NOTES
43 1
impurities to be liquid-soluble solid-insoluble, the triplie point of the pure substance is 467.12 f 0.01OK. The five determinations of the enthalpy of melting yield a mean value of 1653 f 2 cal./mole and 3.549 cal./ (mole OK.) for the enthalpy and entropy of melting.
Table 111:
Melting Data for AZBN.
[Units: cal., mole, " K ]
Designation
TI
Ta
Serien I Series I1 Fusion Run E Fusion Run F Fusion Run G
455.31 458.21 455.61 457.05 454.75
472.53 473.14 479,72 474.30 476.46
Hi75
Av.
=
AHm
=
Acknowledgment. The authors gratefully acknowledge the partial financial support of the Division of Research of the United States Atomic Energy Commission and C. A. W. acknowledges the support of the Institute of Science and Technology of the University of Michigan in the form of a postdoctoral fellowship. (7)
Cf. J. Timmermans, J . P h y s . Chem. Solids, 18, 1 (1961).
- H46sa
3040.4 3037.1 3039,l 3036.6 3038.5 3038.3 f 1 . 5 1653 f 2
Corrected for enthalpy increments between T I and 455"K., Tz and 475"K., and for quasi-adiabatic drifts. a
The Synthesis and Infrared and Nuclear Magnetic Resonance Spectra of Ammonium Dicyanamide
by JameB W. Sprague, Jeanette G. Grasselli, and William M. Ritchey T h e Standard Oil Company ( O h i o ) ,Research Department, Cleveland. Ohio (Received October 2, 1963)
Since the value of ASm is below the (arbitrary) limit of 5 cal./(mole "K.) prescribed by Timmermans' for the definition of a plastic crystal phase, AZBK meets all the macroscopically observable criteria for plastic crystallinity, i e . , solid-solid transition, low entropy of fusion, high melting temperature, and high vapor pressure. The substance is one of a number of compounds related to bicyclooctane that are being investigated in this laboratory. Discussion of the molecular disordering process leading to the plastic crystal phases mill be deferred until more experimentall evidence becomes available. A brief summary of the thermodynamic properties, is made in Table I V ; those for the gaseous phase also involve the sublimation pressure data.6
The metallic salts of dicyanamide have been known in well characterized forms for many years.' Their infrared spectra, have recently been described. hletallic salts are prepared by methods such as the alkali fusion of cyanamide with melon (or other highl-y condensed members of this carbon-nitrogen system) or the reaction of disodium cyanamide with cyanogeii halide followed by metathetical exchange with an appropriate salt. These reactions were not appropriate to the ammonium salt although a crude sample had been prepared.'^^ We have found that the salt may be obtained by the addition of concentrated solutions of cyanogen bromide to liquid ammonia. Over a period of 1.5 hr. 150 ml. of a glyme (1,2dimethoxyethane) solution containing 100 g. of cyano gen bromide was added to 250 ml. of liquid ammonirt with vigorous stirring. The ammonia evaporated slowly from the reaction mixture which then stood over a weekend. Two phases separated. The super.natant solution was decanted from the solids and dis-. carded. The solids which consisted primarily of ammonium bromide and ammonium dicyanamide were extracted with a mixture of 200 nil. of e;chyl acetate and 200 ml. of acetone which was evaporated to about ~
Table IV : Thermodynamic Properties of AZBN. cal., mole, "K.] T
CP
S"
H o - Roo
[Units:
-(Uo
-
Hoo)/T
Crystal I 65.61 12992 28.49 73.40 15809 33.63 80.79 19052 38.46 ... 83.30 20201 40.05 Liquid 467.12 ... 86.84 21854 40.05 500 (75.92)" (91.86) (24281) (43.30) Vapor ... 101,0' 28290' 30.3' 400 a Values in parentheses are extrapolated from ca. 495°K. * Not corrected for deviation from ideality; L e . , S,,,,, -. Sary.tal 1 = R In P f A H s / T = R In 0.1629 a t m . 12480/400. 350 400 450 467.12
56.83 60.28 65.84
+
W. Madelung and E. Kern, Ann., 427, 1 (1922). ( 2 ) M. Kuhn and R.Mecke, Chem. Ber., 3010 (1961). (3) The synthesis of the ammonium salt and its infrared spectrum (1)
a KBr pellet have been presented recently by M. B. Frankel, et al., J . Org. Chem., 28, 2428 (1963). The bands listed by these authors in the C=N saretching frequency region differ slightly from ours, but it is not possible to determine if.partial cation exchange has occurred in their pellet without data in the 900950 cm. -1 region. a8
Volume 68, Number 2
February, 1964
432
NOTE8
100
0
2
4
b
8
10
12
15
25
20
30
WAVELENGTH (MICRONS) Figure 1. Infrared spectrum of ammonium dicyanamide, split mull.
