188 FRYER, GALLIFORD AND YARDLEY: [Analyst, Vol. 88 The Furildioximes Part I. The Structure of the Isomeric Furildioximes BY F. A. FRYER, D. J. R. GALLIFORD AND J. T. YARDLEY (Hopkin & Williams Ltd., Freshwater Road, Chadwell Heath, Essex) The so-called a-furildioxime prepared by the usual procedures is shown to be an approximately 1 + 1 mixture of a and y isomers. When heated under reflux with n-pentanol, the y isomer is converted to a and p isomers, and the mixture is converted in part to the /3 isomer. Pure a-furildioxinie melts at 192" to 193"C, whereas the y and /3 compounds melt a t 182" to 183" C and about 150" to 152"C, respectively. All three isomers are shown to form nickel complexes. FL-RILDIOXIME has been extensively used a s a gravimetric and colorimetric reagent for n i ~ k e l , l + ~ ~ ~ ~ ~ p a l l a d i ~ m ~ , ~ and platinum6 for many years, and more recently it has found favour as a colorimetric reagent for r h e n i ~ m .~ The substance employed by all the workers cited has been called a-furildioxime and, in the absence of any information to the contrary, it seems likely that most samples were prepared by the oximation of furil with hydroxyammonium chloride and then aqueous recrystallisation by MacKair's method.8 This procedure is commonly quoted in the text- b 0 o l t s g ~ ~ 0 ~ ~ ~ and gives a product melting between 160" and 168" C, the higher figure being widely accepted as the melting-point of the pure a isomer. Subsequently, there has been confusion in the literature about the melting-points to be assigned to the several possible configurations.12 9 1 3 We found that repeated recrystallisation from water produced a substance that, after it had been dried, melted at 166" to 168" C; however, assay by treating with an excess of nickel solution and then weighing the precipitate gave an apparent purity of only about 55 per cent.(40 to 60 per cent. on material recrystallised only once). In contrast, by re- peatedly recrystallising the crude reaction product from ethanol, we were able to obtain a specimen melting sharply at 192" to 193" C that gave, when assayed by the excess of nickel method, a purity of approximately 100 per cent. These results led us to suppose that the initial reaction product was a mixture of isomeric furildioximes in which the a (anti-) compound was the minor constituent and that the melting- point most commonly attributed to this isomer was incorrect.Shinra and Tshikawa12 reached a somewhat similar general conclusion, but the configurations they assigned to the three isomers did not correspond with our own tentative findings. Further experiments were therefore conducted to test and amplify our own views, and the results are given below- 1. The "mixture" melting at 167" C: (ex-water) was separated by precipitating the red nickel complex with excess of slightly alkaline nickel solution and then evaporating the filtrate to small bulk, when crystals of a second ( y ) isomer separated. This compound was recrystallised from water, and the dried product was found to melt at 184" C and to contain 12-8 per cent.of nitrogen. (Cl()H8O,N2 requires 12.7 per cent. of nitrogen.) 3. A melting-point diagram for the system a - y isomers was obtained from synthetic mixtures derived from the two procedures outlined above. This gave a eutectic point a t about 164" C, corresponding to a mixture containing about 55 per cent. of the 01 isomer. 3. Ultraviolet and infrared spectroscopic examination showed the differences and similarities listed below- a Y Melting point of isomer, "C . . .. .. .. 193 183 Xmax., m p * * .. .. .. . . . . . . 270to 274 272 to 278 E . . . . .. . . . . . . .. .. 27,000 27,000 Absorption attributed to C : N stretching vibrations Absorption attributed to OH stretching vibrations . . 3210 cm-1 3275 cm-l NOTE-Infrared spectra were produced initially with h'uj 01 mulls in a Perkin Elmer Infracord spectrophotometer, but the absorptions quoted throughout this report are the similar but more precise values kindly determined for us by Dr.J. E. Page, . . 1630, 1580 cm-1 1630, 1560 cm-1March, 19831 THE FURILDIOXIMES. PART I 189 with a Perkin Elmer model 21 spectrophotometer (personal communication from Glaxo Research Ltd.). All ultraviolet spectra were obtained with alcoholic or aqueous solutions and a Beckman DU spectrophotometer. Attempts were then made to produce a sample of j3 (syn-) compound by heating the so-called a and y isomers under reflux in n-pentanol for 7 hours. Treatment of pure y isomer in this way gave a product that consisted largely of the sc compound. The mixed a - y product gave a treacly mass when the pentanol was removed, and this was dissolved in ether and chromatographed twice on silica gel (M.F.C. grade), with ether as eluent.Five fractions were collected, and, after the solvent had been evaporated, the residues were assayed with excess of nickel. The solid obtained from fractions 3 and 4 gave a brown alcohol-soluble nickel complex, which on weighing indicated an apparent purity of 90 per cent., calculated as a 1 + 1 compound of furildioxime and nickel. Other characteristics of this product were- Melting point, "C . . .. . . .. . . .. .. 