A process for the synthesis of n-butyrate from propylene

Abstract

The application belongs to the technical field of ester flavor and fragrance, and particularly relates to a method for synthesizing n-butyl acetate from propylene. The method comprises: directly preparing n-butyl acetate product through one-step methoxycarbonylation reaction of propylene, CO and alcohol under a preferred catalyst system. The catalyst is composed of an active metal compound and a phosphine ligand. The method has the advantages of high atom utilization rate, no water by-product, simple operation steps, cheap and easily available raw materials and low separation cost.

Description

Technical Field

[0001] This invention belongs to the field of ester fragrance and flavor technology, specifically relating to a method for highly selectively converting propylene into n-butyrate ester via a methoxycarbonylation reaction. Background Technology

[0002] Butyrate esters are synthetic flavorings for food as defined in the national standard (GB 30616-2020). GB 1886.194-2016 and GB 1886.286-2016 specify the national food safety standards for ethyl butyrate and butyl butyrate. Therefore, butyrate esters have wide applications in the flavoring and fragrance industry. They can be used to formulate fruit flavorings such as pineapple, strawberry, banana, and grape, as well as flavorings for baijiu (Chinese liquor) and tobacco. They are also used in candies, beverages, ice cream, and other foods. Furthermore, butyrate esters have wide applications in the pharmaceutical and chemical fields, serving as pharmaceutical intermediates or specialty solvents.

[0003] Currently, the synthesis of n-butyrate esters mainly involves the esterification reaction of n-butyric acid with alcohols (CN103058860A). On the one hand, n-butyric acid is relatively expensive, currently priced at approximately 8000 yuan / ton, resulting in high raw material costs. On the other hand, the esterification reaction produces water as a byproduct, which readily forms an azeotrope with the target ester product, requiring the addition of cyclohexane, benzene, resin, or molecular sieves as dehydrating agents, leading to high separation costs. Using a one-step methoxycarbonylation reaction of propylene to prepare n-butyrate esters overcomes these two challenges: propylene is inexpensive and readily available, currently priced at approximately 7000 yuan / ton; the theoretical atom utilization rate of methoxycarbonylation is 100%, with no water byproduct, and product separation is simple.

[0004] For the methoxycarbonylation of unsaturated olefins, CN114539058A previously disclosed a heterogeneous catalyst supported on a porous organic polymer, where the polymer monomers are vinyl-containing phosphine ligands and vinyl-containing organic sulfonates. CN115870002A disclosed another type of copolymer-supported metal catalyst, whose support is obtained by copolymerization of polycarboxyl compounds and polyamine compounds. However, these two types of catalysts are mainly suitable for the methoxycarbonylation of ethylene, and can yield products with high chemoselectivity, i.e., methyl propionate is the main product, but cannot control the regioselectivity of the products, such as the selectivity between n-butyrate (linear product) and isobutyrate (branched product) in the methoxycarbonylation of propylene. Summary of the Invention

[0005] To address the shortcomings of existing technologies, such as high raw material costs and difficult separation in esterification reactions, or the difficulty in controlling the regioselectivity of products in unsaturated olefin methoxycarbonylation reactions, this invention provides a method for the direct synthesis of n-butyrate esters via propylene methoxycarbonylation. This method features low raw material costs, high regioselectivity, and simple product separation.

[0006] The technical solution adopted in this invention is as follows:

[0007] In a first aspect, the present invention provides a method for synthesizing n-butyrate from propylene, the method comprising: reacting propylene with CO and an alcohol in the presence of a catalyst system, wherein the catalyst system is composed of an active metal compound and a phosphine ligand;

[0008] The chemical reaction equation is as follows:

[0009] .

[0010] Compared with the prior art, the present invention has the following advantages:

[0011] (1) The reaction steps of the present invention are simple. The present invention can convert propylene, CO and alcohol into n-butyrate ester with significantly improved economic added value through a one-step reaction, and has high atom utilization rate. This not only reduces equipment investment in the production process, but also reduces waste emissions, which is environmentally friendly.

[0012] (2) The raw materials of the present invention are inexpensive and readily available. The price of propylene, the raw material of the present invention, is significantly lower than that of butyric acid in the existing esterification route, making it highly economical.

