Normal-pressure preparation method of high-purity N, N-dimethyl long-chain alkyl amide

Abstract

The invention belongs to the field of chemical engineering, and particularly relates to a normal-pressure preparation method of high-purity N, N-dimethyl long-chain alkyl amide. Comprising the following steps: melting saturated fatty acid, adding a catalyst, heating a reaction system to a set reaction temperature, introducing dimethylamine gas, and reacting at the set reaction temperature for 0.5-10 hours; standing the reaction product, and centrifuging to remove the catalyst; and slightly heating the liquid obtained by centrifugation to remove dimethylamine so as to obtain the N, N-dimethyl long-chain alkyl amide serving as a product. The method is simple in process, is a one-step method (only melting saturated fatty acid and then introducing dimethylamine for reaction), is simple and convenient to operate, does not need any solvent, is low in process cost, and effectively reduces environmental pollution.

Description

Technical Field

[0001] The invention belongs to the field of chemical industry, and specifically relates to a method for preparing high-purity N,N-dimethyl long-chain alkylamide under normal pressure. Background Art

[0002] N,N-dimethyl long-chain alkylamide has good solubility and reactivity, and is widely used as a solvent for plastic films, synthetic fibers and coatings, as well as an intermediate for emulsifiers and skin penetrants. More importantly, N,N-dimethyl long-chain alkylamide can be used as a synthetic intermediate for preparing higher fatty tertiary amines using fatty acids as raw materials.

[0003] N,N-dimethyl long-chain alkyl amides, wherein the number of carbon atoms in the alkyl group is 8 to 24, include N,N-dimethyl dodecyl amide, N,N-dimethyl tetradecyl amide, N,N-dimethyl hexadecyl amide and N,N-dimethyl octadecyl amide, etc.

[0004] At present, the preparation of high-grade fatty tertiary amines by the fatty acid method requires amination to produce nitrile and catalytic hydrogenation to obtain primary amines or secondary amines, followed by further methylation to generate tertiary amines. The process route is long, the product quality is poor, and there is a serious problem of three wastes discharge. However, if fatty acids and dimethylamine are first used to generate N,N-dimethylalkylamides by one-step amidation, then only catalytic hydrogenation of the amides is required to generate high-grade fatty tertiary amines. This not only retains the advantage of low raw material cost of the fatty acid method, but also solves the complex production process route and the environmental pollution problems it brings, and is conducive to improving product quality.

[0005] At present, there are few reports on the preparation of N,N-dimethyl long-chain alkyl amides. The few reports mainly focus on high-pressure preparation technology. For example, for the fatty acid method, most of the fatty acids are used as raw materials, which undergo amidation reaction with dimethylamine to produce N,N-dimethylalkyl amides (200-290°C, 2-14MPa), and then reduced to the corresponding N,N-dimethylalkyl tertiary amines through catalytic hydrogenation. Although this method has low raw material costs, the reaction needs to be carried out under high temperature and high pressure, and the purity of the resulting product needs to be further improved.

[0006] Example 2 of the invention of 202111371589.2 "A mixed solvent mainly composed of N, N-dimethylhexanamide, preparation method and application" informs: A method for preparing a mixed solvent mainly composed of N, N-dimethylhexanamide specifically comprises the following steps:

[0007] (1) Salt-forming reaction

[0008] 1000g of 06# crude fatty acid was added to the reactor of a small-scale automated amide reaction device, and then dimethylamine was introduced into the reactor at a pressure of 0.15Mpa and a flow rate of 50L / h, and the crude fatty acid and dimethylamine were subjected to a salt-forming reaction at room temperature. During the reaction, the salt-forming reaction liquid bubbled violently, and the salt-forming reaction was terminated when the temperature of the salt-forming reaction liquid in the reactor no longer rose.

