CA1099730A

CA1099730A - Process for the preparation of gamma- hydroxytetrahydrofuran and tetrahydrofuran by the hydroformylation of allyl alcohol

Info

Publication number: CA1099730A
Application number: CA264,936A
Authority: CA
Inventors: Jung W. Kang; William L. Hergenrother
Original assignee: Firestone Tire and Rubber Co
Current assignee: Bridgestone Firestone Inc
Priority date: 1975-11-05
Filing date: 1976-11-03
Publication date: 1981-04-21
Also published as: FR2347360A1; FR2347360B1; IT1066754B; GB1528697A; DE2649900A1

Abstract

ABSTRACT OF THE DISCLOSURE

Gamma-hydroxytetrahydrofuran is prepared fron allyl alcohol according to a hydroformylation reaction in the presence of a RhHCO[-PPh3]3 catalyst complex. An excess of triphenyl phosphine is utilized to improve the selectivity of the catalyst complex to produce a specific intermediate which readily gives Gamma-hydroxytetrahydrofuran. Tetrahydro-furan is then prepared from the Gamma-hydroxytetrahydrofuran compound by dehydration followed by hydrogenation in the presence of a catalyst.

Description

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The present invention relates to the preparation of Gamma-hydroxytetrahydrofuran through the utilization of a highly selective catalyst system and to the preparation of tetrahydrofuran from the prepared Gamma-hydroxytetrahydrofuran compound.
Heretofore, various catalysts have been utilized in hydroformylation reactions. Among these catalysts are various rhodium compounds or complexes such as acetyl acetonate rhodium dicarbonyl. Another specific catalyst is hydridocarbonyltris ~riphenyl-phosphine7-rhodium which has been used in the hy-droformylation of alkenes at atmospheric pressure, see Journal of the Chemical Society ~ 1970, Page 2753-2764. Additionally, similar rhodium compounds or complexes have been utilized to prepare 1,4-butanediol as set forth in U.S. Defensive Publica-tion No. T904,321 or to hydroformylate alpha olefins as in U.S. Patent No. 3,527,809,and The Journal of Organic Chemi~try, Vol. 34, No.2, February, 1969, p. 327-330.
Applicant's process relates to the preparation and production of Gamma-hydroxytetrahydrofuran utilizing a rhodium ~omplex which has been found to be very selective in the forma-tion of a specific intermediate which readily yields said Gamma hydroxytetrahydrofuran compound. Additionally, tetra-hydrofuran is readily prepared from Gamma-hydroxytetrahydro-~ furan by dehydration followed by hydrogenation.
; It is, therefore, an object of the presente invention to provide a process for the preparation of Gamma-hydroxytetra-hydrofuran.
It is another object of the present invention to prepare Gamma-hydroxytetrahydrofuran, as above, through the hydroformylation of allyl alcohol.

It is a further object of the present invention to prepare Gama hydroxytetrahydrofuran, as above, utilizing a 1~
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specific catalyst which is very selective in producing a desired intermediate.
It is an additional object of the present invention to produce Gamma-hydroxytetrahydrofuran, as above, wherein said desired lntermediate readily yields said Gamma-hydroxytetrahy-drofuran.
It is a yet further object of th~e present invention to prepare Gamma-hydroxytetrahydrofuran, as above, utiliæing various pressures and temperatures which favor the preparation lQ of said desired intermediate~
It is yet a further object of the present invention to prepare Gamma-hydroxytetrahydrofuran, as above, wherein organic phosphines and organic phosphites are utilized.
It is yet a further ob~ect of the present invention to produce tetrahydrofuran from Gamma-hydroxytetrahydrofuran.
It is yet a further object of the present invention to produce tetrahyrofuran, as above, from Gamma-hydroxytetra-hydrofuran through dehydration followed by hydrogenation in the presence of a catalyst.
It is ye~ a further object of the present invention to produce tetrahydrofuran, as above, utilizing a dehydration catalysts.
It is yet a further object of the present invention to produce tetrahydrofuran, as above, utilizing supporting catalysts.
These and other objects of the present invention, together with the advantages thereof over existing prior art processes and methods which will become apparent from the following specification are accomplished by the processes and methods herein described and claimed.
In accordance with the invention, there is thus provided a process for the preparation of Gamma-hydroxytetra-r ~.

