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110 AZERBAIJAN CHEMICAL JOURNAL № 3 2022 ISSN 2522-1841 (Online)
ISSN 0005-2531 (Print)
UDC 66.097. 3+54-732
MICROWAVE RADIATION STIMULATED REACTION OF ACYLATION OF DIETHYL-AMINE WITH M-TOLUIC ACID IN THE PRESENCE OF Zn-B-P/Al2O3/Al CATALYST
P.A.Muradova
M.Nagiyev Institute of Catalysis and Inorganic Chemistry, NAS of Azerbaijan
muradovaperi@rambler.ru
Received 07.01.2022 Accepted 25.02.2022
The paper presents the results of microwave synthesis of a Zn-B-P-oxide catalyst, which actively absorbs the energy of microwave radiation, applied to the surface of an aluminum-reinforced Al/y-Al2O3 carrier, in order to further intensify the process of acylation of diethylamine with m-toluic acid to diethylamide m-toluic acid (DETA) under conditions of exposure to a microwave field. The results obtained demonstrate the possibility of realizing the process of acylation of diethylamine with m-toluic acid in a thermal regime, which is formed in the reaction zone due to the transformation of microwave energy by the catalyst mass. The developed method of microwave acylation of diethylamine with m-toluic acid is superior to the existing analogs in technological and energy parameters.
Keywords: microwave radiation, m-toluic acid, diethylamine, acylation, dietylamide of m-toluic acid.
doi.org/10.32737/0005-2531-2022-3-n0-116
Introduction
N,N-Diethylamide of m-toluic acid (DETA) belongs to the class of effective insect repellents of selective action against blood-sucking insects and material- and product-destroying Lepidoptera [1-6].
The widespread method for the preparation of DETA is based on the reaction of acylation of diethylamine with m-toluic acid halide synthesized in the acylation-preceding step by halogenation of m-toluic acid with thionyl chloride, phosgene, or a phosphorus chloride [7-9].
This method has a number of drawbacks, such as the use of highly toxic and corrosive halogenation products, the batch mode of the process and its duration, and low values of the cost/performance ratio (the DETA yield does not exceed 75-80% of the acid taken).
Earlier, we, as well as a number of other authors developed a more efficient way of direct heterogeneous catalytic acylation of diethyl-amine benzoic and m-toluic acids [10-13]. In particular, it was found that in the presence of a modified zinc oxide containing boron phosphate catalyst (Zn-B-P/Al2O3) reacting m-toluic acid and diethylamine proceeds with an acceptable yield for practical realization of the target diethyltoluamide.
Despite the obvious benefits of this process, which excludes the use of m-toluic acid chlorid, as acylating agent the latter due to the endothermic nature of the equilibrium reaction is high-energy, and its intensification requires the of more efficient, compared to traditional, energy, sources such as an microwave electromagnetic radiation, for which there is no need of preheating the raw material and the desired reaction temperature is achieved due to the catalytic conversion of the absorbed energy of the electromagnetic field into the heat [14-18].
For this reason, the method of direct catalytic acylation of diethylamine with m-toluic acid is of undoubted interest for the industrial process of obtaining N,N-diethyltoluamide and can be carried out in both batch and continuous modes.
This work presents the results of studying the reaction of acylation of m-toluic acid diethylamine in the presence of Zn-B-P/Al2O3/A1-catalyst that activety absorbs electromagnetic radiation.
Experimental part
Preparation of microwave-absorbing samples of alumina support reinforced with finely divided aluminum and the subsequent
heat treatment of the active ingredient of zinc borophosphate catalysts (Zn(NO3)2-6H2O, or-thophosphoric and boric acids) deposited on the support surface were carried out in an setup constructed on the basis of a Sanyo EM-G5593V microwave oven with a cavity capacity of 23 liters.
The heat treatment (drying and sintering) of samples was carried out at an operating frequency of 2450 MHz and variation of the input power of the microwave generator in the range of 200-800 W [19]. The catalyst samples obtained by the conventional heat treatment after impregnation in terms of moisture capacity of the carrier (y-Al2O3) with a solution of zinc nitrate, orthophosphoric and boric acids were dried at a temperature of 110-1200C for 2 h and were calcined in a muffle furnace at a temperature 450-4800C for 4 h.
Measurements of the loss of microwave radiation power when passing through the catalytic charge were based on the equivalent conversion of microwave energy into heat, "thermal transformation" and an increase in the temperature of the calorimetric body, in this case, water, which absorbed this energy. Moreover, regardless of the parameters of electromagnetic radiation, the measurement result will be the average power value:
P =
- X
c ■ m ■ AT _ 4,17 • c ■ m ■ AT 0,24t t
(1)
where: 0.24 is the thermal equivalent of work, m is the mass of water, (g); c - specific heat of water = 4.187 kJ/ kgK; AT - increment of water temperature (K); t - exposure time in a microwave oven (s).
