Processes for the preparation of anhydrosugars

Abstract

Disclosed herein are methods for preparing anhydrosugars from aldohexoses and preparations of anhydrosugars prepared using the disclosed methods. In particular, the disclosure relates to processes for preparing anhydrosugars in polar aprotic solutions and in the presence of an acidic heterogeneous catalyst.

Description

PROCESSES FOR THE PREPARATION OF ANHYDROSUGARSSTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

[0001] This invention was made with government support under grant number DMR- 1827894 awarded by the National Science Foundation. The government has certain rights in the invention.CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority from U.S. Provisional Application no. 63 / 659,803, filed on June 13, 2024, the disclosure of which is incorporated herein by reference in its entirety.FIELD

[0003] This disclosure relates generally to processes for preparing anhydrosugars from aldohexoses and preparations of anhydrosugars prepared using the disclosed methods. In particular, the disclosure relates to processes for preparing anhydrosugars in aprotic solutions and in the presence of an acidic heterogeneous catalyst.BACKGROUND

[0004] The global dependence on fossil fuels, which are necessary as raw materials for operating refineries and their conversion to chemical compounds, results in environmental damage including carbon emissions that contribute to climate change. Alternatives, such as biomass used as a reagent in biorefineries provides a carbon- neutral, sustainable, and environmentally friendly solution for producing compounds generally obtained from nonrenewable sources and conventional refineries. See, Cherubini, 2010, The Biorefinery Concept: Using Biomass Instead of Oil for Producing Energy and Chemicals. Energy Convers. Manag. 51 : 1412-1421; Serrano-Ruiz et al., 2011 , Transformations of Biomass- Derived Platform Molecules: From High Added-Value Chemicals to Fuels via Aqueous- Phase Processing. Chem. Soc. Rev. 40:, 5266-5281; Cho et al., 2020, Bioconversion of Biomass Waste into High Value Chemicals. Bioresour. Technol. 298: 122386.

[0005] Anhydrosugars are high-value products typically obtained from renewable sources. They are used as biomass burning markers and have potential use in specialized chemical synthesis. Suciu et al., 2019, Anhydrosugars as Tracers in the Earth System.Biogeochemistry 146:, 209-256.; Czernik et al., 2004, Overview of Applications of Biomass Fast Pyrolysis Oil. Energy and Fuels 18: 590-598. 1 ,6-anhydro-B-D-glucopyranose (levoglucosan) is an anhydrous sugar that is frequently studied and is derived from abundantcellulose and subsequently glucose. Itabaiana Junior et al., 2020, Levoglucosan: A Promising Platform Molecule? Green Chem. 22:, 5859-5880; Ohara et al., 2010, Syntheses of 5-Hydroxymethylfurfural and Levoglucosan by Selective Dehydration of Glucose Using Solid Acid and Base Catalysts. Appl. Catal. A Gen. 383: 149-155; Cao et al., 2015, Dehydration of Cellulose to Levoglucosenone Using Polar Aprotic Solvents. Energy Environ. Sci. 8: 1808-1815. In fact, it is a top-15 candidate feedstock for the US Department of Energy from which levoglucosenone, 5-hydroxymethylfurfural (H F) or styrene can be produced through various chemical, catalytic and biochemical processes. Itabaiana Junior et al., 2020, Id:, US Department of Energy 2004 Annual Report.

[0006] The method most commonly used to produce levoglucosan is based on the conversion of cellulose or starch through a pyrolysis process. Lin et al., 2009, Kinetics and Mechanism of Cellulose Pyrolysis. J. Phys. Chem. C 113: 20097-20107; Luo et al., 2004, Mechanism Study of Cellulose Rapid Pyrolysis, Industrial & Engineering Chemistry Research 43: 5605-5610. However, due to its harsh conditions other approaches have been suggested, which includes tosylation of glucose and subsequent neutralization by sodium hydroxide and supercritical water treatment of glucose. Zottola et al., 1989, A Practical, Efficient Large-Scale Synthesis of 1,6-Anhydrohexopyranoses. J. Org. Chem. 54: 6123-612. More recently, catalytic studies using acidic catalysts and pure polar aprotic solvents have been proposed with the drawback of using homogeneous catalysts or a high ratio of reactant-catalyst, which indicates that further research is required. OHara et al., 2010, Id, Cao et al., 2020, Dehydration of Saccharides to Anhydro-Sugars in Dioxane: Effect of Reactants, Acidic Strength and Water Removal in Situ. Cellulose 27: 9825-9838; Liu et al., 2024, Gamma-Valerolactone-Enabled Control Chemoselective Conversion of Glucose to 1,6-Anhydroglucose over HZSM-5 Zeolite. Appl. Catal. B Environ. 344: 123623.

[0007] Other anhydrous sugars have been less explored because of the low abundance of the reagent carbohydrate compared with glucose. However, with the increasing demand for green chemistry and sustainable materials, it is necessary to study the potential of more molecular entities derived from biomass and their potential applications. Suciu et al., 2019; Czernik et al., 2004, Id.; Torres et al., 2019, Exploring the Treasure of Plant Molecules with Integrated Biorefineries. Front. Plant Sci. 10: 1-7.

[0008] For example, 1,6-anhydro-B-D-mannopyranose (mannosan) is used in the synthesis of sibirosamine, a precursor used in the formulation of the unique antitumor antibiotic sibiromycin. Georges et al., 1982, Stereo- and Regiocontrolled Synthesis of Methyl N -Acetyl-a-D-Sibirosaminide. J. Am. Chem. Soc. 104: 1101-1103; Georges et al., 1984, One-Flask, Two-Step Synthesis of 1,6-Anhydro-p-d-Mannopyranose (d-Mannosan) from d- Mannose. Carbohydr. Res. 127: 162-164. Mannosan is produced during pyrolysis of wasteturnings from manufacturing buttons from the large seeds of the ivory-nut palm (Phytelephas macrocarpa, Ruiz & Pav). Hudson, 1941, D-Mannosan<1,5>p<1 ,6> or Levomannosan. J. Am. Chem. Soc. 63: 2-6. However, the peculiarities of the process, which include the commercial source of the glycan to be pyrolyzed indicate that other routes should be studied. Another route using mannose as a reactant has been proposed, but it uses toxic compounds such as pyridine and toluene. Zottola et al., 1989, Id , Georges et al., 1982, Id.

[0009] Therefore, there is a need in the art for more reliable methods for producing anhydrosugars at higher yields and without toxic solvents or reagents.SUMMARY

[0010] Provided herein are methods for producing anhydrosugars from aldohexoses at higher yields and without toxic solvents or reagents known in the art.

[0011] Disclosed herein are methods for producing 1 ,6-anhydrosugars (e g., 1,6-anhydro- mannofuranose and 1 ,6-anhydro-mannopyranose) from aldohexose sugars (e.g., mannose) in pure polar aprotic solvents using acidic heterogeneous catalysts (e.g., aluminum-beta (Al- beta) zeolites with Bronsted acidity) otherwise used for dehydration reactions. Also provided are methods for producing anhydrosugars using Lewis acidic heterogeneous catalysts (e.g., tin-beta (Sn-Beta) zeolites with Lewis acidity) to effectively catalyze the reaction with a suitable solvent.

[0012] Accordingly, in one aspect, the present disclosure relates to a process for preparing an anhydrosugar. In certain embodiments, the process comprises treating an aldohexose sugar with an acidic heterogeneous catalyst in an aprotic solvent.

[0013] In certain embodiments as described herein, the aldohexose sugar comprises (or is) mannose, and the anhydrosugar comprises (or is) a 1,6-anhydromannose. In some embodiments, the anhydrosugar comprises (or is) 1 ,6-anhydro-p-D-mannofuranose (AMF). In some other embodiments, the anhydrosugar comprises (or is) 1 ,6-anhydro-p-D- mannopyranose (AMP). In some other embodiments, the anhydrosugar comprises (or is) a mixture of AMF and AMP.

