WO1986001512A1

WO1986001512A1 - Preparation of liquid carbohydrate derivatives

Info

Publication number: WO1986001512A1
Application number: PCT/GB1985/000388
Authority: WO
Inventors: Richard Heywood Still; John Lawrence Stanford; John Leslie Cawse; Michael Joseph Donnelly
Original assignee: The University Of Manchester Institute Of Science
Priority date: 1984-08-30
Filing date: 1985-08-30
Publication date: 1986-03-13
Also published as: JPS62500108A; GB8421884D0; EP0221080A1

Abstract

Methods of producing liquid glycosides. In one method the liquid glycoside is prepared by reacting a saccharide or polysaccharide with a substantially non-polar polyol in a solvent in the presence of an acid catalyst. In a further method the liquid glycoside is prepared by reacting together a polysaccharide rendered substantially non-hydrogen bonding by substituent groups and a polyol in a solvent in the presence of an acid catalyst.

Description

PREPARATION OF LIQUID CARBOHYDRATE DERIVATIVES

This invention relates to the preparation of liquid carbohydrate derivatives.

One of the components required in the manufacture of polyurethanes is a polyfunctional hydroxy compound, generally known as a polyol. Polyols are often based either on polyesters or polyethers with the latter having greater versatility. Most polyether polyols are at present based on oil-derived feedstocks, although polyols for certain limited applications have been prepared from natural products such as sucrose and sorbitol. Even these types of polyol however require oil-based chemicals to be used in- their preparation in order to convert the intractable carbohydrate into a liquid form. The conventional method of doing this involves chain-extending the hydroxyl groups of the carbohydrate with alkylene oxides such as propylene oxide and ethylene oxide.

Whilst these polyols are very satisfactory for manufacture of polyurethanes the fact that they are heavily reliant on chemicals derived from oil is making them expensive as oil socks dwindle while the urethane industry expands.

Alternative sources of feedstock will therefore need to be found, but any polyols made from novel sources will have to possess similar characteristics to the oil-derived materials. Some of the polyol characteristics which are required by the polyurethane industry include: low viscosity; high reactivity; miscibility with isocyanates; low volatility and low toxicity; and simplicity of manufacture. In certain types of commercial processes for polyurethane production, the foregoing combination of properties is of great importance. Examples of such processes include Reaction Injection Moulding (RIM) and Reinforced Reaction Injection Moulding (RRIM). In these processes, two liquid reactant streams (diisocyanate and polyol) are made to impinge at high velocity in a mixing head before entering a mould in which the polymerisation and curing reactions are completed.

The literature describes various simple glycosides (i.e. products obtained by reaction of a carbohydrate with an alcohol (the aglycon) having two or more hydroxyl groups).

These glycosides are produced with aglycons of low molar mass and are generally obtained either in the form of amorphous solids with high softening points, or

crystalline solids with high melting points. Also these glycosides are often highly polar and do not mix readily with diisocyanates. In order to utilise these compounds for polyurethane formation, it is necessary to carry out further chemical modification (by chain extension) which is often accomplished by alkoxylation under pressure. Table 1 gives some examples of short chain glycosides, prepared by the direct reaction between the carbohydrate and excess alcohol in the absence of an added solvent, and the subsequent steps necessary to convert them into useful products. The need for a two stage process to convert the glycosides to useful products is obviously disadvantageous as is the fact that the chain extension reaction is effected with oil derived products. It is an object of the present invention to provide one-stage methods of converting carbohydrates into liquid products which are useful in polymer formation, particularly but not exclusively polyurethane formation. According to a first aspect of the present invention there is provided a method of producing a liquid glycoside comprising reacting a saccharide or polysaccharide with a long chain, substantially non-polar polyol in a solvent in the presence of an acid catalyst.

The product of this reaction comprises a saccharide moiety or oligomers thereof bonded at the C₁-site to the long chain polyol which ensures that the original, polar saccharide or polysaccharide is converted to a liquid product miscible with isocyanates used for polyurethane formation.

The saccharide is preferably a mono or di-saccharide, preferred examples being D-glucose, L-glucose, galactose, sucrose, and lactose, although polysaccharides such as starch and simple alkyl glucosides such as methyl glucoside can also be used. Mixtures

of these products may be used. The saccharide may be used in pure form or may be provided by syrups such as glucose syrups, corn syrups or molasses.

