US2831856A - Method for preparing fatty esters of non-reducing oligosaccharides in the presence of an amide - Google Patents

Description

Unite Nathaniel Beverly Tucker, Cincinnati, The Procter & Gamble Company, Cli corporation of Ohio N0 Drawing. Application December 15, 1955 Serial No. 553,198

Claims. or. 260-234) This invention relates to a process for preparing fatty esters of oligosaccharides, and more especially to the preparation of fatty esters of non-reducing oligosaccharides, such as sucrose.

Many methods of preparing fatty esters of polyhydric alcohols, sucrose and other non-reducing oligosaccharides are known and have been heretofore employed. Among these are: the direct esterification of the alcohol or oligosaccharide and fatty acids; the reaction of the alcohol or oligosaccharide with fatty acid anhydrides; the reaction of the alcohol or oligosaccharide with fatty acid halides; and the reesterification. of fatty acid esters with polyhydroxy alcohols. Various disadvantages are identitied with these processes such as, for example, poor yields, excessive time to carry the reaction to the desired cornpleteness, and excessive temperatures necessary to pro- Other objects and disadvantages will be apparent from A the following detailed description.

I have found that these objects can be accomplished by subjecting to interesterification a mixture of a nonreducing oligosaccharide and a fatty acid ester of an aliphatic primary monohydroxy alcohol or a fatty acid ester of a polyhydroxy alcohol in the presence of certain amides in which the reactants exhibit some mutual solubility.

Generally speaking, the invention contemplates reacting the non-reducing oligosaccharides with the fatty acid ester in the presence of an alkaline catalyst, which shows activity in interesterification reactions, at a temperature in the range from about to about 150 C., and in the presence of an amide compound of the general formula CHQCHQ NR crncm Where X is selected from the group consisting of oxygen and CH and R is an acyl radical selected from the group consisting of formyl, acetyl and propionyl radicals. Fol lowing completion of interesterification to the desired degree, the catalyst is inactivated by the addition of water and/or acids such as acetic, phosphoric, citric, hydrochloric, and the like, and the desired reaction products are freed of solvent and purified by any suitable means.

The term oligosaccharides is used herein to differentiate the di, tri, and tetra-saccharides as a group, from the polysaccharides which are composed of a much greater number of single units. Of the oligosaccharides, I have found that only those of the non-reducing type, i. 6., those having no potentially free aldehyde or ketonic group, are

States Patent 0 ice suitable for purposes of this invention. These include the disaccharides; sucrose, trehalose and glucoxylose; the trisaccharides; raffmose, melezitose and gentianose; and the tetra-saccharide, stachyose. Thus, the oligosaccharides of concern here are non-reducing polyhydroxy compounds having from 7 to 16 hydroxyl groups per molecule.

The fatty esters which can be employed in the reaction herein concerned are the fatty acid esters of primary aliphatic monohydroxy alcohols having from 1 to 16 carbon atoms, for example, methanol, ethanol, hexanol, decanol, dodecanol, and hexadecanol, specific examples being methylpalmitate, dodecylpalmitate and hexadecylpalmitate. In addition, fatty acid esters of completely or incompletely esterified polyhydric alcohols having from 2 to 6 hydroxyl groups, such as glycol, ethylene glycol, glycerol, erythritol, pentaerythritol, mannitol, and sorbitol can be employed. Glycol dipalmitate, glycerol mono-, di-, and tripalmitate, mannitol partial palmitates, erythritol tetrapalmitate, pentaerythritol tetrapalmitate and sorbitol hexapalmitate are examples of operative fatty esters. In addition, fatty esters of glycosides, such as methyl glucoside tetrapalmitate, can be employed. The use of fatty acid esters of the aforementioned oligosaccharides having from 7 to 16 hydroxyl groups in the molecule is also contemplated. Thus, just as mono-, and diesters of glycerol can be prepared from the triglyceride, so incompletely esterified sucrose esters can be prepared in accordance with the present invention by reaction of sucrose with completely esterified sucrose. Thus, the reaction of sucrose octapalmitate with sucrose can be carried out advantageously with the aid of the present invention.

The aforementioned polyhydric alcohols and non-reducing oligosaccharides considered as a group will for purposes herein be referred to as aliphatic alcoholic polyhydroxy substances.

