US2948717A

US2948717A - Sugar ester preparation and purification

Info

Publication number: US2948717A
Application number: US786682A
Authority: US
Inventors: Vigen K Babayan; Agop K Atikian
Original assignee: EF Drew and Co Inc
Current assignee: EF Drew and Co Inc
Priority date: 1959-01-14
Filing date: 1959-01-14
Publication date: 1960-08-09
Anticipated expiration: 1977-08-09

Description

SUGAR ESTER PREPARATION AND PURIFICATION No Drawing. Filed Jan; r4,,19's9 seaNo saasr 12 Claims. Cl. 260-234 a The present application is directed to. a method of sugar ester purification, more specifically a method for puritying partial and complete esters of various sugars.

In the past, compounds of the sugar ester type have been manufactured by the use of solvent systems which are toxic. Furthermore these systems present a serious danger of contamination when the ultimate product is to be used for human consumption. As a result, elaborate and expensive refining means are required to insure that the sugar esters produced do not carry any substantial amounts of toxic solvents with them. 7 r r 7 It is among the objects of this invention to provide a method for preparation and purification of sugar esters which will enable the formation of partially as well as completely esterified products.

It is also among the objectsof this invention to provide a' means for purification of sugar esters both partial and complete, which will obviate any danger of contaminationwith toxic substances.

It. is further among the objects of this invention to provide a means of purifying sugar esters which will be suitable for use in the preparation of products for human consumption.

It is still further among the objects of this invention to provide. a method of purification of sugar esters which yields a clean, sharp separation of the desired products from the undesired by-products.

.In practicing this invention, a sugar, preferably sucrose, is dissolved or suspended in an aqueous alkaline medium. An amount of acid chloride. corresponding to the desired degree of esterification is then, addedslowly. Preferably the acid chloride should be at least 98% pure since the presence of any substantial amount of phosphorous trichloride or of phosphorous acid will cause the formation of undesired phosphates rather than the sugar ester sought, and the yield is low; also the separation of the ester from the other constituents of the mass and purification thereof becomes more difficult. Furthermore, if free fatty acids are present, larger quantities of soap are produced and the reaction rate and efiiciency is reduced.

The alkaline aqueous suspension or solution of sugar should be maintained preferably at pH 9 to ll. However, the reaction will proceed as long as the pH of the sugar solution is on the alkaline side. At a pH of greater than 11, the efiiciency of the reaction goes down and more soap is formed. It the pH is permitted to drop below 7, a very substantial increase in the amount of soap or free fatty acid results.

i The reaction is carried out at a temperature below 65 C. and above the freezing point of the acid chloride used. Preferably the reaction temperature should be below 40 to 45;C. as the yield drops oif above this temperature range, and the agitation is continued throughout the reaction. As a general rule, the process is conducted at the lowest permissible temperature based on the fluidityof the reactants.

In carrying out this process, the sugar solution is placed in a mixing device capable of giving turbulent agitation.

- Patented Aug. 9, 1960 2 Y An appropriate acid chloride is added, together with sufficient sodium hydroxide and/or other alkali to maintain. the desired pH. This addition is made slowly and at a point where thorough turbulent mixing is always maintained. The sugar solution as a whole is always in excess over the acid chloride as a whole. However, at the point of entry of the acid chloride into the sugar solution, there will be some local acidification. Rapid and adequate agitation keeps this to a minimum and effectively converts the medium to an alkaline one in a matter of seconds, ensuring that the reaction proceeds in the right direction. Since the reaction is exothermic, it is desirable to cool the reactants preferably by means of a water jacket or cracked ice. If the acid chloride is present in excess, substantial quantities of free fatty acids are formed. which will usually precipitate out and hence impair the efliciency of the reaction.

In other words, it is important that a combination ofv temperature control, rapid and turbulent mixing, alkalinity and slow addition of acid chloride and the alkali be maintained. Once this reaction has taken place and the crude ester is formed, the reaction mass is mixed for about an hour and then it is ready for processing whenthe last traces of acid chloride have reacted. The resultant product is in the form of'a'slurry,""of which approximately 20% constitutes the desired sugar ester.

Concentration and purification of the crude product is obtained by first washing the mixture with hot brine, pref-. erably around 20% solution at to C. This causes the slurry to split into two layers; the upper layer contains the desired sugar ester plus the soap formed as well as some water and salt. The lower layer is primarily the brine and unreacted sugar. The layers are then separated and the top layer rewashed and re-separated as described before.

