Vol. 74 TABLE VAPOR Boiling point,
Water
60.000 65 70
75 80 85 90 95 100 105 110 115 120 125 130
Discussion
111
PRESSURE OC.
1Pentanethiol
76.470 82.569 88.721 94.918 101.167 107.457 113.802 120.193 126.638 133.131 139.671 146,256 152.896 159.580 166.314
OF 1-PENTANETHIOL Vapor pressure pobsd bc~led mm. Eq. 1 Eq.2
-
149.41 187.57 233.72 289.13 355.22 433.56 525.86 633.99 760.00 906.06 1074.6 1268.0 1489.1 1740.8 2026.0
-0.01
-0.01 .00 - .01 .O1 - .01 .06 .05 .06 - .01
+ .01 + .01 -+- .02 - .01 + .06 + .02
+ + + +
3. .05
-
- .11 - .1 - .1
.03 .09
.o
+ ..o1 + .2 + .3
-
.2 .0 -1- . 3
The Entropy in the Liquid and Ideal Gas States.---The calorimetric and vapor pressure data have been used to calculate the entropy of l-pentanethiol in the liquid and ideal gas states a t 298.16'K. Table IV summarizes the results. TABLE IV PENTANETH THIOL MOLALENTROPY, CAL.D E G . - ~ 0-12'K. Debye, 6' freedom, 0 = 134.9 0.218 12-197.46' Solid, graphical .fCsatd d In T 33.863 197.46' Fusion, 4190/197.46 21.219 197.46-298.16' Liquid, graphical JCsatd d In T 18.882 Entropy (fO.15) of liquid a t 298.16'K. Vaporization, 9825/298.16 Compression, R In p/760 Gas imperfection
74.18 32 95 - 7 95 0 00
Entropy (f035) of i d 4 gas at 1 atin. and 298.lfi"K.
[cONTRIBUTION
NO. 112 FROM
!IO
1%
The stated purpose of this investigation is to provide data that will guide the computations by incremental methods of the thermodynamic functions So, (H: - H,"),( H t - F;)/T and CpO for the n-alkane thiols of interest. Reliable computation of such functions is not yet possible on the basis of existing data. However, i t is of interest to compare the difference between ideal gas entropies for ethanethio12 and 1-pentanethiol with that between propane and n-hexane, which differ from the two thiols by the replacement of an SH group by a CH3 group. The experimental ideal gas entropies a t 298.16'K. for ethanethio12 and 1-pentanethiol (this paper) are 70.77 and 99.18 cal. deg.-' mole-l, respectively. The corresponding values for propane7 and n-hexanea are 64.51 and 92.93 cal. deg.-l mole-l. The differences between the respective pairs are 28.41 and 25.42 cal. deg.-l mole-'. This excellent agreement is undoubtedly partly fortuitous but suggests that similar incremental relationships exist between thiols as in hydrocarbons of related structure. Because of the extensive thermodynamic information already available for hydrocarbons, this circumstance will facilitate the compilation of tables of thermodynamic functions for the alkanethiols. (7) (a) K . S. Pitzer, Znd. Eng. Chem., 86, 829 (1944): (b) Kemp and Egan, THIS JOURNAL, 60, 1521 (1938). (8) Liquid entropy 298.16'K. = 70.76 cal. d e g . 3 mole-', D . R Douslin and H. Id Huffman, i b i d . , 68, 1704 (1946); entropy of vaporization 298.16'K. = 25.29 cal. deg.-1 mole-1, from d a t a of N , S. Osborne a n d D. C. Ginnings, J . Research Null. Bur. Sfnndavds, 39,453 (1947); compression, R l n (p/760) = -3.21 cal. deg.-l mole-:; gas imperfection, ( d B / b T ) p = 0.09 cal. deg.-1 mole-', 5 (defined hy PV = RT B P ) = - 455 - 28.5 exp 1175/T cc. mole-1, previously unpublished but based on ( b C , / b p ) ~a n d AHvap d a t a of G. Waddington and D R Douslin, Tms J O U R N A L , 69, 2275 (1947).