The length of the fatty acid chain of the esters above designated is not critical and is dictated primarily by the type of fatty acid material source available. For my purposes, however I have found that fatty acids containing from about 8 to 22 carbon atoms are most useful. Thus, the mixtures of fatty acids obtained from animal, vegetable, and marine oils, and fats, such as coconut oil, cottonseed oil, soybean oil, tallow, lard, herring oil, sardine oil, and the like, represent excellent and valuable sources of fatty acid radicals. in the event it is desired to produce oligosaccharide esters of single fatty acids by this invention, then the fatty acid esters of relatively volatile alcohols (e. g. methanol and ethanol), having from about 12 to about 22 carbon atoms can be reacted with the non-reducing oligosaccharide with the aid of the particular amide reaction medium herein covered.

Of the fatty esters which may be used in the practice of my invention I prefer to use the esters of those alcohols having not more than three carbon atoms.

The crux of my invention lies in the selection of the solvent which comprises the reaction medium. The choice of solvent is essential to the realization of rapid and efficient interesterification of the non-reducing oligosaccharide and the fatty ester under the conditions hereinbefore set forth. i have found that in general the nitrogensubstituted amide compounds as hereinbefore defined are eminently suitable as solvents in my process. These compounds promote a rapid rate of reaction with minimum catalyst requirements and undergo a minimum of decomposition during the interesterification reaction.

With these amide solvents I have found in general that the rate of interesterification decreases with increase in molecular Weight of the amide; that solvent volume requirements in the reaction decrease with increasing solubility of the non-reducing oligosaccharide in the solvent; and that the solubility of the non-reducing oligosacamount of solvent required for any given interesterification will varyldepending upon the particular solventwhich is to be used, the actual amount of solvent is not critical. Amounts of solvent from /3 to 50 times by weight of the fatty ester employed for reaction with the oligosaccharide find application in my process. It is to be understood, however that the solvent usage is normally adjusted depending upon the particular reactants to be interesterified. In any event, sufiicient solvent should be used so that the advantages associated with solvent usage may be realized.

The proportion of reactants is not critical and is dictated primarily by the ultimate product which is desired. For example, in the reaction of sucrose with fatty ester, proportions can be chosen so that from one to all of the hydrogen atoms of the hydroxyl groups of sucrose may be replaced by fatty acyl radicals. Or, where sucrose and a triglyceride are being reacted, proportions can be chosen soth'at the final product may predominate in either glycerides or sucrose esters. As a practical matter, however, molar ratios of non-reducing oligosaccharide to fatty i ester in the range from about 30:1 to about 1:20 are most satisfactory, the proportions being variable Within the range depending on the completeness of replacement desired and on the number of fatty acid radicals in each mole of ester substance. Thus, for example, if 0.1 mole of methylpalmitate is reacted with 1 mole of sucrose under the hereinbefore defined conditions and at reduced pressure essentially all of the sucrose ester formed will be monoester. If the molar ratio is changed to 1:1, one obtains a high yield of monoester of sucrose, but more diester will be present. A product averaging approximately 2 palmitic acid groups per mole of sucrose may be obtained with a molar ratio of methylpalmitate to sucrose of 2:1. When molar ratios of 4:1, 8:1, or 10:1 are used the average number of palmitic acid radicals per mole of sucrose obtained may be 3.5, 6, or 7.5.

Although my process is illustrated herein principally with the use of sodium methoxide as the catalyst, effective practice of the process is not dependent u on the use of any particular catalyst. Rather, any alkaline molecular rearrangement or interesterification catalyst which will pro-mote the interchange of radicals among the reactants of my process is suitable. Examples of usable catalysts are: sodium methoxide, anhydrous potassium hydroxide, sodium hydroxide, metallic sodium, sodium potassium alloy, and quaternary ammonium bases such as trimethyl benzyl ammonium hydroxide. A discussion of other catalysts which are active in interesterification reactions may be found in U. S. Letters Patent 2,442,532, to E. W. Eckey, column 24, line 18 et seq.

The sodium methoxide catalyst may be advantageously used in my process in amounts from about 0.05% to about 2.0% by weight of the fatty ester which is to be reacted, equimolar amounts of other catalysts being usable. The choice of catalyst and the amount which is to be used are of course dependent upon the particular constituents which are to be reacted.

, In the practice of the invention, it was observed that the reaction rate for a given solvent usage and a given catalyst increased with increase in temperature. With optimum amounts of formyl piperidine, for example, and with sodium methoxide as the catalyst, at temperatures of 100 C. I found that equilibrium was reached after about 20 minutes reaction time and that somewhat longer reaction times were required at lower temperatures. How ever, substantial ester formation was observed at reaction temperatures as low as -40 C. Where low temperatures such as 20 C. are employed for special purposes,

longer reaction times are required to achieve desired ester formation. Temperatures above 100 C., such as 150 C. may, of course, be employed, but in view of the high rate of reaction observed in use of the solvents of the present invention, such temperatures may only infrequently be necessary to accomplish the desired ester formation. Generally speaking, with any of the aforementioned reactants, catalysts, or solvents and within the ranges of proportions set forth, the process of my invention is preferably carried out at a temperature in the range from about to about 150 C.