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hydrofuran, which comprises adding from about 0.05 to about 50 millimoles per 100 grams of allyl alcohol or RhHCO CPPh373 to a vessel, adding hydrogen and carbon monoxide to pressurize the vessel, the mole ratio of hydrogen to carbon monoxide being from about 0.5 to about 5.0, adding from about 5 to about 150 of a mole excess based on the catalyst of an organic phosphine or organic phosphite compound, adding allyl alcohol to the vessel and heating the vessel to a temperature of from about . 25C to about 150C to selectively form Gamma-hydroxytetrahy-1~ drofuran.
The present invention further provides a process for the preparation of tetrahydrofuran from Gamma-hydroxytetrahy-drofuran, which comprises adding a catalyst to the gamma-hydro-xyltetrahydrofuran, the catalyst selected rom the group consisting of the lA and 2A metals of pyrosulfate, phosphate and phosphorous pentaoxide, the catalyst ranging from about 0.05 to about 1.0 mole per mole of gamma-hydroxytetrahydro-furan and the dimethyl sulfoxide catalyst ranging from about

2 to about 15 mole per mole of gamma-hydroxytetrahydrofuran heating the gamma-hydroxytetrahydrofuran to a temperature of from about 150C to about 250C to form dihydrofuran, and hydrogenating the dihydrofuran to yield tetrahydrofuran.
According to the concept of the present invention, Gamma-hydroxytetrahydrofuran is prepared from allyl alcohol using a highly selective catalyst as well as various favorable reaction conditions. Additional concepts relate to the p~oduct-on of tetrahydrofuran Erom Gamma-hydroxytetrahydrofuran.

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Il' I A preferred and speci~'jc ca-tal~st utilize~ in the ¦Ipresent invention is RhHCO[PPh3}3 wherein Ph stands for the ~., phen~l radical. U-tiliza-tion oE the specific catal~st in accordance with various reaction conc~itioll~ in the h~droiorm~la-¦1 tion of allyl alcohol strongly ~avors the production oE h~droxy-n-bu~anal in contras-t to a small amount of 2-meth,yl-3-h~drox~ :
¦propanal~ Ge:nerally,,the tautomerism betwe'en Gamma-h~d,roxytetra- ~,~
!h~drofuran and 4-hydroxyl-n~butanal is highly favorable to G~mrn~
¦hydroxytetrahydrofuran. '~nounts generally in excess of 80 per-. 10 ¦cent and usuall~ above 90 per.'cent o a theoretical'arnoun-t-., o:~ Ça~na-hydrox~tetrahydro:Euran can be'prepared accor~'ling.to the present:invention. The amount oE ca-tal~sts utilized can var~ :
rom about'O.OS mill'imoles to about 50' millimoles based upon . .~
100 grams of allyl alcohol. A preferred range extends from about , 0,l'to about 5.0'millimoles ~i'th'the highly preferrea ran~e' , .generally being approximatel~ or about l.O'millimoles' ~er' 100 grams of all~l alcohol~ ~.
,Generall~-, the catalyst is ~added to the'solution in a ~suitable medium suc,h'as toluene,',be'nzene,',and o-ther ar'oma-ti.c ,, hydrocarbon solvents. O:~ COUI-5~, ,any co'nce'ntration' ma~ be' :
.util.. ized such'as one millimole of ca'talysts per 100' mil.l,ili-ters ,, of -toluene.:. The'ca-tal~st ls :~enerally adde~.to an~ conven~.ion~l ':
reaction ves'se~ and p~efera~l~ to a ves'sel which'is e~ulpped wi~,h : . a.temperature :controlling devic,e~ stlrrer ~nd exit ports wh.l.ch Ima~ be'utilized for distillation, ~:
¦ The'-reac-tion vessel is also cha.rge~ with a solution mediurn lor soivent in which the hydroform~lation of al'lyl alcohol ma~ be 73~

