CN115404289A - Reactive fat-liquoring agent and preparation method thereof - Google Patents

Abstract

The invention belongs to the field of leather-making chemical industry, and discloses a reactive fat liquor and a preparation method thereof. According to the invention, epoxidized soybean oil is taken as a raw material, firstly, the ring opening is carried out on the epoxidized soybean oil through a hydroxyl compound, then, the ring opening is reacted with epoxy chloropropane to prepare chlorine-terminated triglyceride, and finally, the chlorine-terminated triglyceride is compounded with an emulsifier to obtain the reactive fat liquoring agent based on the epoxidized soybean oil. During the fatting process, chlorine atoms in the fatting agent can react with amino groups on the collagen fibers so as to be combined with the collagen fibers. Compared with the electrovalence combination mode of the common anionic fatting agent and the collagen fiber, the combination mode is firmer, can endow the fatting agent with better combination property and migration resistance, and is suitable for chrome tanning and chrome-free tanning systems with weaker positive electricity.

Description

Reactive fatliquor and preparation method thereof

technical field

The invention relates to the field of tanning chemical industry, in particular to a reactive fatliquoring agent and a preparation method thereof.

Background technique

Fatliquoring is one of the important processes in the leather production process. It can wrap oil on the surface of collagen fibers through physical and chemical effects, and form a layer of lubricating oil film between collagen fibers, thereby increasing the softness and plumpness of leather. And elasticity, improve its tensile strength and tear strength.

Fatliquor is one of the core materials used in the fatliquoring process, mainly including oil components and emulsifier components. At present, the oil components commonly used in fatliquor are mainly natural animal and vegetable oils such as fish oil, lard oil, modified vegetable oil, and castor oil. sex and fullness. However, the above-mentioned natural animal and vegetable oils often contain a large amount of unsaturated double bonds, and these double bonds are easily oxidized by air, which will cause yellowing, peculiar smell and other phenomena during use of the finished leather, which will affect the quality of the finished leather. In addition, the number of polar groups in the molecular structure of traditional natural animal and vegetable oils is small, and the fatliquoring process can only be combined with collagen fibers through physical adsorption and hydrogen bonding. Washable. In this case, modifying natural animal and vegetable oils to prepare a new type of fatliquoring agent that is resistant to yellowing, has strong binding ability with collagen fibers, and has good storage stability has become the development direction of fatliquor.

Epoxidized soybean oil is a product obtained by epoxidation of soybean oil, which has the characteristics of wide sources and environmental friendliness. Literature (Yu Yajin. Research on Perovskite Oxide/ZnO Quantum Dots/Modified Epoxy Soybean Oil Nanocomposite Fatliquor[D]. Shaanxi University of Science and Technology, 2020.) Esterized Epoxy Soybean Oil and Maleic Anhydride Soybean oil maleic acid monoester was synthesized by sulfonation reaction, and then sulfonic acid groups were introduced by sulfonation reaction to prepare a Gemini modified epoxy soybean oil fatliquoring agent. The fatliquoring agent can not only improve the softness and fullness of chrome tanned leather, but also endow it with good yellowing resistance. It is worth noting that sulfonic acid groups are introduced during the preparation of the fatliquoring agent, and the sulfonic acid groups have strong negative charges. During the fatliquoring process of chrome tanned leather, the sulfonic acid group in the fatliquoring agent can combine with -NH ₂ , Cr ³⁺ in the crust leather through electrostatic interaction, so it shows better migration resistance. However, for organic tanned leather, due to the relatively weak electropositive property of crust leather itself, the currently commonly used anionic fatliquor has a weak binding ability to collagen fibers, and its fatliquoring performance is limited.

In view of this, the present invention is proposed.

Contents of the invention

In order to solve the problems in the background technology, the invention provides an anti-yellowing reaction type fatliquoring agent prepared from epoxidized soybean oil.

For achieving the above object, a scheme that the present invention adopts is:

The reactive fatliquoring agent, in parts by weight, comprises 15-45 parts of chlorinated triglycerides and 2-6 parts of emulsifiers;

，式中，R₁为

、

、

中任一种。Wherein, the structural formula of terminal chlorotriglyceride is:

, where R ₁ is

,

,

any of these.

