SYNTHESIS OF AMINES BASED ON FATTY ACID NITRILE

ABSTRACT

Chemical substances extracted from plants are widely used in various fields of the chemical industry. Aliphatic amines also have various applications, including in the chemical industry as a foaming flotation agent in the production of potassium chloride. In the article, acid amides and nitriles were synthesized on the basis of distilled (containing C₁₆-C₁₈ carbon atoms) fatty acids (DFA) isolated from the waste of oil plants (soapstock). The resulting nitrile was hydrogenated with hydrogen at a pressure of 60 MPa to obtain primary aliphatic amines with a purity of 98%.

The composition of the synthesized compound was confirmed by GX-MS chromatography and infrared spectrum.

АННОТАЦИЯ

Химические вещества, выделяемые из растений, широко используются в различных областях химической промышленности. Алифатические амины также имеют различное применение, в том числе в химической промышленности в качестве вспенивающего флотационного агента в производстве хлорида калия. В статье на основе дистиллированных (содержащих атомы углерода С16-С18) жирных кислот (ДФК), выделенных из отходов масложировых заводов (соапсток), синтезированы амиды и нитрилы кислот. Полученный нитрил гидрировали водородом при давлении 60 МПа с получением первичных алифатических аминов с чистотой 98%.

Состав синтезированного соединения подтвержден методами GX-MS хроматографии и инфракрасного спектра.

Keywords: distilled fatty acids, amide and nitrile of carboxylic acids, aliphatic amines, nickel, aluminum oxide, hydrogenation reaction, catalyst, fluororeagent.

Ключевые слова: дистиллированные жирные кислоты, амиды и нитрилы карбоновых кислот, алифатические амины, никель, оксид алюминия, реакция гидрирования, катализатор, фторреагент.

Introduction. One of the  most important tasks for chemical technologists is to create technologies for the production of products necessary for the chemical industry in economically with efficient ways. In this regard, a program for the localization of raw materials imported by chemical industry enterprises from abroad in exchange for foreign currency has been developed in our republic.

High molecular weight amines are developed and widely used in worldwide. One of the most  important areas of their application is the use of metal salts as a flotation reagent.

Abroad, higher amines are produced from natural acids extracted from the composition of plants. About 85% of the amines produced in America are obtained from natural raw materials. Amino compounds of the aliphatic oil series are widely used in the pharmaceutical and cosmetic sectors of the national economy, in the processes of organic synthesis, and in the industrial sector as a flotation agent in the extraction of potassium chloride salt from sylvinite in technical purity by flotation method. Depending on the season, the Dekhkanabad potash fertilizer plant mainly uses two types of amines, С_16-18NH₂ amines in the winter season, and С_20-22NH₂ amines in the summer. The need for amines in this plant is more than 250-300 t per year and it is brought from abroad at the expense of foreign exchange.

In our republic, there are necessary raw materials for the synthesis of amines: high fatty acids, soap stocks, which are waste of the food industry, sive oil, ammonia, nitrogen, urea and sodium hypochlorite, and other necessary starting materials.

There are several methods of synthesizing aliphatic amines, and it is economically effective to obtain them mainly based on distilled fatty acids containing С₁₆-С₁₈ carbon atoms, which are extracted from waste oil refineries.

Literature review 

In the synthesis of amines, carboxylic acids, carboxylic acid amides and nitriles are also used as starting materials. Amides are compounds formed by the replacement of a hydroxyl group in a carboxylic acid molecule with an amino group and are considered as acyl derivatives of ammonia. Amides cannot be synthesized directly from ammonia and carboxylic acids, because with ammonia the acid forms not amides, but ammonium salts. However, when ammonium salts of carboxylic acids are heated, they decompose to form acid amides.

Under the influence of urea, amides are synthesized from carbonic acid (Cherboule reaction) [1]. As a result of the interaction of stearic and palmitic acids isolated from cottonseed oil with urea, acid amides were also obtained, optimal conditions for the process were found [2]. There are other methods of obtaining high fatty acid amides isolated from various plants [3-5].

The process of obtaining mono and diethanolamides is based on the interaction of triglycerides of vegetable fatty acids with mono- and diethanolamine. In this process, in addition to the main products, acylation products of mono and diethanolamides with fatty acids are acylethanolamides, as well as piperazine, a product of cyclization of two molecules of aminoethanol. These processes mainly occur with the participation of catalysts [6].