[0013] (3) The product separation of the present invention is simple. The n-butyrate product of the present invention has high selectivity, and the methoxycarbonylation reaction does not produce water, which can avoid the formation of an azeotrope between water and n-butyrate, thereby reducing separation energy consumption and cost. Attached Figure Description

[0014] Figure 1 The diagram shows the energy barrier changes of the reaction pathways for the catalytic systems corresponding to triphenylphosphine (a), tris(4-fluorophenyl)phosphine (b), and 1,2-bis(di-tert-butylphosphine-methyl)benzene (c).

[0015] Figure 2 This is a gas chromatogram (GC) of the standard solution.

[0016] Figure 3 This is the gas chromatogram of the reaction corresponding to Example 19. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] The technical terms “first”, “second”, etc. in this application are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features.

[0019] The reference to "embodiment" in this application means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0020] The technical term "and / or" in this application is only a description of the relationship between related objects, indicating that there can be three kinds of relationships. For example, A and / or B can represent three situations: A exists alone, A and B exist at the same time, and B exists alone.

[0021] In addition, the character " / " in this application generally indicates that the objects before and after it are in an "or" relationship.

[0022] In this application, "multiple" means two or more (including two), and "at least one" means one or more.

[0023] It should be noted that, unless otherwise specified in the examples, the conditions should be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0024] The present invention provides a method for synthesizing n-butyrate from propylene, the method comprising: reacting propylene with CO and an alcohol in the presence of a catalyst system, wherein the catalyst system is composed of an active metal compound and a phosphine ligand.

[0025] According to a preferred embodiment of the present invention, the phosphine ligand is selected from one or more of 1,2-bis(di-tert-butylphosphine)benzene, 1,3-bis(di-tert-butylphosphine)benzene, and 1,4-bis(di-tert-butylphosphine)butane, and their structures are as follows:

[0026] , ,

[0027] According to a preferred embodiment of the present invention, the active metal compound is selected from Group VIII active metal compounds, preferably Group VIII active metal salts.

[0028] The Group VIII metal in the compound is selected from one or more of Fe, Co, Ni, Ru, Pt and Pd, with Pd being preferred.

[0029] According to a preferred embodiment of the present invention, in the catalyst system, the molar ratio of the active metal compound to the phosphine ligand is 0.01-10, preferably 0.5-5, and more preferably 1-4.

[0030] According to a preferred embodiment of the present invention, the alcohol is one or more of methanol, ethanol, n-propanol, isopropanol, n-butanol, and isobutanol, preferably ethanol and / or n-butanol;

[0031] According to a preferred embodiment of the present invention, the conditions for the contact reaction include:

[0032] The temperature is 50-300℃, preferably 80-150℃; and / or the reaction time is at least 3 hours.

[0033] The pressure is 0.05-20 MPa, preferably 1-5 MPa.

[0034] The present invention will be described in detail below through examples. In the following examples, the concentrations of each component were determined by gas chromatography, the external standard method was used for quantification, and the conversion rate was calculated by the following formula:

[0035]

[0036] Chemoselectivity is calculated using the following formula:

[0037]

[0038] The ratio of n-butyrate to isobutyrate is calculated using the following formula:

[0039]

[0040] The selectivity of n-butyrate is calculated using the following formula:

[0041]

[0042] Example 1

[0043] A high-pressure batch reactor was used. 12 mL of methanol was added to the reactor. The catalyst system consisted of 0.1 mmol palladium acetate as the active metal compound and 0.2 mmol triphenylphosphine as the phosphine ligand. After sealing, the reactor was pressurized to 1 MPa using propylene / CO syngas at a 1:1 pressure ratio, and the reaction temperature was 90 °C. After 3 h of reaction, the product was analyzed by gas chromatography. The esters in the product mainly included ethyl butyrate (CH3CH2CH2COOCH2CH3) and ethyl isobutyrate ((CH3)2CHCOOCH2CH3). The propylene conversion was 100%, the chemoselectivity was 93.9%, and the regioselectivity l / b = 2.37.

[0044] Examples 2-8

[0045] Similar to Example 1, except that different monophosphine ligands were screened, while the other conditions were the same as in Example 1, as detailed in Table 1. Analysis showed that the linear products of the monophosphine ligands exhibited low selectivity, with the l / b ratio remaining below 3.

