Preparation process of benzocaine crystal form I

Abstract

The invention relates to the technical field of medicine crystallization, and particularly discloses a preparation process of a benzocaine crystal form I. The preparation process comprises the following steps: adding a benzocaine raw material into an ester solvent to obtain a benzocaine suspension in a supersaturated state; and suspending, stirring and crystallizing the benzocaine suspension at 20-25 DEG C, carrying out solid-liquid separation, and drying to obtain the benzocaine crystal form I. The invention also discloses a preparation method of the benzocaine crystal form I. By controlling and selecting specific combination strategies such as crystallization solvent, crystallization temperature, crystallization liquid concentration and the like, effective control over the benzocaine crystal transformation process is achieved, the blocky benzocaine crystal form I product can be prepared through one-time crystallization, the fluidity of the product is good, and the caking problem in the transportation and storage process can be effectively avoided; meanwhile, a long-term stability test proves that the stability of the benzocaine crystal form I product prepared by the invention is higher, so that the quality of the benzocaine preparation product is favorably improved, and the market competitiveness of the product is favorably improved.

Description

Technical Field

[0001] The present invention relates to the technical field of drug crystallization, and in particular to a preparation process of benzocaine crystal form I. Background Art

[0002] Benzocaine (CAS No.94-09-7), English name Benzocaine, also known as ethyl para-aminobenzoate, molecular formula C9H 11 NO2, molecular weight: 165.19. The compound is a white crystal with a melting point of 90-92°C, slightly soluble in water and easily soluble in organic solvents. The structural formula is as follows.

[0003]

[0004] Benzocaine is mainly used in the production of medicine, plastics and coatings. In terms of pharmaceutical production, benzocaine, as a non-water-soluble local anesthetic, has analgesic and antipruritic effects. It is clinically used for wound anesthesia, ulcer surface anesthesia, mucosal surface anesthesia, etc. Its pharmacological effect is mainly to block nerve endings to relieve pain and itching. Anesthetic drugs such as oxoform, oxocaine, and procaine synthesized with benzocaine as a precursor have the advantages of good stability, fast onset, long maintenance time and small side effects, and have been widely used. In terms of materials, benzocaine can be used as a protective agent to block sunlight ultraviolet rays. In the agriculture, forestry, animal husbandry and fishery industry, it is used in the transportation of fish seedlings and adult fish to ensure the freshness and health of the fish during transportation. In addition, it also has the function of absorbing ultraviolet rays and can also be used in the cosmetics industry.

[0005] Benzocaine has multiple crystal forms, including crystal form I, crystal form II and crystal form III. Benzocaine crystal form I will not easily transform into other crystal forms due to temperature changes at room temperature, and has good stability during storage and use, so it has good application prospects in the field of pharmaceutical preparations. However, in the process of preparing crystal form I, the phenomenon of generating non-target crystal form I or generating mixed crystals of crystal form I and crystal form II often occurs, which affects the batch stability of the product. Therefore, most of the benzocaine currently produced and sold on the market is crystal form II. Therefore, it is necessary to provide a preparation process of benzocaine crystal form I to ensure the stability of the raw material and its preparation during the preparation and storage process, and improve the drug treatment and clinical efficacy of benzocaine. Summary of the invention

[0006] In view of the above problems, the present invention provides a preparation process of benzocaine crystal form I. The present invention uses an ester compound as a solvent and prepares a high-purity benzocaine crystal form I with a block-like crystal habit by a suspension crystallization method, which meets the needs of different benzocaine crystal forms under different conditions, and the method is simple to operate, easy to realize industrial-scale production, and has high practical value.

[0007] In order to solve the above technical problems, the technical solution provided by the present invention is:

[0008] A preparation process of benzocaine crystal form I comprises the following steps:

[0009] Step 1, adding benzocaine raw material into an ester solvent to obtain a supersaturated benzocaine suspension;

[0010] Step 2: suspending and stirring the benzocaine suspension at 20° C. to 25° C. for crystallization, separating the solid from the liquid, and drying to obtain benzocaine crystal form I.