[0009] (2) Acylation reaction

[0010] Add 5 g of catalyst to the salt-forming reaction solution obtained in step (1), and then control the temperature to 120° C. to allow the salt-forming reaction solution to undergo total reflux reaction for 2 h;

[0011] Then, the pressure was controlled to be 0.2 MPa and the flow rate was 40 L / h to continue to introduce dimethylamine into the container, and the temperature was controlled to be 145° C. to carry out the acylation reaction for 5.5 hours. At this time, when the acid value of the reaction liquid obtained by the acylation reaction reached less than 2%, the reaction was stopped, and the acylation reaction was completed to obtain an acylation reaction liquid;

[0012] The catalyst is molybdenum trioxide, and the added amount of the catalyst is 0.5% of the mass of the crude fatty acid; the molybdenum oxide is in the form of powder.

[0013] If the pressure of this method is reduced to normal pressure, the conversion rate will be greatly reduced. The reaction process of this method is very complicated, and the main process is salt formation reaction for several hours - reflux for 2 hours - acylation for 5.5 hours - stop dimethylamine, and control the temperature for more than 2 hours. Summary of the invention

[0014] The technical problem to be solved by the present invention is to provide a method for preparing high-purity N,N-dimethyl long-chain alkylamide.

[0015] In order to solve the above problems, the present invention provides a method for preparing high-purity N,N-dimethyl long-chain alkylamide under normal pressure, comprising the following steps:

[0016] 1) First, melt the saturated fatty acid (100 g), then add the catalyst to form a reaction system; heat the reaction system to a set reaction temperature (and after the reaction system is stable at the reaction temperature), introduce dimethylamine gas, and react at the set reaction temperature for 0.5 to 10 hours (preferably 3 to 6 hours); the reaction temperature is 100 to 250° C. (preferably 150 to 230° C., more preferably 175 to 230° C., more preferably 200 to 230° C.), and the amount of the catalyst is 0 wt% to 10 wt% (preferably 0.1 wt% to 5 wt%, more preferably 1 wt% to 5 wt%, and further preferably 3 wt% to 5 wt%) of the mass of the saturated fatty acid;

[0017] The dimethylamine gas flow rate is 10 to 1000 mL / min (preferably 200 to 1000 mL / min, more preferably 600 to 800 mL / min);

[0018] Note: The reaction is carried out under normal pressure;

[0019] 2) The product obtained from the reaction in step 1) is allowed to stand (filtered after standing) and centrifuged to remove the catalyst;

[0020] 3) The liquid obtained in step 2) is slightly heated (20-60° C.) to remove dimethylamine, thereby obtaining N,N-dimethyl long-chain alkylamide as a product.

[0021] Note: The high purity of the present invention means that the purity of the product is greater than 97.4%, preferably the purity of the product is greater than 99%, and the purity of the product can be as high as 99.6%.

[0022] As an improvement of the normal pressure preparation method of the high-purity N,N-dimethyl long-chain alkylamide of the present invention: the chemical structure of the saturated fatty acid is C n H 2n+1 COOH, 7≤n≤23.

[0023] As a further improvement of the normal pressure preparation method of the high-purity N,N-dimethyl long-chain alkylamide of the present invention: the saturated fatty acid is capric acid, lauric acid (dodecanoic acid), myristic acid (tetradecanoic acid), palmitic acid (hexadecanoic acid), stearic acid (octadecanoic acid);

[0024] When the saturated fatty acid is lauric acid, the product is N,N-dimethyldodecylamide;

[0025] When the saturated fatty acid is capric acid, the product is N,N-dimethyldecylamide;

[0026] When the saturated fatty acid is myristic acid, the product is N,N-dimethyltetradecylamide;

[0027] When the saturated fatty acid is palmitic acid, the product is N,N-dimethylhexadecylamide;

[0028] When the saturated fatty acid is stearic acid, the product is N,N-dimethyloctadecylamide;

[0029] As a further improvement of the normal pressure preparation method of the high-purity N,N-dimethyl long-chain alkylamide of the present invention: the catalyst is a basic solid catalyst. The basic solid catalyst is cerium dioxide, silicon dioxide (preferably), zirconium dioxide, titanium dioxide, sodium methoxide.

