Process for the preparation of monothiocarbonic ester compounds

Abstract

Process for the preparation of a compound having at least one monothiocarbonic ester group, by reacting, in the presence of a catalyst, - a compound having at least one thiol group, and - a dialkyl carbonate, wherein the catalyst is a salt of a metal selected from group IIIb or IVb of the periodic table.

Description

[0001] The object of this invention is a method for preparing compounds having at least one monothiocarbonate group, which is carried out by reacting the following substances in the presence of a catalyst:

[0002] - Compounds having at least one thiol group, and

[0003] -Dialkyl carbonate,

[0004] The catalyst is a salt of a metal selected from Group IIIb or IVb of the periodic table.

[0005] Monothiocarbonates are useful starting materials for the synthesis of compounds. Different methods for synthesizing monothiocarbonates are described in the prior art.

[0006] According to the method disclosed in US3349100, alkyl thiocarbonate monothiocarboxylate is obtained by reacting an epoxide with carbonyl sulfide. Synthesis using phosgene as a starting material is known from US2828318. US3072676 and 3201416 aim to prepare ethylene monothiocarbonate monothiocarboxylate via a two-step method. In the first step, mercaptoethanol and a chlorocarboxylic acid ester are reacted to give hydroxyethyl thiocarbonate; in the second step, the hydroxyethyl thiocarbonate is heated in the presence of a metal salt catalyst to obtain ethylene monothiocarbonate monothiocarboxylate.

[0007] According to US3517029, monothioalkyl carbonates are obtained by reacting mercaptoethanol with a diester in the presence of a catalytically active thorium salt. Thorium is a rare and expensive element. Any use of thorium in commercial production appears problematic due to its radioactivity.

[0008] US3201416 discloses a method using 2-hydroxyethyl alkyl thiocarbonate as a starting material. The 2-hydroxyethyl alkyl thiocarbonate undergoes intramolecular transesterification to yield ethylene monothiocarbonate. The method is carried out in the presence of a metal salt as a catalyst. The metal salt is selected from a list of metals, particularly those from Groups IIIb and IVb of the periodic table.

[0009] The object of this invention is to provide a method for preparing monothiocarbonates on an industrial scale. This method should not involve expensive or poorly available raw materials. The method should be easy to implement, as economical as possible, and yield monothiocarbonates in high yield and selectivity.

[0010] Therefore, a method for preparing compounds having at least one monothiocarbonate group has been discovered.

[0011] Compounds having at least one monothiocarbonate group

[0012] The monothiocarbonate group is preferably a five-membered ring monothiocarbonate group. A five-membered ring monothiocarbonate group is a ring system with 5 members, three of which come from the monothiocarbonate group -OC(=O)-S-, and the other two members are carbon atoms used to close the five-membered ring.

[0013] Preferably, the compound having at least one monothiocarbonate group contains 1-5, more preferably 1-2, monothiocarbonate groups, particularly 1 monothiocarbonate group.

[0014] In the most preferred embodiment, the compound having at least one monothiocarbonate group is a compound of formula I:

[0015]

[0016] Where R 1 To R 4 Each of the above can independently represent hydrogen or an organic group having up to 50 carbon atoms, where R 2 and R 4 and R 2 and R 4 The two bonded carbon atoms can form a ring system.

[0017] In any R 1 To R 4 When referring to an organic group, the organic group is preferably an organic group having at most 30 carbon atoms. In a preferred embodiment, the organic group does not contain an additional monothiocarbonate group. The organic group may contain elements other than carbon and hydrogen. In particular, it may contain oxygen, nitrogen, sulfur, and chlorine, for example in the form of ethers, hydroxyl groups, aldehydes, ketones, or carboxyl groups, thioethers, or amino groups.

[0018] The preferred organic group is an aliphatic organic group having up to 30 carbon atoms, which may contain oxygen.

[0019] Particularly preferred organic groups are alkyl groups or groups having 1-30 carbon atoms, such as -CH2-OR. 7 Or -CH2-OC(=O)-R 8 or -CH2-NR 9 R 10 , where R 7 To R 10 It is an organic group having at most 30 carbon atoms, preferably at most 20 carbon atoms. Specifically, R 7 To R 10 This represents an aliphatic or aromatic group, which may contain oxygen, for example, in the form of an ether group. In a preferred embodiment, R 7 To R 10 Indicates alkyl, alkoxy, or polyalkoxy. In the most preferred embodiment, R7 To R 10 Indicates alkyl group.

[0020] R 2 and R 4 and R 2 and R 4 The two bonded carbon atoms can form a ring system, such as a five- or six-membered ring system. The carbon atoms in the ring system can have substituents, such as alkyl or carboxyl groups, or carboxylic acid or carboxylic acid ester groups.

[0021] In a preferred embodiment, R of formula I 1 To R 4 Two, three, or all four of them represent hydrogen, and the remaining groups R 1 To R 4 It represents an organic group.

