ary, the secondary alcohol should react more slowly as is the case for the butanols. This mechanism is in agreement with ester hydrolysis studies in high acid concentrations (10, 1 1 ) . The primary alcohol probably proceeds via an acyl oxygen mechanism. Work is now under way to develop a procedure in which the water formed in the esterification with TFA is measured oia a gas chromatography technique.
(3) S. Veibel. "The Determination of Hydroxyl Groups." Academic Press, New York, N.Y. , 1972, p 77. 1 W. M. D. Bryant, J. Mitchell, Jr., and D. M. Smith, J. Amer. Chem. Soc.. 62, 1 (1940). J . Mitchell. Jr.. and D. M. Smith, "Aquametry," Interscience, 1948, p 267. J. Mitchell, Jr., Anal. Chem., 36, 2050 (1964). V. A. Klimova, M. P. Ch'ang, and F. 6. Sherman, Izv. Akad. Nauk. SSSR, Ser. Khim. 1972, 588;Chem. Abstr., 77, 4 2 8 9 8 ~(1972). American Society for Testing Materials, Designation D1957-63, "Hydroxyl Value of Fatty Oils and Acids, Test Four." 1969. W. J. Youden, "Statistical Methods for Chemists." John Wiiey, New York, N.Y., 1951, p 16. K. Yates and R. A. McClelland, J. Amer. Chem. SOC.,89, 2686 (1967). G. A. Olah, D. H. O'Brien, and A. M. White, J. Arner. Chern. Soc., 89, 5694 (1967).
ACKNOWLEDGMENT Technical contributions of A. G. Chasar of Mobil Chemical are acknowledged.
LITERATURE CITED ( 1 ) S. Siggia. "Quantitative Organic Analysis Via Functional Groups," John Wiiey. New York, N.Y., 1963, p 8. (2) N. K. Mathur, Talanta, 13, 1601 (1966).
RECEIVEDfor review July 26, 1974. Accepted September 26, 1974. The authors wish to acknowledge the financial support of the Sherwin-Williams Company and of the National Science Foundation Undergraduate Summer Student Program.
Quantitative Polarographic Determination of Azides in Cobatt(ll1) Coordination Complexes Leonard F. Druding,' Donna M. Lukaszewski, and Fred D. Sancilio Department of Chemistry, Olson Laboratories, Newark College ofArts and Sciences, Rutgers University, Newark, N.J. 07102
The determination of azide in the more unstable salts has been limited due to inefficient, inaccurate, and sometimes dangerous means of analysis. Numerous adaptations, particularly to small sample size, of gravimetric ( I , 2 ) ,titrimetric (3-71, spectrophotometric (8, 9 1, and polarographic (10-12) methods have been reported. Many of these are inaccurate, and often the errors which occur are due to loss of nitrogen in the decomposition of the azide. Most of the procedures have concentrated on the determination of total azide content, but two (7, I 1 ) have devised procedures for differentiating between coordinated azide and ionic azide in a complex. Biggs and Gaver ( 7 )use titration of two samples to differentiate the types of azides: one is oxidized directly to nitrogen with cerium(1V) to give the free azide ion content, while the second is first reacted with a measured excess of nitrite, and the excess nitrite is then determined with cerium(1V) to give the total azide assay. A polarographic method of analysis offers a number of advantages to this type of analytical determination, principally in the use of very small sample sizes in dilute solutions. Because of its halogenoid character, azide exhibits electrode reactions similar to that of the halogens by forming an almost insoluble mercury(1) salt which creates an anodic current whose magnitude is proportional to the rate of diffusion; this in turn, is dependent upon the concentrat i o n of azide in the sample (13-16). In previous analyses of coordination complexes containing azide, the complex was first hydrolyzed in a buffered solution, and the liberated azide ion was then determined polarographically. Control of the pH was important during hydrolysis to prevent loss by either formation of volatile HN3 or from oxidation of azide to molecular nitrogen. This paper will describe a direct polarographic analysis of the coordinated azide and ionic azide by a rapid, safe, and quite accurate procedure. Author to whom correspondence should be addressed. 176
