US2197339A - Preparation of fatty acid esters of polyhydroxy alcohols - Google Patents

Description

Patented Apr. is, 1940 UNITED STATES PATENT OFFICE PREPABATiON OF FATTY ACID ESTEBS F POLYHYDROXY ALCOHOLS Chester M.

, Jersey City, and Hans W.

tion of Delaware No Drawing.

Application December Serial No. 116,128

.11 Claims. (01. zoo-411) This invention relates to the production of 7 fatty acid esters of polyhydric alcohols and more particularly to the separation of impurities, such as fatty acid soaps, in the production of monoand diglycerides of the higher fatty acids.

It has been suggested that small amounts of higher fatty acid esters of polyhydroxy alcohols be added to many difierent materials to serve as emulsifying agents. Monoor diglycerides are 10 employed, for example, in the manufacture of edible materials, such as margarine, whereby it is possible to prevent the loss of milk serum during manufacture and storage. Such glycerides may also be added to shortenings, cake batters,

etc., where they probably function as emulsifying agents.

The usual method of preparing the hydroxylic esters is to heat the triglycerides of any vegetable or animal fat, directly or after partial or complete hydrogenation, with a polyhydroxy alcohol,

' such as glycerol, in the presence of an alkalinereacting material such as sodium ethylate, sodium glyceroxide, or other metal alkoxide as a catalyst for the alcoholysis. Alkali metal compounds, such as NaHCOa, NaaCOs, NaOH, alkaline earth compounds, such as CaO, Ca(0H)s or metal soaps of the higher fatty acids, may also serve as reesteriflcation catalysts. Y A

All of the above catalysts result in a reaction product containing alkali or alkaline earth salts or soaps as impurities. This is particularly un-' desirable when the product is to be employed in an edible substance because the presence of soaps may lead to an objectionable taste in the finished goods. Another disadvantage is that the soap v causes considerable quantities of unreacted polyhydroxy alcohol to be retained in the product. This results in a loss of material and is, therefore, not an economical method of conducting 40 the process. In other words, the presence of soap and excess polyhydroxy alcohol during the reaction is desirable in order to obtain a more completely reacted product, but after the reaction has reached equilibrium under a given set 5 of conditions, it is then desirable to reduce the quantity of excess polyhydroxy alcohol and soap or salt to a minimum. a

This may. be accomplished by the directaddi-' tion of mineral acid after completion of the reaction whereby the soap is converted to fatty acid and large quantities of glycerol are no longer heldin solution. procedure leaves the re- 0 action product with a content of free fatty acid directly proportional to the amount of soap formerly present and the product may still beobmixture. 'Heretofore it has-been the practice to liquid phases during the entire reaction period oil with more than four parts of glycerol in.a

jectionable to the taste. Attempts to esterify the free fatty acid by continued and necessarily prolonged heating are deleterious to the flavor of the final product.

Soap and glycerol can be removed by washing with warm. brines but this additional step .is troublesome and the product will contain water which is harmful to the keeping qualities of the glycerides unless special precautions are subsequently taken to dry the washed product.

Under the most favorable conditions for reesterification the reaction mixture will contain a fairly large quantity of catalyst-as much as 5% or even more.. The advantage of employing so. large an amount of catalyst is that the reaction 1 will proceed to the greatest possible extent, by virtue of the mutual solvent action on the glycerol and glycerides of the relatively large amount of soap resulting from the catalyst, thus giving a higher concentration of glycerol in the clear keep the quantity of catalyst at a minimum because of the difiiculty of removing the soap after the reaction has proceeded to equilibrium. Asa consequence the reaction took place between two which was necessarily prolonged and the degree of conversion limited.

. Another advantage of employing so large an amount of catalyst is thatthe reaction will take place at a high rate and consequently with formation of fewer decomposition products and less color. The amount of catalyst required to form a homogeneous solution is different for different fats. For example. 2% of NaHCOa based upon the weight of the finished ester will result in a homogeneous mixture when three parts 'of coconut oil are heated with two parts of glyceroll' 0n improved process .whereby'the removal of the 55 free fatty acid in the final product. It is also an object to provide such a procedure as will decrease the ratio of higher acyl groups to polyhyoil droxy alcohols in the partially esterifled polyhydroxy alcohol. Other objects will become apparent.

