Studies with N-Halo Reagents PAUL F. KRUSE, JR., KEN L. GRIST, and THOMAS A. McCOY Laboratory Research Division, The Samuel Roberts Noble Foundation, Inc., Ardmore, O k l a .
S-chloro-, A\--bromo-, and S-iodosuccinimides were used in the differentiation of alcohols, amines, and some position isomers, and the detection of amino alcohols. I n general, the tests were carried out in carbon tetrachloride solution, on a water bath at 80" C. Primary alcohol tests using iV-bromosuccinimide >ield a permanent orange color, whereas the color disappears in secondary alcohol tests to give an orangemottled precipitate. No observable color change occurs with most tertiary alcohols. Thirty saturated alcohols were tested, as well as 25 other alcohols and h?droxy compounds. With lV-iodosuccinimide primary amines yield a permanent brown color, whereas the color fades with secondary amines. Tertiary amines give a brown color and are confirmed by an orange precipitate using A'-bromosuccinimide. Some position isomers have been differentiated with N-halosuccinimides; no color changes occurred with any of the meta-disubstituted isomers. The N-halosuccinimides have been shown to be valuable classification reagents.
T
HE halosuccinimides have been the subject of much research.
Most of these investigations have been concerned with the use of these compounds as halogenating agents. During a course of investigations in this laboratory i t was noted that Nbromosuccinimide could also be used to differentiate primary, secondary, and tertiary saturated alcohols. The test is applicable over a wide range of alcohols. I t is rapid and very simple to perform, a possible advantage over previous proposed tests (10, 13, 19). While this work was in progress it occurred to the authors that the halosuccinimides might be useful in differentiating other groups of compounds. The present report deals with the use of N-bromosuccinimide, N-chlorosuccinimide, and Siodosuccinimide in the differentiat~onof primary, secondary, and tertiary alcohols and amines and Borne position isomers, and the detection of amino alcohols.
Discussion. The results listed in Table I are self-explanatory. A continuous boiling period of 6 or 13 minutes was required for the disappearance of the color in the case of 2-methylcyclohexanol and 4-methylcyclohexanol, respectively. The results listed in Table I1 are worthy of comment. Allyl, propargyl, and benzyl alcohols appear to fade in the manner of secondary alcohols. These exceptions are not surprising, as these a,p-unsaturated compounds are often exceptions to many general rules regarding reactions. Furthermore, Lucas (13) reported that allyl alcohol gave a secondary test, and the same result was noted with the present test. The a-hydroxy esters conform to the rules of the N-bromosuccinimide test, as do five tertiary alcohols listed in this tzble (dimethylbenzylcarbinol excepted). From this i t appears that this test in many cases can be applied to more complex alcohols and other hydroxy compounds. The reaction of N-bromoauccinimide with alcohols and other hydroxy compounds has been the subject of a number of reports. Although this discussion is limited to reactions of N-bromosuccinimide, the reactions of alcohols with similar reagents have been reported-Le., N-bromoacetamide ( I d , 18, 20), X-chlorosuccinimide (5, 8 ) , and N-bromophthalimide (1). Fieser and Rajagopalan ( 4 ) first demonstrated the use of A'-bromosuccinimide for oxidizing a secondary alcohol group to a keto group, using the reagent in aqueous solution. Their first work was the selective oxidation of the 7-hydroxyl group in cholic acid to the 7-keto derivative. I n 1952, Barakat and Mousa (1) reported treating methyl, ethyl, isopropyl, and benzyl alcohols (5, 6, 7, and 4 ml., respectively) with N-bromosuccinimide (2 gram8 each). From the filtered reaction mixtures they obtained the 2,4-dinitrophenylhydrazones of formaldehyde, acetaldehyde, acetone, and benzaldehyde. They indicated the alcohols were converted to
Table I.