carried o~t. Generally, a high boiling liquid is preferred which does not react with any of the various components.
Specific compounds include benæene, cyclohexane, ethyl acetate, mineral oil, and generally any of the phthalates such as dioctyl phthalate.
The reactor is also charged with an organic phosphine, or an organic phosphite, preferably triphenyl phosphine or triphenyl phosphite. A mole execess is utili~ed based upon the amount of catalyst. The excess may range from about 5 to about 150 or more preferablyl from about 40 to about 110~ A
highly preferred excess ranges from about 55 to about 100. An excess of triphenyl phosphine and triphenyl phosphite has been found to suppress hydrogenation and to increase selec-tivity of the catalyst in forming 4-hydroxy-n-butanal as opposed to 2-methyl-3-hydroxypropanal- The 4-hydroxy-n-butanal is a tautomer of gamma-hydroxytetrahydrofuran.
Once the reaction vessel has been charged with the catalyst and a suitable solvent such as dioctyl phthalate and triphenyl phosphine, it is then pressurized with a mixture of hy~
~rogen and carbon monoxide. The pressure may range from about 1 atmosphere (O.lOMPa) to about 100 (lO.lMPa) atmospheres with a preferred range being from about 5 ~0.5LMPa) to about 50 (5.1MPa) atmospheres. A highly preferred range for the present invention is from about 10 (l.OlMPa) to about 12 ~1.22MPa) atmospheres. The ration of hydrogen to carbon monoxide may vary from about 0.75 to about 5.0 and preferably from about 0O80 to about 3Ø A highly preferred range is generally about 1 to 1 on a mole basis.
The mixture is then stirred and heated to a tempera-ture of between about 25 and 150C with preferred range being from about 50C to about 150C. A highly preferred range is from about 75C to about 120C. Generally, temperatures in - 6 ~

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1~9~3}!730 excess of 150C are avoided since the catalyst loses its selec-tivity.
The present invention is generally carried out in a continuous operation although a batch or semi-continuous process may be utilized. In a continuous process, the allyl alcohol is added to the reaction vessel under the above noted operating conditions. Upon reformation of 4-hydro~y-n-butanal which is in dynamic equilibrium with gamma-hydroxytetrahydrofuran, the latter component is generally distilled off through a 10 distillation port of the reaction vessel.
According to the above-noted reaction conditions, a very high ammount of normal aldehyde is formed in contrast to an aldehyde containing a side chain.
The invention will be better understood by the following example which reIates to the formation of Gamma Tetrahydrofuran.
EXAMP~E I
A 1 liter glass reactor equipped with a temperature controlling device, a stirrer and exit ports for distillation 20 was utilized. The reactor was charged with a solution of ;
triphenyl phosphine (100 g) in 400 ml of dry toluene and a solution of RhHCO (PPh3)3, 1 mM in 100 ml of dry toluene. The reactor eas pressurized with a 1 to 1 mixture of carbon monoxide and hydrogen to 1.13 MPa tl50 psig). After the mixture was stirred at 93C for 1.0 hour, solvent was distilled off under vacuum. One mole of allyl aIcohol was then charged to the reactor. The hydroformylation was carried out at 93C under 1.48 MPa (~00 psig) of constant 1 to 1-H2/CO for 30 minutes.
After the hydroformylation was completed, the product was collected by distillation at 100C at 2.5mm of Hg (333Pa). A
conversion to hydroxyalkanol or 4-hydroxy-n-bu~anal was 82 percent. Analysis of the product in a manner as set forth ` ~.g!' 73~

in Example II shows that at least 80 percent of the product was gamma-hydroxytetrahydrofuran.
The determination that the hydroformylated product of allyl alcohol was, in fact,gamma-hydroxytetrahydrofuran was~
made as set orth in Example II.
EXAMPLE II
Preparation of y- butyrolactone _from hydroformyla~ed ally~
alcohol To a suspension of fresh silver oxide, prepared from 60 g of silver nitrate and 28 g of sodium hydroxide in 30 ml of distilled water was added dropwise to a solution of hydro-formylated allyl alcohol ~15 g), ~amme-hydroxytetrahydrofuran, ; in 15 ml of distilled ~ater with a magnetic stirring at o&
for 30 minutes. After addition was completed, the mixture was allowed to stir at room temperature for 60 minutes. The silver and excess silver oxide was filtered, washed with 50 ml of distilled water. The combined filtrate was acidified with concentrated hydrochloric acid and was evaporated at 60C
under vacuum to remove water. The residue was extracted with `~
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methanol and then the methanol solution was removed under vacuum. The viscous liquid was collected at 100C/5 mm of Hg (666Pa), 12 9 (82 percent). The distilled product was confirmed as ~-butyrolactone by infrared, proton magnetic `! resonance and mass spectra.
The following examples relate to the formation of `
gamma-tetrahydrofuran.
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EXAMPLE III

A hydroformylation reaction was carried out in a !~
I manner identical with Example 1 except that the 100 gra~s of ,, triphenyl phosphine was added in 200 grams of toluene. The reaction was carried out for four hours the percent conversion to 4-hydroxylalkanal was 85 percent with approximately 84 ' 9~73~ ~

percent of the product being gamma-hydroxytetrahydrofuran.
EXAMPLE IV
The hydroformylation reaction was carried out in a manner identical to Example I except that 10 grams of triphenyl phosphine and 150 grams of dioctylphthalate was utilized.
After a reaction time of 3.4 hours, a conversion to 4,hydroxy~
alkanal of 86 percent was obtained. Analysis showed that at least 84 pe~cent of the product was gamma hydroxytetrahydrofuran.