[0014] In certain embodiments as described herein, the aldohexose sugar comprises (or is) galactose, and the anhydrosugar comprises (or is) a 1 ,6-anhydrogalactose. In some embodiments, the anhydrosugar comprises (or is) 1 ,6-anhydrogalacto-a-D-furanose. In some other embodiments, the anhydrosugar comprises (or is) 1 ,6-anhydrogalacto-p-D- pyranose. In some other embodiments, the anhydrosugar comprises (or is) a mixture of 1,6- anhydrogalacto-a-D-furanose and 1 ,6-anhydrogalacto-p-D-pyranose.

[0015] In certain embodiments as described herein, the aldohexose sugar comprises (or is) talose, and the anhydrosugar comprises (or is) a 1 ,6-anhydrotalose. In some embodiments, the anhydrosugar comprises (or is) 1 ,6-anhydrotalofuranose. In some other embodiments, the anhydrosugar comprises (or is) 1 ,6-anhydrotalopyranose. In some other embodiments, the anhydrosugar comprises (or is) a mixture of 1,6-anhydrotalofuranose and1.6-anhydrotalopyranose.

[0016] In certain embodiments as described herein, the aldohexose sugar comprises (or is) gulose, and the anhydrosugar comprises (or is) a 1 ,6-anhydrogulose. In some embodiments, the anhydrosugar comprises (or is) 1 ,6-anhydrogulofuranose. In some other embodiments, the anhydrosugar comprises (or is) 1 ,6-anhydrogulopyranose. In some other embodiments, the anhydrosugar comprises (or is) a mixture of 1,6-anhydrogulofuranose and1.6-anhydrogulopyranose.

[0017] In certain embodiments as described herein, the aprotic solvent is a polar aprotic solvent. In some embodiments, the polar aprotic solvent comprises one or more of dimethyl sulfoxide (DMSO), acetonitrile, tetrahydrofuran (THF), acetone, y-valerolactone (GVL), or dioxane In some embodiments, the polar aprotic solvent comprises dimethyl sulfoxide , acetonitrile, tetrahydrofuran , acetone, y-valerolactone , or dioxane in an amount of at least 95 vol%, e.g., at least 97 vol%, or at least 99 vol%, or at least 99.5 vol%, or at least 99.9 vol%, relative to a total volume of the polar aprotic solvent. In some embodiments, the polar aprotic solvent is dimethyl sulfoxide), acetonitrile, tetrahydrofuran, acetone, y-valerolactone, or dioxane.

[0018] In certain embodiments, the aldohexose sugar (e.g., one or more of mannose, galactose, talose, or gulose) is provided in an amount in a range of about 0.5 to 5 wt%, or about 0.5 to 3 wt%, or about 0.75-3 wt%, relative to the total combined weight of the aldohexose sugar and the aprotic solvent. In certain other embodiments, the aldohexose sugar (e.g., one or more of mannose, galactose, talose or gulose) is provided in an amount of about 0.75 wt%, or about 1.5 wt%, or about 3 wt%, relative to the total combined weight of the aldohexose sugar and the aprotic solvent.

[0019] In certain embodiments, the acidic heterogeneous catalyst is an acidic silica catalyst. For example, in certain embodiments, the acidic heterogeneous catalyst is SBA-15 propylsulfonic acid. As used herein, the term “SBA-15 propylsulfonic acid” refers to a mesoporous silica that has been functionalized with n-propylsulfonic acid.

[0020] In certain embodiments, the acidic heterogeneous catalyst is a zeolite catalyst. In certain embodiments, the zeolite catalyst comprises micropores. In certain embodiments,the zeolite catalyst comprises mesopores. In certain other embodiments, the zeolite catalyst comprises micropores and mesopores.

[0021] In certain embodiments as described herein, the zeolite catalyst has a Brunauer- Emmet-Teller (BET) surface area in a range of about 500 to 750 m2 / g or about 550 to 700 m2 / g.

[0022] In certain embodiments as described herein, the zeolite catalyst exhibits an X-ray diffraction pattern comprising peaks at 7.7, 22.5, 25.5, 27.1 , 29.1 and 44.0 (20 ± 0.1 degrees).

[0023] In certain embodiments as described herein, a molar ratio of the aldohexose sugar (e.g., one or more of mannose, galactose, talose, or gulose) to the zeolite catalyst is about 20 to 1 or about 100 to 1.

[0024] In certain embodiments as described herein, the zeolite catalyst is a Beta zeolite catalyst.

[0025] In certain embodiments, the Beta zeolite catalyst is aluminum (Al)-Beta zeolite catalyst. In some embodiments, the Al-Beta zeolite catalyst comprises Al in an amount of about 3 wt%, relative to the total weight of the Al-Beta zeolite catalyst, as measured using elemental analysis. In certain embodiments, the (Al)-Beta zeolite catalyst has in the range of 800-1300 pmol / g of aluminum sites, e.g., in the range of 900-1200 pmol / g of aluminum sites, as measured using elemental analysis. In certain embodiments, the (Al)-Beta zeolite catalyst has in the range of 1050-1150 pmol / g of aluminum sites, as measured using elemental analysis.

[0026] The person of ordinary skill in the art will appreciate that while some aluminum sites of the zeolite can act as acid sites, not all acid sites of the zeolite are necessarily aluminum sites. In certain embodiments, the (Al)-Beta zeolite catalyst has in the range of 110 to 950 pmol / g of acid sites, e.g., in the range of 200 to 800 pmol / g of acid sites, or in the range of 300 to 700 pmol / g of acid sites, as measured using temperature programmed desorption of ammonia. In certain embodiments, the (Al)-Beta zeolite catalyst has in the range of 400 to 550 pmol / g of acid sites as measured using temperature programmed desorption of ammonia.

[0027] In some embodiments, the Al-Beta zeolite catalyst comprises silicon (Si). In some embodiments, a ratio of Si to Al in the Al-Beta zeolite catalyst is about 13 to 1 by weight

[0028] In certain embodiments, the Beta zeolite catalyst is tin (Sn)-Beta zeolite catalyst.

[0029] In certain embodiments as described herein, the process further comprises removing at least a portion of the Al from an Al-Beta zeolite catalyst to provide the Sn-Betazeolite catalyst. In some embodiments, the process is carried out in the presence of a tin precursor. In some embodiments, the tin precursor comprises (or is) tin chloride (SnCU).

[0030] In some embodiments, the process is carried out at a temperature higher than 70 °C, or higher than 120 °C, or higher than 150 °C.

[0031] In certain embodiments as described herein, the Sn-Beta zeolite catalyst comprises Al in an amount of less than 0.5 wt% or less than 0.1 wt%, relative to the total weight of the Sn-Beta zeolite catalyst.

[0032] In certain embodiments as described herein, the Sn-Beta zeolite catalyst comprises Si. In some embodiments, a ratio of Si to Al in the Sn-Beta zeolite catalyst can be about 919 to 1 by weight, or about 826 by weight. In some embodiments, the Sn-Beta zeolite catalyst comprises Sn in an amount that can be about 2 wt%, relative to the total weight of the Sn- Beta zeolite catalyst. In some embodiments, a ratio of Si to Sn in the Sn-Beta zeolite catalyst is about 97 to 1 by weight.

[0033] As described above, while at least a portion of Al from Al-Beta zeolite catalyst can be removed to provide Sn-Beta zeolite catalyst, the Sn-Beta zeolite catalyst can still comprise small amounts of aluminum. In certain embodiments, the Sn-Beta catalyst comprises aluminum in an amount in the range of 0.04-0.06 wt%, relative to the total weight of the Sn-Beta catalyst. In certain embodiments, the Sn-Beta catalyst has in the range of 1- 50 pmol / g of aluminum sites, e.g., in the range of 5-30 pmol / g of aluminum sites, as measured using elemental analysis. In certain embodiments, the Sn-Beta catalyst has in the range of 10-20 pmol / g of aluminum sites, as measured using elemental analysis.

[0034] In certain embodiments, the Sn-Beta zeolite catalyst has in the range of 15 to 130 pmol / g of acid sites, e.g., in the range of 20 to 110 pmol / g of acid sites, or in the range of 40 to 100 pmol / g of acid sites, as measured using temperature programmed desorption of ammonia. In certain embodiments, the Sn-Beta zeolite catalyst has in the range of 60 to 85 pmol / g of acid sites as measured using temperature programmed desorption of ammonia.

