INDUSTRIAL A N D EA'CILVEERINGCHEMISTRY
62
Vol. 19, No. 1
The Boiling of Linseed Oil'iz By J . S. Long, C. A. Knauss, and J. G. Smull W. H. CHASDLCR CHEMICAL LABORATORY, L U I I I G IUNIVCRSITY, ~ BETHLEHEM, PA.
STUDY of the rate of molecular weight increase during the "boiling" of linseed and China noocl oils gave results which proved helpful in coiitrollirip the process and in throwing light on the mechanism of t,lto rcxtions inv01ved.~ Linseed oil, cnntaining glycerides of linoicnic acid as well as those of linolic acid, offers opportunity for more typcs of reactions than China wood oil. Past widciirc indicated a t least two mnjor types of reactions: (1) 1h::ri:tions leading to a decrease in the number of ethenoid linkngc:s, with little correspoiidinp molecular weight change; : m l ( 2 ) condensations, involving eIiminstion of water a d ot!icr l~roductsand great changes in nioleculnr moiglit,. Fahrion and others4 obscrvcd t)hc r:ipitl dccrcase in the hexabromide number when linseed oil is 1icite:l : l i d aoiicluded that the AIS double bond, one distinguishing fcaturc of linolenic compounds, is the most reactive onc.
A
Experimental
The previous work in this laboratory on this subject has been extended to obtain further evidence on the nature of the types of reactions involved, based on the relation of hexabromide and iodine numbers to the molecular weight changes, and to determine the method of preparation and the properties of linolenic monoglyceride. Materials
Raw linseed oil derived from northwestern seed was used.
It had the following constants when used: specific gravity, 15.5"/15.5" C., 0.9330; iodine number, 187; acid value, 2.34; hexabromide number, 48.1. Thiophene-free benzene, dried with CaClZ, was distilled, and the portion which came over between 80" and 81" C. under a barometric pressure of 755 mm. was collected for use. The freezing point constant of this was determined by means of purified CC14 and CsHsN02. The average value obtained (5065) is identical with that obtained when the,benzene was treated with HzS04 and subsequently frozen as suggested by Richards.5 The preparation of linolenic monoglyceride is given in detail later in this paper. Apparatus and Method
To obtain some measure of the condensation reactions, the gases evolved were led through a train which in run 58 was made up as follows: 500 grams of linseed oil, which had been dried for 3 hours at 100-110" C. in COz,was heated in a 3-liter Pyrex flask. Nitrogen was passed through HzS04 (sp. gr. 1.84) and then over a hot coil of tightly-rolled copper gauze 1 meter long, previously reduced by passing methanol vapors overit while hot, the aldehyde and excess methanol being swept out with nitrogen. This nitrogen was bubbled through the oil by a tube extending nearly to the bottom of the flask. The gases evolved were led through (1) a 50-cc. distilling 1 Received July 30, 1926. Presented before the Section of Paint and Varnish Chemistry a t the 72nd Meeting of the American Chemical Society, Philadelphia, Pa., September 5 to 11, 1926. 2 This work was carried out under the Callender-Carnell Fellowship a t Lehigh University, acknowledgment of which is gratefully made. 8 Long and Srnull, THISJOURNAL, 17, 138,950 (1925). 4 Griin, "Analyse der Fette in Wachse," p. 374. 5 J . A m . Chem. SOC., 47, 2285 (1925).