Although my process is normally carried out at atmospheric pressure, it can if desired be carried out under reduced pressure, an operation which at times'is decidedly advantageous. For example, when a fatty acid ester of methanol is reacted with sucrose, operation under reduced pressure, such as about 80 mm. of mercury, enables the methanol formed as a result of the interesterification to be removed from the reaction zone substantially as rapidly as it is liberated, thus promoting a substantially complete conversion of the methyl ester to sucrose fatty ester.

Since the reaction of the present invention is an interesterification in which sucrose, for example, is reacted with a fatty ester, the resulting product of the reaction will constitute an equilibrium mixture of sucrose, esters thereof, displaced alcoholic substance from the ester originally employed, and ester of such alcoholic substance. Thus, if triglycerides are reacted with the sucrose, then the product of the reaction will contain monoand diglycerides as well as sucrose esters. If it is desired to obtain sucrose esters which are not so contaminated withoriginal esters and derivatives thereof, then it is preferable to react volatile alcohol esters such as methyl or ethyl esters with the sucrose and, as suggested above, to conduct the reaction under vacuum so that displaced alcohol is distilled olf. High yields of sucrose esters are obtainable in this way and, of course, unreacted volatile esters can be separated subsequently by distillation to yield sucrose esters of high purity.

One way of determining whether or not ester has been formed when working with the oligosaccharides is by observing the optical activity of the recovered reaction product. As is well known, sucrose and other oligosaccharides have optical activity which may be readily determined in the usual way by polarimetric measurement. in the present case, specific rotation figures have been determined by means of a Rudolph Model 70 polarimeter, using a filtered light source of 546 millimicrons wave length. The rotation is measured at room temperature (2527 C.) in pyridine solution at a concentration of about 2% using a sample length of 10 cm. Under such conditions of observation, sucrose shows a specific rotation of The esters formed from sucrose also possess optical activity and since the method of recovery, as shown in the examples to follow, eliminates contamination of the product with water soluble substances such as sucrose, then any optical activity of the product recovered is indicative of a content of sucrose ester. For example, the monopalrnitate ester of sucrose has a combined sucrose content of 59% and a specific rotation of 59 to 60 under the above conditions.

Although optical activity can not be accepted as an absolute measure of the percent oligosaccharide content of the ester unless the exact nature of the ester is known, there is a close correlation between the percent combined sucrose content and the observed specific rotation. Thus, for example, the specific rotation of the octa ester of sucrose will be substantially less than the mono-ester of sucrose because of its lower content of combined sucrose. Moreover, the specific rotation of the product will depend on the nature and concentration of the oligosaccharide ester, whatever it is, in the product being measured. Thus, figures for specific rotation, sometimes designated as [0:1 are indicative of ester formation in the interesterification reaction, the degree of esterification being indicated by other characteraesneoc istics such as hydroxyl value, saponification value, and total fatty acid content as determined by procedures well known in the art.

The following examples will illustrate the manner in which the invention may be practiced. It will be understood, however, that the examples are not to be construed as limiting the scope of conditions claimed hereinafter.

Examples 1, 2, 3, 4 and 5 A number of amide compounds coming within the scope of the definition hereinbefore given were employed in the formation of sucrose esters. In each case grams of sucrose, 18 grams of a mixture of 80% soy bean oil and 20% cottonseed oil hydrogenated to an iodine value of about 76, 100 milliliters of the amide reaction medium were mixed and heated to 100;*:3 C. After the above temperature was reached 0.18 gm. of sodium methoxide catalyst was added to the heated mixture and the interesterification reaction was allowed to proceed. At various time intervals after the addition of the catalyst, 20 milliliter aliquots were removed from the reacting mixture and the catalyst in these aliquots was inactivated by the addition thereto l milliliter of a 50% aqueous solution of acetic acid. Following inactivation of the catalyst the aliquot was taken up in 50 ml. of a 4:1 mixture of ethyl acetate and n-butanol and water washed. The water washed fatty products were recovered by evaporating the ethyl acetate-n-butanol solvent on a steam bath under a stream of nitrogen. The recovered reaction product was measured for optical activity in accordance with the procedure described hereinbefore. In the following table the results are given showing substantial production of sucrose ester in all cases.

Specific Rotation After Minutes of React. Time Amide Solvent 1 Taken after 210 minutes reaction time. 1 Taken after 90 minutes reaction time.