[0046] Example 9

[0047] Similar to Example 8, except that the alcohol was changed from methanol to ethanol; all other conditions were the same as in Example 8, as detailed in Table 1. Analysis showed that the type of alcohol had a relatively small impact on the catalyst performance.

[0048] Examples 10-18

[0049] Similar to Example 8, but with different bisphosphine ligands screened; all other conditions were the same as in Example 8, as detailed in Table 1. Analysis showed that the unique bisphosphine ligand structure effectively improved the selectivity of the linear product, n-butyrate. For example, in Example 15, using the 1,2-bis(di-tert-butylphosphinemethyl)benzene ligand increased the l / b ratio to 19.4, corresponding to a n-butyrate selectivity of 92.0%. Similarly, in Example 17, using 1,3-bis(di-tert-butylphosphinemethyl)benzene increased the l / b ratio to 15.8, or in Example 18, the l / b ratio increased to 4.88. These results are significantly higher than with other phosphine ligands, as detailed in Table 1.

[0050] Examples 19-20

[0051] Similar to Example 15, except that the alcohol was changed from methanol to either methanol or n-butanol, while the other conditions remained the same as in Example 15 (see Table 1 for details). In the preferred 1,2-bis(di-tert-butylphosphine)benzene ligand catalytic system, the product selectivity after the reaction with different alcohols was studied. Analysis showed that the "Pd / 1,2-bis(di-tert-butylphosphine)benzene" catalytic system exhibits excellent catalytic performance for the propylene methoxycarbonylation reaction of different alcohols, and can synthesize the linear product n-butyrate with high selectivity.

[0052] Figure 1 The changes in reaction pathway energy barriers for triphenylphosphine, tris(4-fluorophenyl)phosphine, and 1,2-bis(di-tert-butylphosphine-methyl)benzene catalytic systems were demonstrated. The 1,2-bis(di-tert-butylphosphine-methyl)benzene ligand increased the energy barrier difference between the linear and branched pathways from 5.02 kJ / mol in the triphenylphosphine system to 8.23 ​​kJ / mol, thereby improving the regioselectivity (l / b) of the product from 2.37 to 20.4. Furthermore, the "Pd / 1,2-bis(di-tert-butylphosphine-methyl)benzene" catalytic system exhibits good versatility for different alcohol reaction systems and can be used to synthesize various n-butyrate esters, effectively increasing the economic added value of bulk chemicals such as propylene and methanol.

[0053] Figure 2 and Figure 3 Gas chromatographic results for the standard solution and the reaction solution of Example 19 are given respectively.

[0054] For ease of comparison, the main data of the examples and comparative examples are shown in Table 1.

[0055] Table 1

[0056]

[0057] In summary, this invention designs and prepares a unique "Pd / phosphine" catalytic system, achieving highly selective conversion of propylene, CO, and alcohols into n-butyrate esters. Among them, the best-performing phosphine ligand is 1,2-bis(di-tert-butylphosphinemethyl)benzene, whose unique electronic and steric effects significantly reduce the energy barrier of intermediates in the straight-chain reaction pathway.

[0058] The embodiments described above are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for synthesizing n-butyrate from propylene, characterized in that, include: The step of reacting propylene with CO and alcohol in the presence of a catalyst system to obtain the target product; ； In the formula, R is a substituted or unsubstituted alkyl group, preferably a C1 to C6 alkyl group, more preferably a C1 to C4 alkyl group; The catalyst system consists of an active metal compound and a phosphine ligand. The phosphine ligand has the following structure: 、 、 。 2. The method according to claim 1, characterized in that, The active metal compound is a Group VIII active metal compound.

3. The method according to claim 1, characterized in that, The active metal compound is a Group VIII active metal salt.

4. The method according to claim 2 or 3, characterized in that, Group VIII metals are selected from one or more of Fe, Co, Ni, Ru, Pt, and Pd, with Pd being preferred.

5. The method according to claim 1, characterized in that, In the catalyst system, the molar ratio of the active metal compound to the phosphine ligand is 0.01-10, preferably 0.5-5, and more preferably 1-4.

6. The method according to claim 1, characterized in that, The reaction temperature is 50-300℃, preferably 80-150℃.

7. The method according to claim 1, characterized in that, The reaction pressure is 0.05-20 MPa, preferably 1-5 MPa.

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