CA1195687A

CA1195687A - Process for producing polyols with at least one oxacyclopentane ring

Info

Publication number: CA1195687A
Application number: CA000401406A
Authority: CA
Inventors: John Feldmann; Hubert Koebernik; Hans U. Woelk
Original assignee: Unilever Bestfoods North America
Current assignee: Corn Products International Inc
Priority date: 1982-04-21
Filing date: 1982-04-21
Publication date: 1985-10-22

Abstract

PROCESS FOR PRODUCING POLYOLS
WITH AT LEAST ONE OXACYCLOPENTANE RING

ABSTRACT OF THE DISCLOSURE:

Anhydro sugar alcohols having at least one oxacyclo-pentane ring are prepared by dehydrating sugar alcohols having 4 to 6 carbon atoms. The process is carried out at reduced pres-sure and elevated temperature in the presence of a strongly acidic heterogeneous catalyst and in the absence of organic solvent. A
reaction temperature of from about 100° C. to 160° C. is selected as a function of the pressure to minimize distillation of the anhydrous sugar alcohols from the reaction mixture. The process results in high product yields compared to prior art processes.

* * * * * * * *

Description

A ~ 9 5 j ~ 3 2 6 O

PROCES5 FOR P:RODUCING P(:)LYOLS

.

BACKGROUND OF THE INVENTION

Field of the Invention The present invention relates to anhydro sugar al-cohols and particularly rela~es to a process for producing them.

The Prior Art Anhydro sugar alcohols are well known. They can be used for pharmaceutical purposes or as starting materials or inter-mediates for chemical syntheses (of, for example, fine chemicals, emulsifiers on the basis of esters, polyester and alkyd resins, and polyurethanes by serving as starters or cross~linking agents)~
The anhydro alcohols are known to be produced by acid-cataly~ed, intramolecular dehydration of sugar alcohols. This reaction has been thoroughly studied and optimized particularly with regard to the sugar alcohol most readily available, i.e.
sorbitol.
D-sorb.itol, when subjected to thermal treatment in the presence of an acid, first forms a monoannydride~ l,A-anhydro-D-sorbitol~ which immediately undergoes further reaction forming 1,4; 3,6-dianhydro-D-sorbitol~ By-products of this reaction may be 2,5 monoanhydrosorbi~ol and, to a smaller extent, 3,6-anhydrosorbitol.
This reaction today is commonly performed with so-called homogeneous catalysts, i~e., catalyst.s which are molecularly di.s-persed in the reaction system~ such as hydrocholoric acid or sul-furic acidO The use of these acids, however, entails excessive formation of by-products, particularly esters of the catalyzing acid, by halogenations and requires neu~ralization of the reac-tion product mixture with subsequent desalinationO Moreover, the acids used in the reaction are highly corrosive, ~xtremely volatile in part, and produce maximum yields of about 66~ which are not fully satisfactory (Carbohydrate Chemistry, Vol. II, 191-lg8 (1963)).
It is also known to use organic solvents in performing reactions of this type with azeotropic removal of the react.ion water. This does not result in any major improvements~
~lthouyh some of ~he disadvantages of the processes using acid catalysts dissolved in the reaction mixture, such as ~ corrosion problems and the formation of excessive amounts of esterified by-products which are difficult to remove, may be avoided by using heterogeneous catalysts, i.e., specific~ strong-ly acidic, cation exchange resins, this is not satisfactory as it has a number of other disadvantagesf particularly lower maximum yields of about 35% and a need to include organic solvents as '; ' reaction media and entrainers for removing water by azeotropic distillation ~cf. Ropuszynski et al. in Przem Chem. 1969, 48 (11)/ 665-~ and Weisleder et al. in Carbohydr. Res. 79, 133~141 (1980~.) As far as the need to use carefully selected organic solvents (solven~ mixtures) is concerned, ~eisleder et al. stress that in a comparative assay in which 1,4; 3,6~dianhydro-D-sorbitol is produced ~rom sorbitol by means of "dry distilla-~ion wi~h acidic resin" a far lower yield was obtained, iOe., no more than S~.
An object of the invention therelore is~to provide a process f6r producing anhydro sugar alcohols by ~hich the dis-advantages of the prior ar~ are overcome. This includes avoid-ing the problems arising in connection with homogeneous acid catalysts in respect of by-product formation, corrosion~ and lS low yields. Another object is to avoid the use o costly organic solvents.

