Preparation of Alkannin and Naphthazarin for Use as Reagents for

alkannin. Alkannin itself forms only a few per cent of the highly coloreó material extractable from the root, and it xvas shown that the nonalkannin ...
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beryllium-dye lake to come out of solution when dioxane i,i present.

tions must be observed to avoid contamination. These precautions have been well pointed out by Cholak and Hubbard (g).


In the analysis of fairly pure beryllium samples, alkannin and uaphthazarin yield results that compare favorably with other methods which have been proposed. Advantages of the method include the fact that color development is spontaneous and rapid, extremely rigorous pH control is not necessary, and the colored jolutions are stable for a sufficient time to permit convenient quanritative work. The sensitivity is as great as that of other meth')ds except the spectrographic, and the accuracy seems adequate. The two reagents serve equally well, conditions are essentially the 4ame for employing either one, and it becomes a matter of convenience as to which is to be used; naphthazarin is somewhat more easily obtained than alkannin, so that it may be the reagent of 'Bhoice. Like most of the beryllium methods previously employed, dkannin and naphthazarin are subject to considerable interfera c e from extraneous elements, and it appears that a t least a parrial isolation of beryllium will be necessary before application of rhe method to the analysis of such things as biological samples, minerals, alloys, etc. Tn analvzing such small amounts of material, sperial precau-


Cholak and Hubbard, . ~ N A I . .CHEM., 20, 73 (1948). Ibid., p. 970. Cucci, Neuman, and Mulryan, University of Rochester A t o m r Energy Project, Rept. UR-26 (1948). Dubsky and Krametz, Mikrochemie, 20, 57 (1936). Dubsky, Langer, and Wagner, Ibid., 22, 108 (1937). Fischer, 2.anal. C h m . , 73,54 (1928). Fletcher, White, and Sheftel, IND.ENG.CHEM.,ANAL. ED., 18 179 (1946). Hyslop, Palmes, Alford, Monaco, and Fairhall, Natl. Ins1 Health,Bull. 181 (1943). Kosel and Neurnan, Cniversity of Rochester Atomic Enera! Project,Rept. M-1965 (1947). ENG.CHEW,ANAL.ED., 12, 674 (1940). Sandell, IND. Ibid., p. 762. Toribara and Underwood, A x . 4 ~ CHEM., . 21, 1362 (1949). Underwood, Neuman, and Carlson, University of Rocheatw Atomic Energy Project, Rept. M-1951 (1947). White and Lowe, ISD. ESG. CHEM.,ANAL.ED.,13, 809 (1941) RECEIVED August 1, 1949. Based on work performed under contract witL the United States Atomic Energy Commission at the University of Rochester htomic Energy Project, Rochester, N.Y

- Organic Reagenta

B n d Annual Summer Sump~sium

Preparation of Alkannin and Naphthazarin For Use us

Reagents f o r Beryllium

r. Y. T O R I B ~ R AAND A.


?t*html oj Medicine and Dentistry, UniEersity of Rochester, Rochester, N. Y .

ikannin and naphthazarin were shown by Underwood and Neuman to be equivalent reagents for the microdetermination of beryllium. Alkannin (a substituted naphthazarin), which forms only a small fraction of the colored matter extractable from alkanet root (Alkanna tinctoria), was shown to be the only constituent active with beryllium. The bulk of the colored material appears to be a polymer of alkannin, and evidence indicates a dimer. The isolation procedure for alkannin was thoroughly stud-


N SEEKING a more satisfactory method for the microdeter-

mination of beryllium than any previously reported, Underwood and Neuman (8) developed first a method using alkannin and then an equivalent procedure using naphthazarin. Because alkannin is a substituted naphthazarin, the two compounds would be expected to behave similarly. 011