[0035] These and other features, objects, and advantages of the present invention will become better understood from the description that follows. In the description, reference is made to the accompanying drawings, which form a part hereof and in which there is shown by way of illustration, not limitation, embodiments of the invention. The description of preferred embodiments is not intended to limit the invention to cover all modifications, equivalents, and alternatives. Reference should therefore be made to the claims recited herein for interpreting the scope of the invention.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The accompanying drawings are included to provide a further understanding of the systems and methods of the disclosure and are incorporated in and constitute a part of this specification. The drawings are not necessarily to scale, and sizes of various elements may be distorted for clarity. The drawings illustrate one or more embodiment(s) of the disclosure and together with the description serve to explain the principles and operation of the disclosure.

[0037] FIG. 1 A illustrates powder x-ray powder diffraction analysis of Al-beta, dealuminated Al-beta, and Sn beta (I) zeolites produced as disclosed in Example 1.

[0038] FIG. 1 B illustrates powder x-ray powder diffraction analysis of Sn beta (II) zeolites produced as disclosed in Example 1.

[0039] FIG. 2 illustrates nitrogen adsorption isotherms for Al-beta, dealuminated Al-beta, and Sn beta zeolites produced as disclosed in Example 2.

[0040] FIG. 3 illustrates the effect of solvent on conversion and product yield using Al-Beta as catalyst under reaction conditions of 3 g of solution, 1.5 wt% mannose, a temperature of 413 K and 2.4 pmol of aluminum sites.

[0041] FIG. 4 illustrates the effect of solvent on conversion and product yield using Sn- Beta as catalyst under reaction conditions of 3 g of solution, 1.5 wt% mannose, 15 min reaction duration, a temperature of 413 K and 2.4 pmol of aluminum sites.

[0042] FIG. 5 illustrates the effect of mannose concentration in gamma-valerolactone (GVL) on conversion and product distribution yield under reaction conditions of 3 g of solution, 413 K and 2.4 pmol of aluminum sites.

[0043] FIG. 6 illustrates the impact of mannose concentration on product distribution yield under reaction conditions of 3 g of solution, 1.5 wt% mannose, and a temperature of 413 K.

[0044] FIG. 7 illustrates the evolution of product yields with time under reaction conditions of 3 g of solution, 1.5 wt% mannose, and a temperature of 413 K.

[0045] FIG. 8 illustrates the effect of temperature on conversion and product yield using Al-Beta as catalyst under reaction conditions of 3 g of solution (GVL), 1.5 wt% mannose, and 2.4 pmol of aluminum sites.DETAILED DESCRIPTION

[0046] Before the disclosed methods and materials are described, it is to be understood that the aspects described herein are not limited to specific embodiments, and as such can,of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular aspects only and, unless specifically defined herein, is not intended to be limiting.DEFINITIONS

[0047] As used herein, articles “a” and “an” are intended to refer to one or to more than one (i.e., at least one) of the grammatical object of the article. By way of example, “an element” means at least one element and can include more than one element.

[0048] “About” is used to provide flexibility to a numerical range endpoint by providing that a given value can be “slightly above” or “slightly below” the endpoint without affecting the result. The term “about” in association with a numerical value means that the numerical value can vary by plus or minus 5% or less of the numerical value.

[0049] Throughout this specification, unless the context requires otherwise, the word “comprise” and “include” and variations (e.g., “comprises,” “comprising,” “includes,” “including”) will be understood to imply the inclusion of a stated component, feature, element, or step or group of components, features, elements, or steps but not the exclusion of any other integer or step or group of integers or steps.

[0050] As used herein, “and / or” refers to and encompasses any and all possible combinations of one or more of the associated listed items, as well as the lack of combinations where interpreted in the alternative (“or”).

[0051] Recitation of ranges of values herein are merely intended to serve as a succinct method of referring individually to each separate value falling within the range, unless otherwise indicated herein. Furthermore, each separate value is incorporated into the specification as if it were individually recited herein. For example, if a range is stated as 1 to 50, it is intended that values such as 2 to 4, 10 to 30, or 1 to 3, etc., are expressly enumerated in this disclosure. These are only examples of what is specifically intended, and all possible combinations of numerical values between and including the lowest value and the highest value enumerated are to be considered to be expressly stated in this disclosure.

[0052] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by a person of ordinary skill in the art to which this disclosure belongs.

[0053] Disclosed herein are methods for producing anhydrosugars using acidic zeolites as catalysts in aprotic solvents, particularly pure polar aprotic solvents.

[0054] The skilled worker will understand that the term “anhydrosugars” encompasses chemical compounds derived from elimination of one water molecule from the parent carbohydrate of six or more carbon atoms. The skilled worker will appreciate thatanhydrosugars can be provided in a cyclic tautomeric form (e.g., as a 5-membered furanose or a 6-membered pyranose), in an acyclic tautomeric form, or a mixture thereof.

[0055] Disclosed herein are dehydromannose sugars including 1,6-anhydromannose and in particular 1 ,6-anhydro-p-D-mannopyranose (AMP) and 1,6-anhydro-p-D-mannofuranose (AMF). The term “1 ,6-anhydro-p-D-mannopyranose” as used herein refers to (1 R,2S,3S,4S,5R)-6,8-dioxabicyclo[3.2.1]octane-2,3,4-triol. The term “1,6-anhydro-p-D- mannofuranose” as used herein refers to (1R,4R,5R,6R,7S)-2,8-dioxabicyclo[3.2.1]octane- 4,6,7-triol.

[0056] Also disclosed herein are dehydrogalactose sugars including 1 ,6-anhydrogalactose and in particular 1,6-anhydro-p-D-galactopyranose and 1 ,6-anhydro-a-D-galactofuranose.The term “1 ,6-anhydro-p-D-galactopyranose” as used herein refers to (1S,2S,3S,4S,5R)-6,8- dioxabicyclo[3.2.1]octane-2,3,4-triol. The term “1 ,6-anhydro-a-D-galactofuranose” as used herein refers to (1S,4R,5S,6R,7R)-2,8-dioxabicyclo[3.2.1]octane-4,6,7-triol.

[0057] Also disclosed herein are dehydrotalose sugars including 1,6-anhydrotalose and in particular 1 ,6-anhydro-p-D-talopyranose and 1 ,6-anhydro-a-D-talofuranose. The term “1 ,6- anhydro-p-D-talopyranose” as used herein refers to (1 R,2R,3S,4S,5R)-6,8- dioxabicyclo[3.2.1]octane-2,3,4-triol. The term “1 ,6-anhydro-a-D-talofuranose” as used herein refers to (1S,4R,5S,6R,7S)-2,8-dioxabicyclo[3.2.1]octane-4,6,7-triol.

[0058] Also disclosed herein are dehydrogulose sugars including 1 ,6-anhydrogulose and in particular 1 ,6-anhydro-a-L-gulopyranose and 1,6-anhydro-p-L-gulofuranose. The term “1 ,6-anhydro-a-L-gulopyranose” as used herein refers to (1S,2S,3S,4S,5S)-6,8- dioxabicyclo[3.2.1]octane-2,3,4-triol. The term “1 ,6-anhydro-p-L-gulofuranose” as used herein refers to (1 R,4S,5R,6R,7S)-2,8-dioxabicyclo[3.2.1]octane-4,6,7-triol.

[0059] However, the methods and anhydrosugars provided herein include species that are produced from other aldohexose sugars (e.g., glucose, idose, altrose, and allose).

[0060] As used herein, the term “pure polar aprotic solvents” will be understood to refer to solvents that are unable to donate hydrogen bonds to the aldohexose sugar substrate because, inter alia, they lack hydrogen atoms having a polar covalent bond to an electronegative atom. Aprotic solvents include, but are not limited to, gamma-valerolactone, chloroform, dimethyl sulfoxide, acetonitrile, acetone, dimethylformamide, pyridine, tetrahydrofuran, dioxane, and ethyl acetate. As used herein, the term “dioxane” will be understood to refer to 1,4-dioxane.