Preferably, the chloro-terminated triglyceride is obtained from epoxidized soybean oil through ring-opening of a hydroxyl compound, and then reacted with epichlorohydrin.

Preferably, the hydroxyl-containing compound includes but not limited to lactic acid, ethanolamine, diethanolamine.

Preferably, the weight ratio between the epoxidized soybean oil, hydroxyl compound and epichlorohydrin is (2~4):1:(1~2.5).

Preferably, the epoxy value of the epoxidized soybean oil is greater than 6.

Preferably, the emulsifier is selected from Tween 80 and/or Span 80.

Another technical scheme that the present invention adopts is:

The method for preparing reactive fatliquor comprises the following steps:

Mix epoxidized soybean oil and hydroxyl-containing compound at room temperature, add the first catalyst, raise the temperature to 80-130°C, and react for 4-8 hours to obtain the ring-opening product of epoxidized soybean oil;

mixing the ring-opened product of epoxidized soybean oil and epichlorohydrin at room temperature, adding a second catalyst, raising the temperature to 70-90°C for 6-10 h to obtain chloro-terminated triglycerides; and

Mix the chloro-terminated triglyceride and emulsifier and stir at 70-90 °C for 1-2 h.

Preferably, the first catalyst is selected from any one or more of tetrabutylammonium bromide, triphenylphosphine, and zinc chloride;

The second catalyst is selected from triphenylphosphine and/or boron trifluoride diethyl ether.

Compared with the prior art, the present invention has the following beneficial effects:

In the present invention, epoxidized soybean oil is used as raw material. Firstly, the epoxidized soybean oil is ring-opened by a hydroxyl compound, and then it is reacted with epichlorohydrin to prepare end-chlorinated triglycerides. Finally, the end-chlorinated triglycerides are mixed with Compounding is carried out to obtain a reactive fatliquoring agent based on epoxidized soybean oil. During the fatliquoring process, the chlorine atoms in the fatliquoring agent can react with the amino groups on the collagen fibers, thereby combining with the collagen fibers. This combination method is stronger than the electrovalent combination of commonly used anionic fatliquor and collagen fibers, and can endow the fatliquor with better binding and migration resistance. It is also suitable for chrome tanning and chrome-free tanning with weak electropositive properties system.

The invention uses epoxidized soybean oil with high saturation as raw material, and no unsaturated double bond is introduced in the reaction process, so that the product has good light and heat stability, and the leather after fatliquoring is resistant to yellowing and has no peculiar smell.

The raw material of the fatliquoring agent of the present invention is green and environment-friendly, and the product is suitable for chrome-tanned leather and chrome-free tanned leather at the same time, has the advantages of good fatliquoring effect, high absorption rate, and yellowing resistance, and provides a new method for the preparation of reactive fatliquor way.

Description of drawings

Fig. 1 is the infrared spectrum of the product b obtained after epoxidized soybean oil a, lactic acid ring-opened epoxidized soybean oil and terminal chlorotriglyceride c in Example 1 of the present invention;

Fig. 2 is the carbon nuclear magnetic resonance spectrum of epoxidized soybean oil a, lactic acid ring-opening product b and terminal chlorotriglyceride c in Example 1 of the present invention.

Detailed ways

In order to make the object, technical solution and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with specific implementation methods and accompanying drawings. It should be understood that these descriptions are exemplary only, and are not intended to limit the scope of the present invention. Also, in the following description, descriptions of well-known structures and techniques are omitted to avoid unnecessarily obscuring the concept of the present invention. Those who do not indicate the specific conditions in the examples are carried out according to the conventional conditions or the conditions suggested by the manufacturer. The reagents or instruments used were not indicated by the manufacturer, and they were all conventional products that could be purchased from the market.

The first embodiment of the present invention provides a reactive fatliquoring agent, which comprises 15-45 parts of chlorinated triglyceride and 2-6 parts of emulsifier in parts by weight;

，式中，R₁为

、

、

中任一种。Wherein, the structural formula of terminal chlorotriglyceride is:

, where R ₁ is

,

,

any of these.

The chlorine atoms in the chlorinated triglycerides in the fatliquoring agent can react with the amino groups on the collagen fibers to realize the combination with the collagen fibers when fatliquoring. The way of bonding with the electricity of collagen fibers is stronger, which can endow the fatliquoring agent with better binding and migration resistance, and can be applied to both chrome tanning and chrome-free tanning systems with weak electropositive properties.

