Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D307/00—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom
  • C07D307/02—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings
  • C07D307/04—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having no double bonds between ring members or between ring members and non-ring members
  • C07D307/06—Heterocyclic compounds containing five-membered rings having one oxygen atom as the only ring hetero atom not condensed with other rings having no double bonds between ring members or between ring members and non-ring members with only hydrogen atoms or radicals containing only hydrogen and carbon atoms, directly attached to ring carbon atoms

Definitions

• This invention pertains to a process for the preparation of 3-alkyltetrahydrofurans. More specifically, this invention pertains to a two—step process wherein 2 , 3—dihydrofuran is converted to
• 3 alkyltetrahydrofurans.
• the 3 alkyltetrahydrofurans produced in accordance with the present invention are useful as industrial solvents and as monomers in the manufacture of polymers such as elastomers.
• Alkyltetrahydrofurans, or precursors which may be cyclized to alkyltetrahydrofurans, may be prepared by a number of procedures. For example, Zenk et al., Synthesis, 695 (1984) , describe a process for alkylating ⁇ —butyrolactone with alkyl halides to produce ⁇ —alkyl— ⁇ — butyrolactones which may be hydrogenolyzed to 3—alkyltetrahydrofurans.
• aldehyde bearing hydrogen (s) on the a—carbon atom would give crossed aldol condensations, thereby lowering the yield of the desired 3—alkyltetrahydrofuran.
• aldehydes such as benzaldehyde or pivalaldehyde having no hydrogen atoms on their ⁇ —carbon atom would avoid this disadvantageous side reaction.
• the present invention provides a process for the preparation of a 3—alkyltetrahydrofuran having the formula
• step (1) contacting the intermediate compound from step (1) with hydrogen in the presence of a catalytic amount of a Group VIII noble metal or rhenium, water and a strong acid; wherein R 1 is an aliphatic, cycloaliphatic, aromatic or heterocyclic radical and each R 2 is an alkyl radical.
• the acidic material useful for catalyzing the first step of the process may be selected from various Bronsted or Lewis acids.
• Lewis acids include aluminum trichloride, aluminum tribromide, aluminum trifluoride, aluminum triiodide, boron trifluoride, boron trichloride, boron tribromide, boron triiodide, iron (III) chloride, iron (III) bromide, iron (III) fluoride, iron (III) iodide, tin (IV) chloride, tin (IV) bromide, tin (IV) fluoride, tin (IV) iodide, zinc fluoride, zinc chloride, zinc bromide, zinc iodide, titanium (IV) fluoride, titanium (IV) chloride, titanium (IV) bromide, titanium (IV) iodide, zirconium tetra— chloride, zirconium tetrabromide, zirconium tetra—
• Bronsted acids include sulfuric acid, nitric acid, hydrogen chloride, hydrogen bromide, hydrogen iodide, hydrogen fluoride, phosphoric acid, trifluoroacetic acid, and toluenesulfonic acid. Because of its high activity and its liquid form, the most preferred catalyst is boron trifluoride introduced as its diethyl etherate complex.
• the concentration of the acidic catalyst used in the process can be varied significantly depending, for example, on the particular catalyst used although only low concentrations usually are needed. By adjusting the reaction conditions, any concentration from 0.1 ppm to 99 percent for liquid or saturation for solid catalysts, based on the weight of the step (1) reaction mixture, may be used. Preferred concentrations range from 1 ppm to 10 weight percent (same basis) .
• the preferred catalyst, boron trifluoride preferably is used in a concentration within the range of 10 to 3000 ppm, most preferably within the range of 500 to 1500 ppm.
• Step (1) of the process may be carried out over a wide range of temperatures, e.g., from —50 to 200°C, although the use of temperatures in the range of —20 to 50°C normally are preferred.
• the most preferred temperature range is —10°C to 20°C.
• the use of temperatures below the preferred temperature ranges results in slow reaction rates which necessitates the use of excessive reaction times.
• the use of temperatures above the preferred temperature ranges may cause catalytic cracking of acetal (II) , leading to the formation of excessive amounts of byproducts.
• the mole ratio of the acetal to 2 , 3—dihydrofuran should be in the range of 1:1 to 100:1. Because of material handling costs and the energy required to separate and recycle the unused acetal, the most practical acetal: 2, 3—dihydrofuran mole ratio is 3:1 to 10:1.
• the first step of the process is carried out under substantially anhydrous conditions.
