plied fields and in analytical chemistry wherever the evolution of gases is concerned. LITERATURE CITED
(1) Balls, .4.K., Hale, W. S., J . Assoc. O$c. Agr. Chemists 1 5 , 483-90 (1932). (2) Knott, J. E., N . Y . Stale Agr. Espl. Sta. Illem. (Ithaca, N . Y.)106 (1927). (3) Norgarrd, .4.17. S., J . Bid. Chem. 38,
501 (1919).
(4) Pack, D. A., IND.EKG. CHEU., ANAL.ED. 4, 393 (1932). (5) Sumner, J. B., Somers, G. F., “Chemistry and Methods of Enzymes,” 3rd ed., p . 218, Academic Press, New York, 1953. (6) Thompson, R. R., IND.ENG.CHEM., ANAL.ED. 14,585 (1842). ( 7 ) Tressler, D. K., Evers, C. F., (‘Freesing Preservation of Fruits, Fruit Juices and Vegetables,” p. 228, Avi Publishing Co., New York, 1936.
RECEIVED for review December 7 , 1957. Accepted September 8, 1958. Contribution 1126, bfassachusetts Agricultural Experiment Station. Research undertaken in cooperation with the Quartermaster Food and Container Institute for the Armed Forces, assigned number 809 in the series of papers approved for publication. Views or conclusions contained in this report are those of the authors, and are not to be construed as necessarily reflecting the views or endorsements of the Department of Defense.
Rapid Spectrophotometric Determination of Manganese Triethanolamine and Peroxide Complexes of Manganese(ll1) E. R.
NIGHTINGALE, Jr.
Ethyl Corp., Detroit 20, Mich., and University o f Nebraska, Lincoln 8, Neb.
b In alkaline triethanolamine solutions, manganese(l1) is air oxidized to form a green manganese(ll1)-triethanolamine complex. At 438 mp the molar absorbance index of the complex is 1 99. The spectrophotometric measurement of the manganese(lll)-triethanolamine complex in alkaline solution offers a rapid and highly selective method for determining manganese. Evidence is presented for the existence of a manganese(ll1)-peroxide complex in alkaline solution.
Absorbances w r e measured using a Beckman Model DU quartz spectrophotometer. All measurements were made in 1-em. silica or Corex cells a t 25” Z!C 1’ C. PROCEDURE
Although the manganese(II1)-TEA complex has been used for polarographic determinations of manganese (9,4, 6, 7, 8), the complex has not been inveetigated previously for use in a spectrophotometric or colorimetric determination.
Pipet an acid sample containing 0.02 to 0.2 mmole (0.001 to 0.01 gram) of manganese(I1) into a 150-ml. beaker. Evaporate, if necessary, to 25 ml., and add 5 nil. of triethanolamine. Add 10 ml. of 9M sodium hydroxide and stir well to dissolve any manganese(I1) hydroxide precipitated by a local excess of sodium hydroxide. If the sample contains more than 75 meq. of acid, use additional sodium hydroxide. Add 1 ml. of 0.1M potassium bromate, and heat the solution to boiling. Remove the sample from the hot plate, bubble air into the solution for 2 minutes, and cool to room temperature. Add 2 ml. of 2 M sodium sulfite. Transfer the solution t o a 50-ml. volumetric flask and dilute to volume. The final solution is 0.6M in T E A (80% solution) and approximately 0.6M in sodium hydroxide. Measure the absorbance at 438 mp and determine the manganese concentration by comparison with standard samples.
REAGENTS A N D APPARATUS
RESULTS A N D DISCUSSION
Chemicals of C.P. grade and distilled water were used to prepare all reagent solutions. Although 9801, triethanolamine (Matheson Coleman & Bell, No. 2885) was used t o develop the analytical procedure, regular (80% minimum) triethanolamine is satisfactory for routine analyses. The triethanolamine can be dispensed conveniently from a 5-ml. hypodermic syringe fitted with a 13-gage needle. Spectra were recorded on a Cary Model 105 recording spectrophotometer.
