A method for the room temperature preparation of acetylsalicylic acid and a digital monitoring system

Abstract

This invention discloses a room-temperature preparation method and digital monitoring system for acetylsalicylic acid, belonging to the field of chemical synthesis technology. The preparation method involves a direct reaction of salicylic acid and acetic anhydride as raw materials at room temperature (15-30°C) under concentrated sulfuric acid catalysis. The product is obtained after crystallization, neutralization, acidification, and purification. This method eliminates the need for external heating, effectively reducing energy consumption and suppressing side reactions. The yield can reach 75% to 89.2%, and the product purity is significantly improved. The accompanying digital monitoring system integrates temperature, pH, and color sensors. Connected to a central processing unit via a data acquisition unit, it can monitor and record changes in temperature, pH, and impurity content in real time during the reaction and purification stages. This transforms the chemical process into visualized data, enabling precise control and quantitative analysis of the entire synthesis and purification process, providing strong support for process optimization.

Description

Technical Field

[0001] This invention belongs to the field of chemical synthesis technology, specifically relating to a room temperature preparation method for acetylsalicylic acid and a digital monitoring system. Background Technology

[0002] Acetylsalicylic acid (aspirin) is a classic nonsteroidal anti-inflammatory drug. Traditional synthesis methods typically require heating, using salicylic acid and acetic anhydride as raw materials, reacting them in the presence of acids, bases, or other catalysts. However, heating processes are energy-intensive and prone to side reactions (such as the self-condensation of salicylic acid), leading to reduced yield and purity. Furthermore, traditional methods lack real-time monitoring of the reaction process, making it difficult to optimize reaction conditions. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention proposes a room-temperature preparation method for acetylsalicylic acid and a digital monitoring system to reduce energy consumption, improve yield and purity, and effectively monitor the reaction process.

[0004] In a first aspect, the present invention provides a method for preparing acetylsalicylic acid at room temperature, comprising the following steps: S1. At room temperature, salicylic acid and acetic anhydride are mixed in a molar ratio of 1:1.5-1:3, concentrated sulfuric acid catalyst is added, and the mixture is stirred for 5-20 minutes. S2. After the reaction is complete, the product is cooled in an ice-water bath to crystallize and then filtered to obtain the crude product. S3. After neutralizing the crude product with saturated sodium bicarbonate solution, concentrated hydrochloric acid was added dropwise to acidify it to pH=2-3. After standing to crystallize, the product was filtered and dried to obtain acetylsalicylic acid.

[0005] The room temperature is 15-30℃.

[0006] The ratio of salicylic acid to acetic anhydride in the micro-preparation process is 1:2, while the ratio in the macro-preparation process is 1:2.5.

[0007] The amount of concentrated sulfuric acid used is 1-3 drops per 0.50 g of salicylic acid.

[0008] Secondly, the present invention provides a digital monitoring system for the above-described preparation method, comprising: The sensing unit includes a temperature sensor for monitoring the temperature of the reaction solution and a pH sensor for monitoring the pH value during the purification process; The data acquisition and processing unit includes a data acquisition unit and a central processing unit connected thereto; The signal output terminals of the temperature sensor and pH sensor are respectively connected to different signal input ports of the data acquisition unit via data lines; the data acquisition unit is communicatively connected to the central processing unit and is used to transmit sensor signals to the central processing unit. The central processing unit is configured to run control software to receive, display, and record data from the sensors in real time.

[0009] The sensing unit also includes a colorimetric sensor for determining the salicylic acid content in the product; the colorimetric sensor is connected to another signal input port of the data acquisition unit via a data cable; the control software of the central processing unit is configured to: plot a standard curve based on the colorimetric sensor data and calculate the concentration of salicylic acid in the product.

[0010] The probe of the temperature sensor is configured to be directly inserted into the reaction vessel for the esterification reaction; the probe of the pH sensor is configured to be placed in the acidification stage vessel during the purification process.