[0022] Most preferably, R of formula I 1 To R 4 In R, three or all four represent hydrogen. 1 To R 4 The remaining groups represent organic groups.

[0023] In the most preferred embodiment, R 1 To R 4 All four of them are hydrogen.

[0024] reactants

[0025] Compounds having at least one thiol group preferably contain 1-5, more preferably 1-2, and especially 1 thiol group.

[0026] Examples of compounds having more than one thiol group are compounds of formula IIa:

[0027]

[0028] Where m is at least 2, preferably an integer between 2 and 5, and R is an m-valent organic group.

[0029] Most preferably, the compound having at least one thiol group is a compound of formula IIb:

[0030]

[0031] Where R 1 To R 4 It has the above-mentioned meaning and the above-mentioned preferred meaning.

[0032] Therefore, in the most preferred embodiment, the compound of formula II is mercaptoethanol (R... 1 To R 4 It is hydrogen.

[0033] Dialkyl carbonates are preferably compounds of formula III:

[0034]

[0035] Where R 5 and R 6 They can be independent of each other and represent non-aromatic hydrocarbon groups with 1-10 carbon atoms or can be together to form alkylene bridges containing 2-9 carbon atoms.

[0036] Preferably, R 5 and R 6 They can be represented independently as non-aromatic hydrocarbon groups with 1-4 carbon atoms or together as alkylene bridges with 2 or 3 carbon atoms, which are ethylene or propylene bridges.

[0037] In the most preferred embodiment, R 5 and R 6 All are alkyl groups, especially ethyl groups. Therefore, in the most preferred embodiment, the dialkyl carbonate of formula III is diethyl carbonate.

[0038] A mixture of different dialkyl carbonates and / or diene carbonates can be used.

[0039] catalyst

[0040] The catalyst is a salt of a metal selected from Group IIIb or IVb of the periodic table.

[0041] Salts of scandium or titanium are preferred, especially those of titanium.

[0042] The anions in a salt can be inorganic or organic anions.

[0043] Suitable inorganic anions include, for example, anions with sulfur atoms such as sulfate, or anions with phosphorus atoms such as phosphate, anions with nitrogen atoms such as nitrate, or halide ions such as chloride. Preferred inorganic anions are halide ions. Most preferred are chloride ions.

[0044] Suitable organic anions are particularly those having up to 20 carbon atoms, preferably up to 10 carbon atoms. The anion may contain heteroatoms in nonionic form, such as oxygen in the form of ether or aldehyde, sulfur in the form of thioether, and nitrogen in the form of amino.

[0045] Preferably, the organic anion is a monohydric alcohol, dihydric alcohol, trihydric alcohol, monocarboxylic acid, dicarboxylic acid, or 1,3-dicarbonylenol, especially an acetylacetonate.

[0046] The monohydric alcohol radical, dihydric alcohol radical, or trihydric alcohol radical can be aliphatic or aromatic alcohol radicals.

[0047] In particular, the monohydric alcohol radical is an aliphatic alcohol radical, such as R 11 -O-, where R 11 It is an organic group having 1-20 carbon atoms, and may contain the aforementioned heteroatoms in a nonionic form. In a preferred embodiment, R 11 It is C1-C 10 Alkyl group. Preferred alkyl groups are, for example, ethyl or isopropyl; the corresponding anions are ethoxide or isopropanol.

[0048] Specifically, the binary or trihydric alcohol radical is of formula R 12 (-O-) n aliphatic alcohols, of which R 12 It is a divalent or trivalent organic group having 1-20 carbon atoms, where n is 2 or 3, and it may contain the aforementioned heteroatoms in a nonionic form. In a preferred embodiment, it is a diol group, wherein R 12 It is C1-C 10 Alkylene.

[0049] Monocarboxylic acid ions, dicarboxylic acid ions, or tricarboxylic acid ions can be aliphatic or aromatic carboxylic acid ions.

[0050] In particular, monocarboxylate ions are aliphatic carboxylate ions, such as R 13 -(C=O)-O-, where R 13 It is an organic group having 1-20 carbon atoms, which may contain the aforementioned heteroatoms in a nonionic form. In a preferred embodiment, R 13 It is C1-C 10 Alkyl group. Preferred alkyl groups are, for example, ethyl or isopropyl; the corresponding anions are acetate or isopropionate.

[0051] In particular, the dicarboxylic acid group or tricarboxylic acid group is an aliphatic carboxylic acid group, such as hydrogen oxalate or of formula R. 14 (-(C=O)-O - ) m The compound in which R 14 It is a di- or trivalent organic group having 1-20 carbon atoms, m is 2 or 3, and it may contain the aforementioned heteroatoms in nonionic form. As a preferred example of a tricarboxylic acid group, citrate is mentioned. In a further preferred embodiment, m is 2, R 14 It is C1-C 10 Alkylene. Preferred alkylene compounds are, for example, ethylene or butylene.