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r~3 EXA~PLE V
Another hydrofor~ylation reaction was carried out iden-tical to that in Example I except that the reaction time was 50 minutes. A conversion o 77 percent was obtained with analysis showin~ that the Gamma-hydroxytetrahydrofuran content was at least 76 percent.
EXAMPLE VI
Another hydroformylation reaction was carried out in a manner identical with Example I except that the pressure was 150 psig ~1.13 MPa) at a reaction time of 36 minutes. The conversion to 4-hydroxyalkanal was 82 percent with at least 81 percent of the product being Gamma-hydroxytetrahydrofuran.
According to further concepts of the present invention, Gamma-hydroxytetrahydrofuran can be readily converted to Gamma-dihydrofuran by dehydration with subsequent hydrogenation to yield tetrahydrofuran.
The dehydration reaction is generally carried out at a temperature of from about 150 C to about 250C with a preferred temperature range being from about 210 to about 240 C. Atmosphe~
ric pressure is normally utilized. The reaction is generally carried out in the presence of an inert gas such as nitrogen, helium, argon and the like to prevent oxidation of the aldehyde reactant to carboxylic acid and to prevent reaction of the produ-ced olefin. Additionally, the inert gas carries off the generated water and olefin product.

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It is essential that a dehydration catalyst be utilized~A particular group of such desirable catalysts include "active"
catalysts such as the lA and 2A metals of pyrosulfate, phosphates, phosphorous pentaoxide and dimethyl sulfoxide. A particular desirable catalyst is potassium pyrosulfate (K2S207). Generally, the range of the above catalysts and the below supporting catalysts is from about 0.05 moles to about 1.0 mole per mole of gamma-hydroxytetrahydrofuran with a preEerred range being ~ .
from about 0.1 to about 0.6 moles, except for dimethyl sulfoxide wherein a suitable range is from 2.0 to about 15 and preferably ,r about 7.0 moles per mole of gamma-hydrotetrahydrofuran.
Additionally, it has been found that supported catalysts may be utilized in lieu of the above catalysts. These catalysts generally include aluminium catalysts such as A1203.
Aluminium in combination with various metal oxides may be used such as Mo203 and W2O3. Another catalyst is silica gel.
Generally, the supported catalyst may be in the form of a bed.
When the vapor of gamma-hydroxytetrahydrofuran (as from distil-lation~ is passed over a heated bed, the product, 2,3-dihydro-uran, is formed and collected as through condensation~ Un-reacted vapor which is also collected may be readily separated from the product through simple distillation since the boiling points are quite different and recycled back to the supported bed catalyst.
The invention will be better understood by the ~ollowing example :
EXA~_PLE VII
To a 100 milliliter three neck flask equipped with a nitrogen bubbler, addition funnel, thermometer and magnetic stirrer in a vigeraux column was added 2.5 grams of potassium pyrosulfate. Gamma-hydroxytetrahydroEuran ~22.0 grams, 0.25 moles) was added at about 15 to about 20 drops per minute and ,~r, 1~9i?73~

gave a distillate of from about 35 to about 53C. The receiver contained 5.5 grams of a mixture of water and 2,3-dihydrofuran.
Two -7~C cold traps were utilized which contained a total weight respectively of 5.7 and 3.0 grams of the H20 olefin mixture. This product collected at -78C consisted of 5.1 and 2.5 grams of 2,3-dihydrofuran ~identified by I. R. and gas chromatography) and 0.6 and 0.5 grams of iceO NQ 2,3-dihydro-furan was isolated by freezing the distillate in the receiver but from the theoretical yield of water expected this must contain an additional 2.0 gr~ams of product.
The residue in the flask was a red-brown solid, which upon cooling adhered so well to the flask that sections of glass were pulled from the walk. The residue was separated from the glass by powdering and floating it on chloroform f~llowed by decanting the mixture from the precipitated powdered glass. The chloroform extracted 0.9 grams (4.1 percent) of what appeared to be the isomeric 2-methyl-3-hydroxypropanal and left a residue of 8~8 grams of insoluble resin and potassium pyrosul-:
; fate. This solid resin was then extracted with hot water to give 5.3 grams (30 percent of what appears to be polymerized 2,3 dihydrofuran. Thus from this reaction 4 percent of the hy-droformylation mixture did not dehydrate to 2,3-dihydrofuran.
The products obtained were 30 percent of 2,3-dihydrofuran that was polymerized by the acidic catalyst, 49 percent was isolated, 6 percent was lost by partial solubility in the water generated during the reaction and ll percent was swept past the two 78C
cold traps by the nitrogen purge.
In a similar example wherein the catalyst, potassium pyrosulfate, was wet, a lower amount of 2,3 dihydrofuran was isolated (17 percent) with 43 percent polymer and 40 percent volita]i~ation loss. Of course, it is desirable to utilize a dry catalyst.

