Studies of Organic Reagents and Methods Involving Their Use Qualitative Reactions of Salicylaldoxime and Its 5-Chloro, 3,5-Dibromo, and 5-Nitro Derivatives with Inorganic Ions JOKV F. FLAGG' AND N. HOWELL FURMAN Frick Chemical Laboratory, Princeton University, Princeton, N. J.
began to decompose at 210" and was somewhat charred at 220' C. A partial analysis of the compound was made by the semimicromethod of ter Meulen and Hesslinga (11). Carbon: found, 28.27, 28.37; calculated, 28.50 per cent. Hydrogen: found, 1.78, 1.78; calculated, 1.71 per cent. The solubility of the compound is so slight that 1 gram of the oxime dissolved in 75 ml. of alcohol was diluted to 100 ml. to make the test solution. ~-KITROSALICYL.ALDOXIME. The directions in Beilstein (2) were used in reparing 5-nitrosalicylaldehyde, which melted at 123-125" C. gncorrected) as compared with 126" C. reported ( 2 ) . Two grams of the aldehyde in 25 ml. of alcohol and 0.82 gram of hydroxylamine hydrochloride dissolved in a little water formed immediately a heavy white precipitate which was filtered, washed, and dried. The product melted at 220-223" C. (uncorrected) with some decomposition apparent. A partial analysis was made by the semimicromethod (11). Carbon: found, 45.90, 46.01; calculated, 46.16 per cent. Hydrogen: found, 3.51, 3.39; calculated, 3.32 per cent. The test solution contained 0.24 gram of the oxime and 60 ml. of alcohol per 100 ml. SOLUTIOXS OF INORGANIC QUBSTASCES. The solutions were made up from salts of reagent grade, in some cases previously tested in local investigations. The concentrations were such as to give closely 1 mg. per ml. of ion to be tested for. Tests for many of the rarer ions were made at the University of Virginia.
ALICYLALDOXIME was proposed by Ephraim (4) as a reagent for the gravimetric estimation of copper. Several important papers appeared subsequently (1, S, 6, 6, 14, 16) dealing with the reaction in greater detail and de-
S
scribing the separation of copper from other elements. The reagent has also been found useful for the determination of lead (9, 10) and palladium (8). An unsuccessful attempt to utilize salicylaldoxime in the estimation of zinc has been reported ( I S ) . Indirect volumetric methods for copper, nickel, and palladium have been based upon the properties of their salicylaldoxime compounds (7, 16). The polarimetric titration of copper .rTith salicylaldoxime has been studied ( 1 2 ) . The aim of the present investigation was to collect the scattered facts about the reactions of various inorganic ions with salicylaldoxime and by confirmatory and supplementary experiments to gain a more complete picture of the possible qualitative and quantitative applications of the reagent. Three substituted salicylaldoximes were prepared-namely, the 5-chloro, the 3,5-dibromo, and the 5-nitro derivativesin order to test the effect of modification of the reagent. The reactions of the four compounds were determined for nearly all the inorganic ions that are encountered in analytical systems. Comparative studies were made of the sensitivities of salicylaldoxime and the 5-chloro and 5-nitro derivatives in the detection of copper, nickel, bismuth, and lead.
Method of Testing In the survey of the qualitative reactions of the various ions that was made in this laboratory, 1 ml. of the reagent solution was added to 10 mi. of the solution to be tested. In so far as the solubility relations would permit, each ion was tested with each reagent in neutral, slightly acid, and ammoniacal solutions. The so-called neutral solutions were those obtained by dissolving the pure salts in water. Subsequent to this first survey and prior to the revision of this paper, numerous pH measurements were made of the ranges for the precipitation of various ions with salicylaldoxime. The pH measurements were made with a Beckman glass electrode pH meter. Tests of the reactions of many of the rarer ions were made by J. H. Toe and L. G. Overholser at the University of Virginia, and their results communicated to the authors. Their procedure involved the treatment on a spot plate of 0.05 ml. of test solution with 1 to 2 drops of a 1 per cent solution of each reagent, with adequate concentration of alcohol to hold the oxime in solution. After first testing, \vhen possible, in neutral solution the mixture was acidified with 1 drop of 0.3 *V hydrochloric acid, and then after time to permit reaction to occur, t'he solution was made ammoniacal by adding 2 drops of 0.3 S ammonia.