+
R ARTLESVILLR, OKLAHOMA
JACKSUN I,ABURA?ORY,
E. I. D U
h N T . DE x E . \ i O L R S A S D CO.]
Infrared Spectra of Organic Compounds Exhibiting Polymorphism BY A. A. EBERT,JR.,
AND
H. B. GOTTLIEB
RECBIVED OCTOBER 3, 1951 I t has been shown that infrared spectrometry is a new and useful tool for the study of polymorphism. Examples of its use have been cited, including a series of five phthalocyanines and three other crystalline organic compounds. The polymorphic forms of the Iatter, while giving identical spectra in solution, showed as crystals marked differences in infrared absorption.
Little has been published about infrared absorption by polymorphic modifications of the same conipound. If infrared spectra of a compound's crystal modifications were found to be identical, one could confidently conclude that transition from one form to the other does not involve intramolecular changes. If, on the other hand, the spectra of polymorphic crystal modifications were found to be not the same, one could not entirely dismiss the possibility of a transition, accompanied by intramolecular shifts of linkages in the latticed molecules. Dissimilarity of vibrations in crystal modifications of the same compound could be caused by mere difference in latticing, but i t could also be due to a
combination of two causes, different latticing together with different linkages inside the latticed molecules. Actually, we discovered appreciable differences between infrared absorption spectra of diverse crystal modifications of the same compound. Indeed, the spectra could be thought to be those of separate compounds. This was the case with phthalocyanines, 2-chloro-4-nitrobenzoic acid, allylthiourea and anthranilic acid. Hence, it is difficult to identify a compound in its crystalline phase by reference to known spectra, if the latter do not include the spectra of all polymorphic forms of the compound.
SPECTRA OF ORGANIC COMPOUNDS EXHIBITING POLYMORPHISM
June 5, 1952 12
a-form. 20 28
36
12
&form. 20 28
‘1’
-CHLORO-4-NITROBENZ
36 ’
-CHLORO-4-
I
OIC
NITRM)LNLOffi
2807
KID-I
’
’
ACID-U
ANTHRANILIC A C I D - I I
1
>-
t
1
COBALT PHTHALOCYANINE
I
,
I
IA
I
NICKEL PHTMLOCYANINE
1 1
2 c I Y
1 ALLYLTHIOUREA-
I
I ,
ZINC PHTHALOCYANINE
J J
8
24 32 8 16 24 32 Bragg angle, degrees. Fig. 1.-X-Ray diffraction patterns characteristic of the a- and p-forms of phthalocyanine and its derivatives. 16
8 16 24 32 32 Bragg angle, degrees. Fig. 2.-X-Ray diffraction patterns of the polymorphic forms of three crystalline organic compounds. 8
16
24
Barnes, Gore, Williams, Linsley and Petersen’ and also Gore and Petersen* have shown the importance of considering crystal orientation effects in Literature.-Well known are the changes in in- infrared spectroscopy because of the small inherent frared absorption which are caused by changes of polarization of radiation in a prism spectrometer. state (e.g., Richards and Thompson1), but few pub- Study of our X-ray diffraction patterns indicate lications refer to variations in infrared absorption that the materials included in our survey exhibit no which are the result of a compound’s transition strong orientation effects. Information obtained in Germany after the war from one solid modification to another solid modification. Most of these publications have been con- contained two references to polymorphism of metal cerned with detecting infrared absorption changes phthalocyanines and its discovery by the X-ray , ~ ~this discovery, the American inresulting from modification of