[0011] Compared with the prior art, the preparation process of benzocaine crystal form I provided by the present invention adopts an ester solvent as a crystallization solvent, firstly prepares a supersaturated benzocaine suspension, and controls the crystallization temperature of the crystallization process to regulate the crystal growth conditions, thereby preparing a blocky benzocaine crystal form I product with uniform particle size distribution, complete crystal habits, and no agglomeration. The present invention adopts a suspension crystallization method, controls the crystallization conditions, and prepares a high-purity and high-stability benzocaine crystal form I, and the preparation method is simple and the conditions are mild, which provides an important reference and basis for the development of new local anesthetics, and is of great significance for enhancing the market competitiveness of enterprises.

[0012] Furthermore, in step 1, the ester solvent is at least one of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate or ethyl formate.

[0013] The preferred crystallization solvent can fully dissolve the benzocaine crystal form II in the solvent, and by controlling the temperature of the crystallization process, the benzocaine crystal form II undergoes a change in molecular arrangement and conformation under the induction of a specific solvent, thereby obtaining a high-purity benzocaine crystal form I.

[0014] It should be noted that when a plurality of limited solvents are mixed, there is no particular limitation on the mixing ratio.

[0015] Furthermore, in step 1, the mass volume ratio of the benzocaine raw material to the ester solvent is 1 g: (1.3-3) mL.

[0016] The preferred ratio can control the supersaturation of the system within a range that is conducive to good crystal growth, and impurities are not easily generated during the crystallization process, thereby helping to improve the purity of the product. At the same time, the preferred ratio is also conducive to regulating the crystallization nucleation rate and growth process to obtain blocky benzocaine form I, thereby improving the fluidity of the benzocaine product and facilitating storage and application.

[0017] Furthermore, in step 1, the crystal form of the benzocaine raw material is crystal form II, and the purity is ≥98%.

[0018] It should be noted that when the purity of the benzocaine raw material is lower than 98%, the benzocaine single crystal (form I) can still be obtained by the preparation process of the present invention. However, the impurity content in the obtained crystalline product is relatively high. In order to facilitate subsequent applications, the present invention selects a benzocaine raw material with a purity of ≥98%.

[0019] Furthermore, in step 2, the stirring speed is 500 rpm to 1000 rpm.

[0020] Furthermore, in step 2, the crystallization time is 18h to 26h.

[0021] The preferred stirring rate combined with the crystallization temperature, time and concentration is beneficial to improving the particle size uniformity of the prepared benzocaine crystal form I and obtaining blocky benzocaine crystal form I with complete crystal habits.

[0022] Furthermore, in step 2, the drying temperature is 40° C. to 60° C., and the drying is performed under vacuum.

[0023] As a specific embodiment of the present invention, a parallel crystallizer is used to prepare benzocaine Form I.

[0024] Furthermore, the benzocaine crystal form I has Figure 1 The X-ray powder diffraction pattern is shown.

[0025] Furthermore, the benzocaine crystal form I has characteristic diffraction peaks at diffraction angles of 2θ±0.2°=8.86°, 10.71°, 17.84°, 24.03°, 27.62°, and 35.49°.

[0026] Furthermore, the benzocaine crystal form I also has characteristic diffraction peaks at one or more of 2θ±0.2°=13.77°, 14.21°, 16.78°, 18.46°, 20.58°, 20.98°, 21.47°, and 26.83°.

[0027] Furthermore, the melting point of the benzocaine crystal form I is 364±2K.

[0028] Furthermore, the infrared spectrum of the benzocaine crystal form I is at 3419±2cm -1 、3344±2cm -1 、3215±2cm -1 、2951±2cm -1 、1676±2cm -1 、1274±2cm -1 、1169±2cm -1 、3419±2cm -1 、1110±2cm-1 、844±2cm -1 、770±2cm -1 、502±2cm -1 There are characteristic peaks.

[0029] It has been verified that the benzocaine crystal form prepared by the present invention is consistent with the data of benzocaine crystal form I reported in existing literature, which proves that the present invention has prepared high-purity single crystal crystal form I, providing more options for the application of benzocaine and helping to improve the market competitiveness of enterprises.