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The produced 2,3-dihydroEuran may be hydrogenated in any conventional or known manner or method well known to those skilled in the art. Generally, the hydroglenation reaction can be carried out at temperatures ranglng from -20C to about 500C. However, a preferred range is from about 0C to about 150 & . The pressure may range from about 1 (0.10 MPa) atmos- .
phere to about 15,000 psig (103MPa) witha more desirable range being from 1 (0.10 MPa) atmosphere to about 3,000 psig (20.7 . MPa). A preferred range is from about 25 psig (0.273 MPa) to about 2,000 psig (13.9 MPa~.
With respect to the catalyst system employed, generally, any conventional or well known catalyst may be utilized. That is, various known cobalt, nickel and iron catalyst complexes may be employed. Specific examples of desirable catalyst include _ _ /

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Raney nickel~ Raney cobal-t and the like~ Additionally~ examples o~ hydrogenated catalysts include those speci~ically set forth in U.S. patent Nos. 3,625,~27; 3,868,354, 3,872,072; 3,882,094.
, The h~drogenation process can be carried out in any conventlonal manner well known to those skilled in the art and readily yields tetrahydrofuran. .
: Of course, the:tetrahydrofuran produced may be utilized . :.
:as a solvent as well as a starting material for the preparation of various polymers such as polyurethanes.
- 10 While in accordance with the patent statues, preferred embodiments have been~illustrated and described iD detail, it : ~
is to be understoood that the invention is not limited thereto; ~:`
the invention being measured solely by the scope of the attached claims. ~`
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Claims

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for the preparation of Gamma-hydroxytetra-hydrofuran and tetrahydrofuran by the hydroformylation of allyl alcohol, which comprises the steps of:
a) adding from about 0.05 to about 50 millimoles per 100 grams of allyl alcohol of RhHCO [PPh3]3 to a vessel, adding hydrogen and carbon monoxide to pressurize said vessel, the mole ratio of said hydrogen to said carbon monoxide being from about 0.5 to about 5.0, adding from about 5 to about 150 of a mole excess based on said catalyst of an organic phosphine or organic phosphite compound, adding allyl alcohol to said vessel and heating said vessel to a temperature of from about 25°C
to about 150°C to selectively form Gamma-hydroxytetrahydrofuran;
and b) when tetrahydrofuran is desired, adding a catalyst to the Gamma-hydroxytetrahydrofuran, said catalyst selected from the group consisting of the 1A and 2A metals of pyrosulfate phosphate, phosphorous pentaoxide dimethyl sulfoxide, or the group consisting of A12O3, silica gel, Mo2O3 and W2O3, said catalyst ranging from about 0.05 to about 1.0 mole per mole of said Gamma-hydroxytetrahydrofuran and said dimethyl sulfoxide catalyst ranging from about 2 to about 15.0 mole per mole of said Gamma-hydroxytetrahydrofuran, heating said Gamma-hydroxytetrahydrofuran to a temperature of from about 150 C to about 250°C to form dihydrofuran, and hydrogenating said dihydrofuran to yield tetrahydrofuran.

2. A process for the preparation of Gamma-hydroxytetra-hydrofuran by the hydroformylationof allyl alcohol, which comprises the steps of;

adding from about 0.05 to about 50 millimoles per 100 grams of allyl alcohol of RhHCO[ PPh3]3 to a vessel, adding hydrogen and carbon monoxide to pressurize said vessel, the mole ratio of said hydrogen to said carbon monoxide being from about 0.5 to about 5.0, adding from about 5 to about 150 of a mole excess based on said catalyst of an organic phosphine or organic phos-phite compound, adding allyl alcohol to said vessel, and heating said vessel to a-temperature of from about 25°C to about 150°C to selectively form Gamma-hydroxytetrahydrofuran.