The chloro-terminated triglyceride is obtained from epoxidized soybean oil through ring-opening of a hydroxyl compound, and then reacted with epichlorohydrin.

，式中，R和R'为长碳链，碳原子数目为5~10。Wherein, the structural formula of epoxidized soybean oil is

, where R and R' are long carbon chains with 5-10 carbon atoms.

，式中，R₂为

、

、

中任一种。The structural formula of the ring-opening product of epoxidized soybean oil after ring-opening by a hydroxyl compound is

, where R ₂ is

,

,

any of these.

For the selection of hydroxyl-containing compounds, its structure should meet the following requirements: while containing hydroxyl groups, it also contains active functional groups that are more reactive with epoxy groups than hydroxyl groups, so that it can react with epichlorohydrin after ring-opening of epoxy soybean oil Chlorine atoms are introduced. In some preferred embodiments, the hydroxyl-containing compound includes but not limited to lactic acid, ethanolamine, diethanolamine.

For the consumption of each raw material, it is better to be able to fully take place the above-mentioned reaction, in some preferred embodiments, the weight ratio of described epoxidized soybean oil, hydroxyl compound, epichlorohydrin is (2～4):1:(1 ~2.5).

In order to make the ring-opening reaction more complete and facilitate the introduction of more active chlorine atoms in the subsequent reaction with epichlorohydrin, the preferred embodiment of the present invention is epoxidized soybean oil with an epoxy value greater than 6.

The emulsifier is a commonly used emulsifier in the field, and the embodiment of the present invention is preferably Tween 80 and/or Span 80.

The second embodiment of the present invention provides a method for preparing a reactive fatliquoring agent. The method includes the following steps: after mixing epoxidized soybean oil and a hydroxyl-containing compound at room temperature, adding a first catalyst, raising the temperature to 80-130 °C, After reacting for 4-8 h, the ring-opened product of epoxidized soybean oil was obtained;

mixing the ring-opened product of epoxidized soybean oil and epichlorohydrin at room temperature, adding a second catalyst, raising the temperature to 70-90°C for 6-10 h to obtain chloro-terminated triglycerides; and

Mix the chloro-terminated triglyceride and emulsifier and stir at 70-90 °C for 1-2 h.

The first catalyst is selected from any one or more of tetrabutylammonium bromide, triphenylphosphine, and zinc chloride;

The second catalyst is selected from triphenylphosphine and/or boron trifluoride diethyl ether.

In order to better understand the technical solution provided by the present invention, the present invention, preparation method and application performance are respectively illustrated with a plurality of specific examples below.

The yellowing resistance, physical and mechanical properties, softness, thickness and absorption rate of the retanned crust leather mentioned in the following application examples and application comparison examples respectively passed the yellowing resistance test box (GT-7035-NUAB, limited high-speed iron testing equipment) company), tensile tester (GT-AI-7000S, Gaotie Testing Instrument Co., Ltd.), leather softness tester (GT-303, Gaotie Testing Instrument Co., Ltd.), thickness tester (GT-313, Gaotie Testing Instrument Co., Ltd. ) and total organic carbon analyzer (LiquiTOC, Elementar, Germany).

The resistance to organic solvents mentioned in the following application examples and application comparison examples is measured by the following method: cut the crust leather into 2mm×2mm particles, weigh the leather sample particles (mark the mass as m ₁ ), and wrap them with filter paper. The particles wrapped in filter paper were extracted with dichloromethane as solvent, taken out after 4 hours, dried at 105 ℃ to constant weight, and the leather sample particles were taken out after constant weight (the mass was recorded as m ₂ ). At the same time, weigh the unextracted blank skin-like particles (mass is recorded as m ₃ ) and dry at 105 ℃ until constant weight (mass is recorded as m ₄ ). Calculate the dichloromethane extract content ω in the leather according to the following formula. The lower the dichloromethane extract content, the better the leather resistance to organic solvent extraction.