[0030] As a further improvement of the normal pressure preparation method of the high-purity N,N-dimethyl long-chain alkylamide of the present invention: the melting temperature of the saturated fatty acid is T m to T m + 90°C, wherein T m is the melting point temperature of the saturated fatty acid.

[0031] As a further improvement of the normal pressure preparation method of the high-purity N,N-dimethyl long-chain alkyl amide of the present invention: in step 2), the reaction product of step 1) is first allowed to stand for 0.5 to 12 hours, and then filtered, and the filtrate obtained by filtration is centrifuged at a centrifugal speed of 5000 to 10000 rpm and a centrifugal time of 10 to 30 minutes.

[0032] Note: Filtering after standing can remove most of the catalyst, and then centrifugation is used to remove the very small amount of residual catalyst.

[0033] As a further improvement of the normal pressure preparation method of the high-purity N,N-dimethyl long-chain alkylamide of the present invention: in step 3): heating at a low temperature of 20 to 60° C. for 5 to 60 minutes to remove unreacted dimethylamine in the system.

[0034] As a further improvement of the normal pressure preparation method of the high-purity N,N-dimethyl long-chain alkylamide of the present invention: in step 1), the saturated fatty acid is stirred at the melting temperature for 10 to 30 minutes, so as to achieve sufficient melting of the saturated fatty acid.

[0035] As a further improvement of the normal pressure preparation method of the high-purity N,N-dimethyl long-chain alkyl amide of the present invention: the reaction temperature is 200-210°C, the reaction time is 3-6h, the catalyst dosage is 3% of the mass of the saturated fatty acid, the catalyst is silicon dioxide, and the dimethylamine gas flow rate is 600-800mL / min.

[0036] The invention discloses a method for preparing high-purity N,N-dimethyl long-chain alkylamide under normal pressure, comprising the steps of melting saturated fatty acid at a certain temperature, adding a proper amount of catalyst, heating the temperature to a reaction temperature, introducing dimethylamine gas, standing the mixture after the reaction is completed, removing the catalyst by centrifugation, and removing the dimethylamine by slight heating to obtain the high-purity N,N-dimethyl long-chain alkylamide.

[0037] Taking N,N-dimethyldodecylamide as an example, the scheme of the present invention is as follows:

[0038] The saturated fatty acid is lauric acid, and the catalyst can be silicon dioxide, CeO2, ZrO2, TiO2. The following steps are performed in sequence:

[0039] 1) Add 100g of lauric acid into a 250mL container (three-necked flask), then heat to 50-100°C and stir for 10-30min to fully melt the lauric acid, add a catalyst accounting for 0.1-5wt% (preferably 1-5wt%, more preferably 3-5wt%) of lauric acid, stir evenly and raise the system temperature to 150-220°C (preferably 200-220°C), after the temperature of the reaction system becomes constant, introduce dimethylamine gas at a constant flow rate of 10-1000mL / min (preferably 400-800mL / min), and terminate the reaction after 0.5-6h (preferably 2-6h);

[0040] 2) After the reaction product of step 1) is allowed to stand for 0.5 to 12 hours, the silica as the filter residue is removed by filtration, and then the filtrate is centrifuged at 5000 to 10000 rpm for 10 to 30 minutes to remove the residual silica.

[0041] 3) The liquid obtained by centrifugation in step 2) is heated at 20-60° C. for 5-60 min to remove residual dimethylamine.

[0042] Acid value was determined using potassium hydroxide solution (0.1 mol / L) according to GB 1886.81. The detailed steps are as follows: 10 g of the product was placed in a conical flask, 50 mL of neutral hot ethanol (99.5%) was added to dissolve the sample, 2 mL of phenolphthalein indicator was dropped, and the sample was neutralized with potassium hydroxide standard solution until it turned slightly red, and the end point was when the color did not fade for 30 seconds.

[0043] The invention is easy to operate and has a simple process. The whole process is carried out under normal pressure, and the product purity can be as high as 99.6% or more without purification.