• inert (nonreactive) solvents such as aliphatic and aromatic hydrocarbons, ethers and halogenated hydrocarbons may be employed in the first step.
• the desired product in step (1) is a 1:1 adduct of 2,3-dihydrofuran and acetal (II). Since compound (III) is itself an acetal, it also can add 2,3-dihydrofuran to form the 2:1 adduct (several isomers, each of which is also an acetal) . This condensation with additional 2 , 3-dihydrofurans can repeat until the product mixture contains each of 1:1, 2:1, 3:1, 4:1, etc. adducts of 2,3-dihydrofuran and acetal (II) . It is apparent that each additional condensation beyond the 1:1 adduct stage lowers the yield of the desired 1:1 adduct product.
• reaction conditions are chosen to optimize the production of the 1:1 adduct of 2,3-dihydrofuran and acetal and minimize formation of all other adduct/by—products.
• One important determinant of the yield of compound (III), the 1:1 adduct of 2,3-dihydrofuran and acetal (II) is the catalyst concentration. Before adding any 2,3-dihydrofuran, essentially all of the catalyst exists as a catalyst/acetal (II) complex.
• the reaction Upon adding the first increment of 2,3-dihydrofuran, the reaction initially produces a catalyst/1:1 adduct complex.
• This complex reacts either with acetal (II) to reform a catalyst/acetal (II) complex and free 1:1 adduct (a chain transfer step in polymerization terminology) or it reacts with additional 2 , 3—dihydrofuran to form a catalyst/2 :1 adduct complex (a chain propagation step in polymerization terminology) .
• this reaction actually is the first stage of a polymerization and the competition between the chain transfer step and the chain propagation step determines the amount of higher adducts formed and, inversely, the yield of the 1:1 adducts.
• the catalyst When using catalyst concentrations below the preferred catalyst concentration ranges, the catalyst is the limiting reagent permitting an accumulation of unreacted 2,3-dihydrofuran.
• the catalyst/1:1 adduct complex (from the reaction of the catalyst/acetal complex and 2,3-dihydrofuran) contacts unreacted 2,3-di- hydrofuran, it forms some catalyst/2 :1 adduct complex thereby lowering the yield of the 1:1 adduct.
• the 2 , 3—dihydrofuran becomes the limiting reagent so that the catalyst/l:l adduct complex (from the reaction of the catalyst/acetal complex and 2,3-di- hydrofuran) contacts essentially no unreacted 2,3-dihydrofuran. Therefore, it forms almost no catalyst/2 :l adduct complex and resulting in high yields of the 1:1 adduct. Almost all of the catalyst/1: 1 complex has time to exchange with acetal (II) to form fresh catalyst/acetal (II) complex and free 1:1 adduct.
• the alcohol from the acetal cracking also can add to 2 , 3—dihydrofuran to form a 2—alkoxytetrahydro— furan by—product. Consequently, the yield of the desired product falls because both the acetal (II) and 2 , 3—dihydrofuran reactants form products other than their 1:1 adduct.
• intermediate compound of formula (III) is converted to a 3—alkyltetrahydrofuran by the hydrogenolysis of all the alkoxy groups while not affecting the tetrahydrofuran ring.
• the hydrogenolysis is carried out by contacting intermediate compound (III) with hydrogen in the presence of a catalytic amount of a Group VIII noble metal, water and a strong acid under hydrogenolysis conditions of temperature and hydrogen pressure.
• Examples of the catalytic metals which may be employed in the second step of my novel process include palladium, platinum, rhodium, rhenium, ruthenium, iridium, etc.
• the Group VIII noble metal catalyst preferably is rhodium, iridium or, especially, palladium.
• the form of the Group VIII nobel or rhenium metal catalyst is not critical although the most efficient use of the expensive metals is in a finely divided form on an appropriate support.
• supported catalysts comprise 0.1 to 10 weight percent Group VIII noble or rhenium metal deposited on a suitable catalyst support material such as activated charcoal, silica, alumina, titania, zirconia, barium sulfate, and calcium sulfate.
• the catalyst metals may be used as finely divided, unsupported metals, e.g., palladium black, although this mode of catalyst utilization may not represent the most efficient use of the expensive Group VIII noble metal.
• compounds of the Group VIII noble metals or rhenium e.g., salts such the chloride, fluoride, bromide, nitrate, carboxylate, e.g., acetate or benzoate; oxides;, or hydroxides may be used.
• insoluble salts of Group VIII noble metals and rhenium insoluble salts such as the phosphates, sulfates, or iodides can be used.