Example 1

Preparation of reactive fatliquor:

Mix 112.5 g of lactic acid, 2.25 g of tetrabutylammonium bromide, and 4.5 g of triphenylphosphine into a three-necked flask and stir for 10 min at room temperature, then add 300 g of epoxidized soybean oil, raise the temperature to 80 °C and stir for 8 h to obtain Ring-opening products of epoxidized soybean oil. The above product was mixed with 7 g of triphenylphosphine in a three-necked flask at room temperature, then 210 g of epichlorohydrin was added, the temperature was raised to 70 °C and the reaction was stirred for 10 h. The product was taken out and mixed with 56 g Tween 80 at 70 °C for 2 h to obtain a reactive fatliquoring agent based on epoxidized soybean oil.

In this embodiment, the infrared spectrum of epoxy soybean oil a, product b obtained after lactic acid ring-opening epoxy soybean oil and terminal chlorotriglyceride c is shown in Figure 1, and the carbon nuclear magnetic resonance spectrum is shown in Figure 2.

Spectrum a in Figure 1 is the characteristic peak of the epoxy group in the molecular structure of epoxidized soybean oil at 824 cm ^-1 and 1242 cm ^-1 , and this peak completely disappears in spectrum b, which proves that the reaction between lactic acid and epoxidized soybean oil is successful. The carboxyl group of lactic acid completely opens the epoxy group. In addition, the broad association peak at 3442 cm ^-1 in spectrum b is the characteristic absorption peak of hydroxyl groups. The appearance of this peak is due to the reaction of lactic acid and epoxidized soybean oil to form polyol compounds, which also confirms the ring-opening reaction of epoxy groups happened. The C-Cl stretching vibration peak at 668 cm ^-1 in the c-terminal chlorotriglyceride of the spectrum confirmed the successful reaction of the epoxidized soybean oil polyol product with epichlorohydrin. In addition, the absorption peak at 1132 cm ^-1 in Figure c comes from the ether bond formed after hydroxyl ring-opening epichlorohydrin, which also provides strong evidence for the successful reaction of lactic acid ring-opening products with epichlorohydrin.

The absorption peak at 56 ppm in spectrum a in Figure 2 comes from the carbon of the epoxy group in epoxidized soybean oil, and this peak completely disappears in spectrum b, which proves that lactic acid has completely reacted with epoxidized soybean oil, and the epoxy group has been completely consumed. At the same time, the absorption peaks at 62ppm and 66ppm in spectrum b are the characteristic absorption peaks of the carbon connected to the hydroxyl group, which also confirms the successful ring-opening of lactic acid and the formation of polyol compounds. The absorption peak at 46-48 ppm in the spectrum c is the absorption peak of the carbon connected to the chlorine atom in the chlorine-terminated triglyceride generated after the reaction of epoxidized soybean oil polyol and epichlorohydrin, which proves that it is successfully used in fatliquor Chlorine atoms are introduced.

Example 2

Preparation of reactive fatliquor:

Mix 55 g of lactic acid, 1.25 g of tetrabutylammonium bromide, and 3.5 g of triphenylphosphine into a three-necked flask and stir for 10 min at room temperature, then add 200 g of epoxidized soybean oil, raise the temperature to 80 °C and stir for 8 h to obtain Ring-opening products of epoxidized soybean oil. Mix the above product with 3.5 g of boron trifluoride ether in a three-necked flask at room temperature, then add 130 g of epichlorohydrin, raise the temperature to 70 °C and stir for 6 h, take out the product and mix with 20 g of Span 80 at 80 °C After 1 h, the reactive fatliquoring agent based on epoxidized soybean oil was obtained.

Example 3

Preparation of reactive fatliquor:

Mix 65 g of ethanolamine with 1.5 g of tetrabutylammonium bromide, 1.5 g of triphenylphosphine, and 1.5 g of zinc chloride, add to a three-necked flask and stir at room temperature for 10 min, then add 250 g of epoxidized soybean oil, heat up to 80 °C and The reaction was stirred for 6 h to obtain the ring-opened product of epoxidized soybean oil. Mix the above product with 3.2 g of boron trifluoride ether in a three-necked flask at room temperature, then add 160 g of epichlorohydrin, raise the temperature to 80 °C and stir for 8 h, take out the product and mix it with 43 g of Tween 80 at 70 °C 2 h, and get a reactive fatliquor based on epoxidized soybean oil.