Reagents SALICYLALDOXIME. The crude oxime, prepared by the interaction of salicylaldehyde and hydroxylamine hydrochloride, both obtained from the Eastman Kodak Company, was recrystallized first from benzene and then from petroleum ether containing a little benzene; its melting point was 57' C. (uncorrected), which is t'he reported temperature for the pure compound. A fresh solution of the oxime dissolved in alcohol and diluted to contain 1 gram of oxime and 5 ml. of alcohol per 100 ml. was used in the tests. For tests in which the presence of chloride was not misleading, salicylaldehyde and hydroxylamine hydrochloride were allowed to react in alcoholic solution, and the resulting mixture was diluted to contain 1 gram of the oxime and 9 ml. of alcohol per 100 ml. 5-CHLoRoshLrcYLaLDoxIME. This compound was prepared according to directions given in Beilstein's Handbuch (2). The intermediate 5-chloro aldehyde melted at 95-97" C. (uncorrected) as compared with the reported melting point of 98" C. The 5chlorosalicylaldoxime prepared from the aldehyde melted at 123-124' C. The reported temperatures are 122" and 128" C. (2). Because of the smaller solubility of this compound the test solution contained 0.5 gram of the oxime and 25 ml. of alcohol per 100 ml. 3,5-DIBROalos.~LICPL.~LDOXI~fE. The 3,S-dibrorno aldehyde that was prepared according to Beilstein (2) melted at 82-83" C. (uncorrected); reported, 82" C. Eight grams of this aldehyde dissolved in 100 ml. of alcohol and 2 grams of hydroxylamine hydrochloride in a little water were allowed to react for an hour at about 90" C. The oxime precipitated upon adding 300 ml. of cold water. The dried product did not melt sharply but
Experimental Observations The data with regard t o the principal reactions of salicylaldoxime are summarized iii Table 1: which is based on both observations made in this investigation a i d the published observations of others. Ceric solutions and bichromate. the latter after long action, give brown precipitates which appear to be oxidation products of the oxime. An experinient in wliicli approximately 0.1 gram of ceric oxide might have been expected, if the precipitate were a ceric compound, gave 0.0006 gram of nonvolatile matter upon igniting the filter. Only a faint cerium reaction was obtained from this residue. The brown precipitates are gelatinous and very difficult to wash. Auric ion was reported
1 Present address, D e p a r t m e n t of Chemistry, University of Rochester, Rochester, N. Y.
529
I\DUSTRIAL A\D EKGINEERING CHEMISTRY
530
VOL. 12, NO. 9 illumination after 15 minutes. Acetic acid or ammonium hydroxide was added to adjust the pH to the proper range. The solutions of the metals were prepared by careful dilution of standartlized solutions. S a l i c y l a l d o x i m e and 5nitrosalicylaldoxime are of about equal sensitivity for the detection of copper, lead, and nickel, but the former is the most sensit'ive of the reagents in the detection of bismuth. The 5-chloro compound offers no advantages.
T iBLE I
IUll
h l n -a F e + +a
::;E:
Zn++a Pd-+ hIg++
YO? a
IoNb \yHICH 'T-IELD PRECIPITATES TTITH S?LICYLALDOXIXE Color of pH of Initial Precipitate Turbidity Remarks Soluble in acetic acid, a n d in ammonia a t pH 7 5 to 8 . 0 Yellowish white 6.3 Soluble in excess of S a O H Yellow 5.0 Light yellow Insoluble in excess of S a O H 5.3 Greenish yellow Acid solution Complete above D H 2 . 6 ( 3 ) Pale yellow About 7 Gelatinous; soluble in excess of ammonia 6 7-7 Bright yellow Stable t o a t least pH 9 , 4 a n d probably beyond. Insoluble in excess of ammonia Green t o brown S.8-8,Q Soluble in a large excess oi ammonia or of S a O H 6.8-7.0 Brown Soluble in excess of alkali Brown Dissolves a t about pII 0 4 5.3-5.6 Green Complete f r o m p H 7 t o 9 9. Solublein concd. S H I O H (3) W t ? 5 Dissolves in ammonia a t pH S S t o Y . 4 Light yellow Acid solution Reported t o be quantitative in solutions containing free Yellow sulfuric acid (7) Slightly ammoniac Light yellon. S o t quantitatiye Acid solution Best range 0.05-1.0 5 b u t a t inost 60 t o 70 per cent oi l' Black is ureciDitated . .
