Description:TECHNICAL FIELD
[0001] The present disclosure generally relates to production of acetates. More particularly, the presently claimed invention relates to a facile solvent-free process for production of acetates by reacting 1,3-diketones with alcohols in presence of a heterogeneous catalyst.

BACKGROUND
[0002] Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
[0003] Acetates of primary and secondary alcohols are important class of esters having numerous applications in paints, varnishes, lacquers, cleaning mixtures, and perfumes. Moreover, they are also used as solvent in ink and pharmaceutical industries as well as additives for biofuels. For example, n-butyl acetate and iso-isobutyl acetate are indispensable for coating applications. Similarly, iso-isopropyl acetate is a common solvent for printing ink and an important component for preparing perfumes. Other common acetates having tremendous industrial demand include 2-ethylhexyl acetate (emulsion paint), vinyl acetate (adhesive applications) and ethyl acetate (solvent).
[0004] Mostly industrial production of acetates involves esterification of alcohol with acetic acid in presence of an acid catalyst such as sulphuric acid (homogeneous). Unfortunately, the said process is strongly corrosive thus making this process environmentally problematic. Therefore, alternative synthetic pathways towards acetates and other esters using “green” technologies are to be developed for commercial scale production.
[0005] In recent years, the retro-Claisen condensation of alcohol with acetyl acetone has received significant attention as a viable alternative to Fischer’s esterification to produce acetates in high yields with complete selectivity. Significant progress was achieved when Yoichiro Kuninobu, and Kazuhiko Takai reported the first example of indium triflate catalyzed synthesis of esters (including acetates) via retro-Claisen condensation of 2,4-pentanedione with 2-phenylethanol (Angew. Chem. Int. Ed., 2007, 46, 7793 –7795). Other metal triflates (Chem. – Asian J., 2010, 5, 941–945) as well as lewis acids based on Fe(III) (Eur. J. Org. Chem., 2010, 15, 2861–2866) and Ag(I) (Chem. – Eur. J., 2016, 22, 4189–4195) have also been reportedly found to be efficient catalysts for the same transformation.
[0006] Although several elegant homogeneous catalytic systems based on transition metal catalysts have been reported, these catalysts faces challenges in separation of the final product from the catalyst contaminants. Moreover, some of the transition metal catalysts, particularly metal triflate or Pd(0) or even Ag(I) are expensive and hence, not commercially viable.
[0007] All publications herein are incorporated by reference to the same extent as if each individual publication or patent application were specifically and individually indicated to be incorporated by reference. Where a definition or use of a term in an incorporated reference is inconsistent or contrary to the definition of that term provided herein, the definition of that term provided herein applies and the definition of that term in the reference does not apply.

SUMMARY
[0008] The present disclosure generally relates to production of acetates. More particularly, the presently claimed invention relates to a facile solvent-free process for production of acetates by reacting 1,3-diketone with alcohol in presence of a heterogeneous catalyst.
[0009] The present disclosure is on the premise of surprising observation by inventors of the present application that the reaction between 1,3-diketone and an alcohol is very selective to the specific heterogeneous catalysts, more particularly, to heterogeneous catalysts selected from: Zirconium oxychloride octahydrate, and an acidic cation exchange polymeric resin. It was surprising to note that other Zirconium based catalysts such as Zirconyl nitrate hydrate or Zirconium oxide failed to afford desired yield of the acetate. Similarly, acidic zeolites such as H-beta-zeolite, Y-zeolite, H-ZSM-5 and nano-ZSM5, and Acidic clay such as Montmorillonite K-10 also failed to afford desired yield of the acetate. Also surprising was the observation that – if the reaction is conducted in presence of a solvent, it fails to afford the desired yield.
[0010] Accordingly, an aspect of the present disclosure relates to a process for preparation of an acetate, said process comprising: contacting a 1,3-diketone with an alcohol in presence of a heterogeneous catalyst at a temperature ranging from 80 to 110°C to obtain the acetate, said heterogeneous catalyst being selected from: Zirconium oxychloride octahydrate, and an acidic cation exchange polymeric resin, and said process being carried out in a solvent-free condition.
[0011] In some embodiments, the acidic cation exchange polymeric resin comprises a polystyrene based ion exchange resin with sulfonic group. In some embodiments, the catalyst is Zirconium oxychloride octahydrate, wherein the catalyst is present in an amount ranging from 3 to 7 mol%. In some embodiments, the catalyst is acidic cation exchange polymeric resin, wherein the catalyst is present in an amount ranging from 15 mg to 35 mg per millimole of the alcohol. In some embodiments, the reaction is conducted for a time period ranging from about 15 hours to about 18 hours. In some embodiments, the 1,3-diketone is acetyl acetone. In some embodiments, the alcohol is selected from: a C1-C12 straight chain or branched aliphatic alcohol, a cyclic aliphatic alcohol, an aryl alcohol, and a heteroaryl alcohol.
[0012] Various objects, features, aspects and advantages of the inventive subject matter will become more apparent from the following detailed description of preferred embodiments.

