1322
INDUSTRIrlL -4ND ENGINEERING CHEMISTRY
diffraction. The semicircles are due to the side spacings. Having originally such well-defined long spacing diffraction arcs, it would be difficult t o notice any beneficial effect on orientation caused by the addition of a small amount of any of these compounds. However, it has long been a matter of conjecture as to why the side spacings of paraffin do not produce short diffraction arcs a t 90” t o those caused by the long spacing. Such a result is obtained if the film is prepared by careful heat treatment. This method is troublesome, but the addition of a small quantity of oil to the paraffin made it possible to form this type of film by melting on or dipping the rod in the sample. With slight heat treatment, films were obtained which gave side spacing arcs, ranging in length between those of the patterns represented in Figures 3B and C. Bssuming that B represents essentially perfect orientation for the molecules in paraffin and C the mere beginning of the tendency toward a more nearly perfect arrangement of the molecules, t’heorienting effects of the addition compounds can be measured by noting the length of the side spacing arcs. The observations then would be interpreted so that the shorter the arc, the better the orientation of the paraffin molecules. EXPERIMEKTAL. A base mixture of paraffin and oil was prepared by weight. This mixture had a consistency such that it would set at about 20” C. above room temperature. Four blends of this material were made containing 5 per cent of stearic acid, dichlorostearic acid, methyl stearate, and dichloromethyl stearate. These materials were oriented on 0.25-inch brass cylinders. In the preparation of the films for comparisons, the brass rods and samples were heated in an oven until they had reached the same temperature. Then each rod was dipped to a predetermined distance and set on end in an insulated chamber to cool. In taking the pattern, the x-ray beam was passed across points a t equal distances from the place of maximum immersion. A low-temperature wax was blended with 5 per cent dichloro-
VOL. 28, NO. 11
methyl stearate. Patterns were taken of films formed by this material and also the original wax which had been solidified while the rod rotated under slight pressure produced by a strip of metal pressing on the surface.
RESULTS AND COSCLUSIOKS.Figure 4 shows patterns from films of the base material and the methyl dichlorostearate blend. The results are those that would be expected for the improvement of orientation by the addition of a chlorinated compound; the side-spacing arcs from the base material form semicircles and the blend gives two short arcs similar to a fiber structure. This result was confirmed by several repetitions of this experiment. Comparable results were obtained for the low-melting wax fraction and its blend when films were solidified under pressure. These patterns are reproduced in Figure 5 . These two cases show that the addition of this chlorinated compound greatly improves the orientation of the hydrocarbon molecules of paraffin and paraffin-oil films. Thus, besides orienting in films of the pure polar compounds, even in small amounts they show a marked tendency to regiment surrounding molecules which are only weakly polar.
Literature Cited (1) Blodgett and Langmuir, J . Am. Chem. SOC.,56, 495 (1934). (2) Bragg, Nature, 115, 266 (1925). (3) Clark, Lincoln, and Sterrett, PTOC. Am. Petroleum Insl., Sect. 111, 16, 68 (1935). (4) Clark, Sterrett, and Leppla, J . Am. Chem. Soc., 57, 330 (1935). (5) Davis, Lincoln, and Sibley, Proc. Am. PetroEeurn Inst., Sect. 111, 16, 81 (1935). (6) Lincoln, Byrkit, and Steiner, IND. E m . CHEM., 28, 1191 (1936). (7) Trillat, “Modern Views of Friction,” 1928. (8) Wells and Southcombe, Petroleum World (London), 17, 460 (1920).
Molecular Regimentation and Chemical Reactions in Liquid Oils and Blends F A LIQUID is considered as truly amorphous, Q I we would expect themolecules to be in a perfectly random state of distribution. Such being the case, a beam of x-rays would suffer no interference effects. The scattered rays would merely fog the photographic plate; they would be most intense at small angles and decrease as the angle assumed larger values. Debye and Scherrer (2,3) first showed that this was not the case, but that the scattering was confined to certain welldefined regions which had the appearance of halos. The maximum intensities of these halos seemed to correspond to periodicities in the liquid corresponding to molecular dimensions. Since that time several theoretical studies have been made to account for the observed effects and to picture the state of molecular aggregation in a liquid. Raman and Ramanathan (4) were the originators of one theory, and a second is due to Stewart (6). A third theory now generally accepted is based on mathematical distribution functions originally derived b y Zernicke and Prins (8).