Formation of precipitates of these ions first noted by Ephraim
TABLE 11. Substance Tested
(4,
5).
POSITIVE IIE B S D I T S D E R I V I T I V E S
Salicylaldoxime Tellon-white ppt. I-ellow ppt. Light yellow p p t . Greenish-yellow p p t Pale yellow ppt. Bright yellow ppt. Green-bruwn ppt. Brown p p t , Red color Brown ppt. Green p p t . Light yellow p p t . Yellow p p t , Orange color or p p t , Light yellow p p t , Black p p t . Orange color Brown p p t . Brown p p t ,
(General conditions a s in Table I) 5-Chlorosalicyl3,5-Dibromosalicylaldoxime aldoxime Yellowwhite ppt. Inconclusive a Yellow ppt. Yellow ppt. White p p t . Inconclusive Light brown ppt. Green-brown p p t Pale yellow ppt. Inconclusive Bright yellow p p t . Inconclusive Green-broan ppt. Inconclusive Green-brown p p t . Inconclusive Blue color Inconclusive Brown p p t , Orange ppt. Green ppt. Green p p t . Light yellow p p t . Inconclusive Yellow p p t . K o t tested Orange rolor S o t tested Light yellow p p t . Inconclusive Inconclusive Black p p t B r o n n ~ p p.t Orange color Inconclusive Light brown ppt. Brown ppt. K o t tested
Discussion
5-Nitrosalicylaldoxime Red ppt. Orange ppt. Light yellow p p t . Green-yellow ppt. Pale yellow p p t , Orange ppt. Green-brown p p t , Green-brown p p t . \ iolet color Green p p t . Brownish-yellow p p t , Yellow p p t . Yellow p p t Orange color I-ellon p p t . Black p p t , Orange color Red-brown p p t . Yellow p p t , (reagent?)
T h e i n t r o d u c t i o n of a single chloro or nitro group into salicylaldoxime does not alter the properties of the compound as a reagent for inorganic ions to any marked degree. The colors of certain compounds of the 5nitro oxime are more vividfor example, t h e silver salt. The color given by the khloro compound with ferric iron is- noteworttiy. a Inconclusive indicates t h a t test was rendered doubtful b y precipitation of reagent itself. T h e i n t r o d u c t i o n of t w o bromine atoms into the salicylaldoxime molecule proby Holtzer (8) to give a brown-violet precipitate which turned duces a compound that is unsuited for qualitative or quantidark blue. tative applications. COLORREACTIONS. Ferric ion gives a red color wit'h the reagent in neutral or acidified solution. Osmium tetroxide TABLE111. LIMITSOF DETECTIOS solution gives a n orange color with the reagent only in alkaline (Expressed in parts of metal per number of ml. of solution) solution. Gahide ( 7 ) reported the formation of a n orange pre5-Chlorosalicyl5-Sitrosalicylcipitate in this case. Uranyl ion gives a n orange color in a n Cation Salicylaldoxime aldoxime aldoxime alkaline solution of the reagent. CU+T 1:2,000.000 1: 500,000 1 : 2,000,000 Pb++ 1 : 50,000 1: 10,000 1:50,000 The ions of the elements that are listed below were tested Xi+1:3,000,000 1: 1,000,000 1: 3,000,000 in neutral, slightly acid, and ammoniacal solution whenever a BitiT 1:250,000 1: 100,000 1:100,000 solution could be obtained in such p H ranges. Each ion was tested with salicylaldoxime and the 5-chloro and 5-nitro derivatives. Owing t o the slight solubility of the 3,j-dibromo Summary oxime, only a partial st'udy of its reactions could be inacle (see The reactions betTeen sevellty-tTT-o inorganic iolls alld Table 11). I n no case v a s a definite positive reaction obtained salicylaldoxime and its 5-chloro and 5-nitro derivatives have with any of the folloiving: Li, S a , K, Rb*, Cs*, Be, Ca, Sr, L4 been observed in a qualitative ~ T a yin various Ba, B, A41,sc*, Y t * , La*, Ce"', Pr*! Td*, Snl*, E'*, Gd*, limited series of observations has been using the 3,sDy*, Er*9 Tm*, Yh*, Ga*9 In*, T1"' *, Ti, zr*? dibromo oxime, which is of little utility because of its slight Ge04--, Sn '',IV, T;O'+, Cb", Ta*, as"'^', Sb"',Y, Cr"', Mo"', solubility. W"', Se04--, TeO,---, &InOI-, Reoi-, Ir'"*, Pt,"*, Ru"'*, The limits of detection of copper, lead, nickel, and bismuth and Rh"'*. (The tests for ions marked viith a n asterisk were \,,.ith salicylaltloxime and TTithits 5-chloro and 5-nitro derivamade by Yoe and Orerholser at' the Cniversity of Virginia.) tives have been The various reagents react with substantially the same list of ions and under approximately the same conditions of Literature Cited pH. I n some cases there is a distinct,ive difference in color, (1) h s t i n , S., a n d Riley, H. L., J . Chem. Soc., 1933, 314. as may be seen from Table 11. (2) Beilstein, F., "Handbuch der organischen Chemie", Vol. VIII, The relative limits of tlet'ection of the four metallic ions pp. 53-5, Berlin, Julius Springer, 1928. (3) Biefeld, L. P., and H o i v e , D. E., ISD.EKG.CHEY.,Anal. Ed., were found for each of the three reagents (Table 111). The 11, 281 (1939). 