[0011] The system also includes a magnetic stirrer; the central processing unit or data acquisition unit is connected to the magnetic stirrer via a control line and is configured to automatically adjust the stirring rate of the magnetic stirrer based on the temperature data fed back by the temperature sensor.

[0012] The central processing unit is connected to a display, and the control software is configured to display the temperature-time relationship and pH-time relationship on the display as real-time dynamic curves.

[0013] The central processing unit is also configured to communicate with an ultraviolet spectrophotometer to receive its absorbance data, plot a standard curve of acetylsalicylic acid, and calculate its content.

[0014] Compared with the prior art, the beneficial effects of the present invention are: By employing room temperature reaction conditions and optimizing the feed ratio and catalyst dosage, the energy consumption associated with traditional heating methods was avoided, resulting in energy savings and reduced consumption. Simultaneously, side reactions exacerbated by temperature increases were effectively suppressed, thus achieving yields as high as 75% to 89.2% while ensuring high product purity. Secondly, the constructed digital monitoring system, integrating multiple sensors such as temperature, color, and pH, and working in conjunction with a data acquisition unit and central processing unit, enables real-time, visual monitoring and quantitative analysis of the reaction process and purification process. This transforms abstract chemical changes into intuitive data streams and images, significantly improving the accuracy and repeatability of the experiment and providing solid data support for process optimization. Attached Figure Description

[0015] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below.

[0016] Figure 1 This is the synthesis reaction equation for acetylsalicylic acid in this invention, where a is the main reaction and b is the side reaction.

[0017] Figure 2 This is a schematic diagram showing the structural composition and connection relationship of the digital monitoring system of the present invention.

[0018] Figure 3 This is a graph showing the temperature changes in the reaction system under different catalyst dosages, as monitored by a temperature sensor in Example 1 of this invention.

[0019] Figure 4 The images shown are the UV spectrum (a) and standard curve (b) of acetylsalicylic acid plotted using a UV spectrophotometer in Example 3 of this invention.

[0020] Figure 5 This is a comparison of the infrared spectra of the characteristic functional group regions of salicylic acid in the acetylsalicylic acid product prepared by this invention and the standard.

[0021] Figure 6 This is the nuclear magnetic resonance spectrum of acetylsalicylic acid prepared according to the present invention. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0023] Example 1: Micro-synthesis and temperature monitoring Synthetic routes such as Figure 1 As shown, using Figure 2 The monitoring system shown completes trace synthesis.

[0024] 1. Synthesis Procedure: Weigh 0.50 g of salicylic acid using an electronic balance and place it in a 25 mL microtube. Accurately pipette 0.67 mL of acetic anhydride (the molar ratio of salicylic acid to acetic anhydride is approximately 1:2) into the tube. Insert the probe of the temperature sensor (model LW-T803) below the surface of the reaction solution. This sensor, along with the data acquisition unit and computer (i.e., Figure 2 Connect the system shown. Turn on the magnetic stirrer and add 1 drop of concentrated sulfuric acid as a catalyst to the system using a dropper at room temperature (26.6°C).

[0025] 2. Real-time monitoring and data analysis: The digital monitoring system begins operation immediately after the catalyst is added. For example... Figure 3As shown, the data recorded by the temperature sensor was plotted as a temperature-time curve in real time. The curve reveals that the reaction system temperature rose rapidly after the catalyst was added, reaching a maximum of 38.6℃ (ΔT = 12.0℃) at 197 seconds, and then slowly decreased. This typical exothermic peak shape not only visually confirms the vigorous occurrence of the reaction, but also provides precise data on the timing and magnitude of its maximum temperature for judging the reaction progress and intensity—something that traditional methods cannot achieve.

[0026] 3. Post-treatment and yield: After 10 minutes of reaction, 5 mL of ice water was added to the test tube, and the mixture was cooled in an ice-water bath to promote crystallization. The mixture was filtered, and the crystals were washed with a small amount of ice water to obtain crude acetylsalicylic acid. The crude product was neutralized with saturated sodium bicarbonate solution, acidified with concentrated hydrochloric acid to pH 2-3, recrystallized in an ice bath, filtered, and dried to obtain white needle-like crystals. The weight was 0.58 g, and the calculated yield was 89.2%.