A physical picture of the mathematical distribution function theories of Prins and Debye, further extended by Warren ( Y ) , Bernal and Fowler ( I ) , and Randall and Rooksby ( 5 ) ,is consistent with some kind of pseudocrystallinity in liquids, probably similar to that which exists in the solid state. Prins invented plausible distribution functions and from these deduced a diffraction pattern. Debye’s guiding principle was the relative probability that the atoms and molecules will be certain distances apart in the liquid. The use made of liquid diffraction in this investigation does not depend on the type of molecular aggregate but can be interpreted in the light of either concept. For convenience the study of the liquid state may be divided into three parts; each represents a different type of information which may be obtained by the same technic.
Temperature Effect on Regimentation in Oil, Blends, and Pure Liquid Compounds According to any theory of the structure of liquids, we can readily ascertain that a temperature increase should produce a more chaotic arrangement among the molecules because of their increased velocity, thus causing the halo to become diffused, I n addition there should be a shift of the intensity maximum toward a position indicative of an increased spacing. A further conclusion can be drawn that under the same con-
NOVEMBER, 1936
INDUSTRIAL I N D EXGINEERING CHEMISTRY
ditions the patterns of two liquids containing similar asymmetric molecules will indicate by the sharpness of their halos the extent Of regimentation' the cules of the liquid producing the pattern with the sharpest halo should have the more orderly arrangement. The of these twoconceptswill useful information about the state of molecular aggregation existing in the bulk liquid. This phase mould be concerned then not with boundary lubrication but with the conditiolis in an appreciably thick film or in so-called viscous lubrication.
1323
pared with that of the straight 8. A. E. 30 oil at three temperat
'
~
~
~ t ~ ~ ~ ;~o p h o t o m ~eter
analysis, so that curves represented graphically the distribution of intensities radially from the cent,er across the halos, each producing a peak. The height of the peak was measured from the loxvest point on the curl-e adjacent to the central spot. This point of minimum intensity around the central spot was chosen because in truly amorphous scattering the maximum intensity LvOuld be at this point; the advantage of this position of reference, then, was that any change toward disorderly arrangement rvould be more noticeable.
EXPERIMENTAL. In all cases where liquid diffraction patterns were taken, the sample was held in a metal cell fitted with mica windows. The cell was constructed of three strips of copper drilled with a hole approxiThe state of molecular aggregation in the liquid mately 1/4 inch in size; one strip was 1 X X 3/32 phase was investigated for certain of the addition inch, the other two were 1 X 1/2 X inch, Tn-o boll holes were drilled at the edges of the strips. The compounds. The effect of a temperature increase thicker plate formed the cell, and two pieces of thin wasstudied. This same type of investigation was mica were inserted between it and the outer plates, carried out for lubricating oil and two blends. which were placed one on either side. These strips of' mica covered both ends of the hole in the center plate, Several compounds were prepared with known and the complete cell \\-as clamped tight by bolts. To positions for both the chlorine and bromine atoms; the middle plate a strip of copper was fastened by means of silver solder. This served as the core for a a comparison of their liquid patterns with those mica-insulated, nichrome heating element. To increase obtained for the commercial chlorinated addition the temperature of the cell it was necessary only to pass a small current through this coil. agents gave some information on the structures of Temperat'ure was not measured in degrees but by t'he current through the coil. It was assumed t,hat, these latter substances. upon the passage of equal currents, the same t,empera-, The chlorinated addition compounds alone and ture for the cell was attained. A variation of 5" C. (9" F.) would be negligible since the x-ray measurein oil blends when heated in the presence of a ments would be unaffected by such a change. metal form a resistant surface layer on the metal The unfiltered beam of copper radiation was passed and themselves undergo a chemical change. The t'hrough the cell, and the film distance was always 3 cm. Filtering of the beam was used in several cases but its, evidence indicates that a