[0061] The anhydrosugars provided using the methods disclosed herein can be used for organic synthesis of useful compounds, such as oligosaccharides and glycoconjugates andsynthetic precursors to natural products and drug molecules such as antibiotics, antiparasitic agents, and other biologically active compounds (see, for example, Czernik and Bridgwater, 2004, Energy Fuels 18: 590-598; Longley and Fung, 1994, Advances in Thermochemical Biomass Conversion 2: 1484-1494).EXAMPLES

[0062] Various exemplary embodiments of compositions and methods according to this invention are now described in the following non-limiting Examples. The Examples are offered for illustrative purposes only and are not intended to limit the scope of this invention in any way. Indeed, various modifications of the invention in addition to those shown and described herein will become apparent to those skilled in the art from the foregoing description and the following examples and fall within the scope of the appended claims.

[0063] The Examples set forth herein incorporate and rely on certain experimental and preparatory methods and techniques performed as exemplified herein.Materials and MethodsMaterials

[0064] The following chemical compounds and materials were used in the experiments disclosed herein without any additional purification: NH4-Beta zeolite (Alfa-Aesar, SiC^ / AfeOs = 25), deionized water (Thermo Scientific MicroPure UV), nitric acid (Fisher-Chemical, 69.3%), SnCL / Sigma Aldrich, 1M in heptane), 2-propanol (Fisher Chemical, A416-4), N2(Praxair, industrial grade), air (Praxair, zero grade), difructose anhydride (III) (FUJIFILM Wako Pure Chemical Corporation, +97%), D-mannose (Acros Organic, 99%), D-fructose (Acros Organics, 99 %), D-glucose (Fisher Chemical, D16-500), D-galactose (Sigma Aldrich, +99%), D-tagatose (Sigma Aldrich, +99%), alpha-D-talose (Sigma Aldrich, 97%), L-sorbose (TCI America, +98%), L-gulose (TCI America, +98%), 1 ,6-anhydro-beta-D-mannopyranose (Combi-blocks, 97%), 1 ,6-anhydro-beta-D-mannofuranose (Synthose, 98%), 1 ,6-anhydro- beta-D-galactopyranose (Combi-Blocks, 95%), 1 ,6-anhydro-alpha-D-galactofuranose (Synthose, 98%), formic Acid (Acros Organic, 99 %), acetic acid (Fisher Chemical, glacial, ACS certified), DL-lactic acid (Acros Organic, 85 %), pyruvaldehyde (Acros Organic, 35-45 % solution in water), 1 ,3-dihydroxiacetone dimer (Alfa Aesar, 97 %), DL-glyceraldehyde dimer (biosynth, 93 %), glycolaldehyde dimer (Aldrich), L-(+)- erythrulose (Acros Organic, 85 %), 2-hydroxybut, 3-enoic acid (Enamine, 95 %), 5- hydroxymethyl-furfural (Acros Organic, 98%), 2-furaldehyde (Across Organic, 99%), gamma-valerolactone (Sigma Aldrich, + 99%), 1 ,4-dioxane (Acros Organic, 99%), acetonitrile, (Acros Organic, 99.8%), tetrahydrofuran (Acros Organic, 99.9%), dimethyl sulfoxide (Acros Organic, +99.7%), heptane (Sigma Aldrich) and acetone (Alfa Aesar, 99.5%).Catalyst Synthesis

[0065] Tin-beta (Sn-beta) zeolite was synthesized using the procedure reported by Seis and modified by Gounder to provide zeolites Sn-Beta (I) and Sn-Beta (II). See, Vega-Vila et al., 2016, Controlled Insertion of Tin Atoms into Zeolite Framework Vacancies and Consequences for Glucose Isomerization Catalysis. J. Catal. 344: 108-120; Dijkmans et al., 2013, Productive Sugar Isomerization with Highly Active Sn in Dealuminated Beta Zeolites. Green Chem. 15; 2777-2785. The commercial ammonium-exchanged zeolite Beta was calcined (increasing the temperature by 1 K / min to 823 K and then maintained at that temperature for 10 h) to remove ammonium ions, producing its protonated form (Al-Beta), which displays Bnansted acidity. The aluminum was partially removed by a dealumination method following the post-synthesis process. First, the protonated form of the zeolite was suspended in a 14 M aqueous solution of HNO3 in a round bottom flask at 353 K and stirred it at 800 rpm overnight. Once the time elapsed, the powder was filtered through a glass fiber prefilter (Millipore) over a Buchner funnel connected by a rubber stopper to a Kitasato flask and washed with abundant deionized water. If mesoporosity is desired, Al-Beta zeolite was suspended in an aqueous solution of sodium hydroxide (0.2 M, 30 mL / g zeolite) at 318 K for 0.5 h, washed with abundant deionized water, and dried. This process preferentially removes silicon to produce a hierarchical zeolite. Before grafting, the zeolite was dried at 393 K for 2 h and then activated it at 423 K for another 2 h. Then the solvent (heptane), precursor (SnCk in heptane) and zeolite were placed in a round bottom flask and kept at reflux temperature in a nitrogen-inert atmosphere. After 7 h, the catalyst was filtered and washed with isopropanol. Finally, the sample was calcined at 823 K (3 K / min to 333 K, held at this temperature for 4 h, then the temperature increased by 3 K / min to 473 K, held at this temperature for 6 h, 3 K / min to 823 K and held at this temperature for 6 h).Catalyst Characterization

[0066] To assess the zeolite structure of the samples synthesized using the post-synthesis method X-ray powder diffraction (XRD) was used and Galbraith Laboratories (Knoxville, TN) determined the chemical composition of the zeolite samples using inductively coupled plasma-optical emission spectroscopy (ICP-OES). To collect the XRD powder patterns of the samples a Bruker D8 Advance Diffractometer with CuKa radiation (A= 1 .5406 A) and the anode at 40 kV and 44mA was used. Scanning was performed at a speed of 10per minute with a step size of 0.02 in the 5-80020 range. To evaluate coordination of Sn UV-Vis diffuse-reflectance spectroscopy spectra were obtained using a Shimadzu UV-2600 UV-VIS spectrophotometer equipped with an MPC-2600A Multipurpose Sample Compartment. Using BaSO4 as the blank reference spectra were collected from 200 to 800 nm with a 1 nm sampling interval and fast scan speed. To obtain the textural properties of the samples N2adsorption-desorption isotherms were measured at 77 K using a Micromeritics 3-Flex instrument. Samples were degassed under vacuum at 623 K overnight before measurement. To estimate the specific surface area the Brunauer-Emmet-Teller (BET) method was used applying the consistency criteria from Rouquerol (see, Rouquerol et al., 2007, Is the BET Equation Applicable to Microporous Adsorbents? Studies in Surface Science and Catalysis 160:v49-56). To determine the total pore and micropore volumes of the catalysts the t-plot method (Halsey equation) was used with the correction suggested by Galarmeau et al., because it provides a more accurate approximation for zeolites. Galarneau et al., 2019, Specific Surface Area Determination for Microporous / Mesoporous Materials : The Case of Mesoporous FAU-Y Zeolites. Langmuir 34: 14134-14142; Galarneau et al., 2014, Validity of the T-Plot Method to Assess Microporosity in Hierarchical Micro / Mesoporous Materials. Langmuir 30: 13266-13274.Conversion of Mannose

[0067] To study the conversion of mannose 10 mL heavy-wall borosilicate glass reactors with conical stirrers were used. In a typical experiment, a mixture of solvent, mannose, and catalyst was prepared in situ. The mixture was stirred at 550 rpm in an oil bath at the desired temperature for a predetermined time at autogenous pressure. When the time elapsed, the reactors were placed in an ice bath and diluted the product mixture 1:2 in situ with deionized water. The mixture was centrifuged for 15 min at 2500 rpm and analyzed an aliquot of the supernatant liquid using HPLC (Waters HPLC model 2695) equipped with an UV detector (Waters tunable absorbance detector 486), a refractive index detector (Waters refractive Index detector 2410) and the Biorad Aminex HPX-87H column. For the catalyst stability study, the spent catalyst was filtered after each reaction run and washed with abundant water and acetone. After the fourth cycle, the catalyst was calcined using a tube furnace at 823 K for 2 h before using it in a new cycle at the same reaction conditions. The purpose of this last step was to regenerate the catalyst removing adsorbed species.

