A storage method for mercaptopropionic acid, and mercaptopropionic acid compositions and mercaptopropionic acid esters

Abstract

The present application relates to the technical field of optical material, and more particularly to a storage method of mercaptopropionic acid, and mercaptopropionic acid composition and mercaptopropionic acid ester. Specifically, the present application provides a storage method of mercaptopropionic acid, wherein a polymerization inhibitor is added in the mercaptopropionic acid. According to the present application, the content of mercaptopropionic acid is greater than or equal to 98.0% after being placed for 3 months, and the esterification rate can be improved in the esterification reaction, and the mercaptopropionic acid carboxylate can meet the requirement of yellow index less than or equal to 5.0 in the application of optical resin.

Description

Technical Field

[0001] This invention relates to the field of optical materials technology, and more particularly to a method for storing mercaptopropionic acid, as well as mercaptopropionic acid compositions and mercaptopropionic esters. Background Technology

[0002] Mercaptopropionic acid is widely used in esterification reactions, such as methyl mercaptopropionate, pentaerythritol tetra(3-mercaptopropionic acid) ester, inositol hexa(mercaptopropionic acid) ester, and trimethylolpropane tri(3-mercaptopropionic acid) ester. When mercaptopropionic acid is used as a raw material for optical resins, its color requirement is ≤15 Hazen to meet the requirements of optical resins, which places high demands on the color quality of mercaptopropionic acid itself.

[0003] Mercaptopropionic acid itself is unstable. With the influence of storage time and temperature, the thiol and carboxyl groups of mercaptopropionic acid can condense intermolecularly through thioester bonds to form thioesters. These thioesters can be compounds formed by two, three, or more molecules bonding intermolecularly. The presence of these thioesters will affect the purity of the product and its downstream use. As described in patent CN101405261B, when the content of thioester in the raw material mercaptopropionic acid is >5%, the color tone of pentaerythritol mercaptocarboxylic acid ester deteriorates, and the viscosity of the polymerizable composition before polymerization with polyisocyanate compounds increases, resulting in a deterioration in the color tone or cloudiness of the lens.

[0004] The boiling point of the thioester formed after the self-polymerization of mercaptopropionic acid is 394℃ (101.33 kPa). Increased thioester content leads to a corresponding decrease in mercaptopropionic acid content, affecting downstream applications. Currently, mercaptopropionic acid is purified through further distillation, which cannot control the formation of thioesters at the source. Summary of the Invention

[0005] In view of this, the technical problem to be solved by the present invention is to provide a method for storing mercaptopropionic acid, as well as a mercaptopropionic acid composition and mercaptopropionic ester, which improves the storage time of mercaptopropionic acid by controlling the formation of thioester.

[0006] This invention provides the application of polymerization inhibitors in improving the storage stability of mercaptopropionic acid.

[0007] Optionally, the polymerization inhibitor includes one or more of phenolic polymerization inhibitors and quinone polymerization inhibitors.

[0008] The present invention provides a method for storing mercaptopropionic acid, wherein a polymerization inhibitor is added to the mercaptopropionic acid.

[0009] Optionally, the amount of the polymerization inhibitor added is 10 to 600 ppm.

[0010] Optionally, the polymerization inhibitor includes one or more of phenolic polymerization inhibitors and quinone polymerization inhibitors.

[0011] Optionally, the phenolic polymerization inhibitor includes one or more of hydroquinone, p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, and 2-tert-butylhydroquinone.

[0012] The quinone polymerization inhibitors include one or more of p-benzoquinone, tetrachlorobenzoquinone, and 1,4-naphthoquinone.

[0013] The present invention provides a mercaptopropionic acid composition comprising mercaptopropionic acid and a polymerization inhibitor.

[0014] Optionally, the amount of the polymerization inhibitor added is 10 to 600 ppm;

[0015] The polymerization inhibitor includes one or more of phenolic polymerization inhibitors and quinone polymerization inhibitors.

[0016] The present invention provides a mercaptopropionic acid ester, which is prepared by esterification reaction of the above-mentioned mercaptopropionic acid composition and an alcohol compound.