flask filled with glass beads, to catch mechanically entrained oil, ( 2 ) a l--tul)e and stopcocks, (3) two pairs of weighed l,uhes tilled with CaC12, which had been previously treated with dry IICI t u rctmove CaO and then with Nzto sweep out IICI, (4)gas wvnsiiing bottles containing Ca(OH)z and NaHSO:,. l h e oil w i s lieated to 175-190" C. to remove moisture until thc C'aCI, tubes showed no appreciable gain in weight in two siioc:cssii.e SO-minute periods. The temperature was tlicn r:iiscd t o 293" C. and maintained a t this point *2" C. for the duration of the run. In run 57, partly reported before and reproduced now in full, the oil was heated as in run 58 and sent through the same train to a vacuum pump which maintained a vacuum of 14 to 25 mm. during the run. I n runs 59, 60, and 61 the latter part of the train, starting with the CaClz tubes, was replaced by two 500-cc. Erlenmeyer flasks containing 300 cc. of a solution made by dissolving 120 grams CaClz in 700 CC. HzO and adding 300 cc. 15 N ",OH. This solution caught the HzS, Hac, H2Te, and other volatile sulfides, selenides, and tellurides. The gases evolved from the oil during heating were allowed to pass into one pair of flasks until a sample was taken and then diverted, by means of the Y-tube and cocks, to other flasks containing fresh solution. Hexabromide numbers were determined by the method proposed by Steele and Washburn. The rate of molecular weight change was determined by the freezing point method using benzene. The rate of molecular weight change as measured in five other solvents has been shown to be comparable to that in benzene.' Stearic acid has been recommended by Biltz8 and by Seaton and Sawyer.9 Stearic acid was therefore also tried to determine the molecular weight of the linolenic monoglyceride. When heated with stearic acid to dissolve it, the linolenic nionoglyceride changed to a solid substance insoluble in steario acid. Therefore stearic acid could not be used. Experimental Results
The results obtained in these experiments are given in Tables I, 11, and IV. The rapid decrease in the hexabromide number, with the relatively small corresponding decrease in the iodine number, indicates a change in the beginning of the boiling process which results in rather complete saturation of the A, ethenoid linkages. The molecular weight increases only slightly in this period. This suggests, as a working hypothesis, a t least, that the saturation of these linkages is due to molecular rearrangement or to some process like the first stage in the scheme proposed by Salway. The hexabromide number, however, decreases rapidly, practically to zero. This indicates that the AI5 = bonds are saturated in all the molecules of linolenic compounds. It would seem, therefore, that Salway's scheme would require modification to the extent that the molecule of acid be added in some way, such as by the formation of a tetramethylene ring. There are other possible ways of accounting for the observed facts, however. These working hypotheses are used 6
THISJOURNAL, 12, 52 (1920).
7
Long and Wentz, THISJOURNAL, 18, 1245 (1926).
9
THISJOURNAL, 8, 490 (1916).
* Z . physik. Chem., 19, 385 (1896).
INDUSTRIAL AND ENGIAVEERING CHEMISTRY
January, 1927
simply to suggest an experimental study of the boiling process from various angles. The comparison of hexabromide numbers with molecular weights throws light on the main reaction in the early stages of bodying linseed oil by heat. The rapid saturation of the A15 ethenoid linkages of the linolenic glyceride would not have been suspected from the relatively small rate of decrease of the iodine number. The hexabromide number alone would have been of little use as a guide as to which of a number of possibilities explained the type of action involved. The value of the hexabromide number, especially in conjunction with other data, is indicated. Study of the simultaneous rates of change of such constants as hexabromide number, molecular weight, and iodine number is especially illuminating. Table I IODINE SAM- AFTER PRES- WATER MOL. PLE HEATING SURE EVOLVED WT. Hours M m . H g Grams 1
1
=
0
Il/z za/4
41/c 53/4
71/4 8
25 25 22 22 22 14 22 17 18
Run 753 753 753 753 753 753
...
IIExA- No' N&y""g";:' A~~~DRE6fox OF
OIL
Run 57 in uacuum (293' C.) 0.1387 770 160.7 23.64 0.4653 860 5.00 0.3724 988 lk3:l 1.31 0.2435 1161 0.3895 1255 13i:1 1.3 0.3146 1500 0.1130 1609 1iO:O 1.3 0.2109 1678 1752 lZb:5 0.0780 ... 2.1874 98 in stream of nilrogen (693' C.) 0.061 952 2.1 0.220 1144 1.5 0.276 1160 0 0.524 1245 0 0 0.243 1551 0.197 1600 0 0 0.179 1636 1.639
-
... .