PRIURY Methanol" Ethanol 1-Propanol 1-Butanol 2-Methyl-1-propanol 1-Pentanol 3-Methyl-1-butanol 1-Hexanol 1-Heptanol 1-Octanol 2-Ethyl-I-hexano 1-Decanol 1-Dodecanol 1-Hexadeoanol I-Octadecanol
DIFFERENTIATION O F PRIMARY, SECONDARY, AYD TERTIARY ALCOHOLS
Procedure and Results. Three drops of an alcohol (or an equivalent amount of solid) were dissolved in 1 ml. of a solution of 2 drops of bromine in 100 ml of carbon tetrachloride in a 6inch test tube, and treated with S-bromosuccinimide (15 to 30 nip.). Another milliliter of the solvent solution was used to wash down the walls of the tube. The tube was placed in a 600-ml. beaker containing water heated to 77" to 80".
At this temperature the solution will gently boil and any color changes from the initial pale yellow will o x u r in the mixture within 13 minutes. For most compounds tested, changes occurred within 5 minutes. Primary alcohols give a permanent orange color. If the alcohol is secondary, an orange color will appear but will fade (rapidly) to colorless on continued boiling. An orange-mottled precipitate is apparent upon cooling. Tertiary alcohols usually show no color changes, although the behavior of terl-amyl alcohol has been erratic Decolorization of the bromine-carbon tetrachloride solution prior to heating shows that the alcohol is not of the saturated type. Table I groups the 30 saturated alcohols which were tested and gives the identifying characteristics for each class. Table I1 lists the results when the test was applied to 25 other hydroxy compounds.
Differentiation of Saturated Alcohols by N-Bromosuccinimide I n orange color appears usually within 3 minutes during boiling and remains on cooling. Unreacted bromoimide is present a t t h e bottom: succinimide floats a t the top.
SECOSDARS 2.Propanol 2-Butanol 3-1ZIethyl-2-butanol 2-Pentanol 3-Pentanol C yclopentanol 2-Hexanol Cyclohevanol 3-Heptanol 2-4-Dimethyl-3-pentanol 2-i\lethylcycloheuanol 4-Methylcyclohexanol 2-Octanol
An orange color i3 produced during boiling a n d usually disappears (rapidly) within 5 minutes. An orangemottled precipitate will appear on cooling: succinimide floats a t t h e top.
TERTIARY
.z
1319
2-2Zethyl-2-propanol 2-Methyl-2-butanol Color develops slowly.
N o observab!e change Results erratic
ANALYTICAL CHEMISTRY
1320 hypobromites, which dehydrobrominated to yield the carbonyl compounds. These authors stated that primary and secondary alcohols and primary amines can be detected using N-bromosuccinimide, although they gave no experimental details for a detection or differentiation procedure. Presumably the combination of an orange-red color obtained when these (seven total) compounds reacted and the 2,4dinitrophenylhydrazones obtained constituted the method for detection. The alcohol differentiation tests described in the present paper can possibly be explained on the basis that the primary and secondary alcohols give hypobromites which split out hydrogen bromide to yield aldehydes and ketones. With hydrogen bromide present, unchanged N-bromosuccinimide has been reported in other instances to yield succinimide and bromine ( 2 3 ) ,which is probably responsible for the color. The aldehyde formed could react with additional unchanged alcohol to form a hemiacetal which has been postulated to react with S-bromosuccinimide (6) to give a hypobromite. Here primary compounds would produce twice as much halogen as secondary ones, which could account for the fading of color in the secondary test. The presence of bromine is critical in this test, as the solvent system must contain a small amount of bromine to prevent color fading with some primary alcohols. The lack of color formation with tertiary alcohols can be explained by the fact that there is no hydrogen atom on the a-carbon and consequently hydrogen halide is not removed, bromine is not produced, and the alcohol is not oxidized. The inertness of S-chlorosuccinimide toward tert-butyl alcohol was observed by Seliwanow ( 2 1 ) , and he suggested that a tertiary alcohol may be detected in this manner.