[0017] The present invention provides an optical resin prepared from the above-mentioned mercaptopropionic acid ester.

[0018] Compared with the prior art, the present invention provides a method for storing mercaptopropionic acid, wherein a polymerization inhibitor is added to the mercaptopropionic acid. By adding a polymerization inhibitor to the mercaptopropionic acid, the present invention can ensure that the content of mercaptopropionic acid is ≥98.0% after 3 months of storage, and can improve the esterification rate in the esterification reaction. The mercaptopropionic acid carboxylic ester can meet the requirement of yellow index ≤5.0 in optical resin applications. Detailed Implementation

[0019] This invention provides the application of polymerization inhibitors in improving the storage stability of mercaptopropionic acid.

[0020] Preferably, the polymerization inhibitor includes one or more of phenolic polymerization inhibitors and quinone polymerization inhibitors.

[0021] Preferably, the phenolic polymerization inhibitor includes one or more of hydroquinone, p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, and 2-tert-butylhydroquinone.

[0022] Preferably, the quinone polymerization inhibitor includes one or more of p-benzoquinone, tetrachlorobenzoquinone, and 1,4-naphthoquinone.

[0023] In some specific embodiments of the present invention, the polymerization inhibitor is p-hydroxyanisole.

[0024] This invention avoids the formation of thioesters of mercaptopropionic acid by adding a polymerization inhibitor to prevent the thiol and carboxyl groups of mercaptopropionic acid from undergoing thioester bond condensation between molecules.

[0025] Based on this, the present invention provides a method for storing mercaptopropionic acid, wherein a polymerization inhibitor is added to the mercaptopropionic acid.

[0026] The amount of the polymerization inhibitor added is preferably 10 to 600 ppm, specifically 10 ppm, 20 ppm, 30 ppm, 50 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, or any of the above values ​​as the upper or lower limit, more preferably 30 to 600 ppm, and even more preferably 300 to 600 ppm.

[0027] Experimental results show that excessive addition of polymerization inhibitors will increase the color of mercaptopropionic acid and its prepared esters. Therefore, it is necessary to control the amount of polymerization inhibitors added to solve the color problem of mercaptopropionic acid polymerization and its products.

[0028] The introduction of polymerization inhibitors into mercaptopropionic acid allows it to be stored more stably for up to 3 months, maintaining a mercaptopropionic acid content of ≥98.0% and a color of ≤10.0 Hazen.

[0029] The present invention does not impose any particular limitation on the storage temperature of the mercaptopropionic acid, but preferably it is 18–50°C. The freezing point of mercaptopropionic acid is 15–18°C. When the temperature is below the freezing point, mercaptopropionic acid becomes solid and needs to be melted back into liquid before use. To avoid repeated heating of mercaptopropionic acid, the storage temperature is preferably >18°C. Increased temperature will promote the formation of thioesters. Therefore, to avoid the formation of thioesters, the storage temperature is preferably 18–50°C, more preferably 18–40°C.

[0030] Preferably, the polymerization inhibitor includes one or more of phenolic polymerization inhibitors and quinone polymerization inhibitors.

[0031] Preferably, the phenolic polymerization inhibitor includes one or more of hydroquinone, p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, and 2-tert-butylhydroquinone.

[0032] Preferably, the quinone polymerization inhibitor includes one or more of p-benzoquinone, tetrachlorobenzoquinone, and 1,4-naphthoquinone.

[0033] In some specific embodiments of the present invention, the polymerization inhibitor is p-hydroxyanisole.

[0034] p-Hydroxyanisole is a white, flaky or waxy white crystalline solid with a boiling point of 243℃ (101.33 kPa). It is readily soluble in organic solvents such as ethanol, ether, acetone, acetic acid, and ethyl acetate. When p-hydroxyanisole consumes free radicals, it transforms into p-benzoquinone. During use, the polymerization inhibition mechanism of p-hydroxyanisole involves the oxidation of phenols into the corresponding quinones, which then combine with free radicals in the chain to inhibit polymerization.

