sters CATALYTIC OXIDATION T. 31. PATRICK, J R . , AND WILLIARI S . E31ERSQN Monsanto Chemical C o m p a n y , Dayton, Ohio T h e liquid-phase air oxidation of the methyl esters of talloil fatty acids is described. In order to develop a technique for the method, oxidation of ethyl oleate and of oleic acid was studied in some detail. Oxidative scission was expected to take place at or near the double bonds to yield mono- and dicarboxylic acids. Large amounts of high molecular weight by-products, in addition to the expected scission products, were formed in these oxidations. The identified products compriscd most of the members of the homologous series from caproic to palmitic acid and from suberic to undecanedioic acid, inclusive.
A
S PART of an exploratory investigation of the utilization of the methyl esters of Unsaturated fatty acids from talloil (MEUFB), the catalytic liquid-phase autoxidation of this raw material'was undertaken. Although a number of investigators have previously studied the autoxidat,ion of long-chain unsaturated fatty acids, or their est,ers, much of the vork is primarily of theoretical interest only. Some ( 4 , 10, id, 15-17) have been interested in mechanisms and their application t o problems in the drying of oils. Others ( 2 , 7 , 8, 11, 23, 26) have been interested in the products of oxidative scission but have made little effort to obtain optimum conditions for their formation, nor have thep attempted to obtain complete data on the relative amounts of scission products formed. It was a purpose of this work, therefore, to investigate talloil fatty acids as a source of lower molecular weight mono- and dicarboxylic acids, and to determine what acids comprise the scission products and approximately t o what extent. In order to facilitate the development of a set of optimum reaction conditions, ethyl oleate rather than talloil esters was initially employed in the investigation. Two separate techniques were studied. The first involved the use of air under pressure in the presence of a chromium oxide catalyst. No solvent was used. The second utilized acetic acid as a solvent and oxygen as the oxidizing agent. A mixture of the acetates of cobalt, manganese, and lead served as catalyst. Rsther than a fairly clean-cut scission in the immediate neighborhood of the double bonds, it was found that oxidation resulted in the formation of a great variety of scission products, as well as large amounts of high boiling by-products. I n the case of ethyl oleate the predominant scission products were caprylic, pelargonic, suberic, and azelaic acids; smaller amounts of caproic, heptylic, capric, lauric, myristic, palmitic, sebacic, and undecanedioic acids were also present, I n the case of scission products from the methyl esters of unsaturated fatty acids from talloil, the same components were found, but caproic acid occurred in relatively greater amounts.
nearly to the bottom of the liner. A stainless steel paddle stirrer, having a 2 l/le-inch bladc and a speed of 500 r.p.m., provided agitation. A stainless steel thermowell was fitted into the head. The off-gas passed through a water trap of the Stark and Dean type, a water-coobd condenser consisting of 20 feet of 0.25 inch stainless steel tubing coiled in a close-spaced spiral, and finally through a valve which was used to regulate air flow. The air was supplied from a compressed air reservoir and passed through calibrated flowmeters prior to entering the autoclave. Heat was furnished by electric resistance wires embedded in a jacket surrounding the autoclave. Temperatures were automatically controlled and recorded. TUBEOXIDATIONREACTOR.All runs in acetic acid solution were made in an upright glass tube, 42 inches long and 58 mm. in outside diameter, bearing a 40-mm. sintered-glaqs disk of I3 porosity in the bottom end. A 10-mm. tube and stopcock (for draining the reactor) was sealed into the apparatus just above the disk. Oxygen from a cylinder was led through a trap prior to entering the reactor through the disk. The upper end of the reactor was fitted with a 600-ml. calibrated dropping funnel and an outlet for off-gases. The off-gases passed through a bulb condenser and a spiral condenser in series. The reactor was heated by means of a spiral resistance winding regulated with a Variac variable transformer. Temperatures were read by means of an iron-constantan thermocouple inserted in a well through the head of the reactor. FRACTIO~ATING COLUMINS.One column had a 38-inch by 18mm. (outside diameter) jacketed fractionating section packed with single-turn glass helices, and was fitted with an Eclr. and Krebs head. The pot waa heated by an oil bath. The other column had a jacketed fractionating section, 42 inches bv 20 mm., of the Vigreux type mith a Penn State head. The pot was heated by an oil bath. RAW MATERIALS
OLEIC ACID, U. S. P . grade, was obtained from The Coleman and Bell Company, which furnished the following approximate analysis (per cent) : Oleic acid Linoleic acid Saturated acids Unsaponifiable
83-84 10
4-5
2
ETHYLOLEATEwas obtained from The Kessler Chemical Co., Inc. The following approximate percentage composition was given : E t h y l oleate E t h y l linoleate BaturaGed esters (myristic, palmitic, stearic) Ethyl palmitic oleate E t h y l linolenate
73 13 10 4
Practically none
M E T H Y L ESTERS O F U N S h T U R A T E D FATTY hCID5 ? \e're Supphd by the Phosphate Division, Monsanto Chemical Co., Anniston, Ala. The only analytical data available on this material were a s follows:
Acid No. Saponification No.