chemical condensation only effect seemed to be the increase of exposure time. The compounds studied were chlorocety I acetate, has taken place. dichlorooctadecyl acetate, methyl stearate, chlorin-, ated petroleum wax, oleic acid, chlorobutyl stearate, dichlorostearic acid. dichloromethvl stearat,e. dichlorooleic acid, dichloromethyl oleite, chlorooctadecyl methyl ether, dichlorocetyl palmitate, chloromiricyl palmitate, RESULTS. The pure chlorinated compound produced x-ray dichlorooctadecyl stearate, monochlorodiphenylene oxide, tripatterns showing only a single halo. The position of the chlorophenol, trichloronaphthalene, esters from petroleum oxidamaximum intensity in these halos as calculated from microt'ion, dichloroethyl stearate. photometer curves varied over a small range. This range is The liquids were examined at room temperature and that represented by 1.8 amperes through the coil. The solids were melted equivalent t o 0.05 mm. (0.002 inch) on the film, which was not by the passage of a small current, and for the second pattern the of great significance structurally when the halo character of current \?-as raised 1.9 amperes to correspond to the 1.8-ampere the pattern was considered. JTe can safely say that the patincrement employed for the liquids and to take care of radiation terns were alike, and that the periodicity causing them arose to some extent. This gave one difference in temperature for the two patterns of every compound, equivalent to 1.8 amperes from a similar structure in all the molecules. This behavior through the coil. will be discussed in a later section. Blends were made of dichloromethyl stearate with oil, varying Examination of the data showed that, in nearly all cases of in comDosition from 2.5 to 20 Der cent and of methvl stearate compounds producing high film strength, the peak was also from 2.3 to 10 per cent. The pitterns of these blends'were comquite high. This increased sharpness of the halo indicated that the molecules were arranged in more orderly fashion side by side and were held by stronger secondary forces. As in the case described from the study of solid films, such a condition would tend to facilitate slippage of one molecule over t h e other. The study of the effect produced by temperature on the regimentation of the oil molecules in the blends furnished some interesting information. Although there mas no apparent difference in the degree of molecular organization among the two blends and oil a t room temperature, an increase in temperature produced a marked change. The peak heights from microphotometer curves are plotted in Figure 1 against the amperes through the heating coil. The relative positions of these curves in the vertical direction are of no B-l@ Yethyl Stearate Blend C - 1 6 I j i c h l o r o Methyl Stearate 3lend significance since the sensitivity of the microphotometer was I 1 not the same for every series. V The curves representing regimentatioii in the methyl dichlorostearate blend are concave upward, those of the other Temp ra t u r e FIGCRE1. PEAK HEIGHTS FROM MICROPHOTOMETER samples are convex upward. This fact can mean only that CURVESus. AUPERESTHROCGH THE HEATINQ COIL the strong regimenting forces of the chlorinated compound
1
~
~
1324
INDUSTRIAL A11D ENGINEERING CHEhlISTRY
prevent the rather complete disorganization of the oil molecules a t higher temperatures. The patterns of the dichloromethyl stearate blend showed a superposition of the patterns for the tw-o pure liquids. To establish this fact, the different composition blends were used ranging from 2.5 t o 20 per cent. The differences in peak height were determined between the oil halo and the inner halo, partly due to oil and partly to addition compound. I n Figure 2 these differences arere plotted on an arbitrary scale against percentage composition. The measurements on peak differences established the height of the inner peak due to the addition compound; the curve shows that this peak varied directly as the composition. These results indicate that the molecules of the chlorinated addition agent are bound together rather strongly, forming their own nuclei, and are not dispersed by the oil molecules. This more nearly represents the iicybotactic” state and is not a case of true solution. We may conclude from these examinations that molecules of chlorinated compounds are rather highly oriented in the liquid state and, because of the strong binding forces between them, are enabled to group together in the blends. These strong binding forces make their effect felt on the oil molecules by reducing their tendency toward a more random arrangement when the temperature is increased.