It has now been found that the soap remaining in the mixture may be removed without proportionately increasing the free fatty acid content by adding to the mixture a compound capable-of yielding an acid radical of an acid stronger than the fatty acid of-the soap, without adding acid hydrogen.

For example, the soap may be quickly destroyed, p n completion of its usefulness, at relatively low temperatures by the addition of an equivalent quantity of a mineral acid ester, preferably the halogen ester of the polyhydroxy alcohol employed in the reesteriflcation. Mineral acid esters which have been found to be suitable are ethylene chlorohydrin, glycerol chlorohydrin, glycerol dichlorohydrin, epichlorohydrin and chloride esters of polyglycols and polyglycerols. Other halide esters may be used but they are less desirable than the chlorides because of cost andfor other reasons.

By following such a procedure the soap is converted to alkali or alkaline earth chloride, or other halide, and a glyceride of the fatty acid. The chloride is relatively soluble in the excess glycerol which will separate out quickly, in the absence of the; soap. Thus by using these mineral acid esters a product is obtained which contains less excess polyhydric alcohol and is of low ash content tent.

Furthermore, by a judicious choice of mineral acid ester the soap from the catalyst may be largely convertedinto an additional quantity of the desired ester. For example, when a fat such as hydrogenated peanut oil is-reacted with excess glycerol by aid of a catalyst, equilibrium appears to be attained in the production of the maximum of monoglyceride, when the product contains approximately 1.3 higher fatty acyl groups per mol of combined glycerol. By'destroying the soap with an equivalent quantity of glycerol chlorohydrin the reaction product will then be richer in the desired monoglyceride than is possible by merely "carrying the reaction to a state of equilibrium; that is, there will be somewhat less than 1.3' higher acyl groups per mol of combined glycerol. The product is thus more pure and a more emcient agent, and may, therefore, be used in smaller amounts to accomplish the same resultsyobtained by monoglycerides prepared by former methods.

Tire following are some specific examples of our improved procedure, although it is not intended to limit the invention to the particular embodiments given:

Example 1 completely hydrogenated peanut was heated with 300 parts of glycerol. with stirring; to 170-2050. until the contentsvof the reaction vessel were substantially anhydrous. 16.2 parts -of NaHCO: was then added and heating and stirring were continued for one hour.

450 parts of closed vessel. The clear reaction mixture did and of low free fatty acid con- .and z are small whole numbers. the above type include the halogen esters of the .ethylene glycol and polyglycol ethers, such as (CLCHaCHOHCHaOH) at C. for one-half hour. The unreacted glycerol then quickly separated upon standing, ca y ng with it the sodium chloride freed from the soap. The upper fatty layer was found to possess a saponiflcation value of 157.0 and to contain a total of 27.2% glycerol. The ash was reduced to 0.04% and the alkalinity of the ash corresponded to only 0.06% NaHCOa. The fatty layer possessed 1.24-1.26 higher acyl groups per mol of combined glycerol.

Other hydrolyzable organic halogen compounds or mineral acid esters which will exhibit water solubility to a marked degree when the acid group is replaced by a hydroxyl group will be suitable for our purpose. An example of such a compound is 2,2'-dichloroethyl ether (ClCzHsOCzHsCl) when the chlorine atoms are replaced by hydroxyl groups diethylene glycol, a highly water soluble compound, results. Therefore, 2,2'-dichloroethyl ether is an excellent mineral acid ester to use in our process.

Example 2 300 parts of hydrogenated peanut oil and 200 parts of glycerol were homogenized by heating and stirring for one half hour with 10.8 parts of sodium bicarbonate. The reaction product'was then treated with 11 parts of 2,2'-dichloroethyl ether and stirring continued for three quarters of an hour at -l75 C. The resulting fatty layer had an ash content of 0.25% and the alkalinity of the ash corresponds to 0.02% NaHCOi.

