Document LgbGVVoVM2mwMJzzye6vBV4X

E. f. DU PONT DE NEMOURS & COMPANY KREBS PIGMENTS DEPARTMENT 256 VANDERPOOL STREET NEWARK. NEW JERSEY Copy No. 1 Humerleal File Period Covered: NEWARK PLANT PIGMENT COLOR RESEARCH REPORT Final Report CRYSTAL COMPLEXITY OF 5-NITR0-2-AHISO-ANISOLE --* HAS-D December 10,1947 TO June 14, 1948 IL i I l NMm FILE: DATE: 3/30/4$ 221 N42203 Copy to* #1 - Numerical File 2 - Research Office (221) 3 - Library File (221) 4 - #10 Building File $ - V. Chalupski Plant Files 6 * 0. B, Killian 7 * Extra 6 - Extra 9 - Extra Serial So. KH-49-19 Copy So* 1 NEWARK PLANS PIGMENT COLOR RESEARCH REPORT Final Report CRYSTAL COMPLEXITY OF 5~SXTEO-2~AMiSQ-AlfX$0LB -} NAS-D December 10, 1947 to June 14, 1948, DATE SUBMITTED} 3/14/49 DATS ISSUED* 3/30/49 DUP050067226 .mmm&aiK This report attempts to point out that the subject pigment exists in more than one crystal modification and that because of this, anomalous physical behavior can be expected, it is not intended that this be considered a finished pieee of work. More accurately it is designed to point to possibilities Inherent in an heretofore neglected field of pigment research. Extending this work may well modify some of the ideas expresssd here but that in no way detracts from the fundamental idea that much information of value to the pigment industry can be gained through a study of the crystal modifications of our pigments* It has been casually observed, while working with "Naphthanil" pigments, particularly PCOHA~v NOL, that marked changes in color could occur during treatment with solvents such as chloroform or acetic acid* This suggested a major crystal change but nothing was dons to substantiate this idea until certain rather large discrepancies were noted while attempting to determine the chloroform solubility of 5-N02-2NH2anisole~* HAS-D. This information was to be used as an aid in studying the impurities prsssnt in typical "Haphthanil* pigmsnts and also throw some light on the phenomenon of "reactivity*1 of 5-HO2-2NH2 anisole in alkyd systems* Whan it became evident that the solubility was not a simple phenomenon, the attempt was made to find out why* Although this report concerns Itself only with 5-H02-2NH2 anisole--^ HAS-D, the attempt to determine the solubility of other "Haphthanil* pigments gave strong indication that a similar situa tion exists for the other pigments* This was particularly true of MHPT --> KMX. It is entirely reasonable to suppose that considerable of our pigmsnts are polymorphic and that a detailed study from this point of view could lead to the discovery of new products with useful pigment properties* sagGffimsj 1* 5-H022SH2 Anisole HAS-D exists in at least two crystal phases. Crystallisation from chloroform yields one phase and crystallisation from acetic acid yields another phase* 2, The commercial pigment appears to exist in the same phase as that formed by crystallizing from acetic acid but there is strong evidence that a solid solution exists as well as a marked change in crystal habit. 3* The presence of Impurities appears to set as a directing influence (solid solution?) while crystallizing from chloroform, causing the formation of a meta stable phase. This means that the two phases can co-exist in varying amounts* The conversion of this meta stable phase to the less soluble stable phase through recrystallization is very slow* It is the presence of this more soluble meta stable phase in varying amounts that accounts for the variation observed in the solubility determinations. DUP050067227 -2 4* Seeding with crystals of the stable phase hastens the conversion of the nets stable phase to the stable (less soluble) phase but the rate of conversion is still alow. m iaiW)SA%$m For the solubility measurements, a sample of K-2292, lot 55110. (5-S02-2NH2 Anlsole HAS-D) eras purified by slurrying with hot dilute hydrochloric sold, washing free of sold, and drying, this was then crystallised twice from chloroform and had a melting point of 287*0* This was subsequently shown to still contain traces of impurities when compared to a sample of pigment prepared by coupling in alcoholic solution. This sample was prepared by Arllna Mills and designated 1264-11B. After crystallising once from chloro form it had a malting point of 296C. A comparison of the optical extinction coefficient of the two materials in chloroform showed only e slight difference between them. This fact served to indicate that the impure sample contained only traces of impurities or that tbs impurities also were strong light absorbers in the region of the spectrum where the optical density measurements were made. Since the curve shape of the two were in good agreement it Is reasonable to conclude that the less pure sample did, in truth, contain only traces of impurities* Solubility measurements wars made by two alternative methods* A weighed amount of pigment was rafluxad in a given amount of chloro form. This was then transferred to a flask and held at a constant temperature of 25C in a thermostat for a definite length of time. This was usually several days, and on some occasions several weeks* Refluxing always put more into solution than could go in at 25C so equilibrium was always approached from the supersaturated side* The solutions were filtered while in a desicator