I.VD USTRIAL AND ENGINEERING CHEMISTRY
July, 1931
Literature Cited (1) Backstrom, M e d d . 1.elenskapsakad. Nobelinsf., 6, No. 15 (1925). (2) Carothers, J . A m . Chem. Soc., 51, 2548, 2560 (1929). (3) Herzog, 2. angew. Chem., 41, 534 (1928). (4) Katz and Sanwel, ivafur~'issenscha~feilen, 16, 592 (1928). (5) Mark, Melliands' T e x f i l h e r . , Mannheim, No. 9 (1929). (6) Mark and Fickentscher, Kolloid-Z., 49, IS5 (1929). (7) McNally and Sheppard, J . Phys. Chem., 34, 165 (1930).
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(8) Meyer and Mark, Ber.. 593 (1928). (9) Scheiber and Nouvel, 2 . anpew. Chem., 41, 353 (1923). (10) Sheppard, Nature, 121, 9S2 (1928). (11) Sheppard and Houck, J . Phys. Chem., 34, 273 (1930). (12) Sheppard, Nietz, and Keenan, IND.END.CHEM.,21, 126 (1929). (13) Sponsler and Dore, Colloid Symposium Monograph, p. 174, Chemical Catalog, 1926. (14) Stamm, J . A m . Chem. Soc., 51, 304 (1930). (15) Staudinger and Bruson. A n n . , 447, 97 (1926).
Polymerization us. Association and Condensation' Eugene C . B i n g h a m a n d Laurence W. Spooner GAYLEYCHEMICAL LABORATORY, hFAYETTl3
OME years ago Bingham and Harrison (3) devised a
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method for measuring the association of liquids, but they did not suggest how association is related to constitution and their method remained in obscurity. Recently Bingham and Darrall (1) were afforded the opportunity to study twenty-three of the isomeric octyl alcohols. The results proved that association depends to a high degree upon the constitution and in a manner which is readily understandable. I n the first place, there are certain polar groups which acCO, GI, centuate the association, notably OH, COO, "2, and SH. On the other hand, hydrocarbon residues are very little associated, and therefore they tend to lower the association of the molecules in which they occur depending upon the magnitude and the constitution of this hydrocarbon residue. The more exposed a polar group is, the higher will be the association; and the more fully i t is surrounded by alkyl groups, the lower will be the association. The above conceptions are so simple and natural that it is surprising that they have not already become established. There is also a considerable mass of evidence to prove them: (1) In the f i s t place, the normal compound with the polar group a t the end of the chain is the most highly associated. (2) .Lengthening the chain decreases the association, probably without exception. ( 3 ) Bringing the polar group toward the center of the chain further decreases the association. (4) An is0 grouping in the hydrocarbon residue nearly invariably brings about a decrease in association. ( 5 ) The decrease in association is still further accentuated by a further clustering of the hydrocarbon residues around the polar group. (6) In ten classes of compounds thus far investigated, it has been found that the addition of a methylene group lowers the association approximately 9 per cent. (7) In the class of esters it is found (Z), as might have been expected, that methyl formate is the most associated of all esters; furthermore, methyl esters are all associated, as are all formates, but all the esters of the higher alcohols united t o acids above butyric acid appear to be very slightly associated. The theory of protection enables one to estimate the association of the various esters very precisely. The effect of a methylene group is of course quite different, dependent upon whether it is placed in the acid or the alcoholic residue, but it can be exactly calculated. (8) I n the aromatic compounds, like the cresols, the presence of an alkyl residue in the ortho position to a polar group is most effective in lowering association, as would be expected, and in the para position it is least effective. (9) On the other hand, a second polar group in the ortho position should be less effective in raising the association than in the para position, but data are here lacking. (10) By the same reasoning one can explain why maleic acid is less associated than fumaric acid, (11) Finally, in an aryl compound having two alkyl groups, as in the xylenes, the theory explains on the basis of protection why para-xylene is less associated than ortho-xylene. More evidence from the aryl compounds is being sought. 1
Received April 9, 1031
COLLEGE, E a s T o N , P A .
There is not opportunity here to give all the data upon which these conclusions are based, but it is expected to have shortly the associations of some three hundred liquids a t a variety of temperatures and fluidities, and for these substances the associations may be calculated by a series of simple formulas suited to the various classes of compounds. The method has already served to correct certain of the data of the literature, and there are still some compounds, such as ethyl palmitate and propyl propionate, which need verification, but in general the calculated associations are as satisfactory as could be expected. To be able to measure the association will doubtless be important, but i t is much more valuable to he able to calculate the association from the known composition through the relationships established between chemical composition and association for the various classes of compounds. It now becomes possible for the first time to write the formula of a substance which will have a given fluidity a t a certain temperature. Thus there is answered the age-old query of Democritus, "Why is water a liquid?" and it is no longer necessary for the student of organic chemistry to learn "by heart" that hydracrylic acid is "a thick, sirupy liquid." But even wider uses, not hitherto utilized, open out before us. Let us confine ourselves to very simple examples in demonstrating this use of the viscometer. If acetaldehyde were associated in the liquid state to three molecules, the absolute temperature required to produce a fluidity of 100 rhes would be 3 X 159.2 = 477.6' K. 3CH3. CHO 159.2' K.
(CHI. CHO)a 477.6' K.
