NOTES
July, 1963 spectra of diflu~raminoethane~ have been obtained. The F19 spectrum exhibits a single broad band 129 p.p.m. domnfield from trifluoroacetic acid and is otherwise uninformative. The methyl resonance displays a typical 1 : 2 : 1 triplet due t o coupling (7 c./ sec.) with the methylene protons, and its center is 5.9 p.p.m. to the high field side of external benzene (no bulk-susceptibi1it.y corrections). The latter shift compares well with the methyl shift in a host of related ethane derivatives* and supports the assumption that the electron withdrawal power of substituent groups is almost completely attenuated by the C-C bond. The methylene portion of the CZHJKFz spectrum contains twelve peaks: a triplet arising from coupling (28 c./sec.) t o the two fluorines, each component of which is further split into a 1:3 :3 : 1 quartet by the methyl protons. The measured value of B C H ~ - B C H ~ was 2.25 p.p.m., which, according to ( 3 ) , corresponds to X N F ~= 3.27. It is tempting to associate the group electronegativity of -NF2 derived herewith the “orbital electronegativity” of nitrogen, for a three bonding valence state, as calculated by Hinze and JaffB.’O (The calculations were for neutral atoms, so it is important to note that we are neglecting the effect of partial charges on the atoms.) These authors found that the orbital electronegativity for (r orbitals was linearly related to the amount of s character. Thus, the electronegativities of intermediately hybridized orbitals, such as occur in nitrogen compounds, become available by interpolation. From the data of Hinze and Jaff6,1° an N orbital electronegativity of 3.3 (Pauling scale) corresponds to a bonding c orbital of S4Y0 p character. Mashima” attempted to explain the observed dipole moment of NF, in terms of the hybridization of lone pair and bonding wave functions. He concluded that the hybrids of the N atom could be related simply to the observed bond angle, and the latter predicts 83% p character. I n a more general treatment of the same problem, including the contribution of the polarity of the N F bond, La Paglia and Duncan12 calculated a bonding wave function for SFawhich was about SOYo p in the N part. (9) J. W.Fraaer, J. Inorg. Nucl. Chem., 16, 63 (1960). (10) J. Hinze and N. H. JaffB, J . Am. Chem. Soc., 84, 540 (1962). (11) M. Mashima, J . Chem. Phys., 24, 489 (1956). (12) S.R. La Paglia and A. 6. F. Duncan, abzd., 34, 1003 (1961).
RADIOCARBON-LABELED COl\ilPOUNDS PRODTJCED BY THE NEUTRON PRRADIATION OF GUANIDINE
HYDROCHLORIDE‘ BYTHOMAS W. LAPPABD ROBERT W. KISER Department of Chemastry, Kansas State Universitu, Monhattan, Kansas Receiued January 8, 1969
The formation of carbon-lblabeled products resulting from the neutron irradiation of crystalline cyanoguanidine was studied by Lapp and Kiser,2 and they (1) This work was supported in part by the U. U. Atomic Energy Commiseion, under Contract No. AT(l1-1)-751 with Kansas State University, and is E portion of a dissertation to be presented by T. W. Lapp t o the Graduate School of Kansas Stake University in partial fulfillment for the degree of Doctor of Philosophy in Chemistry. Presented a t the 144th National Meeting of the American Chemical Society, Los Angeles, Cahfornia. March 31-April 5, 1963.