placed in the thermostat* The air in the desicator was saturated with respect to chloroform to minimise evaporation. A given volume of the clear solution was pipetted into a tarsd dish and the residue, after evaporation to dryness, was weighed, in the alternative method a given volume of the clear solution was pipetted into a volumetric flask instead of a tared dish and made to a given volume with chloroform, the spectrophotometrio curve of this solution was obtained using 1 cm light path cells. The optical density was recorded at the Wave length of maximum light absorption. With a knowledge of the extinction coefficient of the pigment at that wave-length, the solubility could bs calculated. The extinction coefficient was determined by completely dissolving 0,016 g. of the pure pigment in one liter of chloroform and obtaining the optical density of the solution at the wave-length of maximum light absorption. The extinction coefficient was conveniently expressed in units of reciprocal concentration for a light path of 1 cm. Concentration was expressed as grams per 100 ml and since a 1 cm light path cell was always used, the concentration of the solution oould be calculated from the equation. < DUP050067228 3 co,. - aafagg&g&hw Shis method was always found to he in good agreement with the gravimetric method, hence because of its simplicity it was used exclusively in the letter pert of this work. At the start, "as la" technical grade chloroform was used and later redistilled chloroform was used but no difference could he ascribed to any variation in the quality of the chloroform* light micrographs were obtained using our standard equipment* So difficult or unusual techniques were involved because the crystals obtained from chloroform and acetic acid were quite large and did not require extremely high magnification* X-ray diffraction curves were obtained from the Experimental Station's Sorth American Philips X-ray diffraction unit which pro vides a graph plotting diffraction angle 2 against relative intensity of the diffracted beam* Filtered copper X alpha radiation was used in all cases* That the original phase and the phase after crystallising from chloroform ware different was established by obtaining X-ray diffraction records of each material. The "as is" material was that specially pre pared by coupling in alcoholic solution and designated as 1264-11B. It was considerably purer than commercial materiel but gave an X-ray diffraction curve sufficiently similar to commercial material so no phase change, existed here. Some 1264-11B was crystallised from hot chloroform and this material was shown to exist as a different phase* Figures I end IX show the X-ray diffraction records and clearly illustrate the change of phase* Figure III shows the X-ray record of 1264-11B material after crystallising from hot glacial acetic acid* Uhls curve bears a displaced peek for peak relationship with the Mas is" materiel indicating a larger space lattice for the *as la" material* The region at the diffraction 2,. angle of 25* is also modified with respect to relative intensity* A marked change In crystal habit along with solid solution affects will cause changes such as these observed. That a marked change in crystal habit is possible is illustrated in Figures I? end V which ere light photomicrographs of the crystals forming from hot glacial acetic acid and from hot chloroform* DUP050067229  4 Figure 1 X-Rag Diffraction Curve PUre SNfyZm Artook 7ls /s' zo is Values () 0 Values () DUP050067230 5 30 15 ZO 15 10 S ZQ Values () DUP050067231 -$ Fig. IV Pur 5 N02~2HH2 Anisole --> NAS-B Crystallised from HOA Fig. V Pure 5 HO2-2HH2 Anisole --y S-D Crystallised from CHCl^ DUP050067232 - 7* One of the ways in which the presence of small amounts of impurities can be detected is by noting the increase in amount of dissolved substance when the ratio of substance to solvent is increased* This measured solubility Should be a linear function of the ratio of substance to solvent, and an abrupt change in slope should indicate the saturation point for one of the Impurities, or the mador constituent. A pure substance would show a plot of a 4? line for the region before saturation and aero slops after saturation, In other words, after sufficient pure substance has been added to a solvent to saturate it, adding more will not ohms the amount that. goes into solution* "When such an experiment was performed on purified K-2292 <5-NQ2-2NH2 Anisole^p KAS-D) the amount in solution did Increese with the ratio of substance to solvent suggesting impurities* This was not surprising because impurities were suspected in smell amounts, but no simple linear relationship existed* Identical ratios gave solubilities further apart than could be attributed to experimental error* It was suspected that this discrepancy was in some way connected with the type of crystals produced during the experiments* To test this point, the mother liquor from one of the trials giving an unusually high solubility, was divided into two portions* 1 To a clear filtered portion was added some of the crystals separated from the mother liquor of a trial which had yielded a low solubility* To the other portion, Which still contained the original crystals, was added some original purified K-2292 in an amount such that