US2727857A - Preparation of fatty peroxides - Google Patents

Description

United States Patent 0 PREPARATION OF FATTY PEROXIDES Roscoe Owen Carter, Jr., Cincinnati, Ohio, assignor to The Procter & Gamble Company, Cincinnati, Ohio, a corporation of Ohio No Drawing. Application October 25, 1951, Serial No. 253,221

12 Claims. (Cl. 204-161 This invention relates to improvements in methods. of converting unsaturated fatty materials into unsaturated fatty materials of high peroxide content.

Prior to this invention methods used for the formation of peroxides of unsaturated fatty materials have produced.

materials of low peroxidic oxygen content containing, in

producing peroxides of unsaturated fatty materials by direct'oxidation of unsaturated fatty materials. The prin-- cipal object of this invention is the production of these peroxides in very highly concentrated form. The essence of this invention which renders the foregoing objects possible of accomplishment resides in the provision of means and conditions such that (l) the reaction which produces peroxides of unsaturated fatty materials from unsaturated fatty materials is preferentially accelerated, and (2:) side reactions such as other oxidations, and decompositions or so-called decay of the peroxides are retarded or in some cases essentially eliminated.

Other objects and advantages of this invention willbe apparent during the course of the following description.

By the term unsaturated fatty matter or unsaturated fatty materials I mean the unsaturated fatty acids of from 8 to 24carbon atoms containing in their structure at least one carbon-to-carbon double bond including those obtainable from animal, marine and vegetable fats and oils (e. g. such fatty acids consisting essentially of (a) The unsaturated fatty alcohols obtainable by reduction of the carboxyl group of such fatty acids (e. g. oleyl alcohol and hexadecenyl alcohol), 4

(b) Esters of said unsaturated fatty acids with said unsaturated fatty alcohols (e. g. oleyl oleate),

(c) Esters of said unsaturated fatty acids with saturated aliphatic fatty alcohols of from 1 to 24 carbonatoms and free of other functional groups (e. g. monohydric alcohols such as methyl, ethyl, propyl, butyl alcohols etc., and polyhydric' alcohols such as glycol, glycerol, polyglycols and polyglycerols, and

(d) Esters of said unsaturated fatty alcohols with saturated aliphatic monocarboxylic acids of from 2 to 24 carbon atoms and free of other functional groups '(e. g. acetic, propionic, butyric acids 'et'c.), said unsaturated fatty matter or unsaturated fatty materials being of a molecular structure or-mixture. of such-materials that they are in a liquid state under the conditions of this invention. 1

a By the term peroxides of unsaturated fatty matter I mean members of a class of oxygen addition products of unsaturated fatty matter, the molecules of which have oleic and linoleic acids) and derivatives of of peroxides.

2,727,857 Patented Dec. 20, 1955 been described by Farmer and hisco-workers (J. Chem. Soc., 1943, 119-122) as containing an O-O-H grouping attached to a carbon atom adjacent to an ethylenic (a carbon-to-carbon double bond) group, e. g.

I have discovered that very highly concentrated peroxides of unsaturated fatty matter may be produced by intimately contacting refined unsaturated fatty matter in the liquid or molten form with continuously added oxygen and chlorophyll, the mixture being substantially free of copper compounds, in the presence of visible light that is substantially free of ultraviolet light, at temperatures below 100 0, preferably about 30 C. This photocatalytic combination is very important, particuarly in the preparation of highly concentrated peroxides, since it catalyzes the peroxide formation but not the peroxide decomposition which is in direct contrast to past processes wherein ultraviolet light has been used in the production "Ultraviolet light not only photocatalyzes the formation of the peroxides but also their decomposition. f In fact, photocatalysis by ultraviolet light either in the presence of or absence of chlorophyll rapidly reaches'a stage such that the amount of peroxide decomposed per unit time .is as greater greater than the amount of peroxide formed during the same unit time period.