3. A process for the preparation of Gamma-hydroxyte-trahydrofuran according to claim 2, wherein said organic phosphi-ne is triphenylphosine and said organic phosphite is triphenyl-phosphite, and the excess of said triphenylphosphine or said triphenylphosphite based upon said catalyst is from about 50 to about 110.

4. A process for the preparation of Gamma-hydroxy-tetrahydrofuran according to claim 2, wherein said pressure in said vessel is from about 1 (0.10 MPa) to about 100 (10.0 MPa) atmospheres and said vessel is heated to a temperature of from about 50°C to about 150°C.

5. A process for the preparation of Gamma-hydroxyte-trahydrofuran according to claim 4, wherein said catalyst ranges from about 0.1 to about 5 millimoles, said temperature ranges from about 75°C to about 120°C, said pressure ranges from about 5 (0.51 MPa) atmospheres to about 50 (5.1 MPa) atmospheres, said hydrogen to carbon monoxide ratio ranges from about 0.8 to about 3 and said organic phosphine is triphenyl-phosphine and said organic phosphite is triphenylphosphite.

6. A process for the preparation of Gamma-hydroxyte-trahydrofuran according to claim 5, wherein said catalyst amount is about 1 millimole, said temperature range is from about 75°C to about 120°C, said pressure ranges from about 10 (1.01 MPa) to about 12 (1.22 MPa) atmospheres, said hydrogen to carbon monoxide ratio is about 1 and the excess of said triphenyl phosphine or said triphenyl phosphine ranges from about 55 to about 100.

7. A process for the preparation of tetrahydrofuran from Gamma-hydroxytetrahydrofuran, which comprises the steps of:
adding a catalyst to the Gamma-hydroxytetrahydrofuran, said catalyst selected from the group consisting of the 1A and 2A
metals of pyrosulfate phosphate, phosphorous pentaoxide dimethyl sulfoxide, or the group consisting of Al2O3, silica gel, Mo2O3 and W2O3, said catalyst ranging from about 0.05 to about 1.0 mole per mole of said Gamma-hydroxytetrahydrofuran and said dimethyl sulfoxide catalyst ranging from about 2 to about 15.0 mole per mole of said Gamma-hydroxytetrahydrofuran, heating said Gamma-hydroxytetrahydrofuran to a temperature of from about 150 C to about 250 C to form dihydrofuran, and hydrogenating said dihydrofuran to yield tetrahydrofuran.

8. A process for the preparation of tetrahydrofuran according to claim 7, wherein said catalyst ranges from about 0.1 to about 0.6 moles and said temperature is from about 210°C
to about 240°C.

9. A process for the preparation of tetrahydrofuran according to claim 7, wherein said catalyst is selected from the group consisting of the 1A and 2A metals of pyrosulfate, phosphate and phosphorous pentaoxide.

10. A process for the preparation of tetrahydrofuran according to claim 9, wherein said catalyst ranges from about 0.1 to about 0.6 moles and said temperautre ranges from about 210°C to about 240°C.

11. A process for the preparation of tetrahydrofuran according to claim 7, wherein said catalyst is potassium pyro-sulfate.

12. A process for the preparation of tetrahydrofuran according to claim 11, wherein said catalyst ranges from about 0.1 to about 0.6 moles and said temperature is from about 210°C to about 240°C.

13. A process for the preparation of tetrahydrofuran according to claim 9, wherein said hydrogenation is carried out at a temperature of from about -20°C to about 500°C at a pressure of from about 1 (0.01 MPa) atmosphere to about 15,000 psig (103MPa).

14. A process for the preparation of tetrahydrofuran according to claim 13, wherein the reacted Gamma-hydroxytetra-hydrofuran is purged with an inert gas.

15. A process for the preparation of tetrahydrofuran according to claim 9, wherein said hydrogenation is carried out at a temperature of from about 0°C to about 150°C at a pressure of from about 1 (0.10 MPa) atmosphere to about 3,000 psig (20.7 MPa).

16. A process for the preparation of tetrahydrofuran according to claim 15, wherein the reacted Gamma-hydroxytetra-hydrofuran is purged with an inert gas.

17. A process for the preparation of tetrahydrofuran according to claim 16, wherein said inert gas is selected from a group consisting of nitrogen, helium and argon.

18. A process for the preparation of tetrahydrofuran according to claim 16, wherein said pressure is from about 25 psig (0.273 MPa) to about 2,000 psig (13.9 MPa).

19. A process for the preparation of tetrahydrofuran according to claim 16, wherein said catalyst is potassium pyrosulfate.