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
of organic compounds and the significant temperatures should be sufficiently different to afford positive discrimination among the various compounds within the given class. It should be a relatively simple matter t o find such reagents for acidic or basic substances. Other organic functional groups, however, do not lend themselves as directly to such an identification scheme, as there are few guiding principles for the selection of the reagent. An alternative approach, for n hich there is some precedent in the literature, involves the formation of a derivative of the gi\ en functional group, the reagent used to prepare the derivative being of such a nature that it f o r m molecular addition compounds with certain other types of organic substanew This general approach has been folloived for alcohols ( 2 , I O ) . Esters are prepared from the alcohols and 3,5-dinitrobenzoic acid. The resultant esters are complexed with 1-naphthylamine in solution and the precipitated molecular addition compounds afford a second melting point (in addition to that of the 3,5-dinitrobenzoate) for identification of the starting alcohol. It \vas decided to investigate the application of microscopic mixed fusion methods to the identification of alcohols. If the esters were to be used as the acceptor in a donor-acceptor type niolecular addition compound ( I ) , both the 3,5-dinitrobenzoates and the 2,4,6trinitrobenzoates (3) appeared promising. The latter were selected for study. as the melting points of these esters are generally higher than those of the corresponding 3,5-dinitrobenzoates and the spread in ester melting points is good. Both factors allow for a corresponding spread in eutectic melting points. Preliminary studies similar to those conducted with 2,4,7-trinitrofluorenone (8) indicated that molecular addition compound formation occurs betn-een 2,4,6-trinitrobenzoate esters and a limited number of aromatic compounds. Of these aromatic compounds tivo reagents were selected : phenanthrene, because preliminary studies indicated that the molecular addition compounds between thc 2,4.6-trinitrobmzoates and phenanthrene melt congruently and have a satisfactory spread in values; and naphthalene, because preliminary studies showed that the naphthalene molecular addition compounds with 2,4,6-trinitrobenzoate esters melt incongruently (peritectic reaction). It was believed that the factors contributing to incongruent melting of the molecular addition compounds might be significantly different from those contributing to normal melting. Therefore, i t might be possible to achiere greater discrimination among the alcohols with a combination of two reagents.
Table 1.
Esters of 2,4,6-Trinitrobenzoic Acid
2-Pentanol
Ester Melting Point, C.Literature (3) Found 84.9-86.1 104.5 (de-
czs-9-Octadecen-1-01 2-Heptanol
109.5-111.4 113.9 (de-
3-Pentanol 1-Octadecanol 1-Tetradecanol 1-Hexadecanol 1-Dodecanol 2-Ethyl-1-butanol I-Butanol 1-Nonanol 1-Decanol 2-Methyl-2-propanol 1-Pentanol 1-Octanol 2-Butanol 1-Heptanol 1-Hexanol 2-Methyl-1- entanol 3-Methyl-l-!utanol 1-Propanol 2-Propen-1-01 Cyclohexanol 2-Propanol Eth anol 2-Phenylethanol Methanol Benzyl alcohol
116.3-118.0 119.7-120.5 119 2-120 9 119 6-120 8 120 1-121 7 120 4-121 9 122 1-123 2 122 8-123 4 122 8-123 6 122 9-124 0 123 8-124 4 124 1-124 6 i22 1-124 8 126 5-127 3 128 4-130 3 128 3-130 6 132 4-133 0 145 3-146 7
O
Alcohol 2-Ethy l-l-hexanol
Method of Purification" -4
camp.)
B A
camp.)
1_ 1 ~1 6-147 6 . _ -
151 4-154 1 155 3-158 0 157 1-158 4 157.6-159.0 158.7-160.6 178.8-180.7
A
A C D L,
125-126 121- 125 123-124 124-125 125-126 127-128 129-130 131-135 145-146 146-147 154- 155
156-157
160-1 6 1 176-177
B C C A C C C C C C C C B C C C C
C E
c
E
= A. Recrystallized from petroleum ether. B. Kofler's filter paper absorption method. C. Recrystallized from chloroform-petroleum ether. D. Column chromatography and petroleum ether recrystallization. E. Recrystallized from benzene-petroleum ether.
