United States Patent Office Patented Apr
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2,829,48 United States Patent Office Patented Apr. 1, 1958 1. 2 at least two primaryamino groups para to the central methane carbon atom by a single recrystallization from a relatively small volume of solution. 2,829,148 A further object of the invention is to provide a process PURE FICATION OF CYANDES OF 5 for purifying di- and tri-primaryamino triarylmethane dye TRARYLETHANEDYES cyandies which is readily and economically carried out with a minimum of equipment and which results in a Lyman Chaikley, Washington, D.C. good yield of substantially pure crystalline dye cyanide. No. Drawing. Application December 15, 1955 Other objects of the invention will be apparent from Serial No. 553,83 O the following detailed description of the invention. I have discovered that very surprisingly the di- and tri 11 Claims. (C. 260-391) primaryamino triarylmethane dye cyanides are, as a class, quite soluble in triethyl phosphate, often being as much as 2,000 times more soluble in this solvent than in ethyl The present invention relates to the purification of 5 alcohol, and that the cyanides may be precipitated in Sub cyanides of triarylmethane dyes, and more particularly, stantially pure crystalline form from solution in this sol to the purification of cyanides of di- and tri-primary amino vent. Moreover, triethyl phosphate apparently has the triarylmethane dyes. effect of converting dye carbinol, which, as has... been The triarylmethane dyes are highly colored compounds pointed out, often has properties very similar to the cor having at least one auxochromic group, such as an amino 20 responding dye cyanide, to the more easily separated or hydroxyl group, at a position para to the central original dye. methane carbon atom. The cyanides of these dyes are The usual method of recrystallization by cooling a hot colorless, or nearly colorless, but are photosensitive when, concentrated solution is not applicable to solutions of the in the presence of a suitable activator, they are irradiated cyanides of di- and tri-primaryamino triarylmethane dyes with ultra-violet and shorter wave lengths and the original in triethyl phosphate because the cyanides are little more highly colored dye is regenerated. This makes these dye soluble at 100° C. than at room temperature in this sol cyanides of great value in actinometry and for photo vent. However, they may be precipitated in substantially graphic and photoduplication processes. pure form by the addition of a suitable amount of water. The preparation of the cyanides of triarylmethane dyes Some of the literature presents conflicting data on the by treatment of the dye with a soluble ionized cyanide is 30 solubility characteristics of triethyl phosphate. For ex known. The dye cyanides formed by this process are ample, the 36th edition of the "Handbook of Chemistry necessarily contaminated by the original dye and by dye and Physics' (Chemical Rubber Publishing Company, base (carbinol) formed by hydrolysis of the dye in the Cleveland, Ohio, 1954) on pages 924-5 indicates that 100 presence of alkali in the reaction medium. ml. of water will dissolve only 100.g. at 25 C., and that For use in photosensitive systems, it is necessary that 35 the triethyl phosphate is decomposed by water. On pages the dye cyanides be relatively free from dyes and dye 1386-7 of the same handbook it is indicated that triethyl bases. Since a dye base has a structure and often chemi phosphate is miscible with water with no suggestion of cal properties that are quite similar to the cyanide of the decomposition. I have found the latter data to be correct same dye, separation of the two may require repeated under the conditions in which I use triethylphosphate. recrystallization of the crude dye cyanide obtained by 40 The crude dye cyanide goes readily into solution in the the action of an alkali cyanide on a dye. Some of the triethyl phosphate at room temperature with stirring, al dye cyanides, such as that of malachite green, are rela though the solution may be heated to obtain what little tively soluble in conventional organic solvents used for advantage may be gained. It is preferred that the solu this purpose and can be recrystallized efficiently without tion of crude dye cyanide be concentrated since substan the use of large quantities of solvent and the handling of 45 tially pure, crystalline dye cyanide can be precipitated from large volumes of solutions. However, certain other such a solution and the overall volume of solvent used triarylmethane dye cyanides are relatively insoluble in to purify a given amount of crude dye cyanide will be such solvents, making their purification extremely, difficult. less the more concentrated the solution. The concentra