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Section 13. Chemistry
DOI: http://dx.doi.org/10.20534/ESR-16-9.10-256-258
Agaev Akbar Ali, Doctor of chemical sciences, Professor, Head of the Department of «Petrochemistry and chemical technology», Sumqayit State University E-mail: [email protected] Mustafaeva Nailya Abdulla, Senior Lecturer at the Department of «<Chemistry of high molecular compounds and analytical chemistry», Sumqayit State University E-mail: [email protected] Muradov Mahal Mail, Candidate of chemical sciences, Associate Professor, Dean of the Department of chemistry and biology, Sumqayit State University E-mail: [email protected] Nazarova Mushkinaz Kichmirza, PhD in Chemistry, Associate Professor at the Department of «Petrochemistry and chemical technology», Sumqayit State University E-mail: [email protected]
Alkylation of 2-methylaniline with the methanol in the presence of ferrite catalysts
Abstract: The catalytic activity of ferrite catalyst with different composition in alkylation reaction of 2-methylaniline with methanol in the gas phase was investigated. It was established that copper-ferrite catalyst with the composition (mass.%) of Cu Fe2O4 -30.0, Al203-70.0 was the best contact in selective (95.3%) synthesis of N-, 2-dimethylaniline. The main and side conversions that take place in the catalytic process are discussed.
Keywords: 2-methylaniline, methanol, alkylation, ferrite catalyst, N-, 2-dimethylaniline, 2.6-dimethylaniline, output, selectivity.
Ferrite catalysts successfully used in the processes of petrochemical synthesis, particularly, in the reactions of dehydrogena-tion, oxidative dehydrogenation of paraffines and olefines [1; 2], as well as in the reactions of alkylation of phenols with alcohols [3; 4], have scarcely been researched in the processes of obtaining al-kyl derivative aromatic amines. Alkyl-aromatic amines, particularly methyl derivatives of aniline, are valuable products in the production of stabilizers, antioxidants, coloring agents, medicinal agents, and are mainly obtained by catalytic alkylation of aromatic amines by methanol [5-7].
This article presents the results of research of the reaction of alkylation of 2-methylaniline by methanol in the presence of ferrite catalytic systems.
Experiments on alkylation were conducted in the laboratory reactor with a permanent study area with a layer of catalyst, the volume of which was 10 cm 3. The products of alkylation were condensed in the fridge-separator and analyzed by method of gas-liquid chromatography on the chromatograph Chrom. 5 with the use of a packed column (3.6m x 4mm), containing 60% of SE-30 (silicone
elastomer) on the chromoton N-AW (0.16-0.20mm) by flame ionization detection. The analysis was conducted at the programming of the temperature with the velocity of 8 °C/min within the range of 80-180 °C. Helium served as carrier gas, the consumption ofwhich was 60 ml/min. Relative error at chromatographic analysis does not exceed 3.2%.
Ferrites of magnesium, zinc, ferrum and copper were obtained by method of collective subsidence of nitrite salts of respective bivalent metals on the aluminium oxide with further drying (at 100160 °C) and calcination at 450 °C for 4 hours. Herewith, atomic correlation of bivalent metal to ferrum (M: Fe) was equal to 1:2.33. Catalysts had specific surface of 100-160 m 2/g, and their mechanic strength was not less than 97.0%.
Experimental part
Firstly, catalytic activity of ferrite catalysts of different composition in the reaction of alkylation of 2-methylaniline by methanol was studied. 3 batches of every ferrite catalyst with the concentration of active mass of M Fe204 15.0 mass% (A), 20.0 mass% (B) and 30.0 mass% (C) were examined.
Alkylation of 2-methylaniline with the methanol in the presence of ferrite catalysts
Total output of the products of N-alkylation and C-alkylation of amine calculated using reacted (selectivity) and missed (activity) o-toluidine were selected as comparative criterion.