50 ml. and allowed to crystallize. The crude ammonium bromide amounted to 78 g. or 85% of theoretical. The crystals from the concentrated extracts were filtered, washed with a little acetone, and recrystallized from hot acetone. Ammonium dicyanamide, white crystals weighing 8 g., was obtained in 20% yield from cyanogen bromide. Anal. Calcd. for C2H4K4: C, 28.6; H, 4.8; N, 66.6. Found: C, 29.6; H, 5.4; N, 64.2; melting range: 139-140' to clear melt which solidified to dicyandiamide, identified by its infrared spectrum. The infrared spectrum of ammonium dicyanamide shows characteristic frequencies of the ammonium ion and of the dicyanamide anion. The latter can be assigned as in the excellent discussion of Kuhn and Mecke,2 and the notation of these authors has been followed in listing the bands in Table I. As expected, shifts in the anion frequencies are observed for the ammonium salt, and it is of interest to note that they fall between the values for the E(+ (see below) and Xaf salts. Tl?e bands due to the ammonium ion4are found at 3212, 3160, 3052, 2962, 2842, 1818, 1710, 1451, 1438, 1421, 1377, and 1342 cm.-'. The band positions listed were obtained from a split mull (halocarbon oil, 2-7.4 p ; nujol, 7.4-38 p ) on a Perkin-Elmer 221-G using an expanded abscissa of 25 cm.-l/cm. Positions are reproducible to 2 cm.-'. Figure 1 shows the infrared spectrum of the split) mull on the Perkin-Elmer 21 (15-38 p on PE 221-G with CsBr optics) where it was recorded for comparison with the spectrum of the sample as a KBr pellet. The spectrum of ammonium dicyanamide in water was very similar to that of the mull The infrared spectrum of the ammonium dicyanamide was first obtained as a KBr pellet on a PerkinElmer 21 spectrophotometer. When the high resolution spectrum to obtain accurate band positions was later run on the Perkin-Elmer 221-G with the sample as a mull, some unusual spectral changes were immediately noted. Detailed investigation of these led to the conclusion that almost complete cation exchange occurs I
The Journal of Phvaical Chemistry
Table I : Anion Frequencies for Ammonium Dicyanamide [N(CN)z]- Structure, Czv Cm. -in
Assignment*
505 m 519 m 538 m B1 A N-CN 668 m Ai A C-N-C 927 m 1328 s 2171 s 2229 s 2234 s 2274 8 wg ma (C-N) 3538 w w , (CN) w s (C-PU') 'Intensities given are s, strong; m, medium; w, weak. r, A = bond deformations; wa = symmetrical stretch; wB = asymmetrical stretch.
+
+
in the pellet6 resulting in NH4Br and KN(CN)2. Such occurrences are not uncommon and this observation serves only to emphasize the well documented6need for caution when interpreting spectra of solids in KBr pellets.' The bands due to the potassium dicyanamide are observed at 662, 910, 1316, 1339, and 3460 cm.-l and approximately a t 2114, 2160, 2188, and 2232 cm.-' in the nitrile stretching region (bands too intense for accurate measure). The n.m.r. spectra were obtained on a fully equipped Varian IT-43OOCspectrometer operating at a frequency (4) E. L. Wagner and D. F. Hornig, J . Chem. Phvs.. 18, 296 (1950) : IS, 305 (1950). (5) (a) L. H. Jones and M .M . Chamberlain, ibid., 2 5 , 365 (1956); (b) J. A. A. Ketelaar, C. Haas, and J. van der Elsken, ibid., 24, 624 (1956); (e) F. VrBtnS, J . Inorg. N u c l . Chem., 10, 328 (1959). (6) (a,) A. W. Baker, J . P h y s . Chem., 61,450 (1957); (b) H. Ropke and Wr.Neudert, 2. anal. Chem., 170, 78 (1959); (c) A. Tolk, Spectrochim. A c t a , 17, 511 (1961). (7) Although Kuhn and Mecke present the spectrum of Na[N(CN)Z]as a KBr pellet, no cation exchange is observed (comparing band positions listed by them for N a + salt and those observed by us in exchanged NHI+ salt spectrum). This is probably due to the conditions used in preparing pellets.