[0035] Quinone polymerization inhibitors, such as p-benzoquinone, can also inhibit polymerization under anaerobic conditions. p-Benzoquinone is a yellow crystal, soluble in alcohols and ethers. Benzoquinone compounds have highly conjugated structures, hence they are all colored compounds; para-quinones are mostly yellow, while ortho-quinones are mostly red or orange. Therefore, more polymerization inhibitor is not necessarily better. When the amount of polymerization inhibitor added is 30–600 ppm, it can inhibit the oxidation of mercaptopropionic acid, protect the product content, and avoid the problem of increased color in the mercaptopropionic acid product. Studies have found that when the amount of polymerization inhibitor added is 30–600 ppm, the color of mercaptopropionic acid is ≤10 Hazen, which meets the requirements of downstream product applications.

[0036] The present invention also provides a mercaptopropionic acid composition comprising mercaptopropionic acid and a polymerization inhibitor.

[0037] The amount of the polymerization inhibitor added is preferably 10 to 600 ppm, specifically 10 ppm, 20 ppm, 30 ppm, 50 ppm, 100 ppm, 200 ppm, 300 ppm, 400 ppm, 500 ppm, 600 ppm, or any of the above values ​​as the upper or lower limit, more preferably 30 to 600 ppm, and even more preferably 300 to 600 ppm.

[0038] Preferably, the polymerization inhibitor includes one or more of phenolic polymerization inhibitors and quinone polymerization inhibitors.

[0039] Preferably, the phenolic polymerization inhibitor includes one or more of hydroquinone, p-hydroxyanisole, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, and 2-tert-butylhydroquinone.

[0040] Preferably, the quinone polymerization inhibitor includes one or more of p-benzoquinone, tetrachlorobenzoquinone, and 1,4-naphthoquinone.

[0041] In some specific embodiments of the present invention, the polymerization inhibitor is p-hydroxyanisole.

[0042] After the above-mentioned mercaptopropionic acid composition is stored for 3 months, its mercaptopropionic acid content can still be ≥98.0% and its color ≤10.0 Hazen.

[0043] The present invention provides a mercaptopropionic acid ester, which is prepared by esterification reaction of the above-mentioned mercaptopropionic acid composition and an alcohol compound.

[0044] The present invention does not specifically limit the alcohol compounds mentioned, and they can be alcohol compounds used to prepare mercaptopropionates, and can be monohydric alcohols, dihydric alcohols or polyhydric alcohols.

[0045] The monohydric alcohol is preferably a C1-C10 monohydric alcohol, including but not limited to methanol, ethanol, etc.; the dihydric alcohol is preferably a C2-C10 dihydric alcohol, including but not limited to ethylene glycol, etc.; the polyhydric alcohol is preferably a 3-6 alcohol, such as one or more of C3-C15 trihydric alcohols, C4-C20 tetrahydric alcohols, C5-C20 pentahydric alcohols or C6-C20 hexahydric alcohols, including but not limited to one or more of 1,3-propanediol, trimethylolpropane, pentaerythritol, sorbitol, etc.

[0046] The present invention does not specifically limit the synthesis method of the mercaptopropionic ester, and can use methods well known to those skilled in the art. For example, referring to the esterification reaction in "Basic Organic Chemistry", mercaptopropionic acid and an alcohol compound are added to a four-necked flask equipped with a mechanical stirrer, a thermometer, a reflux condenser and a water separator, and a catalyst and a dehydrating agent are added to carry out the esterification reaction.

[0047] To improve the esterification reaction rate, preferably, an esterification catalyst and a dehydrating agent are added to promote the reaction.

[0048] The present invention does not specifically limit the esterification catalyst, and it can be any catalyst known to those skilled in the art that is suitable for esterification reaction, preferably one or more of hydrochloric acid, sulfuric acid, phosphoric acid, p-toluenesulfonic acid, methanesulfonic acid and trifluoroacetic acid.

[0049] The present invention does not have a particular limitation on the amount of esterification catalyst added, and it can be a general catalytic amount. Preferably, the molar amount of the catalyst is 0.1% to 5% of the molar amount of mercaptopropionic acid.