EQUIPMENT AND REAGENTS
Melting points mere measured with a Kofler hot stage purchased from Arthur H. Thomas, Inc., Philadelphia. Pa. A low power microscope, 16-mm. objective, lox eyepiece, was used to observe melting. Heating rates rrere controlled n-ith a Variac variable transformer. The naphthalene was Eastman Kodak, best grade, purified by recrystallization (melting point 80.2" (2.). Phenanthrene \ x i s obtained from Matheson, Coleman & Bell and \yas purified b y recrystallization (melting point 99.6" C.). The 2,4,6-trinitrobenzoic acid was prepared from 2,4,6-trinitrotoluene. as described in the literature ( 5 ) . The acid chloride was prepared by reaction of 2,4,6-trinitrobenzoic acid with phosphorus pentachloride in boiling toluene. It was recrystallized once from toluene. EXPERIMENTAL
The hot-stage thermometer used in this work was calibrated with knonn melting point standards. All melting points were taken a t a heating rate of 3" C. per minute and were corrected according to the thermometer calibration curve. Esters of 2,4,6-trinitrobenzoic acid
were prepared by heating an excess of the alcohol with 2,4,&trinitrobenzoyl chloride until evolution of hydrogen chloride gas had ceased. K i t h the lon-er alcohols, reaction was rapid; with the higher alcohols, the reaction was much slower. Esters were purified by several recrystallizations from chloroform-petroleum ether. I n the first recrystallization activated charcoal was used. The greater the chain length of the alcohol, the greater the solubility of the ester in petroleum ether; therefore, ith long-chain alcohols, purification by recrystallization became more difficult. With some of the higher alcohols, it was found expedient to purify the ester (even after recrystallization) by Kofler's filter paper absorption method (6). A small amount of the recrystallized ester was powdered and placed on a small square of absorbant filter paper on a microscope slide. The slide was heated on a hot bar to a temperature under the melting point of the ester but above that of its eutectic with residual impurities. The molten impurities were absorbed by the filter paper. B y repeating this process several times, i t was possible to obtain a sufficient quantity of purified ester to perform the mixed fusion studies. VOL. 31, NO. 1, JANUARY 1959
149
,
Table II.
Mixed Fusion Data for Esters of 2,4,6-Trinitrobenzoic Acid with Naphthalene
Alcohol 2-Ethyl-1-hexanol 2-Pentanol" cis-9-Octadecen-1-01 2-Heptanol 3-Pentanol 1-Octadecanol I-Tetradecanol 1-Hexadecanol 1-Dodecanol 2-Ethyl-1-butanol 1-Butanol 1-Nonanol 1-Decanol 2-Methyl-2-propanol 1-Pentanol 1-Octanol 2-Butanol 1-Heptanol 1-Hexanol 2-Methyl-1-pentanol 3-Methvl-l-butanola 1-Propanol 2-Pro en l o 1 CycloReiaiol 2-Propanol Ethanol
Eutectic, esteraddition compound 71.9 85.5 40.4 I
75.8 I
81.3 I
/
60.3 f I
96.8 113.3 I f I f 3
I
97.2
-
hleltinn Points. " C. Eutectic, naphthaleneaddition compound 60.0 67.3b 52. Id 37.4 46.6 56.2 69.7 61.7 65.9 52.6 57.8 61.9 62.8 67.3 76.4 64.6 63.9 57.9 59.5 61.4 62.9 7 0 .3b
Addition compound 79.8 88.1C
117.6e 53.3 56.50 78.6 92,20 82.7 87.10 66,Oo 70.3 86.80 90.20 98.2 154.4 80,20
87.90 79.10 77.00 86.60 89.5 98.7c 94. 8e 93.70 105.70 108.10 91.60 113.80
65.3 70.8 I 71.0 f 64.4 f 73.2 f 2-Pheny lethanol 90.00 63.7 I Methanol 81.90 65.7 / Benzyl alcohol 107.70 75.2 a Ester forms two addition compounds with naphthalene. Eutectic between two addition compounds. Addition compound on ester side of preparation. Eutectic between addition compound (naphthalene-rich) and naphthalene. e Addition compound on naphthalene side of reparation, melts incongruently. f Eutectic absent because addition compound)melts incongruently. 0 Incongruent melting point. f f
When microscopic mixed fusions were prepared with the 2,4,6trinitrobenzoates and naphthalene or phenanthrene, yellow molecular addition compounds were formed. It was possible to measure the significant temperatures (two eutectics, the ester, and the molecular addition compound) for identification of the starting alcohol. Table I lists the melting points and method of purification of the various esters. Table I1 is a compilation of the mixed fusion data for the esters with naphthalene, and Table I11 contains similar data for the esters with phenanthrene. The melting points reported in Tables I1 and 111 are the average of a t least three separate determinations. Although the melting points for the eutectics and the molecular addition compounds are reported to the nearest 0.1' C., a variation of i 0 . 5 " C. is to be understood. The observed melting point range of the esters is recorded as an indication of their purity. DISCUSSION