• the concentration of the Group VIII noble or rhenium metal which is catalytically effective varies significantly depending, for example, upon the particular metal utilized, the form in which the metal is used and other process variables such as temperature, pressure and residence time.
• the amount of catalytic metal present may be from 0.000001 to more than 100 percent based on the g-atoms of Group VIII noble or rhenium metal per g-mole of intermediate compound (III) present.
• the amount of Group VIII noble or rhenium metal present preferably is 0.00001 to 0.2, most preferably 0.001 to 0.1, g-atoms Group VIII noble metal or rhenium per mole of intermediate compound (III) present.
• Examples of the strong acids which may be used in the second step of the process include sulfuric, phosphoric, nitric, hydrofluoric, hydrochloric, hydrobromic, hydriodic, trifluoroacetic, or a sulfonic acid such as alkanesulfonic acids, arylsulfonic acids, e.g., toluenesulfonic acid, and polymeric sulfonic acids, e.g., acidic ion exchange resins comprising styrene/divinylbenzene polymers bearing sulfo groups.
• a sulfonic acid such as alkanesulfonic acids, arylsulfonic acids, e.g., toluenesulfonic acid, and polymeric sulfonic acids, e.g., acidic ion exchange resins comprising styrene/divinylbenzene polymers bearing sulfo groups.
• the concentration of the strong acid may be in the range of 0.000001 molar to 15 molar although concentrations of 0.001 molar to 5 are preferred and concentrations of 0.01 to 1 molar are most preferred.
• the mole ratio of palladium to strong acid is in the range of 1:10 to 1:100.
• the strong acid may be utilized in the form of a catalyst support material impregnated with at least one non—volatile (or low volatile) strong acid, e.g., sulfuric and phosphoric acid.
• a non—volatile (or low volatile) strong acid e.g., sulfuric and phosphoric acid.
• Alumina, titania, zirconia, barium sulfate, calcium sulfate and silica containing 0.0001 to 50 weight percent, based on the total weight of the supported catalyst, sulfuric or phosphoric acid are examples of such supported, strong acids.
• the strong acid may be an acidic, ion exchange resin comprising a polymer bearing sulfonic acid groups.
• compound (III) often is not completely converted into gaseous (at the reaction temperatures) compound (I) , supplemental non—volatile acid must be periodically reintroduced onto the catalyst support to maintain the catalyst activity.
• the second step of the present process may be carried out in the presence of iodine or an iodine compound such as an iodide salt.
• iodine or an iodine compound such as an iodide salt.
• the inclusion of iodine or and iodine compound as a promoter in step (2) of the process permits the use of lower reaction temperatures.
• the hydrogen— olysis temperature can be up to 60°C lower than the temperature without the iodine promoter.
• iodine is a hydrogenolysis catalyst inhibitor so that the required amount of metal catalyst normally must be increased by up to 200 to 1000 percent to counteract this inhibiting effect.
• Use of an iodine promoter depends on the sensitivity of the product yield to lower temperatures.
• the amount of iodine or iodine compound present in the step (2) reaction mixture may range from 0.000001 molar to 10 molar. However, iodine concentrations in the range of 0.0001 molar to 1 molar are preferred with concentrations in the range of 0.001 molar to 0.1 molar being most preferred.
• the second step of the process of the present invention can be achieved through the utilization of at least 3 basic modes of operation: (1) a single, convenient hydrogenolysis reaction removing all alkoxy side groups simultaneously (as described hereinabove) ;
• the simultaneous hydrogenolytic removal of all side alkoxy groups is carried out by contacting the intermediate compound (III) with hydrogen in the presence of a catalytic amount of a Group VIII noble metal—containing hydrogenation catalyst, a strong acid, water, and, optionally, an iodine promoter under hydrogenolysis conditions of temperature and pressure.
• This treatment causes the preferential removal of the alkoxy side groups while leaving the tetrahydrofuran ring largely intact.
• the various stages of the reaction with the accompanying intermediate products may be observed by slowing down or interrupting the reaction at various times of its progression.
• the overall yield of product (I) can be enhanced by separating the reaction into these stages by progressively increasing the severity of the hydrogenolysis conditions recovering whatever product (I) is produced at each stage and providing the rationale for the second case.
• each alkoxy group is removed with a selective hydrogenolysis.