By visible light I mean radiations, the wave lengths of which are substantially entirely inthe range of 400 to 760 m In this range, I prefer to use the light hand between 600 to 660 m sincemy process of peroxidation proceeds most efiiciently with light inthis band. The light spectra emitted from incandescent tungsten electric light bulbs are well suited for the purposes of this invention. Such spectra' are almost entirely within the visible range, and are substantially free of ultraviolet light, there being only a minor portion of the total light produced by the bulb delivered as light in the range of 350 to 400 III/1.. Phosphor" coated electric discharge mercury vapor lamps commonly known as fluorescent lamps can also be used, but care should be used to select lamps having a coating designed to emit light of a wave length that is suitable for the process of this invention, since the various phosphor coatings used emit various wave length bands. A typical example of asatisfactory phosphor coating is one called Pink having a range of 520 to 750 [II/L, whereas an ultraviolet lamp having a fBlue Ultra phosphor, emitting light in the range of 270 to 400 m is undesirable.

In addition to copper, contaminants such as oxides, salts and soaps of some heavy metals, e. g. chromium and iron, and other materials, such as hemin, formic acid, picric acid, caprylic acid, and ethyl glycine, that hasten the development of rancidity in fatty substances, are preferably avoided mall the reaction ingredients or containers used in this preparation, because many of these materials promote peroxide decomposition, i. e. they catalyze the decomposition or degradation of peroxides, often yielding such compounds as hydroxy fatty acid derivatives, and aldehydes and also organic acids of lower molecular weight. (Note that care should be used in selecting the chlorophyll, since copper salts are frequently added to some commercial preparations for the purpose of intensifying the green color of the chlorophyll. Thus only chlorophyll which is known to be substantially free of copper should be used.) The rate of 3 formation and decomposition of the peroxides of this invention will also vary somewhat with the type of oil, its origin, history and treatment, (e. g. degree of unsatura- Refined fatty matter should be used in the preparation of the peroxides of my invention, particularly when preparing very highly concentrated peroxides. By the term refined fatty matter I refer to fatty "matter that does not contain sufficiently large quantities of materials, which I shall call -de-peroxidation catalysts, that will (1) interfere with'or prevent the peroxidation of the unsaturated fatty matter, or (2) promote the decomposition of the peroxides. Naturally occurring crude oils frequently contain materials that inhibit peroxide formation or materials that accelerate the decomposition of the peroxide (e. g. the enzyme catalase may be such a contaminant); and commercially treated oils may frequently contain peroxide decomposition promoters of the types mentioned above, and oxidizable solvents that will react with the peroxide. These materials may be removedby refining methods, such as caustic refining and drying and/ or distillation. Indeed, in some cases bleaching with fullers earth or other-adsorption media and/or water washing followed by drying may provide sufficient refining to permit rapid peroxidation of the fatty matter.

The success of this process is due to the attainment of a rapid rate of peroxide formation and such conditions that the rate of peroxide decomposition is relatively slow. The rapid rate of formation is the result of (l) the maintenance of an effective concentration of chlorophyll (that is substantially free of copper compounds) throughout the oxidation, (2) the use of visible light of high intensity, and (3) the establishment of intimate contact of the reactants. A very slow rate of peroxide decomposition is assured by (l) performing the oxidation at low temperatures, preferably at about C. or below, (2) completing the primary reaction in the shortest possible time, and (3) avoiding factors which accelerate peroxide decomposition, such as ultraviolet light, copper and other de-peroxidation catalysts, that interfere with the productionand/ or stability of the peroxides.

- By applying the controlling factors described above, I have developed a novel method for the production of unsaturated fatty matter of high peroxide content.

The particular importance of this process lies in the introduction of the peroxide group in the fatty molecule without disturbing the double bond. The peroxide group provides an excellent entry into the molecule for the introduction of a double bond without disturbing a double bond that is already in the molecule. Thus the formation of peroxides is an important step in the production of drying oils from oils that have no drying properties. The surprisingly easy and practically quantitative manner in which a peroxide group is introduced at the methylenic group adjacent to a carbon-to-carbon double bond, and the high reactivity of the fatty peroxides therewith produced make these compounds extremely desirable starting materials for the synthesisof unsaturated fatty acid derivatives formerly not attainable on a commercial scale.