SUMMARY OF THE INVENTION

The objects have been accomplished by the invention on ~he basis o the surprising ~inding tha~ in the dehydration ~0 o~ su~ar alcohols in the presence of heterogeneous catalysts, tl~e absence of organic solvents results in an increase of the yield to levels which are higher, sometimes even several times higher, than the levels obtained in the most favorable known processes.

The anhydrous sugar alcohols of the invention are polyols with at least one oxacyclopentane ringO They have the general formula:

~l OH

I ~ ~
R ~ /

where Rl is selected from the group consisting of hydroxyl ~nd the ether oxygen atom of a second oxacyclopentane ring and R
is selected from the group consisting of hydrogen, hydroxymethyl, and a bivalent radical having the formula -CH~-CHOH-, provided that when ~2 is said bivalent radical, R is an ether oxyyen atom and the polyol has the structural formula:

0~

., '' ' ,, /~ ~' .
II ~ ~
Y '.
OH

I)ETAILED DESCRIPTION OF THE INVENTION

The anhydro sugar alcohols of the invention are pre~
pared by dehydra~ing sugar alcohols having 4 to 6 carbon atoms at ~levated temperatures in the presence of a strongly acidic heterogeneous catalyst. Organic solvents are not used in the process of the invention.
Sugar alcohols used as starting ma~erials for the pur-poses of the invention are preferably hexitols and in particular sorbitol, since these alcohols are readily available at low prices and in practically unlimi~ed amoun~s. With these alcohols, the process of the invention produces yields of at least 50% and mostly over 60% 7 In the case of sorhitol, yields of 85 to 90~ and more are generally achieved. It is noted that mixtures of sugar alcohols like, for instance, a mixture of sorbitol and mannitol which is obtained in the catalytic hydrogenation of mixtures of glucose and fructose, are also suitable starting materials. A
startin~ material which is interesting in this regard consists of C4 -C6 -polyol mixture~ which are obtainable by hydrogena-tion of hemicellulose hydrolysatesO Such hydrolysates at the present are prepared commercially in great amounts from side products like for example corn shellst oat shells~ etcO These hydrolysates are in particular used for preparing xylose and xylitol, respectively. The tetroses, different pentoses and ~5 hexoses and their hydrogenation products, respectively inevitably obtained thereby at the present are scarcely useably waste products which according to the process of the present applica-tion can be con~er~ed into valuable intermediates, especially f or the plastics industry.
Heterogeneous catalysts that are useful in the present invention include any strongly acidic acid catalysts which are sufficiently heat resistant. Suitable catalysts i~clude "acidic"
molecular sieves such as zeolites, as well as the cracking or hydrocracking catalysts employed chiefly by the mineral oil industry~ The latter are of interest for purposes of the invention mainly because they are widely used also or the production of sugar alcohols by catalytic hydrogenation of the corresponding sugars and thus open a way for producing polyols of formula I and II from sugars by means o~ integrated uncomplicated processes.
Best results can be achieved with highly acidic syn-thetic cation exchange resins, in particular polystyrene sulfonic acid cation exchange resins cross-linked with divinyl benzene (DVB). Suita~le for the purpose are so-called "gel resins" which should be partially cross-linked, i~e.~ with at most 4% divinyl ben2ene, as well as macroporous resins which sho~ld preferably be cross-linked to a higher degree, iOeO, with at least 10~ divinyl ben~.ene.
In the process of the invention the catalyst is separated from the reaction product mixture by simple solid/liquid separating 2S methods, e.gl, filtration, and may be re-used several times with-out requiring any special ~reatment.