• treating compound (III) with hydrogen in the presence of catalytic amounts of a Group VIII noble metal, water, and a strong mineral acid (like the first mode catalyst system except for the absence of the optional iodine promoter) at moderate temperatures selectively removes the 2-alkoxy group while producing compound (I) in moderate yields. It is believed that this selective hydrogenolysis takes place by hydrolysis of the compound (III) acetal group producing 4-hydroxy-2-(l-alkoxyalkyl)—butanal which undergoes hydrogenation or hydrogenolysis producing compound (I) and 3-(lalkoxyalkyl) tetrahydrofuran.
• the other products are the two isomers of 3—(1—alkoxyalkyl) ⁇ tetrahydrofuran having the formula
• the 3—alkylfuran may be hydrogenated to the corresponding 3—alkyltetrahydrofuran in high yields by known procedures, e.g., the procedure described by Starr et al., Org. Synth. Coll. Vol. II, 566 (1943). With the high activity of the f ran ring, this mode of operation produces a large number/quantity of by—products and therefore does not give optimum yields of compound (I) .
• step (2) The temperatures under which step (2) is performed depends upon the particular mode of operation used.
• the temperature range for the first mode of carrying out step (2) is 50 to 450°C with 150 to 350°C being preferred and 200 to 300°C being most preferred. With iodine present as an optional promoter, the most preferred temperature range falls to 140 to 240°C.
• the temperature range for the removal of the first alkoxy side group is 0 to 250°C with 50 to 200°C being preferred and 70 to 180°C being most preferred.
• the temperature range is 150 to 400°C with 200 to 350°C being preferred and 220 to 330°C being most preferred.
• the temperature range for the dealcoholysis is 20°C to 400°C with 50 to 350°C being preferred and 80 to 300°C being most preferred.
• the temperature range for the hydrogenation of the resulting furan (V) is 0 to 200°C with 50 to 150°C being preferred, and 60 to 140°C being most preferred.
• the hydrogen pressures utilized in step (2) of the process are not critical and may range, for example, from 0.1 to 1000 bars absolute although hydrogen pressures in the range of 2 to 500 bars absolute, especially 10 to 100 bars absolute are preferred.
• the use of an inert solvent such as water, alkanes and halogenated hydrocarbons is optional, but not essential, in the second step.
• the aliphatic, cycloaliphatic, aromatic or heterocyclic radical which R 1 may represent and the alkyl radical which each R 2 may represent are not critical and may contain up to 12 carbon atoms.
• R 1 and each R 2 preferably are independently selected from alkyl, e.g., alkyl of up to 8 carbon atoms, most preferably lower alkyl, i.e., alkyl of up to 4 carbon atoms.
• the equipment used in this example was a 500 mL, round—bottom flask containing an overhead stirrer, an addition funnel, a thermowell with thermometer, a side arm capped with a septum cap, and a reflux condenser topped with a nitrogen inlet through which a dry nitrogen blanket was introduced throughout the duration of the reaction.
• the molar ratio of the total acetal used to the 2 , 3-dihydrofuran was 3.19.
• the product also contained 2—(2—ethoxytetrahydrofuran—3—yl)— 3—(1—ethoxyethyl) tetrahydrofuran, the 2:1 adduct (16 isomers), in 13.2% yield, and 2—(2—ethoxytetrahydro- furan-3-y1)-3-(3-(1-ethoxyethy1)-tetrahydrofuran-2-y1)- tetrahydrofuran, the 3:1 adduct (64 isomers), in 0.9% yield.
• the boiling point of the isolated 1:1 adduct was 91-94 °C/18 mm Hg.
• Example 1 was repeated using a molar ratio of acetal to 2,3-dihydrofuran of 3.24, an addition time of 130 minutes, a boron trifluoride catalyst concentration of 223 ppm, and a reaction temperature of 40 to 55°C.
• the yield of the 2:1 adduct was 10.3 percent and the yield of the 3 : 1 adduct was 1.6%.
• the remainder of the material balance was oligomers of acetal, 5.0%, and 2—ethoxytetrahydrofuran, 3.1%.
• Example 1 was repeated except the mole ratio of the acetal to the 2,3-dihydrofuran was 3.35, the overhead stirrer was replaced by a magnetic stirring bar, the catalyst concentration was 103 ppm boron trifluoride; and the reaction temperature was 3 to 7°C with an addition time of 60 minutes.
• the yield of the 1:1 adduct was 67.9%, the yield of the 2:1 adduct was 22.5%; and, the yield of the 3:1 adduct was 4.0%.
• Example 1 was repeated using a mole ratio of acetal to 2,3-dihydrofuran of 3.62, a catalyst concentration of 106 ppm and a reaction temperature of —2 to 5°C with an addition time of 245 minutes.