I
.
..
-
... ... ... ..... . ... ... 13613
165.1 157.0 144.1 140: 9
136:7
~
Time required to heat up t o 293' C.
I n Run 57 the weight of HzO is 2.1874 grams for a molecular weight change of 1752 - 770, or 982. The molecular weight change in run 58 is 1636 - 952, or 684. If the over-all weight of HzO evolved is proportional to the molecular weight change, then the weight of H20 evolved in run 57 for a 684 molecular weight change of 684 is 9~ X 2.1874 grams or 1.523 grams. This is in fair agreement with the weight of HzO obtained (1.639 grams). The weights of HzOevolved for individual 1-hour periods, however, are not so simply related to the molecular weight change. More than one type of reaction occurs. I n run 57 the gases evolved from the oil passed through NaHSOs solution. Five cubic centimeter portions of this solution were tested with phenylhydrazine in acetic acid solution a t regular intervals. Precipitates of phenylhydrazone of approximately the same size were obtained. This indicated a steady evolution of acrolein a t this temperature (293' C.). This of course may come from decomposition of part of the oil. The fact that more HzO was liberated in run 57 than in run 58 suggests that the escape of HzO is facilitated by heating in vacuum rather than under a pressure of even one atmosphere. Condensation reactions are favored. The weight of HzO liberated is therefore greater. It might be expected that the decrease in the hexabromide number would be reflected in an equivalent decrease in iodine number. This, however, is not borne out by the results in four series of experiments. I n run 57 the decrease in hexabromide number from the first to the third sample is 22.33. The molecular weight of linolenic acid is 278 and that of the 278 hexabromide is 758. 0.2233 gram hexabromide = -=x 7s8 0.2233 = 0.0813 gram linolenic acid. Theoretically, 1 gram of
63
linolenic acid will absorb 278 126'937 or 2.74 grams iodine. The decrease in iodine absorption from sample 1 to sample 3 is 0.076 gram iodine per gram of oil. This corresponds to -x 1.0 gram, or 0.0277 gram linolenic acid.
to;:
The iodine number decrease therefore indicates only 0.34 of the decrease indicated by the decrease in hexabromide number. Action of Sulfur, Selenium, and Tellurium The rate of molecular weight increase when 3 per cent of sulfur is added to the oil had been determined in an effort to see whether sulfur, an element similar to oxygen, would be absorbed by the oil and whether there was any promise that the reactions could be studied more conveniently by means of sulfur compounds than by the usual oxygen compound^.^ The action of sulfur on linseed oil has been studied from another angle by Whitby and Chataway.lo After determining the HZO evolved by condensation reactions, it seemed logical to heat the oil with sulfur, selenium, and tellurium, measure the S, Se, and Te evolved as volatile compounds, and compare the quantities with the corresponding molecular weight changes. It was found that S, Se, and Te dissolved in the oil a t 293" C. The gases which were evolved came over in the slow stream of nitrogen and formed precipitates in the cadmium ammonia chloride solution which were yellow in run 59 (S), orange red in run 60 (Se), and yellow in run 61 (Te). These gases had very irritating odors. The odor in the S run was quite unlike that of HzS and indicated that an organic sulfide was being steadily evolved. A yellow precipitate was first observed in the cadmium chloride solution when the temperature of the oil had reached 70" C. When the oil had reached 290" C. in the Se run, a sudden exothermic reaction occurred and, despite the fact that the flame had been removed, the temperature rose to 320" C. within 2 minutes and remained there for 3 or 4 minutes. The S in the precipitates was determined by iodimetric titration. The Se and T e were determined gravimetrically. The results are given in Table 11. Tahlr 11
SAMPLE
AFTERHEATING MOL. Hours WT.