Tables I1 and 111 show that, in gen-
150
ANALYTICAL CHEMISTRY
eral, the molecular addition compounds of the straight-chain alcohols with naphthalene melt incongruently xhile those with phenanthrene melt normally. There are some important exceptions to this generalization, as the C8 through Clz straight-chain esters form molecular addition compounds with phenanthrene which melt incongruently. There are also three straight-chain esters which form normally melting molecular addition compounds Lvith naphthalene. These departures from the normal behavior are of important diagnostic value in the identification scheme. A number of the branched-chain esters form normally melting molecular addition compounds with naphthalene and the 2-pentanol ester forms two welldefined molecular addition compounds with naphthalene. I n this particular system, it was possible to measure all three eutectic temperatures plus the melting points of both molecular addition compounds. The effectiveness of the mixed fusion method for the identification of the various alcohols may be determined b y considering the data in Tables I1 and 111. The 2,4,6-trinitrobenzoic acid es-
ters of 1-octadecanol, 1-tetradecanol, and 1-hexadecanol all have final melting points in the range of 120.5' to 121' C. Of these three, the l-tetradecanol ester may be differentiated immediately b y its behavior with naphthalene in a mixed fusion. This particular molecular addition compound melts normally while the naphthalene molecular addition compounds of the other two esters melt incongruently. However, the incongruent melting points of the 1-hexadecyl and l-octadecyl esters are 5" C. apart, a value outside experimental error, and hence the three may be identified on the basis of the naphthalene mixed fusion alone. The identifications may be confirmed by reference to the mixed fusion data with phenanthrene, where the measured temperatures have a spread sufficient for identification. I n particular, t h e phenanthrene addition compound Kith the 1-octadecyl ester melts at 99.3' C. while the corresponding addition compound with the 1-hexadecyl ester melts a t 96.1' C. The phenanthrene addition compound of the 1-tetradecyl ester melts a t 91.5' C. and its eutectic temperatures are substantially lower than those of the other two esters. The 1-dodecyl and 2-ethyl-1-butyl esters, both melting at approximately the same temperature (121.7' and 121.9' C.) are adequately differentiated by a naphthalene mixed fusion alone. The addition compound with the 1-dodecyl ester melts incongrumtly while that with the 2-ethyl-1-butyl ester melts normally. As in the previous illustration, the phenanthrene mixed fusion data may be used for confirmation. I n the data reported in Tables I1 and 111, there are seven esters with final melting points in the range 123.2' to 124.8" C., a range barely outside the reproducibility of the measurements. These esters are butyl, m.p. 123.2'; 1-nonyl, m.p. 123.4"; l d e c y l , m.p. 123.6'; 2-methyl-2-propy1, m.p. 124.0"; 1-pentyl, m.p. 124.4'; 1-octyl, m.p. 124.6'; and 2-butyl, m.p. 124.8'. 1Decyl and 2-methyl-2-propyl form normally melting molecular addition compounds with naphthalene, while the others form addition compounds with naphthalene which melt incongruently. The normally melting addition compounds have melting points 56' C. apart and hence may be differentiated. Three of these esters, 1-nonyl, I-decyl, and 1-octyl, form incongruently melting molecular addition compounds with phenanthrene. This behavior differentiates these three esters from the other four of the group, all of which form normally melting molecular addition compounds n-ith phenanthrene. However, the phenanthrene mixed fusion data cannot be used to differentiate between the 1-nonyl and the 1-octyl esters, as.
