitro-2'-hydroxy-5'-methylhydrazobenzene formation, and the second to the product containing the triazole cycle - N-oxide 2-2'-hydroxy-5'-methylphenylbenzotriazole. At the reaction end, these compounds are reduced to 2-2'-hydroxy-5'-methylphenylbenzotriazole and 2-amino-4-methylphenol and 1,2-phenylenediamine, respectively. In the solution at the sodium hydroxide presence, 2-nitro-2'-hydroxy-5'-methylhydrazobenzene transforms into the N-oxide 2-2'-hydroxy-5'-methylphenylbenzotriazole as a result of intramolecular rearrangement.

HYDROGENIZATION OF SUBSTITUTED NITRO-, AZOBENZENES, THEIR MIXTURE AND SUBSTITUTED NITROAZOBENZEN ON SKELETAL NICKEL IN AQUEOUS 2-PROPANOL SOLUTIONS

The article is devoted to the investigation of the hydrogenation of 4-nitroaniline, 4-amino-2'-hydroxy-5'-methylazobenzene, their mixture and 4-nitro-2'-hydroxy-5'-methylazobenzene on skeletal nickel in an aqueous solution of 2-propanol with azeotropic composition (x2 = 0.68) and this solvent with the addition of acid (0.01 M CH3COOH) or sodium hydroxide (0.01 M NaOH). The elucidation of the reasons and the development of approaches to the selective control of the staged transformations of substituted nitroazobenzenes containing two reactive groups in a molecule under the conditions of hydrogenation are of interest from theoretical and practical points of view. The rate of formation of intermediate products during the hydrogenation of nitroazobenzenes is largely determined by the activation of nitro and azo groups. The aim of the work is to conduct a comparative analysis of the rates of conversion of nitro- and azogroups in individual compounds with the rates of hydrogenation of their mixture and the rate of conversion of nitroazobenzene, which simultaneously contains nitro- and azogroups, to discuss the reasons for the influence of the solvent composition on the conversion rates of mono- and disubstituted benzenes. UV-spectroscopic data indicate that the electronic state of the hydrogenated compounds in the solvent compositions used does not undergo significant changes, since the absorption maxima are shifted by no more than 1 nm, both with the addition of acid and base. On the contrary, the observed rates of hydrogenation of mono- and disubstituted benzenes vary within fairly wide limits. A comparative analysis of the rates of hydrogenation of individual compounds, their mixtures and disubstituted benzene allows us to conclude that the priority of reduction of one or another group in 4-nitro-2'-hydroxy-5'-methyl-azobenzene can be made on the basis of calculating the quantitative ratio of the reaction products. When a mixture of compounds containing nitro and azo groups is hydrogenated, their adsorption rather than reactivity begins to play the primary role.