Manganese(I1) reacts with triethanolamine to form a tan complex which is stable above p H 5.5. Triethanolamine is a weak base with a pK, of 7.77 (1). Below p H 5.5, the fraction of the triethanolamine in the basic form is too small to permit complex formation. Curve C in Figure 1 shows the absorption spectrum of a 1mM solution of the manganese(I1)-triethanolamine complex in O.6M triethanolamine a t a p H of 7.5. The spectrum of 2.0mM manganese-
W
MANGANESE(II) is oxidized by air in alkaline triethanolamine (TEA) solutions, a green manganese(111)-TEA complex (6) is formed according to the reaction: O2 Mn(TEA)2+*= HOzMn(TEA)2+a HEX
+
146
+
e
ANALYTICAL CHEMISTRY
(111)-triethanolamine complex in 0.6-11 triethanolamine and 0.6M sodium hydroxide is shown by curve A in Figure 1. A broad absorption maximum occurs a t 438 nip, n i t h a n absorption minimum a t about 377 nip. The positions of the maximum and minimum are not dependent upon the concentrations ol triethanolamine or sodium hydroxide. The previous polarographic proredures for determining manganese using triethanolamine (2, 4, 6, 7) have involved preparation of the manganese(111)-triethanolamine complex by air oxidation of the manganese(I1)-triethanolamine complex. All attempts in these laboratories to achieve rapid quantitative air oxidation at room tempernture have been unsuccessful for solutions containing more than 0.5 mmole of manganese. I n addition, the absorbance of the solution changes appreciably with time in a manner characteristic of the presence of a second colored species. The absorption maximum at 438 mu for curve A in Figure 1 increases about 3y0 in 60 minutes. The absorption minimum increases by about 39Yo,, and the position of the minimum shifts to longer wave lengths. The increase in absorbance may continue for several hours, after which it begins to decrease. After prolonged standing-e.g., 24 hours-the absorbance becomes constant, indicating quantitative formation of the manganese(II1)-triethanolamine complex. I n a n attempt to achieve quantitative oxidation of manganese(I1) more rapidly, hydrogen peroxide was added to an alkaline triethanolamine solution containing manganese, and a red complex was formed. Curve B, Figure 1, shows the absorption spectrum of the red com-
Figure 1. Absorption curves for solutions of manganese and triethanolamine Manganese(ll1)-TEA complex, ZmM, in 0.6M TEA and 0.6M sodium hydroxide E. Same as A plus excess hydrogen peroxide C. Monganese(l1)-TEA complex, 1 mM, in 0.6M TEA at pH 7.5
A.
plcu formed when excess hydrogen peroxide was added to an alkaline triethano!smine solution containing 2mM manganese. The spectral characteristics of this complex are consistent with those of the unstable intermediate formed by the air oxidation of manganese(I1) in the presence of triethanolamine. This complex also may be prepared by adding hydrogen peroxide or other ouidizing agents, such as sodium peroxide, lead dioxide (PbOs), sodium pcriodate, and osmium tetroxide, to alkaline tartrate, alkaline mannitol, or p H 4 pyrophosphate solutions. The complex appears to be a manganese(II1)-perouidc complex, and not a higher oxidation state of manganese. It is formed only in media which stabilize manganese(III), and does not depend upon the presence of a particular anion-e.g., RInCI6---for its formation. Although peroxide complexes of other transition elements are well known ( I O ) , a manganese(II1)peroxide complex has not been reported previously in the literature. The manganese(II1)-peroxide complex decomposes slowly at room temperature and rapidly a t boiling temperature. At elevated temperatures, the complex appears to disproportionate to form manganese(I1) and liberate oxygen. Thus. while hydrogen peroxide will oxidize nianganese(I1) , the manganese(111)-peroxide complex is formed instead of the nianganese(II1)-triethanolamine complex. Quantitative formation of the manganese I11I) -triethanolamine complex is not rapid because some manganese(I1) always results from the decomposition of the peroxide complex. -4 large variety of oxidizing agents mere inrestigated for the quantitative oxidation of manganese(I1). With the exception of lead tetroxide (Pbs04),only oxygen effected the oxidation. As oxygen appears to be specific in the reaction mechanism, it is probable that the lead tetroxide decomposes to liberate oxygen, and that the latter is the active oxi-