As it is seen from Table 1, MgFe2O4 is the worst catalyst subjecting 2-methylaniline to conversion, whereas the ferrites of zinc and copper are the best catalysts. In all cases with the increase of active mass in the catalyst, the conversion of initial amine reduces, which is accompanied with the increase of selectivity of formation of N-, 2-dimethylaniline and reduction of the output of 2.6-xyli-dine calculated using reacted 2.6-demethylaniline. In the case of Zn Fe2O4 • Al2O3, the selectivity of formation of 2.6-xylidine is only 1.0%, whereas it almost doesn't form in the case of copper ferrite catalyst. The increase of active mass in the ferrite catalysts from 20.0 mass% to 30.0 mass% sharply increases the velocity of mono N-alkylation of o-toluidine and, herewith, the selectivity of formation of N-, 2-dimethylaniline increases to 85.0-96.0%. However, with the increase of the share of active mass in the composition of a catalyst, the consistent N-methylation of aromatic amine reduces in almost all cases.
Taking into account the fact that the activity of ferrite catalysts in the reaction of alkylation of 2-methylaniline by methanol is based at the output of N-, 2-dimethylaniline on the missed amine, the figure shows comparative criteria for different ferrite catalysts. Comparing these indicators, a range of the activity of ferrites in the synthesis of this product of N-alkylation of amine is drawn. Cu Fe2O4 • A^ > Fe Fe2O4 ^ >Zn Fe^Al^ Mg Fe2O4 • Al^
In the case of copper ferrite catalyst, the activity is 71.0-77.4%, over FeFe2O4 Al2O3 it is equal to 65.5-73.9%. During the alkylation
of 2-methylaniline by methanol, over zinc and magnesium ferrite catalysts, the output of N-alkylation products on the missed aromatic amine is respectively equal to 63.8-68.8% and 33.0-50.0%.
Considering high catalytic properties of copper and ferrite catalyst, detailed researches of the interaction of 2-methylaline methanol in the presence of C sample of this contact have been presented. As it is seen from Table 2, the influence of the temperature on the indicators of the reaction is ambiguous. The main products of the reaction of N-2-dimethilaniline, 2.6-dimethylaniline, N, N-2-trymethilaniline and other isomers ofxylidine are formed with different outputs, and selectivity of their synthesis depends on the temperature a lot.
It is apparent that at 320 ° C, the main direction of the process is mono-N-alkylation (95.3%) and di-N-alkylation (3.0%) of o-tolu-idine. With the increase of temperature, the selectivity of formation of N-, 2-dimethylaniline reduces, first, to 60.0% (at 350 ° C), and then, to 30.0% (at 380 ° C). Herewith, the selectivity of formation of N-, N-2-trimethylaniline first grows to 20.0% (at 350 ° C), then to 30.8%.
The growth of the temperature increases the velocity of selective formation of C-alkylating products, particularly, 2.6-dimethylaniline and other xylidines. The growth of the temperature from 320 ° C to 350 ° C increases the share of C-alkylating products in alkylates, namely, the output of 2.6-dimethylaniline calculated using reacted amine from 1.0% to 20.0%, and, at 380 ° C, 26.0% is reached. Herewith, the growth of selectivity of formation of other isomers ofxylidine is observed. At 350 ° C, the selectivity of their formation reaches 5.5% and 11.2% at 380 ° C.
