NOTES
April, 1956 of carbon and tin. They tried to produce it in three different kinds of experiments: the first involved the addition of fluorides; the second, vacuum-evaporated silicon. The results of each of these were analyzed by X-ray diffraction a t room temperature. I n the third, Debye photographs were taken of pure silicon a t 700". The first two experiments were, in the opinion of this writer, open to alternative explanation. The following attempts were made to repeat the last experiment. Experiments The first attempt to repeat this experiment was performed with powdered silicon ("Hyper pure" from du Pont) in a fused silica capillary at 700". The Debye-Scherrer hotograph, taken in a camera designed by W. L. Bond, ofthese laboratories, showed none of the lines listed by Heyd, Khol and KochanovsU. A second attempt to repeat the experiment was made with silicon furnished by H. C. Theuerer of these laboratories which was prepared by decomposition of Sic14 with hydrogen. The resulting silicon was deposited from the vapor state onto a tantalum tape. A rod of this polycrystalline silicon was cut and fitted to the specimen holder of a commercially available high-temperature camera built by Central Research Laboratories, Inc., Red Wing, Minnesota. Debye-Scherrer photographs of this sample were taken at room temperature and a t 700, 800 and 900". No extra lines appeared at the higher temperatures, although the film was over-exposed to the point of halation. Additional evidence for the non-existence of the hightemperature form was obtained by P. D. Garn of these laboratories who ran a differential thermal analysis of the "hyper-pure" silicon and found no evidence of a phase transition between room temperature and 1O0Oo. This experiment waa repeated three times.
Conclusions X-Ray diffraction photographs taken a t 700,800 and 900" coupled with differential thermal analysis indicate no phase transition in pure silicon between room temperature and 1000". This evidence is contrary to the report by Heyd, Khol and Kochanovsk6 that a non-cubic modification of silicon exists a t 700". Acknowledgments.-The writer wishes to thank S. Geller for fruitful discussion, F. Barbieri for skillfully and carefully preparing the crystalline rod for the second experiment and V. Bala for taking the high temperature photographs. THE STABILITY OF METAL CHELATES OF SUBSTITUTED ANTHRANILIC ACIDS BY WILLIAM F. HARRIS^
AND
THOMAS R. SWEET
Department of Chsmietry, the Ohio State Uniuersitg, Co2umbu8, Ohio Received October $9, 1966
The effect of a number of substituents on the chelating properties of anthranilic acid was studied. This was done by determination of the apparent formation constants of copper and cadmium with 3 methylanthranilic acid, N - methylanthranilic acid, anthranilic acid, 5-sulfoanthranilic acid, Nphenylanthranilic acid and 3,5-diiodoanthranilic acid in 50% dioxane solutions. The Bjerrum2
-
(1) Abstracted from the doctoral dissertation of W. F. Harris presented to the Graduate School of the Ohio State University, August, 1955. (2) J. Bjerrum, "Metal Amine Formation in Aqueous Solution," P.Haase and Son,Copenhagen, 1941.
509
5
/
O
4
> Y 4 0 _I
2 PKa.
Fig. 1.-Correlation
of log ICav. with pKa: 0,Cu chelabe; , Cd chelates.
titration method as modified by Calvin and Wilson' was adapted to the present work. Experimental Materials .-The metal ion solutions were prepared and standardized by the method described in an earlier publication.' The dioxane waa urified by the method EU gested by Calvin and Wilson.8 &he anthranilic acid was oftained from Coleman and Bell Chemical Go. and was prepared for use by crystallizing several times from 50% acetic acid. The N-methyl, N-phenyl, and 3,5-diiodo derivatives were Esstman Kodak Go. white label reagents. The 3-methylanthranilic acid was obtained from Dr. H. Shechter of Ohio State University. It was prepared by reaction of 3-methylphthalic anhydride and hydrazoic acid in sulfuric acid.' 5-Sulfoanthranilic acid was prepared as described in an earlier publication.4 Procedure.-The weighed rea ent waa added as a solid to 50 ml. of purified dioxane. d a t e r , nitric acid and metal ion were added in this order. The final volume was 100 ml. Nitric acid was not used with the 5-sulfoanthranilic acid. The titration procedure was the same as that described previously.' Calculations.-The constants for the 5-sulfoanthranilic acid complexes were calculated by using the equations that the authors previously derived.'
TABLEI pKa VALUESOF ANTHRANILIC ACID AND SUBSTITUTED ANTHRANILIC ACIDSIN 50% DIOXANE Reagent
3,5-Diiodoanthranilic acid N-Phenylanthranilic acid 5-Sulfoanthranilic acid Anthranilic acid N-Methylanthranilic acid 3-Methylanthranilic acid
P K ~
5.59 6.09 6.24 6.53 6.58 6.64
(3) M. Calvin and K. W. Wilson, J . Am. Chum. Soc., 61, 2003 (1945). (4) W. F. Harris and T. R. Sweet, ibid., 77, 2893 (1955). (5) H. Barkemeyer. Master's Thesis, The Ohio State University, 1952.