Iodine No.
Unsaponifiable, %
2.4
175 135 9
Anderson and Wheeler ( 1 ) reported the average percentage composition of six samples of American tall oil fatty acids t o be:
APPARATUS
AUTOCLAVE. The autoclave for carrying out pressure oxidations was a cast iron, conical-seal type of about 1-liter capacity, equipped with a close-fitting stainless steel liner. A 0.25-inch stainless steel inlet tube, perforated with small holes, extended
Oleic &id Linoleic acid Saturated acids (mostly pa!mitio)
636
45 48
7
March 1949
~
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE I. EFFECT OF TEMPERATURE (Air oxidation of ethyl oleate a t 200 Ib./sq. inch for 6 hours) Scission High Boiling Products, By-products, Tar, Recovery, Temp., O C . Wt. % Wt. % Wt. % Wt. % 80-90 110-120 140-150 J70-180
9.2 22.0 11.6 7.8
38.4 40.2 21.4 18.4
5.1 18.7 58.2 44.7
39.9 6.2 2.7 2.5
TABLB 11. EFFECT OF ERESSURE (Air oxidation of ethyl oleate a t 110' t o 120' C. for 6 hours) Scission High Boiling Pressure, Products, By-products, Tar, Recovery, Lb./Sq. Inch Wt. % Wt. % Wt. % Wt. % 50
17.8 20.5 22.0
100 200
57.4 47.1 40.2
11.1 14.6 18.7
10.3 14.5 6.2
631
through the dropping funnel. The temperature was always held in the range 105' t o 115' C. and the oxygen flow was regulated so as to be fed as fast as possible without causing the condensers to flood or the li uid t o bump. A foaming action was thus obtained, allowing goo% liquid-vapor contact. At the end of the reaction period the acetic acid was stripped from the liquid under reduced pressure and the cooled residue was treated with 10% hydrochloric acid t o convert metallo-organic compounds t o metal chlorides. The mixture was filtered to remove insoluble lead chloride, and the filtrate was separated into an organic phase and a cobalt- and manganese-bearing aqueous phase. The organic material was saponified with alcoholic potassium hydroxide. The procedure from this point was the same as that used for pressure runs. I n Table IV are shown the results of a series of runs in which time was made the variable. OXIDATION O F OLEIC ACID
TABLE 111. EFFECT O F TIME (Air oxidation of ethyl oleate E t 110' to 120' C.) Scission High Boiling Tar, Recovery, Products, By-products, Time, Pressure, Wt. % Wt. % Wt. % Wt. % Hr. Lb./Sq. Inch 6 12 18 6 12 24
50 50 50 100 100 100
17.8 25.9 29.3 20.5 27.7 32.4
57.4 45.2 46.8 47.1 45.5 35.8
11.1 12.1 12.3 14.6 14.5 21.2
10.3 6.9 3.7 14.5 5.4 3.1
OXIDATION OF ETHYL OLEATE
PRESSURE OXIDATION USINGAIR. T h e charge (430 grams of ethyl oleate and 4.4 grams of Baker's C.P. chromium oxide) was sealed in the autoclave, the desired pressure applied, a flow rate of 5 cubic feet of air per hour started during stirring, and the temperature brought up to the desired range. At the end of the reaction the charge was rinsed out of the bomb with 500 ml. of absolute ethanol. This material was then filtered to remove suspended catalyst. The filtrate was boiled under reflux with potassium hydroxide t o saponify polyesters as well as ethyl esters. The mixed acids were then treated with ether t o precipitate 9,lO-dihydroxystearic acid (high-melting form), which was removed by filtration. The remaining acids were esterified with ethanol in the presence of sulfuric acid in standard fashion. The esters were distilled through a 10-inch Vigreux column and cuts were made arbitrarily corresponding t o scission products (boiling point < 165 O C. at 2 mm. of mercury), recoveredethyl oleateor "recovery" (boilingpoint 165" to 175' C. at 2 mm. of mercury), and high boiling by-products (everything boiling above 175 C. at 2 mm. of mercury which could be distilled using a vacuum pump capable of producing a pressure