[0050] The present invention does not specifically limit the dehydrating agent, and it can be any dehydrating agent suitable for esterification reaction that is well known to those skilled in the art. The dehydrating agent is preferably one or more of toluene, xylene, dichloroethane, chloroform, cyclohexane, n-hexane and chlorobenzene.

[0051] The preferred temperature for the esterification reaction is 80–90°C, and the preferred time for the esterification reaction is 8–20 h.

[0052] After the reaction was completed, the system was cooled, separated, washed with water, and the product was depressurized to remove the low-boiling substances to obtain mercaptopropionic acid ester.

[0053] The mercaptopropionate prepared by this invention can be used to prepare optical materials.

[0054] The optical materials include, but are not limited to, optical resins.

[0055] Based on this, the present invention provides an optical resin prepared from the above-mentioned mercaptopropionic acid ester.

[0056] The present invention does not impose any particular limitation on the preparation method of the optical resin, and can be any optical resin preparation method known to those skilled in the art.

[0057] For example, it can be prepared using the following methods:

[0058] Using the aforementioned mercaptopropionate as a raw material, it was then thoroughly mixed with a mixture of toluene diisocyanate, dimethyl tin dichloride, butoxyethyl phosphate, and di(butoxyethyl) phosphate at room temperature. The resulting mixture was then degassed under reduced pressure to obtain a homogeneous monomer mixture. This monomer mixture was injected into a molding die containing a pair of glass molds and a resin gasket. The wall thickness and diameter of the plastic lens were set, and the molding die was assembled.

[0059] After the above monomer mixture is injected into a molding die, it is heated and polymerized to obtain an optical resin lens.

[0060] The heating polymerization is preferably carried out by raising the temperature from 20°C to 120°C and then heating and polymerizing at 120°C for 3 to 6 hours.

[0061] Preferably, the time for heating from 20°C to 120°C is 10–20 hours.

[0062] When polymer materials such as resins and plastics are exposed to environmental factors such as ultraviolet radiation, their internal molecular chains and structures change, resulting in yellowing on the material surface. The degree of yellowing is typically characterized by a yellowness index, and a yellowness index meter is used to measure the extent and trend of yellowing.

[0063] The yellowness index (YI) is used to characterize the degree to which colorless, transparent, translucent, or nearly white polymer materials turn yellow (yellowing).

[0064] Representation method: YI = 100(C x XC z Z) / Y

[0065] X, Y, and Z are tristimulus values, while Cx and Cz values ​​can be found in relevant ASTM standards.

[0066] The yellow index can be positive or negative; the higher the yellow index, the more yellow the sample.

[0067] This invention uses the Vista spectrophotometer to characterize the yellow index YIE313. First, a circular flat lens with a wall thickness of 5mm and a diameter of 75mm is made. Then, the Vista spectrophotometer is used to measure the spectral range of 400nm to 700nm. A yellow index YI≤5.0 is considered qualified.

[0068] In some specific embodiments of the present invention, pentaerythritol tetra(3-mercaptopropionic acid) ester is prepared using mercaptopropionic acid and pentaerythritol, the product has a color ≤15 Hazen, and is used to prepare optical resin, the resulting optical lens has a yellow index ≤5.0.

[0069] To further illustrate the present invention, a detailed description is provided below with reference to embodiments. However, it should be understood that these descriptions are merely for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims.

[0070] There are no particular restrictions on the source of any raw materials used in this invention; they can be purchased from the market or prepared using conventional methods known to those skilled in the art.

[0071] In the following examples, the content of mercaptopropionic acid was analyzed using the following method: An Agilent 1260 Infinity II liquid chromatography system was used, with a 0.01M H₃PO₄ / acetonitrile (40 / 60) aqueous solution as the mobile phase. The column temperature was 40°C, the flow rate of the mobile phase was 0.95 ml / min, and the wavelength was 230 nm. The sum of the areas of both was 100%.

[0072] The colorimetry of mercaptopropionic acid and mercaptopropionic ester was measured using a UV752 ultraviolet-visible spectrophotometer.