1 Alkannin



ittr 0 I1 Naphthazarin

Formaaek (6) first referred to the color reaction of berylliuni with an alcoholic extract of the root Alkanna tinctoria. Dubsky and Krametz ( 4 ) used both alkannin and naphthazarin in the microdetection of beryllium in a solution containing ethylenediamine. The alcoholic extract of Alkanna tinctoria (roots were

ied. The difficulties in obtaining large amounts of alkannin made it desirable to find a reagent that could be more readily procured. Naphthazarin was synthesized according to the method of Zahn and Ochwat, but the purification procedure was modified. The synthetic method was found to be much simpler than extraction from the root. Absorption spectra of the compounds alone in carbon tetrachloride and at several pH's in aqueous medium, with and without beryllium, were determined. obtained from the S. B. Penick Company) was tried, and a methoc for the microdetermination of beryllium was developed using such an extract. The variation from batch to batch of root led tc. the isolation of the active ingredient, which was alkannin -4lkannin itself forms only a few per cent of the highly coloreci material extractable from the root, and it was shown that the nonalkannin material gave no color reaction with beryllium. Brockmann (2) made a very complete study of alkannin ana its related compounds, and gave directions for its extraction and isolation. He extracted the root with petroleum ether and ther extracted the red material from the solvent with sodium hydroxide solution. After the deep blue alkali solution was washed severa! times with benzene and petroleum ether, the addition of acetic wid caused the precipitation of a red material. This was r e crystallized repeatedly from benzene to give pure alkannin which melted a t 148°C. Underwood and Neuman (9) attempted to follow Brockmann'c directions, but found that alkannin was too soluble in benzene to permit recrystallization. Evaporation of the solvent left a tarry, resinous mass. A different procedure was employed for the purificstion After precipitation with acetic acid, the solid w s

V O L U M E 2 1 , NO. 11, N O V E M B E R 1 9 4 9



Figure 1. Absorption Spectra of Alkannin and 'M Naphthazarin in Carbon Tetrachloride, 5 X




, , , , , , , , , , , , , , \,\:\p4 500 550 600 h MILLIMICRONS ~

Figure 2. Absorption Spectra of 4llcannin and Alkannin Polymer in Carbon Tetrachloride

I353 tiikell up with sodium hydroxide, then reprecipitated with acetic. acid. This cycle was repeated five or six times. The final precipitation with acetic acid produced bright red floes whicli were filtered and washed thoroughly with water. The solid was dissolved in alcohol and precipitated by dilution with water The dried product melted a t 143-4" C. Other workers attempting to follow this procedure on a larger scale obtained a considerable quantity of crude material from which no pure alkannirl muld be derived. . ; ithorough study of the isolation procedure yielded a numbei The bulk of the solid precipitated i j f interesting observations. upon the addition of acetic acid was not alkannin but whal appeared to be a polymer of it. The nature of the precipitatr was such that it clogged the filter and made washing extremel? difficult, and the early workers left unwashed cakes of thiF material for considerable periods of time before processing them further. No alkannin could be isolated from such cakes. Evidence indicates that polymerization of the alkannin occurF through the side chain, and the reaction was favored by the prolonged contact with acetic acid and sodium acetate in the unwashed cake. The bleaching of alkaline solutions upon standing in air indicates that oxidation occurs and destroys the chrornophoric group. Khen contacts with acid and alkali were kept to a minimum and the temperature was kept low, good yields of pure alkannin were obtained. Despite all precautions, the large bulk of the material extracted from the root was the polymer. The material probably exists as such in the root, and the alkannin content may be a seasonal function, as has been found to be the case for other natural products. The polymer is useless as a reagent, as it gives no noticeable color with beryllium under t,he conditions tried. Because of the difficultj- encountered in the preparation of large quantities of alkannin, attention was turned to a, synthetic material. Naphthazarin was formerly available commercially as alizarin black, but attempts to obtain a sample were unsuccessful. Several syntheses reported in the literature were tried. The first vias that of a patent by Ellis ( 5 ) ,which consisted of a condensation of succinic anhydride with hydroquinone in the presence of boric and sulfuric acids to yield a hydroxy-substituted 3-benzoylpropionic acid, which was subjected to simultaneoue ring closure and oxidation without isolation. From 100 g r a m of succinic anhydride and 40 grams of hydroquinone it, was PORsible to isolate only 400 mg. of pure naphthazarin. A synthesis according to Zahn and Ochwat ( I O ) proved much more satisfactory. In this reaction maleic anhydride and hydro. quinone are added to a melt of aluminum chloride and sodium chloride. The method of purification was modified, and piire naphthazarin was obtained in good yield. ISOLATIOY OF A L K A N h I h

