V O L U M E 21, NO. 8, A U G U S T 1 9 4 9
945
At a concentration of 0.4 S sodium hydroxide, the optical densities a t 290 mp of several concentrations of 3,Pdimethylphenol were measured. A plot of concentration against optical density yielded a straight line from which the individual points deviated no more than 1% over the optical density range 0.2 to 1.2. APPLICATlOY OF N E T H O D
The spectrophotometric method for phenols liaa been applied 111 the author's laboratory thus far to the determination of phenols in several hundred samples of thermally and catalytically cracked gasoline and to a few straight-run gaaolines. Approximately one hundred petroleum phenols or fractions thereof have been 3tudled. The method should apply to other petroleum products outside the gasoline range, provided it is realized that the specific extinction coefficient changes with n~olecularweight of the phenols arid that an appropriate coefficient must be used in the calculation. For calibration purposes, actual isolation and careful
purification of a sample of the phenols from a distillate in the boiling range to be studied are highly desirable. ACKNOW LEDGMEXT
The author wishes to express his appreciation for the suggestions and cooperation given by Warren W.Johnstone and Charles Wankat. Thanks also are due to IT. S.Gallaway for the infrared evamination of the petroleum phenols and to Charles Berg for a portion of the ultraviolet absorption study. LITERATURE CITED
(1) Field, E., Dempster, F.H., and Tilqon, G. E., Ind. Eng. Chem., 32, 489 (1940).
(2) Lykken, Louis, Treqeder, K. 9 , and Zahn, Victor, ISD.CNG. CHEM.,ANAL.ED.,18, 103 (1946). (3) Stoughton, R. W., J . BioZ. Chern., 115, 293 (1936). (4) Wetlaufer, L. A., Van Natta, F. J., and Quattlebaum, H. B.,
I N D . ENG.C H E M . , RECEIVED M a y 20, 1948.
~4x41,.E D . , 11, 438 (1939).
Determination of Carboxy Group in Aromatic Acids MAX H. HUBACHER Research Laboratory, Ex-Lax, Inc., Brooklyn 17, IV. Y . The carboxy group attached to an aromatic nucleus can be split off in the form of carbon dioxide by heating the acid with quinoline in the presence of a catalyst. In the apparatus described, the carboxy group can be estimated on samples of from 0.002 to 0.02 mole of acid. A comparative study of inorganic catalysts showed that basic cupric carbonate was the most efficient in most cases. Where this proved inefficient, silver carbonate acted as a decarboxylation catalyst.
I
S M A S Y cases the carbox) group attached to an aromatic
ring can be split off by merely heating; however, in the ma1 nork. N o r e than jority of cases, this procedure alone ~ 1 1 not half a century ago, several chemists ( 1 , 6) observed that the cleavage of the carboxy group in hydroxy acids can be speeded up by the presence of certain tertiary amines. Later, Killstatter and Pummerer found that copper exerts a catalytic effect in eliniinating the two carboxy groups from chelidonic acid (9). Shepard, Winslow, and Johnson were the first to combine these two observations and thus found an efficient method for the decarboxylation of aromatic carboxylic acids ( 7 ) . Though this reaction has been increasingly utilized in synthesis since 1930, the author has been unable to find a comparative study on the relative merits of the various catalysts proposed for this reaction, nor a simple apparatus for the quantitative study. The carbon dioxide developed in this reaction can be determined by recording the increase in pressure, or the increase in volume, or by 1% eighing. I n this work. the last two methods were employed. The apparatus shown in Figures 1 and 2 \$-as constructed for this purpose. By thia means, the carboxy group can be determined quantitatively, and a t the same time there is a11 opportunity to study the speed of reaction. The c a r b o y group can usu:illy be determined accurately and precisely by titration, T h e method described in this paper is of special interest in cases where the carbovy group is of such weak acidity that it cannot be titrated, or when the acid contain: other acidic groups besides the carboxy group that make titration valueless. APP4RATUS