Empirical determination of the depth of penetration of an electromagnetic wave into a catalytic mixture with a complex composition consists in identifying such a thickness of the catalyst layer at which almost complete absorption of the acting microwave energy is ensured [20]:
X
nyj 2s'(Vl + tg2S-1)
(2)
where is the distance at which the amplitude of the electric field strength vector (E0) decreases by a factor of e (e ~ 2.7 is the base of the natural logarithm) s - is the real part of the relative permittivity of the catalyst material, tgS is the tangent of the dielectric loss angle. The calculation of the value is also reduced to an estimate of the maximum temperature difference of the ballast water loading without a catalyst sample and with it, while varying the output power of the magnetron.
Experiments on the microwave-assisted conversion of m-toluic acid and diethylamine were carried out in a flow reactor made of optically transparent quartz glass with inner diameter = 25 mm and height = 50 mm in a setup constructed on the basis of a Panasonic NE1064F multimode microwave oven with a cavity capacity of 14 L.
The operating frequency of the microwave generator magnetron was 2450 MHz, and the maximum input power was 1200 W. The temperature of the catalyst charge was measured with a VA6520 noncontact infrared thermometer having the measurement range of -50 to + 6000C.
To avoid overheating of the reactor by excess absorption of microwave radiation, a shunt tank with circulating distilled water was installed in the oven cavity. The dosing of the reaction mixture to the contact zone was facilitated by feeding it as a saturated aqueous solution of the diethylammonium salt of m-toluic acid to the top of the reactor.
Analysis of the composition of the liquid component of the catalyzate carried gas chromatography (LCM-80 MD unit, the 3-rd model, a flame ionization detector, column l = 2.4 m, d = 3.0 mm, separating the phase - Silicone is the SE-30 10% hezosorbe AWHMD, fraction 0.35-0.5 mm internal standard - n-octyl alcohol. for the separation phase of gaseous products - CO2 and ethylene TGNM was used as the for NZ-600).
Results and discussion
Figure 1 shows the results of the influence of the variable power of the magnetron on the dynamics of the change in the temperature of the samples of Al /y-Al2O3 absorbing micro-
wave radiation of the carrier [9] impregnated with aqueous solutions of zinc nitrate, boric and phosphorus acids, with different ratios of the active mass and the carrier in terms of oxides.
For comparison of the level of absorption of microwave radiation; data on the microwave heat treatment of samples impregnated with a solution of metal nitrates of samples of an y-Al2O3- carrier unreinforced with aluminum are also presented here.
It can be seen that at a minimal (in the range examined) value of the magnetron power (W = 200 watt), all the initially wet samples intensely absorb microwave radiation because of a high level of dielectric losses. In this case, the mass-average temperature of the charge passes through a maximum and stabilizes in the region of 100-1150C until the complete evaporation of water.
Fig. 1. Influence of microwave power (watt,) on the dynamics of the temperature change of Al/y-Al2O3 support samples impregnated with a Zn nitrate, H3BO3, and H3PO4 solution in an amount of (1) 10 or (2) 20 wt % and (3) a sample of the unreinforced y-Al2O3 support impregnated with a solution of the same active components in an amount of 20 wt % (on an oxide basis).
It is noteworthy that the drying process proceeds with a much greater intensity in the case of carrier samples reinforced by finely divided aluminum and impregnated with active components.
With an increase in the magnetron power (W = 400 W), the temperature rise of the samples with the active ingredient deposited on the surface of the reinforced substrate significantly exceeds the growth in the temperature of the samples deposited on unreinforced y-Al2O3. In this case, the thermolysis of zinc nitrate releasing nitrogen oxides is observed as early as 7.07.5 min after the beginning of irradiation in the temperature range of 250-3000C.
Further exposure to microwave radiation, at a maximum power of 800 W, leads to a faster heating of the charge to a temperature range of 580-6000C, in which the possibility of the formation of catalytically active phases: zinc boro-phosphate, is realized (through a sequence of stages of dehydration of boric and orthophos-phoric acids into metaboric and metaphosphoric acids and their interactions with zinc oxide), as well as pyrophosphate and zinc borate:
H3BO3+H3PO4 ^BP04
ZnO+HB02+HP03 2ZnO + 2H3PO4 —
-1H2° > HB02+HP03 >
->ZnB2P208
-3H°
>Zn2P2O7
ZnO + 2H3B03
-3H°
-> ZnB204
(1) (2)
(3)
(4)
The formation of the active mass of Zn-B-P/y-Al2O3/Al catalysts in the microwave field occurs within a relatively short exposure time, in contrast to the longer time of the thermal treatment of the samples under conventional heating conditions.