the melting points are too close together (eutectics 69.4' and 69.8' C., addition compounds 84.2' and 84.0" C., respectively). T h e incongruent melting points of the naphthalene addition compounds (1-nonyl ester, 90.2' C.; 1-octyl ester, 87.9" C.) differ by a n amount greater than experimental error. However, i t would be desirable if a larger spread were obtained; this particular pair of compounds represents a borderline case with the reagents chosen. In this case, i t would be advisable to investigate reagents other than naphthalene or phenanthrene for positive identification. Apart from this specific pair of compounds, the other members of the group of seven are adequately differentiated by one or more significant melting points. It can be concluded t h a t the microscopic mixed fusion method may be used for the identification of alcohols as their 2,4,6-trinitrobenzoates.Although only a limited number of alcohols have been tested so far, i t appears that naphthalene and phenanthrene as reagents afford sufficient differentiation in most cases. However, it can be anticipated that as more data become available, there will occur other borderline cases similar to the I-octyl, I-nongl alcohol pair. K i t h these, a third or a fourth reagent then may be used t o afford positive identification. Table IV shows mixed fusion data for four esters with 2-naphthol as the reagent, and Table V s h o w fusion data for the same compounds with 2-naphthylamine as the reagent. It may be seen that the 1octyl and 1-nonyl esters are adequately differentiated b y either new reagent. The mixed fusion technique for the identification of alcohols should be applicable to situations where the alcohols are separated as a group by reaction with 2,4,6-trinitrobenxoyl chloride, followed b y separation methods (fractional crystallization, chromatography, etc.) which yield small amounts of the individual esters. It should be equally applicable in a general qualitative organic analysis scheme, where the unknown compound is first classified according to functional group. I n this case, the 2,4,6-trinitrobenzoate would be prepared as a derivative. Mixed fusions would then be conducted with one or more reagents to obtain confirmatory data. It is believed that this general technique may be expanded to include other functional groups b y the proper selection of functional group reagents which are also capable of forming molecular addition compounds.
LITERATURE CITED
q(1) Andrews, L. J., Chem. Revs. 54, 713 (1954).
Table 111.
Mixed Fusion Data for Esters of 2,4,6-Trinitrobenzoic Acid with Phenanthrene
Alcohol 2-Ethyl-1-hexanol 2-Pentanol cis-9-Octadecen-1-01 2-Heptanol 3-Pentanol I-Octadecanol 1-Tetradecanol 1-Hexadecanol 1-Dodecanol 2-Ethyl-l-b~t~lol 1-Butanol 1-Nonanol I-Decanol 2-Methyl-%propanol 1-Pentanol 1-Octanol 2-Butanol 1-Heptanol 1-Hexanol 2-Methyl-1- entanol 3-Methvl-l-!utanol@
Eutectic, esteraddition compound 75.4 89.2 (I
90.3 99.8 97.9 88.6 94.3 L) (I
109.4 (1
0.
114.4 101.7 D
100.5 104.9 113.3 a
Melting Points, ' C. Eutectic, phenanthreneaddition compound 71.2 71.9 51.3 72.9 84.8 82.8 75.3 80.0 62.9 63.9 88.1 69.4 71.9 90.7 84.0 69.8 79.1 80.7 87.0 69;2
107.4
Addition compound 88.1 18.8
62.9* 96.0 17.1 99.3 91.5 96.1 75. lb 79.4b 21.7 84.2 86. 3b 165.7 106.2 84. gb 105.9 108.8 121.0 88. 3b 11.76 ii2.8~ 116.9 122.0 136.9 124.0 132.5 142.6 127.3 153.1
88.3' 114.8 85.8 119.3 87.6 129.5 86.5 123.3 86.3 129.9 89.2 2-Pheny lethanol 139.1 94.0 Methanol 125.2 89.5 Benzyl alcohol 152.1 94.2 a Eutectic missing because addition compound melts incongruently. * Incongruent melting point. Ester forms two addition compounds with phenanthrene. Eutectic between two addition compounds, not measured. e Addition compound on ester side of preparation. f Eutectic between phenanthrene-rich addition compound and phenanthrene. 0 Addition compound on phenanthrene side of preparation. 1-Propanol 2-Pro en-1-01 Cjvloiexanol 2-Propanol Ethanol
Table IV.