S. SE, OR T E I N CD PPT. Gram
Run 5 9 (7.5 gram S i n 250 grams oil, 293' C.) 1
a
921 1061 o .'21'95 1081 0.0645 1131 5 1167 0.0365 1198 0.0049 6 2'12 Run 60 (18.5 grams Se i n 250 grams oil. 293O C . )b a 1 792 880 2 112 3 12/a 673 0.3490 599 0.1180 4 21/2 5 3 601 0.0879 Run 61 (10 grams Te in 250 grams oil, 293O C . ) 1 738 1/ 9R4 2 .__ 3 1 1050 0 .'0228 4 2 1167 0.0108 3 5 1140 0.0064
2 3 4
112
1 l'/a 2
...
...
(I
b
Time required to heat up to 293" C. Some Se sublimed into the delivery tube during the heating.
I n runs 57 and 58 with the oxygen compounds of the natural oil, and also in runs 59, 60, and 61, the weight of H2S,H2Se, and HzTe evolved in 11/4-hour periods decreased toward the end of the run. The percentage of S, Se, or Te evolved per hour diminished greatly towards the end of 3 hours, despite the fact that in the Se and Te runs excess (undissolved) Se and T e were present. The rate of molecular weight change indicates that re10
J . SOC.Chem. Ind., 46, 115 (1926).
INDUSTRIAL AND ENGINEERING CHEMISTRY
64
actions leading to the coupling of two or more molecules, either by condensation with elimination of gaseous products or by the formation of a tetramethylene ring between the A15 ethenoid linkages of 2 linolenic radicals, have been greatly decreased. In fact, in the Se run, the elimination of volatile organic Se compounds more than balanced any gain in molecular weight and led to a steady decrease in molecular weight. These results, which bore out our expectations for the substitution of S, Se, and Te for 0, offer additional evidence that one type of reaction a t temperatures of 293" C. or higher is the condensation of several molecules to form bodies of a t least double the original molecular weight. The steady evolution of HzOobserved in many experiments (runs 57 and 58), coincident with rapid molecular weight increase, suggested that at least part of the condensations were due to OH groups present in the oil as used or formed during the earlier part of the heating process. Mono- or diglycerides could be formed by the action of enzymes on the oil during storage or by hydrolysis during boiling. Change in linolenic triglyceride to indicate the formation of the diglyceride and also conform to the rapid decrease in hexabromide number is represented as follows: C H I O C O ( C H ~ ~ C=HCHCHiCH = CHCHzCH
I
-
CHCHzCHa
-
CHOCO(CHn) C H = CHCHzCH = CHCHzCH = CHCHzCHa
+ HOH -j
C!HZOCO(CHI)~CH CHCHnCH = C H C H C H = CHCHnCHa CHnOCO(CHd 7CH = CHCHzCH = CHCHnCHzCHCHzCHa -L
CH~CH~CH~HCH =~CC HH CH~CH =CH(CH,),OC~
I
I
CHOCO(CHr)rCH = CHCHtCH = CHCH:CH~HCHZCHI
1
CHiOH
To subject this circumstantial evidence to more direct test it seemed logical to prepare the mono- or diglyceride of linolenic acid and study the rate of molecular change on heating. If condensations occur between mono- or diglycerides or other similar bodies present in the oil during heating, the pure or nearly pure mono- or diglycerides should show this action t o a pronounced degree. Accordingly, an attempt was made to prepare these substances. Glycerides of saturated acids had been previously synthesized and a few glycerides of unsaturated acids have beenmade. Thus, Krafftll reports the formation of monoolein from a-monochlorhydrin and potassium oleate. Berthelot1* claims to have obtained a diglyceride of oleic acid by heating a-monoolein with 5 parts of oleic acid a t 250" C. Schoenfeldi*has prepared a-a-dilinolin from a-a-dichlorhydrin and potassium linolate. No reference was found for the preparation of a glyceride of linolenic acid, and the methods used by Krafft and by Schoenfeld for the preparation of less unsaturated glycerides were unsuccessful in our hands for the preparation of a glyceride of linolenic acid. We were, however, successful in preparing a glyceride, which seems to be the monoglyceride of one of the linolenic acids, by heating a mixture of linolenic hexabromide with zinc dust and glycerol. The method in detail is as follows: Saponify linseed oil by alcoholic KOH. Distil off the ethanol and liberate the free fatty acids by means of HC1. Wash these with warm water until free from mineral acid and then dry over NaZSOd. Dissolve in one to two times their volume of ethyl ether containing 10 per cent of glacial acetic acid. Immerse the flask in a freezing mixture and add a solution of bromine in its own volume of chloroform, at the rate of approximately 30 drops per minute, mechanically stirriig the solution during the operation.