150 t o 152 Xitrogen content, yo . . . . . . . . . . . . 11.4 (C,,H,O,N, requires 12.7) .Absorption attributed t o C : N stretching vibrations . . -\bsorption attributed t o OH stretching vibrations . . . .3200 t o 3260 cm-l Xrnax., mp - * . . . . .. . . .. . . .. 272 t o 276 ( E = 27,000) . . 1635, 1565 cm-l TABLE I DIFFERENCES IN THE XICKEL COMPLEXES OF THE THREE ISOMERS Nickel Conditions for Colour of precipitation of Amax., content, * Isomer complex complex Solubility mP E % a Red Nearly neutral Insoluble in ethanol 290 t o 292 52,000 11.8 P Brown Nearly neutral Soluble in ethanol 275 t o 287 36,000 24.8 Green Above pH 8 Slightly soluble in ethanol 274 t o 282 37,700 22.6 Y * A ratio of furildioxime t o nickel of 2 t o 1 corresponds t o a nickel content of 11.8 per cent. and a ratio of 1 t o 1 corresponds t o a nickel content of 21.3 per cent. The hydroxyl stretching frequencies shown by the parent dioximes suggest that a higher degree of hydrogen bonding exists in the Q isomer than in the y isomer, and this is consistent with their respective anti- and amphi- configurations.The intermediate position of the. p isomer suggests a moderate degree of intramolecular hydrogen bonding that might be expected with the syn-configuration. Such small differences as were observed with the C : N absorptions are also consistent with the previously reported results for a and /3 mon- oximes .I4 From the evidence offered there seems good reason to supp0s.e that the three compounds we have referred to as a, ,8 and y isomers (melting-points 193", 152" and 183" C) are, respec- tively, the anti-, syn- and aniphi-stereoisomers of furildioxime. All three form nickel com- plexes, that formed with the p isomer being least expected in view of the work of Meisen- heimer,15 but it is suggested that its structure may closely resemble that reported for the palladium - /3-benzildioxime complex.16 The ultraviolet spectra of the ,8 and y complexes (tabulated above) suggest closely similar structures.Other nickel - y dioxime complexes have been reported and shown to be 1 + 1 compoiind~.~~J7~~8 Nickel - a-furildioximate is stoicheiometric, and we found its ultraviolet absorption spectrum to be similar to those reported for nickel dimethylglyoximate and nickel - a-furildi- 0 ~ i r n a t e . l ~ However, unlike nickel dimethylglyoximate, it shows no infrared absorption around 1775 cm-l. Absorption in this region is considered20 to be due to hydroxyl stretching vibrations. We thank the Directors of Hopkin & Williams Ltd.for permission to publish this paper. 1 . 3. 3. 4. 6. 6. 7. 8. REFERENCES Harwood, H. F., and Theobald, L. S., Analyst, 1933, 58, 673. Taylor, C. G., Ibid., 1956, 81, 369. Soule, B. A,, J . Amer. Chem. SOC., 1925, 47, 981. Gahler, A. R., Mitchell, A. M., and Mellon, M. G., Anal. Chem., 1951, 23, 500. Ogburn, S. C., jun., J . Amer. Chem. SOC., 1926, 48, 2493 and 2507. Menis, O., and Rains, T. C., Anal. Chem., 1955, 27, 1932. Meloche, V. W., Martin, R. Id., and Webb, W. H., Ibid., 1957, 29, 527, MacNair, D. S., Annalen, 1890, 258, 226.190 9. 10. 1 1 . 12. 13. 14. 15. 16. 17. 18. 19. SO. FRYER, GALLIFORD AND YARDLEY [Analyst, Vol. 88 Rodd, E. H., Editor, “The Chemistry of Carbon Compounds, Volume IV A, Heterocyclic Com- Welcher, F. J., “Organic Analytical Reagents,” D. Van h‘ostrand Co. Inc., New York, 1947, Huntress, E. H., and Mulliken, S. P., “Identification of Pure Organic Compounds,” John Wiley Shinra, K., and Ishikawa, K., J . Chem. SOC. Japan, 1953, 74, 353. Yamasaki, K., Matsumoto, C. L., and Ito, R., Nippon Kagaku Zasshi, 1957,78, 126; Chem. Abstr. Palm, A., and Werbin, H., Canad. J . Chem., 1953, 31, 1004. Meisenheimer, J., and Theilacker, W., Annulen, 1929, 469, 128. Dwyer, F. D., and Mellor, D. P., J . PYOC. .Roy. SOC. N.S. Wales, 1934, 68, 107. Atack, F. W., J . Chem. SOC., 1913, 103, 1317. Hieber, W., and Leutert, F., Bey., 1929, 62, 1839. Sone, K., J . Amer. Chem. SOC., 1953, 75, 5207. Rundle, R. E., and Parasol, M. I., J . C h ~ m . Phys., 1952, 20, 1487. pounds,” Elsevier Publishing Co., Amsterdam, 1957. Volume 111. & Sons Inc., New York, 1941. 1958, 52, 7003. Received July 26th, 1962