WO2021168072A1

WO2021168072A1 - Efficient and selective route for the synthesis of alkyl 2-benzoylbenzoate

Info

Publication number: WO2021168072A1
Application number: PCT/US2021/018516
Authority: WO
Inventors: Souvagya BISWAS; Ruth Figueroa; Muhunthan Sathiosatham
Original assignee: Dow Global Technologies Llc; Rohm And Haas Company
Priority date: 2020-02-20
Filing date: 2021-02-18
Publication date: 2021-08-26
Also published as: KR20220143880A; JP2023514166A; CN115279725A; EP4107143A1

Abstract

A method for preparing an alkyl 2-benzoylbenzoate comprising reacting a dialkyl phthalate with a Grignard reagent in the presence of an oxygenated solvent. The Grignard reagent may be selected from phenyl magnesium bromide, phenyl magnesium chloride, and phenyl magnesium iodide.

Description

EFFICIENT AND SELECTIVE ROUTE FOR THE SYNTHESIS OF ALKYL 2-

BENZOYLBENZOATE

FIELD OF THE INVENTION

[001] The present invention relates to a process for preparing alkyl 2- benzoylbenzoate.

BACKGROUND OF THE INVENTION

[002] Alkyl 2-benzoylbenzoates are typically prepared by a Friedel-Crafts reaction. For example, methyl 2-benzoylbenzoate(M2BB) is conventionally prepared by a Friedel-Crafts reaction of phthalic anhydride with benzene in the presence of a stoichiometric amount of Lewis acid followed by a second step esterification reaction. The esterification reaction may occur under acidic conditions with methanol in the presence of a strong acid (Vogel et. al. Practical Organic Chemistry, 5^th Ed. pp 1016). Alternatively, the esterification reaction may occur under basic conditions with iodomethane in the presence of a base (ChemCatChem 2017, 9, 3989-3996).

[003] Methyl 2-benzoylbenzoate can also be synthesized via a Palladium- catalyzed acylation chemistry between benzaldehyde and 2-halomethylbenzoate. However, this chemistry needs expensive transition metal catalysts and a stoichiometric amount of oxidant (J. Org. Chem. 2016, 81, 6409).

[004] Additionally, methyl 2-benzoylbenzoate could be potentially synthesized by a Suzuki coupling between the activated amide and corresponding boronic acid {Org. Process Res. Dev. 2018, 22, 1188).

[005] It would be desirable to develop a process for preparing an alkyl 2- benzoylbenzoates that can: (1) avoid the use of stoichiometric Lewis acid in production, (2) does not require use of toxic reagents and strong acids or bases, (3) can prepare an alkyl 2-benzoylbenzoate in single step operation, and/or (4) reduce the cost of manufacture.

[006] The present invention provides a process that addresses one or more of the problems with existing alkyl 2-benzoylbenzoate synthesis processes. SUMMARY OF THE INVENTION

[007] The present invention is directed to a process for preparing an alkyl 2- benzoylbenzoate.

[008] The process comprising reacting a dialkyl phthalate with a Grignard reagent selected from phenyl magnesium bromide, phenyl magnesium chloride, phenyl magnesium iodide, and phenyl lithium in the presence of an oxygenated solvent.

[009] Surprisingly, the selectivity of the reaction for an alkyl 2-benzoylbenzoate is very high and only minor quantities of the diketone byproduct are formed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 shows GC-FID data of the reaction of dimethyl phthalate with phenyl magnesium bromide for 16 hours according to an embodiment of the present invention.

[0011] FIG. 2 is a ¹H NMR spectrum of the product methyl 2-benzoylbenzoate according to an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0012] As used herein, the terms “a,” “an,” “the,” “at least one,” and “one or more” are used interchangeably. The terms “comprises,” “includes,” “contains,” and variations thereof do not have a limiting meaning where these terms appear in the description and claims. Thus, for example, a mixture that includes a polymerization inhibitor can be interpreted to mean that the mixture comprises at least one polymerization inhibitor.

[0013] As used herein, recitations of numerical ranges by endpoints includes all numbers subsumed in that range (e.g. 1 to 5 includes 1 , 1.5, 2, 2.75, 3, 3.80, 4, 5, etc.). For the purposes of the invention, it is to be understood, consistent with what one of ordinary skill in the art would understand, that a numerical range is intended to include and support all possible subranges that are included in that range. For example, the range from 1 to 100 is intended to convey from 1.1 to 100, from 1 to 99.99, from 1 .01 to 99.99, from 40 to 6, from 1 to 55, etc.

[0014] As used herein, the recitations of numerical ranges and/or numerical values, including such recitations in the claims, can be read to include the term “about.” In such instances, the term “about” refers to numerical ranges and/or numerical values that are substantially the same as those recited herein.