Table 11. Differentiation of Other Alcohols and Hydroxy Compounds by N-Bromosuccinimide PRIMARY Pale orange color which disappears during heating F a i n t orange color which disappears during heating Pale orange color which disappears during heating C o m d e t e solution, no color change Prim. test initially with black ppt., complete black solution on continued heating Permanent yellow-orange color, prim. test Yellow changes t o permanent orange, prim. test Yellow changes t o orange, gradual fading in 10-min. heating Permanent orange color, prim. test. on standing overnight ora&e ppt. settles Permanent orange color, prim. test Permanent orange color, prim. test Permanent orange color, prim. test Faint prim. test
Allyl alcohol Propargyl alcohol Benzyl alcohol Cinnamyl alcohol Furfuryl alcohol Tetrahydrofurfurol 2-Phenvlethanol 3-Phenylpropanol 2,3-Dibromo-l-propanol Ethylene glycol monomethyl ether Ethylene glycol monoethyl ether Ethylene glycol mono-n-butyl ether Ethylene glycol monophenyl ether
SECOKDARY Orange color fades test Orange color fades test Orange color fades test Orange color fades test Orange color fades test Orange color fades orange ppt.
oL-Phenylmethylcarbinol E t h y l m-lactate E t h y l nL-a-hydroxybutyrate Ethyl n~-mandelate E t h y l DL-a-hydroxyhydrocinnamate Benzhydrol
rapidly, sec rapidly, sec. rapidly, sec. rapidly, sec. rapidly, sec on standing,
TERTIARY Diacetone alcohol Trichloro-tert-butyl alcohol Triphenylcarbinol 2,5-Diinethyl-3-hexyne-2,5diol a-Terpineol Dimethylbenaylcarbino
No observable change, tert. test
K O observable change, tert. test KO observable change, tert. test No observable change, tert. test
Succininiide forms, change Slight yellow color
no
color
Table 111. Differentiation of Saturated Amines by N-Iodosuccinimidea PRIMARY
KOcolor fading occurs.
n-Amylamine Isoamylamine Cyclohexylamine n-Heotvlamine n-Ociyiamine 2,4,4-Trimethyi-2-amyIamine n-Decylamine n-Dodecylamine n-Octadecylamine Diethvlamine Di-n-firopylamine Diisoyrupylamine Di-n-butylaniine Diisobutylaniine Di-sec-butylamine Di-n-amylamine Diisoamylamine Dicyclohexylamine Di-n-octylauiine
SECONDARY T h e color which develops during heating in the water bath is usually brown, although it ranges among deep yellow, orange-brown, and red-brown. T h e color then fades while heating t o pale yellow or t a n or colorless.
TERTIARY T h e color becomes verv dark brown or brown-viol2 upon heating in the water bath. This test must be confirmed by the immediate appearance of a n orange precipitate when N-bromosuccinimide is added t o a sample of the tertiary amine i n carbon tetrachloride. a All tests were run heating in a water bath a t 80-90° C. for 10 minutes. T h e color changes occur within this period of time. Furnished through the courtesy of Rohm & Haas Co., Philadelphia. Triethylamine Tri-n-butylamine Tri-n-amylamine Triisoamylamine Tri-n-hexylamine Tri-n-heptylamine
~
DIFFERENTIATION OF SATURATED AMINES AND SOME POSITION ISOMERS AND DETECTION OF AMINO ALCOHOLS
Procedure and Results. Six drops of the liquid amine (or an equivalent amount of the solid) were introduced into a test tube containing 1 ml. of carbon tetrachloride. A small amount (ca. 30 mg.) of N-iodosuccinimide and a few particles of benzoyl peroxide were added and the walls of the tube were washed with an additional milliliter of carbon tetrachloride. The reactants were placed in a water bath a t 80" C. At this temperature the solvent gently boiled and the reaction(s) was observed for 10 minutes. The test was interpreted as follows: If the amine was primary, the color that developed during heating was usually brown, although