From 40 to 46 cc. of bromine solution (20-23 cc.Br) are required for each 100 grams of mixed fatty acids from linseed oil. Ber., 84, 4343 (1903). Ann. chim. (3)41, 252 (1854). 18 Inaugural Dissertation, Zurich, 1912.
11 12
Vol. 19, No. I
The temperature should not rise above -5' C. Light should be excluded as far as possible. All materials should be dry, Excess Br is removed by amylene, and the white crystalline hexabromide is removed from the ethereal solution by centrifuging. This hexabromide has a melting point of 179" C. As a check, the ethyl ester of linolenic acid was prepared by treating the hexabromide with freshly reduced zinc dust in absolute ethanol saturated with dry HC1 gas. The zinc dust is filtered off and the solution washed with water to remove ethanol and zinc bromide. The ethyl ester is distilled off. It boils a t 137-138" C. under a pressure of 1mm. The methyl ester made by the same process boils at 207" C. under a pressure of 15 mm. All operations are conducted in carbon dioxide or nitrogen. Two hundred grams of the hexabromide, 200 grams of anhydrous glycerol saturated with dry HC1 gas, and 25 grams of freshly reduced zinc were heated together, with mechanical stirring (400 r. p. m.), for 15-30 hours in an atmosphere of nitrogen a t 125-135" C. A decided excess of glycerol was used, not only with the thought of obtaining the monoglyceride rather than the di- or tri-compound, but also in order to furnish a fluid medium and thus get more rapid action than would be possible if the mass were pasty. I n order to extract the glyceride this mixture was refluxed for 1 hour with twice its volume of benzene. The benzene solution obtained was washed thoroughly with water to remove excess glycerol and most of the zinc bromide. It was distilled off and the residue was dissolved in petroleum ether. The petroleum-ether solution was washed with water and dried, and the petroleum ether was distilled off in an atmosphere of Cot. The product. was a clear reddish oil, which decomposed a t 175" C. under a pressure of 2 mm. of mercury. Further purification of i t by distillation was therefore impracticable. To demonstrate qualitatively that this substance is a glyceride a few grams of it were heated with potassium bisulfate. A strong odor of acrolein was detected on repeated tests with various samples as prepared. The ultimate analysis of the glyceride thus prepared, with the theoretical for linolenic monoglyceride, is given in Table 111. Table 111 SYNTHESIZED GLYCERIDE No. 1 No. 2 Per cent Per cent Carbon Hydrogen Oxygen (by difference)
73.97 11.41 14.62
73.87 11.37 14.76
THEORETICAL LINOLENIC
MONOGLYCERIDE Per cent
71.53 10.28 18.19
The iodine number of this synthesized glyceride was found to be 176. The theoretical for linolenic acid is 273.7, but the iodine absorption obtained by Erdman and Bedford is 227. On this basis, the monoglyceride (theoretical mol. wt. 352) should have an iodine number of 278.24 X 227, or 179. This agrees closely with the value obtained (176). The molecular weight of the pure linolenic acid, determined by the freezing point method in benzene, is 452. The molecular weight of the glyceride derived from it is 601. The substance prepared was heated, without driers, in the air (runs 62 and 64) and in nitrogen (run 63). The substance behaved like a glyceride in all cases. It thickened steadily and finally changed to a solid gel-like mass just as does linseed oil under the same conditions. The thickened oils dried and formed smooth dry films on amalgamated plates of tinned iron. I n run 62, 100 grams of linolenic glyceride was heated in an open porcelain casserole with mechanical stirring. The glyceride was brought up to 293' C. in 15 minutes and maintained at 293 * 2' C. The mass was solid in 27 minutes. '
3m
INDUSTRIAL AATD ENGINEERING CHEMISTRY
January, 1927
I n run 63, 125 grams of glyceride were heated in a stream of pure nitrogen in a 500-cc. Pyrex flask. The glyceride was brought up to 293' C. in 15 minutes and held at this temperature, *2O, for the duration of the run. T a b l e IV SAMPLE
Glyceride 1 2 3
AFTERHEATING MOL. Minutes WT.