the crystal form of m e t h ~ d . ~For inorganic compounds and one paper refers to crys- vestigators gave credit to George Susich, who also tallization in a polymer. However, the infrared discovered the polymorphism of metal-free phthalospectral differences associated with the polymor- cyanine. l1 J$’e have adopted Susich’s nomenclaphic modifications of crystalline organic compounds ture12 calling “alpha,” in all cases, the phthalocyado not appear to have been previously investigated. nine modification which is unstable to transition in Hunt, Wisherd and Bonham,2 Keller and HalfordI3 aromatic solvents, and “beta” the modification and Wagner and Hornig4 have reported that dif- which is stable to transition when stored in aroferences exist between infrared spectra of inorganic matic solvents a t room temperature. The patent polymorphic forms. Mochel and Hall5 have ob- literature mentions polymorphic pairs of copper, (7) R. B. Barnes, R. C. Gore, E. F. Williams, S. G. Linsley a n d E. M. served that new or more intense bands occur in A n a l . Chem., 19, 620 (1947). crystallized neoprene which are absent in the Petersen, (8) R . C. Gore and E. M. Petersen, Ann. N . Y . A c a d . Sci.. 61, 924 amorphous polymer. (1949). Lecomte6 has described the effect of water of (9) U. S. Office of Technical Services, Publication Board Report crystallization together with other studies on infra- 74892 (1947), pp. 9060-61. Obtained information of work by Kircher a n d Berthold. red spectra of inorganic crystals. (10) Field Information Agency Technical German Dyestuffs and (1) R . E. Richards and €1. W . Thompson, Proc. Roy. Sac. (London), A196, 1 (1948). (2) J. M.H u n t , hI P. Wisherd and L. C. Bonham, A n a l . Chcm., 22,
1478 (1950). (3) W. E. Keller and I?. S Halford, J . Chcm. P h y s . , 17, 26 (1049). (4) E. L. Wagner and D P. Hornig, ibid., 18, 296 (1950) (5) E. Mochel and M. €3. Hall, THISJ O U R N A L , 71, 4082 (1949). (6) Jean Lecomte, “Lc Ragonnement Infrarouge,” GauthierViilars, Paris, 1949.
Intermediates, FIAT Final Report 1313, Vol. 111. Dyestuff Research, Technical Industrial Intelligence Division, U. S . Department of Commerce, Washington, D. C., 1948. Publication Board Report 85172. Obtained information of work b y G. Susich. pp. 412 and 462. (11) George Susich, Anal. Chem., 22, 426 (1950). (12) R. H. Kienle13 reversed this nomenclature. H e calls Susich’s alpha form “beta” a n d Susich’s beta form “alpha.” (13) R. H. Kienle, Official Digest, Federation of Paint a n d Varnish Production Clubs, January, 1950, p. 48.
A. A. EBERT,JR., AND H. R. GOTTLIEB
2808
'
jY
VOl. 74
CORAL1
PHTHbl.OCYANlhlf
- AL%A
FORM
C004LT
PHTH4LOCY4NINE
-
FORM
~
I'
11
Y
\I
*Z!NC ,
- BET4 FORM
PH'nPLOCIAhiihE ! I ,
- BETA FORM ,
~
1
I
I ~
8 9 10 11 12 13 14 15 Microns . Fig. 3.-Infrared spectra of the alpha and beta forms of copper phthalocyanine and phthalocyanine in Kujol suspensions.
9 10 11 12 13 14 I 5 Microns. Fig. 4.-Infrared spectra of the a- and ,%forms of three phthalocyanines in Nujol suspensions.
nickel and zinc phthalocyanines.14 a- and pcopper phthalocyanine have also been found to give two characteristically different electron diffraction patternslj The polymorphic modifications of allylthiourea and anthranilic acid have been described by LV.C. McCrone.16 When this paper had just been completed, our attention was called to David N. Kendall's lecture on infrared spectra of polymorphic forms, given a t the A.C.S. Meeting in Boston, Mass., April, 1951.17 Experimental