dizing agent. This postulate is supported by x-ray analyses and weight-loss measurements (‘3) which indicate that lead(1V) dioxide decomposes to the lead(I1) monoxide through a well defined series of intermediate oxides including Pb304. each step being accompanied by the liberation of oxygen. The ability of certain oxidizing agents such as the leadIIT’) diovide or sodium periodate to form the peroxide complex, probably through the oxidation of hydroxide to form the hydroperoxide ion, is attributed to the mechanism of the particular reaction; equally strong oxidizing agents, such a. hypochlorite and bromate, do not form the peroxide complex. Similarly, the absence of the peroxide complex in solutions containing lead tetroxide may he explained by the catalytic decomposition of hydroperoxide by lead tetroxide in alkaline solution (9). The addition of lead tetroxide to solutions containing the manganese(111)-peroxide complex causes a rapid decomposition of the complex, and is a n effective procedure for the quantitative preparation of the nianganese(II1)-triethanolamine compleu. In this procedure the oxidation is carried out at boiling temperature because the air oxidation of manganese(I1) is more rapid and the manganese(II1)peroxide complex is less stable than a t lower temperatures. Potassium bromate is added to hasten the oxidation of the hydroperoxide formed upon the reduction of oxygen and to prevent interference by the manganese(II1)-peroxide complex. Bromate n ill not oxidize manganese(I1) in the absence of air. After oxidation is completed, the solution is cooled and a n excess of sodium sulfite is added t o remove the excess oxygen and to decompose any remaining hydroperoxide. If the bromate and the sulfite are omitted, some peroxide complex may form, and the analysis will be less precise. With the previously outlined procedure, calibration data were prepared for
solutions of 0.6 to 5.0mM manganese. These data, which are tabulated in Table I, indicate that the oxidation is quantitative, and that Beer’s law is obeyed in the concentration range studied. The molar absorbance index of the manganese(II1)-triethanolamine complex is calculated to be 199 2. Oxidation of manganese(I1) by air in the presence of bromate is complete within 1 to 2 minutes only if the s o h tions are more dilute than about 4 to 5mM. For this reason. and because t h e practical upper limit in absorbance of 0.8 is obtained with 4mW solutions, the spectrophotometric determination is not recommended for solutions more than about 4 m M in manganese. More concentrated solutions may be oxidized readily with lead tetroxide. It is possible to determine spectrophotometrically the empirical composition of the manganese(I1)-triethanolamine complex, but not of the Inanganese(111)-triethanolamine complex. Solutions of 1 m M manganese(I1) containing 0.75 to 8 m M triethanolamine were prepared with a p H of 7.5. At this pH the manganese(I1) complex was sufficiently stable so that a negligible amount of the triethanolamine remained in the acid form. At 325 mp the absorbances of the solutions increased linearly with Table 1. Relation of Absorbance and Molar Absorbance Index to Concentration of Manganese(lll)-Triethanolamine Complex
Molar Absorbance
Absorbance, Index, mM A ( h = 438 A l p ) uv 0 O(b1ank) 0 005 0 60 0 125 202 Concn.,
1 00 2 00 3 00 4 00
0 206 401
201
606
200
794 999
197 199 199 i 2
0 0 0 0
5 00
198
Av.
Table II. Precision and Accuracy of Spectrophotometric Method
Sample KO. 1 2 3
4 7
8
9
10
11
Precision Absorbance, A 0.415 0.420
0.419 0,418 0.421 0.421 0.419 0.414 0.418 Av. 0 418 f0 0002
Bccuracy Method Spectrophotometer Titration with arsenite Flame photometer
Manganese,
M g . per Liter 57 6 & 0 3 57 5 i0 . 1 579*03
VOL. 31, NO. 1, JANUARY 1959
147
Table 111.
Noninterfering Metal Ions
Antimony(II1) and (V) Bismuth(II1) and (V) Cadmium( TI) Chromium(TI) Copper( IT) Iron(I1) and (111) Lead( TI) I\Iercury(I) and (TI)
Molybdenum( 17) Silver(I) Thallium( I) Tin(I1) and (IV) Titanium(111) Tungsten(VI) Vanadium( IV) Zinc(TI)
triethanolamine concentrations up to 2.0mM. Above 2.0mM the absorbance remained constant, indicating that the empirical formula of the manganese(I1) complex is LIn(TEA)2+Z. Similar formulas have been given by Tettamanzi (11) for other divalent metal complexes of triethanolamine. It has been determined polarographically that the manganese(I1) and (111) complexes have the same empirical formulas, and the empirical formula of the manganese(II1) complex is given as ~ I I I ( T E A ) ~ + ~ . PRECISION AND ACCURACY
The procedure has been applied to samples of iso-octane containing (met hylcyclopentadienyl) manganese tricarbonyl. The samples !yere irradiated with ultraviolet light to decompose the compound, and the manganese was extracted by refluxing the sample with
