V O L U M E 25, NO, 1 1 , N O V E M B E R 1 9 5 3 acid is one of the products, it may be sufficiently stable for a quantitative procedure. For example, the odor of acetic acid is easily recognized during the oxidation of rhamnose, a methyl carbohydr:tte, and calculation taking this into account gives a yield of 102.0%. Ethyl alcohol, also, is oxidized within a few per cent of theoretical to acetic acid. llethylene groups are less stable than CH, groups, and their presence in propionic, succinic, and malic acids apparently causes these substances to be less stable than acetic acid. However, the effect of CH2 groups depends entirely upon neighboring groups, for, whereas malonic and citric acids are quantitatively oxidized, malic and succinic acids are resistant to considerably differing degrees, as are lauric and stearic acids. The presence of an OH group apparently renders a carbon atom quantitatively oxidizable, as in the carbohydrates and glycerol, tartaric acid, inositol, and perhaps, most strikingly, glycolic (hydroxyacetic) acid. The difficultly oxidizable CHs group in methanol is rendered quantitatively oxidizable by the OH group. In this respect the CH,O group, and the ether linkage, -C+-C, are apparently in the same category as the OH group, as shown by the results with methyl mannoside, methyl galacturonide, methyl galacturonide methyl ester, and trimethyl methyl mannoside. In fact, it appears possible to generalize t h a t the presence of an oxygen atom of any type, alcohol, carbonyl, carboxyl, ester, and ether renders the particular carbon atom to which it is attached completely oxidizable to carbon dioxide. This general effect of oxygen seems to arise from a specifically engendered oxidizability, rather than merely an oxidative opening wedge, inasmuch as nitromethane, with a partially oxidized carbon atom, is not completely oxidizable to carbon dioxide by the present technique. The effect of amino nitrogen, itself quantitatively nonoxidizable ( 2 , S), vanes greatly. Glycine is more oxidized by the reagent than acetic acid; serine is almost but definitely less than completely oxidized: nicotinic acid, which resembles benzoic acid except that it has nitrogen in place of the meta carbon atom, is, however, practically nonoxidizable. In other positions the NH? group has little or no effect, as in acetamide or anthranilic acid. The f3 nitrogen of p-nitrophenol was quantitatively oxidized to the +5 state by the reagent. The aromatic ring as well as unsaturated structures like malic acid are completely oxidized, although the yields for the aromatics tend to be somewhat l o r e r than those of the aliphatics. CONCLUSIONS
The results indicate that organic substances whose carbon atoms are all individually attached to oxygen atoms, or aromatics,
1769 caz1 be determined with small error in the presence of moisture, ash, and other nonoxidizables, or as pure components in a binary mixture, with the method described, assuming complete oxidation of carbon to carbon dioxide. On the other hand substances reproducibly oxidized to carbon dioxide plus a fairly stable intermediatelike acetic acid can be approximately quantitatively determined by taking this product into account theoretically, or accurately by standardizing the reagent against the pure substance. For samples with one oxidizable component, A:
% A = -
;x
100
For samples with pure components A and B:
where V = volume in liters of dichromate solution of normality N reduced per gram of actual weight of sample, and a and b = equivalents of dichromate reduced per gram of pure components A and B. These values are either theoretical ones deduced from formula or empirical ones determined by experiment, in accordance with the results presented in this paper. ACKNOWLEDGMENT
The authors take pleasure in thanking R. M. hlcCready for his helpful advice and for his contribution of sugars, A. I,. Potter for his contribution of purified starch, and E. A. McComb for the Karl Fischer analyses. LITERATURE CITED
(1) Cardone, J. J., and Compton, J. W., ANAL.CHEM.,24, 1903 (1952);25, 518 (1953). (2) Christensen, B. E., Williams, R. J., and King, A. E., J. Am. Chem. Soc., 59, 293 (1937). (3) Christensen, B. E., Wong, R., and Facer, J. F., IND.ENG.CHEM., ANAL. ED.,12, 364 (1940). (4) Lsuner, H. F.,and Tomimatsu, Y., ANAL.CHEM.,25,1769 (1953). (5) Launer, H.F., and Tomimatsu, Y., Food TechnoE., 6,59 (1952). (6) Moore, W. A,, Kroner, R. C., and Ruchhoft, C. C., ANAL. CHEM..21. 953 (1949). (7) Segal, L.1 Tripp, R. C.,.Tripp, V. W., and Conrad, C. M., Ibid., 21, 712 (1949). (8) Tomimatsu, Y . . and Launer, H. F., Food Technol., 6,281 (1952). RECEIVED for review June 1 , 1953. Accepted August 10, 1953. Presented before the Division of Cellulose Chemistry at the 123rd Meeting ,of the Los Angeles, Calif. AMERICAN CHEMICAL SOCIETY,
Rapid Accurate Determination of Cellulose with the Dichromate Heat-of -Dilution Method BERBERT F. LAUNER AND YOSHIO TOMIMATSU Western Regional Research Laboratory, Albany, Calif. method for the determination of carbohyTdratesheat-of-dilution and certain types of other substances (6) is also apHE
plicable to celluloses. The a-cellulose determination is extensively used (2, 7, 8) in research and industrial control work on paper, rayon, wood pulps, and related products, and a t least three standard (1,IO) methods are in use in this country, whereas total cellulose is routinely determined in cotton (a). In most of these applications, speed and/or precision are essential, and many efforts have been made toward this end. This report presents comparable results with the heat-of-dilution method and another method requiring external heating, applied to identical samples of celluloses, starch, and glucose, with identical reagents.