of 0.3 to 0.5 mm. of mercury in the system). Table I summarizes the results obtained at 200 pounds per square inch for 6 hours, with temperature varied. Inasmuch as 110" t o 120" C. was indicated as optimum, t6e effect of pressure was studied in this temperature range. Table I1 shows the results obtained under these conditions for 6-hour runs. Time was next varied in two sets of experiments at 110" to 120" C., and 50 and 100 pounds per square inch, respectively (Table 111). One experiment was performed t o determine -whether the presence of water would affect the extent of oxidation. The addition of 100 grams of water to the initial charge did not change the results within the limits of experimental error.
Table V shows the effect of time on the oxidation of oleic acid in acetic acid solution at 105 to 115" C. These runs were made early in the work when ethyl sulfate was being used as the esterifving agent. The acetic acid was stripped off after filtering the oxidation mixture. The residue was neutralized with 10% sodium hydroxide and then dried on a Iaboratory drum dryer heated by low pressure steam. The tan sodium salts were added slowly with stirring to a slight molar excess of ethyl sulfate at room temperature. After about two thirds of the salt had been added, it was necessary t o use a solvent t o thin the mixture. One liter of benzene caused gel formation, but subsequent addition of 500 ml. of ethanol thinned the material sufficiently to permit addition of the remaining salt. The mixture was heated to reflux (71 ' C ) for 5 hours with stirring. A slight ex'cess of sodium acetate was then added t o rid the mixture of excess ethyl sulfate, and stirring and refluxing were continued 5 hours longer. The esterified product was washed thoroughly with water The low-boiling materials (benzene, ethyl acetate, and alcohol) were then stripped off and the remainder was distilled as usual. OXIDATION OF METHYL ESTERS
PRESSURE OXIDATIONS USINGAIR. The procedures used for runs on methyl esters of unsaturated fatty acids from tall oil were the same as those described for ethyl oleate. As 440 grams of ethyl oleate are approximately equivalent on a molar basis to 420 grams of these methyl esters, 420 grams (or 210 grams) of the latter were used in each case and calculation of weight per cent conversions to ethyl esters was based on 440 grams (or 220 grams) of starting material. Table VI summarizes the results obtained from runs in which temperature, pressure, and time, respectively, were varied. One per cent chromium oxide catalyst was used i n each case.
TABLE IV. EFFECT OF TIME Time, Hr.
(Oxidation of ethyl oleate in acetic acid solution) Scission High Boiling By-products, Tar, Recovery, Products. Wt. % Wt. % Wt. % Wt. %
Time, Hr.
(Oxidation of oleic acid in acetic acid solution) Scission High Boiling By-products, Tar, Recovery. Products, Wt. % Wt. % Wt. % Wt. %
TABLE V. EFFECT OF TIME
OXIDATION IN ACETIC ACID SOLUTION USING OXYGEN
These oxidations were erformed in the glass tube reactor. One per cent each (basef on the ethyl oleate) of manganese acetate, lead acetate, and cobalt acetate ("mixed acetate" catalyst) were dissolved in acetic acid with warming and added t o the ethyl oleate. Either 220 or 440 grams of ethyl oleate and an equal weight of acetic acid were used in these runs. Oxygen was started through the warm reactor, and then the charge (previously heated nearly to the operating temperature) was added
4.5 6 8
20.9 25.5 33.7
29.2 24.9 33.8
16.8 9.5 2.3
13.2 6.2 2.6
These figures are probably all low on account of the method used i n working u p the runs. However, they serve to show qualitatively the effeot of reaction time.
