Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D493/00—Heterocyclic compounds containing oxygen atoms as the only ring hetero atoms in the condensed system
  • C07D493/02—Heterocyclic compounds containing oxygen atoms as the only ring hetero atoms in the condensed system in which the condensed system contains two hetero rings
  • C07D493/04—Ortho-condensed systems

Definitions

• This invention concerns a process for the manufacture of anhydro- and dianhydro- hexitols, pentitols, and tetritols by the dehydration of sugar alcohols (alditols) and an integral dehydration reactor for conducting said process.
• TECHNICAL BACKGROUND OF THE INVENTION Anhydro sugar alcohols, in particular derivatives of maimitol, iditol, and sorbitol, are known for their therapeutic uses and uses in food.
• isosorbide l,4:3,6-dianhydrosorbitol
• isosorbide is a derivative of sorbitol, which can be derived from various natural resources. Sorbitol may be regarded as a renewable natural resource for the manufacture of polymers.
• Anhydro sugar alcohols are known to be produced by dehydration of the corresponding sugar alcohols (or monoanhydro sugar alcohols) by the action of various dehydration catalysts, typically strong acid catalysts.
• these catalysts include sulfonated polystyrenes (H + form) (German Patent DE 3 041 673 C2; Canadian Patent Disclosure CA 1 178 288 Al); and various mineral acids, such as HC1 (U.S. Patent 4,169,152; German Patent Disclosure DE 3 233 086 Al), H3PO4 (East German Patent Disclosure DD 1 32 266; Can. J. Chem., 52 (19) 3362-72 (1974)), HF (International Patent Disclosure WO 89/00162 A; Carbohydr. Res. 205 (1990) 191-202) and H 2 SO 4 (German Patent Disclosures DE 3 521 809 Al and DE 3 229 412 Al).
• a batch process for the formation of the dianhydro sugar alcohol isosorbide has been described in the literature as a two step process involving intramolecular dehydration of sorbitol to sorbitan (1,4-monoanhydro- sorbitol), and further reaction of sorbitan to isosorbide (l,4:3,6-dianhydrosorbitol) in an acid catalyzed dehydration - cyclization.
• an aqueous solution of sorbitol is charged to a batch reactor. The temperature is increased to 130°C-135°C under vacuum (35 mm Hg) to remove the water.
• a catalyst usually sulfuric acid
• the operable temperature range of the reaction is very narrow. Higher temperatures lead to decomposition and charring of the end product, while lower temperatures inhibit the reaction rate due to difficulties in removal of the water of reaction.
• This reaction produces isosorbide and a higher molecular weight by-product. The by-product is presumably produced by water elimination between two or more sorbitol molecules, but its exact nature is not clearly defined. See Starch/Starke (1986), 38(c), 26-30 and Roland Beck, Pharm. Mfg Inc. (1996), 97-100.
• Such a process improves product safety and reduces the process waste load.
• a process for the preparation of a dianhydro sugar alcohol comprising the steps of: a) introducing to the first stage of a multistage reactor a process stream comprising at least one sugar alcohol or monoanhydro sugar alcohol and, optionally, water; b) intimately contacting said process stream with a counter current flow of an inert gas at elevated temperature to remove the bulk of any water present to yield a dewatered process stream; c) intimately contacting said dewatered process stream with a dehydration catalyst in the presence of a counter current flow of an inert gas at elevated temperatures to remove water of reaction as formed; and d) removing the reaction product from the bottom of the reactor.
• Figure 1 is a schematic representation of a preferred embodiment of the process of the present invention.
• Figure 2 is a schematic representation of the dehydration reactor utilized in a preferred embodiment of the process of the present invention.
• the present disclosure describes a process for the production of anhydro and dianhydro sugar alcohols, most preferably, a process for the production of isosorbide, 1 ,4:3,6-dianhydrosorbitol.
• the process is directed toward the production of anhydro sugar alcohols and generally includes the steps of introducing at least one sugar alcohol or monoanhydro sugar alcohol, usually in the form of an aqueous solution, into a vertical reaction vessel, in a downwardly flowing fashion, in the presence of a countercurrent flow of an inert gas; removing most of the water from said aqueous solution by evaporation; dehydrating the sugar alcohol or monoanhydro sugar alcohol in the presence of a catalyst to form a reaction product comprising anhydro sugar alcohol and water; removing the water of reaction from said reaction product by evaporation in the presence of a countercurrent flow of an inert gas; and removing the reaction product from the bottom of the reactor for subsequent use or purification.