Figure 2 shows the dependence of the ability of catalysts, synthesized under heat treatment in a microwave field, to absorb microwave energy and the depth of its penetration on the component composition of the samples.
It can be seen that the level of absorption of microwave radiation by borophosphate-containing samples deposited on the surface of the y-Al2O3/A1 carrier and the depth of radiation penetration into their mass, practically do
not differ from those for the alumina carrier reinforced with microcrystalline aluminum.
Modification of BPO4/Al2O3/A1 samples with zinc oxide in the investigated limits of its content (2.0 - 5.0 wt %) leads to an increase in the amount of absorbed microwave radiation energy and its transformation into heat sufficient to maintain the temperature regime of a stationary the course of the reaction (320-
420°C) with a magnetron power of 400-800 watts.
The observed high thermotransformation capacity and heating rate of the catalytic charge indicate the possibility of reaching the reaction temperature (400-450°C) due to the absorption of microwave energy sufficient for the acylation of diethylamine with m-toluic acid.
Fig. 2. Dependence of the thermal transformation properties of Zn-B-P/ Al2O3/A1-catalysts and the depth of penetration of microwave radiation into their mass (weigh. 50 g) on their composition A - y-Al2O3/A 1 -carrier; B - BPO4/Al2O3/A1; C - ZnO^BPO4/y-Al2O3/A1 (ZnO 2.0%); D - ZnO^BPO4/y-Al2O3/A1(ZnO 3.0%); E - ZnO^BPO4/y-Al2O3/A1 (ZnO 5.0%). Conditions: magnetron=800W, exposure time 2.5 min
Figure 3 shows the dependence of the conversion of m-toluic acid and selectivity for the desired product and byproducts of the acylation of N,N-diethylamine on the temperature in the contact zone, in which fixed values of temperature were provided by varying both the microwave power in the range of 400-800 W and heat loss in the cavity through changing the space velocity of the reaction mixture.The space time (~3 s) was maintained constant in this case
and compensated for by the corresponding volume of the catalyst charge.
It was found that as the temperature in the examined range of320-4000C increases, the conversion of m-toluic acid continuously increases but the selectivity of the target product diethyltoluamide - decreases because of the enhancement of its subsequent conversion into the byproducts monoethyl-m-toluamide, m-tolu-amide, and m-tolunitrile.
Fig. 3. Dependence of (1) the degree of conversion of m-toluic acid and (2-6) selectivity for the products of diethylamine acylation in the presence of a Zn-B-P/y-Al2O3/Al catalyst upon the reaction temperature. (2) N,N-diethyl-toluamide, (3) monoethyltoluamide, (4) toluamide, (5) toluene, and (6) tolunitrile. Conditions: a magnetron power of 400-800 W, an m-CH3C6H4COOH:(C2H5)2NH:H2O molar ratio of 1 : 2 : 4, and a space time of ~3 s
With an increase in the reaction temperature above 3700C, a more pronounced reduction in selectivity for DETA is observed, which is not compensated by an increase in the conversion of m-toluic acid in terms of the yield of the desired product.
Similarly, a decrease in the selectivity for diethyltoluamide is observed with an increase in the space time above 4 s (Figure 4). The specified space time of contact with the reaction me-
et, S
1,0 2,0 3,0 4,0 T (c)
To ultimately evaluate the effectiveness of the microwave field influence on the course of the reaction, Table compares the parameters of the diethylamine acylation reaction carried out under conventional heating conditions in a reactor in the presence of a catalyst that also has been prepared under the conditions of conventional heat treatment (column A, see [8]).
Column B lists the reaction parameters obtained during the conventional heating of the reactor in the presence of the catalyst sample prepared using microwave heating.
dium (~3 s), a reactants molar ratio of m-CH3C6H4COOH: N(C2H5)2 = 1:2 and a temperature of 365-3700C achieved by absorption of 600-800 W microwave radiation are apparently optimal reaction conditions in the presence of the Zn-B- P/ y-Al2O3/Al catalyst synthesized by microwave heat treatment to ensure a DETA selectivity of about 85- 88% acceptable for practical purposes and an m-toluic acid conversion as high as 90-95%.