As the react~nts and/or reaction products and, in some cases, even the catalysts are sensitive to oxidation, the process of the invention is best carried out in an atmosphere of in~rt gas, preferably nitrogen, i~ being advantageous as a rule to bubble the inert gas through the reaction mixture to achieve a good stirring effect and to improve removal of water from the reaction mixture by distillation According to a preferred embodiment of ~he inventionr the reaction is carried out at reduce~ pressure, particularly a pressure in the range of 0.001 to 0.5 bar. This i5 recommended especially when using a relatively high melting starting material whose melting point is depressed below the maximum ~emperature of 160 C., preferably below 155 C. and more preferably below 145 C. by the addition of wa~er. It is also recommended if the starting material is an aqueous solution of sugar alcohol which is concentrated in situ. In the latter case, the vacuum is applied and gradually increased, preferably after the water content has dropped to a level at which the reaction mixture~ when exposed to normal pressure, no longer boils in the ~emperature range of 100 C. to about 150 C. and in particular 110 C. to 140 C.
which is preferred according to the invention.
The process of the invention may be carried out not only batchwise, but also continuously. In the continuous pro-cess, agitated vessel-type or fluidiæed bed-type reac~ors are 2S particularly well suited and a two- or multistep operation is preferable as a rule mainly because it facilitates adjustment of the reaction condi~ions to the composition of the reaction mixture.
When the reaction products o the present invention are us~d for technical purposes, for instance a~ the polyol component in synthetic resin syntheses, they may freyuently be used without any further processing or purification. If a higher degree of purity appears to be necessary or at least desirable with regard to the intended use; the crude reaction product mixtures may be further processed or purified~ This can be done, for instance, by treating with activated carbon or ion exchange resins, or applying optional commonly known methods such as fxactionated crystallization, distillation or column chromatography. The total yield may be increased in that fractions rich in unreacted starting material or, in the case of hexitols~ monoanydropolyols, which are obtained during the separating process, are recycled into the reaction.
The invention is further illustrated by the following examples.

~O ~ le 1 A commercial mixing vessel was charged with 25 kg of a 70~ sorbitol solution and 1 ]cg of a strongly acidic ion exchanger in the H~ form (macroporous polystyrene sulfonic acid resin, cross linked with 14~ DVB). The mixture was concentrated to dryness -- 8 ~

and then stirred ~or two hours at a pressure of 0O03 bar and at a temperature of 140 C, The result.ing melt was removed from the ion exchanger by filtering while hot~ The yield was 13,900 g of raw product containing 91 w/w % of dianhydrosorbitol~

Example ~
250 g o sorbitol and 20 g of the ion exchanger de-scribed in Example 1 were placed in a l-liter ~hree-necked flask and treated as in Example lo Af~er a reaction time of 3 hours, 10 the melt was filtered off as describedO The yield was 190 ~ of raw product containing B7 w/w % of dianhydrosorbitol~

Example 3 Example 2 was repeated except that macroporous poly-styrene sulfonic acid resin cross-linked with 20% divinyl benzene was used as catalyst and the reaction time was reduced to 2 hours. The yield was 191 g of raw product containing 89 w/w~
of dianhydrosorbitol.

Example. 4 Example 3 was repeated except that a strongly acidic .0 polystyrene acid gel ion exchange resin (in the H form) cross-linked with 2~ DVB was used. The yield was 191 g of raw product containing ~7 w/w% o~ dianhydrosorbitol~

r_~ ` :

Example 4 was repeated except that a gel resin9 highly cross-linked with 10~ DVB, was used as a catalyst and the reaction time was extended to 5 hours. The yield was 190 g of raw product containing 86 w/w% of dianhydrosorbitol, Example 6 200 g of mannitol~ 50 ml of water and 30 g of the ion exchanger described in Example 3 were placed in a l-liter three necked flask and stirred for 2 hours at 1~0 C~ The pressure was gradually reduced to 0.03 bar with the temperature being kept constant causing water to be evaporated. The reaction mixture was then stirred for another 5 hours under constant conditions, after which the catalyst was remoYed by filtering wh}le hot. The yield was 151 g of raw product containing 76 W/W~ of dianhydro-mannitol.

Example 7 250 g of a mixture of equal parts by weight of sorbitol and mannitol and 30 g of the catalyst described in Example 3 were placed in a l-liter three-necked flask and stirred for 4 hours 7~ at 0.03 bar and 145 C. The catalyst was then removed by filter~
ing while hot. The yield was 192 g of raw product containing 46 w/w% of dianhydrosorbitol and 40 w/w% of dianhydromannitol.

Example ~
Analogously to Example 3, 200 9 meso-erythrite was stirred for 4 hours at 0.03 bar and 140 C. During the reaction process, nitrogen was caused to bubble through the reaction mixture. The yield was 175 g of raw product containing 86 w/w~ of anhydroeri=~
thrite.

