DESC:A novel catalyst for the synthesis of O-isopropylidene derivatives from sugars 

TECHNICAL FIELD
[0001]Embodiments are generally related to the field of chemistry and biochemistry. Embodiments are also related to the field of ordered mesoporous materials. Embodiments are further related to the process of acetonation of D-glucose using sulfonic acid modified mesoporous materials.
Background of the Invention
[0002]Sugars are key intermediates in biomass conversion and, in particular, D-glucose is one of the important sources for the production of wide range of value added chemicals, e.g., sorbitol, glucaric acid, etc. In this context, the protection of 1,2-diols of D-glucose as O-isopropylidene derivatives (acetonides) is critical in multi-step syntheses in organic, medicinal, and carbohydrate chemistry. In addition, monoacetonide derivatives are also well known for their anti-inflammatory and antipyretic activities with very low toxicity; therefore, become commercially demanding as a starting material for a diverse range of bioactive molecules such as antibiotics, cytotoxic, anti-inflammatory and antipyretic agents. In general, 1,2-monoacetone-D-glucose is produced in high yield by hydrolysis of diacetone-D-glucose using mineral acids and or enzymes.
[0003]The use of mineral acids has many regulatory barriers in India as per amended laws, which makes it difficult and inconvenient to procure and safeguard the same. Using enzymes for catalysis in industries could not be cost effective due to their high pricing and the use of microorganisms and biotechnological method which could be lengthy processes. Therefore, the development of environmentally benign and recyclable heterogeneous catalysts is of paramount importance.
[0004]In view of the above, sulfonic acid functionalized ordered mesoporous silicas, designated as RSO3H-OMS; R = alkyl/aryl, are suggested to be possible catalysts for D-glucose acetonation reaction as they are water tolerant (imparted by functionalized organic moiety); possesses high acid strengths which allows greater selectivity for the products; large and uniform pores with high surface areas that permit bulky molecules to enter the active sites; high thermal and hydrothermal stabilities offers greater flexibility in terms of reusability.

summary of the Invention
[0005]The following summary is provided to facilitate an understanding of some of the innovative features unique to the disclosed embodiment and is not intended to be a full description. A full appreciation of the various aspects of the embodiments disclosed herein can be gained by taking the entire specification, claims, drawings, and abstract as a whole.
[0006]One aspect of the disclosed embodiments is to provide a stable and recyclable catalyst for the synthesis of O-isopropylidene derivatives from sugars.
[0007]Another aspect of the disclosed embodiments to is to provide an improved process for the synthesis of O-isopropylidene derivatives from sugars using the said catalyst.
[0008]The aforementioned aspects and other objectives and advantages can now be achieved as described herein. A series of sulfonic acid functionalized Ordered mesoporous silicates (OMS), i.e., RSO3H-MCM-41, RSO3H-IITM-56 and RSO3H-SBA-15 (R = CH2CH2CH3) were prepared by post-synthesis grafting method. In a typical manner, OMS were evacuated in a vacuum oven at 150°C for 5 h initially and then cooled down to room temperature; it was then suspended in 30 mL of dry toluene and 3-MPTMS ((3-mercaptopropyl) trimethoxy silane)) was added with OMS : 3-MPTMS (wt. ratio). The mixture was refluxed for 6 h at 110°C under N2 atmosphere. The obtained product was filtered and washed with excess dry toluene to remove unreacted 3-MPTMS present, if any, and dried at 60°C. The resulting thiol-functionalized OMS, viz., RSH-OMS, was refluxed for 20 h at 60°C with 30% H2O2 (in 2 mL methanol) and then cooled down to room temperature. To this mixture, 10 mL of 0.1 M H2SO4 was added and stirred for 4 h at room temperature for complete oxidation. The obtained product was then centrifuged, washed with water and ethanol. The solid material was ?nally dried at 60°C overnight to obtain the desired material, i.e., RSO3H-OMS. Likewise, a series of RSO3H-MCM-41 having MCM-41: 3-MPTMS (wt. ratio) of 1:0.125; 1:0.25; 1:0.5, and 1:1 were also prepared. In a similar way, sulfonic acid functionalized IITM-56 and SBA-15, i.e., RSO3H-IITM-56 and RSO3H-SBA-15, with optimized sulfonic acid loading of OMS: 3-MPTMS (wt. ratio) of 1:0.5 were also synthesized. We have also prepared a sample, designated as RSO3H-SBA-15(IS) with OMS: 3-MPTMS (wt. ratio) of 1: 0.125 loading, wherein the parent SBA-15 was prepared at 80°C instead of 100°C so as to generate large amount of weak acid sites/silanol groups. The catalysts so developed as above shows higher selectivity for converting o-isopropylidene derivatives from sugars.