The particular value of this invention is shown by comparing it with the ultraviolet light catalyzed peroxidation. The latter is accompanied by so much peroxide decay and iodine value drop that past workers have found it necessary to stop the peroxidation when each mole of the unsaturated fatty matter contained about 0.03 to 0.29 mole of peroxidic oxygen. Products of peroxidations carried beyond this range contained so much peroxide decay material that purification was impractical. Furthermore the production of such weak and impure peroxides required from 4 to over 100 hours, After that many more tedious hours were required to purifythe peroxide, the product often being of inferior quality In contrast this invention enables one to prepare con-j centrated peroxides in the comparatively short time of only 5 to 6 hours, preferably at temperatures of about 30 C., that contain one mole or more of peroxidic 4 oxygen per mole of unsaturated fatty matter, without any appreciable peroxide decay or loss in unsaturation. Peroxides containing 0.5 mole of peroxidic oxygen per mole of unsaturated fatty matter can be produced in less than 2 hours. Indeed, in some instances, e. g. Example 7, peroxide contents of over 0.7 mole are readily produced in 2. hours. It is to be noted that all peroxides prepared according to this invention in the hereinafter described examples attained a peroxidic oxygen content of at least 1000 millimoles of oxygen/kilogram of the product. 7

The invention will be better understood by the following typical examples illustrating conditions under which this invention may be carried out, wherein parts and percentages are given on a weight basis unless otherwise indicated; and peroxide value determinations have been performed according to the method of Wheeler, Oil and Soap 21,53, (1944).

Example 1.-A quantity of 78 cc. of distilled methyl esters of mixed fatty acids derived from cottonseed oil (I will refer to 'such mixtures as cottonseed oil methyl esters) was placed in a water-jacketed vertical glass tube (30 cm. long and 28 mm. inside diameter) which was illuminated by four 300 watt tungsten filament electric light bulbs of the type generally known as reflector spot bulbs which direct a concentrated beam of light on the subject being illuminated. The oil was intimately contacted with oxygen gas introduced at the bottom of the tube in the form of very fine gas bubbles through a sintered-glass disc. A quantity of 0.03 gram of substantially copper-free chlorophyll in the form of a 10% mixture with vegetable oil was added to 10 cc. of hexane. A half cc. of this mixture was added to the ester at the start of the reaction followed by 0.20 cc. portions at 10 minute intervals, a total of 0.018 g. of chlorophyll being used. The temperature of the reacting mass was maintained between 25-30 C. throughout the preparation of the peroxide by the circulation of cooling water through the water jacket. After the very short time of only 5 /2 hours the ester acquired a peroxide value of 2600 millimoles of oxygen per kilogram. This product would appear to contain not only monoperoxidic methyl esters (which contain one mole of peroxidic oxygen permole of unsaturated'matter) but also diperoxidic esters, since on the basis of one mole of oxygen per mole of unsaturated ester the theoretic peroxide value of the monoperoxidic ester would be about 2390 millimoles/kilogram.

Example 2.In a manner similar to that in Example 1, cc. of distilled methyl esters of mixed fatty acids derived from olive oil were oxidized, at a temperature of 2530 C., to a peroxide value of 2775 m.moles/kg. in 5 hours. This peroxide value is very close to the calculated theoretic peroxide value for the monoperoxidic esters which in this case is about 2760.

Increasing the concentration-of chlorophyll, intensity of light, gas pressure, concentrationof oxygen in the gas used (e. g. air), uniformity of distribution of gas throughout the liquid fatty matter all increase the rate of peroxide formation. Also, as will be shown herein, the increase of time and temperature within reasonable limits canincrease the amount of peroxide formation.