[0044] The beneficial effects of the present invention are:

[0045] 1. The present invention prepares N,N-dimethyl long-chain alkylamide (the number of carbon atoms in the alkyl group is ≥7)

[0046] 2. The N,N-dimethyl long-chain alkylamide product prepared by the present invention has high purity, which can be as high as 99.6% at most, without any purification operation, and the raw material conversion rate reaches 99.63%.

[0047] 3. The process of the present invention is simple, a one-step process (only the saturated fatty acid needs to be melted and then dimethylamine is introduced for reaction), easy to operate, and does not require any solvent, with low process cost and effectively reducing environmental pollution.

[0048] 4. The present invention does not require the use of solvents and is easy to operate. The entire process of the present invention is carried out under normal pressure, has low requirements on equipment, and has a high process safety factor.

[0049] 5. High conversion rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0050] The specific implementation modes of the present invention are further described in detail below with reference to the accompanying drawings.

[0051] Figure 1 This is the infrared spectrum of the product N,N-dimethyldodecylamide obtained in Example 1-1.

[0052] Figure 2 This is the hydrogen nuclear magnetic resonance spectrum of the product N,N-dimethyldodecylamide obtained in Example 1-1.

[0053] Figure 3 This is the H NMR spectrum of the reference standard of the product N,N-dimethyldodecylamide obtained in Example 1-1.

[0054] Figure 4 This is the carbon nuclear magnetic resonance spectrum of the product N,N-dimethyldodecylamide obtained in Example 1-1.

[0055] Figure 5 This is the carbon NMR spectrum of the reference standard of the product N,N-dimethyldodecylamide obtained in Example 1-1.

[0056] Figure 6 This is the gas chromatogram of the product N,N-dimethyldodecylamide obtained in Example 1-1.

[0057] Figure 7 This is a gas chromatogram of the reference standard of the product N,N-dimethyldodecylamide obtained in Example 1-1. DETAILED DESCRIPTION

[0058] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto:

[0059] Example 1-1, a method for preparing N,N-dimethyldodecylamide, wherein lauric acid is selected as the saturated fatty acid, silicon dioxide is selected as the catalyst, and the following steps are performed in sequence:

[0060] 1) Add 100g of lauric acid into a 250mL three-necked flask, then heat to 90-100°C and stir for 20min to fully melt the lauric acid, add 3wt% of silicon dioxide based on the lauric acid, stir evenly and raise the system temperature to 200°C, after the system temperature is constant, introduce dimethylamine gas at a constant flow rate of 600mL / min, and the reaction pressure is normal pressure (i.e. 0.1013MPa); after the reaction for 3h, close the reaction;

[0061] 2) After the reaction product of step 1) was allowed to stand for 0.5 h, the silica as the filter residue was removed by filtration, and then the filtrate was centrifuged at 8000 rpm for 15 min to remove the residual silica.

[0062] 3) The liquid obtained by centrifugation in step 2) is heated at 40-60° C. for 10-20 min to remove residual dimethylamine, thereby obtaining the product, N,N-dimethyldodecylamide.

[0063] Acid value was determined using potassium hydroxide solution (0.1 mol / L) according to GB 1886.81. The detailed steps are as follows: 10 g of the product was placed in a conical flask, 50 mL of neutral hot ethanol (99.5%) was added to dissolve the sample, 2 mL of phenolphthalein indicator was dropped, and the sample was neutralized with potassium hydroxide standard solution until it turned slightly red, and the end point was when the color did not fade for 30 seconds.

[0064] According to the formula: acid value (mg KOH / g) = volume of potassium hydroxide standard solution consumed in titration (mL) * concentration of potassium hydroxide standard solution (mol / L) * millimolar mass of potassium hydroxide (g / mmol) / mass of product weighed (g).

[0065] After calculation, the acid value of the product is as shown in Table 1:

[0066] Fatty acid conversion rate (%) = (theoretical acid value of fatty acid (mg KOH / g) - millimolar mass of potassium hydroxide (g / mmol) * concentration of potassium hydroxide standard solution (mol / L) * volume of potassium hydroxide standard solution consumed in titration (mL) / mass of product weighed (g)) / A × 100%.

[0067] After calculation, the fatty acid conversion rate is shown in Table 1 below.