Figure 3. Absorption Spectra of Naphthazarin in Aqueous Medium at Different pH's

A continuous extraction apparatus vas constructed by using a 4-liter filter Hask to contain t,lie ground root. The side neck was connected so that the overflow from the flask fed into a heated flask, from which the solvent was distilled and flowed into a tube that extended to the bottom of the filter liask. I n this w:ty the solwnt fioived up through the ground root and was concentrated in a flask. The filter flask .contained 1 kg. of the root, and the colored matter was eoncentrated to 500 ml. in a 1-liter flask. One batch was extracted in one day. Inasmuch as the procedure of Brockmann in which t,he petroleum ether extract was treated R-ith sodiuim I-lydroxide resulted iu emulsions, the solvent W B . S bionm off with a st,ream of air before treatment with alkaii. Heating on a steam bath may be employed to hasten the process. The residue is cooled, and 250 ml. of 1 hr sodium hydroxide are added and stirred vigorously for 5 minutes. Then I50 ml. of water arc added, stirred for a few minutes, and the mixture is centrifuged to settle the solid matter. The supernatant liquid is saved, and the solid it. stirred for 5 minutes with 100 ml. of 1 X sodium



dropping the powder into 250 ml. of alcohol during stirring. After stirring for about 15 minutes, the alcohol solution is filtered. Most of the solid is nonalkannin material and will not dissolve i n alcohol. The alkannin is precipitated by diluting the alcohol solution with four or five times its volume of water. The suspension is centrifuged to settle as much of the solid as possible The supernatant liquid is poured through a Buchnrr funnel, using a Whatman S o . 41 filter paper Finally, the solid is transferred to the filter and washed with a little water. As much of the li uid as possible is removed by suction and thp s j i d allowed to dry. The solid is dissolved in RLI little alcohol as possible and the procedure of precipitation by dilution with water is repeated A third precipitation from an alcohol solutiori gives a very pure product, melting at 143-4” C. The solid left after the first alcohol extractiou is stirred with alcohol and filtered again. Heating is not recommended because the solid will becomt gummy. This extraction with alcohol is continued until dilution with water followed bv centrifuging yields‘ no appreciable amount of solid Some additional alkannin may be recovered froni the colloidal supernatant liquid of the first feu alcohol extractions by precipitating the solid a it11 the addition of sodium chloride. The colloidal particles appear to have a negative charge, as sodium chloride is much more effective in roagulation than sodium sulfate. This solid should be filtered off and washed with water. ilfter drying, the solid is dissolved in alcohol, and the solution is filtered and diluted with water. Running through the cycle several times will give atmiit Figure 4. Absorption Spectra of Naphthazarin in Aqueous Medium 10% more of the pure material. with Excess Beryllium at Different pH’s Contact with sodium hydroxide and acetic acid should be kept as brief as possible, and temperatures should be kept below 20” C. If it is necessary to interrupt the procedure after treatment 15 itki either of the above reagents, the solutions should he kept in a refrigerator. The crude alkannin precipitated by acetic acid should not be allowed to stand for longer 600 than 1 hour after separation from the liquid. I t should be redissolved in sodium hydroxide or covered tsith di+ tilled water and kept refrigerated.



The yields were low and variable, ranging froni 700 mg. t o 4 grams per kg. of root. Inasmuch a? the dye is contained only in the bark of the root, it would be much more efficient to extract the bark alone if there were an easy way to separate it from the bulk of the root, Part of the variation in yield may be attributed to a difference in the amount of bark present in the different hatches extracted.