it ranged from deep yellow and orange-brown to redbrown. No color fading occurred. In the case of a secondary amine, the color that developed during heating was usually brown (deep yellow, orange-brown, or red-brown) and this color faded to pale yellow, tan, or colorless during the period of heating. The tertiary amines tested exhibited a permanent dark brown or brown-violet color upon heating in the water bath. Their detection must be confirmed by the immediate appearance of an orange precipitate when ,V-brornosuccinimide is added to a fresh sample of the tertiary amine in carbon tetrachloride. The results of the test when applied to 30 saturated amines are listed in Table 111. When the method was applied to the differentiation of some position isomers, equivalent conditions and amounts of the sample and reactants were used where indicated (see Table 11'). The dihydroxybenzene tests were carried out a t room temperaturp in the presence of benzoyl peroxide. This series was the only group of position isomers which required benzoyl peroxide. The test can also be used to detect amino alcohols. The reagent used was LV-bromosuccinimidewithout benzoyl peroxide. A positive test for these compounds was the presence of a brown ring floating on the top of the solution after heating. Upon cooling, succinimide appeared a t the top of the solution. The com-
V O L U M E 2 6 , NO. 8, A U G U S T 1 9 5 4 pounds tested in this group were ethanolamine, diethanolamine, triethanolamine, and diethylaminoethanol. All gave the characteristic brown ring test. Discussion. I n applying the amine differentiation test to unknowns, it is difficult to detect the difference between primary and tertiary amines with Ai-iodosuccinimide. Therefore N bromosuccinimide must be used to confirm a tertiary amine. The present test can be used equally as well as the benzoyl peroxide tests (15, 1 6 ) , the chloranil test ( 2 2 ) , the quinhydrone test (11), or the well-known Hinsberg test ( 9 ) for differentiating saturated amines. The function of benzoyl peroxide in the present test is catalytic. This was evident when the tests with N iodosuccinimide were carried out without benzoyl peroxide. The same color changes occurred, but were not as pronounced as when benzoyl peroxide was used. The benzoyl peroxide test reported by de Paolini and Ribet ( 1 6 ) required the addition of Fehling's solution in an alkaline medium for differentiating aliphatic amines.
Table IV.
Differentiation of Position Isomers by N-Halosuccinimides
Compound I-Xaphthol %Naphthol 1-Saphthylamine 2. Naphthylamine Catechol Resorcinol Hydroquinone o-Aminophenol m-Ammophenol p-Aminophenol 0-Brornoaniline m-Bromoaniline p-Bromoaniline o-Nitroaniline m-Nitroaniline p-Sitroaniline
Conditions a n d Reagents Used"
Result
+A XIS + A NBS + A NBS f A XIS +BeiOr N I S + BzzOz XIS + BmOz NCS + A SCS + A NCS f A NCS + A NCS f A NCS + A KCS f A h*IS
Purple Yellow t o light pink Purple N o color change Purple Light t a n Pink D a r k brown Dark ?io color change D a r k red D a r k blue-brown N o color change Orange-brown Green-yellow Green-vellow NCS f A S o colbr color change change KO color change; KCS f A yellow precipitate Brownish black o-Toluidine XCS f A m-Toluidine N C S 4- A N o color change p-Toluidine Red-brown XCS A Brownish black o-rlnisidine NCS A p- Anisidine Red-brown KCS f A Dark brown o-Phenetidine NCS A Brownish purple p-Phenetidine NCS A Dark green-brown o-Phenylenediamine NCS f A m-Phenylenediamine ?iCS 4- A N o color change p-Phenylenediamine Purple KCS 4- A NIS. X-Iodosuccinimide. NBS. .V-Bromosuccinimide. BezOz. Benzoyl peroxide. XCS. 2%'-Chlorosuccinimide.