Mixed Fusion Data for Esters of 2,4,6-Trinitrobenzoic Acid with 2-Naphthol
Melting Points, C. Eutectic, Eutectic, esteraddition addition compoundAlcohol compound 2-naphthol b 1-Octanol 62.2 b 1-Nonanol 68.3 b 1-Pentanol 76.6 b 2-Butanol 78.1 a Addition compounds are yellow. Eutectic absent because addition compound melts incongruently. c Incongruent melting point. Table V.
Addition' compound 65.3" 70.0" 81.OC 83. 5c
Mixed Fusion Data for Esters of 2,4,6-Trinitrobenzoic Acid with 2-Naphthylamine
Melting Points, ' C. Eutectic, addition compoundAddition" Alcohol 2-naphthylamine compound I-Octanol 87.7 89.6 1-Xonanol 92.3 95.3 1-Pentanolb 107.3O 108.7d 100.5° 108.4' 2-Butanol 78.9 89.9 94.8 a Addition compounds with 2-naphthalamine are red. Ester forms two addition compounds with 2-naphthylamine. Eutectic between two addition com ounds. Addition compound on ester side o?pre aration. Eutectic between 2-naphthylamine and t%e 2-naphthylamine-rich addition compound. Addition compound on 2-naphthylamine side of preparation. Eutectic, esteraddition compound 78.3 82.0 94.5
VOL. 31, NO. 1, JANUARY 1959
151
(2) Benfey, 0. T., Stanmeyer, J. R.,
Jr., Milligan, B., Westhead, E. W., Jr. J . Org. Chem. 20, 1777 (1955). (3) dhang, Ming-Che, Kao, Chen-Heng, J . Chinese Chem. Soc. 3, 256 (1935). ( 4 ) Dajac Laboratories, Leominster, Mass., data sheet on 2,4,7-trinitrofluorenone, 1954. (5) Gilman, ,H Blatt, 9. H., “Organic Syntheses, 6011. 1701. I, p. 543, Wiley, Sew York, 1947.
(6) Kofler, L., Kofler, A., ‘(Mikromethoden Bur Kennzeichnung organischer Stoffe und Stoffegemische,” Univ. Wagner, Innsbruck, 1948. (7) Laskoffski, D. E,, ~ ~ D. G,, ~ ‘IcCrone, T.TT. c., ANAL. CHEM. 25, 1400 (1953). (8) LaSkowSki, D. E., McCrone, W *c.7 Ibzd., 26, 1497 (1954). (9) Ibzd., 30, 542 (1958).
(10) Sutter, P., Helv. Chim. Acta 21, 1266 (1938). bRECEIVEI) ~ for ~ review , Ma!: 14, 1958. Acce ted August 18, 1958. Based in part to be submitted by Otis It’. on
Bdams to the graduate school of Illinois Institute of Technology in partial fulfillment of requirements for the degree of doctor of philosophy.
Spectrophotometric Determination of Beryllium and Fluoride Using Chrome AzuroI S LOUIS SILVERMAN and MARY E. SHIDELER Atomics International, A Division o f North American Aviation, Inc., P.O. Box
b Chrome Azurol S has been applied to the spectrophotometric determination of beryllium and fluoride. The colored beryllium-Chrome Azurol S complex is formed a t pH 6.0 in the presence of a pyridine-hydrochloric acid buffer, which enhances the sensitivity of the dye to beryllium and increases the sensitivity of the metal-dye complex to fluoride. The procedure described can be used to determine from 1 to 30 y of fluoride per 50-ml. volume with a precision of =k 1 y, and from 0.2 to 10 y of beryllium per 50ml. volume with a precision of k0.2 y. Studies were made on the variables of the system, interferences, and an ion exchange method to separate uranium from beryllium.