[0015] Unless stated to the contrary, or implicit from the context, all parts and percentages are based on weight and all test methods are current as of the filing date of this application. For purposes of United States patent practice, the contents of any referenced patent, patent application or publication are incorporated by reference in their entirety or its equivalent U.S. version is so incorporated by reference especially with respect to the disclosure of definitions (to the extent not inconsistent with any definitions specifically provided in this disclosure) and general knowledge in the art.

[0016] In the process of the present invention, an alkyl 2-benzoylbenzoate is prepared in a Grignard reaction, as shown in Formula (I) below. A dialkyl phthalate is reacted with a Grignard reagent in the presence of an oxygenated solvent.

(I)

[0017] In the dialkyl phthalate, R and R’ may be the same or different. Preferably, R and R’ are identical, as shown in Formula (II) below.

[0018] R and R’ may be independently selected from an alkyl group comprising 1 to 4 carbon atoms, such as, for example, a methyl group, an ethyl group, a propyl group, or a tert-butyl group. Preferably, R and R’ are independently selected from a methyl group and an ethyl group. More preferably, R and R’ are both methyl groups, and the product is methyl 2-benoylbenzoate, as shown in Formula (III) below.

[0019] The Grignard reagent may be selected from phenyl magnesium bromide, phenyl magnesium chloride, and phenyl magnesium iodide.

[0020] The Grignard reagent selectively reacts with one of the ester functionalities of the dialkyl phthalate to form an alkyl 2-benzoylbenzoate with an average 60% yield. When R and R’ are both methyl groups, the single step reaction is highly selective for methyl 2-benzoylbenzoate (12:1) and only minor quantities of byproduct (e.g., diketone) are formed. Little over-Grignard reaction was observed in the system on either the newly formed keto-carbonyl functionality or on the second ester functionality of the dimethyl phthalate.

[0021] The process of the present invention can be performed without the use of expensive reagents, additives, or ligands and provide significantly improved process yields compared to traditional two-step reactions.

[0022] Examples of the oxygenated solvent that may be used in the present invention include, but are not limited to, diethyl ether, 1 ,4-dioxane, tert-butyl methyl ether, tetrahydrofuran, and 2-methyl tetrahydrofuran.

[0023] The reaction is preferably run with an overall concentration of the oxygenated solvent of 0.2 to 1 .0 M.

[0024] Preferably, the reaction is carried out at a temperature ranging from -78°C to 150°C. More preferably, the reaction is carried out at a temperature ranging from - 40°C to 100°C. Even more preferably, the reaction is carried out at a temperature ranging from 0°C to 40°C. Preferably, the reaction is carried out for at least 1 hour, preferably at least 3 hours, and more preferably at least 12 hours.

[0025] The compounding ratio of dialkyl phthalate and the Grignard reagent is preferably in the range of 0.90 to 3.0 moles of the dialkyl phthalate per mole of the Grignard reagent, more preferably in the range of 1 .0 to 2.75 moles of the dialkyl phthalate per mole of the Grignard reagent, still more preferably in the range of 1.25 to 2.5 moles of the dialkyl phthalate per mole of the Grignard reagent, and even more preferably in the range of 1 .4 to 1 .6 moles of the dialkyl phthalate per mole of the Grignard reagent.

EXAMPLES

[0026] The following examples illustrate the present invention but are not intended to limit the scope of the invention.

EXAMPLE 1

[0027] A 3-neck 250 mL round bottom flask was charged with dimethyl phthalate (1 .0 equivalence) and tetrahydrofuran (cone. 0.2 M) under nitrogen atmosphere and phenyl magnesium chloride (1 .0 equivalence) was slowly added to the reaction mixture at -78 °C. The reaction was kept at -78 °C for an hour. After 2h, thin-layer chromatography (TLC) and gas chromatography-flame ionization detector (GC-FID) showed mostly starting material and the reaction was warmed up to 0 °C. The reaction was kept running at 0 °C for another 3 h. TLC showed product formation, but the majority was starting material. The reaction was slowly warmed up to room temperature and kept running for another 12 h. After that, the reaction was quenched by adding 1 N HCI solution to the reaction mixture. Diethyl ether was added and the reaction mixture was transferred to a separatory funnel. The organic layer was separated and the aqueous layer was further washed with diethyl ether. The organic layers were combined and dried over MgS04. The solvent was removed under reduced pressure to yield a brownish oil which was purified by silica gel chromatography (10%-25% ethyl acetate in hexane) to yield the product methyl 2-benzoylbenzoate (49% yield) and diketone product (6% yield).