638
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLEVI.
Results of distilling the esters are listed in Table IX. Calculations are based on 109 grams of starting material (109 grams of ethyl ester are equivalent to 100 grams of acid).
AIR OXIDATIONOF METHYLESTERS
Scission Products, w t . 70
Temp., "C.
High Boiling By-products. Wt. 70
Tar,
n-t. %
Recovery Wt. 7,
Effect of Temperature (100 Lb.iSq. Inch for 6 Hours) 80-90 110-120
14.3 15.1
50.6 4i.8
17.9 19.3
11.7 10 8
Effect of Prepsure (110' t n 120' C. for 3 Hours) Pressure Lb./Sq. d c h 60 100
12.7 10.8
30.6 47.8
8.3
7.1
45.8 28.2
Effect of Time (100" t o 120' C arid 100 Lb./Sq. Inch) Time, Hr. 3 6 11.5
7.1 16.1 8.8
47 8 47.8 26.9
10 8 19.3 43.4
28 2 10.8 3 .O
OXIDATIONIK ACETICACIDSOLUTION USINGOXYGEN. Table VI1 shows the effect of time on the results of methyl eater oxidation in acetic acid, using oxygen and the mixed acetate catalyst, at l05Oto 115' C.
TABLE VII. EFFECTOF TIMEON OXIDATIONIX ACETIC ACID SOLUTION Time, Hr.
Scission Products, Wt. %
High Boiling By-products, Wt. %
3 6
26.5 35.4
41.6 35.5
'
~
Tar, W t ~yG
Recovery. Wt. %
9.1
9.8 4.0
3.7 ~~
~
REOXIDATION O F HIGH MOLECULAR WEIGHT RY-PRODUCTS
The high-boiling by-products from several runs (both pressure runs and acetic acid runs) were reoxidized in acetic acid solution a t 105" t o 115" C. The procedure was essentially the same as that used for ethyl oleate, except that the step t o isolate 9,10dihydroxystearic acid from the crude oxidation product was eliminated. I n a few instances the xeight of solvent used (acetic acid) exceeded the weight of starting material, in order t o give a larger and more workable volume of liquid. One per cent of each of the metal acetate catalysts n a s used in every case. Results are listed in Table VIII. "Recovery" is material boiling above 170" C. a t 2 mm. of mercury
TABLEVIII.
OXIDlTION O F HIGH ROILING BY-PRODUCTS ACETICACIDSOLUTION
Source of High Boiling By-products Oleic acid oxidized in acetic acid Ethyl oleate (bomb-CrlOs) M E U F A oxidized in acetic atid MEUFA (bomb), b. 175-200 C./2 mm. M E U F A (bomb), b. 200' C./2 mm.ca. 320' C./6 mm.
