INDUSTRIAL AND ENGINEERING CHEMISTRY
October 15, 1931
oxide or, if only the percentage of cobalt is desired, the cobalt may be precipitated directly with phenylthiohydantoic acid (6) and the electrolysis carried out as described in the discussion. Tools intended to contain from 13 to 14 per cent cobalt were found to have 13.81 and 13.83 per cent cobalt. Acknowledgment The author wishes to acknowledge the cooperation of Charles Van Brunt and Margaret 0. St. Louis of this depart-
365
ment; also Roger L. Jones, of Syracuse University, who spent last summer in this laboratory. Literature Cited (1) Brenner and Ross, J . Am. Chem. Soc., 33,493 (1911). (2) Exner, Ibid., 26, 896 (1903). (3) Smith and Kollock, Ibid., 26,1595. 1606 (1904); a7, 1255 (1905). ~B ~18, t ~ 447 ,~ (1921). l ~ (4) Wagenman, ~ (5) Willard and Hall, J . Am. Chem. SOL,44,2219 (1922).
A Test for Aldehydes Using Dimethylcyclohexanedione' Woltor Weinberger THEMENNENCOMPANY, NEWARK, N. J.
IIIS valuable test, since its introduction by Vorlander in 1896 (5,Y),has been neglected by and is still unknown to the majority of chemists. Of late it has been in-
T
frequently used in work in photosynthesis and in detecting traces of aldehydes in biological material, but it has never received the place it deserves as a routine and definite test for aldehydes. There are several distinct advantages inherent in this test: (1) reliability; (2) sensitivity; (3) definiteness (it yields a crystalline precipitate); (4) simplicity of technic; (5) a reagent which does not react with ketones; and (6) which can often be used when other better known reagents cannot give the information sought. Its chief disadvantage, formerly, was that the reagent was not readily available. It may now be purchased easily from the Eastman Kodak Company, Rochester, N. Y. The reagent is dimethylcyclohexanedione, commonly called dimetol and dimethylhydroresorcin. It unites with aldehydes, the condensation product so formed being soluble in water with difficulty. The result of work undertaken to determine how this reagent might best be used, its defects, and its sensitivity, is here presented. The melting points of a number of derivatives are also included. The original experiments were performed with formaldehyde. Subsequent experiments, however, show that the method adopted and the conditions and cautions laid down here apply equally well to other aldehydes. The reagent is soluble in alcohol and water. It oxidizes slowly in the presence of air, and when kept in well-stoppered bottles keeps indefinitely (6). Test Procedure The solution of the reagent is added to the solution of the aldehyde. Under proper conditions the condensation product separates out of the solution as a fine crystalline and exceedingly insoluble precipitate. The oxygen of one molecule of formaldehyde unites with a hydrogen atom of each of two molecules of the reagent, water splitting off, and the residue is the insoluble compound (4, 5; 7 ) . Let us assume for the sake of simplicity that the reagent is dihydroresorcin 0
0
II
HzC@
+
C=O
HIC
O=C
Received May 26, 1931.
CHI CH2
HzC
Method for Precipitation of Aldehydes The method decided upon for the precipitation of aldehydes by dimetol is as follows: A 5 to 10 per cent alcoholic solution of the reagent is prepared. Sodium chloride is added to the aqueous solution of the
aldehyde. The aqueous solution containing the aldehyde is neutralized and left neutral or very faintly acid-e. g., with dilute acetic acid-and cooled. To this cold solution a few drops of the reagent are added. The solution is then vigorously stirred, or permitted to stand until the precipitate takes its final crystalline form.
0
CII H HC! R CI H O F K ( ) C H + H ~ C u i \ & o H 2
CH2 1
0
I1
This condensation product is soluble in hot water, alcohol ether, petrolic ether, gasoline, acetone, and, very probably, in most organic solvents. It is essential as a first condition, then, that the aldehyde be precipitated from a cold aqueous solution, although small amounts of alcohol do not interfere. It may be noted here that the condensation can take place in an alcoholic solution and the condensation product precipitated by the addition of water. These solubilities in hot water and in alcohol are put to good use in purifying the crystals for melting-point determinations. The condensation product is easily soluble in fixed and carbonate alkalies and in acids, but it is not appreciably soluble in cold, very dilute solutions of organic acids. The reagent should, therefore, be added to a neutral solution of the aldehyde. Since this is impracticable, the solution of the aldehyde should be made faintly acid with some weak organic acid. A saturated aqueous solution of the condensation product formed by the reaction of formaldehyde and dimetol contains a t 19" C. 0.0005 gram per 100 ml. (6), and much less than that in the presence of excess dimetol. The condensation product is still less soluble in the presence of salt. The addition of sodium chloride was resorted to in order to increase the sensitivity of the test. The precipitate does not come immediately, but comes down slowly, becomes bulkier on standing, and then takes its final crystalline form. The formation of the precipitate and its crystallization is materially hastened by vigorous stirring. This precipitate shows a characteristic structure under the microscope (5).
'2x0 O=C CHr
CHz
CHz
The precipitate may be recrystallized from a suitable solvent (for example, alcohol or hot water), and its melting point determined. By means of this determination the presence of a specific aldehyde may be confirmed. A number of melting points for dimetolaldehyde derivatives and their sources are given in Table I.
