INDUSTRIAL A S D ENGINEERING CHEMISTRY
SeDtember, 1925
905
Rate of Molecular Weight Increase in the Boiling of Linseed Oil',* By J. S. Long and Graham Wentz IJiHIGH
UNIVERSITY, BETHLEHEM, PA .
Materials OLECCLAR weight The rate of molecular weight increase is a simple means of studying the effect of various factors on the The raw linseed oil was dedeterminations of oils rived from northwest seed and and varnishes by the boiling of drying oils. had the following constants: freezing point method have The rate of molecular weight increase offers a fundamental chemical criterion for testing prevailing theSpecific gravjty been made by several investia t 1 5 . 5 ' / 1 ~ . 5C. ~ 0.9335 189 gator% and numerous Objecories of the mechanism of the chemical reactions that gdi;;ayy+:s 2.05 % tions to these determinations during the boiling. have been pointed ReThe experimental evidence indicates in a prelimiThiophene-free benzene was nary way that the reactions that take place during the dried over calcium chloride and cently other solvents have distilled. That portion which been suggested as preferable boiling of linseed oil include condensations. came over between 80.0" and to benzene, since it is gen80.5' C. under a barometric erally known that association pressure of 755 mm. was used. The freezing point constant employed was determined for this benof fatty acids takes place in b e n ~ e n e . ~ In previous work on this subject done in this laboratory5 Zene by means Of pure anthracene. The value obtained is K = weight Of 5268. it TVas found that the apparent average The mixed free f a t t y acids used in several of the were dethe oil, as determined by the freezing point method in benzene, rived from the same oil by the usual method6 involving saponifiincreased in a regular manner from 722 to 3053. The results cation with alcoholic potash. Oxidation was prevented by obtained indicated that despite association, the rate a t which maintaining an atmosphere of nitrogen in the flask. The perpurity of the acids was determined by titration with in- centage the apparent molecular weight changed w o u ~ doffer 0.1 N potassium hydroxide as 96 t o 99 per cent calculated as oleic sight into the factors affecting the boiling of linseed and China acid. The low result seems to indicate partial saturation of the wood oils and afford a means of testing the various t'heories on acids during preparation despite the precaution mentioned.
M
M o l e c u l a r Weight I n c r e a s e in t h e Boiling of L i n s e e d Oil
--
Run 21 22 23 24 23 26 2s 30 :i 1 92 34 85 :3 6
T,emp. U p t o C. heat 149 763 149 762 149 780 293 774 293 777 293 293 293
NATUREOF RUN 200 grams linseed oil in open 13-cm. casserole 200 grams linseed oil 0 . 4 gram PbO in open 13-cm. casserole 2aO grams linseed oil in pure oxygen 200 grams linseed oil in 13-cm. casserole covered with glass plate Same, open t o air 200 grams linseed oil in 500-cc. Pyrex flask in stream of pure dry h-2 Same as ~~~~. R.u n _. 26 ~. _ 200 grams blown linseed oil in covered 13-cm. casserole 200 grams linseed oil in 500-cc. Pyrex flask, in stream of pure d r y S z carrying acrolein (25 cc. in 2.5 hours) 200 grams linseed oil heated in stream of N 2 200 grams linseed oil heated in stream of S z carrying acrolein (15 cc. in 2.5 hrs.) 225 Prams linseed oil and 22.5 Prams f a t t v acids from linseed oil in oDen 13-cm. c&serole 400 grams linseed oil and 40 grams fatty acids from linseed oil in open 13-cm.
+
-
C 1SS T -. Olr ._. .P -.
37 4
R-2 38 39 40 41 42
43 4b
250 grams linseed oil and 25 grams f a t t y acids from linseed oil heated in stream of N? in 500-cc. Pyrex flask 300 grams linseed oil 0.6 gram PbO in open 13-cm. casserole 300 grams linseed oil 0.6 gram hXn2BaOl in same open casserole 300 grams linseed oil 30 grams free f a t t y acids from linseed oil heated in S > in flask 125 grams of free f a t t y acids from linseed oil in 13-cm. casserole open t o air 200 grams linseed oil in N? in 500-cc. Pyrex flask 200 grams linseed oil in N*in 500-cc. Pyrex flask 200 grams linseed oil 20 grams of fatty acids from linseed oil in N? in 500-cc. flask 200 grams free f a t t y acids from linseed oil in 13-cm. casserole open t o ai1 200 grams oleic acid, in open 13-cm. casserole
+ ++
+
the mechanism of bhe reactions that occur when these oils are heated. This indication has had some confirmation, and although the researches are not complete, a few of the results are presented herein. 1 Presented under the title "Factors Affecting the Boiling of Linseed and China Wood Oils" before t h e Section of Paint and Varnish Chemistry a t the 69th Meeting of the American Chemical Society, Baltimore, Lid., April ti t o 10, 192:. 2 This work was carried out under the New Jersey Zinc Company Fellowship, acknowledgment of which is gratefully made, Seaton a n d Sawyer, TFIISJ o w n ~ a L ,8 , 490 (1916); Friend, J . Chem. SOL.( L o n d o n ) , 111, 162 (1917); Morrell, J . Oil Colouv Chem. A s s o r . , 7, 146 (1924). 4 Biltz, Z. p h y s i k . Chem., 19, 385 (1896); Rast, Z dricl. Oel F e f / I n d , , 44, 375 (1924). Long a n d Smull. Tms J O U R N A L , 17, 138 (1925).