[0068] For a better understanding of the results, products detected were categorized into groups: C6 carbohydrates (fructose and glucose), 1 ,6-anhydromannose (AHM: AMF and AMP), retro aldol products include retro aldol condensation products and other intermediates related to the formation of alfa-hydroxy acids (glyceraldehyde, dihydroxyacetone, pyruvaldehyde, erythrulose and glycolaldehyde) and furans (5-hydroxymethyl furfural and 2- furaldehyde). For quantification of the conversion of mannose, product yields and the productivity the following equations were used:„ . , , inititial mol of mannose - final mol of mannose . „ „Conversion (mol %) = - - — — - 100 initial mol of mannose (1)moles of carbon in productProduct Carbon Yield = 100 initial mol of carbon of mannose (2)Carbon Balancemol of carbon of AHMProductivity = mol of Al ■ time of reaction (4)Example 1 : Catalyst Characterization

[0069] The X-ray diffraction (XRD) patterns of the samples (FIG. 1 ) show characteristic peaks for a Beta zeolite for each case. The main peaks were at 7.7, 22.5, 25.5, 27.1 , 29.1 and 44.0°, indicating that the zeolite structure was preserved after each synthesis step. There was no evidence of crystalline tin oxide phases (110) at 29 = 26.7°, (101) at 29 = 34.0° and (200) at 29 = 38.0°; see, Dijkmans et al., 2013, Productive Sugar Isomerization with Highly Active Sn in Dealuminated Beta Zeolites. Green Chem. 15: 2777-2785. However, it is important to note that its presence cannot be disregarded because if the particles were amorphous, small or if the amount of crystalline SnCh was lower than the detection limit the technique will not detect extra framework SnC ; Dijkmans et al., 2015, Cooperative Catalysis for Multistep Biomass Conversion with Sn / AI Beta Zeolite. ACS Catal. 5: 928-940.; Hammond et al., 2015, Identification of Active and Spectator Sn Sites in Sn- Following Solid-State Stannation, and Consequences for Lewis Acid Catalysis.ChemCatChem 7:, 3322-3331 . To study whether the catalyst framework was expanding or contracting during the synthesis the shift of the diffraction peak associated with the d302 spacing at 22.4° was monitored. After dealumination, the peak shifted from 22.30° to 22.50° indicating contraction of the framework. Following grafting, the peak increased to 22.48° consistent with an expansion of the framework.

[0070] The absorption edge energy for Sn-Beta was 4.50 eV, which is characteristic of bands for tetrahedral tin sites. According to previous studies, the biggest particles formed during the post-synthesis process had a diameter of around 4.1 nm (Roy et al., 2013, Probing Lewis Acid Sites in Sn-Beta Zeolite. ACS Catal. 3 , 573-580), and tin oxide particle sizes of 5.90 and 3.50 nm correspond to band gap energies of 3.65 and 3.97 eV which were not detected in these experiments. Pang et al., 2001 , Controlling the Particle Size of Calcined SnO2 Nanocrystals. Nano Lett. 1 :, 723-726. These particles are too large to fit within the pores of the zeolites, so they are expected to be located on the external surface. However, adsorption studies suggest that SnC species exist within the zeolite pores, indicating that they are distributed inside and outside of the zeolite. Roy et al., 2013, Id. In the UV / vis spectroscopy the larger particles that were outside seemed to dominate, while thepresence of SnO? clusters within the zeolite micropores influence other properties. The maximum absorption occurred at 203 nm corresponding to tetrahedral framework tin species.

[0071] After dealumination there was a drastic reduction in the aluminum content from 2.97% to 0.04% (Table 1 ). Incorporation of tin gave a Si / Sn ratio of 97 with 1.89 wt%. This Sn loading was less than the 2% for which inactive catalytically extraframework metal oxides species have been observed. Hammond et al., 2018, Porous Metallosilicates for Heterogeneous, Liquid-Phase Catalysis: Perspectives and Pertaining Challenges. R. Soc. Open Sci. 5: 2. The XRD and UV-Vis results disclosed herein did not present evidence for extraframework Sn. After the dealumination process, there was an increase in surface area and after grafting there was a decrease, which is consistent with other studies known in the art. See, Al-Nayili et al., 2016, Hierarchically Porous BEA Stannosilicates as Unique Catalysts for Bulky Ketone Conversion and Continuous Operation. J. Mater. Chem. A 4: 1373-1382. The isotherms (shown in FIG. 2) showed a combination of type I isotherm, characteristic of microporous materials, and type IV isotherms, indicating the presence of mesoporosity. Beta zeolites are microporous materials, but their particles were aggregated generating mesopore sized cavities. To calculate the total pore and the micropore volume the t-plot method (Halsey equation) was used. To calculate the micropore volume according to the classical method, usually the linear fit in the low-pressure range is extrapolated and the intercept is taken as the microporous volume and after the micropore filling, the first point which leaves from the linear regime is taken as the total volume pore. However, this approach underestimates the true microporous volume of the materials, highlighting the lack of validity of the t-plot for microporous, hierarchical and mixtures of microporous and mesoporous materials. The Coasne group propose an Abacus to correct this misleading statement, although other amendments should be made for purely microporous materials, it supposes a first correction from the classical t-plot method. See, Galarneau et al., 2019, Id. and Galarneau et al., 2014, Id.Table 1. Textural Properties of the Pristine and Modified ZeolitesExample 2: Effect of Solvent and Type of Acid Sites

[0072] To test the effect of the solvent Al-Beta zeolite was selected as a Bronsted acid catalyst because it is active for dehydration reactions (shown in FIG. 3). In water, the conversion was low, reaching 5% after 1 h of reaction, which is consistent with the low catalytic activity observed for biomass reactions in pure water (Cao et al., 2020, Id.). The reaction rate increased when polar aprotic solvents combined with water were used in the range of 20-100% of content. Zhaoet al., 2021 , y-Valerolactone-lntroduced Controlled- Isomerization of Glucose for Lactic Acid Production over Sn-Beta Catalyst. Green Chem. 23: 2634-2639. Using GVL as a polar aprotic solvent with a GVL:H2O 9:1 ratio, 21% conversion was observed after 1 h of reaction. Pure acetonitrile exhibited limited activity with 22% conversion after an 1 h of reaction. Pure DMSO, THF and acetone demonstrated moderate activity to AMF and AMP production with a yield of 43% at a conversion of 46% in acetone after 15 min. For DMSO there was an induction period before observing appreciable reaction; after 15 min the conversion was 9% of versus 78% after 1 h of reaction. DMSO is known to decompose autocatalytically producing several mild and strong acids such as lactic and sulfuric acid which can influence in the reaction results. See, Deguchi et al., 2020, A. Study on Autocatalytic Decomposition of Dimethyl Sulfoxide (DMSO). Org. Process Res. Dev. 24: 1614-1620.

[0073] The behavior of mannose was comparable to that of glucose that dehydrates to 1 ,6-anhydroglucopyranose and 1 ,6-anhydroglucofuranose under equivalent reaction conditions; see, Ohara et al., 2010, Id.', Liu et al., 2024, Id. Unfortunately, 1 ,6- anhydromannopyranose and 1 ,6-anhydromannofuranose have the same retention time under HPLC analysis conditions and accordingly they were not quantified independently.

[0074] For mannose conversion Sn-Beta (I) zeolite in pure GVL was not as selective as Al-Beta zeolite. After 0.25 h of reaction the 1 ,6-anhydromannose yield was 54% at 93% conversion compared to 73% 1 ,6-anhydromannose yield and 91% conversion using Al-Beta (shown in FIG. 3 and FIG. 4). Sn-Beta (I) zeolite exhibited higher yields to fructose than Al- Beta and produced the intermediate difructose anhydride to finally produce HMF in higher yields, 5% vs 1 %.