[0068] In Examples 1-2 to 1-11, the reaction temperature, reaction time, amount of catalyst and dimethylamine gas flow rate are changed compared to Example 1-1. The specific parameters are shown in Table 1 below, and the rest are the same as Example 1-1. The results are shown in Table 1 below.

[0069] Table 1

[0070]

[0071]

[0072] The infrared spectrum of N,N-dimethyldodecylamide prepared in Example 1-1 is as follows: Figure 1 As shown, the product was not subjected to any purification treatment. Figure 1 It can be seen that the product after the reaction is at 1640-1600cm -1 and 1530-1500cm-1 There is no NH characteristic absorption peak (amide II band) at 1100cm -1 The characteristic absorption peaks are CN (CN(CH3)2, not CN in the amide bond) stretching vibration peaks, and are at 1420-1400cm -1 and 1300-1260cm -1 The third band of CN amide does not appear at 1657 cm -1 The CC stretching vibration peak is about 1250cm -1 Place.

[0073] The hydrogen nuclear magnetic resonance spectrum of N,N-dimethyldodecylamide prepared in Example 1-1 is as follows Figure 2 As shown, the product has not been purified. The two absorption peaks at chemical shifts of 3.31ppm and 4.87ppm are both solvent peaks of the deuterated reagent CD3CD. The remaining characteristic peaks correspond to: -CH3(Ha, t, δ H =0.92, 0.90, 0.88); -CH2(H b , H e , m, δ H =1.36, 1.34, 1.33, 1.30); -CH2(H c , m, δ H =1.61, 1.59, 1.57, 1.55); -CH2(H d , t, δ H =2.39, 2.37, 2.35); -CH3(H f , s, δ H =2.92); -CH3(H g , s, δ H =3.06). In addition, H a , H b +H e , H c , H d , H f , H d The peak area ratio of the product is close to 3:16:2:2:3:3, which is consistent with the theoretical value. It should be noted that both the peak shift and the peak area ratio of the product are consistent with the commercially available N,N-dimethyldodecylamide (Fluorochem Reagent Co., Ltd., UK, >95%) standard (see Figure 3 )The test results are basically consistent.

[0074] The carbon NMR spectrum of N,N-dimethyldodecylamide prepared in Example 1-1 is as follows: Figure 4 As shown, the product was not subjected to any purification treatment. 13 C-NMR (CDCl3, 150MHz): δ C 14.60 (Ca), 23.77 (Cb), 26.34 (Cc), 30.52 (Cd), 30.63 (Ce), 30.73 (Cf), 30.81 (Cg), 33.11 (Ch), 34.13 (Ci), 35.75 (Cj), 37.85 (Ck), 175.44 (Cl) and the carbon spectrum of N,N-dimethyldodecylamide standard ( Figure 5 ) are also basically the same.

[0075] The gas chromatogram of N,N-dimethyldodecylamide prepared in Example 1-1 is as follows: Figure 6 As shown, the product has not been purified. As can be seen from the figure, the product without purification has a single composition, low impurity content, high purity of more than 99.6%, and a retention time of 13.822 min. Among them, the retention time of the N, N-dimethyl dodecylamide standard sample is 13.824 min (purity 99.3%), which is basically consistent with the retention time of the product prepared in Example 1-1 (see Figure 7 ). Therefore, based on the above analysis, it can be confirmed that the prepared product is N,N-dimethyldodecylamide, and a product with extremely high purity can be obtained without any purification treatment.

[0076] In Examples 2-1 to 2-15, the reaction temperature, reaction time, amount of catalyst, type of catalyst and dimethylamine gas flow rate are changed compared to Example 1-1. The specific parameters are shown in Table 2 below, and the rest are the same as Example 1-1. The results are shown in Table 2 below.

[0077] Table 2

[0078]

[0079]

[0080] Embodiment 3,

[0081] Compared with Example 1-1, the selected saturated fatty acid was changed, and the melting temperature and time, as well as the reaction temperature and time were changed accordingly; the details are shown in Table 3 below, and the rest are the same as Example 1-1. The obtained results are shown in Table 3 below.