++ ++
The authors do not propose this test in preference to the Hinsberg test in any qualitative organic flow chart. Preferably they propose its use in conjunction with the Hinsberg test. There are several advantages to this arrangement: Occasionally difficulties are encountered in the Hinsberg test when too much benzenesulfonyl chloride is added. The AV-iodosuccinimidetest is amenable to the differentiation of several amines a t the same time; this includes the simultaneous observation of the color changes of known and unknown amines. The rapidity of the N-bromosuccinimide confirmatory test can be used to advantage in confirming the tertiary amine result in the Hinsberg test. The chemistry of these amine reactions with .$--iodosuccinimide is not well known a t present when compared with the Hinsberg reactions. Nevertheless, some suggestions can be made as to reaction mechanisms. Mechanisms can be postulated which would cause the production of twice as much iodine in the primary test as in the secondary test. This involves the substitution of the positively charged iodine for one of the active hydrogens in the primary amine. This could be followed by the splitting out of the hydrogen iodide and the formation of an imine. Upon metathesis of the hydrogen iodide with additional Ilr-iodosuccinimide, succinimide and iodine are released. The iodine, which would impart a color to the solution, could add across the point of
1321 unsaturation of the imine. At this point two possible reactions could occur, both yielding hydrogen iodide again as one end product. The first possibility would be a repetition of the series of reactions just described up to the point of iodine formation. The second possibility would involve a condensation of the N iodoamine with unchanged amine to form a hydrazo compound and hydrogen iodide. I n all, 4 moles of the N-iodosuccinimide would be used per mole of the amine, and iodine would be one of the end products. I n the case of secondary amines, which have only one active hydrogen, the suggested series could take place only once. The addition of iodine to the double bond may be responsible for the color fading. The fading may not be detected with primary amines, since twice as much iodine is formed. The reactions regarding tertiary amines could involve the addition of iodine to the nitrogen of the amine, resulting in a quaternary salt. This could be followed by a dehydrohalogenation involving one of the hydrogens on a carbon alpha to the functional group. Similar reactions have been suggested by Meisenheimer ( 1 4 ) and Price, Pohland, and Velzen (17). However, in aqueous solution, they reported the cleavage of a carbon-nitrogen double bond and the formation of a secondary amine and an aldehyde. While it is difficult to conceive of this latter reaction occurring in a nonpolar solvent (such as was used in the present study), Crane, et al. (5)and Cosgrove and Waters ( 2 )reported the presence of secondary amines and aldehydes when tertiary amines were caused to react with .Lr-2',4',6'-tetrachlorobenzanilide and with chlorine in carbon tetrachloride. Furthermore, they stated the reaction produced much hydrogen chloride. De Paolini and Ribet (16) demonstrated a similar type of reaction using benzoyl peroxide and tertiary amines in 95% ethanol. In any event, the production of hydrogen iodide (in the present study) could form iodine in the presence of the LV-iodosuccinimide. If the tertiary amine is converted to a secondary amine, more halogen would be liberated for tertiary amines than in the case of the secondary amine test. Some deductions can be made concerning the color reactions observed in the isomer differentiation studies. 4 s no color changes were produced with the meta isomers irrespective of the X-halosuccinimide used, the color formation with other isomers was not due to the halogen. Consequently i t could arise from the formation of a chromophoric group. The chromophore formation is supported by the fact that all of the compounds listed in Table IV contain auxochromes, hydroxy, or amino groups. Furthermore, the 0-,m-, and p-xylenes were tested and no visible color was produced. Since ortho and para isomers are much more easily oxidized than meta isomers, the color could be due to oxidation products or to more complicated products formed between these and the original compound. In all, these postulated mechanisms are reasonable, in that they account for the color changes observed. The reactions suggested for N-iodosuccinimide are closely analogous to those which have been found and reported for reactions of its N-chloro- and N bromo- counterparts with hydroxy and amino compounds (1, I , 6-8). Irrespective of reaction mechanisms, i t is clear that the N halosuccinimides are valuable analytical reagents, in addition to their well-known uses in synthesis. They represent one homologous series of compounds which can be used in differentiating alcohols, saturated amines, and some position iscmers and detecting amino alcohols. Students under the direction of P. L. Pickard, University of Oklahoma, and J . R. Entrikin, Centenary College of Louisiana, have used some of these differentiation tests; the results were very satisfactory. LITERATURE CITED
(1) Barakat, 11. Z.. a n d M o u s a , G. M., J . Pharm. Pharmacol., 4 , 115 (1952). (2) Cosmove. S. T2., a n d W a t e r s , W. A., J . Chem. Soc., 1949, 907.