A
METHOD !vas required in this labora-
tory to determine microgram amounts of fluoride in enriched uranium sulfate, which is used as the fuel in the water-boiler type of nuclear reactors. A commercial preparation of uranium sulfate for reactor fuel necessitates its conversion from the uranium hexafluoride, and some fluoride would be expected in the sulfate salt produced. As fluoride in acid solution speeds the corrosion of stainless steel vessels, the quantity of fluoride present, however small, must be known. * The number of methods reported for the determination of microgram amounts of fluoride shows that the determination is difficult and not completely satisfactory. Fluoride is best determined spectrophotometrically by its bleaching action on metal-dye colored complexes. A great variety of metals and dyes have been used for this purpose (1, 9, 4-7)J including the Chrome Azurol S-aluminum complex ( 1 ) . Willard and Horton (13) report that Chrome Azurol S is one of the more sensitive in152
ANALYTICAL CHEMISTRY
309, Canoga Park, Calif.
a broivn bottle. The solution is stable dicators for the titration of fluoride using for several weeks. thorium. Pyridine-Hydrochloric Acid Buffer, Theis (8)and Wood (14) used Chrome p H 6.0. Slowly add 35 ml. of conAzurol S as a sensitive indicator for the centrated hydrochloric acid t o 215 ml. presence of small amounts of beryllium. of pyridine. This solution is stable for As beryllium also forms a strong complex at least 3 weeks. with fluoride, it seemed that beryllium might have advantages as a Chrome PROCEDURES Azurol S complex for the determination of microgram quantities of fluoride. Standard Curve for Fluoride. PreChrome Azurol S, the sodium salt of pare t h e standard curve by pipetting 3”-sulfo -2”,6”-dichloro-3,3’-dimethyl-4- aliquots containing from 0 to 30 y of fluoride into a series of 50-ml. voluhydroxyfuchson-5,5’-dicarboxylic acid, metric flasks. Add water to bring the is also known as Solochrome Brilliant volume to about 40 ml., and add an Blue B, Polytrop Blue R, and has the aliquot containing 10 y of beryllium British Colour Index No. 723. I n to each flask. Then add 3 ml. of 2% weakly acidic beryllium solution the dye hydroxylamine hydrochloride solution, forms a pink to purple-blue color which 2 ml. of pyridine-hydrochloride buffer, is bleached by the presence of fluorides. and 1 ml. of Chrome Azurol S reagent, Although the preliminary aim of this mixing the contents of the flask after study was to investigate the berylliumeach addition. (The p H should be 6.0 at this point.) Dilute the solutions Chrome Azurol S complex for use in t o volume with distilled water and allow determining fluoride, it was immediately to stand for 15 minutes. Measure the apparent that this work could also be absorbance with a Becknian Model applied to a method for determining D U spectrophotometer in 5-cm. cells microgram quantities of beryllium. Bea t 575 mp, using as the reference cause the majority of the experimental solution a reagent blank containing all work was essentially the same for the reagents except beryllium and fluoride. determination of either fluoride or Prepare a standard curve from these beryllium, a procedure for beryllium is values. Fluoride Determination. If interincluded here. fering substances are present in t h e sample, they must be separated a s REAGENTS discussed below. If necessary, t h e sample may be adjusted to p H 6 f Standard Beryllium Solutions. Dis0.1 with a minimum amount of solve 1 gram of beryllium metal in hydrochloric acid or ammonium hydroxdilute (10%) hydrochloric acid and ide. Then follow the procedure for the dilute t o 1 liter with distilled water. standard curve. Determine the microMake suitable dilutions t o obtain solutions containing 1 and 10 y of beryllium grams of fluoride present from the standard curve. per ml. It is recommended t h a t all Standard Curve for Beryllium. solid or powdered beryllium compounds be handled in a hood, and that an aspiraPrepare t h e standard curve b y pipetting aliquots containing from 0 t o 10 tor mask be worn. y of beryllium into 50-ml. volumetric Chrome Azurol S, 0.05%. Disflasks. Dilute with distilled water to solve 0.50 gram of Chrome Azurol S 40 ml. Add the amounts of hydroxyl(Geigy Chemical Co., Los Angeles, amine hydrochloride, pyridine-hydroCalif.) in 1 liter of distilled water chloride buffer, and Chrome Azurol containing 2 grams of gum arabic powS specified for the fluoride procedure, der. Allow the solution to stand then follow the fluoride procedure. several days, then filter and store in