Scission Products, Wt. %
Tar, Wt. %
IN
Recovery, Wt. %
21.2 32.7 35.0
31.6 4.4 6.8
12 46.4 40.4
31.0
8.4
39.0
20.8
9.5
36.2
Vol. 41, No. 3
OXIDATION OF POSSIBLE IRTERMEDIATE PRODUCTS
MIXED MOXOHYDROXYSTEARIC ACIDS. T o 282 grams (1.0 mole) of oleic acid in a 1-liter, 3-necked flask, equipped with thermometer, stirrer, and dropping funnel, there were added 120 grams (1.2 moles) of concentrated sulfuric acid over a 4-hour period. The temperature was maintained at 2 " to 10" C. by cooling the flask with a n ice bath. Stirring was conbinued 45 minutes longer after removing the ice bath, allowing the contents to reach room temperature. Finely crushed ice was added to the flask to dilute the acid, yielding a nearly white slurry. This was transferred t o a 5-liter flask fitted with a stirrer and a reflux condenser. Water was added to a total volume of 2500 ml. Concentrated hydrochloric acid (25 ml.) was then added, and the mixture was refluxed 15 hours. The aqueous layer Tws separated from the clear broxw organic layer while hot,, and the latter was washed once v i t h hot water. A solution of 100 grams of sodium hydroxide in 500 grams of ethylene glycol was mixed with the organic material and refluxed for 7 hours t o saponify polyesters. The saponification mixture was diluted with 1 liter of water and acidified wit,h dilute hydrochloric acid, liberating the acids as a brown oil. The latter was washed several times with hot water, arid finally with cold water. The cold water caused the organic matter to solidify. The solid was crystallized three times from hexane, giving 128 grams (43% yield) of a nearly white, soft powder that melted at 66" to 72" C. One gram of each of the acetate catalysts Kas dissolved in 250 grams of acetic acid and mixed with 100 grams of the. mixed hydroxystearic acids. Oxidation as carried out as usual for B hours at, 10.5' to 115' C. After the product had been filtered, stripped of acetic acid, and washed with 5yGhydrochloric acid, it was saponified by refluxing for 4 hours with 200 grams of 15% aqueous sodium hydroxide. The product was then worked up in the usual way. The results of distilling the est,ers are given in Table IX. Percentages are calculated on the basis of the ethyl esters of hydroxystearic acids. MIXED KETOSTEARIC ACIDS. IIydroxystearic acids were prepared from oleic acid as above, except that the crystallizations from hexane were o m i t t d . The crude product was oxidized essentially by the procedure used for the preparation of 1,3-dichloro-2-propanone(9), except that benzene was used as a diluent for the hydroxystearic acids. The keto acids boiled a t 174" t o 198' C. a t 0.5 mm. of mercury. One gram of each of the acetate catalysts was dissolved in 150 grams of acetic acid and mixed with 100 grams of the crude ketostearic acids. Oxidation was carried out a t 105" t'o 115" C. for 6 hours. The product, was worked up in the usual way. Results appear in Table 1X. Figures are based on 109.5 grams of ethyl ketostearates. 12-KETOSTEARIC ACID. Ricinoleic acid was hydrogenated catalytically to 12-hydroxystearic acid, which was oxidized t o 12-ketostearic acid, boiling point 204' to 207" C. a t 1 mm. of mercury, by the same method employed for the preparation of the mixed lietostearic acids. One gram of each of the acetate catalysts was dissolved in 200 grams of acetic acid and charged to the reactor during introduction of a stream of oxygen. One hundred grams of 12-ketostearic acid wcre melted and charged all at once t o the reactor. Reaction was continued for 3.2.5 hours a t 105" to 115" C. The reaction mixture was worked up in the usual way, eliminating the saponification step.
acid was obtained by ~ , ~ ~ - D I H Y D R O X Y ~ TACID. E A R IThis C oxidation of oleic acid v i t h dilute potassium permanganate. The method was an adaptation of several given in the litrrature (18, 19, 81).
TABLE Ix. OXIDATION OF POsSIR1,E INTERMEDIATE IN ACETICACID SOLUTION
One hundrcd grams (0.32 mole) of 9,lO-dihydroxystearic acid were dissolved in 300 grams of acetic acid containing 1.0 gram of each of the metal acetate catalysts. Oxidation was conducted at 103' t o 115' C , for 6 hours. The solution mas filtered hot, aiid the acetic acid dibtilled under reduced pressure. The residue was treated with 10Vo hvdrochloric acid to remove metal ions, and esterified in the usual way (ethanol) without prior saponification.
Material Oxidized 12-Ketostearic acid 9,lO-Dihydroxy~tearic acid Mixed ketostearic acids Mixed hydroxystearic acids
HighBoiling Scission ByProducts, products, Wt. 7, Wt. % 92.4 8.5 50.6 26.6 76.1
4.1
4.6 20.2
Tar,
wt.