[0075] Adding 10% of water to GVL changed the product distribution, with mannose isomers being the main products (73% yield) without the detectable presence of anhydrous chemical compounds. The main product was fructose, with a 63% yield. Thus, in the presence of water and a Lewis acid catalyst, mannose shifts towards lactic acid production instead of 1 ,6-anhydromannose, through the previous mannose open ring to isomerize to fructose, which suffers a retro aldol condensation, and a 1 ,2 hydride shift to produce lacticacid. Onda et al., 2008, A New Chemical Process for Catalytic Conversion of D-Glucose into Lactic Acid and Gluconic Acid. Appl. Catal. A Gen. 343: 49-54; similar results were observed with the aldehyde glucose. In pure dioxane, Sn-Beta (I) isomerized mannose to fructose with high yields, around 55% yield at 84% of conversion. These results show the important effects of the solvent and the role of water when using Lewis acid zeolites such as Sn-Beta (I) to promote isomerization before dehydration. Cui et al., 2016, Conversion of Carbohydrates to Furfural via Selective Cleavage of the Carbon-Carbon Bond: The Cooperative Effects of Zeolite and Solvent. Green Chem. 18: 1619-1624.Example 3: Effect of Mannose Loading

[0076] A practical industrial process should convert efficiently high concentrations of the reactant. As the mannose loading was increased from 0.75 to 3 wt% the conversion and AHM yield decreased (see FIG. 5). For 15 min of reaction the conversion decreased from 93 to 83% and the AHM yield, from 83% to 37%. An intriguing observation from experiments having 3 wt% mannose was poor carbon balance (CB) compared to lower mannose loading. After 15 min of reaction, the CB for 3 wt% mannose was of only 62% versus 97% for 0.75 wt% of mannose. These unknown compounds are intermediate products because their yield decreased significantly after 1 h of reaction while the yield to AHM increased to 62%. For similar conversions, the higher the mannose concentration, the lower the 1 ,6- anhydromannose yields. However, this result is not necessarily negative. The productivity was higher for the 3 wt% of mannose than for 0.75 wt% at 15 min, with 2042 mol of carbon AHM I (mol of Al ■ h) compared to 1071 mol of carbon AHM / (mol of Al ■ h). In other words, more moles of the product were produced per mole of active aluminum site for the same reaction time, when using 3% wt of mannose instead of 0.75 wt% of mannose.Example 4: Effect of Catalyst Loading

[0077] For biomass derived feedstocks conversion studies, low ratios of reactant mass to- catalyst mass are common. Ohara et al., 2010, Id. Zhou et al., 2021 , Id. As disclosed herein, a ratio of 20 was employed for most experiments with Al-Beta as a catalyst, but when 0.5 mg of catalyst was used the ratio of reactant to catalyst was 100:1. When the catalyst mass was reduced from 2.2 mg to 0.5 mg the conversion decreased from 91 % to 78% and the 1 ,6-anhydromannose yield from 73% to 54% (shown in FIG. 6). For 4.4 mg of Al-Beta high yields of unknown products were observed, likely corresponding to unidentified degradation products.

[0078] If experiments having similar conversions were compared (around 92%), the 1 ,6- anhydromannose yield decreased from 72% to 62% when the amount of catalyst was increased 9 times probably because of 1 ,6-anhydromannose degradation. The productivityfor the runs with 0.5 mg Al-Beta, 6250 mol of carbon AHM / (mol of Al ■ h), was higher than the result for 2.2 mg of Al-Beta, 1869 mol of carbon AHM / (mol of Al ■ h).Example 5: Effect of Reaction Time

[0079] At the reaction conditions shown herein anhydrous sugars are intermediate products that will be converted to secondary products for long reaction times. For example, difructose dianhydride (DFA) is an intermediate to HMF (Huang et al., 2016, Design of Sulfonated Mesoporous Silica Catalyst for Fructose Dehydration Guided by Difructose Anhydride Intermediate Incorporated Reaction Network. Chem. Eng. J. 283: 778-788.). Levoglucosan, another anhydrosugar produced from glucose at similar reaction conditions, can react to levoglucosenone and or HMF under appropriate reaction conditions; see, Ohara et al., 2010, Id.; Jiayue et al., 2017, Production of Levoglucosenone and 5- Hydroxymethylfurfural from Cellulose in Polar Aprotic Solvent-Water Mixtures. 19: 3642- 3653. The reaction between levoglucosan and glucose is reversible, see, Abdilla-Santes et al., 2019, Conversion of Levoglucosan to Glucose Using an Acidic Heterogeneous Amberlyst 16 Catalyst: Kinetics and Packed Bed Measurements. Chem. Eng. Res. Des. 152: 193-200. For conversion of mannose on Al-Beta zeolite, after 1 h of reaction AHM started to degrade (shown in FIG. 7). After 5 h there was still 53% AHM yield, suggesting that the dehydrated molecules were final products at these reaction conditions. Furans, formic acid, and acetic acid were the product degradation species detected. Formic and acetic acid were formed in considerable amounts after 15 min of reaction. The absence of a significant increase in the furans yield is evidence that their formation was primarily from ketoses rather than aldoses (see, Van Putten et al., 2013, Dehydration of Different Ketoses and Aldoses to 5-Hydroxymethylfurfural. ChemSusChem 6: 1681-1687; Binder et al. ,2010, Mechanistic Insights on the Conversion of Sugars into 5-Hydroxymethylfurfural. Energy Environ. Sci. 3: 765-771). Additional evidence supporting that conclusion was that mannose conversion in dioxane with Sn-Beta (I) gave a 55% fructose yield after 15 min of reaction. An increase in reaction time to 1 h decreased the yield to 45%, with an increase in furans yields from 2% to 9%. The production of 1 ,6 anhydromannose also declined, whereas the yield for products such as DFA, retro aldol condensation products, acetic and formic acid products increased. The production of fructose for low reaction times favored the formation of those products at longer reaction periods. The run in GVL-H2O with Sn-Beta (I) also gave results consistent with a higher availability of fructose and Lewis acidity.Example 6: Effect of Temperature

[0080] An increase in reaction temperature increased the conversion and the yield to 1 ,6- anhydromannose (see FIG. 8). At 428 K it only took 15 min to exceed 92% conversion andonly trace amounts of acetic and formic acid were detected. The 1 ,6-anhydromannose yield was the same at 443 K as it was at 428 K, but with larger undesirable yields of acetic and formic acid.Catalytic conversion of Other SugarsExample 7: Conversion of Galactose

[0081] The Al-Beta zeolites and Sn-Beta (II) zeolites from Example 1 were used to convert galactose. The reactions with galactose were performed in 10 mL heavy-wall borosilicate glass reactors with conical stirrers. A mixture of 3 g of solvent, galactose, and 0.0022 g of Al- Beta or 0.016 g of Sn-Beta (II) (each corresponding to 2.4 pmol of aluminum sites) was prepared in situ. The mixture was stirred at 550 rpm in an oil bath at 413 K for 0.25 h, 1 .00 h, or 3.00 h at autogenous pressure. When the time elapsed, the reactors were placed in an ice bath and diluted the product mixture 1 :2 in situ with deionized water. The mixture was centrifuged for 15 min at 2500 rpm and analyzed an aliquot of the supernatant liquid using HPLC (Waters HPLC model 2695) equipped with an UV detector (Waters tunable absorbance detector 486), a refractive index detector (Waters refractive Index detector 2410) and the Biorad Aminex HPX-87H column. The product mixtures were analyzed using standards of 1 ,6-anhydrogalactopyranose (AGTP) and 1 ,6-anhydrogalactofuraranose (AGTF), which are commercially available.

[0082] For a better understanding of the results, the products detected were categorized into groups: C& carbohydrates (tagatose and talose), 1 ,6-anhydrogalactose (including 1 ,6- anhydrogalactopyranose (AGTP) and 1 ,6-anhydrogalactofuranose (AGTF)), retro aldol products include retro aldol condensation products and other intermediates related to the formation of alfa-hydroxy acids (glyceraldehyde, dihydroxyacetone, pyruvaldehyde, erythrulose and glycolaldehyde) and furans (5-hydroxy methyl furfural and 2-furaldehyde).For quantification of the conversion of galactose, product yields and the productivity the following equations were used:„ . , , inititial mol of galactose - final mol of galactose . „ „Conversion (mol %) = - - — ■ — — — - - - 100 initial mol of galactose (5) moles of carbon in productProduct Carbon Yield = 100 initial mol of carbon of galactose

[0083] The results of the experiments conducted with Al-Beta as the catalyst are summarized in Table 2.Table 2:

[0084] As demonstrated in Table 2, entry 2, the maximum yield for AGTP and AGTF is obtained after 1 h when using Al-Beta as the catalyst. Prolonging the reaction to 3 h (Table 2, entry 3) results in the degradation of AGTP and AGTF into unidentified chemicals.