The ester, soap layer is then drained and the vacuum dried to a virtually anhydrous conditionj this operation is important for the subsequent separation of sugar ester from the soap present in the reaction mass. The dry ester, soap mixture is then extracted with hot acetoner This dissolves out the sugar ester which is soluble in acetone but does not dissolve the undesired soap impurity. Consequently it is then only necessary to distill oil the acetone to recover the pure product. 1

It should be noted that for the best operation of this purification process it is very important that the crude.

' ester soap mixture be dried to a virtually anhydrous con-1 dition. Alternatively, if substantial quantities of waterare present, then when extracted with hot acetone thewater will also dissolve in the acetone and carry some soap with it. Under these conditions, it becomes necessary to very carefullydistill off the acetone until the water. separates out as a second layer carrying with it the soap. At this point the material must be permitted tostand so that all the water and soap will goout of solution. The? water layer is drawn OE and the remainder is then filtered v r and the acetone redistilled to obtain the pure ester. 3

The purified compounds find substantial'use as emulsi-" has in the food, pharmaceutical, medicinal and cosm etic industries. In the food industry it is suitable forluse in margarine, shortening, ice'creams and many allied uses as in candy coatings, baked goods, etc. They are emulsifiers, anti-spattering agents, emulsion stabiliz e foaming aerating agents, gloss additives, and suspendi and thickening agents. Also in the pharmaceutical field larly, these esters have many industrial uses in such' fields. as textiles, leather, paper making, and others. j j] The following specific examples of this invention are intended to be illustrative only and not toindi cat limitations to be imposed thereon;

Example 1 In a vessel capable of good mixing and turbulent agitation, there is charged 350 lbs. of sucrose and 200 lbs. of water. To the homogeneous solution while under turbulent agitation, there is slowly added a 50% sodium hydroxide solution, together with 310 lbs. of stearoyl chloride. The sodium hydroxide is added at such a rate as will maintain the pH between 9 and 10. The additions take approximately 4 to 5 hours and mixing is maintained for one hour after all addition has been completed. A thick paste containing the crude ester results. This product is then washed with sodium chloride solution at a temperature of approximately 80 to 90 C. The sugar ester and soap formed separate from the unreacted sugar and alkaline water. The brine solution layer is drawn off and discarded. This cycle is repeated to get a better separation of the ester.

The ester layer is then dried slowly under vacuum until completely dry and then extracted with hot acetone at a temperature close to the boiling point of the acetone. This effects the separation of the pure sugar ester from the soap formed as a by-product of the initial reaction. The extraction is repeated until the bulk of the ester has been recovered. The acetone is then flashed off to recover the pure sugar ester, which can either be ground to a powder, flaked off on a roll or recovered in any of the ordinary forms.

Example 2 350 grams of sugar were dissolved in 200 grams of water in a mixing vessel equipped with efficient agitation and cooled to about 25 C. While maintaining agitation and cooling, a small amount of a 20% NaOH solution was added to bring the pH to about 8, after which 280 grams of palmitoyl chloride together with NaOH solution was introduced slowly to maintain a pH of about 9-l0, over a period of about 34 hours.

The temperature at the start was about 2025 C. and gradually rose to 3035 C. at the height of the reaction and gradually dropped to 30 C. when the reaction was completed. The batch was agitated one hour after all the additions were made and the traces of free acid chloride present were given the opportunity to react and become neutralized.

The thick, syrupy, white, precipitate which resulted from the above initial esterification reaction was then transferred to a wash tank where the entire batch was given a hot brine wash (15 NaCl solution at 80-90" 0.). Equal volumes were used for convenience and rapid washing. However, smaller volumes can be used and one, two, or three such washes can be given to ensure the elimination of the unreacted sugar from the batch. The concentration of the brine solution may vary and even solid NaCl may be used to separate layers.

The brine wash separated the batch into two layers. The top layer contained a curd of the sucrose ester and any soap which was formed as a side reaction. The bottom layer contained the water, alkali, salt, and especially the unreacted sugar in the batch. In order to prevent formation of dark colors, bad odors and flavors on decomposition of sugar, it is important to wash out the sugar as thoroughly as possible to ensure a final product of a high degree of purity, quality in taste and flavor and odor.

When the brine washed crude sucrose ester was obtained free from unreacted sugar, it was placed in a kettle equipped with agitation, heat (indirect) and vacuum. While under agitation the batch was slowly heated and vacuum applied to draw off all the water present in the batch, after which the batch was cooled while still being agitated and the vacuum kept on until the temperature was reduced to 50 C. to ensure good color to the product. The vacuum was gradualy broken and about 3500 grams of hot acetone gradually introduced into the batch and extracted. The hot acetone .4 slurry containing the sugar ester in solution and the soap and salts in suspension were filtered, maintained at the same temperatures, where the press cake of salts and soap built up while the clear acetone solution containing the sugar ester filtered through and collected in a receiver. The acetone was distilled from the sugar ester solution and recycled as long as necessary to ensure that all the sugar ester had been extracted from the press cake. The final residue, obtained after the acetone is distilled from the receiving flash, was the pure sugar ester.