Example 4

Preparation of reactive fatliquor:

Mix 100 g of diethanolamine with 2.5 g of zinc chloride and 4 g of triphenylphosphine, add to a three-necked flask and stir for 10 min at room temperature, then add 300 g of epoxy soybean oil, raise the temperature to 120 °C and stir for 4 h to obtain epoxy macromolecular Ring-opening product of soybean oil. The above product was mixed with 5 g of triphenylphosphine in a three-necked flask at room temperature, then 160 g of epichlorohydrin was added, the temperature was raised to 70 °C and the reaction was stirred for 8 h, and the product was taken out and 32 g of Span 80 were stirred and mixed at 70 °C for 1 h, to obtain a reactive fatliquoring agent based on epoxidized soybean oil.

Example 5

Preparation of reactive fatliquor:

Mix 135 g of diethanolamine with 2 g of tetrabutylammonium bromide, 2 g of triphenylphosphine, and 2 g of zinc chloride, add to a three-necked flask and stir at room temperature for 10 min, then add 300 g of epoxidized soybean oil, and heat up to 100 °C And stirred for 4 h to obtain the ring-opened product of epoxidized soybean oil. Mix the above product with 7.5 g of boron trifluoride ether in a three-necked flask at room temperature, then add 176 g of epichlorohydrin, raise the temperature to 90 °C and stir for 4 h, take out the product and mix with 60 g of Tween 80 at 70 °C 2 h, the reactive fatliquor based on epoxidized soybean oil was obtained.

Application example 1

This application example uses the reactive fatliquor prepared in Example 1 to fatliquor cowhide sofa leather:

Put the shaved blue skin of the raw material of cowhide sofa leather into the drum, and then carry out softening, washing and retanning according to the conventional process, and then add 8% reactive fatliquor and 100% water based on the tare weight of the shaved blue skin , rotated at a temperature of 50 °C for 1 h, and then fixed by adding acid four times, adding 0.5% formic acid each time and rotating for 15 min.

The cowhide wetblue leather treated by this process has a thickening rate of 21.15% after fatliquoring, a softness of 8.84 mm, a tear strength of 99.77 N/mm, a fatliquoring agent absorption rate of 94.26%, and a dichloromethane extract content of 4.98%. , Anti-yellowing grade 4, flat and fine grain, plump and soft.

Application example 2

This application example uses the reactive fatliquor prepared in Example 3 to fatliquor sheep garment leather:

Put the shaved blue leather raw material of sheep clothing leather into the drum, and then carry out softening, washing and retanning according to the conventional process, and then add 8% reactive fatliquoring agent and 100% water based on the tare weight of the shaved blue leather , rotated at a temperature of 50 °C for 1 h, and then fixed by adding acid four times, adding 0.5% formic acid each time and rotating for 15 min.

The sheepskin wetblue treated by this process has a thickening rate of 18.97% after fatliquoring, a softness of 8.91 mm, a tear strength of 83.25 N/mm, a fatliquoring agent absorption rate of 93.35%, and a methylene chloride extract content of 5.23%. , Anti-yellowing grade 4, plump and soft, excellent comprehensive performance.

Application example 3

This application example uses the reactive fatliquor prepared in Example 4 to fatliquor aldehyde tanned cowhide shoe upper leather:

Put the raw material of aldehyde tanned cowhide shoe upper leather, the shaved white leather into the drum, and then carry out softening, washing and retanning according to the conventional process, and add reactive fatliquoring agent 10 based on the tare weight of the shaved white leather after draining %, water 150%, rotate at a temperature of 50 °C for 1 hour, then add acid to fix it in two times, add 0.4% formic acid each time and rotate for 15 min.

The cowhide wet white leather treated by this process has a thickening rate of 18.84% after fatliquoring, a softness of 8.58 mm, a tear strength of 104.22 N/mm, a fatliquoring agent absorption rate of 95.78%, and a dichloromethane extract content of 5.54%. , Anti-yellowing grade 3.5, full leather, excellent physical and mechanical properties.

Application example 4

This application example uses the reactive fatliquor prepared in Example 5 to fatliquor TWLZ tanned cowhide shoe upper leather:

The raw material of TWLZ tanned cowhide upper leather, shaved white leather, is put into the drum, followed by softening, washing and retanning according to the conventional process. %, water 150%, rotate at a temperature of 50 °C for 1 h, and then add acid to fix it in two times, add 0.4% formic acid each time and rotate for 15 min.