METHOD
The heat-of-dilution method has been described ( 5 ) . No attempt was made to dissolve the celluloses and precision oxidation wa8 secured in the heterogeneous system. A eriod after the addition of the acid was found to suffice for cellurose, starch, and glucose. The method requiring external heating was essentially that used by Kettering and Conrad (S),in which 0.09 gram of cellulose, dry basis, is dissolved in 25 of 1 2 sulfuric ~ acid. Then 20 mi. of water and 10.00ml. of 1.835N dichromate solution are added, and the mixture is boiled under reflux for 1 hour, and and titrated a8 Usual. MATERIALS
The surgical cotton was a commercial product of unknown
ANALYTICAL CHEMISTRY
1770 origin and was used without purification. Ground (20-mesh) and unground specimens gave the same oxidimetric results. The three samples of purified cellulose were prepared and contributed by C. M. Conrad, Southern Regional Research Laboratory, and were used without further treatment. The high- and low-viscosity celluloses n-ere commercially purified and derived from cotton; the viscose rayon, from wood. The latter had been extracted with hot ethyl alcohol to remove resins, etc., a t the Southernal Regional Research Laboratory. Moisture in the celluloses was determined with a vacuum oven a t 3 mm. of mercury and 110" C. for 20 hours. Ash was determined for all materials at 550" C. for 16 hours, after precharring with infrared. -4sh values for the celluloses in the order of Table I were 0.04, 0.13, 0.02, and 0.05%. The starch and glucose have been described ( 6 ) .
The latter is thus oxidized through heat of dilution; subsequent external heating completes the oxidation of resins. Errors in the alkali-soluble fraction are the only critical ones-; those in the alpha fraction cancel out, practically speaking, inasmuch as a 1.5% error therein would result in an error of only 0.1% in an CYcellulose value near 90%, as calculated from total cellulose. CONCLUSION
Cellulose can be determined rapidly and with slight error, in the presence of moisture and usual inorganic impurities, by applying the theoretical factor 0.01240 gram of cellulose per ml. of 1.835 AT (90.00 grams per liter) potassium dichromate solution, with the dichromate heat-of-dilution method.
RESULTS AND DISCUSSION
The results by the two methods on the celluloses, starch, and glucose are shown in Table I. The yield values were calculated as in previous work ( 6 ) . Of the sources of error previously discussed, only two need be stressed. Moisture in cellulose is particularly difficult to determine because the last traces of water are tenaciously retained by such high polymers. Both sets of values are probably too low, by the same amount, because of this effect. Nelson and Hulett (6) found by extrapolation to 250" C. that 0.41% water remained in their cellulose a t equilibrium a t 115" C. and 0.001 mm. of mercury. If such a value could be applied to the celluloses of Table I, the heat-of-dilution method could be assumed to give truly theoretical yields for celluloses. The high yield for surgical cotton would then have to be ascribed to oxidizable impurities of a more reduced nature than cellulose.
Table I.