\ \



A synthesis according to Zahn and Ochwat (10) g:ivc’ the best yield. A MILLIMICRONS

h mixture of 10 grams of maleic anhydride and 11 grams of hydroquinone is added to a melt of 100 grams of anhydrous aluminum chloride and 20 granis of sodium chloride a t 180” and heated to 200-220” C The melt turns blue-red with foaming and solidifies after about an hour. I t is allowed to cool, the solid mass is pulverized and boiled with water, and concentrated hydrochloric acid is added until the purple color of the aluminuninaphthazarin complex turns to a brown color due to precipitated naphthazarin. The crude naphthazarin is dried and extracted with benzene. Zahn and Ochwat evaporate the benzene and sublime the residue. Sublimation was not satisfactory for the final purification because impurities sublimed along with naphthaaarin. The benzene solution is extracted with 2 X sodium hydroxide, and the benzene layer is discarded. The aqueous la) er is acidified with hydrochloric acid until the blue color disappears, and the naphthazarin comes down as a red-brown precipitate. The precipitate is filtered off, washed with water, dried in a vacuum desiccator, and recrystallized from “practical heptane,” a highboiling petroleum ether fraction. A yield of about 2 grams is obtained. Because naphthazarin slowly decomposed on heating in the open air, no melting point is reported and it was n e c w

Figure 5. Absorption Spectra of Alkannin with and witha,ut Beryllium in Aqueous Medium at pH 6.5 hydroxide and 150 ml. of water. The mixture is centrifuged again and the supernatant liquid is combined with the previous liquid. The solid matter remaining from the centrifuging operation is discarded. This solid is insoluble in both sodium hydroxide and acetic acid solutions. Centrifugation is employed rather than filtration because the filters are clogged by the mixture. The sodium hydroxide solution is acidified by the addition of acetic acid (1 to 1) until the solution turns red. The solid material is settled by centrifuging, and the supernatant liquid is discarded. This solid is dissolved in 200 ml. of 1 N sodium hydroside solution, and any insoluble material is separated by centrifuging. The alkaline solution is again acidified with acetic acid, and the solid is settled by centrifuging. The solid is washed with water and centrifuged again. It is freed from any solution by use of suction, or by centrifuging if cups for dr ing solids are available. If the solid is gummy, it is chilled wit% dry ice and powdered. The solid is dissolved by

V O L U M E 21, N O

11, N O V E M B E R 1 9 4 3

,arg to prepare the diacetate to characterize the material obtained by following the above procedure. A golden yellow material wvas obtained melting sharplv at 192" C., i n good agreement with reported values for the diacetate.

1355 the alkannin polymer the curves in Figure 6 are obtained. lium does not affect the spectrum of the polymer.



.ilk:rnnin sublimes readily at a temperature of 130" C. and a i,ressurc of 10-2 mm. Even when pure alkannin was sublimed iising temperatures as low as 120 ', a large amount remained in the heated portion of the tube as a dark, tarry mass. This residue \vas not appreciably soluble in alcohol hut as readily soluble in i wnzenc. The "alkannin polymer" obtained as the main bulk of the colored material in the root gave no sublimate at temperatures nim. lip to 180' C. and pressures from lo-* to Saphthazarin sublimes readily under the conditions employed 1'01. :tlkannin. The material in the heated portion of the sublimer wriinins R bright red, in contrast to alkmnin, which decomposes.

Alkannin has one asymmetric carbon atom, and it would be expected to be optically active. Brockmann ( 2 ) measured its optical activity using the cadmium red line a t 643.85 mg because of too much absorption in the conventional yellow sodium region. A special spectrum cadmium-mercury H4 type lamp was used with a Corning 2404 filter to cut out the mercury lines. A Franz Schmidt and Haensch KO.9123 polarimeter with a vernier reading to 0.01 ' was used. The solutions were necessarily dilute in order to pass enough light, and the angle measured was very small. For this reason twenty readings were taken on each blank and each sample, and the results were treated statistically. In chloroform the following results were obtained: (a):d'


(-0.223 X 100)/(1 X 0,0901) = -248" X 0.1028) = -254'