EXPERIMENTAL A Princeton Applied Research Electrochemistry System, Model 170, was used to collect the direct current polarograms. A standard H-cell with anode and cathode separated by a porous glass frit was first used. However, if the solution was allowed to remain in contact with the internal calomel reference electrode for any length of time, it was observed that chloride ions were interfering and distorting the azide waves. An H-cell with a very fine glass frit does give acceptable results but, in s u b s e q u b t experiments, the polarograms were run us. an external calomel reference electrode where no distortion of the azide waves was observed. A PAR controlledrate dropping mercury electrode was used, and best results were obtained with a drop time of 0.5 sec. T h e usual procedures of deaeration with nitrogen and use of Triton X-100 as a maximum suppressor were followed. T h e compounds analyzed were prepared by methods previously NO ~ )( ~N, H ~ ) ~ ( N ~ ) ] ( cisC~O~)~, described ( I 7 ) : [ C O ( N H ~ ) ~ ( N ~ ) ] [( C and trans- [ C O ( N H ~ ) ~ ( N ~ ) ~ cis] ( Nand ~ ) trans- [Co(NHs)d(N02)2](N3), cis- and trans- [Co(en)~(N3)2l(N03),[C0("3)3(N33], [Co(dien)(N3)3], [Co(dien)(NO~)z(N3)](where dien is diethylenetriamine), and NaN3. WARNING:Most of these azides of cobalt are
EMF
IS
SCE,VOLTS
Figure 1. Polarogram of Co[(NH3)s(N3)](N&. Note the observation of two distinct anodic waves
A N A L Y T I C A L C H E M I S T R Y , VOL. 47, N O . 1, J A N U A R Y 1975
Table I. Results Obtained from the Polarographic Analysis of Several Azide Complexes and Salts Compound
NaN, [Co(NH,),(N,)l(C10,), [Co(NH,),(N,) l(N3l2 cis- [Co("J&NOz) >IN3
Concn S 3
id total
(mequiv/liter)
(mA)
1.00 1.02 3.02 1.00 ~~U~S-[CO(NH,),(NO~)~]N~ 1 . 0 0 2.87 cis-[Co(NH,),(N,),I(N,) 2.25 trans- [Co("J,(NJ J(N3) cis- [ C O ( ~ ~ ) , ( N , ) ~ I ( N O ~ ) 1.00 1.00 trans- [Co(en),(N,) 2](N03) [Co(dien)(NO,), (N3)] 1.00 1.59 [ C o ( d i e d (N3 1.76 [Co(",),(N3)3l0 [Co("&(NJ zI[Co("3) 2(N?),I 1.76
),la
a
4.10 4.14 12.28 4.08 4.08 11.70 9.17 4.04 4.04 4.10 6.38 7.24 7.24
idlmequiv ( X ) (mA-mequiv-l-1.
4.10 4.06 4.07 4.08 4.08 4.08 4.08 4.04 4.04 4.10 4.01 4.11 4.11
-I)
(V,
Eli2 US. SCE)
0.25 0.12 0.11, 0 . 2 1 0.26 0.26 0.17, 0 . 2 2 0.17, 0.22 0.20 0.20 0.15 0.20 0.20 0.19, 0 . 3 4
KO.
of
IX-x 1
measuements
0.03 0.02 0.02 0.01
5 5
0.01 0.02 0.02 0.04 0.04 0.02 0.07 0.03 0.03
6 5 5 6 6 5 3
5 6 6 6
Samples decompose rapidly in solution; polarograms must be run immediately after preparation,
easily detonated, especially as dry salts a t elevated temperatures. Use extreme caution when handling dry salts, store in small quantities. Solutions ranging in concentration from to w 4 M were carefully prepared by weighing samples on a microbalance and dissolving in 0.1M KN03. These concentrations were found to give the best results, as well as being safer to handle in terms of sample size. T h e polarograms were determined a t 25.00 f 0.25 "C in a thermostated cell, and the analyses were run immediately after solution preparation. There was no observable change in p H during electrolysis so that buffering was unnecessary. On long standing, however, there was considerable change in pH, presumably as a result of hydrolysis of t h e azide ligand followed by oxidation. T h e azide diffusion currents were analyzed by t h e procedures described by Bryant and Kemp ( I 1 ).