Fig.4. Dependence of (1) the degree of conversion of m-toluic acid and (2-6) selectivity for the products of diethylamine acylation in the presence of a Zn-B-P/y-Al2O3/Al catalyst upon the space time. (2) N,N-Diethyltoluamide, (3) monoethyl-toluamide, (4) tol-uamide, (5) toluene, and (6) tolunitrile. Conditions: a magnetron power of 800 W, a steady-state reaction temperature of 360 ± 100C, and an m-CH3C6H4COOH: (C2H5)2NH:H2O molar ratio of 1 : 2 : 4.
Column C includes the results of the microwave-stimulated reaction in the presence of catalysts prepared under microwave heating conditions. It can be seen, that both the microwave-stimulated reaction and the reaction under conditions of conventional heating in the presence of catalyst samples prepared by thermal treatment in the microwave field are characterized by a higher rate of total conversion of m-toluic acid with comparable selectivity values for the desired (target) product.
Parameter A B C
Reaction temperature, 0C Contact time, s Total conversion rate under optimal conditions, mol/(m2h) Selectivity for diethyltoluamide (DETA), % 370 8.0 2.72x10-5 88.3 370 6.5 3.56 x 10-5 88.8 370 3.6 5.02 x 10-5 87.4
Comparison of the parameters of the diethylamine acylation reaction with m-toluic acid proceeding under conventional and microwave heating conditions in the presence of catalyst samples prepared using different methods of heat treatment action
Thus, the results obtained demonstrate the possibility of realizing the process of acylation of diethylamine with m-toluic acid in a thermal regime, which is formed in the reaction zone due to transforming the energy of microwave electromagnetic radiation by the catalyst charge.
The developed method for carrying out the reaction, under the conditions of exposure to microwave radiation, also favorably differs from the existing ones, carried out under conditions of traditional thermal exposure, by the absence of the need for preliminary heating of the raw material before feeding into the contact zone.
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Zn-B-P/Al2O3/Al-KATALIZATORUN I§TIRAKI ILO m-TOLUIK TUR§USU ILO DIETILAMININ ASÍLO§MO REAKSÍYASININ MÍKRODALQALI §UALANMASI
P.A.Muradova
Maqalada mikrodalgali sahaya maruz qalma §araitinda dietilaminin m-toluik tur§usu ila m-toluik tur§usu dietilamidina (DEET) asilla§ma prosesinda gevrilmasini daha da intensivla§dirmak ügün alüminium ila armirlanmi§ Al/y-Al2Ü3 da§iyicisinin sathina tatbiq olunan mikrodalgali ¡jüalanmanin enerjisini aktiv §akilda udan Zn-B-P-oksid katalizatorunun mikrodalgali sintezinin naticalari taqdim olunur. Naticalar mikrodalgali enerjinin katalizator kütlasi ila gevrilmasi naticasinda reaksiya zonasinda amala galan termal rejimda dietilamin ila m-toluik tur§usu ila asilla§ma prosesinin hayata kegirilmasinin mümkünlüyünü nümayi§ etdirir. Dietilaminin m-toluik tur§usu ila mikrodalgali asilla§masinin i§lanib hazirlanmi§ üsulu texnoloji va enerji parametrlarina göra mövcud analoqlari üstalayir.
Acar sözlar: Mikrodalgali §üalanma, m-toluik tur§usu, dietilamin, asilh§m3, m-toluik tur§usu dietilamidi.
МИКРОВОЛНОВОЕ ИЗЛУЧЕНИЕ РЕАКЦИИ АЦИЛИРОВАНИЯ ДИЭТИЛАМИНА м-ТОЛУИЛОВОЙ КИСЛОТОЙ В ПРИСУТСТВИИ Zn-B-P/Al2O3/Al- КАТАЛИЗАТОРА
П.А.Мурадова
В работе приводятся результаты микроволнового синтеза активно поглощающего энергию СВЧ излучения Zn-B-P-оксидного катализатора нанесенного на поверхность армированного алюминием Al/y-А^О^носителя, с целью дальнейшей интенсификации протекания процесса ацилирования диэтиламина м-толуиловой кислотой в диэтиламид м-толуиловой кислоты (ДЭТА) в условиях воздействия поля СВЧ. Результаты демонстрируют возможность реализации процесса ацилирования диэтиламина м-толуиловой кислотой в тепловом режиме, который формируется в зоне реакции за счет преобразования микроволновой энергии массой катализатора. Разработанный метод микроволнового ацилирования диэтиламина м-толуиловой кислотой превосходит существующие аналоги по технологическим и энергетическим параметрам.
Ключевые слова: микроволновое излучение, м^алуиловая кислота, диэтиламин, ацилирование, диэтиламид м-талуиловой кислоты.