copper sulfate and 13 g. of ammonium sulfate was heated to 105' and a stream of gaseous ammonia was passed through the suspension until ammonia was no longer absorbed. Then, the flow of ammonia was reduced to a slow current. The reaction mass was heated t o 225 to 230' over 0.5 hour and held a t this temperature for 5 hours. After cooling to loo', the crude pigment was isolated by filtration and washed with methanol.18 The 8-modification, thus obtained, may be ground to a finely divided pigment by the finishing method, disclosed in reference,lS e.g., by milling the crude pigment with sodium chloride and tetrahydronaphthalene. a-Nickel Phthalocyanine.-A mixture of 120 g. of phthalic anhydride, 180 g. of urea, 49.7 g. of nickel chloride hexahydrate, 0.5 g. of ammonium molybdate and 200 ml. of trichlorobenzene was heated to 200' and agitated a t this temperature for 4.5 hours. The reaction mass was cooled to loo', filtered and the filter cake was placed in a steam still together with one liter of water and 110 ml. of 30% sodium hydroxide. The trichlorobenzene was removed by steam distillation and the crude pigment (@-form)was extracted with 1% hydrochloric acid at 70' for 1.5 hours, filtered, washed and dried. The dry product was then extracted with acetone in a soxhlet apparatus. Twenty grams of the extracted dry powder was milled with 180 g. of dry sodium chloride and 1800 g. of s/a-inch steel balls for 72 hours a t 70 r.p.m. The salt was removed by extraction with 1% aaueous hvdrochloric acid a t 70'. The isolated pigment- cokained -9.82% Ni. Calcd. for CanHlsNsNi: Ni, 10.28; yield 82%. @-Nickel Phthalocyanine.-The crude phthalocyanine, which served as starting material for the a-form, was subjected to the finishing method described in reference 19, e . g . , to milling with sodium chloride and tetrahydronaphthalene. A finely divided P-nickel phthalocyanine was obtained. u-Zinc Phthalocyanine.-A mixture of 128 g. of phthalonitrile, 18.0 g. of zinc powder, and 450 ml. of trichloroben-
3
4
5
6
NICKEL PHTHALOCYANINE
BET4
7
Sample Preparation. a-Copper Phthalocyanine.-A mixture of 82 g. of phthalonitrile with 10.6 g. of copper bronze was agitated in 400 ml. of ethyleneglycol a t 137-140' for 24 hours. After cooling to 80°, the reaction mass was drowned into ethyl alcohol, isolated by filtration and then extracted with ethyl alcohol to remove all unreacted phthalonitrile. T h e alcohol was displaced by water and the aqueous presscake slurried in 1.5 1. of water containing 10 ml. of concentrated aqueous ammonia and 0.5 g. of ammoniun chloride for 1.5 hours a t 70". After filtration, this purification step was repeated. The yield of the dried a-copper phthalocyanine was 777,. Found: Cu, 11.37; N, 19.13. Calcd. for C32H1&;8Cu: Cu, 11.04; N, 19.48. The copper phthalocyanine separated from the ethyleneglycol in the modification which is unstable in aromatic solvents. P-Copper Phthalocyanine.-A mixture of 155 g. of phthalonitrile, 315 1111. of nitrobenzene, 49.6 g. of anhydrous - _. - -. (1.1) K. 1%. W i s w a l l , Jr , U. S. €'.iteut 2,486,351(issued 10-25-49). ( 1 5 ) 12. A . llaiiiumnt-l arid E L'ao Norman, J . Appi Physics, 1 9 . IIO!J7 1lU4s).
(16) \V. C. hlcCrone, A n d . Chent., 21, 421, 1016 (1949). (17) David N. Kendall, abstracts of papers read a t A . C . S. bleeting, Boston, hlass.. April, 1951, Division of Physical and Inorganic
Chemirtry. p. 21'.
3
4
5
6
7
8
(18) H. T. Lacey, U. S. Patent 2,318,787(issued 1-13-50). (1'3) D. P. G r a h a m , I:. S. P. 2,656,730(issued 6-12-51).