Comparison of Results by Two Methods on Celluloses, Starch, and Glucose
Substance High viscosity cotton Surgical cotton Viscose rayon Low vlscoslty cotton Starch Glucose
Heat-of-Dilution h l s d External Heating Method Yield, Standard No. of Yield, Standard No. of Yo of devia- repli% of devia- replitheory tions cates theory tions cates 99.70 100.05 99.65
0.18 0.27 0.12
6 12 6
98.50 98.20 98.50
0.24
6
0.08
4
0.24
6
99 60 99 35 99 40
0 21 0 21
16
9 8 45 98 25 99 20
0 18 0 22 0 21
8 8 8
0 12
10 12
The other error is due to carbon monoxide formation and escape. Segal, Tripp, Tripp, and Conrad (9) have shown that 1.0 to 1.6% of glucose and cellulose was converted to carbon monoxide when they used the same method of external heating applied herein for comparison. They measured the amount of carbon monoxide which escaped from solution and thus accounted for their low results, which were in essential agreement with those in Table I, column 5, the glucose value of which fits into their range of values (their Table IV). It appears reasonable to account for the difference between the two sets of yield values as being due to smaller quantities of carbon monoxide formed or escaping in the heatrof-dilution method. This could be the result of the much more rapid heating, together with the two- to fivefold greater concentrations of acid and dichromate in the present method over t h a t of external heating. Furthermore, in the latter method, some oxidation, approximately 9%, occurs during the addition of dichromate to the cellulose solution. Since under these conditions cellulose is in excess a part of the time, carbon monoxide formation may be favored. Both procedures are combined in the a-cellulose determination developed a t the National Bureau of Standards ( 4 ) and used as ASTM and TAPPI standard methods ( 1 , IO). Solution of cellulose by 12M acid, followed by dichromate, is used in the alpha fraction. whereas addition of concentrated acid to the dichromate-cellulose mixture is used for the alkali-soluble fraction.
ACKNOWLEDGMENT
The authors take pleasure in thanking C. M. Conrad for the purified celluloses. LITERATURE CITED
(1) American Society for Testing Materials, ASTM Standard hlethod No. 588. (2) Burton, J. O., and Rasch, R. H., Bur. Standards J . Research, 6, 603 (1931). (3) Kettering, J. H., and Conrad, C. M,, IND.ENG.CAEM.,A N ~ L . ED.,14, 432 (1942). (4) Launer, H. F., J . Research Natl. Bur. Standards. 18, 333 (1937); 20, 87 (1938). (5) Launer, H.F..and Tomimatsu. Y.. b x a ~CHEM.. . 25.1767 (1953). (6) Nelson, 0. A , , and Hulett, G. A , , J . I n d . Eng. Chem., 12, 40 (1920). (7) Scribner, B. W., P a p e r I n d . a n d P a p e r W o r l d , 30, 2 (1948). (8) Scribner, B. W., and Wilson, W. K., J . Research ~2'atl. Bur. Standards, 39, 21 (1947). (9) Segal, L., Tripp, R. C., Tripp, V. W., and Conrad, C. AI., ASAL. CHEM.,21, 712 (1949). (10) Technical A4ssociationof the Pulp and Paper Industry, TAPPI Standard Method No. 42911. ~I
RECEIVED for review June 1, 1953. Accepted August 10, 1953. Presented before the Division of Cellulose Chemistry a t the 123rd Meeting of the Los Angeles. Calif. AMERICAN CHEMICAL SOCIETY,
Infrared Determination of Total Aromatics In Naphthas and Catalytic Reformates Boiling between 200' and 400' F. JOSEPH BOMSTEIN Sinclair Research Laboratories, Inc., Harvey, I l l . of total aromatics in hydrocarbon fractions is D of considerable interest to petroleum refiners, and has been the subject of many investigations Methods have been deETERMISATION
veloped through use of several techniques, including acid absorption ( 1 , 5 ) , ultraviolet (8), Raman ( 6 ) , mass spectrometry (g), and adsorption (3). The infrared method was developed to overcome difficulties encountered in several of these techniques, and is found to provide a rapid, reasonably accurate analysis, with limitations, interference. and errors as discussed below. APPARATUS AND MATERIALS
All spectra were obtained with a Perkin-Elmer Model 21 spectrometer, using rock salt cells and prism. The maker's recommended quantitative conditions were used throughout (9). Recordings were linear in wave length. All pure compounds were obtained from the National Bureau of Standards and were of better than 99% purity, except o-tertbutyltoluene, which was obtained from the National Advisory Committee for Aeronautics, Washington, D. C., and was of unknown purity.