The reaction flask-, d (Figure I ) , of 30-ni1. capacity, has a side neck iihich i. closed by a glaw stopper, a. The defhgrator,
or spoon, c, has a cup OII o w eiid to hold the catdyst, and a flat, handle on the ot,her end. In experiments where nitrogen g:t3 is introduced, tube b is used. This ha3 a cup on one elid and a small hole right behind it. The function of the condenser, B , is to hold back the quinoline which is condensed mostly in the lower air-cooled part. The eudiometer, E , is connected with B by means of a short rubber tube which ensures more flexibility than a taper joint at that p3int. The graduation on E is froin 0 to 1-10 ml., with 1-mi. subdivisions, and is shielded from the hot flask, A , by means of an ashestos board, F . Slightly above the zero mark of the eudiometer is a sintered-glass plate, D, of coarse porosity, which serves to hold bark any mercury that' might surge hack into the condenvr, aud at the same time pxniits paasage of the gas. C is a three-way stopcxk. The whole apparatus is clainped t.o a special stand having two vertical rods 13 em. apart; one rod is used only for the leveling bulb support. Sot, shown in Figure 1 is a t,hermometer hugging E. -4 dip3 into a beaker containing Fisher bat,h wax, heated by a microburner. If more than 140 ml. of carbon dioxide is developed, it' c.in be measured in this manner: After the gas has filled the eudiometer t o the 140-ni1. mark, stopcock C is turned to po3ition 3 and the mercury is raised to the zero mark, thereby ejecting the gad through the side tube without losing any carbon dioxide developed during this operation. The stopcock is then turned back to position 2. If it is desired to xveigh the carbon dioxide, the top of B is connected with the assembly shon-n in Figure 2. The gas first passes through a t,ube containing 10 nil. of conceritrated sulfuric acid, rhich retains not only water but also traces of quinoline. Then it is passed through a weighing tube filled with 6 to 7 grams of Ascarite, sufficient for eight t o ten determinations of 0.005 mole of carbon dioxide each. This tube neighs 27 to 30 gr:tms when filled and has an indentation on one end to keep it from rolling off the balance pan.
ANALYTICAL CHEMISTRY
946 Table I.
Decarboxylation of 0.005 Mole of Acid in 5 M1. of Quinoline (Method A)
Catalyst Mg.
Carbon Dioxide D ~ ~ TemVolu- Gravi- boxylated Time perature metric metric Acid .Win. C. % of theory % of theory
Cupric carbonate Cupric carbonate Cupric acetate Copper metal, powder Copper chromite Silver carbonate Silver carbonate
o-Benzoylbenzoic Acid 50 6 240 100.1 10 20 240 99.3 50 9 240 97.0 50 34 240 99.7 50 15 240 101.3 50 6 240 99.2 5 37 240 98.0
98.5 97.9 98.4 97.9 97.4 98.7 99.2
88 90 82 89
Cupric carbonate Cupric acetate Copper metal, powder Copper chromite Silver carbonate
3,5-Dinitrobenaoic Acid 60 18 240 108.4 50 34 240 104.3 50 11 240 107.6 50 46 240 103.3 60 13 240 100.3
100.3 99.3 100.2 99.1 98.7
77 86 72 84 95
4',"'-Dihydroxytripheny1methane-2-carboxylic Acid 50 25 Cupric carbonate 240 91.8 89.6 20 77 Cupric carbonate 240 93.9 87.6 Cupric acetate 50 62 240 91.4 89.4 933 240 Copper metal,,powder 50 90.3 82.4 50 244 Copper chromite 240 89.6 85.6 Cupric carbonate Cupric acetate Copper metal, powder Copper chromite Silver carbonate Silver carbonate
Coumariiic 50 51 50 72 50 201 50 102 50 23
Acid 176 176 176 170 176
2,4-Dichlorobeneoic 50 94 170
84 8