the ratio of solid to solution was the same for eaeh of the two portions of mother liquor* The reasoning was that if there was something about the crystals that could alter the amount in solution, seeding a "high concentration" solution with "low concentration" crystals should cause a lowering of the high concentration* The original purified K-2292 was added to an identical portion of the high con* centration mother liquor to act as a control, eliminating the possibility of the existence f a state of super-saturation as an explanation for the high concentration. As a parallel experiment, some of the pure 5-KO2-2HH2 Anisole-> KAS-D (1264-11B) after crystallization from chloroform was also used as tho seed crystals for a different high concentration" solution* The concentration of all of these seeded solutions was examined as a function of time* It was observed that the solubility did fall off with time for all but the control* The pure crystals caused the greatest decrease in solubility* The control, which was that seeded with original purified K-2292, showed a slight increase in Solubility* This was expected since purified K-2292 still does contain some impurities. Table I shows the solubility figures obtained. DUP050067233 T*BLB 1 aouream HBAsroEwaiTS af t er c h t mal s bk d is q BL3-|alatiipy..at gfg-ig Seed crystals A an b ** C (Control) ...J2-------- .-48.--........at- 0,069 0.072 0.069 0.055 0.066 0.071 3MU 0,060 These sere obtained from a solubility trial in which the ratio of solid to solvent mas 0.100 g./lOO ml. The solubility of the crystals for this trial was 0.064 g./lOO ml. These crystals were added to a mother liquor derived from a ratio of solid to solvent of 0.080 g./lOO ml. JL These were obtained by a CEG1* crystallisation of pure 5~N02-2NH2 Anlsole --^NAS-D (1264-1IB). They had a solubility before crystallisation of 0.042 g./lOO ml. These crystals were added to a mother liquor derived from a solid to solvent ratio of 0.100 g./lOO ml. These were simply more purified K-2292. They were added t the same mother liquor used for seeding with crystals *A". They were added in such an amount that the ratio of solid to solvsnt was increased from 0.080 g./lOO ml, to 0,100 g./lOO ml. making it com parable to the ratio in the HAM experiment, after the addition of the seed crystals. These observations can be explained on ths basis of a poly morphic existence for 5**B0g2ilH2 Anlsole --7 NAS-0, For the sake of simplicity. 1st it be assumed that ws are concerned with only two phases, under normal c onditions, pure 5-HO2-2HH2 Anlsole ---7 5AS-D will crystallise from chloroform to give a phase that is stable for the set conditions of temperature and solvent. This phase can be designated alpha phase. In Idle presence of impurities, and these impurities used be present in only small amounts, the tendency for another phase to appear can become quite marked. The mechanism by which this tendency operates can be through the forma* tion of a solid solution of the impurity and a new phase of the 5-K02-2HH2 Anlsole SA8-D. It is also conceivable that a solid solution of an impurity with ths original phase eould constitute DUP050067234 9 the heir phase. This phase which is really a meta stable phase, can be designated beta phase. It then becomes possible to have both phases co-exiat and the amount of beta phase will be roughly determined by the amount of *phasa directing4* impurity in solution. This amount Is in turn dependent on the ratio of pigment to solvent and on the tem perature. It mey be quite critical and be decided to some extent by the whim of the crystal that is forming. The type of nuoleation pro vided for the crystal can play a very important role in the nature of the crystal that is produced. Since a mete stable phase is a more soluble phase. It is evident that the measured solubility of a system when the solid phase conslets of two phases will be e variable depending on the ratio of these two phases. This will not be an equilibrium con dition, but where the surface energy difference between the two phases is slight or where the stable phase is present in only smell amounts, the conversion of mats stable to stable can be very slow. In the crystal seeding experiment previously described, increasing the amount of alpha phase by deliberately adding it, changed the rate of conversion to alpha phase by supplying a greater number of alpha phase nuclei. The measured solubility then fell off with time as would be required for the then new ratio of alpha to beta phase, it follows that no simple statement can be made regarding the solubility of this Naphthanil** pigment in chloroform as long as poly-phase materiel exists in eontect with the solution. 1* Prepare 5-H022KH2 Anlsole NAS-D in a phase different from that of the commercial pigment in large enough quantities to test its pigment properties. This may be accomplished by refluxing in a proper solvent and possibly seeding with the right type of crystal. 2. Examine other pigments for evidence of heretofore unknown polymorphism and evaluate for pigment properties the various poly morphic forms. 3. Study in greater detail the conditions of temperature, solvents, addition agents, etc., that control the phase and crystal habit of a pigment. rS.B. 1232 3? P* 1268 P* 1285 3 P. DUP050067235