%
1.6 3.3 2.5 1.0
PRODUCTS
Recovery, Wt. %
.4.9 .. ..,
46.4
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
March 1949
I40130120-
/-
110-
ETHYL PELARGONATE
100-
90-
p. (6
80-
7060,-
-ETHYL
CAPROATE
639
were then separately fractionated-the former through the helix-packed column and the latter through the Vigreux column. The products from the oxidation of ethyl * oleate under pressure were chosen for identification purposes. Appropriate cuts (as shown by boiling point and refractive index) were saponified with aqueous or alcoholic alkali. On acidification of the saponification mixtures the organic acids were liberated. I n the case of cuts containing both monobasic and dibasic acids, the latter were extracted with hot water. Liquid acids were converted into acyl chlorides with thionyl chloride and thence to amides. Solid monobasic acids were recrystallized from ethanol, and dibasic acids were recrystallized from water. Compounds shown to be present are listed with their derivatives in Table X. DISCUSSION
Franke and Jerchel (14) summarized three mechanisms for the initial oxidation of an unsaturated molecule: VOLUME OF DISTILLATE
IN
mi.
0-0
FRACTIONATION AND IDENTIFICATION OF SCISSION PRODUCTS
Combined ethyl esters of scission products from three different sources-( 1) ethyl oleate oxidized under pressure, (2) ethyl oleate oxidized in acetic acid solution, and (3) methyl esters of unsaturated fatty acids from talloil oxidized in acetic acid solution-were carefully fractionated under reduced pressure. The fractionations were started a t 100 mm. of mercury until the head temperature reached about 80" C. The pressure was then reduced to 10 mm. of mercury for the remainder of the operation. The first part of the fractionation 'was carried out in a column packed with glass helices. When the head temperature reached about 100" C. a t 10 mm. of mercury the fractionation was continued in a Vigreux column. The reflux ratio was maintained at 5 to 1.
TABLE X. DERIVATIVES OF ETHYL ESTERS Ester Caproate Heptylate Caprylate Pelargonate Caprate
Derivative Caproamide Heptylamide Caprylamide Pelargonamide Capramide Capric acid Laurate Lauric acid Myristate Myristic acid Palmitate Palmitic acid Suberate Suberic acid Azelate Azelaic acid Sebacate Sebacic acid Undecanedioate Undecanedioic acid Undecanediamide All melting points are corrected.
Melting Point, O C. Found" Literature 101-102 101 (80) 97-98 96 (20) 107-108 106 (N) 99-100 99 (80) 99-100 99 (20) 29-30 31 )'6 40-42
53-54 63 137-140 105-106 128-131 105-107 172-174
I%
525: 62.3 86) 140 117) 106 17) 133-133 5 (17) 109 (6) 173 (3)
The boiling points are plotted against the volume of distillate in Figures 1, 2, and 3. Only the first portion of each curve is shown in the figures, inasmuch as there were no well-defined plateaus a t higher temperatures where both mono- and diesters were distilling. Figure 2 is discontinuous a t about 118 ml. of distillate. This break occurred because in this case the lower boiling components were first stripped from the entire charge through a short, inefficient column. The distillate and residue
+
-CH=CH-
Results, calculated on ethyl 12-ketostearate, are listed in Table IX.
-CH=CH-
+
/
'/202
+
-CH=CH-CHz-CH=CH-
-CH-CH-
0 2
\
do\
--+
- H-CH--
(1)
(2)
+
0 2
OOH I
-CH=CH-~H-CH=CH-
(3)
Athert>onand Hilditch ( 8 ) treated methyl oleate with oxygen in daylight a t 20" and 120" C., respectively, then oxidized the products further with permanganate. From the lower temperature run the products were suberic, azelaic, pelargonic, and caprylic acids, but from the higher temperature run azelaic and pelargonic acids were the principal scission products. From these data they reasoned that the initial attack is on the active methylene groups as well as the double bond a t lower temperturea, but that a t higher temperatures it is chiefly a t the double bond. On the other hand Farmer (IS)believes that nearly sll oxidation is initiated at the active methylene groups in an unconjugated olefin to give hydroperoxide structures, and that decrease in iodine number is due to secondary reactions a t the double bond rather than to direct addition of oxygen. Peroxides then decompose, resulting in cleavage of some molecules and formation of "oxygeno" groups in others. If an oleate forms a 9,lO-epoxystearate, according to Equation 2, which then rearranges to a mixture of a 9-ketostearate and a 10-ketostearate, subsequent oxidation would be expected to occur as follows:
,/f CHa (CHdaCO(CHz)+%H 9-ketostearic acid
\ ,/f
CHs(CHs)rCO(CH,) 8COzH 10-ketostearic acid
\
.