Example 3 Follow Example 2 up to the washing with sodium chloride. After the brine washing of the crude sucrose ester the curd was immediately put through the pressure leaf filter press and pressed out to as dry a cake as possible. The press cake was then extracted with the hot acetone as before. The extracted material contained, beside the sugar ester, the soap impurity which is soluble in the aqueous acetone. As the acetone was evaporated, an aqeuous layer formed. This aqueous layer contained most of the soap which is not soluble in anhydrous alcohol. The water layer was drawn 01f from the bottom of the vessel and the acetone solution concentrated to the point where no more water layer formed. It was then filtered through a fine filter to ensure the elimination of any fine suspended particles of soap. The concentrate was now completly freed from acetone to yield the sugar ester free from impurities.

Example 4 11,000 grams of sucrose was dissolved in 6,000 grams of water and cooled to 10-12 C.

To the above sugar solution, while maintaining vigorous agitation and temperatures below 20 C., a solution of 640 grams of sodium hydroxide dissolved in 2,200 grams of water was added in a slow stream to maintain the pH of the sugar solution at 9-10. At the same time 2,800 grams of palmitoyl chloride (99% purity) was gradually added to the sugar solution over the course of 3 hours. The temperature of the batch never exceeded 18 C.

When the last of the palmitoyl chloride was added, the batch was immediately brine washed with saturated brine solution at 60-65 C. The brine solution was separated and the remaining washed sugar ester extracted with acetone. The extracted acetone solution was distilled to eliminate the acetone, then filtered to recover the pure sugar ester as a white solid. The yield of pure sucrose ester was 2,050 grams.

Although the invention was described in connect-ion with several specific embodiments thereof, certain changes and variations in the details may be introduced. By varying the molar ratios of the acid chloride, sugar esters ranging from monoto octa-sucrose esters may be prepared. Mixed esters of sugars may be produced by following the above procedures. The use of high purity acid chlorides is important.

Other solvents than acetone are suitable, such as mono alcohols having 2-4 carbon atoms, alkylene dichlorides wherein the alkylene group has 24 carbon atoms, carbon tetrachloride, chloroform, hexane, and benzol. They may be characterized as volatile organic solvents for sugar esters but not solvents for soaps. The alkyl radical of the esters may have from 2. to 24 carbon atoms, but preferably they have from 12 to 18 carbon atoms for many applications; saturated and unsaturated fatty acid chlorides are contemplated. The products range from viscous liquids to light colored friable solids.

Important to the invention are the following conditions: (1) the use of a pure acid chloride, (2) a low temperature of reaction, (3) maintaining a moderately alkaline pH, (4) efficient agitation during the reaction, and (5) the purification of the crude ester by brine, and (6) then extraction with an organic solvent.

Various sugars may be used as starting materials for the operation. While acetone has been found, up to the present time, to be the most effective solvent for the purpose, the other solvents named above are usable with lesser efiiciency; the solvents should be volatile at temperatures below the decomposition point of the products. It is preferred to operate at the lower range of the temperatures' set forth, but the higher temperatures are also operative; while as high as 65 C. has been found efiective, better results are obtained in working as close to 0 C. as is practical, but the temperature should be above the melting point of the acid chloride used. The reaction being exothermic, cooling the reaction mass is advisable. In the reaction it is preferable to have an excess of sugar present to minimize the formation of free fatty acids. Allowing the reaction mass to stand for at least one hour after the reaction is apparently complete insures that no traces of acid chloride remain.

If the acid chloride does not find suitable media to react and form the sucrose ester it will hydrolize and form free fatty acid or else if there is suflicient alkali, form soap. Both these side reactions must be kept to a minimum. In order to do this the most suitable conditions for ester formation are maintained, i.e. adequate mixing, low concentrations of acid chloride at any given moment, low concentration of alkali at any given moment, and reaction at the lowest temperature possible at which the sugar, the acid chloride and the alkali are still fluid.