[0009]The process proposed herein is an exemplary demonstration of working of the proposed concept of sulfonic acid functionalized ordered mesoporous materials The standards and operating protocol of the use of such proposed concept can be standardized and adapted by a person skilled in the art to achieve the same or enhanced results.

Brief description of drawings

[0010]The accompanying figures, in which like reference numerals refer to identical or functionally-similar elements throughout the separate views and which are incorporated in and form a part of the specification, further illustrate the present invention and, together with the detailed description of the invention, serve to explain the principles of the present invention.
[0011]FIG. 1 illustrates XRD patterns and TEM images of: (a,e) RSO3H-MCM-41; (b,f) RSO3H-IITM-56; (c,g) RSO3H-SBA-15; (d,h) RSO3H-SBA-15(IS).
[0012]FIG. 2 illustrates physico-chemical characteristics of OMS and RSO3H-OMS.
[0013]FIG. 3 illustrates acidity data and acetonation of D-glucose over RSO3H-OMS.

detailed description
[0014]The particular values and configurations discussed in these non-limiting examples can be varied and are cited merely to illustrate at least one embodiment and are not intended to limit the scope thereof.
[0015]The embodiments now will be described more fully hereinafter with reference to the accompanying drawings, in which illustrative embodiments of the invention are shown. The embodiments disclosed herein can be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.
[0016]The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.
[0017]Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0018]One embodiment of the invention of disclosing the sulfonic acid functionalization of the OMS can be achieved as disclosed herein. The disclosed process is also the best mode of achieving the same. A series of sulfonic acid functionalized OMS, i.e., RSO3H-MCM-41, RSO3H-IITM-56 and RSO3H-SBA-15 (R = CH2CH2CH3) were prepared by post-synthesis grafting method. In a typical manner, OMS were evacuated in a vacuum oven at 150°C for 5 h initially and then cooled down to room temperature; it was then suspended in 30 mL of dry toluene and 3-MPTMS was added with OMS : 3-MPTMS (wt. ratio). The mixture was refluxed for 6 h at 110°C under N2 atmosphere. The obtained product was filtered and washed with excess dry toluene to remove unreacted 3-MPTMS present, if any, and dried at 60°C. The resulting thiol-functionalized OMS, viz., RSH-OMS, was refluxed for 20 h at 60°C with 30% H2O2 (in 2 mL methanol) and then cooled down to room temperature. To this mixture, 10 mL of 0.1 M H2SO4 was added and stirred for 4 h at room temperature for complete oxidation. The obtained product was then centrifuged, washed with water and ethanol. The solid material was ?nally dried at 60°C overnight to obtain the desired material, i.e., RSO3H-OMS. Likewise, a series of RSO3H-MCM-41 having MCM-41: 3-MPTMS (wt. ratio) of 1:0.125; 1:0.25; 1:0.5, and 1:1 were also prepared. In a similar way, sulfonic acid functionalized IITM-56 and SBA-15, i.e., RSO3H-IITM-56 and RSO3H-SBA-15, with optimized sulfonic acid loading of OMS: 3-MPTMS (wt. ratio) of 1:0.5 were also synthesized. We have also prepared a sample, designated as RSO3H-SBA-15(IS) with OMS : 3-MPTMS (wt. ratio) of 1: 0.125 loading, wherein the parent SBA-15 was prepared at 80°C instead of 100°C so as to generate large amount of weak acid sites/silanol groups.