+
caprylic acid sebacic acid
pelargonic acid azelaic acid pelargonic acid azelaic acid capric acid 4subcric acid
+
+
(4)
Vol. 41, No. 3
INDUSTRIAL AND ENGINEERING CHEMISTRY
640
Furthermore, if oxidation also is initiated a t the active methylene groups according to Equation 3, the following sequence of reactions appears plausible:
OOH
I -CHCH=CHCH~-
7 -CH&X=CHCHZ11 10 9 8
OOH
0 ----f
I
bCH=CHC-I/
OOH
I
-CHzCH=CHCH-
-+
caprylic acid and azelaic acid
-+
caprylic acid and suberic acid
0
--+ -
+ -CHCH=CHCH-
I
I/
-CCH=CHCHz-
0
OOH
I
Resolution of the complicated mixture of by-products boiling higher than the raw material was not attempted during this work. However, Table VI11 shows that these by-products are at least
0
+ -CHZCH=CHC-
Thus, the initial scission products of oleic acid would be caprylic, pelargonic, suberic, azelaic, capric, and sebacic acids, the last two in relatively small amounts. The scission products previously reported ( 2 , 7, 8, 11, dS, 26) from autoxidation of long-chain unsaturated fatty' acids or their esters include formic, acetic, butyric, caproic, caprylic, pelargonic, oxalic, suberic, azelaic, and sebacic acids, as well as carbon dioxide and heptaldehyde. Schaeffer, Roe, Dixon, and Ault ($4) demonstrated that a number of isomeric hydroxystearic acids are formed during sulfation and hydrolysis of oleic acid, and attributed the phenomenon to a shifting of the hydroxyl group. Subsequently ($7) it was reported that a variety of scission products of low molecular weight were obtained by permanganate oxidation of the high boiling material from catalytic air oxidation of methyl oleate. Their formation was believed t o be due to a shifting of the double bond during the initial oxidation. In like manner it is possible that such shifting of hydroxyl groups could account for the diversity of oxidation products that have been encountered. However, since the authors found very little undecanedioic acid and no higher dibasic acids, it is likely that the preponderance of the low boiling acids result from degradation of those predicted by Equations 4 and 5. The relative amounts of myristic and lauric acids found suggest that they were initially present in the raw material or were formed by degradation of palmitic acid (as), a common impurity of commercial oleic acid.
ll
+ pelargonic acid and suberic acid
partially convertible to useful scission products of lower molecular weight Further oxidation of recovered high boiling material was not attempted. The fractionation curves clearly demonstrate that the ethyl e>ters of caproic, heptylic, caprylic, and pelargonic acids can be separated without difficulty by the technique chosen. Higher boiling components cannot, and it appears that for practical purposes selective extraction of dibasic acids from monobasic acids would be necessary. Table X I contains estimated values for the relative amounts of components of the scission product cuts. The data are contingent upon the validity of reading the fractionation curves, and hence are of limited reliability. Furthermore, the assumption was made that the scission products consisted of no compounds other than the mono- and dibasic straight-chain aliphatic acids. Other possibilities include aldehydes, ketones, alcohols, unsaturated acids, and polyfunctional compounds, but it is not likely that these occurred in significant amounts. In comparing the two techniques of oxidation used, several striking differences are noted (Tables I11 and IV). Oxidation obviously proceeds much more rapidly in acetic acid solution, and the proportion of scission products to by-products and tar formed is appreciably greater. On the other hand the total material recovered from the process is smaller. This loss may be due to carbon dioxide formation or to formation of more water-soluble products which are lost in washing operations. I
40
'
FIG -3 lOOmm
IOmmVOLUME OF DISTILLATE IN
ml.
