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THE THERMAL STABILITY OF COPPER PHTHALOCYANINE1 BY EMILA. LAWTON' Contribution from Battelle Memorial Institute. Columbtu, Ohia Received November 21, 1967
In the course of investigating the thermal propertiw of copper phthalocyanine and related materials, a sample of copper phthalocyanine was quickly heated t.0 900" in a sealed evacuated Vycor ampule with no visible change in its properties. A second sample maintained at 800" for one hour was also apparently unchanged and its infrared spectrum was identical to unheated material from the same preparation. Although it has been long known that copper phthalocyanine can be sublimed at atmospheric pressure at 580°13this unusually high thermal stability is much greater than might be expected for such a complex organic molecule.4 These results suggested that dicopper heptabenzobis-(tetraazaporphin) (I) might also be sublimable. Using a modification of the method of Ebert and Gottlieb6 for nickel phthalocyanine, a mixture of copper phthalocyanine I and higher polymers was prepared by treating excess phthalic anhydride with pyromellitic anhydride in the presence of urea and CuC12.2Hz0. I and higher polymers are characterized by absorption bands a t 7.5-7.6, 9.1-9.2 and 13.5-13.6~.
a
c-3
I (1) This research was supported by the United States Air Force under Contract No. AF 33(616)-3477, monitored by the Aeronautical Research Laboratory, Wright Air Development Center. (2) Rocketdyne, Canoga Park, California. (3) C. E. Dent and R. P. Linstead, J . Cham. SOC.,1027 (1934). (4) Vanadyl porphyrin is also very stable, subliming in vacuo at 880". W. H. Bonner, Jr., U.8. 2,740,794 (April 3, 1956). (5) A. A. Ebert, Jr., and H. B. Gottlieb, J . Am. Chem. SOC.,74, 2806 (1952).
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The copper phthalocyanine was removed easily from the mixture by sublimation in high vacuum below 530". Further increasing the temperature slowly to 696" gave no additional sublimate but led to total decomposition of the sample. The residue ' of the original sample and represented 81 weight % contained free copper, carbon and an amorphous nitrogen-containing material. Condensable gaseous decomposition products were collected a t - 196". The condensate contained HCN (90%) and NH3 (10%) by mass spectographic analysis. The stability of copper phthalocyanine for one hour at 800" in a closed system contrasts with the total decomposition of similar polymeric materials at 700" under continuous pumping. This difference in behavior seemed to indicate an unusual reversible dissociation as a first step in the pyrolysis of this type of compound. An attempt was made to determine whether a reversible decomposition of copper phthalocyanine could be observed by measuring its sublimation pressure in a static system. Pure sublimed copper phthalocyanine (230 nig.) was sealed off at a pressure of less than mm. of mercury in a quartz Bourdon gage having a precision of better than A 2 mm. up to a total pressure of three atmospheres. The gage registered no pressure until the sample was heated above 500". The pressure rose slowly at temperatures above 550°, but an equilibrium pressure never was attained. For example, after two days it had risen to 945 mm. and was still increasing. The sample evolved gaseous products corresponding to a maximum of about 9% decomposition during a five-day period. Five days at temperatures between 550 to 575" resulted in the formation of 3.6 cc. of gas. The per cent. decomposition was calculated from the measured volume of the gaseous decomposition products. By analogy with the measured decomposition of I, it was assumed that the evolved gas was HCN and it represented one-fifth of the total decomposition products. It must be concluded that the stability displayed by copper phthalocyanine at 800" and higher is due to a very slow rate, i.e., high activation energy, of decomposition and is not a measure of the intrinsic thermal stability of this compound. Acknowledgments are due Mr. Jerry W. Moody for the initial measurements and Mrs. Donna D. McRitchie for preparing the compounds employed in this investigation.