Example 3.In a manner similar to that of Example 1, cc. of distilled cottonseed oil methyl esters were oxidized at a temperature of 25 to 30 C. In this case a total of 0.024 g. of copper-free chlorophyll was added as in Example 1 at 10 minute intervals throughout the runoff 6% hours. The longer reaction period gave a product having a peroxide value of 3015 m.moles 02/ kg. or about 16% higher than that obtained in Example 1.

Example 4 wherein unsaturated fatty acids are peroxidized illustrates the effect of lack of intimate admixture of the oxygen and of using less catalyst. At the temperature used the fatty acids were so viscous that much larger oxygen bubbles were formed than were formed in the previous examples, so that the amount of intimate contact; of oxygen with the fatty matter and chlorophyll was greatly reduced, resulting in a product of lower-peroxide value.

' Example 4.-Fifty cc. of distilled red oil were oxidized in a manner similar. to that of Example lat a tempera-. ture of 27 t9. 32 C. using only three 300 watt reflector spot bulbs? A total of 0.007 gm. of copper-free chlorophyll was added to the oil in a manner similar to that ofjExam ple 1 except the successive portions were added at approximately /2 hour intervals throughout a 7 /2 hour oxidation period. The peroxide value of the prodnot was 1140 rnz'moles 'O2/k Example 5.-A batch of fatty alcohols, prepared by sodium reduction of sperm oil was distilled atan absolute pressure of 3 mm. mercury. The fraction that distilledover between 146 and 154 'C. was chilled first at 20 F. and later at F. At each temperature the crystalline fattyalcohols were removed by filtration. Analysis of the filtrate indicated that it was composed almost entirely of oleyl alcohol.

. In a manner similar to that of Example 1, 75 cc. of the above oleyl alcohol preparation were oxidized at a temperature of 15 to 20 C. In this preparation 0.03 gm. of substantially copper-free chlorophyll were added to cc. of hexane and 0.5 cc. of this solution was added to the oleyl alcohol atthe start and 0.2 cc. portions were added at 10 to minute intervals over a period of 7 hours. 'Analyses of samples taken of the reacting mixture at 4 and 7 hours showed the alcohols to have peroxide values of 1131 and 1667 m.moles Oz/kg. re-

spectively. The peroxide value was still rising at a rapid rate at the end of 7 hours when irradiation and addition of chlorophyll were discontinued.

The methods described in the above examples are equally applicable to the production of peroxides of fatty esters of unsaturated fatty alcohols.

Example 6. 75 cc. of distilled methyl estersof mixed fatty acids derived from soybean oil were oxidized under conditions such as used in Example 1. The perox ide value of the esters had reached 2490 m.moles/kilo and was still rising rapidly at the end of 4 /3 hours when the peroxidation was discontinued.

Note that the mixed fatty acids contained in the fatty materials of the above examples represent varying degrees of unsaturation. The following table shows the proportions of acids containing 1, 2 and 3 carbon-tocarbon double bonds (C=C) usually found in mixed fatty acids such as used in these preparations.

Examples #1, #3

' The percentage of saturated fatty matter present in theifatty mixture appears to act as a diluent and does not appear to afiect the degree of peroxidation of the unsaturated .fatty matter present. On the other hand the typeof fatty matter may affect the rate of the peroxidation. Thus, for example, methyl esters are peroxidized aboutthree times more rapidly than are the triglycerides from which they are derived.

, Example 7.In this preparation which was similar to that of ,Example 1, only 3 reflector spot bulbs were used andlthe reaction was stopped at the end of only 2 hours, at which time the cottonseed methyl esters had been oxidized to a peroxide value (P. V.) of 1750, which is equivalent'to .73 mole of oxygen per mole of unsaturated fatty t e the end of the 2 hour oxidation period in Example 7,"nitrogen was substituted for oxygen and irradiation with visible light and chlorophyll addition were continued for 4 hours, during which period no measurable change in peroxide value was observed. This serves to illustrate that visible light and chlorophyll do not catalyze peroxide decay.