RESULTS AND DISCUSSION The results of the polarographic determination of azide in coordination complexes of cobalt(II1) are summarized in Table I. A typical polarogram is shown in Figure 1. The values observed for E 112 show a clear pattern of differentiation between coordinated and ionic azide ligands. [ C O ( N H ~ ) ~ ( N ~ )(Figure ] ( N ~ )1)~ shows two distinct anodic potential breaks; one a t 0.11 volts (us. SCE) and the other a t 0.21 volt. [ C O ( N H ~ ) ~ ( N ~ ) ] ( Chas ~ Obut , ) ~ one break, a t 0.12 volt, while sodium azide has a single break a t 0.25 volt. As a general rule for these complexes, the value for E 112 for the coordinated azide was less than 0.2 volt while that for the ionic azide was greater than 0.2 volt. There may be a correlation between the ease of hydrolysis ofsthe coordinated azide and its half-wave potential, with the more labile azides being closer to 0.2 volt. However, t h r e is not yet sufficient quantitative kinetic evidence to support this observation. This technique led to an interesting observation when applied to the analysis of some triazidotriammine complexes. Synthesis of "Co(NH3)3(N3)3" gave two products; a green powder, and shiny, dark green-black crystals, which were first thought to be the geometrical isomers of triazidotriamminecobalt(II1). The green compound showed only one polarographic wave a t 0.19 volt, and three azides per cobalt, while the black crystals showed two breaks a t 0.19 and 0.34 volt, whose diffusion currents were in an approximate ratio of 1:2. Chemical analysis of this compound indicated a ratio of Co:NHs:N3 of 1:3:3. The ihfrared and NMR
spectra gave evidence which was subsequently confirmed by single crystal X-ray diffraction studies (18) that the black crystals were the ionization isomer [Co(NH:,),(N&] [ C O ( N H ~ ) ~ ( NWhy ~ ) ~the ] . azide ligands in the anionic portion of the compound give rise to such a positive halfwave potential exceeding that of ionic azide is not yet clear. The number of known anionic azide complexes are so few, and their properties so hazardous, that no attempts have been made to determine if this high half-wave potential is part of a consistent pattern for anionic complexes. Finally, it should be noted that the diffusion current is the same for coordinated as well as ionic azide (which suggests the same oxidation mechanism a t the electrode) and that it does depend on the concentration of the azide in the system. For all samples analyzed under the experimental conditions stated, an average value of 4.08 mA/ mequiv N3- was obtained. Polarography of micro and semimicro samples of coordination complexes involving the azide ion or ligand is feasible as a rapid and accurate method of analysis that also permits the differentiation between the types of azide in the complex. This method of analysis has been supported by crystallographic studies of other cobalt azido compounds (19).
LITERATURE CITED (1) M. Marqueyrol and P. Loriette, Bull. Soc. Cbim. Fr., 23, 401 (1918). (2) A. L. J. Rao and B. K. Puri, Fresenius' 2. Anal. Cbem., 248, 33 (1969). (3) J. H. Van der Muelen, R e d . Trav. Cbim. Pays-Bas, 67, 600 (1948). (4) R. A. W. Haul and G. Uhlen, 2. Anal. Chem., 129, 21 (1949). (5) E . Krejzova, V. Simon, and J. Zyka. Cbem. Listy, 51, 1764 (1957). (6) R. G. Klem and E. H. Huffman. Anal. Cbem., 37, 366 (1965). (7) W. R. Biggs and R. W. Gaver, Anal. Cbem., 44, 1870 (1972). (8) C. E. Roberson and C. M. Austin, Anal. Cbem., 29, 854 (1957). (9) A. Anton, J. G. Dodd, and A. E. Harvey, Anal. Cbem., 32, 1209 (1960). (10) J. Masek, Collect. Czech Cbem. Commun., 25, 3137 (1960). (11) J. I. Bryant and M. D. Kemp, Anal. Cbem., 32, 758 (1960). (12) R. Schrader and G. Pretzsehner, Talanta, 13, 1105 (1966). (13) J. Revenda. Collect. Czech. Chem. Commun., 6, 453 (1934). (14) I. M. Kolthoff and C. S. Miller, J. Amer. Cbem. Soc., 63, 1405 (1941). (15) H. P. Stout, Trans. Faraday Soc., 41, 64 (1945). (16) R. A . W. Haul and E. Schoiz, Z.Electrochem., 52, 226 (1948). (17) L. F. Drudinq, H. C. Wana. R. E. Cohen, and F. D. Sancilio. J. Coord. Cbem., 3, 165 (1973). (18) L. F. Druding, F. D. Sancilio. and D. M. Lukaszewski, submitted to lnorq.
Cbem., in press. and F. D. Sancilio, Acta
(19) L. F. Druding
Crystallogr., Sect 6, 37, in
press.
RECEIVEDfor review July 22, 1974. Accepted September 12, 1974.
A N A L Y T I C A L CHEMISTRY, VOL. 47, N O . 1, J A N U A R Y 1975
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