• the yield of the 1:1 adduct was 68.7%; the yield of the 2:1 adduct was 24.0%; and the yield of the 3:1 adduct was 5.2%.
• Example 1 was repeated except that the reaction pot was a 5000 mL round bottom flask.
• the mole ratio of the acetal to the 2,3-dihydrofuran was 3.52, the boron trifluoride catalyst concentration was 43 ppm, and the reagent addition time was 200 minutes.
• the yield of the 1:1 adduct was 66.5%; the yield of the 2:1 adduct was 25.9%; the yield of the 3:1 adduct was 5.8%; and, the yield of the 4:1 adduct was 0.5%.
• Example 4 was repeated using recycled acetal as the acetal reagent and a different means of dehydrating the apparatus and the reagent.
• the acetal from prior experiments flash distilled from a basified distillation pot, containing acetal and a few lower boiling impurities was fractionally distilled until the temperature in the distillation head reached 101°C. At this point, the distillation ceased and a reflux began separating any water condensing in the reflux head with a Dean—Starke trap. Within 6 hours after the removal of the last of the water, the reflux was interrupted and the flask contents were allowed to cool to room temperature. At this point, analysis of the flask contents showed a water content less than 10 ppm.
• the product yield determined by gas chromatography was 63.2% of the 1:1 adduct compared with an isolated yield of 61.3%.
• the yield of the 2:1 adduct was 25.8% by gas chromatography compared with an isolated yield of 22.9%. This experiment demonstrates the feasibility of using recycled acetal and a catalyst removal procedure, both of which may be used in a commercial process.
• Example 5 was repeated using an acetal to 2 , 3—dihydrofuran molar ratio of 3.21, a reaction temperature of —6 to —2°C, a catalyst concentration of 1018 ppm, and a reagent addition time of 175 minutes.
• Gas chromatographic analysis of the reaction mixture showed a 91.2% yield of the 1:1 adduct, a 7.1% yield of the 2:1 adduct, and a 0.2% yield of the 3:1 adduct.
• Example 5 was repeated using an acetal to 2 , 3—dihydrofuran molar ratio of 3.48, a reaction temperature of -9 to -6°C, a catalyst concentration of 2125 ppm, and a reagent addition time of 165 minutes.
• Gas chromato— graphic analysis of the reaction product showed an 84.3% yield of the 1:1 adduct, a 5.0% yield of the 2:1 adduct, a 0.1% yield of the 3:1 adduct, a 6.5% yield of 1,1,3-triethoxybutane, a 0.1% yield of 1, 1, 3 , 5-tetra- ethoxyhexane, and a 3.8% yield of 2-ethoxytetra- hydrofuran.
• Adct means adduct
• TEB is 1, 1, 3-triethoxy- butane
• TEH is 1, 1, 3 , 5—tetraethoxyhexane
• ETHF is 2—ethoxytetrahydrofuran.
• tubular reactor consisting of a 30.5 cm (12 inch) section of 304 stainless steel tubing having an interior diameter of 9.5 mm (3/8 inch) and containing 10.0 g of 3—10 mesh (about 1—2 mm particles) diatomaceous earth impregnated with 12 weight percent phosphoric acid maintained in place with glass wool.
• a thermocouple was positioned in the middle of the catalyst bed to record reaction temperature. With a gas flow of 55 L per minute, the reactor was heated in an oven to the required reactor temperature ⁇ 3°C which was maintained throughout the reaction by a temperature controller.
• the reaction began by pumping 2—ethoxy—3—(1—ethoxyethyl) tetrahydrofuran (EEETHF) into the reactor at a rate of 10 mL per hour through a preheater to vaporize the sample. The vaporized material then was passed over the catalyst at the designated temperature. The effluent from the reactor flowed into a 50 mL round bottom flask containing anhydrous potassium carbonate to neutralize any acid eluting from the catalyst support and the flask was topped by a dry ice cooled trap to capture any volatile liquids exiting the reactor.
• EETHF ethoxy—3—(1—ethoxyethyl) tetrahydrofuran
• EtFuran is 3—ethylfuran
• MEEDHF means monoethoxyethyldi— hydrofurans
• VDHF vinyldihydrofurans
• Heavies means higher molecular weight compounds.
• the autoclave was sealed and the contents thereof were stirred and heated at 220°C under a hydrogen pressure of 35.5 bars absolute (500 psig) for 60 minutes.