[0085] No evidence of tagatose or talose formation (i.e., Ce carbohydrate yield) is observed when GVL is used as the solvent. However, the addition of water (Table 2, entry 4; a 9:1 GVLH2O solvent mixture) decreases the conversion of galactose to only 7.4%, resulting in a 1 .9% yield of tagatose.

[0086] The results of the experiments conducted with Sn-Beta (II) zeolite as the catalyst are summarized in Table 3.Table 3:

[0087] While the isomerization of galactose into tagatose was not observed with Al-Beta above, the reaction of Sn-Beta with galactose leads to a 2.0% yield of tagatose in addition to the 36.7% yield of AGTP and AGTF (Table 3, entry 5). The addition of water to the solvent leads to -19% yield of tagatose and -11% yield of talose (Table 3, entry 6). Using dioxane as the solvent generally leads to lower conversion of the galactose, and increased formation of degradation products (formic acid and acetic acid) and furans (Table 3, entries 7 and 8).Example 8: Conversion of Talose

[0088] The Al-Beta zeolite from Example 1 was used to treat talose. The reaction with talose was performed in a 10 mL heavy-wall borosilicate glass reactor with a conical stirrer. A mixture of 3 g of GVL, 0.75 wt% talose, and 0.0022 g of Al-Beta (corresponding to 2.4 pmol of aluminum sites) was prepared in situ. The mixture was stirred at 550 rpm in an oil bath at 413 K for 0.25 h at autogenous pressure. When the time elapsed, the reactors were placed in an ice bath and diluted the product mixture 1 :2 in situ with deionized water. The mixture was centrifuged for 15 min at 2500 rpm and analyzed an aliquot of the supernatant liquid using HPLC (Waters HPLC model 2695) equipped with an UV detector (Waters tunable absorbance detector 486), a refractive index detector (Waters refractive Index detector 2410) and the Biorad Aminex HPX-87H column.

[0089] For quantification of the conversion of talose, product yields and the productivity the following equation was used:„ . , inititial mol of talose - final mol of talose . > _Conversion (mol %) = - - - 100 initial mol of talose (7)

[0090] After 0.25 h of the reaction, 87.2% conversion of the talose was observed. Peaks that may correspond to the 1,6-ahydrosugar were observed, suggesting a 53.9% yield of the 1,6-anhydrosugars.Example 9: Conversion of Gulose

[0091] The Al-Beta zeolites and Sn-Beta (II) zeolites from Example 1 were used as catalysts for gulose conversion. The reactions with gulose were performed in 10 mL heavywall borosilicate glass reactors with conical stirrers. A mixture of 3 g of solvent, 1.5 wt% gulose, and 0.0022 g of Al-Beta or 0.016g of Sn-Beta (II) (each corresponding to 2.4 pmol of aluminum sites) was prepared in situ. The mixture was stirred at 550 rpm in an oil bath at413 K for 0.25 h or 1.00 h at autogenous pressure. When the time elapsed, the reactors were placed in an ice bath and diluted the product mixture 1 :2 in situ with deionized water. The mixture was centrifuged for 15 min at 2500 rpm and analyzed an aliquot of the supernatant liquid using HPLC (Waters HPLC model 2695) equipped with an UV detector (Waters tunable absorbance detector 486), a refractive index detector (Waters refractive Index detector 2410) and the Biorad Aminex HPX-87H column.

[0092] For a better understanding of the results, the products detected were categorized into groups: Ce carbohydrates (sorbose), 1 ,6-anhydrosugars, retro aldol products include retro aldol condensation products and other intermediates related to the formation of alfa- hydroxy acids (glyceraldehyde, dihydroxyacetone, pyruvaldehyde, erythrulose and glycolaldehyde) and furans (5-hydroxymethyl furfural and 2-furaldehyde). For quantification of the conversion of gulose, product yields and the productivity the following equations were used:„ . inititial mol of gulose - final mol of gulose . > _Conversion (mol %) = - - - - - - - 100 8 initial mol of galactose, r. i i moles of carbon in product .Product Carbon Yield = - - - 100 9 initial mol of carbon of gulose

[0093] The results of the experiments conducted reacting gulose with Al-Beta and Sn-Beta (II) as the catalysts are summarized in Table 4.Table 4:

[0094] In the absence of water, the reaction of gulose with both Al-Beta and Sn-Beta lead to the formation of 1 ,6-anhydrosugars in around 36.6% yield and 27. 8% yield, respectively (Table 4, entries 9 and 10). However, the inclusion of water in the reaction lowered the yield of 1,6-anhydrosugar to 6.7% and 5.2% for both Al-Beta and Sn-Beta zeolite catalysts (table 4, entries 11 and 12). Sn-Beta zeolite promoted isomerization of the gulose into sorbose to provide 11.1% yield of sorbose in pure GVL and 37.2% yield of sorbose in 9:1 GVLH2O.

[0095] All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, and patent application was specifically and individually indicated to be incorporated by reference.

[0096] While some embodiments have been illustrated and described in detail in the appended drawings and the foregoing description, such illustration and description are to be considered illustrative and not restrictive. Other variations to the disclosed embodiments can be understood and effected in practicing the claims, from a study of the drawings the disclosure, and the appended claims. The mere fact that certain measures or features are recited in mutually different dependent claims does not indicate that the combination of these measures or features cannot be used. Any reference signs in the claims should not be construed as limiting the scope.

Claims

WHAT IS CLAIMED IS:

1. A process for preparing an anhydrosugar, the process comprising treating an aldohexose sugar with an acidic heterogeneous catalyst in an aprotic solvent.

2. The process of claim 1, wherein the aldohexose sugar comprises mannose, and the anhydrosugar comprises a 1,6-anhydromannose.

3. The process of claim 2, wherein the anhydrosugar comprises 1 ,6-anhydro-p-D- mannofuranose (AMF).

4. The process of claim 2, wherein the anhydrosugar comprises 1, 6-an hydro- p-D- mannopyranose (AMP).

5. The process of claim 2, wherein the anhydrosugar comprises a mixture of AMF and AMP.

6. The process of claim 1, wherein the aldohexose sugar comprises galactose, and the anhydrosugar comprises a 1,6-anhydrogalactose.

7. The process of claim 6, wherein the anhydrosugar comprises a 1 ,6-anhydro-a-D- galactofuranose.

8. The process of claim 6, wherein the anhydrosugar comprises a 1 ,6-anhydro-p-D- galactopyranose.

9. The process of claim 6, wherein the anhydrosugar comprises a mixture of 1 ,6- anhydro-a-D-galactofuranose and 1 ,6-anhydro-p-D-galactopyranose.

10. The process of claim 1, wherein the aldohexose sugar comprises talose, and the anhydrosugar comprises a 1,6-anhydrotalose.

11. The process of claim 10, wherein the anhydrosugar comprises a 1,6-anhydro- talofuranose.

12. The process of claim 10, wherein the anhydrosugar comprises a 1,6-anhydro- talopyranose.

13. The process of claim 10, wherein the anhydrosugar comprises a mixture of 1,6- anhydrotalofuranose and 1 ,6-anhydrotalopyranose.

14. The process of claim 1, wherein the aldohexose sugar comprises gulose, and the anhydrosugar comprises a 1,6-anhydrogulose.

15. The process of claim 14, wherein the anhydrosugar comprises a 1,6- anhydrogulofuranose.

16. The process of claim 14, wherein the anhydrosugar comprises a 1,6- anhydrogulopyranose.

17. The process of claim 14, wherein the anhydrosugar comprises a mixture of 1,6- anhydrogulofuranose and 1 ,6-anhydrogulopyranose.

18. The process of any of claims 1-17, wherein the aprotic solvent is a polar aprotic solvent.

19. The process of claim 18, wherein the polar aprotic solvent comprises dimethyl sulfoxide (DMSO), acetonitrile, tetrahydrofuran (THF), acetone, y-valerolactone (GVL), or dioxane.