June 5, 1952
SPECTRA OF ORGANIC COMPOUNDS EXHIBITING POLYMORPHISM
2809
Microns. 3 4 5 6 7 8 9 10 11 12 13 14 15 Microns. Fig. 5.-Infrared spectra showing variations between specFig. &-Infrared spectra showing the variations occurring tra of the polymorphic forms of a compound, solid phase. among three polymorphic forms of a compound. In soluThe modifications in solution give identical spectra. tion, all three give identical spectra. zene was heated to 200” over the period of one hour and kept agitated a t that temperature for 12 hours. The reac- obtained by crystallization from solvents and Modification tion mass was allowed to cool to IOO’, was filtered, and the I1 by crystallization from the melt. filter cake was extracted with cold trichlorobenzene, then Anthranilic Acid.-Anthranilic acid of du Pont manufacwith warm ethyl alcohol to remove unreacted phthaloni- ture consisted principally of Modification 11. Crystallizatrile. The product was then twice extracted with 1.5 liters tion from water produced Modification I , and from the melt, of water, containing 42 ml. of concentrated hydrochloric Modification I11 was obtained. acid, a t 70” for 1.5 hours to remove all excess zinc metal and Instruments.-The X-ray diffraction patterns were obzinc oxide. The isolated dried pigment was pure; yield tained with a Norelco Geiger counter X-ray spectrometer 25%. Found: Zn, 11.19; N, 19.13. Calcd. for CIHI~- employing nickel filtered radiation from a copper target N8Zn: Zn, 11.32, N, 19.40. This was the @-modification. tube. The samples were in the form of dry powders held The a-modification was obtained by milling the pigment with in a recessed block of “Lucite” acrylic resin. dry sodium chloride, in the manner described in detail under The infrared spectra were produced by a Perkin-Elmer a-nickel phthalocyanine. singlebeam spectrometer (model 12C) using rock salt optics. /?-Zinc Phthalocyanine.-The transition of a- to &zinc All the crystalline samples were ground in Nujol and scanned phthalocyanine was very easily effected by heating the a- in an 0.025-mm. cell. The solutions, used in the infrared, form for 8 hours in boiling acetone. 2-chloro-4-nitrobenzoic acid, allylthiourea and anthraCobalt Phthalocyanine.-The @-modificationwas synthe- of nilic acid were made up in concentrations of about 10% and sized by reacting finely divided cobalt metal with phthalo- were scanned in an 0.12-mm. cell. nitrile in ethylene glycol a t 190’. When the pigment was solutions of a- and @-copperphthalocyanines used in ball-milled with sodium chloride, the a-form was obtained. theThe region were prepared by agitating the crystalAlthough the cobalt phthalocyanine was not as pure as the line ultraviolet sample in cu-chloronaphthalene a t room temperature other phthalocyanines described in this paper, it is believed and clarifying the solution by filtering through one inch of to be satisfactory for our purpose. #209 Celite. The filtered solutions were clear and gave no Metal-free Phthalocyanine.-Phthalocyanine may be perceptible Tyndall effect. synthesized by any of the conventional methods. We used the phthalonitrile fusion with cyclohexylamine as reducing Discussion of Figures.-The X-ray diffraction agent and followed reference 20. The a-modification was patterns are shown in order to characterize the obtained by milling the crude pigment with sodium chloride as described in detail under a-nickel phthalocyanine. The polymorphic crystal modifications whose infrared @-modification was obtained by following the finishing spectra were measured. The distinctive patterns method, disclosed in reference,*’ e.g., by milling the pig- of Figs. 1 and 2 show that the crystals of all inment with sodium chloride and xylene. vestigated modifications were well developed, 2-Chloro-4-nitrobenzoic Acid.-Modification I was produced by crystallization from benzene. Modification I1 excepting thdse of cobalt phthalocyanine. The infrared spectra of the phthalocyanines in suspenformed from the slowly cooling melt of the acid. Ally1thiourea.-Modification I (Eastman Kodak Co.) was sion in Nujol are shown in Figs. 3 and 4. The (20) W. L. Rintelman, U.S. Patent 2,486,167 (issued 10-19-48). (21) 0. Stallmann, U. S. Patent 2,556,729 (issued 6-12-61),
strong bands a t 3.4, 6.85 and 7.25 microns in the suspension spectra in Figs. 3, 4,5 and 6 are due pri-
2x10
1 1 \‘.WL)BRHAEG~IE, ~ E.
K.KATZENELLENBOGEN, K. DOBKINER AND T. F. GALLAGHERVol. 74
inarily to Nujol absorption. There is marked similarity between the modifications of the same compound in the 3-5 micron region with noticeable difierences occurring among the skeletal frequencies, particularly in the range of 12.5 t o 14.5 microns. a-Copper phthalocyanine, when suspended in cyclohexanol, undergoes transition to the p-form. This was followed, a t room temperature, by the change iii infrared absorption as rccorded in Table I. ‘rA131,E 1 l i n e i:i minutes
I &rorIli
by I . K . ,