• the process may further include one or more purification steps such as evaporation, distillation, extraction and ion-exchange or combinations thereof.
• the process is preferably continuous such that the steps of introducing the starting sugar alcohol, removing water from the starting sugar alcohol, dehydrating the sugar alcohol, and removing the water of reaction, and removing product from the reactor occur simultaneously and the rates of reactant feed, and product removal are coordinated to maintain a steady amount of the reaction mass in the reactor.
• Typical sugar alcohols in particular tetritols, pentitols and hexitols, are suitable for use in the process as starting materials.
• the starting materials may be sugar alcohols, monoanhydro sugar alcohols, or a mixture thereof.
• Particularly preferred starting materials include erythritol, threitol, xylitol, arabinitol, ribitol, glucitol (also known as D-sorbitol or sorbitol), D-mannitol (mannitol), galactitol and iditol.
• sorbitol is most preferred because sorbitol is readily available and can be obtained on a large industrial scale by the reduction of glucose with hydrogen, as known to one of ordinary skill in the art, and the resulting product, isosorbide, is especially valuable for use in the preparation of polyester polymers and copolymers.
• the preferred form of sorbitol is as its aqueous solution in water, available as an article of commerce as sorbitol, 70%, from Archer Daniels Midland, (Minneapolis, MN) or Cerestar or, Roquette Freres, Lestrem, France or in experimental quantities, from chemical supply houses such as Aldrich (Milwaukee, WI).
• the catalysts used to facilitate the dehydration reaction are typically strong acid catalysts.
• Several types of acid catalysts may be used, each having specific advantages and disadvantages.
• One class of acid catalyst that may be used includes soluble acids. Examples of such acid catalysts include sulfuric acid, phosphoric acid, p-toluene sulfonic acid, methanesulfonic acid and the like. Sulfuric acid is a preferred catalyst from this class.
• acid anion exchange resins may also be used, such as sulfonated polystyrenes, for example, AG50W-X12 from BioRad or perfluorinated ion-exchange polymers, such as National®, available from E. I. du Pont de Nemours and Company (Wilmington, DE).
• Inorganic ion exchange materials may also be used, such as acidic zeolites.
• H-beta zeolite from Degussa (Frankfurt, Germany) may be used in the process disclosed herein.
• a soluble catalyst for the process of the present invention it is preferable to use a soluble catalyst and most preferable is the use of sulfuric acid.
• sulfuric acid is used such that it comprises 0.25 to 2.5 wt % of the reaction mass, preferably 0.5 to 1.5 wt %.
• the sulfuric acid is supplied to the reactor as an aqueous solution ranging from 1 to 97% sulfuric acid. Acid strength is optimized such that the most concentrated solution of acid that results in no detrimental by-product formation at the point of introduction is used in order to reduce the overall water removal load on the reaction system.
• the dehydration is performed at elevated temperatures between 100 and 180°C, preferably at temperatures between 115 and 160°C, and most preferably at temperatures between 115 and 145°C.
• the dehydration is carried out by intimately contacting the reaction mass with a stream of counter currently flowing inert or non-reactive gas, preferably nitrogen or carbon dioxide, most preferably nitrogen.
• a stream of counter currently flowing inert or non-reactive gas preferably nitrogen or carbon dioxide, most preferably nitrogen.
• the nitrogen is recycled to the reactor system after cooling to reduce entrapped volatiles, predominantly water.
• the amount of nitrogen is typically between 0.5 to 1.5 lb per lb of sugar alcohol - water free basis.
• intimately contacting is meant that the non-reactive gas, e.g. nitrogen, is injected into the system as a continuous stream of small bubbles so that effective contact with the reaction mass occurs.
• the dehydration is preferably performed at approximately atmospheric pressure, although elevated or reduced pressures can also be used with minor adjustments to other process parameters, such as time and temperature. In one preferred embodiment, in commercial size equipment, there is a pressure gradient across a staged reaction ranging from approximately atmospheric to approximately 1.2 atmospheres pressure.