hydrochloric acid. Replicate samples were analyzed to determine the precision and accuracy of the method. The absorbances measured for nine aliquots of the iso-octane standard are shown in Table 11. The average deviation is 0.5y0of the amount of manganese present. By comparison with standard solutions of manganese sulfate, the manganese content of this iso-octane was calculated to be 57.6 i 0.3 mg. per liter. The results of analyses using a flame photometer and a chemical method are compared in Table 11. On the basis of these determinations the accuracy of the method is given to Zk 0.5%. INTERFERENCES
TiTenty-four metal salts hare been investigated for interference in this determination. Table I11 lists 21 cationic species that do not interfere. Silver(1) and titanium(IT1) give precipitates in alkaline solution which may be removed by filtration. The blue copper(I1)-triethanolamine complex does not interfere because its absorbance a t 438 mp is negligibly small. Of the other ions tested, cobalt(I1) and nickel(I1) interfere slightly. As the molar absorbance indices of the cobalt(I1)-triethanolamine and nickel-
(11)-triethanolamine complexes a t 438 mp are 16 and 25, respectively, large concentrations of either are not permissible. Chromium(II1) interferes more seriously (aM = 110 at 438 mp), and, if present. it must be separated prior to analysis. LITERATURE CITED
(1) Bates, R. G., Schwarzenbach, G., Helv. Chim. Acta 37, 1437 (1954). (2) Issa, I. hl., Issa, R. M., Hewaidy, J. F., Omar, F. E., Anal. Chim. Acta 17, 434-9 (1957). ( 3 ) Lamb, F. K., Ethyl Corp. Research Laboratories, Detroit 20, >rich., unpublished work. (4) ,I.lojzis, J., Proc. Intern. Polarog. Congr. Prague, 1st Congr. 1951, Pt. I, D. 638. ( 5 ) Yovak, J. V. .4.,Kuta, J., Riha, J., Chem. listy 47, 649 (1953). (6) Perisi, R., Ann. chim. (Rome) 44, 59 (1954). (7) Pleva, AI., Chem. lzsty 49, 262 (1955). (8) Riha, J., Serak, L., Ihid., 49,32 (1955). (9) Schumb, W. C., Satterfield, C. W., T1 entworth, R. L., “Hydrogen Peroxide,” p. 480, Reinhold, Kew York, 195.6
-I--.
(10) Ihid., p. 657. (11) Tettamanzi, A., Carli, B., Gazz. chim. ital. 63, 566 (1933). RECEIVED for review June 16, 1958. Accepted -4ugust 6, 1958. Pittsburgh Conference on Analytical Chemistry and Applied Spectroscopy, Pittsburgh, Pa., ?*larch 1958.
Identification of Alcohols by Microscopic Mixed Fusion Analysis DONALD
E.
LASKOWSKI and OTIS W. ADAMS
Department of Chemistry and Chemical Engineering, Armour Research Foundation of Illinois Institute o f Technology, and Department of Chemistry, Illinois Institute of Technology, Chicago, 111.
b
Work was undertaken to investigate microscopic mixed fusion methods for identification of compounds other than polynuclear aromatics and ben2,4,6zene derivatives. The trinitrobenzoate esters of 29 alcohols were prepared and purified. With naphthalene and phenanthrene as reagents, mixed fusion preparations were made with each ester and each reagent. The significant melting points were then measured for identification purposesl)and it was found that naphthalene molecular addition compounds of most of the esters melt incongruently while most phenanthrene molecular addition compounds melt congruently. The spread of the significant melting points was sufficient for positive identification in most cases. Alcohols may be identified rapidly by microscopic mixed fusion analysis, if
148
ANALYTICAL CHEMISTRY
they are first converted to a derivative which forms molecular addition compounds with another reagent.
T
identification of aromatic compounds by microscopic mixed fusion analysis with 2,4,7-trinitrofluorenone as the reagent has been described (7-9). In this identification scheme, a mixed fusion (6, 7) is prepared beta-een the compound to be identified and the reagent. The preparation is examined microscopically as i t cools to determine if molecular addition compound formation occurs. B y this simple process, compounds may be divided into two classes: those which form molecular addition compounds with 2,4,7-trinitrofluorenone and those which do not. For compounds which do form molecular addition compounds, identificaHE
tion is achieved on the basis of the melting points of the original compound, of the molecular addition compound, and of the two eutectics present in the system. These significant temperatures are usually determined on a single preparation with one heating cycle. Because there is an uncertainty of approximately 1 0 . 5 ” C. in any given melting point, an average of three values of a given significant temperature is usually employed. Compounds which form molecular addition compounds with 2,4,7-trinitrofluorenone include polynuclear aromatics and certain substituted benzenes (4, 8 ) . I n principle, this identification scheme could be employed for any class of organic compounds, provided a suitable reagent can be found. This reagent should form molecular addition compounds selectively with a given class