Nitriles are organic compounds with the general formula R-C≡N and are regarded as homologues of cyanic acid with a radical substituted for the hydrogen. They are also often derivatives of carbocyclic acids (amide dehydration products). Nitriles react with unsaturated compounds (Ritter reaction) to form amides. This reaction is a method for the synthesis of N-substituted amides of carboxylic acids by alkylation of nitriles with carbocations. For the synthesis of nitriles, distilled fatty acids (DFA) obtained from oil industry wastes were used [7]. Most nitriles are toxic, their toxicity is lower than that of cyanic acid, and their homologues are water-soluble liquids [8].

There are several methods of obtaining nitriles: dehydration of amides and dehydrogenation in the presence of an aluminum oxide catalyst at 500°C, dehydration of aldoximes and Kolbe synthesis [9].

Amines are used as selective solvents in the separation of uranium from sulfuric acid solutions, in the flotation of potassium chloride from sylvinite, as organic bases, and in amination reactions. In addition, aromatic amines are widely used in the production of dyes, vulcanization accelerators, antioxidants, pharmaceutical synthesis, synthetic resins, and other fields  [10].

There are several ways to obtain amines: reducing nitriles with hydrogen or lithium aluminum hydride (LiAlH₄), catalytic hydrogenation of oxime compounds, and primary, secondary, and tertiary amines from carboxylic acids or their derivatives by Schmidt, Hoffmann, Lossen, and Curtius methods [11, 12].

Nitriles of acids were synthesized on the basis of distilled fatty acids extracted from waste oil plants. Primary aliphatic amines were obtained with 98% purity by hydrogenation of nitriles with hydrogen at a pressure of 5,5-5,7 MPa [13].

Aliphatic amines are available in our republic as raw materials, and a step-by-step extraction method was created with the participation of distilled fatty acids with composition C₁₆-C₁₈ ammonia, hydrogen and local catalysts [7].

Research of the methodolog. For the synthesis of acid amides and nitriles, distilled fatty acids containing C₁₆-C₁₈ carbon atoms extracted from oil industry waste were used. The reaction was carried out stepwise in a high-pressure apparatus. 1000 g of distilled fatty acid is heated in a hermetic reactor equipped with a mixer at a temperature of 50-60 C⁰ under a pressure of 0,5-0,6 MPa for 10-15 minutes under the influence of ammonia, and heated at a temperature of 180 C⁰ for 6 hours in the presence of ammonium soap, a catalyst of 30 g of aluminum oxide (Al₂O₃) acid amide, continuing the reaction without changing the temperature, acid nitrile was synthesized. In order to accelerate the separation of water and prevent the mixture from oxidizing, nitrogen gas was injected to create an inert environment. The synthesized acid nitriles were separated from the catalyst by distillation and filtration.

1- stage : RCOOH + NH₃ → RCOONH₄   ammonium soap

2- stages:RCOONH4 →RCONH₂ + H₂O    acid amide

3 -stage: RCONH₂ →RCN + H₂O    acid nitrile

Hydrogenation was carried out from the synthesized acid nitrile in a high-pressure reactor (figure-1) in the presence of a 0.7% nickel catalyst in an ammonia atmosphere, and aliphatic amines with composition C₁₆-C₁₈ were synthesized.

4- stage :     RCN + 2H₂→RCH₂NH₂           primary amino compound

2RCN + 4H₂→ (RCH₂)₂NH + NH₃     secondary amino compound

3RCN + 6H₂→ (RCH₂)₃N + 2NH₃      tertiary amino compound

Figure 1. High pressure reactor

1.Cylinder for ammonia. 2, 2^I, 2^II-manometers. 3.3^I-valves. 4. reactor. 5. Hydrogen cylinder.

300 g of the synthesized and purified nitrile was placed in the reactor. Ammonia (1) was supplied to the reactor through the valve (3) from the cylinder and a pressure of 15 atm was created. Ammonia pressure was controlled by (2) monometer, and 70 atm of hydrogen was supplied to the reactor from cylinder (5) through valve (3^I). Hydrogen pressure was measured using a monometer (2^II). The pressure of the reactor (2I) was determined by a monometer, the reaction was carried out for 3-4 hours. A nickel catalyst was used in the process (table 1).

Table 1

Technological parameters of nitrile hydrogenation process

Conducting the hydrogenation process in an ammonia atmosphere increases the primary amine yield. The primary amine produced in the process reacts with nitrile to form a secondary amine with the release of ammonia. According to the Le-Chatelet principle, when ammonia is introduced into the process, the formation of ammonia is inhibited and the formation of secondary and tertiary amines is stopped, resulting in an increase in the primary amine yield [3, 4].