• the dehydration catalyst (acid) addition can be performed in such a way that the catalyst is added in the requisite quantity initially, and further catalyst is added on an as-needed basis. However, it is also possible, and preferable, to add the catalyst in continuous fashion during the dehydration reaction.
• the elevated temperature of the dehydration reaction promotes rapid dehydration of the starting materials.
• over-temperature, or prolonged high-temperature operation promote the formation of byproducts and/or the further conversion of the desired product to undesired secondary products over time. Therefore, it is desirable to remove the resultant reaction product from the high temperature reaction mixture rapidly to protect it against further reaction/decomposition.
• the reaction product is drawn off from the reaction vessel continuously during the course of the dehydration reaction.
• the acid catalyst may be deactivated and/or removed from the reaction product, which, preferably, has been removed from the reaction vessel.
• the deactivation may be accomplished by any method known in the art, such as addition of a metal hydroxide base to form an insoluble salt.
• Polymeric or inorganic ion exchange materials may be recovered by filtration.
• Purification of the crude reaction product may occur by distillation, recrystallization, melt recrystallization or a combination thereof. A combination of distillation and recrystallization from an aliphatic alcohol such as methanol or ethanol maybe employed in order to minimize the number of purification steps while maximizing the purity of the reaction product.
• This purification of the reaction product may occur as part of the continuous process or in a separate process.
• the purity of the resultant anhydrosugar alcohol should be at least 99.0%, preferably at least 99.5%, most preferably at least 99.8%, and preferably meets the purity requirements for use in polymer production.
• a preferred process of the invention is described below in relation to Figure 1.
• the dehydration takes place in a reaction vessel (1), which is provided with supply lines for the starting materials such as aqueous sugar alcohol solution (2), acid catalyst (3) and nitrogen (4).
• Vessel (1) is heated by means of heaters (5) and (6).
• Heater (5) supplies the majority of heat to the reactor and provides heat sufficient to remove the bulk of the water that enters the reactor with the feed of sorbitol 70% at (2). Any means of heat input at (5) can be used.
• a calandria is schematically represented. The heat input to heater (5) is adjusted to hold the temperature in the evaporation zone of the reactor (7) at approximately 120-130°C.
• Heaters (6) supply heat to the various dehydration stages of the reactor.
• the cooled nitrogen stream (12) is conducted to a heater (13) where the nitrogen is heated back to process temperature prior to reintroduction to the reactor at (4).
• Product stream comprising 70-80% isosorbide with the balance comprising isosorbide oligomers, decomposition products and monoanhydro sorbitol derivatives exits the reactor at outlet (14).
• the reactor of Figure 1 is sized, and flow rates are adjusted such that hold up time for the sorbitol to isosorbide reaction mass is in the range of 1 to 3 hours, preferably 1.5 to 2.5 hours with the assumption that the temperature at the top of the reactor is 120-130°C and the temperature of the exit stream is approximately 140-145°C.
• Figure 2 presents an expanded view of the reactor vessel (1).
• Features 2, 3, 4, 5, 7, 9 and 14 are identified as in Figure 1.
• the five dehydration zone heaters (6-1 to 6-5) and five dehydration stages (8-1 to 8-5) are individually identified.
• the temperature gradation down the column and pressure gradient down the column is anticipated to be as in the chart below:

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• Chemical & Material Sciences (AREA)
• Organic Chemistry (AREA)
• Heterocyclic Carbon Compounds Containing A Hetero Ring Having Oxygen Or Sulfur (AREA)
• Low-Molecular Organic Synthesis Reactions Using Catalysts (AREA)
• Organic Low-Molecular-Weight Compounds And Preparation Thereof (AREA)

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• 2001
  • 2001-05-22 AU AU2001264848A patent/AU2001264848A1/en not_active Abandoned
  • 2001-05-22 EP EP01939318A patent/EP1294727A2/en not_active Withdrawn
  • 2001-05-22 JP JP2002500860A patent/JP2003535085A/ja active Pending
  • 2001-05-22 CN CN01810097A patent/CN1430619A/zh active Pending
  • 2001-05-22 WO PCT/US2001/016662 patent/WO2001092246A2/en not_active Ceased
  • 2001-05-24 US US09/864,466 patent/US6407266B2/en not_active Expired - Fee Related
  • 2001-05-25 TW TW090112665A patent/TW558555B/zh active

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