[0027] 4. Purity test: Dissolve a small amount of product in ethanol and add 1% FeCl3 solution. If no purple color is observed, it indicates that no salicylic acid impurities are detected in the product and the purity is good.

[0028] Example 2: Constant Synthesis and System Verification This embodiment aims to verify the feasibility of the room-temperature synthesis method on a scale-up basis, and also uses... Figure 2 The system is monitored.

[0029] 1. Synthesis Procedure: Weigh 5.00 g of salicylic acid into a 100 mL round-bottom flask and add 8.50 mL of acetic anhydride (molar ratio approximately 1:2.5). Connect a temperature sensor and, under magnetic stirring, add 10 drops of concentrated sulfuric acid at a time, and react at room temperature (26℃).

[0030] 2. Monitoring and Results: Temperature sensor monitoring showed that the highest reaction temperature reached 44℃. After 6 minutes of reaction, post-processing was performed according to the method described in Example 1. The final yield was 4.87 g of acetylsalicylic acid, with a yield of 74.92%. Qualitative testing with FeCl3 showed no color change, indicating that high-purity products can also be obtained through constant-scale synthesis.

[0031] Example 3: Digital Content Analysis and Structural Characterization This embodiment utilizes a digital monitoring system to perform quantitative analysis and structural characterization of the product.

[0032] 1. UV Spectrophotometry Analysis of the Main Product: For high-purity products (such as those obtained in Example 1), the content was determined using a UV spectrophotometer. An acetylsalicylic acid standard solution was prepared, and the absorbance was measured at a wavelength of 276 nm. A standard curve was plotted using the system software as shown below. Figure 4As shown. After measuring the absorbance of the product solution, the software automatically calculated that the content of acetylsalicylic acid in the product was as high as 98.27%. This method... Figure 4 The standard curve shown demonstrates good linearity, enabling rapid and accurate quantification.

[0033] 2. Colorimetric Sensor Analysis of Byproducts: For products that turn purple in qualitative tests (such as substandard products obtained using other catalysts), a colorimetric sensor can be used to quantify the residual salicylic acid. A series of salicylic acid standard solutions of different concentrations are prepared and reacted with Fe... 3+ After the solution develops its color, its absorbance is measured using a colorimetric sensor, and a standard curve is automatically plotted. Subsequently, the absorbance of the product solution is measured, and the software automatically calculates the content of salicylic acid in the product; for example, a measurement result of 37.66% may be obtained in one instance.

[0034] 3. Infrared Spectroscopic Characterization: The product of Example 1 was characterized using an ATR (Aspect-Transform Infrared) spectrometer. Figure 5 As shown, the infrared spectrum of the obtained product is at 1749.52 cm⁻¹. -1 The characteristic absorption peak of the ester carbonyl group is shown at 1679.67 cm⁻¹. -1 The absorption peak at ~1650 cm⁻¹ is for the carbonyl group of carboxylic acid, and salicylic acid was not observed at ~1650 cm⁻¹ at all. -1 and ~3300 cm -1 The characteristic absorption peak of the phenolic hydroxyl group in the region is consistent with that of analytical grade acetylsalicylic acid, which strongly proves that the product obtained by the method of the present invention has extremely high purity.

[0035] 4. Nuclear Magnetic Resonance Characterization: The product is subjected to nuclear magnetic resonance analysis, and the obtained proton nuclear magnetic resonance spectrum (NMR spectrum) is obtained. 1 H NMR) such as Figure 6 As shown in the spectrum, δ 2.35 (s, 3H, -COOCH3) and δ 7.13-8.13 (m, 4H, Ar-H) are displayed. The positions, splits, and integrated areas of all peaks are in perfect agreement with the standard 1H NMR data of acetylsalicylic acid, thus confirming the structure and high purity of the product at the structural level.