3,5-dibromo derivative was not tested because the insolubility of the compound itself renders the tests doubtful. In each 1925 (193")' case 10 ml. of the solution to be tested were treated with 0.5 (6) Feigl, F.,and Bondi, il., zbiti.. 64, 2815 (1931). ml. of the solution of the reagent, and observed with suitable (7) G a h i d e , SI., B d l . S O C . chim. B e l y . , 45, 9 (1936). Thj
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SEPTEAIBER 15, 1940
ANAL'k-TICAL EDITION
(S) Holtzer, H., 2. anal. Chem., 95, 392 (1933). (9) Ishibashi, M., and Kishi, H., Bull. Chem. SOC.Japan, 10, 362 (1935). (IO) Ishibashi, M.,and Kishi, H., J . Chem. SOC.J a p a n , 55, 1060 (1934): Brit. Chem. A b s . , A720 (1935). (11) Meulen, H. ter, and Hesslinga. J., "New Methoden der organisch-chemischen Analyse", Leipzig. Akadeniische 1-erlagsgesellschaft. 1927.
*
(12) (13) (14) (15) (16)
531
Keuberger, .4.,2. anal. Chem., 116, 1 (1939). Pearson, Th. G., Ihid., 112, 179 (1038). Reif, K., .Vikrochemie, 9, 424 (1931). Riley, H. L., J . Chem. SOC.,1933, 895. Tougarinoff, M.,Ann. SOC. sci. Rrztselles, 54B, 314 (1934).
PRESENTED before t h e Division of Physic31 and Iiiorgiiiiic Ctiriniatry at
the
99th Meeting of t h e ;\iiirrican Ctieniical Society, Cincinnati. Ohio.
A Simplified Alkali-Lability Determination for Starch Products 1
THO3IAS JOHS SCHOCH A?D C. C. JENSEN, Corn Products Refining Company. Edgewater, N. J.
A
S I M P L I F I E D alkalimetric method has been devised to estimate the relative hydrolytic degradation of starch products, analogous to the concept of alkali-lability (6, 7 ) . If the starch molecule is conceived as a glucopyranose chain terminating in a free aldehyde group, then any glucosidic hydrolysis should be reflected in increased aldehydic properties. Since the ordinary analytical procedures for reducing sugar are not applicable to starch, Richardson, Higginbotham, and Farrow (6) h a r e developed a special copper reduction technique to est'imate aldehyde content. The writers have found this method of questionable value, since the reducing value is largely influenced by the degree of dispersion of the starch in the alkaline copper medium. Raw starch slon-ly decomposes in hot aqueous alkali to give simple acidic substances, principally formic, acetic, and lactic acids, as well as pyruvic aldehyde. This immediately suggests that the reaction is initiated by enolization of free terminal aldehyde, as formulated by Evans ( 3 , 4 ) for the aldose sugars. T i t h acid-modified starches, alkaline decomposibion proceeds more rapidly, indicative of increased aldehyde content. Taylor (6, 7 ) has employed this concept of alkalilability as a n index of starch hydrolysis, by determining the amount' of iodine-reducing substances produced during a n arbitrary period of alkaline digestion. However, this iodometric technique is both complicated and tedious, and results cannot be duplicated by various operators. Also, starches which have been precipitated with acetone or et'hyl alcohol consume abnormal quantities of iodine, apparently because of retention of these solvents even after prolonged drying. Estimation of the acidic substances produced by decomposition of starches in hot alkali affords a much simpler and more precise measurement of alkali-lability. The procedure resembles that employed for saponification number of a fat :digestion of the starch in a measured volume of standard sodium hydroxide follon-ed by titration of the unconsumed alkali. The rate of decomposition of the starch, here termed the alkali number, is expressed as the cubic centimeters of 0.1 N sodium hydroxide consumed by 1 gram of st,arch during digestion in alkali for 1 hour a t 100" C.