(6)
March 1949
64 1
INDUSTRIAL AND ENGINEERING CHEMISTRY
TABLE XI.
COMPOUNDS OBTAINED BY FRACTIONATION OF ScIssIoN PRODUCTS F r o m E t h y l Oleate Oxidized in Bomb Vol., ml. Wt., g. W t . %
Compound Ethyl caproate Ethyl heptylate Ethvl csurvlate
;e
26 33 49 63 12 7 74 91 30 26 20 93
23 29 43 55 10 6
73 89 26 25 19
80
4 4 7
8
2 1 11 13 4 4 3 12
From Ethyl Oleate Oxidized in Acetic Acid Vol., ml. W t , , 6. Wt. 7 0
21
28
43 48
;
64 62
18 13 A
From M E U F A Oxidized in Acetic Acid Val., ml. Wt., g. Wt. % 17 15 8
5 6 9 11 1 2 16
19
25
38 43 4 6 63 61 16 13 6 40
11 17 17 3 6 27 24
15
4 3 1 10
LITERATURE CITED
8
8 17
s
5 15
5
8
8
1 3 14 12 4 4 8
8
H. S., IND.ENG.CHEM.,
(18)
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Vulcanization of Neoprene with Antimony Trisulfide J
M. F. TORRENCE Rubber Laboratory, E. I . du Pont de Nemours & Company, Inc., Wilmington, Del. Antimony trisulfide increases the modulus, hardness, and resilience, and decreases the permanent set and heat build-up of neoprene compounds. The magnitude of the effect is directly proportional to the concentration of antimony trisulfide and is obtained with less loss of processing safety than when Permalux is used. The effects of antimony trisulfide are less noticeable on the hardness and stress at low elongations than they are on the stress at elongations near hrealr. Antimony trisulfide is effective in the absence of other activating materials such as magnesium oxide and zinc oxide. Certain other sulfides display the same activating effects as antimony trisulfide.
E O P R E N E is generally cured with a combination of magnesium oxide and zinc oxide, a s proposed by Bridgwater and Krismann ( 1 ) in 1932. Many of the properties attributed t o proper vulcanization, such as maximum tensile, near-maximum modulus, and near-maximum hardness, can be obtained with these oxides alone in a normal curing time of 30 t o 40 minutes at 287” F. However, t o obtain low permanent set and high resilience, other activating materials are frequently added. Torrence and Fraser ( 4 )showed t h a t various amines, phenols, and quinones are effective. T h e most commonly used material is the di-otolylguanidine salt of dicatechol borate ( 2 ) , sold under the trade name Permalux. Antimony trisulfide is in many respects a more effective activator than Permalux. I t s influence on the properties of the
vulcanizate is different from t h a t of Permalux and from t h a t which would be expected from merely increasing the rate of cure. Antimony trisulfide affects the modulus at low elongatioiie much less than a t high elongations, and the hardness of stacks coritaining i t is lower than would be expected for stocks with so low a permanent set and so high a resilience. Varying amounts of antimony trisulfide and Permalux were tested by adding them t o a stock having the following conventional composition: ,
Neoprene GRM-10 Sodium acetate Stearic acid Extra light calcined magnesia EPC carbon black Light process oil Zinc oxide
100.0 parts 1 .o
1 .o
4.0 31 . O 3.0 5.0
One batch of the base stock was mixed on a 30-inch mill. Antimony trisulfide, in the ratios of 0.125, 0.26, and 0.5 part, and Permalux, in the ratios of 0.5 and 1.0 part, on 100 parts by weight of neoprene were added on a 12-inch mill t o portions of this batch. T h e stocks were then cured and tested according t o standard A.S.T.M. procedure. T h e heat build-up was obtained with a Goodrich flexometer ( 3 ) on pellets 0.75 inch in inch, the diameter and 1 inch in height; the stroke was load 150 pounds per square inch, and the speed 1800 cycles per minute. The compression set was run according t o A.S.T.M. Method A, D 395-40T-i.e., 400-pound load for 22 hours at 70 O C. (158” F.). T h e resilience was determined on the Yerzley oscillograph in accordance with A.S.T.M. Specification D 945-48T.