The fatty peroxides prepared according to this invention show essentially all the unsaturation of the original fatty material; e. g., iodine values determined on a sample of cottonseed oil methyl esters were 108.5 before oxidation and 103 after oxidation to a P. V. of 1750 in a manner similar to that in Example 7. Theoretical calculation of the iodine value after oxidation, assuming that no carbon-to-carbon double bonds were destroyed during the reaction, gives a value of 102.8 or practically a perfect check. (The above iodine value of 103 was determined by the commonly used Wijs method for iodine value, corrected for the amount of iodine liberated from the potassium iodide by the peroxide grouping. The correction was determined by measuring the iodine liberated from a potassium iodide solution prepared and used in the same manner as the Wijs solution except that the iodine chloride had been omitted.)

Peroxides as a class of compounds are relatively unstable, the decomposition reaction of the peroxides being highly exothermic. At temperatures in the neighborhood of 70 to C. or higher the decomposition becomes violent if no provision is made for removal of the heat of decomposition. The decomposition may also be accelerated by impurities such as pro-oxidants. .However, peroxides are surprisingly stable at lower temperatures, particularly if prepared according to this invention wherein care is used to exclude decomposition catalysts. For example, a sample of peroxidized methyl esters of fatty acids derived from olive oil that had a peroxide value of 2700 lost only 10 units during storage at about 5 C. in an icebox for 22 days. Even at higher temperatures the decomposition proceeds in an orderly manner if the heat of decomposition is removed as produced.

For example, portions of a sample of peroxides of cottonseed oil methyl esters having an initial P. V. of 2220 were subjected to isothermal storage at various temperatures. The peroxide content decreased approximately logarithmically with time, the reaction appearing to' be first order. The following table shows the loss in perox: ide value sustained at the end of 6 hours, the losses at the lower temperatures being extrapolated values calculated by using reaction constants determined experimentally at the higher temperatures of 110, and 138 C.

Loss in Peroxide Value Temperature, C.

P. V. Loss Percent in 6 hrs. Loss If the decomposition rate shown in the table above at 5 C.-were continued for 22 days the total loss would be about .1 P. V. 24/6 22 or 8.8 P. V. units, which is in marked agreement with the experimentally determined value of 10 units loss shown above for theperoxides of olive oil methyl esters which were stored at about the same temperature.

From these data it is obvious that whenever stability of peroxides is required, low temperatures are usually desirable, for example during their ticularly during storage.

The above data represent the loss in peroxide value manufacture and panthe active chlorophyll in about this same concentration range. Optimum peroxidation rates can usually be maintained by continuous or intermittent addition (preferably several times per hour) of chlorophyll at a rate of about from to 80 mg./liter/hour. v

For any degree of illumination used in the process the peroxidation rate appears to increase in proportion to the concentration of chlorophyll employed up to what may be called an optimum chlorophyll concentration. Above this concentration the increase in peroxidation rate is lower per unit increase in chlorophyll concentration and at least in some instances if the concentration of chlorophyll is increased too far the rate of peroxidation may actually show a decrease. Thus for example, this optimum concentration of chlorophyll in a peroxidation, in which the degree of illumination is of the order of that used in Example 1, is of the order of 15 to 20 milligrams of pure chlorophyll per liter of unsaturated matter. It further appears that the optimum chlorophyll concentration may increase or decrease as the degree of illumination increases or decreases.

In the above examples the amounts of chlorophyll used in each individual addition were so small that it was found convenient to dilute it with hexane to facilitate its measurement. It should be noted that care was taken to use minimal amounts of a very volatile and unreactive diluent. Under the conditions used in the above examples the hexane was immediately volatilized and swept out of: the reaction mixture by the continuous stream of gas bubbles before it (the hexane) had any opportunity to react. Indeed, in the preparation of large batches of peroxides, where dilution is no longer necessary to facilitate measurement of the chlorophyll, a diluent is not employed. The use of such additives or the use of solvents for the fatty matter merely introduces another material that can interfere with the formation of the peroxide, or react with or otherwise promote the decomposition of the peroxide. Thus, for example, the use of ethyl ether could be very undesirable since not only could it interfere with the desired peroxidation but it might also be oxidized to explosive peroxidic materials. It is obvious that care should be used in selecting unsaturated fatty matter for peroxidation and possibly even greater care must be exercised in selecting the refining method to suit the fatty matters so as to insure the removal of reactive solvents or other materials (such as have already been described) that will interfere with the production and/or stability of the peroxide.