3Iethod REQUIREDREAGESTS.Approximately 0.4 N sodium hydroxide, free from carhonate; 0.2 N sulfuric acid, accurately standardized; and 0.1 per cent alcoholic thymol blue solution. PROCEDCRE.The starch should be pulverized to pass a 60mesh sieve. Moisture is separately determined by drying 4 hours in VUCZLO a t 105' C., and the alkali number is calculated to the dry basis. Occasionally, a starch product will be encountered with added alkali or acid sufficient to affect the alkali number. In such cases, 1 gram of the starch is gelatinized in hot water and neutralized to t,hymol blue with standard acid or alkali, properly correcting the alkali number for this titer. The alkaline digestion may be conveniently run in an 8ounce narrowmouthed Pyrex nursing bottle. rldequate pro-
tection against carbon dioxide is afforded by the gum rubber caps marketed for bhis type of bottle, pierced with a hot needle to provide an exit for steam. Five hundred milligrams of the powdered starch are introduced into the bottle, 10 cc. of distilled water are added, and the contents are gently sn-irled to wet and suspend the sample. Then 25.00 cc. of 0.4 N sodium hydroxide are added by pipet, meanwhile agit,ating the sample to ensure uniform gelatinization in the alkali. If lumping occurs at this point, the determination should be repeated. Finally, 65 cc. of hot distilled water are added, and the bottle is immediately capped and placed in a vigorously boiling water bath. If a number of determinations are to be run, digestions may be commenced at intervals of 10 to 12 minutes. With starch products n-hich gelatinize in cold water, a slightly different technique is advised, to avoid the formation of insoluble lumps. The sample is introduced into a perfectly dry digestion bottle and \vetted with 1 to 2 cc. of benzene; 25.00 cc. of 0.4 N sodium hydroxide are then added with agitation, followed by 75 cc. of hot water. In this Tvay, complete dispersion of the starch is readily obtained, even with starches which have been precipitated from boiled pastes by alcohol. The bottle is heated for exactly 60 minutes, then placed in cold water, the cap is removed, and 50 t o 75 cc. of cold distilled water are quickly added. In this manner, the decomposition is halted almost immediately. One cubic centimeter of t,hymol blue indicator is added and the excess alkali titrated to a yellow end point with standard acid. Phenolphthalein has likewise been employed, but thymol blue seems somewhat more satisfactory. With highly converted starches, the end point is difficult because of the amber color which develops during digestion. In such instances, titration with the glass electrode t o a pH of 8 gives excellent results, though with practice visual titration to thymol blue can be applied t o all starch products. The titer value of t,he alkali is det'ermined by neutralizing 25.00 cc. of 0.4 A ' sodium hydroxide to thymol blue with standard acid. This procedure acts as a blank, balancing out indicator errors. Then the alkali number is calculated as: (cc. of acid to titrate blank - cc. of acid to titrate sample) normality of acid x 10 weight of sample on dry basis
x
Providing excess alkali is present, the concentration of sodium hydroxide employed for digestion does not materially affect the alkali number. However, variations in the amount of starch and T-olume of the digestion medium have a n appreciable influence, and close adherence to the recommended procedure is advised. From 365 determinations on 164 different starch products, the average deviation calculated +0.17 unit in the alkali number. Each value here reported represents the average of two or more determinations.
-4pplications This method of analysis has been applied to a number of theoretical and pract'ical starch problems, of n-hich the following are typical inst,ances. RAW STARCHES.Commercial corn and wheat starches possess alkali numbers which are consistently higher than