Determination of Molecular Configurations in Liquids We have seen that a certain periodicity in the moIecuIar regimentation of liquids was able to produce an intensity maximum in the form of a halo on the photographic plate. Bragg’s equation for diffraction by crystals was modified by Warren (7) to be applicable to liquids. Warren assumed a hexagonal close-packed arrangement for the molecules and used the value given by Langmuir for the space occupied by a hydrocarbon chain. He then made an analysis over all the carbon atoms in the chain, starting with any one as representing zero distance. From theee calculations he determined that the equation for calculating the sidewise closest approach of the molecules should be
VOL. 28, XO. 11
broniination of oleic acid. Patterns were taker of theee compounds in the liquid state. Pentachloroet ne was chosen as the material in which the chlorines r have a fixed arrangement. With these three patterns the spacings could be calculated and compared with those values demanded by theory for the introduction of halogen atoms into the chain. RESULTS AXD DISCUSSION. Each of these pure compounds produced tn-o very sharp halos in contrast to the diffused one for the addition compounds prepared by direct chlorination used previously. Pentachlorcethanejs such a molecule that, if we compared its spacing to the 5.4 A. of a hydrocarbon chain, it should show a spacing increase corresponding to the introduction of two chlorines between chains. These chlorine atoms do not contribute their whole diameter, but allowance must be made for their attachment to the carbon a t the tetrahedral angle. Calculating the spacing for such an arrangement, using Pauling‘s radii of the ‘;true” atomic domain, if -7as found that it should beJ0.0 A. The value calculated n the outer halo is 10.1 A. which is rather good agreeriAent. Ethane would not have the zigzag structure of the h g e r carbon chains and, when a similar arrangement for this type of chain was assumed and the spacing calculated, a yalue of 11.25 A. was obtained. A formula for calculating the length of molecules from film measurements was also given by Warren. Using this formuia for the inner halo from pentachloroethane, a value of 12.0 A. was obtained. The g a l u e calculated from structural considerations was 12.3 A. The outer halo of both brominated compounds gave a spacing of 8.55 A. In this case there would be only one bromine between chains, and the calculated value was 8.50 A.
nX = 0.814 X 2 0 sin e
and that the mean sidewise spacing was 5.4 K. for straight hydrocarbon chains. Since the derivatives to be originally studied here were straight hydrocarbon chains, an investigaticn of their liquid patterns should give some information as to position and arrangement of atoms and groups in the molecules, for without a doubt the spacing represented by the principal halos is for sidewise closest approach. These halos were quite diffused for those long-chain compounds where the chlorine was introduced into the molecule b y chlorination of the corresponding unsubstituted compound. There was a chance for the chlorine to attach itself in different places, thus accounting for the diffused ring. Therefore, a compound with known positions for the chlorines had to be chosen. T o establish the fact that these differences in side spacings between unsubstituted and chlorinated chains n-ere due to the introduction of a chlorine molecule, two other compounds were used containing a bromine a t a known position. Since the bromine is much larger than the chlorine, it will produce a greater increase in spacing. EXPERIMENTAL. a-Bromobehenic acid was prepared by the Hell-Volhard-Zelinsky method and after repeated crystallization gave the melting point recorded in the literature. The compound 9,lO-dibromostearic acid was prepared by the
t
Percent D i c h l c r o Methyl S t e a r a t e
FIGURE2, INNER-OUTER PEAK HEIGHTDIFFERENCES 1’s. PERCENTAGE DICHLOROMETHYL STEARATE
When we consider the spacing calculated from the diffused halo of the chlorinated compounds, it is evident that this spacing too must be produced by the introduction of one or more chlorines between chains. The spacing calculated from measurements to the point of mafimum intensity in the halo has a mean value of about 11.8 A. for the fifteen compounds studied. The diffuseness of these single halos as compared with the sharpness of the two of the pure compound would suggest that these chlorinatoed compounds were possibly mixtures. This spacing of 11.8 .4.,producing the maximuom intensity of scattering, was in the neighborhood of 11.25 A., the value calculated for a chlorine on either side of the zigzag carbon chain.