In the preceding examples the rates of peroxidation obtained varied with the operating conditions used. Thus the time required for the absorption of 0.5 mole of peroxidic oxygen per mole of unsaturated fatty matter varied from about 1 to 11 hours. While I may operate at rates beyond this range as I change operating conditions, I prefer to employ conditions (e. g. chlorophyll concentration and light intensity) such that 0.5 mole of peroxidic oxygen is absorbed per mole of unsaturated fatty matter in about 6 hours or less. The unique advantages of the process tend to diminish if the time for this amount of peroxidation extends beyond about 11 hours particularly when the reaction temperature is above 30 C. Applicant desires the following claims to be understood in the light of the foregoing definitions.

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

l. The process for preparing, from unsaturated fatty matter, peroxides of unsaturated fatty matter of high peroxidic oxygen content which comprises intimately contacting refined unsaturated fatty matter in liquid condition and at a temperature not over 100 C. with oxygen and chlorophyll which are added throughout the reaction in the presence of visible light that is essentially free of ultraviolet light and contains a major proportion of light in the 600-660 mg. wave band, the liquid mixture being essentially free of copper and other de-peroxidation catalysts, the peroxidation reaction being continued until the unsaturated fatty matter contains at least 1000 millimoles of peroxidic oxygen per kilogram.

2. The process of claim 1 wherein the reaction is carried out at temperatures below C.

3. The process of claim 1 wherein the reaction is carried out at temperatures of about 30 C.

4. The process of claim 3 wherein the unsaturated fatty matter contains one carbon-to-carbon double bond per molecule.

5. The process of claim 3 wherein the unsaturated fatty matter contains 2 carbon-to-carbon double bonds per molecule.

6. The process of claim 3 wherein the unsaturated fatty matter is oleic acid.

7. The process of claim 3 wherein the oxygen is added under superatmospheric pressure.

8. The process of claim 3 wherein air is used as an oxygen supply.

9. Theprocess of claim 3 wherein the chlorophyll is diluted with a volatile hydrocarbon.

10. The process of claim 3 wherein the process is continued until the product contains at least 0.5 mole of peroxidic oxygen per mole of unsaturated fatty matter.

11. The process of claim 10 wherein said 0.5 mole of peroxidic oxygen is obtained in less than about 11 hours.

12. The process of claim 3 wherein the resultant prodnot is substantially free of peroxide decomposition products.

References Cited in the file of this patent UNITED STATES PATENTS 2,165,130 Coe July 4, 1939

Claims (1)

1. THE PROCESS FOR PREPARING FROM UNSATURATED FATTY MATTER, PEROXIDES OF UNSATURATED FATTY ACID MATTER OF HIGH PEROXIDIC OXYGEN CONTENT WHICH COMPRISES INTIMATELY CONTACTING REFINED UNSATURATED FATTY MATTER IN LIQUID CONDITION AND A TEMPERATURE NOT OVER 100* C. WITH OXYGEN AND CHLOROPHYLL WHICH ARE ADDED THROUGHOUT THE REACTION IN THE PRESENCE OF VISIBLE LIGHT THAT IS ESSENTIALLY FREE OF ULTRAVOILET LIGHT AND CONTAINS A MAJOR PROPORTION OF LIGHT IN THE 600-660 MU WAVE BAND, THE LIQUID MIXTURE BEING ESSENTIALLY FREE OF COPPER AND OTHER DE-PEROXIDATION CATAYLST, THE PEROXIDATION REACTION BEING CONTINUED UNTIL THE UNSATURATED FATTY MATTER CONTAINS AT LEAST 1000 MILLIMOLES OF PEROXIDIC OXYGEN PER KILOGRAM.