Exam~le 9 Example 2 was repeated except that the reaction time was extended to 5 hours. The reaction mixture was filtered as usual. The yield was 189 9 of raw product which contained 94 w/w% of dianhydrosorbitol.
The results achieved according to the invention, as evidenced in the examples, are unexpected, slnce one would expect that, normally, a) at high temperatures and more intimate contact and/or im-proved transport of material to and from the hetero~eneous catalyst brought about by the solvent should tend to at least accelerate the approach of reaction equilibrium conditions and ~0 b) the continuous removal of either or both of the two main reaction proAucts from the system taking place in "dry dis-tillation" would favor the formation of anhydropolyols.

Example 10 In a l-liter three-necked flask 250 y of a cata-lytically hydrogenated anhydrous hemicellulose hydrolysat2 obtained from corn shells and 20 g of a strongly acidic ion exchanger in the H~ -form (polystyrene sulfonic acid~gel resin,

2 % DVB cross-linked~ were placed and stirred 2 hours at 130 C.
at a pressure of 0,03 bar.

The resulting melt was removed from the ion exchanger by filtering while hot, dissolved in water and treated with active carbon. After filtration and concentration 180 g of a product were obtained having a hydroxyl number of 985 in comparison to a hydroxyl number of 1790 of the starting materialO

.
A HPLC-examination showed that the polyols present in the raw material ~ca. 75 ~ pentitol, from which more than 55 %
consisted of xylitol, sorbitol and gallactitol) had been converted into anhydroderivatives in an extent of more than 9~ %0 Having set ~orth the general nature and some examples of the present invention, the scope is now particularly set forth in the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A process for making polyols having at least one oxacyclopentane ring of the general formula:

wherein R1 is selected from the group consisting of hydroxyl and the ether oxygen atom of a second oxacyclopentane ring, and R2 is selected from the group consisting of hydrogen, hydroxy-methyl, and a bivalent radical having the formula -CH2-CHOH-, provided that when R2 is said bivalent radical, R1 is an ether oxygen atom and the polyol has the structural formula:

comprising dehydrating sugar alcohols having 4 to 6 carbon atoms in the presence of a strongly acidic heterogeneous catalyst at a temperature from about 100° C. to about 160° C. in the presence of water in an amount which corresponds to less than the amount of reaction water liberated in the reaction.

2. The process of claim 1 wherein dehydrating is conducted at reduced pressure.

3. The process of claim 2 wherein the temperature is selected as a function of the pressure to minimize distillation of said polyols from the reaction mixture.

4. The process of claim 3 wherein the strongly acidic heterogeneous catalyst is selected from the group consisting of a strongly acidic cation exchange resin, a strongly acidic inor-ganic molecular sieve, an acidic cracking catalyst, and an acidic hydrocracking catalyst.

5. The process of claim 4, wherein a polystyrene sul-fonic acid cation exchange resin in the H-form which has been cross-linked with divinyl benzene is used as said catalyst.

6. The process of claim 3 wherein the reaction is carried out in an atmosphere of inert gas.

7. The process of claim 6, wherein inert gas is bubbled through the reaction mixture.

8. The process of claim 3 wherein the reaction is carried out at reduced pressure in the range of 0.001 to 0.5 bar.

9. The process of claim 3 wherein the reaction is carried out at reduced pressure in the range of 0.01 to 0.2 bar.

10. The process of claim 3 wherein the reaction tempera-ture is allowed to rise to a maximum of 155° C.

11. The process of claim 3 wherein the reaction tempera-ture is allowed to rise to a maximum of 145° C.

12. The process of claim 3 wherein a solution or melt of the starting material which contains up to 50 w/w% water is used.

13. The process of claim 3 wherein at least one hexitol is used as the sugar alcohol.

14. The process of claim 13 wherein the sugar alcohol is sorbitol.

15. The process of claim 13 wherein the reaction is continued until at least 50% of the starting material has been converted into dianhydrohexitol.

16. The process of claim 3 wherein the reaction is car-ried out continuously.

17. The process of claim 16 wherein the reaction is carried out in an agitated vessel-type reactor.

18. The process of claim 16 wherein the reaction is carried out in a fluidized bed-type reactor.

19. The process of claim 3 wherein the starting materials are selected from the group consisting of hexitol, sorbitol, at least two different C4 - C6 sugar alcohols and hydrogenated hemicellulose hydrolysate.

20. The process of claim 19 wherein the reaction is continued until at least 50 percent of the starting material is converted into the corresponding anhydrotertitols, pentitols, and dianhydroxitols.