ANALYTICAL EDITION
366
It is worth mentioning here that dimetol gives no precipitate with ketones, so that it may be used to determine aldehydes in the presence of ketones. Sensitivity of Test A solution containing 4 mg. of formaldehyde Per liter gives a definite precipitate in 15 minutes, using salt. This degree of sensitivity was determined as follows: -
i t may be put to a wider use, notably in differentiating between and in confirming the presence of certain specific aldehydes, the melting points of the condensation products formed by the reaction of dimetol and certain aldehydes are described (Table I). It is hoped that this list may be expanded in time. T a b l e I-Melting
Points of C o n d e n s a t i o n P r o d u c t s of Dimetol and Various Aldehydes ALDEHYDE MELTINGPOINT
- L. A
Formaldehyde Acetaldehyde Anhydride of acetaldehyde Citral Citronellal Anisic aldehyde Acetylvanillin Piperonal Vanillin Salicylic aldehyde
A number of formaldehyde solutions properly neutralized and
of various strengths were prepared, sodium chloride was added to each, and they were all kept at 25" C. To a portion of each solution a few drops of the reagent were added, and the weakest
concentration of formaldehyde that gave a definite precipitate within 15 minutes was taken as the limit of the sensitivity of the test. The time limit was set because it was desired that the test be used as a rapid test and in routine analysis. Long waiting would, obviously, have made it unfit for such a purpose. Under the conditions stated, formaldehyde was definitely detected in a $ohtion containing only four parts of formaldehyde per million. Because of its extreme sensitivity, the definiteness of the precipitate, and the very simple technic required, this test should rank high among the classic tests for aldehydes. That
Vol. 3, No. 4
"
187 138 to 140 (4) 173 t o 175 (4) approx. 25 7 0 t o 7 1 (1)
% 8 E: $1 208 to 209
Literature Cited (1) Bernardi, ilnn. chim. afipiicata, 17, 163 (1927). (2) Bernardi and Tartarini, Ibid., 16, 132 (1926). (3) Leffman and Pines, Ball. Wagner Free Inst. Sci. Phila , 4, 15 (1929).
ii;
:;,4"~,$~~'
~ ~ ~ ~ n ~ 'l4$~ 301 ,(lg21). ~ (6) Vorlander, Ibzd., SSB, 2656 (1925). (7) Vorlander and Kalkow, Ann. chim., 39, 366 (1899).
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Method for Determination of Fluorine in Phosphate Rock and Phosphatic Slags' D. S. Reynolds and K. D. Jacob FERTILIZER AND FIXED NITROGEN INVESTIGATIONS, BUREAU OF CHEMISTRY A N D SOILS, WAFHINGTON, D
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The fluorine in highly phosphatic, calcareous matealkali fusion in order to deN AN investigation of the rials, such as phosphate rock, cannot be brought into termine fluorine ia the slags. volatilination of fluorine the water-soluble condition by a single fusion with At the same time it was deduring the smelting of alkaline fluxes. Three fusions usually fail to convert sired to obtain, if possible, a phosphate rock it was necesmore than about 90 per cent of the fluorine into the method that would be apsary to determine the fluorine water-soluble condition. The failure of alkaline plicable also to the determicontent of slags containing fusions to effect complete decomposition of such nation of fluorine in phosvarious quantities of phosmaterials is due to the setting u p of equilibrium rephate rock, inasmuch as the phate. Preliminary studies actions involving insoluble fluorphosphates of the volatilization method, under showed that the volatilization fluorapatite type. the m o s t f a v o r a b l e condim e t h o d (1.2, 16), which is A method for the determination of fluorine in phost i o n s , seems to give a rewidely usedfor the determinaphate rock and phosphatic slags is described. The covery of only about 92 to 94 tion of fluorine in phosphate method involves a single fusion of the sample with per cent of the fluorine presrock, gives very low and ersodium carbonate and silica, followed by extraction ent in this material (19). ratic results when applied to of the water-insoluble residue with dilute nitric acid. The lead c h l o r o f l u o r i d e the analysis of fluorine-bearAfter removal of the dissolved calcium and phosphoric method; first s u g g e s t e d by ing slags, such as those obacid, the fluorine is determined by the lead chloroStarck (24) and later studied tained in the manufacture of fluoride method. The method gives satisfactory rein some detail by Hawley (4). phosphoric acid by furnace sults on fluorine-bearing phosphatic slags and on the has recently been applied by processes, The low results domestic types of phosphate rock with the exception Hoffman and Lundell(6,7) to obtained with this method of Tennessee blue-rock phosphate. Comparative rethe determination of fluorine may be due in part to failure S U h are given for fluorine in various phosphatic matein glasses and enamels, with of the sulfuric acid to effect rials, as determined by this method and by the volaexcellent r e s u l t s . Hoffman complete decomposition of tilization method. and Lundell state, however, the fluorine compounds prest h a t t h e method a s deent in the slag. The principal source of error seems to lie, however, in the formation of a veloped by them is not suitable for determining fluorine in non-volatile oxyfluoride, probably SiOF2 ( I ) , by the action phosphate rock, This was confirmed by the writers in sevof hydrofluoric acid on the silicic acid resulting from the action eral experiments, only about one-half of the fluorine being of sulfuric acid on silicates present in the slag.2 It seemed recovered. It seemed desirable, however, to make a further necessary, therefore, to resort to some method involving study of the method to determine whether it might be modified to give satisfactory results on phosphatic materials. 1 Received M a y 14, 1031. Presented before the Division of Fertilizer After considerable experimental work a modification was deChemistry a t t h e 80th Meeting of the American Chemical Society, Cinveloped which seems to give fairIy satisfactory results for cinnati, Ohio,September 8 to 12, 1930. fluorine in phosphate rock and phosphatic slags. The results 2 See the immediately following paper, "Effect of Certain Forms of of this study are given in the present paper. Silica on Determination of Fluorine by Volatilization Method."
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