[0030] The preparation process of benzocaine crystal form I provided by the present invention realizes effective control of the benzocaine crystal transformation process by controlling and selecting a specific crystallization solvent, crystallization temperature, crystallization liquid concentration and other combination strategies, and the block benzocaine crystal form I product that can be prepared by one crystallization has good fluidity and can effectively avoid the agglomeration problem during transportation and storage; at the same time, it is proved by long-term stability test that the benzocaine crystal form I product prepared by the present invention has higher stability, which is conducive to improving the quality of benzocaine preparation products and helping to improve the market competitiveness of products. In addition, the process of the present invention is simple to operate, mild in conditions, convenient for industrial production, and has high promotion and application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The X-ray powder diffraction pattern of the benzocaine crystal form I prepared in Example 1;

[0032] Figure 2 This is the TGA-DSC graph of the benzocaine crystal form I prepared in Example 1;

[0033] Figure 3 This is the infrared spectrum of the benzocaine crystal form I prepared in Example 1;

[0034] Figure 4 X-ray powder diffraction patterns of benzocaine raw material (crystalline form II), comparative example 1, comparative example 2 and benzocaine crystalline product prepared in Example 1;

[0035] Figure 5 This is an X-ray powder diffraction pattern of the benzocaine crystal form I prepared in Example 1, which is sealed and placed in the dark for a long time at room temperature;

[0036] Figure 6 This is a microscope photograph of the benzocaine crystal form I prepared in Example 1. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0038] The benzocaine raw material used in the following examples and comparative examples is solid powder with a purity of ≥98%.

[0039] Crystal characterization methods:

[0040] 1. X-ray powder diffraction

[0041] Instrument: D / MAX-2500 (Rigaku, Japan);

[0042] Scanning range (2θ): 2.0°~50.0°;

[0043] Target: Cu-Kα radiation;

[0044] Light tube voltage: 40kV;

[0045] Light tube current: 100mA;

[0046] Scanning step: 0.02°.

[0047] 2. Differential Scanning Calorimetry

[0048] Instrument: Synchronous thermal analyzer (STA 449F3)

[0049] Temperature range: 30~300℃;

[0050] Heating rate: 10℃ / min;

[0051] Nitrogen flow rate: 20 mL / min.

[0052] 3. Infrared spectroscopy analysis

[0053] Instrument: Fourier transform infrared spectrometer (Bruker)

[0054] Scanning frequency range: 4000cm -1 Up to 400cm -1 ;

[0055] Resolution: 4cm -1 .

[0056] 4. Microscopic Analysis

[0057] The morphology of the samples was observed using a BX53 biological microscope (OLYMPUS, Japan). A small amount of the sample was placed on a glass slide and covered with a coverslip, and then the appropriate eyepiece and objective lens were adjusted for observation.

[0058] 5. High Performance Liquid Chromatography

[0059] Instrument: Waters e2998 high performance liquid chromatograph;

[0060] Chromatographic column: ZORBAX BONUS-RP (250mm*4.6mm, 5μm);

[0061] Mobile phase: glacial acetic acid: methanol = 60:40;

[0062] Flow rate: 1 mL / min;

[0063] Column temperature: 30°C;

[0064] Detection wavelength: 290nm.

[0065] Example 1

[0066] A preparation process of benzocaine crystal form I:

[0067] Step 1: adding the dried benzocaine raw material to ethyl formate at a ratio of 1 g:1.8 mL to obtain a benzocaine suspension;

[0068] Step 2: Transfer the benzocaine suspension to a parallel crystallizer, suspend and stir at a constant temperature of 25° C. for 24 h at a stirring speed of 850 rpm, filter, and vacuum dry the product at 50° C. to constant weight to obtain benzocaine Form I.

[0069] The X-ray powder diffraction pattern of the benzocaine crystal form I prepared in this example is as follows: Figure 1 As shown, there are characteristic diffraction peaks at 2θ=8.86°, 10.71°, 13.77°, 14.21°, 16.78°, 17.84°, 18.46°, 20.58°, 20.98°, 21.47°, 24.03°, 27.62°, 35.49°, and 26.83°, which are consistent with the data of Form I in the literature, proving that the product prepared in this example is Benzocaine Form I.

[0070] The TGA-DSC graph of the benzocaine crystal form I prepared in this example is as follows: Figure 2 As shown in the figure, it can be seen that the melting point of benzocaine form I is 364±2K.