Polyols for use in the method are preferably polymeric in nature and have a minimum molar mass of about 130 with a preferred maximum of about 2000. The preferred polyols are of the general formula

in which R is H or lower alkyl (particularly methyl) m is 2 to 4 and n gives a maximum molar mass of about 2000. Preferred examples of polyols are 1,4-butane diol (R=H; m=4; n=1), poly(tetra-hydrofuran), and hydroxy-functional natural oils, e.g. castor oil, all of which are derived from renewable natural resources, as of course are the saccharides. Thus PTHF is prepared from tetrahydrofuran which can be obtained from oat. hulls, corn cobs, or cellulose via the intermediate product furfural. Castor oil is a triol obtained from the castor plant.

Catalysts useful for the reaction include mineral acids, organic acids and Lewis acids, preferred examples being HF, HCl (gaseous or concentrated aqueous), H₃PO₄, HClO₄, H₂SO₄, HCOOH, p-toluene sulphonic acid, AICI₃ and BF₃.

As indicated above, the reaction is conducted in a solvent. It is important to note that attempts at direct reaction between carbohydrates and high molar mass polyols fail owing to incompatibility of the two reactants. This leads to a number of undesirable side reactions: for example, if an attempt is made to react polytetrahydrofuran with glucose using an acid catalyst, in the bulk state, the PTHF udergoes coupling, dehydration and depolymerisation reactions (giving THF), while the glucose reacts mainly with other glucose molecules to produce intractable unreactive oligosaccharides.

The use of a suitable solvent enables reaction between carbohydrate and polyol to be achieved smoothly, with the minimum of side reactions, and thus allows the preparation of glycosides which cannot be prepared by the bulk method.

The solvent for the reaction is preferably a polar, aprotic solvent, preferred examples being dimethylformamide, tetramethyl urea, dimethyl acetamide, N-methyl pyrolidinone (NMP), dimethyl sulphoxide, and acetonitrile.

According to a second aspect of the invention there is provided a method of producing a liquid glycoside comprising reacting together a polysaccharide rendered substantially non-hydrogen bonding by substituent groups and a polyol in a solvent in the presence of an acid catalyst.

Preferably the substituent groups on the polysaccharide are substantially non-polar.

Glycosides produced by the method described in the preceding paragraph comprise monomeric or oligomeric units derived from the polysaccharide chain (the monomeric or oligomeric units being substantially non-hydrogen bonding by virtue of their substituent groups) bonded to one of the polyol moieties which provide reactive sites for subsequent polymer formation. The nature of the monomeric or oligomeric units (i.e. non-hydrogen bonding) ensures that the products are liquids which are miscible with isocyanates.

Suitable substituents for rendering the polysaccharide substantially non-hydrogen bonding are, for example, alkyl groups, ester groups, halogen atoms, nitro groups and phosphate groups. It should be noted that the use of substituents rendering the polysaccharide substantially non-hydrogen bonding is essential as attempts to prepare liquid glycosides from unsubstituted cellulose were unsuccessful. Examples of substituted polysaccharides which may be used in the method of the second aspect of the invention are starch ethers, cellulose ethers, dextran ethers, and simple glucosides thereof (e.g. methyl, ethyl, butyl). Mixtures of these polysaccharides may be used. It may be necessary to pretreat certain carbohydrates before they can be used in the method of the second aspect of the invention. Thus certain starches may require partial hydrolysis by acids or enzymes to convert the starch into more reactive forms. It will be appreciated that the glycosides produced in accordance with the second aspect of the invention are to a large extent derived from materials (i.e. the polysaccharide) obtained from renewable natural resources.

The polyols used in the method of the second aspect of the invention are, for preference, low molar mass polyols although it is possible to use long chain, substantially non-polar polyols as used in the method of the first aspect of the invention.

Particularly suitable polyols are monomeric alkylene glycols, particularly those having 2-4 carbon atoms, i.e. ethanediol, propanediol and butanediol. Low molecular weight triols, e.g. glycerol, are also suitable.

Whereas the preferred solvents for the method of the first aspect of the invention are relatively expensive, polar aprotic solvents, the solvents used for the method of the second aspect may be the cheaper aliphatic ketones (e.g. butanone); aromatic hydrocarbons and chlorinated hydrocarbons.

The preferred acid catalysts for this aspect of

the invention are as given above for the first aspect of the invention.

A typical procedure for effecting the method of either the first or second aspect of the invention is as follows:

The selected carbohydrate (pretreated by enzymes, hydrolysis etc. if necessary) is dissolved in the selected solvent along with the required amount of polyol. Typically the reaction is carried out either in a stepwise or simultaneous addition manner using a total reactant concentration of 20 to 50% w/w. The reaction mixture is warmed if necessary, preferably in a nitrogen atmosphere, to facilitate dissolution of the carbohydrate. The selected acid catalyst is then added and reaction allowed to proceed at the selected temperature (typically in the range ambient to 150°C) for a specified time, which depends upon the degree of conversion required. The latter is dependent on the temperature, nature of acid and . solvent, and concentration of reactants.