NOTES
of 60 Mc./sec. The compound was examined a t 25.0 0.5’ in dilute solutions (-loyo wt. vol.) in both dimethyl sulfoxide-& (DIMS) and 1 1 2 0 utilizing tetramethylsilane (TAIS) as the reference, internally in DMS and externally in DZO. Radiofrequency poweir was held m7ell below saturation intensity and a sweep rate of approximately 0.95 c.p.s./sec. was employed. The spectra were calibrated by linear interpolation between the reference and its BOO-C.P.S. side band. A triplet with broad resonances of equal intensity a t approximately 7.7 p.p.m. below ThlS with a coupling constant of approximately 50 C.P.S. was observed in DMS spectra. No other resonances were observed which were not due to the solvent or the reference. Upon examination in acidified D20,the triplet coalesced with the H2O resonance and the resulting singlet was observed shifted slightly downfield from the normal location of the HzO resonance line. These results are interpreted8j9a,s being due to the presence of protonig attached to a quaternary nitrogen and indicating that no other protons are present in the compound. Spectroscopic as well as chemical evidence therefore has characterized the a,mmonium salt of dicyanamide:
4;33
fluence of ultraviolet irradiation. The set of cornpounds used are metal hexacarbonyls of Cr, Mo, and W. Irradiation is carried out with a 1-kw. high pressure Hg lamp (AHs) in 1 : l ether isopentane mixture st room and a t liquid nitrogen temperatures. The electronic spectrum is obtained using the Beckman spectrometer Model DKI. At 77OK., the formation of a yellow color is observed as soon as the glass is exposed to ultraviolet light. It is formed also in vacuo and at different wave lengths of excitation. The yellow color is relatively independent of the metal that is bound to the carbon monoxide molecules. It disappears a few minutes after the glass is allowed to warm up to room temperature. Exposure at room temperature in ether-isopentane is also found to produce the yellow color. Figure 1 (A) shows the electronic absorption spectra of Mo(CO), solution in 1 : 1 ether-isopentane mixture at room temperature before exposure. This carbonyl has two structureless bands a t 2892 and 2270 8.and
Acknowledgment. The authors wish to acknowledge the experimental assistance of Mr. Harry Adams, Misci Patricia L. Keibecker, and Mr. Herb Grossman. (8) E. Grunwald, A. Loewenstein, and 5.Meiboom, J. Chem. Phys., 27, 630 (1957). (9) J. A. Pople, W. G. Eichneider, and H. J. Bernstein, “HighResolution Nuclear Magnetic Resonance,” MoGraw-Hill Booh Co.. Inc., New York, N. Y., 1959, p. 455.
A New Class of Photochromic Substances: Metal Carbonyls1
by M. A. El-Sayed Contribution N o . 1638, Chemistry Department, 1Jniversity of California, Los Anyeles 34, California, (Received October %, 1963)
WAVE LENGTH (A”)
Figure
Photochromism2 is defined as the reversible coloring of compounds on irradiation with ultraviolet light, y - ~ a y s , ~or&electrons.ab There are a great number of organic molecujles and, to a lesser extent, a smaller number of inorganic clompounds which undergo these reversible color changes. The mechanism for color changes is not unique and differs from one class of compounds to thle other.2 In this communication we report a class of compounds which undergo a reversible color change under the in-
1.
The
electronic
spectra of ultraviolet-irradiated
Mo( CO)e solutions in 1: 1 ether-isopentane mixture: A, spectrum of 415 X l o n 3mole/l. unexposed solution; B, of the same so lution immediately after 20-see. exposure; C, a few minutes a f t e r exposure.
(1) Work supported by the U. S. Atomic Energy Conimissicn, partly from a contract with the University of California a t Los Angeles and partly from a contract to Florida State University, Tallahassee, Fla. (2) For a review on the subject see G. Brown and W. Shaw, Re$. P u r e A p p l . Chem., 11, 2 (1961).
(3)
(a) Y . Hirshberg, B u l l . Res. Council Israel, 7A, 228 (1958); (b) J . Chem. P h y s . , 27, 758 (1957).
V o l u m e 68. Number 9
February, 1964