(a)$' = (-0.261 X l O O ) / ( l ABSORPTIOF; SPECTRA

The absorption spectra of alkannin, alkannin polymer, and rmphthazarin were determined in carbon tetrachloride solutions in n hich the chromophore concentrations were equal. I t can be seen from Figure 1 that the spectra of alkannin and iiaphthazarin are similar. The curve for alkannin checks very ,-lusely with that obtained by Brockmann (8). Figure 2 shows rhc spectra of alkannin and alkannin polymer and here again rhe curves are similar, indicating that the same chromophoric groups are involved. I n aqueous media, the spectra depend upon the pH. Figure 3 shows the spectra of an aqueous solution of the same concentration as for the carbon tetrachloride solution at several pH's. The solution goes from a red at 5.3 to a blue at 8.3. Figure 4 shows the effect of adding a large excess of beryllium ratio of 7 to 1 or more). The spectra undergo a great change due to the formation of the beryllium-dye complex, but pH has Little effect on the spectra of the complex. When beryllium is added to an excess of the dye a t constant pH, a combination of the curves shown in Figures 3 and 4 is obtained, and Figure 5 shows the difference between such a curve and a dye curve. Curves such as these were used by Underwood and Seuman to ?elect the optimum wave length and pH for analytical purposes. K h m an excess of beryllium is added to a solution containing



* 7"

Brockiiiann reported -225' and -227 ' C. on two samples, and his values are not too far from those reported here. The alkannin polymer showed no optical rotation. DISCUSSION

The empirical formula and structure of alkannin were disputed until the work of Brockmann. Raudnitz, Redlich, and Fiedler (7') gave the formula C16H1404, whereas Dieterle, Salomon, and Nosseck (3) gave ClbH1404, but neither group postulated a structure with oxygen in the side chain. Betrabet and Chakravarti ( I ) gave the formula CSoH2,Oa to alkannin, and their description of the compound fits that of the polymer reported in this work. Brockmann found the formula to be C16Hle05 with the structure as shown above. He attributed the discrepancies to the fact that none of the previous workers had obtained pure alkannin. The results of the present work would indicate that those before Brockmann worked with either the polymer or an impure compound. A rough determination of the molecular w i g h t of the polymer by the melting point depression of camphor gave a value of 520 to 580. This would indicate that the polymer wa,s dimer of alkannin which has a molecular weight of 288. The polymer shows the same chromophoric group as alkannin b j absorption spectra studies, but it shows no optical rotation. The latter fact shows that the OH in the side chain reacts, inasmuch as the asymmetry of the molecule is destroyed. This would indicate that the polymeriza. tion occurred in the side chain. Other factors which are consistent with the higher molecular weight of the polymer are its inability to undergo sublimation and the increase in the melting point. The polymer is also less soluble in alcohol than alkannin, although it remains extremely soluble in benzene. The reactivity of the side chain of alkannin may be seen in its behavior during sublimation. At temperatures as low as 120" a t a pressure of mm. a large amount of pure alkannin turns to the nonvolatile, benzene-soluble mass. This is in contrast to naphthazarin, which has the same structure without the side chain, is completely volatile, and undergoes no change under similar conditions. The sperific rotation of alkannin in chloroform solution is not too far from that reported by Rrockmann. However, if the calculations in the conventional formula are carried out using his data, a t ,,,,,,I,, ,,,,,,I,, 400 450 500 550 600 650 value one tenth that which he reports would be A MILLIMICRONS obtained. Because the magnitude of the angle measured is almost the same as that found in Figure 6. Absorption Spectra of Alkannin Polymer with and this work, it is believed that his concentration iS w-ithout Beryllium in Aqueous \Tedium at pH 6.5



expressed in granis par liter instead of the grams per 100 cc. used In the formula for specific rotation. If the value he gives were grams per 100 cc., the solution would be so highly colored that i t would be impossible to pass enough light to operate a polarimeter. If his concentrations are interpreted to be grams per liter, they would be approximately the same as for the solutions in this work. No difficulties were encountered in following the synthesis of uaphthazarin reported by Zahn and Ochmat, although it was necessary to modify the method of purification. Practical heptane, a high-boiling petroleum ether, was found t o be an excellent solvent for recrystallizing naphthazsrin. Naphthazarin may be synthesized in the necessary quantities much more readily than an equivalent amount of alkannin may be extracted from the root. Inasmuch as Underwood and Neuman (8) have shown the two reagents to be equivalent, it is recommended that naphtha7arin he iiqerl in the microdetermination of beryllium.