It is ii%crcsting t u note that the side spacings from solid chkorina .J compounds were not increased hy the presence of the chlr ne %toms. Since presence of the chlorines on the molecule causes the ha1r.s to be much smaller than those fur hydrocarbon chains, any change appearing in these halos can be interpreted as some efiect of the chlorine. For instnncr, if tlie chlorine is removed, the halo for a hydrocarbon chain rea,ppearn. . A ~ '
of the corresponding niisuhtititutcd ones because the distance of closest approach was r h n n g d hg the introduction of the chlorine a t ~ m i s . Aftcr Iienting soiiie of these chlorinated conrponnds with zinc at 130" C . fur 2 hours, the liquid patterns giver1 by all of then1 were markedly changed from those originally obtained. Figure 3 shows the two patterns obtained for each of the compoiin~lsinwstigated. The halo due to the closest ap-
Compound Formation The possibility of dianical reaction in blends colitaininy chlorinated iiddit,ion agents subjected to heat, especially in the presence of mt:L.als, can be investigated readily from liquid diffraction patterns. Heat seenis to cause the long-chain chlorinated acids and estcrs, etc., to undergo change; thk heat efiect is more rapid in the presence of a metal. There is no o v b ~nce as to t,he actual conipounds formed, but it s s possible that molecnlar condensation has taken pi. 1. It is well known that benzyl chloride, heated in ti&- prcscim of zinc, condenses to prodnce R Inngchaii,cornpriund of the following type:
proneti of pure hydrocarbon chains now h g d n to appear. In the original pattern there had been no scattering at small anglev cven for specimen-to-plate distances of 10 em. (3.9 inches). IIowever, all pat,terns obtained on the heated product slrowed such a scattering in this nrea. On increasing the film distance to 10 em., the inner halo could not be re-
RSSULTB. An x-ray exiunin:ition uf the nictal rods from the first eapcrimcnt disrloses a laycr of solid material formed on the stirface. Tire ri?slsiiltsare given in Table 1.
.41 I'e
nrnra
:I !iO nune 7.01
Random
..
oriented tsuordelr
i. !2 7.03 7.10
solved. No such clianges or evidences of reaction of any kind were found for pure nnsuhstituted compounds or their blends in oil. CONCLUSIONS.We find here conclusive proof that some reaction is taking place between the chlorinated molecules or blend v h e n it is heated in contact with a metal. The reartion seems to produce a stable solid material which attaches to and orients on the metal surface in the forni of a thin but resistant film. This reaction seems to be catalyzed t o varying degrees, depending on tile metal. The liquid patterns prove that the chlorines have heen pulled out of some of t.lic molecules, leaving only the pnre hydrocarbon chain. The scattering at small angles indicates that probably Stewart's cybotactic sta.te exists, with rather large inolecules in the minute aggregates. This scattering does not resolve itself into a distinct halo because chains oi iunlecules produced by a condensation reaction vary considerably in lcngtlr. These observations may have a considerable boaring on the problem of efficient performance of chlorinated compounds as addit.ion agei1t.s in lubricating oils.
Italidoi"
Literature Cited
Oriented t r u lrrdera Oriented t r o orders
When the qnalitative estimates on tlie catalytic effect of the inetals were made, it wa8 found that the number of hours required for the reaction mixtnres to reach the sanie color were as follows: iron, 35; aluminum, 35; brass, 1.5. As was previously pointed out, the liquid patterns fur the clilorinat~ed compounds were dist.inctly different from those
~l!tltij. (4) Kunmn. C . V., and R;mmniltlrao. K . R . , Pruc. Indian Aa Cultiuatilm Sci.. 8,127 (1923) (5) Randdl and Rouiia1,y. Nutiwe. 134, 473 (1'332). 27, 104 (1'336). (6) Stewart. G. W., Phius. Reo.,
(8) Zernioke and
Prim. Z. Phgsik. 41, 184 (1927).
(The third part of this article folkjwa on the next page.)