EXAMPLE 2

[0028] A 3-neck 250 mL round bottom flask was charged with dimethyl phthalate (1 .0 equivalence) and tetrahydrofuran (cone. 0.2 M) under nitrogen atmosphere and phenyl magnesium bromide (1 .0 equivalence) was slowly added to the reaction mixture at -78 °C. The reaction was kept at -78 °C for an hour. After 2h, TLC and GC-FID showed mostly starting material and the reaction was warmed up to 0 °C. The reaction was kept running at 0 °C for another 3 h. TLC showed product formation, however the majority was still starting material. The reaction was slowly warmed up to 40 °C and kept running for another 12 h. After that, reaction was quenched by adding 1 N HCI solution to the reaction mixture. Diethyl ether was added and the reaction mixture was transferred to a separatory funnel. The organic layer was separated and the aqueous layer was further washed with diethyl ether. The organic layers were combined and dried over MgSC>4. The solvent was removed under reduced pressure to yield a brownish oil which was purified by silica gel chromatography (10%-25% ethyl acetate in hexane) to yield the product methyl 2-benzoylbenzoate (60% yield) and diketone product (5% yield).

EXAMPLE 3

[0029] Various experiments using techniques similar to those described above in Examples 1 and 2 were run to test Grignard reaction conditions with dimethyl phthalate. These experiments are summarized below in Table 1 . Representative GC-FID data of dimethyl phthalate reacted with phenyl magnesium bromide after 16 hours is shown in FIG. 1 .

Table 1 . Representative examples of Grignard reaction conditions with dimethyl phthalate

EXAMPLE 4

[0030] Phenyl magnesium bromide (45 ml, 135 mmol, 1 .05 equivalence) was dropwise added over a period of 30 mins to a THF solution (600 ml, 0.2 M) of dimethyl phthalate (25.0 g, 128.8 mmol, 1 equiv.) under nitrogen atmosphere at 0 °C and the reaction was slowly warmed up to room temperature followed by mild heating to 40 °C and kept running for 12 h. Reaction aliquots were taken at 6 h and 12 h interval and the results are shown below on Table 2. At 12 h, the reaction was quenched with 1 N HCI solution and the organic layer was isolated from the aqueous layer. The organic layer was concentrated down and the concentrated material was diluted with diethyl ether and hexane (3X) was added to crash out the product (see Figure 2 for ¹H NMR). On the other hand, the aqueous layer was analyzed by UPLC- method and it showed very small amount of organic compound leached out on the aqueous layer.

Table 2. Results of the Grignard reaction with dimethyl phthalate on 25g scale

EXAMPLE 5

[0031] A 1000 ml round bottom flask equipped with overhead stirrer, ice-bath, addition funnel, dry nitrogen inlet was charged with dimethyl phthalate (100 g, 0.51 mole) and cooled down to -10 °C. To the addition funnel was added phenyl magnesium bromide (250 g of 16 wt. % solution, 0.22 mole). To the cold dimethyl phthalate, phenyl magnesium bromide was added over a 75 minute period from the addition funnel while maintaining the reactor temperature at -10 °C. The contents of reaction mixture were stirred at -10 °C for 30 minutes. During this time period the addition funnel was charged with aqueous hydrochloric acid solution (247 g of 12 wt. % solution). After the 30 minute hold the hydrochloric acid solution was added to the reaction mixture at -10 °C over a 30 minute period from the addition funnel. The reactor contents were allowed to warm to ambient temperature and organic layer was separated with an aid of a separatory funnel. Organic layer was dried anhydrous sodium sulfate and analyzed by ¹³C-NMR spectroscopic analysis. Selectivity for methyl 2-benzoylbenzoate was 93.5%.

Claims

We claim:

1. A process for preparing an alkyl 2-benzoylbenzoate, comprising: reacting a dialkyl phthalate with a Grignard reagent in the presence of an oxygenated solvent, wherein the Grignard reagent is selected from phenyl magnesium bromide, phenyl magnesium chloride, and phenyl magnesium iodide.

2. The method according to claim 1 , wherein the dialkyl phthalate is selected from dimethyl phthalate, diethyl phthalate, dipropyl phthalate, and bi-tert-butyl phthalate.

3. The method accord to claim 2, wherein the dialkyl phthalate is selected from dimethyl phthalate.

4. The method according to claim 1 , wherein the wherein the oxygenated solvent is selected from diethyl ether, tert-butyl methyl ether, 1 ,4-dioxane, tetrahydrofuran, and 2-methyl tetrahydrofuran.

5. The method according to any one of the preceding claims, wherein the reaction is carried out at a temperature ranging from -78°C to 150°C.

6. The method according to claim 5, wherein the reaction is carried out at a temperature ranging from -40°C to 100°C.

7. The method according to any of the preceding claims, wherein the dialkyl phthalate is present in an amount ranging from 0.9 to 3.0 moles of the dialkyl phthalate per mole of the Grignard reagent.

8. The method according to any of the preceding claims, wherein the oxygenated solvent is present in a concentration of 0.2 to 1 .0 M.

9. The method according to any of the preceding claims, wherein the reaction is run for at least 1 hour.

10. The method according to claim 9, wherein the reaction is run for at least 12 hours.