For example, Pararosaniline cyanide is quite difficultly tion of the triethyl phosphate solution, however, is not soluble in the usual recrystallizing solvents. L. C. Joffe, 50 : critical in the process. "Photochemische Studien inder Triphenylmethanreihe" Solutions of the present dye cyanides in triethyl phos (Dissertation, Zurich, 1921), pp. 36-37 recrystallized this phate have a peculiarity which may be used to advantage dye cyanide from alcohol, but found that the crude prod in this method of purifying them. While the cyanides uct had to be extracted 15 to 20 times with hot alcohol to are virtually insoluble in pure water, they may be more get it into solution, and that the whole recrystallization soluble in a mixture of critical proportions of triethy process had to be repeated 2 to 3 times in order to obtain phosphate and water than in pure triethyl phosphate. a pure, product. This requires liters of alcohol and ex This is particularly true of New Fuchsine cyanide and a pensive equipment to handle this volume and put it real advantage may be obtained in this case by initially through the additional operations of heating and cooling. dissolving the crude dye cyanide in a mixture of tri However, this is the best method of purification of this 30 ethyl phosphate and up to 40% of water based on the type of crude dye cyanide reported in the literature. volume of the solution and in that way obtain a more The di-and tri-primaryamino triarylmethane dye cya concentrated solution of crude dye cyanide. nides are, as a class, difficultly soluble in most organic The amount of water to be added to precipitate the solvents and examples of such dye cyanides are Rosaniline 65 dye cyanide from solution is not critical and will vary in cyanide, the cyanide of Cclour index No. 677, Pararos accordance with such factors as the relative ease of aniline cyanide, the cyanide of Colour index No. 676, precipitation of the particular di- or tri-primaryamino and New Fuchsine cyanide, the cyanide of Colour Index triaryl methane dye cyanide being purified, whether tri No. 678. ethyl phosphate, alone, or a mixture of this solvent and It is the primary object of the present invention to M. v. water was used to dissolve the crude dye cyanide, and provide a process for purifying sufficiently for photo 70 the purity required of the final product. In general, chemical use, a crude triarylmethane dye cyanide having when liquid water is added, its amount will be 2 to 10 2,829,148 3 4. volumes based on the volume of the original triethyl The following examples, which must be carried out in phosphate solution. the absence of ultra-violet radiation because the triethyl The dye cyanide will, of course, be precipitated re phosphate is a photoactivator for the tye cyanides, are gardless of how rapidly the water is added. However, presented as illustrative of the invention. if the water is added very rapidly the dye cyanide is 5 likely to be precipitated initially as a tar (even though Example I.-Purification of New Fuchsine cyanide, the this may crystallize on standing) and to carry down with cyanide of Colour Index No. 678 it dye that would have remained in solution if the pre Teng, of dry, crude New Fuchsine cyanide, prepared cipitate had been produced initially in a crystalline form, by the reaction of the dye with sodium cyanide in aqueous The preferred rate for adding water, based on volume of O solution, is put in a 400 ml. beaker with 75 ml. of tri the original dye cyanide as unity, is 400 volume of water ethyl phosphate and 25 ml. of water and brought into per hour to 2 volume of water per hour. The slower solution at 25 C. by stirring. Solution is complete in rates of addition give the larger and purer crystals. For a few minutes. The solution is filtered, returned to its best results, the solution should be stirred while the water beaker and treated with water added slowly at 2 ml, per is being added. 5 hour while the solution is stirred. After 100 ml. of water One preferred method is to add slowly a relatively has been added the nearly colorless crystalline powder is small proportion of water and obtain a first crop of large, collected on a filter, washed with water and air dried. easily separated crystals of very pure dye cyanide and This is pure enough for use in photosensitive preparations. then to add more... water rapidly to the mother liquor to A second crop of slightly less pure material may be obtain a second crop of less pure product. 20 obtained by treatment of the mother liquor with 700 ml. The precipitated crystalline dye cyanide may be sepa more water added all at once. rated by any suitable means, for example, by filtering. Example 2.-Purification of pararosaniline cyanide, the The separated material may be washed with hot water cyanide of Colour Index No.