The acid catalyst is then neutralised, the solvent and other volatiles removed by vacuum distillation and the resulting liquid carbohydrate polyol (i.e. the glycoside), filtered, if necessary, to removed unreacted carbohydrate. The precise ratio of carbohydrate to polyol used in the preparation depends on the required properties of the final liquid glycoside. These properties can be varied over a wide range by using different stoichiometric amounts of polyol and carbohydrate. It may however be inadvisable to use excess of polyol in the preparation, particularly when it is of high molecular weight, since substantial amounts of unreacted polyol may remain at the end of the reaction and be too involatile for removal by vacuum distillation: volatile glycols may however be used in initial stoichiometric excess if required, and removed along with solvent in the final stage of the preparation.

The glycosides produced by the method of the first and second aspects of the invention are polyols useful forpolymer formation. In particular they satisfy the requirements for polyurethane formation, namely low viscosity, high reactivity, low volatility, miscibility with iscocyanates and low toxicity. Also the ability to use different starting polyols and carbohydrates means that the liquid glycosides produced can be tailored to meet the specific requirements of a polymer manufacturer. Thus depending on the molecular weight of the polyol from which the glycoside is produced, polyurethanes can be produced ranging from flexible or semi-rigid foams to soft rubbers and tough glasses. By using liquid glycosides with high carbohydrate contents such as those obtained by the alcoholysis of ethyl cellulose or a simple saccharide with a low molar mass polyol, glasses can be produced which are dimensionally stable upto 140°C. The glycosides are suitable for RIM,RRIM, and other processes such as casting and low-pressure dispensing.

The number of hydroxyl groups which a polyol possesses is clearly instrumental in determining whether a polyurethane prepared from the polyol is linear or cross-linked. Polyol glycosides prepared from a mono-saccharide in accordance with the first aspect of the invention possess at least five hydroxyl groups (Formula I) but the number of these

Formula 1. Typical glycoside structure (α - form shown).

R = polyol skeleton derived from e.g. PTHF, castor oil. R' = H or a second saccharide unit. R" - H

available for reaction with the isocyanate group can vary depending upon the reaction conditions, owing to the different intrinsic reactivities of hydroxyl groups on the carbohydrate molecules as well as steric hindrance effects. Thus for example, a liquid glycoside produced by the method of the first aspect of the invention may be reacted In excess with diisocyanate under mild conditions to produce an essentially linear polymer whereas the same glycoside in the presence of an excess of diisocyanate and at higher cure temperatur'es add longer reaction times will produce a cross-linked polymer.

The glycosides obtained by the method of the second aspect of the invention are of the formula II:

Formula III: R^{1 1 1}= substituent group vhlch renders the molecule substantially non- hydrogen bonding m = 1 to 6 (typically) R = polyol skeleton n = 0 or m It will thus be seen that it is possible to produce mono- or bis-glycosides (i.e. n=O and n-m respectively) depending on the molar ratio of substituted polysaccharide to polyol to compounds of Formula (II). The glycosides obtained by the method of the

second aspect of the invention have fewer hydroxyl groups per saccharide unit and so will tend to produce linear polymers on reaction with difunctional reagents since the most accessible hydroxyl groups will be at the hydrolysed sites.

The invention will be further described by way of example only with reference to the following Examples in which Examples 1 to 4 illustrate methods in accordance with the first aspect of the invention, Example 5 illustrates a method in accordance with the

secondaspect of the invention, and Examples 6-8 illustrate the production of polyurethanes.

In the examples, reducing content was measured by means of quantitative Fehlings anlysis involving gravimetric determination of cuprous oxide. The hydroxyl equivalent weight was determined by acetylation using the method of Sorenson and Campbell in which the polyol is refluxed for 3 hours with acetic anhydride/pyridine mixture. It was also necessary to determine the equivalent weight of the polyols towards isocyanate. In the method employed the polyol was mixed with diisocyanate in bulk using varying weight ratios, the mixtures were cured and the Tg of the polymer determined. The ratio at which a maximum in Tg was observed was taken as the effective equivalent weight of the polyol.

Residual solvent levels in the polyol glycosides were determined by gas-liquid chromatography. The glucose conversion was calculated from the reducing end group concentration of the solution immediately prior to catalyst neutralisation and is quoted relative to the reducing power of glucose. Example 1. Preparation of polytetrahydrofuan 670 monoglucoside.