293 293
84 1 908
MOLECULAR WEIGHT
After After After 0.5 1.0 1.5 hour hour hours 767 780 780 840 951 1090 819 969 1040
914 944
1278
2642
989 961
1164
After
2.0 hours
After 2.5 hours
After 3.0 hours
757
802 .~ ~
785
1291 1287
1450 1651
1374
1276 1473
1248 1630
1343
1412
1582
1947 1334 1362
293
836
940
I005
1103
293
890
1025
1786
2606
Mass solidified t o gel a t 1 7 5 hours
293
873
1017
1618
261 7
Mass solidified t o gel a t 1.75 hours
293 293 293
846 889 810
899 903 949
1023 1200 1220
1698 1888
232 232 232 205
750 789 829 803
769 94 1 852 837
79? 1425 Si6 851
819 2262 1210
205 205 205
758 1144 487
764 1255 499
819 1355 318
833 1506 524
1266
1496
842
1643
868
89 1
1268 832
826
1409 836
848 1718 03A
827 181i
813 197;
Method Essentially the same apparatus and method were used as has been described p r e ~ i o u s l y . ~Two hundred grams of oil were heated and mechanically stirred a t the rate of 200 r. p. m. The temperature was maintained constant t o * 2 O C. I n some cases, as indicated in the tabulated data, the oil was heated in 500-cc. Pyrex flasks provided with three openings. In these cases stirring was done by bubbling pure dry nitrogen through the oil a t the rate of 0.5 liter per minute. The nitrogen inlet tube projected approximately 2.5 cm. below the surface of the oil. Samples were withdrawn a t regular intervals-up to heat, after 0.5 hour, 1, 1.6, 2, 2.5, and 3 hours-and the molecular weights of these were determined by the freezing point method in benzene. Accurately weighed samples of 1 gram 1 5 per cent Lewkowitsch. "Chemical 6th ed., Vol. I, p. 111.
Technology of Oils, F a t s . and Waxes,"
906
I N D CSTRIAL AND ENGINEERING CHEMISTRY
Vol. 17, No. 9
the free fatty acids from linseed oil. Thus, in Run 28 the condensed vapors had a molecular weight of 326. This led t o a study of the rate a t which the molecular weight increased Experimental Results when 10 Der cent of free fatty acids derived from linseed oil The results are shown in the table and some of them are was added to the oil. The results in the table show that the presence of an additional 10 per cent of free fatty acids in further shown graphically (Figures 1 to 3). the oil during boiling led to a very great increase in the rate a t which the molecular weight increased. The percentage of free fatty acids present would therefore be adjudged to be a factor of the first magnitude in affecting the reactions that occur during the boiling. This is in agreement with other methods of studying the boiling. Although the apparent molecular weight of the free fatty acids as prepared was 1319, as determined in benzene, the molecular weight of the early samples in runs containing 10 per cent of added fatty acids was uniformly lower than in runs where oil alone was used. This seems to indicate that association or polymerization of the free fatty acid molecules was lessened by the heating, and was not to be ascribed entirely to effects produced when the samples were dissolved in benzene. The following tests further seem to show that the molecular weight of the free fatty acids is an indication of chemical action of the nature of condensation, rather than association, as a simple function of the solvent employed. Twenty grams of free fatty acids, with an apparent molecular weight of 1319 in benzene, were heated rapidly over the full flame of a T e c h burner in a 50-mm. porcelain crucible. The temperature rose from 20" C. to 317" C. in 2 minutes. Samples taken rapidly showed much lower molecular weights, as indicated by data. were used to eliminate any molecular weight variation due t o the concentration of the solution in benzene.