1559
indicated that the cyanamide radical, produced by the carbon-14 atom and/or by the accompanying y-radiation, might play an important role in the formation of the radiocarbon-labeled products observed in solution. I n an effort to obtain a better understanding of the actual processes occurring during the recombination period, we have extended these studies to the neutron irradiation of crystalline guanidine hydrochloride and subsequently studied the various carbon-14-containing compounds present when the target material was dissolved in water. It was anticipated that if the recoil carbon-14 atom or the associated y-radiation produced the cyanamide radical, it would be possible to explain the production of the various carbon-14-containing compounds observed in the neutron-irradiated sample as arising from reactions of the radio-labeled cyanamide radicals. Specifically, if the cyanamide radical is involved in the cases of both cyanoguanidine and guanidine HC1, we expect to observe very similar radiolabeled products. If these results were realized, nt would then suggest that the formation of “simple compounds” from the reaction of carbon-14-containing radicals with the solvent may be relegated to a position of minor importance (at least where a large 7-flux js associated with the neutron flux). The formation of “simple compounds” has been discussed in the studies of acetamide3 and a-cyan~acetamide.~We present in this paper our experimental approaches and findings. We utilize these results in the discussion of the possible reactions producing the radio-labeled species observed in aqueous solution. Experimental Sample Preparation and Irradiation-Guanidine hydrochloride (Eastman Yellow Label) was purified by multiple recrystalliaations from methanol and subsequently dried for two hours a t loo0; 4.8 g. of the sample was placed in a quartz ampoule which was then attached to a vacuum system. The ampoule and contents were repeatedly flushed with argon and evacuated t o less than one micron to rigorously exclude any oxygen, not trapped or dissolved in the solid, from the sample. The quartz ampoule was sealed off under vacuum while the contents of the ampoiile were maintained a t liquid nitrogen temperature. The irradiations were carried out a t Oak Ridge National Laboratories in the graphite reactor. Pertinent data are as follows: neutron flux of approximately 5 X 1011 cm.-2 see.-’; irradiation time of 670 hours; 7-ray flux of 4.9 X lo5 r. hr.-l; maximum sample temperature of 80’. The sample was stored for 39 monthi3 following irradiation to allow for the decay of the S 3 5 activity, which was also produced during the irradiation as a result of the C135(n,p)S35reaction. The ampoule was opened ana the tan colored contents were transferred to a Pyrex storage bottle. The sample was maintained in a desiccator over CaCILduring the course of the experimental study. Preliminary Experiments.-Each carrier, or its derivative, isolated from the aqueous solution of a portion of the irradiated guanidine hydrochloride was dissolved either directly or by mean8 of a suitable solvent into the scintillator solution. All carbon-14 radioactivity measurements were made using a Paekard TriCarb liquid scintillation spectrometer. The coun cies and the scintillator solution used in this study have already been described.2 The total carbon-14 activity present in the irradiated guanidine hydlrochloride was determined by dissolution of known portions of the irradiated sample in water. Aliquot8 were taken and the total activity determined by liquid scintillation counting. An average v d u e for three determinations was 16.1 rt 0.8 pcuries for the 4.8-g. sample; i.e., 3.38 i 0.2 murieslg. In order to establish the distribution of the carbon-14 activity among the various species likely to result from the neutron irra(2) T. W. Lapp and R. W. Kiser, J. (3) T. W. Lapp and R. W. Kiser, aba (4) T. W. Lapp and R. W. Kiser, %bad.,67, 612 (1863).
1560
NOTES
diation and subsequent dissolution of the sample in water, solutions of the irradiated guanidine hydrochloride were subjected to analyses for the chemical species listed in Table I.
TABLE I DISTRIBUTION AMONG VARIOUS COMPOUNDS RESULTING FROM NEUTRON IRRADIATION OF GUANIDINE HYDROCHLORIDE
CARBON-14
_---_-%‘
Fraction
NH*C(h”)SH2 (guanidine) CHsC(NH)NHg (acetamidine) “CNHC(NH)NH2 (cyanoguanidine) ?;HzC( NH)NHC(NH)NHs (biguanide) KHN=C(NH2)N=CH (3-amino-
__ -1
L
1,2,4-triazole) NH&=NC(NHZ)=NC(NH2)=N
Average
of total &ctivity---Values obtained
6.4 11.1 12.1
6.5, 6.0, 6.8 11.1, 10.7, 11.4 13.8, 10.8, 11.6
16.3
15.4, 15.7, 1 7 . 7
aqueous solutions of the original irradiated guanidine hydrochloride sample. The total activity isolated in this study was 73.3 =t4.7% of the total carbon-14 activity induced in the guanidine hydrochloride sample by neutron irradiation. Nearly S4Y0of the total activity isolated in this study occurred in four compounds: cyanoguanidine, acetamidine, biguanide, and melamine. Less than 1%of the total activity was found in eight additional chemical species. These eight chemical species are given below with the average value for each compound. The individual values obtained in each determination are given in parentheses. Formaldehyde: 0.2% (0.2, 0.1, 0.3); formic acid: 0.1 (0.1, 0.1, 0.0); acetonitrile: 0.2% (0.2, 0.2, 0.2); methanol: 0.1% (0.1, 0.1, 0.2); methylamine: 0.7% (0.8, 0.5, 0.8); acetone: 0.1% (0.1, 0.1, 0.1); urea: 0.0% (0.0, 0.1, 0.0); oxnmidine: 0.1% (0.0, 0.0, 0.3).
