THE results reported in Part I (preceding paper) suggested the possibility of preparing the iron pigment and similar substances by the action of metals on the dehydration products of phthalamide (I), namely, o-cyanobenzamide (11) and phthalonitrile (111).
As has been indicated (Part 11), o-phthalonitrile was not at first thoroughly investigated as a source of phthalocyanines because preliminary experiments with magnesium oxide, which yields a pigment with great facility when heated with o-cyanobenzamide, had shown no comparable reaction. Moreover, it was at first believed that the formation of pigment proceeded through the fixation of metal by an acidic hydrogen atom.In 1931, Heilbron and Irving directed our attention to the reaction between o-dibromobenzene, cuprous cyanide, and pyridine, first studied by de Diesbach and van der Weid (Helv. Chiwz. Acta, 1927, 10, SSS), who formulated the intensely blue, insoluble product as a complex pyridine salt, [C,H,(CN),,C,H,N],Cu.The same substance was also formed from phthalonitrile , cuprous bromide, and pyridine, and Heilbron and Irving suggested that it might in reality be a copper phthalocyanine. Furthermore, they showed that sodamide reacted with phthalonitrile in quinoline at 150" to yield some 15% of a substance resembling metal-free phthalocyanine in properties. We are greatly indebted to Professor Heilbron for communicating these facts to us.We find that many metals and metallic derivatives react with phthalonitrile to yield compounds of the phthalocyanine type. The reaction is generally more ready with the nitrile than with o-cyanobenzamide, but magnesium oxide and antimony are exceptions in this respect. In the most favourable cases the reaction proceeds with considerable evolution of heat : it may become uncontrollable when large quantities of reagents are used. The temperature necessary to start the reaction varies from 135" to the boiling point of the nitrile (294") according to the nature of the metal and its availability (see p. 1027). A general examination of the capacity of metals for combination with phthalonitrile is in progress, but the results of preliminary work may be classified as follows :
Dent, Linstead, and Lowe : Phthalocyanines. Part V I . 1033 217, Phthalocyanines. Part V I . The Xtructure of the Phthalocyanines.
Limtead and Lowe : Phthalo G ya.tziiaes. Part V . 1031 216. Phthnlocyanines. Part V . The iWoleculaz. Tt'eiqht of Nagnesium Phthulocyunine. DETERMINATION of the molecular weights of phthalocyanines enables an independent estimate to be made of the number of C, units in the molecule. The magnesium compound (dihydrate) was selected for examination, as its solubility is greater than that of other phthalocyanines. It did not dissolve sufficiently in molten naphthalene, benzophenone, thymo!, or camphor to furnish accurate cryoscopic determinations ; even when the delicate thermometer described below was used, the experimental error was comparable with the observed depressions. 4-Chloroquinoline dissolved rather more of the compound and had a convenient melting point, but was unsuitable on account of its hygroscopic nature and great tendency to supercool.The ebullioscopic method has the advantage that stronger solutions can be made, but even so, 100 parts of boiling naphthalene dissolve only about 0.4 part of magnesium phthalocyanine and the maximum possible elevation of the boiling point is about 0-04°, and quinoline proved to be an unsuitable solvent. A very delicate platinum resistance thermometer was therefore constructed for use in conjunction with the ordinary apparatus of Beckmann (2. physikal. Chem., 1908, 63, 187). The molecular weights obtained a t different concentrations were 550, 565, 538; mean, 551 (calc. for C,,H,,0,N8Mg, 572). The molecule therefore contains one atom of magnesium and four C, units.The apparatus could not be used for deterrning the molecular weight of phthalocyanine itself for the remarkable reason that the metal of the heating coil attacked phthalocyanine with the formation of metallic derivatives. A platinum heater could not be constructed. EXPERIMENTAL.Apparatus.-The platinum resistance thermometer, P, was made from 48 cm. of platinum wire, 1/500" in diameter, wound on a former of thin mica. The leads were of silver wire, the end effect of these being compensated by the incorporation of one turn of the same wire on a similar former. The measurement of resistance was carried out by means of a standard Callendar-Griffiths bridge. Owing to the exceptionally high " fundamental interval " of the thermometer (7.629 ohms) it was necessary to insert an additional standard resistance in the compensator arm of the bridge for measurements at the b. p. of naphthalene in order to bring
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