BRIEF DESCRIPTION OF DRAWINGS
[0013] Fig. 1 illustrates an exemplary graph showing reusability of the heterogeneous catalyst (zirconium oxychloride octahydrate) in accordance with embodiments of the present disclosure.

DETAILED DESCRIPTION
[0014] The following is a detailed description of embodiments of the present invention. The embodiments are in such detail as to clearly communicate the invention. However, the amount of detail offered is not intended to limit the anticipated variations of embodiments; on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.
[0015] Each of the appended claims defines a separate invention, which for infringement purposes is recognized as including equivalents to the various elements or limitations specified in the claims. Depending on the context, all references below to the “invention” may in some cases refer to certain specific embodiments only. In other cases it will be recognized that references to the “invention” will refer to subject matter recited in one or more, but not necessarily all, of the claims.
[0016] Groupings of alternative elements or embodiments of the invention disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience and/or patentability.
[0017] Unless the context requires otherwise, throughout the specification which follow, the word “comprise” and variations thereof, such as, “comprises” and “comprising” are to be construed in an open, inclusive sense that is as “including, but not limited to.” It is to be appreciated that the terms "comprising", "comprises" and "comprised of" as used herein includes the terms "consisting of", "consists" and "consists of" within their meaning.
[0018] Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments.
[0019] As used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. Also, as used in the description herein, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise.
[0020] In some embodiments, the numbers expressing quantities of ingredients, properties such as concentration, and so forth, used to describe and claim certain embodiments of the invention are to be understood as being modified in some instances by the term “about.” Accordingly, in some embodiments, the numerical parameters set forth in the written description are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the invention are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable.
[0021] The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
[0022] The headings and abstract of the invention provided herein are for convenience only and do not interpret the scope or meaning of the embodiments.
[0023] All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the invention and does not pose a limitation on the scope of the invention otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the invention.
[0024] The following discussion provides many example embodiments of the inventive subject matter. Although each embodiment represents a single combination of inventive elements, the inventive subject matter is considered to include all possible combinations of the disclosed elements. Thus if one embodiment comprises elements A, B, and C, and a second embodiment comprises elements B and D, then the inventive subject matter is also considered to include other remaining combinations of A, B, C, or D, even if not explicitly disclosed.
[0025] Various terms as used herein are shown below. To the extent a term used in a claim is not defined below, it should be given the broadest definition persons in the pertinent art have given that term as reflected in printed publications and issued patents at the time of filing.
[0026] The presently claimed invention relates to production of acetates. More particularly, the presently claimed invention relates to a facile solvent-free process for production of acetates by reacting 1,3-diketones with alcohols in presence of a heterogeneous catalyst.
[0027] An aspect of the present disclosure relates to a process for preparation of an acetate, said process comprising: contacting a 1,3-diketone with an alcohol in presence of a heterogeneous catalyst at a temperature ranging from 80 to 110°C to obtain the acetate, said heterogeneous catalyst being selected from: Zirconium oxychloride octahydrate, and an acidic cation exchange polymeric resin, and said process being carried out in a solvent-free condition.
[0028] In some embodiments, the catalyst (heterogeneous catalyst) is Zirconium oxychloride octahydrate and it is present in an amount ranging from 3 to 7 mol%, for example, from about 3 to about 6 mol%, or from about 4 to about 6 mol%, or from about 4.5 to about 5.5 mol%. In a preferred embodiment, Zirconium oxychloride octahydrate is present in an amount of about 5 mol%.
[0029] In some embodiments, the acidic cation exchange polymeric resin comprises a polystyrene based ion exchange resin with sulfonic group. Exemplary polystyrene based ion exchange resin with sulfonic group includes, but not limited to, Amberlyst™ 15, Tulsion® 6812 and Tulsion® 8052. In some embodiments, the acidic cation exchange polymeric resin is selected from Amberlyst™ 15, Tulsion® 6812 and Tulsion® 8052.
[0030] In some embodiments, the catalyst (heterogeneous catalyst) is an acidic cation exchange polymeric resin and it is present in amount ranging from 15 mg to 35 mg per millimole of the alcohol, for example, from about 15 mg to about 30 mg per millimole of the alcohol, or from about 20 mg to about 30 mg per millimole of the alcohol, or from about 22 mg to about 30 mg per millimole of the alcohol. In a preferred embodiment, the acidic cation exchange polymeric resin is present in an amount of about 25 mg per millimole of the alcohol.
[0031] In some embodiments, the catalyst (heterogeneous catalyst) is a polystyrene based ion exchange resin with sulfonic group and it is present in amount ranging from 15 mg to 35 mg per millimole of the alcohol, for example, from about 15 mg to about 30 mg per millimole of the alcohol, or from about 20 mg to about 30 mg per millimole of the alcohol, or from about 22 mg to about 30 mg per millimole of the alcohol. In a preferred embodiment, the polystyrene based ion exchange resin with sulfonic group is present in an amount of about 25 mg per millimole of the alcohol.
[0032] While any other 1,3-diketone as known to a person skilled in the art, it is preferred that the 1,3-diketone is acetyl acetone.
[0033] In some embodiments, the reaction is conducted for a time period ranging from about 13 hours to about 20 hours, for example, from about 14 hours to about 20 hours, or from about 13 hours to about 18 hours, or from about 15 hours to about 18 hours. In a preferred embodiment, the reaction is conducted for a time period ranging from about 15 hours to about 18 hours.
[0034] In some embodiments, the alcohol is selected from: a C1-C12 straight chain or branched aliphatic alcohol, a cyclic aliphatic alcohol, an aryl alcohol, and a heteroaryl alcohol. Exemplary alcohols that are suitable for the process of the present disclosure are structurally represented below:

[0035] In some embodiments, the alcohol is any of a primary alcohol and a secondary alcohol. In some embodiments, the alcohol is selected from: 1-butanol, iso-butanol, 2-ethyl hexanol, iso-propanol and 1-dodecanol.
[0036] In some embodiments, the 1,3-diketone is contacted with the alcohol in presence of the heterogeneous catalyst at a temperature of about 100°C for a time period ranging from about 15 hours to about 18 hours, said catalyst being present in an amount of about 5 mol% when the catalyst is Zirconium oxychloride octahydrate, or said catalyst being present in an amount of about 25 mg per millimole of the alcohol when the catalyst is the acidic cation exchange polymeric resin (e.g. a polystyrene based ion exchange resin with sulfonic group).
[0037] While the foregoing description discloses various embodiments of the disclosure, other and further embodiments of the invention may be devised without departing from the basic scope of the disclosure. The invention is not limited to the described embodiments, versions or examples, which are included to enable a person having ordinary skill in the art to make and use the invention when combined with information and knowledge available to the person having ordinary skill in the art.
EXAMPLES
[0038] The presently claimed invention is illustrated by the non-restrictive examples which are as follows:
[0039] Example 1: To a mixture of 1-butanol (185µL, 2 mmol) and acetyl acetone (225 µL, 2.2 mmol) was added zirconium oxychloride octahydrate (5 mol%, 33 mg) at room temperature. The mixture was stirred at 100 °C for 16 hours. The solid catalyst was separated by filtration to obtain the butyl acetate in 96% yield.
[0040] Example 2: To a mixture of 1-butanol (185µL, 2 mmol) and acetyl acetone (225 µL, 2.2 mmol) was added Amberlyst-15 (50 mg) at room temperature. The mixture was stirred at 100 °C for 16 hours. The solid catalyst was separated by filtration to obtain the butyl acetate in 99% yield.
[0041] Example 3: To a mixture of 1-butanol (185µL, 2 mmol) and acetyl acetone (225 µL, 2.2 mmol) was added Tulsion T-6812 (50 mg) at room temperature. The mixture was stirred at 100 °C for 16 hours. The solid catalyst was separated by filtration to obtain the butyl acetate in 97% yield.
[0042] Example 4: To a mixture of iso-butanol (185 µL, 2 mmol) and acetyl acetone (225 µL, 2.2 mmol) was added zirconium oxychloride octahydrate (33 mg) at room temperature. The mixture was stirred at 100 °C for 16 hours. The solid catalyst was separated by filtration to obtain the iso-butyl acetate in 97% yield.
[0043] Example 5: To a mixture of iso-butanol (185 µL, 2 mmol) and acetyl acetone (225 µL, 2.2 mmol) was added Amberlyst-15 (50 mg) at room temperature. The mixture was stirred at 100 °C for 16 hours. The solid catalyst was separated by filtration to obtain the iso-butyl acetate in 99% yield.
[0044] Example 6: To a mixture of 2-ethyl hexanol (313 µL, 2 mmol) and acetyl acetone (225 µL, 2.2 mmol) was added zirconium oxychloride octahydrate (33 mg) at room temperature. The mixture was stirred at 100 °C for 16 hours. The solid catalyst was separated by filtration to obtain the 2-ethylhexyl acetate in 94% yield.
[0045] Example 7: To a mixture of 2-ethyl hexanol (313 µL, 2 mmol) and acetyl acetone (225 µL, 2.2 mmol) was added Amberlyst-15 (50 mg) at room temperature. The mixture was stirred at 100 °C for 16 hours. The solid catalyst was separated by filtration to obtain the 2-ethylhexyl acetate in 98% yield.
[0046] Example 8: To a mixture of iso-propanol (155 µL, 2 mmol) and acetyl acetone (225 µL, 2.2 mmol) was added Amberlyst-15 (50 mg) at room temperature. The mixture was stirred at 100 °C for 24 hours. The solid catalyst was separated by filtration to obtain the iso-propyl acetate in 94% yield.
[0047] Example 9: To a mixture of 1-dodecanol (450 µL, 2 mmol) and acetyl acetone (225 µL, 2.2 mmol) was added Amberlyst-15 (50 mg) at room temperature. The mixture was stirred at 100 °C for 16 hours. The solid catalyst was separated by filtration to obtain the dodecyl acetate in 95% yield.
[0048] The reaction between 1-heptanol (2 mmol) and acetyl acetone (2.2 mmol) was carried out in presence of different heterogeneous catalysts in a sealed vial at varying temperatures, reaction times and amounts of the catalyst, details whereof are provided in Tables 1-3 below:

Table 1: Effect of variation of the catalyst and catalyst amounts
Acid catalyst Cat. amount
(mol % / mg) Temp. (oC) Time (h) Yieldb (%)
ZrO(NO3)2·xH2O 5 mol % 100 16 62
ZrOCl2.8H2O 5 mol % 100 16 97
ZrO2 5 mol % 100 16 0
Nb2O5 5 mol % 100 16 0
CeO2 5 mol % 100 16 2
H3PW12O40 5 mol % 100 16 53
Amberlyst-15 50 mg 100 16 98
H-beta (Si/Al:12.5) 50 mg 100 16 49
H-ZSM-5 (Si/Al:15) 50 mg 100 16 1
H-ZSM-5 (Si/Al:40) 50 mg 100 16 3
Nano-ZSM-5 (Si/Al:40) 50 mg 100 16 4
HY (Si/Al:2.6) 50 mg 100 16 8
NaY (Si/Al:2.6) 50 mg 100 16 0
Tulsion-8052 50 mg 100 16 85
Tulsion-6812 50 mg 100 16 94
Montmorilonite K-10 50 mg 100 16 7
Amberlyst-15 25 mg 100 16 73
Amberlyst-15 75 mg 100 16 98
b Note: Indicates isolated yield
Table 2: Effect of variation of reaction temperature and time
Acid catalyst Cat. amount
(mol % / mg) Temp. (oC) Time (h) Yieldb (%)
Amberlyst-15 50 mg 80 24 89
Amberlyst-15 50 mg 60 16 58
Amberlyst-15 50 mg rt 24 6
No catalyst 50 mg 100 16 0
Amberlyst-15 50 mg 100 4 84
Amberlyst-15 50 mg 100 8 90
Amberlyst-15 50 mg 100 12 96
b Note: Indicates isolated yield