Hydroxy terminated poly tetrahydrofuran of average molar mass 670 (261g) glucose (70.3g) and N-methyl pyrrolidinone (NMP) (98% Lab. grade) (332g) were charged into a 1 L 3-necked flask equipped with a stirrer, condenser and thermometer. The slurry was heated to 132°C giving a clear solution, to which a

45% w/w solution of borontrifluoride in ether (6.5cm³) was added via the condenser. The contents of the reaction vessel was maintained at 130° ± 2°C for 277 minutes during which time samples were withdrawn periodically and analysed for glucose content. At the end of the reaction, the resulting dark brown solution was cooled to ambient and neutralised via the addition of Zerolit DM-F/Duolit DMF ion exchange resins.

The resin was removed by filtration and washed with NMP which was returned to the filtrate. The majority of the NMP was removed from the filtrate by rotary film evaporation under vacuum. The recovered NMP may be utilised in further reactions without adverse effects. The slurry so produced was filtered hot (50°C) to yield the polyol glucoside as a clear brown liquid and the unconverted carbohydrate as a brown paste.

The polyol glucoside had the following properties:- Experimental Equivalent Weight : = 176.1 Theoretical Equivalent Weight : = 166.4 Effective functionality : = 2.00 ± 0.05 towards diisocyanate

Reducing power (%w/w glucose) : = 1.62 Residual NMP (% w/w) : = 0.25 Glucose conversion (%) : = 79 Example 2 Preparation of low colour Poly tetrahydrofuran 629 monoglucoside Reaction was effected as previously under a nitrogen atmosphere. Nitrogen was purged through the apparatus for 20 minutes at ambient and throughout the reaction period of 40 minutes at 127°C. The product was isolated as previously described as a pale amber liquid with the following properties:

Experimental Equivalent Weight : = 183.1 Theoretical Equivalent weight : = 158.2 Effective functionally : = 2.00 ± 0.05 towards diisocyanate Reducing Power (%w/w glucose) : = 1.71 Residual NMP : = <0.1 Glucose conversion : = 83.5 Example 3 Preparation of Poly tetrahydrofuran 670 bis glucoside Hydroxy terminated polytetrahydrofuran of average molar mass 670 (130g) glucose (70.0g) and NMP (200g) were charged into the apparatus as described in Example 1. Reaction conditions and the isolation of the product after a reaction time of 155 minutes were as previously described. The product polyol was a dark brown clear viscous liquid at ambient. It had the following properties: Experimental Equivalent weight : = 151.8 Theoretical Equivalent Weight : = 124.3 Effective functionality : = 2.03 ± 0.05 towards diisocyanate

Reducing power (%w/w glucose) : = 1.41% Residual NMP : = 1.49%

Glucose conversion : = 80.8% Example 4 Preparation of Polypropylene glycol 450 monoglucoside

Polypropylene glycol of average molar mass, 450,

(12.5g), glucose (5.0g) and freshly distilled NMP (17.5g) were placed in the apparatus as described in

Example 1. The reactants were heated to 130°C and held for 40 minutes at this temperature. The product was obtained as an amber liquid by the procedure described in Example 1. It had the following properties:

Experimental Equivalent Weight : = 171.5 Theoretical Equivalent Weight : = 122.4 Effective functionally : = 2.00 ± 0.05 towards diisocyanate Reducing power (% w/w glucose) : = 2.71 Residual NMP (% w/w) : =<0.1

Glucose conversion (%) : = 68.7

Example 5 Preparation of a Liquid glucoside from Ethyl Cellulose and Ethane Diol 99% Ethane diol (80g) and dry butanone (800cm³) were placed in a 2L flanged reaction vessel equipped with a nitrogen inlet, stirrer and condenser. Ethyl cellulose (150g) (previously dried at 105°), having an ethoxyl content of 47.5 - 49% was added with stirring. When the mixture became homongeneous heating was commenced and when refluxing occurred perchloric acid (5.3cm³, S.G. 1.54), was added. Heating under reflux conditions was continued for 1½ hours. The solution was then cooled and Zerolit DM-F was added and the suspension was stirred for 2 hours during which time the liquor changed in colour from brown to pale orange. The resin was removed by filtration and the filtrate subjected to rotary film evaporation. The last traces of ethane diol were removed at 0.05mm/100°C. The product (159g) was an amber oil which had the following properties: Effective Equivalent Weight (a) : = 167 Theoretical Equivalent Weight (b) : = Monoglucoside =

117.6 Diglucoside = 176.6

(a) measured via the Tg method since the acetylation method failed due to steric hindrance effects.