Table 1. - The results of the reaction of alkylation of 2-methylaniline by methanol in the presence of ferrite catalysts Conditions of the reaction: Temperature — 320 ° C, specific load 1.0 h-1, molecular ratio 2-methylaniline: methanol = 1:4
Name Catalyst composition
Mg Fe204 • Al203 Zn Fe2°4 • Al203 Fe Fe O • Al O 2 4 2 3 Cu Fe2°4 • Al2°3
A B C A B C A B C A B C
Output of the products of reaction calculated using reacted 2-methylaniline,% — including:
N-, 2-dimethylaniline 80.5 90.0 93.0 74.0 81.0 85.0 84.0 92.0 95.0 78.0 91.0 95.2
N, N-, 2-trimethylaniline 5.0 3.5 3.0 18.5 16.5 13.0 2.0 0.5 - 10.0 7.7 3.0
2.6-dimethilaniline 8.5 5.0 2.5 5.0 2.0 1.0 9.5 6.5 3.5 10.0 1.0 1.0
Other xylidines 5.0 - - 1.5 - - 4.0 - - 1.0 - -
Conversion of 2-methylaniline 62.0 50.0 35.5 93.0 83.0 75.0 88.0 80.0 69.0 91.0 85.0 79.0
Figure 1. Activity of ferrite catalysts in the reaction of alkylation of 2-methylaniline by methanol 1. Mg Fe2O4 ■ Al2O3 2. Zn Fe2O4 ■ Al2O3 3. Fe Fe2O4 ■ Al2O3 4. Cu Fe2O4 ■ Al2O3
In the catalytic process, the following conversions apparently take place. At low temperature (320 ° C), mono N-alkylation of 2-methyl-aniline prevails. With the increase of temperature, its di-N-alkylation and partial isomerization into the products of C-alkylation of amine,
particularly, by xylidines, strengthens. However, the increase of temperature enhances the velocity of C-alkylation of amine and, apparently, this direction is primary in the obtaining ofxylidines. Schematically, these conversions can be presented as follows:
Considering mean acidic properties of copper ferrite catalyst, the flow of such conversions as isomerization and disproportion-ation of N-alkyl- and C-alkyl derivatives in the catalytic environment is hardly possible.
The increase of specific load to 1.5 h-1 is favorable to N-alkylation of amine, the general selectivity of which reaches 98.8%. Herewith, mono-N-alkylation prevails. As it is seen, the selectivity of N-, 2-dimethylaniline is equal to 97.0% (Table 2).
The increase of time of contact has a negative effect on N-alkylation of o-toluidine, particularly, its N-methylation, the share of which reduces to 80.8% in the catalytic process.
An interesting peculiarity of copper ferrite catalyst lies in the fact that the reduction ofpartial pressure of methanol from four-time to two-time as well as its increase to six-time in the initial mixture is not favorable for the selective synthesis of N-,2-dimethylaniline, because the deterioration of the output of this product calculated using reacted amine is observed in both cases. In the latter case,
despite the increase of conversion of 2-methylaniline, its certain part is consumed on consistent methylation with the formation of N-, N-,2-trimethylaniline. The increase of partial pressure of alcohol enhances its side conversions with the formation of formaldehyde, methyl formate and products of their condensation, which sharply reduces the output of products of the reaction calculated using reacted alcohol.
Thus, the studies of catalytic properties of ferrite catalysts in the reaction of alkylation of 2-methylaniline by methanol established their activity and selectivity in the catalytic process.
It was established that the best catalytic properties are shown by copper ferrite catalyst with the concentration of active mass (Cu Fe2O4) in the catalyst of -30.0 mass%.
In the obtained conditions of reaction (T-320 ° C, u -1.0 h-1, v -1: 4 mol/mol), in the presence of this catalyst, it is possible to obtain N-,2-dimethylaniline with the output on reacted and missed 2-dimethylaniline of 95.3 and 75.8% respectively.
Table 2. - Results of the reaction of alkylation of 2-methylaniline by methanol in the presence of Cu Fe2O4 Al2O3
Conditions of reaction Conversion of 2-methylani-line Output of products of the reaction calculated using reacted amine,%
T °C u, h-1 v, mol/mol N-,2-dimethyl-aniline 2.6-dimethyl-aniline Other xylidines N-, N-,2-tri-methylaniline
320 1.0 1:4 79.5 95.3 1.0 - 3.0
350 1.0 1:4 88.5 60.0 12.0 5.5 20.0
380 1.0 1:4 94.0 30.0 26.0 11.2 30.8
320 0.5 1:4 87.9 80.8 8.9 2.2 7.7
320 1.5 1:4 65.9 97.0 1.2 - 1.8
320 1.0 1:2 52.0 87.0 3.3 1.0 3.3
320 1.0 1:6 93.3 94.0 1.3 - 4.5
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