[0071] The infrared spectrum of the benzocaine crystal form I prepared in this example is as follows Figure 3 As shown in the figure, it can be seen that at 3419cm -1 、3344cm -1 、3215cm -1 、2951cm -1 、1676cm -1、1274cm -1 、1169cm -1 、3419cm -1 、1110cm -1 、844cm -1 、770cm -1 、502cm -1 There are characteristic peaks.

[0072] The optical microscope image of the benzocaine crystal form I prepared in this example is as follows: Figure 6 As shown in the figure, it can be seen that the benzocaine crystal form I prepared in this example is a block crystal with complete crystal habit and no agglomeration.

[0073] Example 2

[0074] A preparation process of benzocaine crystal form I:

[0075] Step 1: Add the dried benzocaine raw material to methyl acetate at a ratio of 1 g:1.3 mL to obtain a benzocaine suspension;

[0076] Step 2: Transfer the benzocaine suspension to a parallel crystallizer, suspend and stir at a constant temperature of 25° C. for 18 h, with a stirring speed of 700 rpm, filter, and vacuum dry the product at 55° C. to constant weight to obtain benzocaine Form I.

[0077] The characterization data of X-ray powder diffraction, TGA-DSC and infrared spectrum of the crystals obtained in this example are basically the same as those in Example 1, proving that the product prepared in this example is benzocaine crystal form I.

[0078] Example 3

[0079] A preparation process of benzocaine crystal form I:

[0080] Step 1: adding the dried benzocaine raw material to ethyl acetate at a ratio of 1 g: 2 mL to obtain a benzocaine suspension;

[0081] Step 2: Transfer the benzocaine suspension to a parallel crystallizer, suspend and stir at a constant temperature of 20° C. for 26 h at a stirring speed of 900 rpm, filter, and vacuum dry the product at 40° C. to constant weight to obtain benzocaine Form I.

[0082] The characterization data of X-ray powder diffraction, TGA-DSC and infrared spectrum of the crystals obtained in this example are basically the same as those in Example 1, proving that the product prepared in this example is benzocaine crystal form I.

[0083] Example 4

[0084] A preparation process of benzocaine crystal form I:

[0085] Step 1: Add the dried benzocaine raw material to propyl acetate at a ratio of 1 g: 2 mL to obtain a benzocaine suspension;

[0086] Step 2: Transfer the benzocaine suspension to a parallel crystallizer, suspend and stir at a constant temperature of 23° C. for 25 h, with a stirring speed of 600 rpm, filter, and vacuum dry the product at 60° C. to constant weight to obtain benzocaine Form I.

[0087] The characterization data of X-ray powder diffraction, TGA-DSC and infrared spectrum of the crystals obtained in this example are basically the same as those in Example 1, proving that the product prepared in this example is benzocaine crystal form I.

[0088] Example 5

[0089] A preparation process of benzocaine crystal form I:

[0090] Step 1: Add the dried benzocaine raw material to isopropyl acetate at a ratio of 1 g: 2.5 mL to obtain a benzocaine suspension;

[0091] Step 2: Transfer the benzocaine suspension to a parallel crystallizer, suspend and stir at a constant temperature of 25° C. for 19 h, with a stirring speed of 500 rpm, filter, and vacuum dry the product at 50° C. to constant weight to obtain benzocaine Form I.

[0092] The characterization data of X-ray powder diffraction, TGA-DSC and infrared spectrum of the crystals obtained in this example are basically the same as those in Example 1, proving that the product prepared in this example is benzocaine crystal form I.

[0093] Example 6

[0094] A preparation process of benzocaine crystal form I:

[0095] Step 1: Add the dried benzocaine raw material to butyl acetate at a ratio of 1 g:2.3 mL to obtain a benzocaine suspension;

[0096] Step 2: Transfer the benzocaine suspension to a parallel crystallizer, suspend and stir at a constant temperature of 24° C. for 23 h, with a stirring speed of 800 rpm, filter, and vacuum dry the product at 40° C. to constant weight to obtain benzocaine Form I.

[0097] The characterization data of X-ray powder diffraction, TGA-DSC and infrared spectrum of the crystals obtained in this example are basically the same as those in Example 1, proving that the product prepared in this example is benzocaine crystal form I.