Table 3: Effect of variation of reaction temperature, solvent and catalyst amount
Acid catalyst Cat. amount
(mol % / mg) Solvent Temp. (oC) Yieldb (%)
ZrOCl2 5 Toluene 100 45
ZrOCl2 5 DCE 100 24
ZrOCl2 5 THF 100 21
ZrOCl2 5 1,4 Dioxane 100 48
ZrOCl2 5 Acetonitrile 100 10
ZrOCl2 5 Chlorobenzene 100 16
ZrOCl2 5 Neat (Solvent Free) 100 98
ZrOCl2 5 Neat 60 21
ZrOCl2 5 Neat 80 55
ZrOCl2 2.5 Neat 100 81
ZrOCl2 7.5 Neat 100 99
b Note: Indicates isolated yield
[0049] For assessing reusability of the heterogeneous catalyst, the crude product mixture was filtered post completion of the reaction to separate the catalyst. The catalyst so obtained was then reused for conducting another batch of the reaction. It could be noted that the heterogeneous catalyst i.e. zirconium oxychloride octahydrate could be used again without significant loss of activity. Fig. 1 illustrates an exemplary graph showing yields of the product/acetate upon reusing zirconium oxychloride octahydrate upto 5 cycles. Accordingly, it could be concluded that the process of the present disclosure further dramatically reduces the costs of catalyst in comparison to conventional process(es) utilizing the homogeneous catalyst(s).

ADVANTAGES
[0050] The present disclosure provides a process for preparation of acetate that is economical and industrially applicable.
[0051] The present disclosure provides a process for preparation of acetate that affords production of acetate in high yield.
[0052] The present disclosure provides a process for preparation of acetate that obviates the need of solvent, and which allows recycling of the catalyst.
, Claims:1. A process for preparation of an acetate, said process comprising:
contacting a 1,3-diketone with an alcohol in presence of a heterogeneous catalyst at a temperature ranging from 80 to 110°C to obtain the acetate,
said heterogeneous catalyst being selected from: Zirconium oxychloride octahydrate, and an acidic cation exchange polymeric resin, and
said process being carried out in a solvent-free condition.

2. The process as claimed in claim 1, wherein the catalyst is Zirconium oxychloride octahydrate, and wherein the catalyst is present in an amount ranging from 3 to 7 mol%.

3. The process as claimed in claim 1, wherein the acidic cation exchange polymeric resin comprises a polystyrene based ion exchange resin with sulfonic group.

4. The process as claimed in claim 3, wherein the catalyst is present in an amount ranging from 15 mg to 35 mg per millimole of the alcohol.

5. The process as claimed in any of the preceding claims, wherein the 1,3-diketone is acetyl acetone.

6. The process as claimed in any of the preceding claims, wherein the alcohol is selected from: a C1-C12 straight chain or branched aliphatic alcohol, a cyclic aliphatic alcohol, an aryl alcohol, a heteroaryl alcohol, and phenol.

7. The process as claimed in any of the preceding claims, wherein the 1,3-diketone is contacted with the alcohol in presence of the heterogeneous catalyst at a temperature of 100°C for a time period ranging from 15 hours to 18 hours, and wherein the catalyst is present in an amount of 5 mol% when the catalyst is Zirconium oxychloride octahydrate, or the catalyst is present in an amount of 25 mg per millimole of the alcohol when the catalyst is polystyrene based ion exchange resin with sulfonic group.