ANALYTICAL CHEMISTRY
880 Principal Lines d
I/Il
d
1/11
7.49 5.65 5.33 5.18 4.73 4,279 3.848 3.746 3.591 3.328 3.175 3,040 2,972 2,868 2.805 2.672
0.08 0.04 0.33 0.19 0.08 0.16 1.00 0.73 0.35 0.13
2.621 2.583 2.526 2.481 2.356 2.311 2,247 2.211 2.179 2.116 2.060 2.011 1.959 1,930 1.874 1.826 1.786
0.02 0.08 0.05 0.02 0.02 0.09 0.02 0.06 0.05 0.08 0.06 0.03 0.04 0.03 0.03 0.04 0.07
0.05 0.17 0.10 0.05
0.12 0.02
.
OPTICALPROPERTIES (determined and checked by V. Gilpin, P. T. C h e w , a n d W. C. McCcone). Refractiie Indices (5893 A.; 25" C,), a = 1.534 * 0.002. 1.670 * 0.002. y = 1.74 * 0.01. OpticAxialAngles(5893.~.; 2 5 ° C . ) . 2V = 67". 2 E = 112'. Dispersion. T > v, very alight. Optic ilxial Plane. 100. Sign of Double Refraction. Negative. Molecular Refraction ( R ) (5893 25' C.). = 1.645. R (calcd.) = 40.5. R (obsd.) = 33.6. FUSION DATA (determined by W. C. 1lcCrone). @-Pyridinesulfonic acid melts at 356-357" C. with slight de@ =
w.;
a
composition, There is a very slight sublimation at t h e melting point, a n d o n supercooling solidification is very rapid, with a needlelike crystal front. Transverse shrinkage cracks a r e typical (Figure 1 )
acid cannot. Thus, polyuronides present in plants, whether soluble or insoluble, will not interfere in the aconitic acid method. Aconitic acid is not decarboxylated in strongly acidic solutions and does not interfere in the uronic acid methods (4, '7). Therefore the carbon dioxide obtained from sugar cane products by Browne and Phillips ( 2 ) originated from material other than aconitic acid.
Noninterference of Pectinous Substances in Aconitic Acid Method and of Aconitic Acid in Uronic Acid Method SIR: Inasmuch as galacturonic acid is decarboxylated in the potassium acetate-acetic acid reagent for aconitic acid ( 6 ) ,it vas expected t h a t the "uronic acids" of Browne and Phillips ( 2 ) would interfere when the method for aconitic acid was applied to sugarhouse materials. However, no interference of this nature has yet been found ( 1 ) . It has been found t h a t polyuronic acids and derivatives, such as pectic acid and pectin, are insoluble in the reagent and are not decarboxylated by it. I t was desirable to test the method with a uronir acid derivative which is soluble in acetic acid and basically similar in structure to pectic acid. It is generally accepted that pectic acid is constituted as a chain of galacturonic acid units, each linked by glycosidic union through its C-1 position to the C-4 position of the next unit. The last unit of each chain has no attachment on its C-1 position, but functions through its C-4 position as an aglucon to the preceding unit. Thus each of the units but the last one may be considered as functioning as the carbohydrate residue in a glycoside of a uronic acid. The simplest substance of this constitution, methylgalactnronide dihydrate, melting point 112' C . , was prepared by the mcthod of 3Iorell and Link ( 5 ) . I t is easily soluble in the potassium acetate-acetic acid reagent. but during 3 hours in the reagent boiling under reflux i t gave no carbon dioxide. When similarly tested with the aqueous hydrochloric acid reagent for uronic acids (4,7 ) it underwent extensive decarboxylation. The evidence therefore indicates that only the free galacturonic acid is decarboxylated in the aconitic acid method, and that the potassium acetate-acetic acid reagent, being practically anhydrous, is unable to hydrolyze soluble uronides to the free uronic acid. Experiments showed that galacturonic acid in the boiling reagent for aconitic acid yielded furfural simultaneously d t h the carbon dioxide, b u t that the methylgalacturonide, pectin, and pectic acid produced no furfural. It is well known t h a t decarboxylation of uronic acids and polyuronides in mineral acids (4,7 ) is always accompanied by production of furfural and reductic acid by interdependent reactions t h a t have been discussed by Isbell ( 3 ) . From all known evidence it may be assumed t h a t uronic acids and their derivatives are decarboxylated by chemical agents only when i t is possible for them to yield furfural or reductic acid. Neither of these compounds can be formed from any of the galacturonic acid units In pectic acid and polyuronides until the uronic acid units have been freed by hydrolysis from attachments a t both positions C-1 and C-4. The aqueous mineral acids used in the uronic acid method (4, 7) can do this, but the practically anhydrous acetic acid reagent for aconitic
LITERATURE CITED
Ambler and Roberts, AN.~L.CHEM.,19, 877 (1947). Browne and Phillips, Intern. Sugar J . , 41,430 (1939). Isbell, J . Research iyatl. Bur. Standards, 33, 45 (1944). Lefevre and Tollens, Ber., 40, 4513 (1907). Morel1 and Link, J . B i d . Chem., 100,385 (1933). Roberts and Ambler, A l i . 4 ~ CHEM., . 19, 118 (1947). Whistler, Martin, and Harris, J . Research S a t l . Bur. Standards, 24, 13 (1940). J. A. AMBLER
E.J. ROBERTS Bureau of Agricultural and Industrial Chemistry United States Department of .Igriculture Kew Orleans 19, La.
Identification of Crystalline Progesterone with 2,4-Dini trophenylhydrazine SIR: I n a recent issue of this journal, Klein el al. [ANAL.CHEM., 20, 174 (1948)] described a gravimetric procedure for the determination of progesterone which was based on the reaction of the hormone with excess 2,4-dinitrophenylhydrazine. To the product was assigned the structure of a 3,5-pyrazo1yl-20-dinitrophenylhydrazone, since prolonged heating of the compound with ethanolic hydrogen chloride removed only one hydrazine group, the presumable pyrazoline ring being unaffected. Actually, such evidence for pyrazoline formation of A