[0052] The preferred salt is a titanium salt having anion selected from halide ions, alkoxides or carboxylate ions.

[0053] The preferred salts are titanium alkoxides, especially titanium tetraisopropoxide.

[0054] reaction

[0055] Compounds having at least one thiol group and dialkyl carbonates can react in any molar ratio. To avoid excessive unreacted compounds, the preferred molar ratio of the thiol group to the dialkyl carbonate is preferably 0.5:1 to 1:0.5, particularly 0.7:1 to 1:0.7.

[0056] The amount of catalyst used can be, for example, 0.0001-0.2 mol of catalyst per mol of thiol groups. Preferably, the amount of catalyst used is 0.001-0.05 mol per mol of thiol groups. In the most preferred embodiment, the amount of catalyst used is 0.005-0.05 mol per mol of thiol groups.

[0057] Compounds having at least one thiol group and dialkyl carbonates can react at elevated temperatures, such as 50-150°C, particularly 80-140°C. The reaction can be carried out under decreasing or increasing pressure. The reaction is typically carried out at atmospheric pressure. An alcohol is given as a byproduct in the reaction. The alcohol is R... 5 -OH,R 6 -OH. Preferably, the alcohol is removed by distillation during the reaction.

[0058] Since at least one of the raw materials is typically a liquid, no additional solvent is required. However, a solvent may be used if necessary. Suitable solvents include, for example, aromatic compounds, toluene, xylene, ethers, polyethers such as glycol dimethyl ether, dimethylformamide, THF, dioxane, acetonitrile, and dimethyl sulfoxide.

[0059] The reaction can be monitored, for example, by gas chromatography. Once the starting materials have been consumed to a certain level, the reaction mixture can be cooled to room temperature and the reaction stopped. The resulting product mixture can be post-processed using conventional methods. In particular, the product mixture can be distilled under vacuum to separate and purify the obtained monothiocarbonate compounds.

[0060] The above method is a very economical and efficient approach, and is well-suited for industrial-scale preparation. It does not involve low-availability raw materials such as thorium. This method yields compounds with monothiocarbonate groups in very high yields and with high selectivity. Example

[0061] Example 1: Tetraisopropoxide Titanium Catalyst

[0062] Tetraisopropoxide titanium (2.27 g, 0.008 mol) was placed in a 400 mL four-necked round-bottom flask equipped with a magnetic stir bar, dropping funnel, thermometer, and reflux condenser. The reaction apparatus was purged with an inert gas, and then diethyl carbonate (118.13 g, 1 mol) was added to the catalyst at room temperature. Mercaptoethanol (59.38 g, 0.76 mol) was slowly added over 15 minutes at room temperature. The bright orange solution was heated to 110–130 °C, during which time the ethanol was removed from the reaction mixture by distillation. The reaction was monitored by gas chromatography. After approximately 11 hours, when the residual mercaptoethanol was determined to be less than 1% by the peak area of ​​the gas chromatography, the reaction mixture was cooled to room temperature. The reaction mixture was then subjected to vacuum fractionation at 4 mbar and 45–90 °C to obtain a monothiocarbonate fraction with a purity >98%. The yield of monothiocarbonate was determined by comparing the peak area of ​​the thiocarbonate peak in gas chromatography with the total area of ​​all peaks (total count). The selectivity of monothiocarbonate was determined by comparing the peak area of ​​the thiocarbonate peak with the area of ​​all peaks except the peak of mercaptoethanol, the starting material.

[0063] Examples 2-5

[0064] Repeat Example 1, but replace titanium tetraisopropoxide with the same amount (in mol) of other catalysts listed in the table.

[0065] Table: Yields and selectivity of monothiocarbonates in Examples 1-6

[0066]

Claims

1. A method for preparing a compound having at least one monothiocarbonate group, wherein the following substances are reacted in the presence of a catalyst: - Compounds having at least one thiol group, and -Dialkyl carbonate, The catalyst is a salt of a metal selected from Group IIIb or IVb of the periodic table; The compounds having at least one monothiocarbonate group are those of formula I: Where R 1 To R 4 It represents hydrogen; The compound having at least one thiol group is mercaptoethanol; Dialkyl carbonate is a compound of formula III: Where R 5 and R 6 This indicates a non-aromatic hydrocarbon group having 1-4 carbon atoms or forming an alkylene bridge containing 2 or 3 carbon atoms, wherein the non-aromatic hydrocarbon group is an alkyl group and the alkylene bridge is an ethylene or propylene bridge; The catalyst is a titanium salt, and the anion of the salt is a halide, alkoxide, or carboxylate.

2. The method according to claim 1, wherein the dialkyl carbonate of formula III is diethyl carbonate.

3. The method according to claim 1, wherein the anion of the salt is an alkoxide.

4. The method according to claim 2, wherein the anion of the salt is an alkoxide.

5. The method according to any one of claims 1-4, wherein the catalyst is tetraisopropoxide titanium.

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