20. The process of any of claims 1-19, wherein the aldohexose sugar is provided in an amount in a range of about 0.5 to 5 wt%, relative to a total combined weight of the aldohexose sugar and the aprotic solvent.

21. The process of any of claims 1-19, wherein the aldohexose sugar is provided in an amount in a range of about 0.5 to 3 wt%, relative to a total combined weight of the aldohexose sugar and the aprotic solvent.

22. The process of any of claims 1-19, wherein the aldohexose sugar is provided in an amount in a range of about 0.75-3 wt%, relative to a total combined weight of the aldohexose sugar and the aprotic solvent.

23. The process of any of claims 1-19, wherein the aldohexose sugar is provided in an amount of about 0.75 wt%, relative to a total combined weight of the aldohexose sugar and the aprotic solvent.

24. The process of any of claims 1-19, wherein the aldohexose sugar is provided in an amount of about 1.5 wt%, relative to a total combined weight of the aldohexose sugar and the aprotic solvent.

25. The process of any of claims 1-19, wherein the aldohexose sugar is provided in an amount of about 3 wt%, relative to a total combined weight of the aldohexose sugar and the aprotic solvent.

26. The process of any of claims 1-25, wherein the acidic heterogeneous catalyst is an acidic silica catalyst.

27. The process of claim 26, wherein the acidic silica catalyst comprises SBA-15 propylsulfonic acid.

28. The process of any of claims 1-25, wherein the acidic heterogeneous catalyst is a zeolite catalyst.

29. The process of claim 28, wherein the zeolite catalyst comprises micropores.

30. The process of claim 28, wherein the zeolite catalyst comprises mesopores.

31. The process of claim 28, wherein the zeolite catalyst comprises micropores and mesopores.

32. The process of any of claims 28-31 , wherein the zeolite catalyst has a Brunauer- Emmet-Teller (BET) surface area in a range of about 500 to 750 m2 / g.

33. The process of any of claims 28-31, wherein the zeolite catalyst has a BET surface area in a range of about 550 to 700 m2 / g.

34. The process of any of claims 28-33, wherein the zeolite catalyst has a total pore volume in a range of about 0.2 to 0.3 cm3 / g.

35. The process of any of claims 28-33, wherein the zeolite catalyst has a total pore volume in a range of about 0.25 to 0.3 cm3 / g.

36. The process of any of claims 28-31 , wherein the zeolite catalyst has a micropore volume in a range of about 0.05 to 0.2 cm3 / g.

37. The process of any of claims 28-31 , wherein the zeolite catalyst has a micropore volume in a range of about 0.05 to 0.15 cm3 / g.

38. The process of any of claims 28-37, wherein the zeolite catalyst exhibits an X-ray diffraction pattern comprising peaks at 7.7, 22.5, 25.5, 27.1 , 29.1 and 44.0 (20 ± 0.1 degrees).

39. The process of any of claims 1-38, wherein a molar ratio of the aldohexose sugar to the acidic heterogeneous catalyst is about 20 to 1.

40. The process of any of claims 1-38, wherein a molar ratio of the aldohexose sugar to the acidic heterogeneous catalyst is about 100 to 1.

41. The process of any of claims 28-40, wherein the zeolite catalyst is a Beta zeolite catalyst.

42. The process of claim 41 , wherein the Beta zeolite catalyst is aluminum (Al)-Beta zeolite catalyst.

43. The process of claim 42, wherein the Al-Beta zeolite catalyst comprises Al in an amount of about 3 wt%, relative to a total weight of the Al-Beta zeolite catalyst, as measured by elemental analysis.

44. The process of claim 42 or claim 43, wherein the Al-Beta zeolite catalyst has in the range of 800-1300 pmol / g of aluminum sites, as measured using elemental analysis.

45. The process of claim 42 or claim 43, wherein the Al-Beta zeolite catalyst has in the range of 900-1200 pmol / g of aluminum sites, as measured using elemental analysis.

46. The process of claim 42 or claim 43, wherein the Al-Beta zeolite catalyst has in the range of 1050-1150 pmol / g of aluminum sites, as measured using elemental analysis.

47. The process of any of claims 42-46, wherein the Al-Beta zeolite catalyst has in the range of 110 to 950 pmol / g of acid sites, as measured using temperature programmed desorption of ammonia.

48. The process of any of claims 42-46, wherein the Al-Beta zeolite catalyst has in the range of 200 to 800 pmol / g of acid sites, as measured using temperature programmed desorption of ammonia.

49. The process of any of claims 42-46, wherein the Al-Beta zeolite catalyst has in the range of 300 to 700 pmol / g of acid sites, as measured using temperature programmed desorption of ammonia.

50. The process of any of claims 42-46 wherein the Al-Beta zeolite catalyst has in the range of 400 to 550 pmol / g of acid sites as measured using temperature programmed desorption of ammonia.

51. The process of any of claims 42-50, wherein the Al-Beta zeolite catalyst comprises silicon (Si).

52. The process of claim 51 , wherein a ratio of Si to Al in the Al-Beta zeolite catalyst is about 13 to 1 by weight.

53. The process of claim 41 , wherein the Beta zeolite catalyst is tin (Sn)-Beta zeolite catalyst.

54. The process of claim 53, wherein the process further comprises removing at least a portion of Al from an Al-Beta zeolite catalyst to provide the Sn-Beta zeolite catalyst.

55. The process of claim 54, wherein the process is carried out in the presence of a tin precursor.

56. The process of claim 55, wherein the tin precursor comprises tin chloride (SnCU).

57. The process of any of claims 1-56, wherein the process is carried out at a temperature higher than 70 °C.

58. The process of any of claims 1-56, wherein the process is carried out at a temperature higher than 120 °C.

59. The process of any of claims 1-56, wherein the process is carried out at a temperature higher than 150 °C.

60. The process of any of claims 53-59, wherein the Sn-Beta zeolite catalyst comprises Al in an amount of less than 0.5 wt%, relative to a total weight of the Sn-Beta zeolite catalyst.

61. The process of any of claims 53-59, wherein the Sn-Beta zeolite catalyst comprises Al in an amount of less than 0.1 wt%, relative to a total weight of the Sn-Beta zeolite catalyst.

62. The process of any of claims 53-61 , wherein the Sn-Beta zeolite catalyst comprises Si.

63. The process of claim 62, wherein a ratio of Si to Al in the Sn-Beta zeolite catalyst is about 919 to 1 by weight, or about 826 to 1 by weight.

64. The process of any of claims 53-63, wherein the Sn-Beta zeolite catalyst comprises Sn in an amount of about 2 wt%, relative to a total weight of the Sn-Beta zeolite catalyst.

65. The process of any of claims 62-64, wherein a ratio of Si to Sn in the Sn-Beta zeolite catalyst is about 97 to 1 by weight.

66. The process of any of claims 53-65, wherein the Sn-Beta catalyst comprises aluminum in an amount in the range of 0.04-0.06 wt%, relative to the total weight of the Sn- Beta catalyst.

67. The process of claim 66, wherein the Sn-Beta catalyst has in the range of 1-50 pmol / g of aluminum sites, as measured using elemental analysis.

68. The process of claim 66, wherein the Sn-Beta catalyst has in the range of 5-30 pmol / g of aluminum sites, as measured using elemental analysis.

69. The process of claim 66, wherein the Sn-Beta catalyst has in the range of 10-20 pmol / g of aluminum sites, as measured using elemental analysis.

70. The process of any of claims 53-69, wherein the Sn-Beta catalyst has in the range of 15-130 pmol / g of acid sites, as measured using temperature programmed desorption of ammonia.

71. The process of any of claims 53-69, wherein the Sn-Beta catalyst has in the range of 20-110 pmol / g of acid sites, as measured using temperature programmed desorption of ammonia.

72. The process of any of claims 53-69, wherein the Sn-Beta catalyst has in the range of 40-100 pmol / g of acid sites, as measured using temperature programmed desorption of ammonia.

73. The process of any of claims 53-69, wherein the Sn-Beta catalyst has in the range of 60-85 pmol / g of acid sites, as measured using temperature programmed desorption of ammonia.

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