We claim:

1. The method of preparing sugar esters comprising dissolving sugar in water, making the solution alkaline, slowly adding organic acid chloride while turbulently agitating and maintaining the mixture alkaline whereby crude sugar ester is formed, maintaining the temperature of the reaction below 65 C. and at which the acid chloride is still fluid, washing said crude ester with a solution of a salt which does not change the alkalinity of the mixture and is adapted to cause precipitation of ester and soap from aqueous solutions and permitting said mixture to separate into an ester-soap layer and an electrolyte-sugar layer, removing said electrolyte-sugar layer, drying said ester-soap layer, extracting the ester with a ketone, and recovering substantially pure ester from said ketone.

2. The method of preparing sugar esters according to claim 1 wherein the reaction is carried out at a temperature of about 25 -45 C.

3. The method of preparation of sugar esters according to claim 1 wherein the ketone containing the ester is filtered to remove suspended salts and soap and then distilled to recover the pure ester.

4. The method of preparation of sugar esters according to claim 1 wherein the pH of the reaction mixture is 7-11.

5. The method of preparation of sugar esters according to claim 1 wherein the pH of the reaction mixture is 9-10.

6. The method of preparation of sugar esters according to claim 1 wherein the molecular ratio of sugar to acid chloride is 3 :1 to 1:3.

7. The method of preparation of sugar esters according to claim 1 wherein the acid chloride is substantially free from phosphorus compounds.

8. The method of preparing sugar esters comprising dissolving sugar in water, making the solution alkaline, slowly adding organic acid chloride While turbulently agitating and maintaining the mixture alkaline whereby crude sugar ester is formed, maintaining the temperature of the reaction below C. and at which the acid chloride is still fluid, washing said crude ester with a solution of a salt which does not change the alkalinity of the mixture and is adapted to cause precipitation of ester and soap from aqueous solutions and permitting said mixture to separate into an ester-soap layer and an electrolyte-sugar layer, removing said electrolyte-sugar layer, drying said ester-soap layer, extracting the ester with an organic solvent which is volatile at temperatures below the decomposition point of the product, and recovering substantially pure ester from said solvent.

9. The method of preparation of sugar esters according to claim 8 wherein said solvent is taken from the class consisting of mono-alcohols having 2-4 carbon atoms and hydrocarbons having 2-7 carbon atoms.

10. The method of preparation of sugar esters according to claim 8 wherein said solvent is taken from the class consisting of chlorinated hydrocarbons having 2-4 carbon atoms and l-4 chlorine atoms.

11. The method of preparing sugar esters comprising dissolving sugar in water, making the solution alkaline, slowly adding organic acid chloride while turbulently agitating and maintaining the mixture alkaline whereby crude sugar ester is formed, maintaining the temperature of the reaction below 65 C. and at which the acid chloride is still fluid, washing said crude ester with a solution of a salt which does not change the alkalinity of the mixture and is adapted to cause precipitation of ester and soap from aqueous solutions and permitting said mixture to separate into an ester-soap layer and an electrolyte-sugar layer, removing said electrolyte-sugar layer, extracting the ester with an organic solvent which is volatile at temperatures below the decomposition point of the product, and recovering substantially pure ester from said solvent.

12. The method of preparation of sugar esters according to claim 11 wherein the temperature of the ester forming reaction is below 20 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,024,036 Funaoka Dec. 10, 1935 2,052,029 Harris Aug. 25, 1936 2,602,789 Schwartz July 8, 1952

Claims

1. THE METHOD OF PREPARING SUGAR ESTERS COMPRISING DISSOLVING SUGAR IN WATER, MAKING THE SOLUTION ALKALINE, SLOWLY ADDING ORGANIC ACID CHLORIDE WHILE TURBULENTLY AGITATING AND MAINTAINING THE MIXTURE ALKALINE WHEREBY CRUDE SUGAR ESTER IF FORMED, MAINTAINING THE TEMPERATURE OF THE REACTION BELOW 65*C. AND AT WHICH THE ACID CHLORIDE IS STILL FLUID, WASHING SAID CRUDE ESTER WITH A SOLUTION OF A SALT WHICH DOES NOT CHANGE THE ALKALINITY OF THE MIXTURE AND IS ADAPTED TO CAUSE PRECIPITATION OF ESTER AND SOAP FROM AQUEOUS SOLUTIONS AND PERMITTING SAID MIXTURE TO SEPARATE INTO AN ESTER-SOAP LAYER AND AN ELECTROLYTE-SUGAR LAYER, REMOVING SAID ELECTROLYTE-SUGAR LAYER, DRYING SAID ESTER-SOAP LAYER, EXTRACTING THE ESTER WITH A KETONE, AND RECOVERING SUBSTANTIALLY PURE ESTER FROM SAID KETONE.