Run 62
...
771 999 2687 Solid Run 63
(1
15 27 0
5
10 15 7 8 9 10 11 .-
Glyceride 1 2 3
4
34.2
... ... ...
176
34 17 15 2
162.3 162 162 160.3 158.9 151.6
1 ... ... ... ...
20
a
HEXABROMIDEIODINENo. No. OF OIL
31 40 50 60 70 95
Run 64
...
601 1095 1760 2618 Solid
a
10 20 23
... ... ...
145:2
... ...
132:o 126.9
... ... b
... ...
b
b b
b
b
_______ (I
b
Time required to heat up to 293" C. Duplication of run 62 with slightly purer linolenic glyceride.
65
The rate of molecular weight increase for runs 62, 63, and 64 is given in Table IV which also shows the rate of decrease of the hexabromide and iodine numbers in run 63. Escape of HzO and other products of condensation is hindered by the slow stream of nitrogen in a closed flask and is facilitated when the heating is carried out in an open dish. Condensation reactions, with consequent large increase in molecular weight, are therefore favored by heating in the open dish. Conclusions
A study of the relative changes in hexabromide number, iodine number, and molecular weight indicates that in the first stages of heating linseed oil intramolecular change is the main reaction. When linseed oil was heated with sulfur, selenium, and tellurium in nitrogen, little or no condensation occurred. Organic sulfides, selenides, and tellurides were evolved and in the selenium run the molecular weight decreased. A linolenic glyceride was synthesized and studied. When heated it thickened and changed to a solid jelly. The rate of molecular weight increase was the most rapid observed so far for linseed oil and any of its derivatives. The thick products obtained by heating linolenic glyceride dry and form films similar to those derived from linseed oil.
Effect of Velocity on Corrosion of Steel under Water' By R. P. Russell, E. L. Chappell, and A. White DEPARTMENT OF CERhfICAL ENDINBRRING, MASSACHUSRTTS INSTITUTE
OF
TECHNOLOGY, CAMBRIDGE,
MASS.
The present conception of the corrosion process' under water is that at the anode the reaction Fe 2 @ = Fe++ takes place. Simultaneously, a t the cathode, there is a reaction, which, under ordinary conditions, consumes dissolved oxygen. The anode and the cathode may be quite widely separated or may be very close together.
surface. The data in the literature on this subject are, however, decidedly contradictory. Heyn and Bauer3 report that if iron is corroded by water, the rate increases rapidly a t first with the rate of flow. They find that a maximum is reached, however, a t about 0.004 foot per second, and that subsequent increases in water velocity cause a decrease in corrosion. These tests were carried out by passing water over iron plates suspended in beakers. The velocities studied were all low
1 Received August 27. 1926. Presented before the Division of Industrial and Engineering Chemistry at the 72nd Meeting of the American Chemical Society, Philadelphia. Pa., September 5 to 11, 1926.
* Except under exceptional conditions, such as high acidity, high temperatures, etc. 8 Mitt. kgl. Maferiulprilfungsamt, 28, 62 (1910).
Theoretical Considerations and Previous Work
+