510
NOTES
VOl. 60
TABLE I1 CADMIUM A N D COPPER CHELATES Metal
Reagent
hf eta1
3-Methylanthranilic acid
Cd Cd
3-Methylanthranilic acid
cu
N-Methylanthranilic acid N-Methylanthranilic acid
cu Cd Cd cu CU
Anthranilic acid Anthranilic acid 5-Sulfoanthranilic acid 5-Sulfoanthranilic acid N-Phenylanthranilic acid N-Phenylanthranilic acid 3,5-Diiodoanthranilic acid 3,5-Diiodoanthranilic acid
concn. lo', M
Reagent concn. X IO', M
1.283 1.283 1.004 1.004 1.283 1.283 1.004 1.004 I .05 1.05 1.004 0.502 1.283 1.283 1.004 1.004 1.283 1.283 1.004 0.502 1.283 1.283 1.004 0.502
7.07 13.41 6.62 10.52 7.54 12.31 6.75 9.96 7.20 10.91 7.47 7.39 4.47 6.66 4.59 6.86 5.34 8.86 7.08 7.11 10.51 6.50 5.38 5.17
x
Cd Cd cu CU Cd Cd cu cu Cd Cd cu cu Cd Cd cu cu
The equations uwd to cnleulute the formation constants for the metal chelates of anthranilic acid and the 3-methylK-methyl-, N-phenyl- and 3,5-diiodoanthranilic acid were .. .
n=
Na+
+H+-
+A +
K A - OH- - H - (TER + TU
K R- = H 7( T a n
+ A + OH-
- Na+ - H+)
K~ x
10-4
(from graph)
RI X l o - * K a v X 1 0 - 8 (from (from graph) graph)
0.32 0.28 7.9 7.9 0.30 0.28 3.7 3.0 0.16 0.16 14 14 0.26 0.26 8.7 6.0 0.21 0.19 0.63 0.54 0.05 0.06 0.45 0.45
4.9 4.9 44
18
44
18
6.0 4.4 24 24
1.1 0.9 11
5.8 4.4
1.4
K, X lo-* (calcd. from K I and Ksv.)
1.2
1.o
11
0.48 0.48 40 40 0.33 0.33 11 10 0.98 0.73 2.0 1.6 0.21 0.28 1.6 1.6
1.4 1.4 110 110 0.44 0.44 13 16
6.3 4.7 1.3 5.6 5.6
1. &me of the deviation in this graph may be attributed to the presence Of the amino group, since changes in the availabilitv of the N electrons for chelation are Got necessarily indicated OH- - Na+ - H+) by the pKa values. The stabilities of the copper chelates are considerably more deDendent than the cadmium chelates on the pKa of the reagents, as is shown by the greater slope of the copper curve in Fig. 1.
HR represents the reagent A represents the total added concentration of HNOa K represents the ionization constant of the carboxyl group T Mrepresents the total added metal concentration THRrepresents the total added reagent concentration
-
THE IONIC CHARACTER OF TRANSITION METAL HYDRIDES
Since titrations of the reagents with NaOH showed that the pK Of the protonated nitrogen wa8 less than for all the reagents, this ionization constant waa not considered in the ca1c';lations.
Results and Discussion The negative logarithms of the ionization constants, obtained from the half equivalence points of titration Curves made in 50% dioxane, are given in Table I. The chelate formation constants are shown ill Table II. The concentrations of metal ion and reagents in the table are the total added concentrations of each of these substances before the addition of sodium hydroxide. No marked increase in the stability of the metalanthranilic acid complexes was observed as a result Of any Of the ring or N-substitutions that were studied. In general, the stability constants follow the same trend as the ionization constant,^ of t)he reagent,. This correlation is shown graphically in Fig.
BY G. G . LIBOWITZ AND T.R. P. GIBB, JR. Department of Chemistry, Tufts Un~uermty,Medford, Mass. Received December 8 , 1966
The available l i t e r a t ~ r e ~reveals -~ that the radius of the hydrogen atom does not remain constant in different transition metal hydrides. Neither the assumption of covalent bonding nor of metallic bonding with the hydrogen in interstices of the metal structure, yield a consistent relation between the radii of the atomsand the observed internuclear distances, Values ranging from 0.27 to 0.80 8. have been reported for the radius of the hydrogen atom in these compounds. Because of the similarity between the heats of formation of rare earth hydrides and saline hy(1) This research WVBSsrmmmd by the Atomic Energy Commission.
:I
z:
~~;;f;,P'~$';,;i~~~;
22 (1952). (4) K. E. Rundip, J . A
Fr$i;,an,
Acla Cryrf., ',
~ Chem. . Ror., T S , 4172 (1951).
