INTERFERENCES
1,4-Naphthoquinone, its adducts and addition products, and o-toluic acid are possible sources of interference in refined PAA. Any maleic anhydride, maleic acid, or fumaric acid present in the material will react similarly to the P h A and will not interfere. 1,4-Naphthoquinone is soluble in alkali with decomposition. Under the conditions of the procedure some naphthoquinone, its decomposition products, or its adducts are extracted and absorb a t various wavelengths between 290 and 240 mp, A series of samples containing 2 grams of recrystallized PAA, 4 mg. of benzoic acid, and various amounts of 1,4-naphthoquinone was treated according to the sample procedure. The data in Table I show that up to 50 p.p.m. of 1,4-naphthoquinone will not cause more than experimental error in the final result. For PAA containing higher concentrations of 1,4-naphthoquinone the following procedure was used. To the 2-gram sample of PAA add 25.0 ml. of 1 to 19 (by volume) sulfuric acid solution. Heat the mixture under reflux to 75’ to 80’ C. on a steam bath. .4dd 5 ml. of 5% potassium permanganate solution and continue heating for 30 minutes. Neutralize the mixture with 5 ml. of 10X sodium hydroxide solution and heat for 10 minutes or until all of the PAA is in solution. Cool to room temperature. Adjust the p H of the solution to 4.0 with 6.V HC1. Filter through Whatman KO.1 filter paper. Dilute, extract, and measure the absorbance as directed in the procedure. Prepare the blank and calibration accordingly. By this pretreatment benzoic acid has been suc-
cessfully determined in P.4A containing as high as 500 p.p.m. of 1,4-naphthoquinone. o-Toluic acid was found to exhibit the same properties as benzoic acid, in that it can be extracted under the conditions of the test, and its absorptivity in chloroform is of the same order as that of benzoic acid. Claims have been made (1) that i t can be converted into phthalic acid by heating with basic potassium permanganate. Ten milliliters of a solution containing 0.5 gram of o-toluic acid per liter, 5 ml. of 1.OM sodium hydroxide, and 5 ml. of 570 potassium permanganate were refluxed for 30 minutes. The solution was cooled, filtered, and treated according to the procedure. There was no absorbance in the 300- to 250-mp region, which indicates that the interference of o-toluic acid was removed. Using the above data the recovery of benzoic acid in the hydrolysis-extraction procedure is 92%, and with the permanganate pretreatment is 84Y0. Since no equivalent methods were available for the determination of these quantities of benzoic acid, the respective absorptivities were used with each procedure, and the relative recovery of benzoic acid was assumed to be 100%. A statistical study of the hydrolysisextraction procedure was conducted by three analysts on 2 days. Benzoic acid was determined in two production and three competitive samples of refined PAA which were manufactured from both naphthalene and mixed (0-xylenenaphthalene) feeds (Table 11). Since the ratio 0.0014/0.0017 from the analysis of variance is less than I,
the analyst error is obviously not significant when the F test is applied. The “experimental error,” u E 2 , is an estimate of the reproducibility of duplicates by a given analyst. As usuaI, it is a gross understatement of the true error of the method. For this reason the effects are tested against the interaction error. The precision of the method obtained from the pooled error mean squares is estimated a t &0.04% or 25% of the amount present. The standard deviation of duplicate determinations is &0.02%; the standard deviation for the method is = ! ~ 0 . 0 4 ~ ~ , which amounts to 20% relative error in P A 4 containing less than 0.2% benzoic acid. ACKNOWLEDGMENT
The authors acknowledge the technical assistance of J. R. Lutchko, Milton Manes, and J. J. Petty. LITERATURE CITED
(1) Claus, A., Pieszcek, E., Ber. 19, 3085 (1886). (2) Gilman, H., Kirby, J. E., J. Am. Chem. SOC.54,345 (1932). (3) Kappelmeier, C. P. A., Farben-Ztg. 40, 1141 (1935); 41, 161 (1936); 42, 561 (1935); Paint Oil Chem. Rev. 6 , 10 (1937). (4) Miller, O., Chern. Zentr. 1914, I, 790. (5) Peters, H., ANAL. CHEAI.31, 1326 (1959). (6) Swann, M. H., Adams, M. L., Weil, D. J., Ibid., 28,72 (1956). RECEIVEDfor review .4ugust 2, 1961 Accented October 30. 1961. Division of Analitical Chemistrk, 139th Meeting, ACS, St. Louis, No., March 1961.
The Spectrophotometric Determination of AbieticType Dienoic Rosin Acids ROBERT L. STEPHENS and RAY V. LAWRENCE Naval Stores laboratory, Olustee, Fla.
b A procedure employing a modified Liebermann reaction for the quantitative determination of abietic-type dienoic rosin acids is presented. The acids are determined spectrophotometrically at a wavelength of 570 mp in the concentration range of 30 to 150 pg. The behavior of related compounds under the test conditions is discussed.
T
HE PRESENCE of many organic compounds in natural and synthetic mixtures can be demonstrated by qualitative color tests which vary in
degree of selectivity and sensitivity. In the field of rosin chemistry, several tests have been used to detect rosin and rosin derivatives under a variety of conditions. A discussion of these tests has recently been presented by Conner (2). The Liebermann reaction (4) with modification by Storch (6), Burchard ( I ) , and other investigators (2, 3) has been widely applied to the detection of rosin and rosin derivatives. In general, a positive t,est is based on the formation of a “fugitive or transient violet” color when the sample, in acetic anhydride,
is treated with concentrated sulfuric acid. In most cases, the violet rapidly changes to a nondescript brown which is not specific for this group of constituents. Swann (6) has modified the general test and applied it to the qualitative and quantitative determination of rosin and rosin derivatives in surface coatings. Since the Liebermann reaction is highly sensitive, there is some danger in the application of this test to complex materials, for even trace impurities may produce colors which are similar, therefore creating some confusion with respect VOL. 34,
NO. 2,
FEBRUARY 1962
199
to interpretation. The violet produced with rosin is undoubtedly due to the presence of the abietic-type diene acids @)-namely, abietic, palustric, neoabietic, and levopimaric acids-which are detectable in very low Concentration in the absence of interfering constituents. The Liebermann reaction has been modified to give a more stable and reliable color system which will allow the quantitative estimation of rosin and the abietic-type diene acids at concentrations of 30 to 150 pg. For quantitative determination, the color is measured spectrophotometrically a t a wavelength of 570 mM,
anhydride was added (about 5 parts excess per 100 parts of glacial acetic acid), The excess anhydride throws the mixture out of balance so that the color develops rapidly and fades t o give a light yellow to almost colorless blank solution. Kecessary corrections for the blank n-ere made for each determination according t o established standard procedures. RESULTS AND DISCUSSION I
I
450
500
1 550
1
I
1
600 650 700 WAVE LENGTH (mp)
I 750
1 1 800
Figure 1, Maximum absorption curve for abietic acid color complex
EXPERIMENTAL
Apparatus. T h e spectrophotometric determinations were carried out on a Coleman Universal Model 14 spectrophotometer, employing 19 x 150-mm. round bottomed cuvettes. Reagents. DEVELOPIXGAND DILUTING SOLUTION. The preparation of the solution must be carried out carefully to produce consistent results. I n a n appropriate sized, glassstoppered flask t h e following volume proportions of reagents were mixed: glacial acetic acid (dried over anhydrous CaS04) 100 parts, concentrated sulfuric acid, 24.5 parts, a n d acetic anhydride 12.0 parts. The sulfuric acid was added t o the glacial acetic acid, with cooling, and the acetic anhydride combined with this cooled mixture. The contents were mixed thoroughly and kept stoppered when not in use. Precautions should be taken t o avoid undue contact with the atmosphere since the mixture will absorb water readily and thus decrease the effectiveness of the reagent. For use in the quantitative procedure, this reagent can be stored for 2 t o 3 weeks under proper conditions. It can be stored for considerably longer periods when used on1 as a qualitative reagent. STANDARD&osm ACID SOLUTIONS. The standard solutions of rosin and rosin acids were prepared by dissolving appropriate concentrations of the materials in glacial acetic acid. The samples were prepared fresh for each set of determinations. All reagents used in the preparation of solutions were analytical grade. Procedure. Before the analytical procedure was performed, t h e developing and diluting reagent was added t o a 50-ml. buret which had been fitted a t t h e t o p with a drying tube packed with anhydrous CaSOd. This precaution was necessary t o keep t h e solution out of contact with atmospheric moisture during analyses a n d t o eliminate undue changing of t h e solution in t h e buret due t o moisture pickup. Under these conditions, the reagent was held in the buret for several days with little loss of effectiveness. The color reaction was carried out directly in 19 X 105 mm. round bottomed cuvettes. The glacial acetic 200
ANALYTICAL CHEMISTRY
acid sample solution was added to the tube to give a maximum of 0.5 ml. If less than 0.5 nil. of sample solution was used, additional glacial acetic acid was added t o bring the volume to 0.5 ml. To the 0.5 ml. of sample solution was added, from the buret, exactly 0.5 ml. of the developing solution. The solutions were mixed and placed in a water bath a t 70" C. for 1.5 minutes t o develop the violet complex. After the necessary time, the cuvettes were removed and cooled for 10 to 20 seconds in ice water. To the colored solution, exactly 4.0 ml. of the diluting solution were added from the buret, and the contents of the tube were mixed thoroughly. After allowing a few seconds for the air bubbles to disappear, the color was read on the spectrophotometer at 570 m l , Generally, the color was stable for 2 t o 3 minutes with absorbance values changing less than 0.5% after 5 t o 6 minutes. Visibly, the color may last for 10 minutes or longer. The stability of the color limits the determinations at any one time t o about three, which allows triplicate values to be measured when necessary for a n y one concentration. Blank determinations were made on duplicate samples according t o the same procedure; hom-ever, the developing and diluting reagent for the blank was a special mixture in which excess acetic
The Reproducibility of Abietic Acid Determinations rlbietic Observed Deviation, Acid, pg. Values, pg. MLg.
Table 1.
121 120 118
+A
90
90 92 91
0 +2
60
61 60 62
$1 0 +2
120
Std. dev.
= f1 . 2 pg.
-2
$1
Although the color reaction was carried out a t T O O C. in all instances reported here, other temperatures-lon er and higher-can be used. At temperature higher than 70" C., the time necessary for niaximuni color developnlent is very short; )Thereas, a t room temperature (25' to 28' C,),35 to 40 minutes are required for maximum color tirvclopment. The spectrophotometric niuasurement of the absorption curve of a sample of abietic acid treated with the m0difit.d Liihvmann reagent established that t h r maximum absorption of the purple color occurred a t 570 mp, as s h o m in Figure 1. A test of the other abietictype diene rosin acids, neoabietic, palustric, and levopimaric, samples of tall oil, and other rosins demonstrated the occurrence of the same color and absorption maximum as that for abietic acid. Under the conditions employed in this procedure, it is known that the abietic-type diene rosin acids, other than abietic acid, are isomerized to abietic acid. This clearly indicates the association of these acids to the formation of the color complex, whether as individual acids or in the rosin misture. In the concentration range of 30 to 150 pg. of abietic acid, the relntionship of color intensity to the acid concentration follows Beer's laiv. The reproducibility of triplicate determinations of several concentrations of ahietic acid is shown in Table I. Similar determinations with the other abietic-type diene acids shored only slight deviation in slope from the abietic acid curve. The discrepancies could be attributed to slight impurities in the samples lvhich are difficult to prepare free of other con-tituents. The same straight line relationahip results when tall oil rosin is analyzed for diene acid content. Since abietic-type dienr acids are associated 11-ith rosin composition, the presence of rosin can be determined in a relative manner. Dehydroabietic, isodextropimaric, and dextropimaric acids, which lack the conjugated double bond systeni of the abietic-type diene acids, do not give any color with this modified reagent when heated at 70" C. for several minutes. The same results were noted with pure fumaropimaric and maleopimaric acids. Tests of rosins modified
with vniious concentrations of maleic and fumaric acids gave positive rcactions to the reagent indicating that not all of the abietic-type diene acids had In preliminary studies, the reactd nir,thod has also been used to follow the diiappearance of abietic-type diene acids during the preparation of rosin polymers. The method may be applied also to determine the abietic-type diene acid contcnt of gum, wxd. and disproportionated rosins, as wcll as other matc.rials which might contain the abietic-type diene rosin acids. ‘The 1 1 of~ the Lieberniaiin reaction in testq for cholesterol and other sterols prompted tests on such compounds n ith the modified rcagent. Cholcderol and miwd phytosterols gave only very faint pink tests under the conditions outlined earlier in this paper. TT hich R ould eliminate them as srrious interfwing con5tituents. I n tests with oleic a i d Iinoloic acids. only linoleic acid
gives any appreciable color at low concentrations. It produces a reddish color with an absorption maximum which was shifted considerably from that of the rosin acids. However, the presence of large quantities of fatty acids with respect to the rosin acids, as in the case of tall oil fatty acids. does produce a sizable blank reading and therefore decreases the sensitivity of the determination. It is felt that the modified Liebermann method presented offers the advantage over many other tests, in that the specificity and sensitivity of the test for abietic-type rosin acids is increased considerably. I n addition, the stability of the color affords more dependence upon the actual color produced rather than on the fleeting glimpse of a color which may or may not hare been present. This remores some of the guesswork from the interpretation of the qualitative results and provides a
more reliable quantitative means of estimating the abietic-type rosin acids. LITERATURE CiTED
(1) B,urchard, H., Dissertation, Rostock
University, Germany (1889); Chem. 25 (1890). ( 2 ) Conner, A. Z., “Chemical Analyses of Resin-Based Coating Materials,” C. P. A. Kappelmier, ed., p. 31, Interscience, New York, 1959. (3) LaLande, W. A., Jr., J . Am. Chem. Soc. 5 5 , 1536 (1933). (4) Liebermann, C., Ber. 17, 1884 (1884). (5) Storch, L., Ber. osterr. Ger. Z. Ford., Chem.-tech. Ind. 9, 93 (1887); Chem. Zentr. 1419 (1887). (6) Su-ann, M. H., ANAL.CHEM.2 3 , 885 (1951). RECEIVEDfor review August 28, 1961. Accepted Xovember 30,1961. The Naval Stores Laboratory is a laboratory of the Southern Utilization Research and Development Division, .4gricultural Research Service, U. S. Department of Agriculture. R. L. Stephens was a fellow of the Pulp Chemicals Association while this work was in progress. Zentr.
Spectrophotometric Determination of Furfural in the Presence of Sulfur Dioxide JOHN F. HARRIS and LAWRENCE L. ZOCH Forest Products laboratory, Forest Service, U . S. Department of Agriculture, Madison, Wis.
b The absorbance of aqueous furfural solutions is depressed by the presence of sulfur dioxide, because of the formation of the aldehyde-bisulfite complex. The equilibrium constant for the complexing reaction was measured. The strong absorptivity of furfural, together with its property of complexing with bisulfite ion, suggests its use as an indicator for measuring bisulfite ion concentra tion.
A
basis for making a quantitative determination of furfural is provided by the fact that aqueous furfural solutions strongly absorb ultraviolet light. The spectrophotometric methoci has been thoroughly studied by Root (9,S ) , who investigated the effect of storage conditions upon the stability of dilute furfural solutions and developed a n analytical procedure for determining micro quantitirs (less than 1.0 fig.). The method was extremely accurate n lien eniployctl for the determination of pure aqueous solutions of furfural. W i r n crude solutions are to be analyzed, the furfural may be readily distilled from acidic or neutral medium without loss. If no other volatile materials are present, Root’s method is applirable,
but in the event that other substances are present in the distillate, it is necessary to determine their effect on the absorption spectra. The presence of sulfur dioxide in aqueous solutions of furfural would be expected to have a pronounced effect on the absorptive 07
I
I
270
280
FURFURAL No MOLAL R A V ~
li EXCELLEST
-0 -5 I
$
04
8 8
3
03
02
01
1 0250
I
260
-
I 290
300
WAYELENGTH i -mp
Figure 1. Ultraviolet spectral curves for furfural-sodium bisulfite solutions Constant furfural mg. per liter
level
approximately
3.5
capacity of the solution because of the addition complex formed (4, 5 ) . EXPERIMENTAL
Reagents. The furfural n a s t h e middle-third fraction obtained from t h e distillation of material obtained by double distillation of comrnercially available material. It had been sealed in a glass ampoule and stored in a freezer for a 4-year period. When originally stored it was water-white; when used it was clear, with a very pale yellow color. Sodium bisulfite, analytical reagent grade (Baker). Apparatus. A Beckman Model DK2 recording spectrophotometer was used for curve plotting (Figure I ) and a Beckman Model DU was used t o measure t h e absorbance of solutions at 276 mp. Solutions. Fifteen solutions containing the same total concentration of furfural b u t 1Vith varying amounts of sodium bisulfite were prepared by mixing stock solutions of furfural and sodium bisulfite. The molal ratio of furfural t o bisulfite ion in these solutions ranged from 1 : O t o 1: 100. RESULTS
The curves of Figure 1 illustrate the effect of increasing the bisulfite ion conVOL. 34, NO. 2, FEBRUARY 1962
* 201