[0082] Table 3

[0083]

[0084]

[0085] Note: The products in Table 3 were verified by conventional NMR, IR and gas chromatography to verify the correctness of the conclusions.

[0086] Finally, it should be noted that the above examples are only some specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by a person skilled in the art should be considered as the protection scope of the present invention.

Claims

1. A method for preparing high-purity N,N-dimethyl long-chain alkylamide under normal pressure, characterized in that The following steps are involved: 1) First, melt the saturated fatty acid, then add the catalyst to form a reaction system; heat the reaction system to a set reaction temperature, introduce dimethylamine gas, and react at the reaction temperature for 0.5 to 10 hours; the reaction temperature is 100 to 250° C., and the amount of the catalyst is 0wt% to 10wt% of the mass of the saturated fatty acid; The flow rate of dimethylamine gas is 10-1000 mL / min; 2) The product obtained from the reaction in step 1) is allowed to stand and centrifuged to remove the catalyst; 3) The liquid obtained in step 2) is slightly heated to remove dimethylamine to obtain N,N-dimethyl long-chain alkylamide as a product.

2. The method for preparing high-purity N,N-dimethyl long-chain alkylamide at normal pressure according to claim 1, characterized in that: The chemical structure of the saturated fatty acid is C n H 2n+1 COOH, 7≤n≤23.

3. The method for preparing high-purity N,N-dimethyl long-chain alkylamide at normal pressure according to claim 2, characterized in that: The saturated fatty acids are capric acid, lauric acid, myristic acid, palmitic acid, and stearic acid; When the saturated fatty acid is lauric acid, the product is N,N-dimethyldodecylamide; When the saturated fatty acid is capric acid, the product is N,N-dimethyldecylamide; When the saturated fatty acid is myristic acid, the product is N,N-dimethyltetradecylamide; When the saturated fatty acid is palmitic acid, the product is N,N-dimethylhexadecylamide; When the saturated fatty acid is stearic acid, the product is N,N-dimethyloctadecylamide.

4. The method for preparing high-purity N,N-dimethyl long-chain alkylamide at normal pressure according to any one of claims 1 to 3, characterized in that: The catalyst is a basic solid catalyst.

5. The method for preparing high-purity N,N-dimethyl long-chain alkylamide at normal pressure according to claim 4, characterized in that: The alkaline solid catalyst is cerium dioxide, silicon dioxide, zirconium dioxide, titanium dioxide and sodium methoxide.

6. The method for preparing high-purity N,N-dimethyl long-chain alkylamide at normal pressure according to any one of claims 1 to 5, characterized in that: The melting temperature of saturated fatty acids is Tm~Tm+90°C, where Tm is the melting point temperature of saturated fatty acids.

7. The method for preparing high-purity N,N-dimethyl long-chain alkylamide at normal pressure according to any one of claims 1 to 6, characterized in that In the step 2): The reaction product of step 1) is first allowed to stand for 0.5 to 12 hours, and then filtered. The filtrate obtained by filtration is centrifuged at a speed of 5000 to 10000 rpm for 10 to 30 minutes.

8. The method for preparing high-purity N,N-dimethyl long-chain alkylamide at normal pressure according to claim 7, characterized in that In the step 3), heating is performed at a temperature of 20 to 60° C. for 5 to 60 minutes to remove unreacted dimethylamine in the system.

9. The method for preparing high-purity N,N-dimethyl long-chain alkylamide at normal pressure according to any one of claims 1 to 8, characterized in that In the step 1): The saturated fatty acid is stirred at the melting temperature for 10 to 30 minutes to achieve full melting of the saturated fatty acid.

10. The method for preparing high-purity N,N-dimethyl long-chain alkylamide at normal pressure according to any one of claims 1 to 9, characterized in that: The reaction temperature is 200-210° C., the reaction time is 3-6 hours, the catalyst dosage is 3% of the mass of the saturated fatty acid, the catalyst is silicon dioxide, and the dimethylamine gas flow rate is 600-800 mL / min.

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