ANALYTICAL CHEMISTRY
1322 Vrane, C . W., Forrest, J . , Step!ienson, O., and Waters, W. A , , Ibid., 1946, 837. Fieser, L. F., and Rajagopalan, S..J . Am. Chem. Soc., 71, 3935. 3938 (1949).
Grob, C. A , , and Schmid, H. U., Ecperientia, 5 , 199 ( 1 9 4 9 ) . Grob, C. A , , and Schmid, H. U , Helu. Chim. Acta, 36, 1763 (1953).
Hebbelynck, hl. F., and Martin, R. H.. Bull.
S O C . chim. Relg., 60,5 4 (1951). Hebbelynck, AI. F., and Xartin, R. H., Ezperientia, 5 , 69
(1949).
Hinsberg, O., Der., 23, 2902 ( 1 8 9 0 ) ; 33, 3526 ( 1 9 0 0 ) . Kamm, 0.. "Qualitative Organic .lnalysis," 2nd ed.. p . 5 3 , Kern York, John Wiley 8: Sons, 1948. Kroller, E., Siiddeut. Apoth. Zty.. 90, 724 ( 1 9 5 0 ) . Lecomte, J., and Dufour, C., Compt. rurcd., 234, 1887 ( 1 9 5 2 ) . Lucas, H. J., J . Am. C'hrm. Soc., 52, SO2 ( 1 9 3 0 ) .
lleisenheilner, J., Bcr.. 46, 1145 (1913). Paolini, I. de, Gatz. c h i m . ital., 60,859 ( 1 9 3 0 ) . Paolini, I. de, and Hihet. G., I b i d . , 62, 1041 ( 1 9 3 2 ) . Price, C. C.. Pohland, d.,and \-elsen, B. H., J . Org. Chem., 12, 303 (1947).
Reich, H., and Reichstein, T., H e h . China. Acta, 2 6 , 562 ( 1 9 4 3 1 . Ritter, F. O., J . Chem. Educ., 3 0 , 395 ( 1 9 5 3 ) . Sarett, L. H., J . Am. Chem. SOC.,7 1 , 1185 ( 1 9 4 9 ) . Seliwauow, Th., Ber., 2 5 , 3617 ( 1 8 9 2 ) . Sivadjian, J., Bull. SOC. chim., 2 , 623 (1935). Wieland. P., and Miexher, K., Helr. C h i m , Acta, 30, 1876 (1947).
R E C E I V Efor D review October 26, 1953. .Iccelited 3Iay 6, 1954. Prea3 part of a report a t t h e Joint Southwest-Southeast Regional Meeting, h X f E R I C A S C H E M I C A L S O C I E T Y , y e w Orleans, L a . , December 10, 1953. sented
Titration of Bismuth with Ethylenediaminetetraacetic Acid Spectrophotometric End Points A. L. UNDERWOOD D e p a r t m e n t o f Chemistry, Emory University, Emory University, G a .
Prior to the development of ethylenediaminetetraacetic acid, the volumetric methods for determining bismuth were indirect and unsatisfactory. Since this reagent offers a simple and direct titration but suffers from a lack of good indicators, an attempt has been made to extend its usefulness by application of the photometric titration technique. The progress of the titration may be assessed by following spectrophotometrically the disappearance of the yellow bismuth-thiourea complex. or the appearance of the blue complex formed by cupric ion with the titrant. Quantities of bismuth from 0.5 to 100 mg. can be titrated accurately when present in a volume of 100 ml. Large quantities of lead do not interfere with the titration, and bismuth can be determined rapidly in a mixture with tin, lead, arsenic, and antimony by a simple procedure.