Run 44 Time Minutes
Temterature
C. 200 293 317
0.5 1.0
2.0
Free fatty acids Per cent
568 572 557
90.6 89.7 90.9
~-
Time of heating in hours Figure 1
I
I800
It will be noticed that when linseed oil was heated i.n an atmosphere of purified nitrogen the oil thickened and the coincident molecular weight increase, although less than in air, was considerable. At lower temperatures than 293" C. the rate of molecular weight increase was less. Since the glycerides present and glycerol itself break down slightly a t 293" C., it was thought that the reactions might be of the nature of aldehyde condensations. However, 150 grams of oil after 2 to 3 hours' heating gave negative tests for aldehydes in all cases. This in itself would be inconclusive, because the velocity with which the aldehydes react with the unsaturated glycerides might be so great that the quantity of free aldehyde found in the oil after heating would be vanishingly small. It was believed that more conclusive evidence would be obtained by conducting several boilings in an atmosphere of nitrogen and aldehyde and with the added feature of introducing the aldehyde below the surface of the oil. Accordingly, boilings were made in which nitrogen was bubbled through acrolein and this mixture then bubbled through the hot oil. However, as indicated by comparison of Runs 31 and 34 with Runs 32 and 33, the rate a t which the molecular weight increased in the presence of acrolein was not appreciably increased. The condensed vapors from the boilings had molecular weights corresponding approximately to the theoretical for
Molecular weight
TOOL
I
1
1
1 .5 1
-1 - -
1
~
I
I
1 1
I
I -
l
i
!
1
I:
I
1
l,
15
i
i
E
l
(
2.5
I
I
I
3
Time of heating in hours Figure 2
the molecular weight of 1319 obtained for the free fatty acids represented associated or polymerized molecules which when heated yielded molecules of less than half this molecular weight, The high value is therefore not a function of the solvent alone.
INDUSTRIAL AND ENGINEERING CHEiMIXTRY
September, 1325 Run 45 10
M i n u t e s a f t e r heating Temperature, C. Molecular weight
20 200 560
184 561
30
40
218 570
244 582
50 265
615
60 295 705
The gradual rise in the figures shows that furtJherchemical change is taking place during the heating. I n several cases the free fatty acids alone were heated and samples withdrawn for molecular weight determination. The number of cubic centimeters of 0.1 N potassium hydroxide required to neutralize 0.7 gram of the sample decreased steadily with successive samples, as shown in the following table, the corresponding molecular weights being shown for reference: -Rus
Mol.
Time Hours U p t o heat 0.5 1.0 1.5 2.0 2.5 3.0
wt.
789 941 1425 2262
39Free f a t t y acids Per cent 81.7 78.9 71.9 59.8
-RUN
Mol. wt. 758 764 819 833 848 827
815
42Free f a t t y acids Per cent 12.78 12.02 11.11 10.39 10.21 10.04
307
the rate of formation of free fatty acid, which rate is slow at temperatures much below 293" C. The total number of double bonds in one molecule after the first step has occurred once has been reduced from nine to eight. Opportunity for further addition of free fatty acid is therefore less, but this would be masked by the condensation of two of these molecules with elimination of water. This causes a molecular weight increase from 872 to 1726. If this did not occur the rate of molecular weight increase would diminish rapidly. Curves such as 25 and B-2, which show increase in the rate of molecular weight increase, therefore furnish some support to the premise of condensation with the formation of a polyglycerol derivative and elimination of water.
--RUN
43-Free Mol. f a t t y acids wt. Per cent 1144 75.7 1255 74.4 1355 70.6 1506 69.3 1718 65.2 1817 63.4 1977 60.4
Although the curves showing the rate a t which the molecular weight increases are regular, the variations shown are suggestive of underlying reactions. The curves seem to support a theory of the mechanism of oil boiling presented by S a l ~ v a y . ~This theory premises the liberation of free fatty acid, which condenses a t the unsaturated linkages of the oil. As a result of the liberation of the free fatty acid, a glycerylOH group becomes free. Salway offers the suggestion that these molecules then condense with the formation of polyglyceryl derivatives, the course of the reactions being indicated by the following scheme in the case of linolenic glyceride. Step I CHzOCO (CH2)r CH=CH.CHzCH=CH
1 I
CHzCH=CH.CHCHx
4- H O H +
CHOCOR CHzOCOR
C HzO C 0 (CHZ) 7 CHz. CHCHzC H=C H C Hz C H=C H C Hz C €13 CHOCOR I
b C O R
I
l
CHzOH (Two of the foregoing condense with the elimination of HzO)
S t e p 11 CHzOCO (CH2)7 C H Z . C H C H ~ C H = C H C H C H = C H C H ~ C H ~ 1 I CHOCOR +COR CI H z - F l CH2O-W 1 CHOCOR
I
&COR
I
CH20CO (CHz) 7 CHzCHCHzCH=CHCHzCH=CHCHzCIT~
Salway supports this theory by experimental evidence showing decrease in iodine value accompanied by decrease in acid value, but states that experimental evidence supporting the formation of the polyglyceryl derivative is needed. The writers found that samples withdrawn a t regular intervals during the boiling showed decrease in iodine value and decrease in free fatty acid content, as shown in Runs 39, 42, and 43. Furthermore, when the oil was heated in a stream of dry nitrogen, the vapors condensed by passage through coils immersed in a freezing mixture gave a test for water with anhydrous cupric sulfate. This was true even after boiling had been continued for several hours a t 233" C. to drive off any moisture present a t the start. I n case the RCOOH is derived from the glyceride by hydrolysis, the rate of molecular weight increase is dependent on 7
I
600
J . Sac. Chem Ind.. 39, 324T (1920).