The actual temperature as obtained by considerable extrapolation is 191' K., so that acetaldehyde is only associated to a slight degree (n = 1.20). I n the process of polymerization of acetaldehyde, the compound C6HI203is formed with the loss of three double bonds and the gain of a ring grouping. It has already been proved that n double bond or ring grouping has the same effect upon the flow as if hydrogens were present. The paraldehyde should have the same temperature for a fluidity of 100 rhes as a straight-chain compound equally unassociated having the formula of CeH1403, which is 276" K. As a matter of fact, the observed temperature is 301' K., so that even paraldehyde is somewhat associated (n = 1.09), but this is 176'K. lower than would have been the case had acetaldehyde been merely associated into trimolecules. If polymerization is less effective than association in lowering the fluidity, there is a third method for bringing molecules together which lowers the fluidity still less, as in the familiar condensation. Two molecules of acid condense with elimination of water:
+
2CzFsCOOH +(CzHaC0)zO Hz0 2 X 232.2 K. = 321.3' K. f 143.1' K. a t 200 rhes
INDUSTRIAL AND EiVGINEERING CHEMISTRY
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Two molecules of alcohol condense in a similar way t,o form ether: 2C3HsO +(C3H7)zO 2 X 207.7' K. = 272.3' K.
Hz0 ++ 143.1'
+
+
GHbCOOH CsHlOH +CZHGCOOC~H~HzO 232.2'K. f 207.7' K. = 296.8' K. 143.1' K.
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The case is somewhat different in the formation of lactones:
0.co
K.
A molecule of alcohol and of acid unite to form an ester: d I
Vol. 23, No. 7
I n the b t ca? the temperature is not 2 X 232.2 = 464.4' K., bat 321.3' K. lkhich is 143.1' K. lower than this, 143.1 being the temperature value for water. I n the case of propyl alc&I, two associated molecules would require a temperature of"415.4' K., but owing to the elimination of water the temperature is again 143.1' K. lower, or 272.3' K. I n the
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third case the temperature required is not 232.2 207.7 = 439.9' K., but 296.8' K., which is again 143.1' K. below the value calculated on the basis of union by association.
C H ~CHOH . . CH, . C H ~COOH . ----t CH?.CH/ 'CHs. 299.8' K. 275.3' K.
+ HzO
CHp 143.1' K.
The ring formation in this case makes up for the loss of two hydrogens, so that the temperature required to produce a fluidity of 200 rhes is not 143.1' K. lower but simply 24.5' K., corresponding to one oxygen atom. Elsewhere there will be given examples of the practical application of the method. Literature Cited (1) Bingham and Darrall, J . Rheology, 1, 174 (1930). (2) Bingham and Fornwalt, I b i d . , 1, 372 (1930). (3) Bingham and Harrison, 2. physik. Chem., 66, 1 (1909).
Studies in the Drying Oils XV-Some Aspects of the Oxidation of Linseed Oil up to Gelation' J. S. Long and W. 0. W. McCarter2 LEHIGHUNIVERSITY, BETHLEHEM, PA.
This work is a continuation of the work of Long and Chataway (2) designed to test the original work and to extend it to a study of the effect of the following factors on the rate of oxidation up to the point of gelation: temperature, driers, inhibitors, degree of unsaturation, degree of complexity of the molecule, and acid value. Free fatty acids unite with linseed oil during oxidation a t 160' C., thus increasing the complexity of the molecule and playing a role of primary importance in facilitating gelation. Linolenic triglyceride takes up nearly twice as much oxygen as its isomer, eleostearic triglyceride, before gelation. Gelation is a colloidal association process and depends on the size, complexity, polarity, and free energy of the molecules. Oxidation is a contributory cause.
Sodium oleate and selenium lower the rate of oxidation and thus delay gelation. Metallic driers increase the rate of oxidation and decrease the time required for gelation. The presence of lead materially decreases the weight of oxygen required for gelation and also the percentage of the original oil in volatile oxidation products. Lead therefore has a specific action in promoting formation of groups t h a t associate. From 50 to 85 per cent of the oxygen absorbed u p to the point of gelation remains in the oil gel. The other 15 to 50 per cent appears in volatile oxidation products which contain 3.5 t o 5 per cent of the carbon and hydrogen of the original oil.
T WAS at first thought that the transition of liquid dry-
at room temperature by action of stannic, ferric, aluminum, and other metallic chlorides. (2) Polymerization is accelerated by heat, light, and electrical energy, and this absorption of energy can be greatly influenced by the presence of intermediate sensitizers such as halogens. (3) Polymerization takes place a t room temperature under the influence of very high pressure.
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ing oils into solid film was entirely a matter of oxidation. Later work introduced the concept of polymerization and classified a t least the latter stages of the process as colloidal phenomena, the solid film being regarded as an association colloid gel. A recent survey and resume of existing ideas is given by Eibner (1). The words "polymerization," "association," "gelation," and "resinification" define processes that are closely related, often confused, and in some respects identical. No attempt will be made here to differentiate these terms, but it may be well to set down certain criteria of the phenomenon as applied to oils, although no sharp dividing line is drawn between oils and resins or the combination products thereof with oils. The phenomenon of thickening or bodying which results in gelation or resinification is influenced by the following considerations: (1) Contrary to similar phenomena in the case of gases or of many liquids, polymerization of oils is greatly facilitated by elevation of temperature. However, it can be accomplished Received April 9, 1931. Archer-Daniels-Midland and Wm. 0. Goodrich Fellow a t Lehigh University. 1 f
These factors can be considered together. Inasmuch as energy change is a universal characteristic of chemical reaction, even the polymerization caused by the presence and reaction of other chemical substances can be considered on the basis that these substances serve as reservoirs of energy to supply the oil with the energy quanta necessary for the polymerization or association process. Therefore, the major considerations are free-energy changes. Incidentally, this guiding principle is broad enough to cover most, if not all, of the varied phenomena and data that come under the heading of polymerization. Polymerization or association can be likened in some respects to crystallization; i. e,, there are forces which tend to orient the molecules into a t least multiple units. The resultant product has not yet yielded fundamental evidence of definite arrangement such as obtains in crystals. Thus, the