The cowhide wet white leather treated by this process has a thickening rate of 18.41% after fatliquoring, a softness of 8.23 mm, a tear strength of 106.57 N/mm, a fatliquoring agent absorption rate of 94.77%, and a dichloromethane extract content of 4.86%. , Anti-yellowing grade 3.5, the finished leather is firm and has excellent physical and mechanical properties.

Application comparison

This comparative example is to use commercial rapeseed oil fatliquoring agent to fatten cowhide sofa leather:

Put the shaved blue skin of the raw material of cowhide sofa leather into the drum, and then carry out softening, washing and retanning according to the conventional process, and then add 8% reactive fatliquor and 100% water based on the tare weight of the shaved blue skin , rotated at a temperature of 50 °C for 1 h, and then fixed by adding acid four times, adding 0.5% formic acid each time and rotating for 15 min.

The softness, fatliquor absorption rate, physical and mechanical properties, resistance to organic solvent extraction performance and yellowing resistance performance of the resulting leather test obtained after application example 1 and application comparative example fatliquoring are compared, and the results are shown in the following table:

。

.

It can be seen from the table that the softness of the cowhide sofa leather after fatliquoring with the reactive fatliquoring agent prepared by epoxidized soybean oil is similar to that of the commercial fatliquoring agent, while the physical and mechanical properties and the absorption rate of the fatliquoring agent are all the same. It is better than the commercial fatliquoring agent, indicating that the epoxidized soybean oil reactive fatliquoring agent prepared by this method has better fatliquoring performance. Simultaneously, the dichloromethane extract content of the crust leather of application example 1 is obviously lower than the crust leather of application comparison example, and the anti-yellowing grade is higher than application comparison example, shows that the application of the fatliquoring agent prepared by this method is carried out the crust leather of fatliquoring The resistance to organic solvent extraction and yellowing resistance are better than those of crust leather fatliquored with commercial fatliquor.

It should be noted that at last: above each embodiment is only in order to illustrate technical scheme of the present invention, and is not intended to limit; Although the present invention has been described in detail with reference to foregoing each embodiment, those of ordinary skill in the art should understand that: It is still possible to modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the technical solutions of the various embodiments of the present invention. range.

Claims (8)

1. The reactive fatting agent is characterized by comprising 15-45 parts of chlorotriglyceride and 2-6 parts of emulsifier by weight;

wherein the structural formula of the chlorine-terminated triglyceride is as follows:

in the formula, R ₁ Is composed of

、

、

Any of the above.

2. Reactive fatliquor according to claim 1, characterised in that the chlorotriglyceride is obtained by ring opening of epoxidized soybean oil with a hydroxyl-containing compound and subsequent reaction with epichlorohydrin.

3. Reactive fatliquor according to claim 2, wherein the hydroxyl containing compound comprises but is not limited to lactic acid, ethanolamine, diethanolamine.

4. The reactive fatliquor according to claim 2, wherein the weight ratio of the epoxidized soybean oil to the hydroxyl compound to the epichlorohydrin is (2 to 4) to 1 to (1 to 2.5).

5. Reactive fatliquor according to claim 2, wherein the epoxidized soybean oil has an epoxy value of greater than 6.

6. Reactive fatliquor according to claim 1, characterised in that the emulsifier is selected from tween 80 and/or span 80.

7. Method for preparing a reactive fatliquor according to any one of claims 1 to 6, comprising the steps of:

mixing the epoxidized soybean oil and a hydroxyl compound at room temperature, adding a first catalyst, heating to 80 to 130 ℃, and reacting for 4 to 8 hours to obtain an epoxidized soybean oil ring-opening product;

mixing the ring-opening product of the epoxidized soybean oil with epichlorohydrin at room temperature, adding a second catalyst, heating to 70-90 ℃, and reacting for 6-10 h to obtain a chlorine-terminated triglyceride; and

mixing the chlorotriglyceride and the emulsifier, and stirring for 1 to 2 hours at the temperature of 70 to 90 ℃.

8. The method of claim 7, wherein the first catalyst is selected from any one or more of tetrabutylammonium bromide, triphenylphosphine, and zinc chloride;

the second catalyst is selected from triphenylphosphine and/or boron trifluoride diethyl etherate.

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