Other compounds may be used of thetype XaHROMJR/O) It/l; where X represents halogen or oxy mineral acid groups, the latter being linked to carbon through oxygen, 0 represents 0 78811. B, R, R" are aliphatic groups of the same or diflerent numbers ofcarbon atoms and may or may not bear free hydroxyl groups, n and m are small whole numbers or zero, and w Compounds of 2 chlorethyl ether, 2-chloro-2' ethoxyethyl ether,- etc.

In'using the term mineral acid ester it is intended to include hydrolyzable organic mineral acid compounds. We do not limit ourselves tothe use of compounds actually obtained by the elimination of, water between a mineral acid' and a hydroxylic organic compound or by other well knownmethods of preparing esters. For example, chloroacetic acid is best prepared by the direct chlorination of acetic acid. However,

chlo'roacetic acid can be considered to be a halide ester of glycolic acid and is therefore ap-.

plicable to our process. likewise 2,3-dichloro-" dioxane is also prepared by the direct chlorinaallowing'any water vapor formed to escape through a discharge tube from the otherwise tion of :dioxane although it may also be considered to be the dihalide esterof the unstable 2.3-dihydroxydioxane.

The following are further specific examples of the use of such compounds:

Example 3 together'with heating for one hour at 200-210 C. The temperature is allowed-to fall to 140-150 -C. before adding 10 parts of methyl monochloroacetate. The fatty layer separating after onehalf hour is found to contain only traces of ash.

' Example 4 300 parts of hydrogenated peanut oil and 200 parts of glycerol are homogenized by heating and stirring at 200 C. for one-half hour with 10.8

The temperature is allowed to fall somewhat before adding 12 parts of 2, dichlorodioxane.

two layers. The fatty layer is found to possess a saponiflcation value of- 162.3. The ash is only 0.12% and is not alkaline as shown bytitration.

We do not wish tolimit our invention to the use of halogen esters, since we have foundthat other mineral acid esters such as neutral esters .of oxy- 1 acids of sulphur and. phosphorus will also serve to yield a product of low ash content.

' Example 5 450 parts of hydrogenated peanut oil is heated with 300 parts of glycerol and 16.2 parts of NaHCOa for one hour. at 200-210 C. while stirring. The temperature is then allowed tofall .to 140 C. before adding 32 parts of diethyl sulphate (Cal-115M504. After stirring for one-half hour the fatty layer which separates is found to have a saponification value of 167.0, and is free of Example 6 300 parts of hydrogenated peanut oil and 20 parts of glycerol are heated one-half hour at 200 C. under'stirring with 14.5 parts of Nal-ICOa.

Sulphur dioxide is then passed into the clear reaction mixture (160 C.) until the excess glycerol is found to easily separate from the fatty ester. The product has an ash content of only 0.35% and the alkalinity of the ash corresponds to 0.46% NaHCOa. It possesses 1.3 higher fatty acyl groups per mol of combined glycerol.

Anhydrides of organic acids may also be used for this purpose. For example, acetic anhydride (C2HaO)2O may be added to the reaction mixture. The above improvement also may be applied to the removal of soaps from other reactions wherein they are formed. As an example, it may be used in the removal of soaps in the preparation of other partially esteriiied polyhydro'xy alcohols in the presence of an alkaline reacting material. Also, compounds capable of yielding acid radicals of other mineral or organic acids, stronger Stirring is continued for one-" half hour whereupon it is found that the con-- tents of the reaction vessel quickly separate into than the fatty acid of the soap to be removed, may be added in place of the particular compounds mentioned in this specification.

An important feature of the invention is to effect the conversion of the soap and liberation of the glycerol without addition of acid hydrogen. It is also desirable to maintain'an anhydrous atmosphere during the separation. This is, of course, particularlyimportant where the acid anhydride is used.

' By following the above described procedure, the alkali or alkaline earth portion of the soap present in the mixture is converted to an inorganic salt. Such salts may be separated from the mixture so that a substantially ash free product is obtained which-is also substantially free of free fatty acids. When excess glycerol is prescut the conversion of the soap to the salt of the acid ester or anhydride will liberate the glycerol held in suspension and the salt will be dissolved 'in and may be readily separated with the glycerol. The absence of water in the mixture avoids the formation of emulsions, whereby the sepafacilitated.