[0098] Example 7

[0099] A preparation process of benzocaine crystal form I:

[0100] Step 1: adding the dried benzocaine raw material to isobutyl acetate at a ratio of 1 g:3 mL to obtain a benzocaine suspension;

[0101] Step 2: Transfer the benzocaine suspension to a parallel crystallizer, suspend and stir at a constant temperature of 20° C. for 20 h, with a stirring speed of 1000 rpm, filter, and vacuum dry the product at 60° C. to constant weight to obtain benzocaine Form I.

[0102] The characterization data of X-ray powder diffraction, TGA-DSC and infrared spectrum of the crystals obtained in this example are basically the same as those in Example 1, proving that the product prepared in this example is benzocaine crystal form I.

[0103] Through liquid phase detection, the purity of the benzocaine crystal form I prepared in Examples 1 to 7 was ≥99.5%.

[0104] Comparative Example 1

[0105] This comparative example provides a preparation process of benzocaine crystals, which is different from Example 5 only in the crystallization temperature. The specific steps are as follows:

[0106] Step 1: Add the dried benzocaine raw material to isopropyl acetate at a ratio of 1 g: 2.5 mL to obtain a benzocaine suspension;

[0107] Step 2: Transfer the benzocaine suspension to a parallel crystallizer, suspend and stir at a constant temperature of 27° C. for 19 h, with a stirring speed of 500 rpm, filter, and vacuum dry the product at 50° C. to constant weight to obtain a benzocaine crystalline product, recorded as mixed crystal (A).

[0108] The X-ray powder diffraction pattern of the benzocaine crystalline product prepared in this comparative example is as follows Figure 4 As shown in the figure, it can be seen that the product prepared in this comparative example is a mixed crystal of crystal form I and crystal form II.

[0109] Comparative Example 2

[0110] This comparative example provides a preparation process of benzocaine crystals, which is different from Example 7 only in the crystallization solvent and the crystallization method. The specific steps are as follows:

[0111] The dried benzocaine raw material was added to anhydrous ethanol at a ratio of 1 g:3 mL. After it was completely dissolved, the temperature was lowered to 15°C at a rate of 1°C / min. Crystals precipitated and were filtered and dried to obtain a benzocaine crystal product, which was recorded as mixed crystal (B).

[0112] The X-ray powder diffraction pattern of the benzocaine crystalline product prepared in this comparative example is as follows Figure 4 As shown in the figure, it can be seen that the product prepared in this comparative example is a mixed crystal of crystal form I and crystal form II.

[0113] Liquidity test

[0114] The angle of repose of the benzocaine crystal form I and the benzocaine raw material prepared in Example 1 was measured according to the method provided in the "Guidelines for Determination of Powder Flowability" issued by the National Pharmacopoeia Commission, and the results are shown in Table 1. The angle of repose of the crystal form I shown in the table is the average of all examples.

[0115] Table 1

[0116]

[0117] The above results prove that the blocky benzocaine crystal form I product prepared in the embodiment of the present invention has a smaller angle of repose and better fluidity than the benzocaine raw material, can effectively avoid the agglomeration problem during transportation and storage, and has better drugability and processability.

[0118] The repose angles of the benzocaine crystal form I prepared in Examples 2 to 7 are all between 39.22° and 43.91°, indicating that the block benzocaine crystal form I prepared in the examples of the present invention has good fluidity.

[0119] Bulk and tapped density testing

[0120] Bulk density test: Place an appropriate amount of product into a 10mL measuring cylinder, shake it slightly horizontally to make the upper part of the powder in the measuring cylinder flat, and read the volume.

[0121] Tap density: Oscillate the bulk density measuring cylinder repeatedly until the volume of powder in the measuring cylinder stops decreasing and read the volume.

[0122] Compression = (tapped density - bulk density) / tapped density. Compression is a simple method to predict the fluidity of powders. Since the bulk density, particle size, shape, surface area, moisture and adhesion of powder materials will affect the compression, compression is generally used as an indirect indicator to measure these parameters. The results are shown in Table 2. The data of the examples in the table are the average bulk density, tapped density and compression of the crystal form I products obtained in the above 7 examples.

[0123] Table 2

[0124] sample Bulk density / (g / mL) Tap density / (g / mL) Compression / % raw material 0.5901 0.7564 21.99％ Example 0.2917 0.3829 23.81％

[0125] Stability test

[0126] The benzocaine crystal form I prepared in Example 1 and the benzocaine raw material were subjected to accelerated stability studies. The purity of the samples was determined by Waters e2998 high performance liquid chromatograph. The test results are shown in Table 3.

[0127] Table 3

[0128]

[0129] As can be seen from the above table, the stability of the block benzocaine crystal form I prepared in the embodiment of the present invention is better than the stability of the benzocaine raw material, and the crystal form does not change during the storage process, which helps to improve the quality of the benzocaine preparation product.

[0130] The benzocaine crystal form I prepared in Example 1 was sealed and stored at room temperature and pressure in the dark for 2 weeks. The X-ray powder diffraction patterns of the samples at different storage times were as follows: Figure 5 As shown, the results show that no obvious changes were found in the color, morphology and crystal form of the sample, proving that the benzocaine crystal form I product prepared in the embodiment of the present invention has good long-term stability.

[0131] In summary, the preparation method of benzocaine crystal form I provided by the present invention has the advantages of simple process and high purity of prepared crystals. The benzocaine crystal form I prepared by the present invention is a block crystal with an angle of repose between 39.22° and 43.91° and a bulk density between 0.26 g / mL and 0.33 g / mL, which can improve the fluidity of benzocaine, facilitate subsequent storage and use, and has higher stability than commercially available benzocaine raw materials, and has great advantages in pharmaceutical preparations.

[0132] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modification, equivalent substitution or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A process for preparing benzocaine crystal form I, characterized in that: The following steps are involved: Step 1, adding benzocaine raw material into an ester solvent to obtain a supersaturated benzocaine suspension; Step 2: suspending and stirring the benzocaine suspension at 20° C. to 25° C. for crystallization, separating the solid from the liquid, and drying to obtain benzocaine crystal form I.

2. The process for preparing the benzocaine crystal form I according to claim 1, characterized in that: In step 1, the ester solvent is at least one of methyl acetate, ethyl acetate, propyl acetate, isopropyl acetate, butyl acetate, isobutyl acetate or ethyl formate.

3. The process for preparing the benzocaine crystal form I according to claim 1 or 2, characterized in that: In step 1, the mass volume ratio of the benzocaine raw material to the ester solvent is 1 g: (1.3-3) mL.

4. The process for preparing the benzocaine crystal form I according to claim 1, characterized in that: In step 1, the crystal form of the benzocaine raw material is crystal form II, and the purity is ≥98%.

5. The process for preparing the benzocaine crystal form I according to claim 1, characterized in that: In step 2, the stirring speed is 500 rpm to 1000 rpm.

6. The process for preparing the benzocaine crystal form I according to claim 1 or 5, characterized in that: In step 2, the crystallization time is 18h to 26h.

7. The process for preparing benzocaine crystal form I according to claim 1, characterized in that: The benzocaine crystal form I has an X-ray powder diffraction pattern as shown in FIG1 .

8. The process for preparing benzocaine crystal form I according to claim 1, characterized in that: The benzocaine crystal form I has characteristic diffraction peaks at diffraction angles of 2θ±0.2°=8.86°, 10.71°, 17.84°, 24.03°, 27.62°, and 35.49°.

9. The process for preparing benzocaine crystal form I according to claim 8, characterized in that: The benzocaine crystal form I also has characteristic diffraction peaks at one or more of 2θ±0.2°=13.77°, 14.21°, 16.78°, 18.46°, 20.58°, 20.98°, 21.47°, and 26.83°.

10. The process for preparing benzocaine crystal form I according to claim 1, characterized in that: The melting point of the benzocaine crystal form I is 364±2K; Its infrared spectrum is 3419±2cm -1 、3344±2cm -1 、3215±2cm -1 、2951±2cm -1 、1676±2cm -1 、1274±2cm -1 、1169±2cm -1 、3419±2cm -1 、1110±2cm -1 、844±2cm -1 、770±2cm -1 、502±2cm -1 There are characteristic peaks.

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