(b) The product was shown to be a mixture of mono and di-glucoside species by gel permeation chromotography. Unreacted Ethane diol (33g) was recovered from the reaction further supporting this observation. Example 6 Preparation of a Polyurethane Elastomer

Poly tetrahydrofuran 2035 monoglucoside (11.3g) (prepared by the method described in Example 1) was reacted with diphenyl methane diisocyanate MDI (1.1g) at 50°C for ten minutes. The reacting mixture was then poured into a flat mould and cured at 100°C for 24 hours. The resulting opaque dark amber rubber had a Tg of -76.5°C when measured by differential scanning calorimetry (DSC) at a heating rate of 20°C min^-1 on a Dupont 990 Thermal Analyser. Example 7 Preparation of a Segmented Polyurethane

Poly tetrahydrofuran 629 monoglucoside (35.0g), ethane diol (8.75g) and MDI (45.97g) were reacted together at 50°C and then cured at 105°C for 21 hours.

The resulting polymer was a pale yellow, semi-rigid tough solid. Torsion pendulum studies showed this material to have a higher modulus over the temperature range (-20-140°C) than a polymer from

PTHF 629, EG, MDI, under the same conditions. Example 8 Preparation of a Clear Polyurethane

Glass

Liquid polyol derived from Ethyl Cellulose as in

Example 5, (60.24g) was stirred under vacuum for 30 minutes at 80°C. MDI (45.18g) was then added and stirring continued under vacuum for 10 minutes. The clear amber reaction mixture was then poured into a flat mould and cured at 150°C for 2 hours.

An orange, rigid, clear glass was obtained with a Tg ~ 150°C. In tensile tests (23°C, 2mm min^-1 extension rate) it had a strength of 61 MPa and an ultimate strain of 7.5%. It showed a yield point at

6.3% strain.

Claims

CLAIMS :

1. A method of producing a liquid glycoside comprising reacting a saccharide or polysaccharide with a substantially non-polar polyol in a solvent in the presence of an acid catalyst.

2. A method as claimed in claim 1 wherein the saccharide is a mono- or di-saccharide.

3. A method as claimed in claim 2, wherein the saccharide is selected from D-glucose, L-glucose, galactose, sucrose and lactose.

4. A method as claimed in claim 1, wherein the polysaccharide is starch.

5. A method as claimed in claim 1, wherein the saccharide is provided by a syrup.

6. A method as claimed in claim 5, wherein the syrup is selected from glucose syrup, corn syrup and molasses.

7. A method as claimed in claim 1, wherein the polyol is of the formula

in which R is hydrogen or. lower alkyl, m is 2 to 4 and n gives a maximum molar mass of about 2000.

8. A method as claimed in claim 7 wherein the polyol is polytetrahydrofuran.

9. A method as claimed in claim 1, wherein the polyol is a hydroxy-functional natural oil.

10. A method as claimed in claim 9, wherein the natural oil is castor oil.

11. A method as claimed in claim 1, wherein the catalyst is a mineral acid, organic acid or Lewis acid.

12. A method as claimed in claim 11, wherein the catalyst is selected from HF, HCl, H₃PO₄, HClO₄, H₂SO₄, HCOOH, p-toluene sulphonic acid, AICI₃ and BF₃.

13. A method as claimed in claim 1, wherein the solvent is a polar aprotic solvent.

14. A method as claimed in claim 13, wherein the solvent is selected from dimethylformamide, tetramethyl urea, dimethyl acetamide, N-methyl pyrollidone, dimethyl sulphoxide, and acetonitrile.

15. A method of producing a liquid glycoside comprising reacting together a polysaccharide rendered substantially non-hydrogen bonding by substituent groups and a polyol in a solvent in the presence of an acid catalyst.

16. A method as claimed in claim 15, wherein the substituent groups are substantially non-polar.

17. A method as claimed in claim 15, wherein the substituents are selected from alkyl groups, ester groups, halogen atoms, nitro groups and phosphate groups .

18. A method as claimed in claim 15, wherein the substituted polysaccharide is selected from starch ethers, cellulose ethers, dextran ethers, and glucosides thereof.

19. A method as claimed in claim 15 wherein the polyol is a monomeric alkylene glycol.

20. A method as claimed in claim 19, wherein the monomeric alkylene glycol is selected from ethanediol, propanediol and butanediol.

21. A method as claimed in claim 15, wherein the catalyst is a mineral acid, organic acid or Lewis acid.

22. A method as claimed in claim 21, wherein the catalyst is selected from HF, HCl, H₃PO₄, HCIO₄, H₂SO₄.