[0073] Examples 1-5

[0074] The mercaptopropionic acid provided by Yifeng New Materials Co., Ltd. was analyzed by Agilent 1260 Infinity II liquid chromatography. The mercaptopropionic acid content was 99.5%, and the mercaptopropionic acid thioester content was 0.5%. The color of mercaptopropionic acid was measured to be 3.7 Hazen using a UV752 ultraviolet-visible spectrophotometer.

[0075] Different types and amounts of polymerization inhibitors were added to mercaptopropionic acid, and the content and color were measured after being placed at 18℃-40℃ for 3 months.

[0076] Mercaptopropionic acid with added polymerization inhibitor was used as a raw material to synthesize mercaptopropionic acid ester. The mercaptopropionic acid ester was then stored at 18℃-40℃ for 3 months before its content and color were analyzed. Examples of mercaptopropionic acid stability verification are shown in Table 1 below.

[0077] Table 1

[0078]

[0079]

[0080] Comparative Example 1

[0081] No polymerization inhibitor was added to mercaptopropionic acid, and the rest of the operation was the same as in Examples 1-5.

[0082] Example 6 Preparation of pentaerythritol tetra(3-mercaptopropionic acid) ester

[0083] Using mercaptopropionic acid that had been stored for 3 months as a raw material, the synthesis process for mercaptopropionic ester is as follows:

[0084] In a 1000ml four-necked flask equipped with a mechanical stirrer, thermometer, reflux condenser, and water separator, 4.2 mol of mercaptopropionic acid and 1.0 mol of pentaerythritol, which had been stored for 3 months in Examples 1-5 and Comparative Example 1, were added, along with 6.5 g of 70% methanesulfonic acid aqueous solution and 310 g of cyclohexane as a dehydrating agent. After refluxing at 80-90℃ for 11 hours, the mixture was cooled, separated, washed with water, and the product was depressurized to remove low-boiling substances to obtain pentaerythritol tetra(3-mercaptopropionic acid) ester.

[0085] The esterification rate and color of the prepared pentaerythritol tetra(3-mercaptopropionic acid) ester were detected, and the results are shown in Table 2.

[0086] Example 7: Preparation of Optical Resin

[0087] Using 43.9 g of pentaerythritol tetra(3-mercaptopropionic acid) ester prepared in Example 6 as a raw material, it was mixed with 50.7 g of toluene diisocyanate, 0.02 g of dimethyl tin dichloride, and 0.30 g of a mixture of butoxyethyl phosphate and di(butoxyethyl phosphate) (mass ratio 1:1) at room temperature. The resulting mixture was then degassed under reduced pressure of 500 Pa to obtain a homogeneous monomer mixture. This monomer mixture was injected into a molding die containing a pair of glass molds and a resin gasket. The pair of glass molds used an upper mold with a curvature of 600 mm and a lower mold with a curvature of 120 mm, and the molding die was assembled with a center wall thickness of 5 mm and a diameter of 75 mm for the plastic lens.

[0088] After the monomer mixture was injected into the molding die, the temperature was increased from 20°C to 120°C over 15 hours, and polymerized at 120°C for 4 hours. After cooling, the plastic lens was removed from the molding die to obtain an optical resin lens. The evaluation results are shown in Table 2.

[0089] Table 2

[0090]

[0091] By adding a polymerization inhibitor of 30ppm-600ppm to mercaptopropionic acid, the product content can be guaranteed to be ≥98.0% after 3 months of storage, and the esterification rate can be improved in the esterification reaction. Mercaptopropionic acid carboxylic ester can meet the yellow index ≤5.0 in optical resin applications.

[0092] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. Application of polymerization inhibitors in improving the storage stability of mercaptopropionic acid; The amount of the polymerization inhibitor added is 30~600 ppm; The polymerization inhibitor is p-hydroxyanisole.

2. A method for storing mercaptopropionic acid, characterized in that, The mercaptopropionic acid contains a polymerization inhibitor; The amount of the polymerization inhibitor added is 30~600 ppm; The polymerization inhibitor is p-hydroxyanisole.

3. A mercaptopropionic acid composition comprising mercaptopropionic acid and a polymerization inhibitor; The amount of the polymerization inhibitor added is 30~600 ppm; The polymerization inhibitor is p-hydroxyanisole.

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