It is to be understood that in the foregoing examples the sucrose may be replaced by any of the non-reducing oligosaccharides with comparable results.

Having thus described my invention, I claim:

1. A process for preparing fatty esters of non-reducing oligosaccharides which comprises reacting a non-reducing oligos'accharide with a fatty acid ester selected from the group consisting of fatty acid esters of aliphatic primary monohydroxy alcohols having from 1 to 16 carbon atoms and fatty esters of aliphatic alcoholic polyhydroxy substances, the fatty acid chain of the said fatty esters containing from about 8 to about 22 carbon atoms in the presence of an interesterification catalyst, at a temperature in the range from about 20 to about 150 C. and in the presence of an amide of the general formula:

where X is selected from the group consisting of oxygen and CH, and R is an acyl radical selected from the group consisting of formyl, acetyl and propionyl radicals, the said non-reducing oligosaccharides being in a molar ratio to the said fatty acid ester of from about :1 to about 1:20 and the amide being present in an amount from /3 to 50 times by weight of the said fatty acid ester.

2. The process of claim 1. wherein the non-reducing oligosaccharide is sucrose.

3. The process of claim 1 wherein the amide is formyl piperidine.

4. The process of claim 1 wherein the amide is formyl morpholine.

5. The process of claim 1 wherein the amide is acetyl morpholine.

6. A process for preparing fatty esters of sucrose which comprises reacting sucrose with a fatty acid ester selected from the group consisting of fatty acid esters of aliphatic primary monohydroxy alcohols and the fatty acid esters of polyhydroxy alcohols, the fatty acid chain of the said fatty esters containing from about 8 to about 22 carbon atoms, all of said alcohols having not more than three carbon atoms, in the presence of an interesterification catalyst, at a temperature in the range from about to about 150 C. and in the presence of an amide of the general formula where X is selected from the group consisting of oxygen and CH and R is an acyl radical selected from the group consisting of formyl, acetyl and propionyl radicals.

7. A process for preparing fatty esters of sucrose which comprises reacting sucrose with a fatty acid ester 7 of glycerol containing from about 8 to about 22 carbon atoms in the fatty acid chain, in the presence of from about 0.05 to about 2% of an interesterification catalyst, by weight of the glycerol ester, at a temperature in the range from about 80 to 150 C. in a reaction medium comprising essentially formyl morpholine.

8. The process of claim 7 wherein the fatty acid ester is a triglyceride.

9. A process for preparing fatty esters of sucrose which comprises reacting sucrose with a fatty acid ester of methanol containing from about 8 to about 22 carbon atoms in the fatty acid chain, in a reaction medium comprising essentially formyl morpholine in the presence of from about 0.05 to about 2% of an interesterification catalyst, by weight of the methyl ester, at a temperature in the range from about 80 to about 150 C. and at such a sufficiently low pressure that the methanol liberated during the reaction is continuously distilled from the reaction mix whereby the reaction proceeds to substantial completeness.

10. The process of preparing fatty esters of sucrose which comprises reacting sucrose and a fatty triglyceride containing from about 8 to about 22 carbon atoms in the fatty acid chain, in the presence of an interesterification catalyst at a temperature of about C. in a reaction medium comprising essentially formyl morpholine, inactivating the catalyst by acidulation, distilling substantially all of the formyl morpholine. from the reaction mixture and water-washing the residue whereby undistilled solvent and unreacted sucrose are removed therefrom.

Journal of The American Oil Chemists Society, July 1948, pp. 258-260.

Claims (1)

1. A PROCESS FOR PREPARING FATTY ESTERS OF NON-REDUCING OLIGOSACCHARIDES WHICH COMPRISES REACTING NON-RE DUCING OLIGOSACCHARIDE WITH A FATTY ACID ESTER SELECTED FROM THE GROUP CONSISTING OF FATTY ACID ESTERS OF ALIPHATIC PRIMARY MONOHYDROXY ALCOHOLS HAVING FROM 1 TO 16 CARBON ATOMS AND FATTY ESTERS ALIPHATIC ALCOHOLIC POLYHYDROXY SUBSTANCES, THE FATTY ACID CHAIN OF THE SAID FATTY ESTERS CONTAINING FROM ABOUT 8 TO ABOUT 22 CARBON ATOMS IN THE PRESENCE OF AN INTERESTERIFICATION CATALYST, AT A TEMPERATURE IN THE RANGE FROM ABOUT 20* TO ABOUT 150*C. AND IN THE PRESENCE OF AN AMIDE OF THE GENERAL FORMULA: