Spectrophotometric Determination of Anthraquinone and Benzanthrone KERJIIT B. WHETSEL Tennessee Eustmun Co., Division of Eustman Zcodak Co., Ziingsport, Tenn.
can be analyzqd by utilizing the differences at 266 and 513 mp. Benzanthrone can be determined at 515 nip without interference from anthraquinone. The solutions are stable for seieral hours. .inthrone does not interfere with the benzanthrone determination and the interference is not serious in the determination of anthraquinone. The proposed method has been found quite useful as a routine control measure for the rapid and accurate analysis of anthraquinone-benKanthrone mixtures.
. i s part of an investigation of the preparation of
benzanthrone from anthraquinone it became necessary to analyze a large number of mixtures of these compounds. Since the existing methods did not appear suitable for routine analyses, the ultrai iolet and visible absorption characteristics of the compounds were studied. The absorption spectra of sulfuric acid solutions of anthraquinone and benzanthrone differ in many respects. Mixtures of the two compounds covering a wide concentration range
I
T RECESTLY became necessary in this laboratory to tlelermine the quality of a large number of samples of benzanthrone [7H-benz(de)anthracen-7-one],particularly with respect' t o the amount of anthraquinone present'. While the melting point of benzanthrone has oft'en been used in the patent literature as a criterion of purity, a more sensitive test, one n-hich would allow the determination of anthraquinone] was needed in order to evaluate properly the results of development work. Sokolov and Gurerich (8) have reported a method for determining benzanthrone in the presence of anthraquinone based upon the controlled oxidation of the former by chromic acid. Under certain conditions, benzanthrone dissolved in glacial acetic acid is oxidized to anthraquinone-a-carboxylic acid which is water-soluble and can thus be separated from the anthraquinone which has remained unchanged during the oxidation. The length of the procedure and t,he fact that the acid is further oxidized to anthraquinone if the conditions are not carefully controlled do not favor this method for routine control work. ..iccording to Sokolov and Gurerich ( 8 ) , the method based u p m the hjposulfite extraction of anthraquixone which Sielisch ( 7 )used to determine this compound in anthracene is not suitable for t,he analysis of ant,hraquinone-benzanthrone mixtures. ?*lore recently F-ainshtein (IO) has described a polarographic method of analyzing mixtures of these compounds, but a number of considerat,ions made it' impossible t o use their procedure in this work. The ultraviolet and visible absorption spectra of anthraquinone have been reported ( 1 , 3, 5, B ) , and Friedel and Orchin (f?) have published the spectrum of benzanthrone, but apparently no attempt has been made to analyze mixtures of these compounds spectrophot,omet,rically. -1more complete invest,igation of the ultraviolet and visible absorption spectra of anthraquinone and benzanthrone has result,ed in a method of analysis nhich allows either the siniultaneous determination of both compounds or the direct determination of henzanthrone alone. The method is based upon the different absorption characteristics of the two compounds when dissolre(1 in concentrated sulfuric acid.
ing point 171' to 173" C., was obtained by steam distillation of a crude sample. Kearly identical absorption data were obtained using a sample chromatographed on Doucil from acetone solut'ion. AXTHRONE.This compound, melting point 153.5' C., v a s prepared according to the procedure in "Organic Syntheses" (4). I'ROCEDURE
\\'eigli 50.0 mg. of t,he sample into a 250-ml. beaker, dissolve in reagent grade sulfuric acid, t,ransfer the solution into a 500-ml. volumetric flask, and dilute to the mark with wlfuric acid. Pipet a 10.00-ml. aliquot int'o a 100-ml. volumetric flask and dilute to volume with solvent. Measure the absorbance of the dilute solution a t 266 and 515 mp using 1.OO-cm. silica cells and reagent grade sulfuric acid as the reference liquid. Determine the cell correction by measuring the absorbance a t the analytical wave lengths r i t h pure solvent in both cells. Using the corrected ab-
APPARATUS A N D M A T E R I A L S
1
1
2.0
A
:I
O.OIL
*o:
A0
\
I
0.02
I 3 o:
4h-l
\ I
\
\I
I 450
, so0
I
so
WAVE LENGTH,mp.
SPECTROPHOTOMETER. All absorption measurements were made with a Beckman Model DU spectrophotometer equipped with an ultraviolet accessory set and 1.00-cm. silca and Cores cells. Cell corrections were applied when necessary. SULFURIC ACID. hlerck reagent grade sulfuric acid, sp. gr. 1.835, was used throughout this work. ANTHRAQUINONE, sublimed material, melting point 284" C. RESZANTHRONE.A reference sample of benzanthrone, melt-
Figure 1. Absorption Spectra in Concentrated Sulfuric Acid
-. --
-Anthraquinone Benzanthrone Anthrone All s o l u t i o n s 1 to 100,OOO (wt./vol.) 1.00-Cm. c e l l
-
1334
'
V O L U M E 25, NO. 9, S E P T E M B E R 1 9 5 3
1335
sorbnlicies, calculate the concent'rations of anthraquinone an(1 benzanthrone as follows:
yoant'hraquinone = 55.07 -4266 mr - 41.07 A 5 1 5 mr yo berizanthrone = 211.0 A j i j mr \vhrre .4 represents the corrected absorbancies
(loglo 1).
Table I.
.intliraqiunonr Part per 100,000 P a r t s Acid
7
I
I
I
1166
0 10 0 20
RESULTS
Spectra. Preliminary results showed that many crude heiizanthrone samples did not dissolve completely in common organic solvents in spite of the fact that pure anthraquinone and belizanthrone are fairly soluble in these solvents. The crude samplw were completely soluble, however, in concentrated sulfuric arid. and since comple1.e solution of the sample \yas considered a distinct advantage in a routine control analysis, all further ~ ~ I J I ~ ] . ; \vas carried out using this solvent.
ibsorhancics of Sidfiiric icid Solutions of .itithraqriinone
0 I82 0 36