• Example 18 The procedure described in Example 18 was repeated except that the iodine was omitted and the hydrogenolysis was carried out at 300°C over a period of 60 minutes. Gas chromatographic analysis showed the conversion of the starting material to be 100% with a selectivity to 3—ethyltetrahydrofuran of 38.7%.
• Example 18 was repeated except the catalyst was replaced with 5 weight percent rhodium on activated charcoal and the hydrogenolysis was carried out at 220°C for one hour at 35.5 bars hydrogen pressure. Gas chromatographic analysis of the reaction mixture showed a 100.0% conversion of the EEETHF starting material and a 3—ethyltetrahydrofuran yield of 61.2%.
• Example 18 was repeated except the catalyst was replaced with 5 weight percent rhodium on alumina, the iodine was omitted and the hydrogenolysis was carried out at 120°C for one hour at 35.5 bars of hydrogen pressure. Gas chromatographic analysis of the reaction mixture showed a 100.0% conversion of the starting material and a 3—ethyltetrahydrofuran yield of 45.1%.
• Example 18 was repeated except the catalyst was replaced with 5 percent iridium on activated charcoal, the iodine was omitted and the hydrogenolysis was carried out at 180°C for one hour at 35.5 bars hydrogen pressure. Gas chromatographic analysis of the reaction mixture showed a 100% conversion of the starting material and a 3-ethyltetrahydrofuran yield of 31.2%.
• the solid catalyst was removed by vacuum filtration of the reaction mixture through a Buechner funnel and the filtrate was steam distilled until 500 mL of distillate had been collected.
• This distillate contained over 98% of the 3—ethyltetrahydrofuran and 3—(1—ethoxyethyl)—tetrahydrofuran produced.
• the aqueous distillation residue still containing the phosphoric acid catalyst was suitable for recycling to another hydrogenolysis.
• the steam distillate separated into two phases.
• the lower aqueous phase still contained substantial organic values which were recoverable by returning it to another steam distillation.
• the upper, organic phase was separated, dried, and subjected to a careful fractional distillation.
• the fraction boiling at 114—116°C consisted of 98% pure 3—ethyltetrahydrofuran.
• the pot residue consisted of 96% pure 3—(1—ethoxyethyl) tetrahydrofuran and was suitable for converting to 3—ethyltetrahydrofuran.
• Hastelloy B alloy autoclave was 20 mL of the impure 3—(1—ethoxyethyl) tetrahydrofuran recovered in Example 23, 100 mL of heptane, and 1.03 grams of 5 weight percent palladium on alumina.
• the experiment began by stirring and heating the autoclave contents to 290°C for one hour at a hydrogen pressure of 35.5 bars.
• gas chromatographic analysis showed that the conversion of the starting material was 22.8% and the selectivity to 3—ethyltetrahydrofuran was 51.7%.
• the overall yield of 3—ethyltetrahydrofuran through this two—stage hydrogenolysis is 81.9%.
• Example 24 The procedure of Example 24 was repeated using 7.52 g of 5 weight percent palladium on carbon, 1.50 g iodine, 1.69 g 85 weight percent phosphoric acid, 50 mL of 3—(1—ethoxyethyl) tetrahydrofuran, 50 mL water and 50 mL methanol, and a hydrogenation temperature, pressure and time of 230°C, 35.5 bars absolute and 1 hour, respectively. Gas chromatographic analysis showed that the conversion of the starting material was 78.2% and the selectivity to 3—ethyltetrahydrofuran was 65.4%.
• Example 26 13.04 g of 5 weight percent Pd on carbon, 1.0 mL concentrated sulfuric acid.
• Example 27 5.02 g of 1 weight percent Pd on carbon
• Example 28 5.01 g of 1 weight percent Pd on carbon,
• Example 26 1.0 mL 85 weight percent phosphoric acid. Iodine (1.0 g) was used only in Example 26.
• Example 26 20 mL EEETHF, 100 mL water.
• Examples 27—28 100 mL EEETHF, 900 mL water.
• Example 29 150 mL EEETHF, 850 L water.
• Examples 30-35 200 L EEETHF, 800 mL water.
• Example 26 180°C for 1 hour.
• Examples 27-30 120°C for 2 hours, 160°C for 2 hours.
• Example 31 110°C for 2 hours, 150°C for 2 hours.
• Example 32 100°C for 2 hours, 140°C for 2 hours.
• Examples 33-35 90°C for 4 hours, 130°C for 2 hours.

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