[0036] In summary, Example 1 used a temperature sensor to monitor and record the efficient synthesis process at room temperature in real time (corresponding to...). Figure 3 This confirms the room-temperature, low-energy synthesis method of the present invention; Example 2 successfully scaled up the reaction while maintaining high yield and high purity, verifying the scalability and process stability of the method of the present invention; Example 3 comprehensively utilizes digital analysis methods such as ultraviolet, infrared, and nuclear magnetic resonance (corresponding to...). Figure 4 , Figure 5 , Figure 6This confirmed the chemical structure and extremely high purity of the product, and demonstrated the application of the colorimetric sensor in the quantification of impurities, fully demonstrating the comprehensiveness and superiority of the digital and quantitative monitoring and analysis system of this invention.

[0037] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not describe all details exhaustively, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification.

Claims

1. A process for the room temperature preparation of acetyl salicylic acid, characterized in that, Includes the following steps: S1. At room temperature, salicylic acid and acetic anhydride are mixed in a molar ratio of 1:1.5-1:3, concentrated sulfuric acid catalyst is added, and the mixture is stirred for 5-20 minutes. S2. After the reaction is complete, the product is cooled in an ice-water bath to crystallize and then filtered to obtain the crude product. S3. After neutralizing the crude product with saturated sodium bicarbonate solution, concentrated hydrochloric acid was added dropwise to acidify it to pH=2-3. After standing to crystallize, the product was filtered and dried to obtain acetylsalicylic acid.

2. The process for the room temperature preparation of acetyl salicylic acid according to claim 1, characterized in that, The room temperature is 15-30℃.

3. The method for preparing acetylsalicylic acid at room temperature according to claim 1, characterized in that, The ratio of salicylic acid to acetic anhydride in the micro-preparation process is 1:2, while the ratio in the macro-preparation process is 1:2.

5.

4. The process for the room temperature preparation of acetyl salicylic acid according to claim 1, characterized in that, The amount of concentrated sulfuric acid used is 1-3 drops per 0.50 g of salicylic acid.

5. A digital monitoring system for use in the method of any one of claims 1-4, characterized in that, include: The sensing unit includes a temperature sensor for monitoring the temperature of the reaction solution and a pH sensor for monitoring the pH value during the purification process; The data acquisition and processing unit includes a data acquisition unit and a central processing unit connected thereto; The signal output terminals of the temperature sensor and pH sensor are respectively connected to different signal input ports of the data acquisition unit via data lines; the data acquisition unit is communicatively connected to the central processing unit and is used to transmit sensor signals to the central processing unit. The central processing unit is configured to run control software to receive, display, and record data from the sensors in real time.

6. The digital monitoring system of claim 5, wherein, The sensing unit also includes a colorimetric sensor for determining the salicylic acid content in the product; the colorimetric sensor is connected to another signal input port of the data acquisition unit via a data cable; the control software of the central processing unit is configured to: plot a standard curve based on the colorimetric sensor data and calculate the concentration of salicylic acid in the product.

7. The digital monitoring system of claim 5, wherein, The probe of the temperature sensor is configured to be directly inserted into the reaction vessel for the esterification reaction; the probe of the pH sensor is configured to be placed in the acidification stage vessel during the purification process.

8. The digital monitoring system of claim 5, wherein, The system also includes a magnetic stirrer; the central processing unit or data acquisition unit is connected to the magnetic stirrer via a control line and is configured to automatically adjust the stirring rate of the magnetic stirrer based on the temperature data fed back by the temperature sensor.

9. The digital monitoring system of claim 5, wherein, The central processing unit is connected to a display, and the control software is configured to display the temperature-time relationship and pH-time relationship on the display as real-time dynamic curves.

10. The digital monitoring system of claim 6, wherein, The central processing unit is also configured to communicate with an ultraviolet spectrophotometer to receive its absorbance data, plot a standard curve of acetylsalicylic acid, and calculate its content.

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