Discussion 4.1 21.8
4.2,
4.6, 3 . 4
2 2 . 3 , 19.9, 23.2
(melamine) Chemical Separations.-Analyses were usually made for one or two carriers in each solution of the target material. The principal problem encountered in the procedures employed in this study was the separation of the various activities free from contamination. Therefore, in an attempt to achieve radiochemical purity, all carriers or their derivatives were isolated and purified to constant specific activity by repeated recrystallizations or distillations. Separation techniquw for essentially all of the chemical species listed in Table I have been previously described.2.8 We note briefly here only those analytical procedures which are new to this study. 0xamidine.-Oxamidine was separated utilizing two different procedures. The first procedure consisted of the addition of a carrier amount of oxamide to an aqueous solution of the irradiated sample. The oxamide was recrystallized and acid hydrolyzed to oxalic acid with concentrated hydrochloric acid. Addition of guanidine resulted in the formation of guanidine oxalate, which was treated in the same manner as described previously.2 This procedure assumes that oxamidine behaves in the same manner as acetamidine when placed in water. The second procedure consisted of an acid hydrolysis of an aqueous solution of the irradiated sample without carrier addition. Following the hydrolysis, a carrier amount of oxalic acid was added and separated as described above. These two procedures gave ewentially identical results. Biguanide (Guanylguanidine).-Biguauide was separated as biguanide sulfate by a modification of the procedure described by Ray.6 The derivative was recrystallized from an ethanol-water mixture. Dissolution into the scintillator solution was accomplished by adding an aqueous solution of the biguanide sulfate to the scintillator solution. Melamine.-Melamine was separated by multiple recrystallizations from water. A portion of the recrystallized melamine was dissolved in a known quantity of dilute hydrochloric acid and an aliquot of the dilute acid solution added to the scintillator solution. J-Amino-l,P,4-triazole.-The triazole was purified by multiple passes through a neutral alumina chromatography column using 95% ethanol. Evaporation of the ethanol solution to a small volume, followed by cooling, resulted in the precipitation of the triazole. A portion of the recrystallized 3-amino-1,2,4-triazole was dissolved in distilled water and an aliquot of the aqueous solution added to the scintillator solution. Evolved Gases.-Upon opening the quartz ampoule containing the target material, the gaseous products, produced by the neutron irradiation and/or the awociated ?-radiation, were collected and analyzed by mass spectrometric techniques. The only product present in detectable quantities was hydrogen. Results of Analysis.-The results obtained by the procedures described above are given in Table I. In all cases, the data presented are based on specific activity measurements and the percentage activity is based on the total activity of aliquot8 of ( 6 ) A.
Vol. 67
X. Ray, 2. And, Cham., 156, 18 (1967).
The recoil carbon-14 atom in guanidine hydrochloride does not appear to be stabilized within the solid matrix in the form of “simple” compounds or in the form of a chemical species which could undergo reaction, such as decomposition or rearrangement, in the presence of water to produce “simple” compounds. Similar observations have also been noted in the investigations of the chemical compounds, containing the recoil carbon-14 atom, produced during the neutron irradiation of crystalline acetamide3 and a-~yanoacetamide.~ This small degree of carbon-14 labeling produced in the “simple” compounds suggests that the radiocarbon labeling process occurs primarily as a result of replacement reactions within the solid matrix in which the recoil carbon-14 atom replaces the carbon atom in the unlabeled molecule of guanidine hydrochloride. As a result of this replacement reaction, a fragmentation of the molecule occurs in which only one or two chemical bonds are broken and the multiple rupture of bonds to produce small fragments containing only a single carbon atom does not occur to any significant extent. The results of this study indicate that the cyanamide radical plays an important role in the production of the final chemical species incorporating the recoil carbon-14 atom. This indication is supported by the results observed in the neutron irradiation of crystalline cyanoguanidine. The production of the cyanamide radical may occur by a replacement reaction of the carbon-14 atom with a guanidine molecule within the solid matrix, after the recoil atom has been slowed down to the point where it is stable toward recombinations. This replacement reaction results in the rupture of a C-NH, bond. This leads to the formation of the radiocarbon labeled cyanamide radical, which may then undergo reactions with other molecules of the matrix to produce the final chemical compounds observed. There appears to be no significant interaction of the solvent with the irradiated target material. This can be observed by a comparison of the percentage activity found in urea and in the target material, guanidine. If the solvent reacted significantly with the various matrixstabilized species, we would expect that the radiocarbon activity in the urea would have been greater than that observed experimentally. Significant amounts of activity were found in four chemical compounds: cyanoguanidine (12%), acetamidine (ll%), guanylguanidine (biguanide) (16%), and melamine (22%). The formations of cyanoguanidine, acetamidine and melamine are suggested to occur in a manner similar to that previously postulated in the study of the neutron irradiation of crystalline cyano-
XOTES
July, 1963 guanidine.2 A. possible method for the formation of biguanide may be postulated to 0ccu.r by equation 1.