[0019]The embodiment consisting the process of achieving sulfonic acid functionalization of OMS can also be achieved with similar or enhanced results, as disclosed herein. A series of sulfonic acid functionalized OMS, i.e., RSO3H-MCM-41, RSO3H-IITM-56 and RSO3H-SBA-15 (R = CH2CH2CH3) were prepared by post-synthesis grafting method. In a typical manner, OMS were evacuated in a vacuum oven at 100-300°C for 5 h initially and then cooled down to room temperature; it was then suspended in 10-50 mL of dry toluene and 3-MPTMS was added with OMS : 3-MPTMS (wt. ratio). The mixture was refluxed for 3-9 h at 80-150°C under N2 atmosphere. The obtained product was filtered and washed with excess dry toluene to remove un-reacted 3-MPTMS present, if any, and dried at 40-80°C. The resulting thiol-functionalized OMS, viz., RSH-OMS, was refluxed for 15-25 h at 30-80°C with 20-40% H2O2 (in 2 -5mL methanol) and then cooled down to room temperature. To this mixture, approximately 10 mL of 0.1 - 0.2M H2SO4 was added and stirred for 4 - 6 h at room temperature for complete oxidation. The obtained product was then centrifuged, washed with water and ethanol. The solid material was ?nally dried at 30-70°C overnight to obtain the desired material, i.e., RSO3H-OMS. Likewise, a series of RSO3H-MCM-41 having MCM-41: 3-MPTMS (wt. ratio) of 1:0.125; 1:0.25; 1:0.5, and 1:1 were also prepared. In a similar way, sulfonic acid functionalized IITM-56 and SBA-15, i.e., RSO3H-IITM-56 and RSO3H-SBA-15, with optimized sulfonic acid loading of OMS: 3-MPTMS (wt. ratio) of 1:0.5 were also synthesized. We have also prepared a sample, designated as RSO3H-SBA-15(IS) with OMS : 3-MPTMS (wt. ratio) of 1: 0.125 loading, wherein the parent SBA-15 was prepared at 60-90°C so as to generate large amount of weak acid sites/silanol groups.
[0020]The other aspect of providing an improved process for the synthesis of O-isopropylidene derivatives from sugars using the said catalyst can be achieved as disclosed herein. The method has to be given here.
[0021]All the materials under study were systematically characterized by various analytical, spectroscopic and imaging techniques, viz., XRD, BET, TEM, 29Si MAS-NMR, FT-IR, XRF and NH3-TPD.
[0022]The bonding of 3-MPTMS with different types of silanol groups, viz., isolated, vicinal and geminal species, in OMS produce different acid sites. Sulfonic acid functionalized ordered mesoporous materials, viz., RSO3H-OMS, are found to be efficient for acetonation of D-glucose with high selectivity of diacetone-D-glucose owing to the presence of medium-to-strong acid sites. The maximum activity with selective formation of diacetone-D-glucose is achieved at an optimum loading of sulfonic acid, i.e., with a silica-to-3-MPTMS ratio of 1 : 0.5. SBA-15 can be tuned in such a way that it can produce weak acid sites. The product 1,2-monoacetone-D-glucose is mainly catalyzed by weak acid sites which are produced in the case of RSO3H-SBA-15(IS) while the product diacetone-D-glucose is catalyzed by medium-to-strong acid sites, which are generated in the case of RSO3H-SBA-15. The catalyst, RSO3H-SBA-15(IS), produce considerable amount of 1,2-monoacetone-D-glucose, hitherto, not reported so far.