B
ISMUTH is usually determined gravimetrically or colorimetrically. The volumetric methods previously available are indirect, based on precipitation of bismuth with oxalate, chromate, molybdate, etc., followed by titration of the anions. Such methods are not considered completely reliable ( 4 , IO). Thus a direct volumetric method, in xhich bismuth itself is tivated, is of interest. Pribil and IIatyska have recently shown that bismuth may be titrated amperometrically with ethylenediaminetetraacetic acid ( 6 ) . A visual titration based on the disappearance of the yellox bismuth-thiourea complex upon the addition of ethylenediaminetetraaceticacid has also been described (S), but the recommended quantities of bismuth are large (100 t o 200 nip.). Photometric titrations with ethylenediaminetetraacetic acid have recently been reported by Sweetser and Bricker ( 7 , 8), IIalmstadt and Gohrbandt (LT), and Cnderwood (9). I n the present paper, the photometric technique may be applied with advantage to the titration of bismuth with this reagent. -4s little as 1 mg. of bismuth can be titrated easily. Furthermore, the bismuth complex Lyith ethylenediaminet,etraacetic acid is very stable. Thus, moderate quantities of numerous other ions do not interfere, and in certain cases, separations prior to the actual titration need not be performed with great rigor. Two photometric methods for obtaining the end point are described: the disappearance of the bismuth-thiourea complex may be
followed, or cupric ion may serve as indicator. I n the latter case, the formation of the cupric complex of ethylenediaminetetraacetic acid (less stable than the bismuth complex) indicates the end point in the bismuth titration. The use of both indicators is described because they supplement each other in extending the useful range of the method. APPARATUS AND REAGENTS
The titration cell was similar to that described by Goddu and Hume (2), with a light path of about 2.2 em. Such a cell can be mounted in the test tube attachment supplied for use with the Beckman Model DU spectrophotometer. The cell is thus entirely enclosed within the sample compartment) minimizing difficulties due to stray light. Holes drilled in the cover of the compartment to admit st'irrer and buret were fitted with felt gaskets. The stirrer and the 5-ml. Esax buret were painted black for a short distance on either side of the level where they entered the compartment. pH measurements were made with a Beckman Model G p H meter equipped with a glass electrode. Standard bismuth solutions (generally 0.01M) Tvere prepared by dissolving Baker's analyzed bismuth metal (99,8'%) in the minimal quantity of 1 to 1 nitric acid with gentle heating, followed by dilution with distilled water containing sufficient nitric acid to make the final solution about 0.5M in acid (to prevent hydrolysis of the bismuth). -411 the titrations were carried out at a pH of about 2, although the pH is not extremely critical. A chloroacetate buffer is appropriate because of the pK value of chloroacetic acid. However, chloroacetate solutions slowly liberate, on long standing, sufficient chloride ion to form a precipitate with bismuth (BiOCli. Thus, buffer solutions were not kept on hand, but rather, apprnpriate quantities of solid chloroacetic acid were added as desirel. folloJYed by p H adjustment with ammonia or sodium hydroside in the final solutions to be titrated. Eastman Kodak Co., Rochester, S . Y., practical grade, monochloroacetic acid, distilled to remove dark-colored impurities, was employed. The disodium salt of ethylenediaminet'etraacetic acid (Benworth Chemical Co., Framingham, Mass., disodium versenate. analytical reagent) was dissolved in distilled water to prepare solutions of the titrant (0.1 or 0.01M) which were standardized by photometric titration against the st'andard bismuth solutions. 411 other materials were reagent grade or the equivalent. TITRATIONS WITH CUPRIC ION AS INDICATOR
The titration of a bismuth-copper mixture with ethylenediaminetetraacetic acid is very similar to the titration of an ironcopper mixture previously reported from this laboratory (9). Figure 1 shows the type of titration curve obtained a t a wave