NH&14NH
+ ?;HZC(NH)KHa --+KH,C14(NH)KHC(SH)NHZ (1)
Certainly, alternate possibilities for the formation of biguanide-CI4 could be written. Degradation studies of cyanoguanidine, melamine, acetamidine, and biguanide, which would indicate the percentage of the carbon-14 labeling a t each carbon position, mere not performed, so we are unable to indicate specifically the degree of labeling of the carbon-14 positions in the product molecules. The neutron irradiation of crystalline guanidine hydrochloride does not cause incorporation of carbon-14 into the "simple" molecules. We would suggest that the incorporation of the recoil carbon-14 atom into the more complex chemical species occurs oia replacement reactions of the recoil carbon-14 atom with the guanidine molecule of the matrix to produce the cyanamide radical. This radical then further reacts with other species present in the matrix to produce the final products observed. The study of the radiocarbon-labeled compounds produced by the neutron irradiation of cyanoguanidine2 and the results of this study appear to occur by the same process, i.e., the intermediate formation of the radiocarbon-labeled cyanamide radical. Certainly the final products observed in solution in both of these studies are readily explained in terms of similar reactions. Acknowledgments.--The initial stages of this research were supported in part by a grant from the Petroleum Research Fund administered by the American Chemical Society. Grateful acknowledgment is hereby made to the donors of said fund. PREPARATION AND STUDY 03' ORDERING I N A(B1o.33Nb0.6~)03 PEROVSKITE-TYPE COMPOUNDS BY FRANCIS GALASSO AND JANE PYLE rnzted Azrcraft Corporatzon, Research Laboratorzes, East Hartford, Connectacul Recezued Janunrg 16, 1963
The perovskite structure adopted by many ABQ3type compounds can be described by a cubic unit cell with a large X ion at the center, smaller B ions situated a t the corners, and oxygen ions on the edges. When ions of more than one element are present in the B position, the possibility of these ions being ordered exists. A study of Ba(B'o.3bo5)03-type compounds demonstrated that size and charge difference of the B position ions had an important, effect on their ordering.' In a more recent investigation of A(B'o.33Tao.67)03-type compounds, where A is a barium or strontium ion and B' is a smaller divalent ion, these results not only were substantiated but it also was found that the degree of longrange ordering in the B position ions decreased as the difference in the size of these ions became smaller.2 In order t o test the generality of these results for other perovskite-type compounds with two different ions in the B position, a study of ordering was undertaken in a n (1) F. Galasso and W. Darby, J . Phya. Chsm., 60, 131 (1962). (2) F. Galasso and J. Pyla, Inoru. Chcm,, P, 482 (1963).
1561
_1
i
w
u
t 3 E
1. 4
z
0 0 4 X
w
r
U
0
LT
0 i
W
u
c2 a
0 3 0 U
oa 0
06
07 IONIC
Fig. 1.-Ionic
os RADII
69 OF
I O
I I
12
B' I O N , A H R E N S V A L U E S .
radii of B' ions us. cell size for A(B'0.33B''o.6,)013type compounds.
analogous series produced by substituting niobium for tantalum in the A( B'0.33Tao.6,)03 compounds. The results of this study are presented in this note. Experimental Most of the compounds were mixed according to the equation
ACOs
+ '/3B'O + '/&b205
A(B'o.aNbo.e7)03
+ COz
--+
where A is a strontium or barium ion and B' is a divalent metal ion. The mixtures were heated a t 1000" for 10 hr., reground, and reheated a t 1400'' for 4 hr. Powder X-ray photographs then were taken of the compounds using a Philips 57.3-mm. radiiis camera with Cu Ka! radiation and settings of 40 kv., 30 ma. for 4 hr. For compounds in which B' was cadmium or lead, the X-ray photographs urged for indexing were taken using the powders prepared a t 1000" because the perovskite phafie was found to decompose a t higher temperatures and either a phase became predominant.8 BasNbrOla or SrsSb4OI6 When the B' ion was iron, strontium or barium oxide was used in place of the carbonates and the compounds were mixed in proportions dictated by the equation
A0
+ 'IsFe + '/J7ez03 + II3Nb2O5 A( Ferro33XbV0.6i) 0
3
These samples were made into pellets, sealed under vacuum in silica capsules, and heated for approximately 10 hr. a t a maximum temperature of 11100° because they melted through the silica a t higher temperatures The procedure of heating the compounds to approximately 1400", when possible, before taking Xray powder diffraction photographs a t room temperature was adopted from a similar study of A(B'o.3aTao.o7)Oa-type compounds for the following reason.2 When the samples in that study were prepared a t 1000" or lower, their X-ray pattern showed ordering lines which were often weak and diffuse and sometimes not even visible. However, if the samples could be heated several hundred degrees higher, presumably the size of the ordering domain8 was increased which in turn caused the reflections due to ordering to become much sharper. Since similar behavior was oherved (3) F,Galasso and L. Kate, Acta Cryet,, 14, 647 (1961).