[0023]The disclosed invention has the following improvements over the closest prior art, as describes herein. This investigation points out that different types acid sites, viz., strong acid sites which are generated by bonding of sulfonic acid moiety with isolated and vicinal silanols whereas moderate acid sites are produced by bonding of sulfonic acid moiety with isolated and geminal silanols. On the other hand, the weak acid sites can be tuned by bonding of sulfonic acid moiety with isolated silanols. In addition, it is also concluded that the product, i.e., 1,2-monoacetone-D-glucose, is mainly produced by weak acid sites, while the products, viz., diacetone-D-glucose and 5,6-monoacetone-D-glucose, are catalyzed by the moderate-to-strong acid sites. In general, all the catalysts, viz., RSO3H-OMS, showed maximum activity with selective formation of diacetone-D-glucose. However, RSO3H-SBA-15 showed considerable amount of 1,2-monoacetone-D-glucose owing to the presence of weak acid sites. Therefore, this catalyst can be tuned in such a way to produce more weak acidic sites. In this way, we could successfully modify/prepare weak acidic material, designated as RSO3H-SBA-15(IS), and the resulting novel catalyst selectively produces 1,2-monoacetone-D-glucose in good yield, hitherto, not reported so far.
[0024]The process proposed herein is an exemplary demonstration of working of the proposed concept of sulfonic acid functionalization of OMS and its efficiency in catalysing the synthesis of O-isopropyledene derivatives from sugar. The standards and operating protocol of the use of such proposed concept can be standardized and adapted by a person skilled in the art to achieve the same or enhanced results.
[0025]It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the field. ,CLAIMS:I/We Claim,
1.A method of synthesis of sulfonic acid functionalised ordered mesoporous silicates, steps comprising;
evacuation of ordered mesoporous silicate (OMS) in vacuum oven at 100- 300°C for 5 h and then cooled down to room temperature,
further suspending it in 10-50 mL of dry toluene,
adding (3-Mercaptopropyl)trimethoxysilane with OMS : 3-MPTMS (wt. ratio),
mixture is refluxed for 3-9 h at 80-150°C under N2 atmosphere,
obtained product was filtered and washed with excess dry toluene to remove un-reacted (3-Mercaptopropyl)trimethoxysilane present,
dried at 40-80°C, to obtain thiol-functionalized OMS,
which is further refluxed for 15-25 h at 30-80°C with 20-40% H2O2 (in 2 - 5mL methanol) and then cooled down to room temperature.
2. The method as claimed in claim 1, further comprising steps of;
adding approximately 5- 10 mL of 0.1 - 0.2M H2SO4 was added and stirred for 4 - 6 h at room temperature for complete oxidation,
the obtained product was further centrifuged, washed with water and ethanol,
to obtain a solid material which is dried at 30-70°C overnight to obtain sulfonic acid functionalised ordered mesoporous silicates.
3.The method as claimed in claim 1 and 2, wherein; the ordered mesoporous silica comprises MCM-41, IITM-56, SBA-15, SBA-15(IS).
4.The method as claimed in claim 1 and 2, wherein; the ordered mesoporous silica SBA-15(IS) can be synthesized at 60-90°C to generate plurality of weak acid sites/silanol groups.
5.The method as claimed in claim 1 to 4, wherein; (3-Mercaptopropyl) trimethoxysilane bonds with silanol groups viz isolated vicinal and geminal species in ordered mesoporous silicates to produce acid sites of different strengths.
6.The method as claimed in claim 1 to 5, wherein; the sulfonic acid functionalised ordered mesoporous silicate RSO3H-OMS catalyses acetonation of D-glucose with high selectivity of diacetone-D-glucose owing to the presence of medium-to-strong acid sites.
7.The method as claimed in claim 1,2 and 6, wherein, the catalyst ratio of silica-to- (3-Mercaptopropyl) trimethoxysilane ratio of 1 : 0.5. SBA-15 produces weak acid sites with optimum activity and selective formation of diacetone-D-glucose.
8. The method as claimed in claim 1,2 and 6, wherein, RSO3H-SBA-15(IS) catalyzes the conversion of 1,2-monoacetone-D-glucose to diacetone-D-glucose in 40-50% yield by weak acid sites.
9. The method as claimed in claim 6, wherein; sulfonic acid functionalised ordered mesoporous silicate RSO3H-OMS catalysesdiacetone-D-glucose and 5,6-monoacetone-D-glucose, are catalyzed by the moderate-to-strong acid sites.