In using the term "soaps" in the specification and claims it is intended to include the reaction products of the alkaline reacting catalysts with the organic materials present in the mixture. .In using the term acid hydrogen" reference is made to ionizable hydro'ge It is apparent that many modifications may be made in the utilization of the invention and in giving illustrative examples, it is not intended to restrict the invention to such examples. The terms used indescribing the invention have been used in a descriptive sense and not as terms of limitation and it is intended that all equivalents of the terms usedbe included within the scope of the appended claims.

We claim:

1. A process of removing asoap from substantially anhydrous mixtures thereof with an ester of a fatty acid comprising adding to the mixture 9., compound capable of yielding an acid radical of an acid stronger than the fatty acid of the soap, without adding the acid hydrogen of such acid.

2. A process of removing a, soap from substantially anhydrous mixtures thereof with an ester of a fatty acid comprising treating the mixture with a compound capable of yielding an acid radical of an acid stronger than the fatty acid of the soap in a substantially anhydrous atmosphere and in the absence of added free acid hydrogen.

3. A process of removing a soap from substantially anhydrous mixtures of the soap with a fatty acid ester of a polyhydroxyalcohol comprising adding to the mixture 0. compound capable of yielding an acid radical of an acid stronger than the fatty acid of the soap, without adding the acid hydrogen of such acid and maintaining the mixture at a-temperature of about 100 to- 4. A process of removing a soap from substantiallyanhydrous mixtures of the soap with a] fatty acid ester of a polyhydroxy alcohol; comprising adding to the mixture a compound capable of yielding an acid radical of an acid stronger than the fatty acid of the soap, without adding the acid hydrogen of such acid and maintaining the mixture at a temperature of about 140-1'l5 C. I

5. A process for removing a soap from substantially anhydrous mixtures of the soap with fatty acid esters of polyhydroxy alcohols comprising adding to the mixture a neutral aliphatic ester of an acid stronger than the fatty acid of the soap and maintaining the mixture at a temperature of about 140-175" C.

7. A process of removing a soap from substantially anhydrous mixtures thereof with an ester of. a fatty acid comprising adding a compound of the type Xw[(RO)n(R'O) mR"]z, where X is a substance selected from the class consisting of halogen and oxy mineral acids groups, the latter being linked to carbon through oxygen, is oxygen, R, R, R" are aliphatic groups, n and m are small whole numbers or zero, and w and z are small whole numbers.

8. A process of removing a soap from mixtures thereof with an ester of a fatty acid comprising adding an acid-anhydride in a substantially anhydrous atmosphere.

9. In a process of preparing partially esterifled polyhydroxy alcohols in the presence of a metal soap, the step which comprises destroying the fatty acid salt present in the product by the addition of-a neutral ester of a mineral acid stronger than the fatty acid of said soap in a substantially anhydrous atmosphere.

10. In the process of preparing fatty acid esters in the presence of a metal soap, whereby esters containing unesterified hydroxyl groups are obtained, the step which comprises addin after the production of the fatty esters, a quantity of an ester of a mineral acid stronger than the fatty acid in said soap slightly in excess (stoichiometrically) of the quantity of catalyst employed under substantially anhydrous conditions.

11. In the process of preparing monoand diglycerides in the presence of a metal soap, the

step which comprises adding, after the production eral acid ester is glycerol monochlorohydrin.

14. The process as in claim 10 wherein the mineral acid ester is of thetype where X is a substance selected from the group consisting of halogen or mineral oxy-acid groups, the latter being linked to carbon through oxygen, 0 is oiwgen, R, R, R" are aliphatic groups, n and m are small whole numbers or zero, and w and z are small whole numbers.

15. The process as in claim 10 wherein the mineral acid ester is dietlrvl sulphate.

16. In the process of preparing fatty acid esters in the presence of a metal soap, whereby esters containing unesteritled hydroxyl groups are obtained and a soap is suspended therein, the step whichcomprises adding an anhydride of an acid stronger than the fatty acids of the soap, in a substantially anhydrous atmosphere.

17. The process as in claim 16 wherein the aci anhydride is sulphur dioxide.

CHESTER M. GOODING. HANS W. VAHLTEICH.