I
509' 5 ' *
m
I
i
1
15
"
'
2
'
1
4
2.5
3
Time of heating in hours
Figure 3
I n Runs 35 and 36 an additional 10 per cent of free fatty acids was introduced to see whether the rate of the action was dependent on the concentration of free fatty acid. As shown by comparison of Runs 25 and 35, the rate of molecular weight increase a t 293' C. in an open vessel is much greater and this rate increases as boiling continues. In a stream of nitrogen the results are less conclusive, possibly because the free fatty acids are carried off by the stream of Nz thus decreasing their concentration in t4e oil mass. The free fatty acids when heated alone under the same conditions a t 293" C. vaporized too rapidly to get a comparison a t this temperature. At 205' or 232OC. comparisons with linseed oil alone and linseed oil containing an added 10 per cent of free fatty acids were obtained. Where the free fatty acids alone are heated, the number of double bonds in one molecule increases by two a t each condensation of another molecule of free fatty acid with the original, the number of double bonds increasing in the progression 3, 5, 7, etc., when starting with linolenic acid. The rate of molecular weight increase would therefore be expected to show a steady increase up to a certain complexity of the molecule. The presence of linoleic, oleic, and other acids with less than three double bonds would diminish this rate. The data ob-
!MIS
Val. 17, 30.'3
I.\~IIt~~YTMA I, :I:VD ICNGINBBfil.\'(~ CXE.VISTI1Y
tairied fur t.lic mixed free fatty acids done show, as expected. a straady gain in the rate of molecular wcight inrrease. Work in Progress 'J%I! h e r v a t i o n s mentioned naturally lod to a study of the lwliiiyior of tlie individual pure acids and of piire glycerides
surb NS that o i linolenic acid. Tliis work is iii progren-; at this time. Oleic acid, as expected, sliowcd a low rate of molecular weight increase at 205" C . A little preliminary work Iias been done on linolenic acid The resuks obtained with other solvents such as acetic acid. rampbiir, and ethylene dibromide osi boilings with litineerl and China wood oils, are also being compared.
Rapid Determination of Phosphorus in Bronze' Method Ive oix- grain of sample in 5 c r . of l i y d r d ~ l ~ x acid iv c gravity 1.20) and 10 ec. of 1 : 1 nitric acid. Iioii t.o drive off brinvii fumes and then wilsli down tlie iiisidr of the beaker with warm water. The total voliiirie of the , d o tion should be about 40 cc. Cool to .iO"C.,then add 25 cc. o i dear molybdate solution und stir iint,il a precipitate forins. Transfer to a Goetz tribe iising as l i t t l e water as possihle. TIE total d u m e of tho sohition in thr tiil)e oiight not to exw e d 75 co. Twirl for 5 Ininrtt,es at 1300 r. 1). m. Ibmove from t.lie shield and read pliosphorrrs iwntrrlt (IirPrt. Each division equals 0.01 per w i l t ptiasphoriis.
Notes Solutions that are too warm (100- C.) or too a c i d niav t h r o w out molybdic acid and cause high results. The solution of the sample must be clcar ( d l tin in solution) before adding the molybdate solution. Check solution anti apparatus with a standnrd samolc of ohosuhor bronze. .The E?ur&u ol Standards has a phosphor bronze standard sample, No. 63. The method is applirvhlc to material containiiig 0.4 per cent of ,,hosphorus, por sam. FIRure Z--Tuhrs and Iiolder. Note Precipitate in End of Tubes i,lcs hkher than this use i~ropuriionatclysmaiter charges. The tubes must be perfectly clean and free from oil or dirt: otherwise the precipitate will stick to the sides of the tubes. .4rnmonia nil1 dissolvc the piecipitati. thns permitting quick clcaning.
"
B ~ i r c i i i of i Stitndiirdi phosphor 1bio1111. s $ z n i A No. 88.
Mine Rescue Contest Amouoced--The Bureau oi Mines will :onduct the fourth international contest in first aid and mine I C S C ~ I Pwork at Sprinpfield, 111.. September 10 to 12, 1925.