RCH₂NH₂ + RCN→RCH₂NH–N=CНR+ 2H₂→RCH₂NHCН₂R + NH₃↑

The solubility value of the synthesized amine in organic solvents: methanol, ethanol, benzene and hexane was determined and used for purification (Table 2).

Table 2

Solvent solubility of synthesized octadecylamine

To remove amines from the catalyst, the catalyst was dissolved in methanol or ethanol at 50-55C⁰ and filtered. . The resulting filtrate was cooled to 0 ⁰C, the precipitated white amine was extracted, filtered and dried at room temperature. The liquefaction temperature of the dried mass was determined in the BIOBASE BMP-1C setup (62 - 68.8 ⁰С).

Analysis аnd results

The substances obtained as a result of each step were analyzed by infrared IR-spectroscopy and GX-MS (gas chromatography with a mass spectrometric detector) in the laboratory.

Initially, when the raw material was subjected to IR-spectroscopy, it was found that there were peaks characteristic of high molecular carbonic acids. When the product of the first stage was analyzed, absorption areas characteristic of ammonium salts of high molecular carboxylic acids were observed. The analysis of the products of the second and third steps confirmed the presence of peaks characteristic of acid amides and nitriles.

Based on the results of IR-spectroscopy analysis, it was shown that when the product of the third stage is hydrolyzed with hydrogen under the high pressure, amines are synthesized from amides and nitriles, and the main part of the product consists of amines С₁₈N₃₇NH₂ , С₁₆N₃₃NH₂

Figure 2. IR spectrum of synthesized aliphatic amines

IR spectra were obtained on a Bruker INVENIO-S Fure spectrometer (4000-400 cm^-1, ATR) In the IR-spectrum of the synthesized substances, absorption lines formed due to the valence vibrations specific to the -N-H bond of the primary amine group were observed at 3392.37 cm^-1. So the absorption lines of the C-H bond bound to the sp³ hybridized carbon atom in the 2912-2846 cm^-1 range became invisible. Absorption lines formed due to symmetric deformation vibrations characteristic of the methyl group were observed in the region of 1420 cm^-1. The shear deformation vibrations characteristic of -CH₂ bond in the methylene group became invisible at 1466 cm^-1.

Acid amides and nitriles were formed by the action of ammonia on distilled fatty acids (DFA) obtained from the secondary raw materials of the oil industry or vegetable oil. These products were analyzed by GX-MS (gas chromatography with mass spectrometric detector) method (Table 3, Figure 3).

Table 3

Chromato-mass spectrum analysis of the synthesized amide

Figure 3. GX-MS chromatogram of the synthesized amide

The analysis of the results shows that the product of the reaction of distilled fatty acids with ammonia mainly contains tetradecanamide and hexadecaneamide and partially pentadecanitrile and heptadecanitrile (Table 4, Figure 4).

Table 4

Chromato-mass spectrum analysis of synthesized nitrile

Figure 4. GX-MS chromatogram of the synthesized nitrile

According to the results of the analysis, nitriles, amines and partially amides are formed in the process. At the last stage, aliphatic amines were synthesized from acid nitriles in the presence of hydrogen in an ammonia environment under high pressure. The obtained product was qualitatively and quantitatively analyzed by GX-MS method (Table 5, Figure 5).

Table 5

Chromato-mass spectrum analysis of the synthesized amine

Figure 5. GX-MS chromatogram of the synthesized amine

In the process, mainly aliphatic amines: octadecanamine and hexadecaneamine are formed as products.

Conclusions and suggestions

• 98% pure amide and nitrile were obtained by dehydrogenation of the compounds formed by the action of ammonia on distilled fatty acids containing S16-S18 carbon atoms in the presence of an aluminum oxide catalyst, their properties and mass chromatography analysis were studied.
• amines of aliphatic fatty acids of 98% purity were obtained by hydrogenation of nitriles in the presence of a nickel catalyst, their properties were studied, and their composition was proven by  using mass chromatography methods.
• amines of aliphatic fatty acids of 98% purity were obtained by hydrogenation of nitriles in the presence of a nickel catalyst, their structure was obtained by synthesis of aliphatic fatty acid amines, and their IR-spectroscopy (4000-400 cm^-1, ATR) analysis was proved.
• optimal conditions for the synthesis of aliphatic amines were found: temperature 175-180 0С; ammonia pressure 10 MPa; hydrogen pressure 50 MPa; total pressure 60 MPa; reaction duration is 4-5 hours, product purity is 98%.

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