Betrabet, M. V., and Chakravarti, G. C., J . Indian Inst. 8ci.. 16A,41 (1933). Brockmann, H., Ann., 521,l (1935). Dieterle, H.,Salomon, A,, and Nosseck, E., Ber., 64, 208n (1931). Dubsky, J. V., and Kramets, E., Mikrochemie, 20,57 (1936). Ellis, G.H., Olpin, H. C., and Kirk, E. W., U. 9. Patent 1,911.945 (1933). Formanek, J., 2.anal. Chem.,39,417 (1900). Rraudnics, H., Redlich, L., and Fiedler, F., Ber., 64,1835 (1931, Underwood, A. L.,and Neumsn, W. F., ANAL.CHEM.,21, 134h (1949). Underwood, A.L.,and Neuman, W. F., University of Rochester Atomic Energy Project, Rept. UR-19 (1947). Zahn, K.,and Ochwat, P., Ann. 462,81 (1928). RECEIVED August 3, 1949. Based on work performed under contraoi with t h e United States Atomic Energy Commission a t t h e University of Rochester Atomic Energy Projert, Rochester, N. Y.


Chloroform Extraction of Ferric Cupferrate E. B. SANDELI,


PIIYLI,TS F. CI:XIRIINGS, University of Minnesota, fifinneapolis, Minn.

The distribution of ferric iron between chloroform and an aqueous phase containing much chloride in the presence of nitrosophenylhydroxylamine is governed by the relation

The value of K f depends upon the chloride concentration and also upon the indifferent electrolyte concentration. Values of K' for various chloride concentrations are reported.


HERE are a considerable number of scattered references in

the analytical literature on the extraction of metal cupferrates from aqueous medium by various immiscible organic solvents such as chloroform, carbon tetrachloride, and ether. The metals extracted are those forming cupferrates slightly soluble in mineral acid medium-e.g., ferric iron, vanadium, and molybdenum. Particularly, the extraction separation of ferric iron from such metals as aluminum and beryllium has been applied by H number of workers. I t seemed worth while t o determine the value of the extraction coefficient of ferric cupferrate as an aid to the evaluation of the wparation. The instability of cupferron in acid solutions prevents accurate quantitative data from being obtained, but even approximate results should have some analytical utility. DISTRIBUTION OF A METAL BETWEEN AQUEOUS AND IMMISCIBLE SOLVENT PHASES IN PRESENCE OF CUPFERRON

The following equilibria exist in this system:


HCf (HCf), A ueous &as,


+ Cf-

(hICf,), Aqueous phase

+ m Cf-

(MCfl), Organic solvent

[ H + l [Cf-I = fic,

[HCflu -[HCflo = [HCf],

(partition coefficient of nitrosophenylhydrox 1. pcf amine between organic solvent and watery [ l I + m ] [Cf-lm = kM [1VICfmll. [-= LlCfmlo [llCf,lW


The combination of these expressions gives:

The value of the equilibrium constant, K , may be found by direct experiment. It may also be obtained by calculation if certain data are known:

(aqueous phase). (HCf = nitrosophenylhydroxylamine) (1)

(HCf), Organic solvent

T=51 +m

The respective equilibrium constants are:

(aqueous phase).

(M+" = metal ion) (3) (4)

The value of p ~ / isk obtained ~ by dividing the molar solubility of the metal cupferrate in the organic solvent by the solubility product in water saturated with the organic solvent; the value of kcr/pcr is found similarly. The values of the solubility products of the cupferrates of ferric iron, copper(II), aluminum, bismuth, and tin(1V) have been reported(1). The solubility of the cup-