July 15, 1941
ANALYTICAL EDITION
Table I1 for comparison with the results obtained by the other methods and a more complete list of results is compiled in Table I. Some typical rates of hydrogenat’ion curves are shown in Figures 2 , 3 , and 4. PERBENZOIC ACIDTITRATIONS. Perbenzoic acid was readily and reproducibly prepared in good yield by the method of Braun (3) using benzoyl peroxide. One to 1.5 milliequivalents of the terpene were dissolved in 10.00 ml. of a dried, approximately 0.5 N solution of perbenaoic acid in chloroform and allowed to stand a t 5’ for 24 hours and then the excess perbenzoic acid was titrated in the usual manner ( 3 ) . Blanks were simultaneously run on 10.00-ml. portions of the reagent. Other samples were allowed to stand a t 5’ from 48 to 96 hours, but the results showed clearly that in all cases the reaction was over a t the end of 24 hours. The other determinations, results of which are indicated in Table 11, were carried out as described in the literature. HIGH-PRESSUREHYDROGEKATION. A bomb with a total void of 183 ml. was used, but the use of a glass liner (7) reduced the void to 142 ml. Calibration of this bomb and liner using acetone made up to a volume of 40 ml. with alcohol showed the pressure drop to be 3800 pounds per mole of hydrogen absorbed. Reduction of 17.09 grams of or-pinene made up to 40 ml. with alcohol was complete in about 12 hours a t 75” (initial pressure 1670 pounds a t room temperature). The pressure-drop was 480 pounds, which corresponds to 1.01 moles of hydrogen per mole of a-pinene. A similar experiment with P-pinene gave a value of 1.06 double bonds. Raney nickel catalyst ( 2 ) was used in all these experiments.
Literature Cited (1) Adams, Voorhees, and Shriner, Org. Syntheses, Call. Val. I, 452 (1932). (2) Adkins, “Reactions of Hydrogen”, p. 20, Madison, Wis., University of Wisconsin Press, 1937. (3) Braun, Org. Syntheses, 13, 86 (1933). (4) Conant and Carlson, J . Am. Chem. Soc., 51, 3464 (1929). (5) Fieser and Hershberg, Ibid., 60, 940 (1938). (6) Gal’pern and Vinogradova, Khim. Tverdogo Topliva, 8 , 384 (1937).
449
TABLE11. COMPARISOS O F METHODS IWESTIGATED~ Method e-Pinene (1) 6-Pinene (1) Hanus 0.95-1 61b 1. 12 mercuric acetate 1.25 Hanus 1.42 Rosenmund and Kuhnhenn 1 70 1.65 2.15 KaufmannC 2.02 Potassium permanganate 0.90 1.23 1 83-1.60b Perbenzoic acidd 1 37-1.63b Hydrogenation (Pd) 0 99 1 00 1 03 1 0.5 Hydrogenation (Pt) a Results are expressed a s number of double bonds iound per moleoule, and t h e number in parentheses following name of terpene indicates number of bonds theoretically present. b Depending upon size of sample. Other figures represent averages of check analyses. C Kauimann method gave a value of 2.15 double bonds for alloocimene (3) and 1.99 for dipentene ( 2 ) . d Perbeneoic acid also gave following results: myrtenol (11, 0.89; pinocarve01 ( l ) , 1.23: myrcene (31, 2.17; alloocimene (3), 2 . 3 5 ; dihydromyrcene (2), 2.10; dipentene (21, 2.03; terpineol (1). 0.87.
+
(7) Hershberg and Feiner, ISD. ENG.CHEM.,Anal. Ed., 11, 73 (1939). (8) Hoffman and Green, Oil and Soap, 16,236 (1939). (9) Jamieson, “Vegetable Fats and Oils”, p. 344, New York, Chemical Catalog Co., 1932. Kaufmann, Z . Untersuch. Lebensm, 51, 3 (1926). Knowles, Lawson, and McQuillen, J. Oil Colour Chem. Assoc., 23,4 (1940). Kranz, Hrach, and Franta, Chem. Obror, 3, 365 (1928). Kubelka and Zuravlev, Chem. Listy, 25, 124 (1931). Kubelka and Zuravlev, Chem. U m c h a u Fette, O d e , Wachse H a r m , 38, 105 (1931). Rosenmund and Kuhnhenn, 2. Untersuch. Nahr. u. Gencssm., 46, 154 (1923). Ruzicka, Balas, and Vilim, Helv. Chim. Acta, 7 , 458 (1924). Rueicka and Meyer, Ibid., 5, 315 (1922). Shaefer, IND.EXG.CHEM.,Anal. Ed., 2, 115 (1930). Skarblom and Linder, T e k . T i d . U p p l . A-C. Kemi, 67, 25 (1937). Winkler, Pharm. Zentrslhalle, 68, 433 (1927) I
Colorimetric Determination of Formaldehyde in the Presence of Other Aldehydes W. J. BLAEDEL AND F. E. BLACET University of California at Los Angeles, Los Angeles, Calif.
T
HE method of detecting formaldehyde in the presence of higher aldehydes suggested by Denigks (3) can be made semiquantitative in charact,er with the aid of a colorimeter. The errors involved vary from 2 to 10 per cent, becoming greater as the proportions of higher aldehydes are increased. The limit of sensitivity under the experimental conditions described herewith is of the order of 0.02 mg. of formaldehyde in 5 ml. of solution. The test depends upon the fact that, the magenta color given by Schiff’s reagent with formaldehyde in the presence of sulfuric acid does not fade appreciably during 6 hours, whereas the color given by the higher straightchain aldehydes, glyoxals, and their polymers fades completely within 2 hours. Trioxymethylene reacts the same as formaldehyde. The reagent is prepared by first dissolving 0.5 gram of fuchsin in 500 ml. of water, then adding 5.15 grams of sodium bisulfite. Approximately 15 minutes later, 17 ml. of 6 N hydrochloric acid are added and the whole solution is allowed to stand for 3 hours. During this time the solution fades to a permanent, pale yellow color. In a determination, 5 ml. of an aqueous solution of the substance to be analyzed are added to a mixture of 5 ml. of the Schiff’s reagent and 1.2 ml. of 75 per cent sulfuric acid. A known comparison solution is made up a t the same time using a standard formaldehyde solution and the two solutions are compared after they have stood for 2 hours in stoppered test tubes.
Too long a time should not be allowed to elapse before the comparison is made, for even the color due to formaldehyde fades slightly on standing. Before results are considered final, the formaldehyde concentrations of the unknown and standard solutions should be within 5 per cent of each other. Accordingly, an ap-
TABLE I. TYPICAL ANALYTICAL DATA AXD RESULTS Compositions of Standard Comparison Solutions Ratio of second Per cent aldehyde HzCO t o HlCO
Ratio of Second Aldehyde HzCO in Unknown to HzCO in Present Determined Unknown
5%
70
Error
%
Formaldehyde Solutions 0.0050 0.0050 0.0040 0.0015
.. .. ..
0 0067 0.0050 0.0040 0.0020
0.0068 0.0050 0.0039 0.0019
.. .. ..
+1.5 0.0
..
-2.5 -5.0
40 20 3 10
-4.0 +6.7 -2.9 -5.0
Formaldehyde-Acetaldehyde Solutions 0.0040 0.0040 0.0040 0 0040
0.0040 0.0040
50 50
5 10
0 0025 0,0045 0.0070 0.021
0.0024 0.0048 0,0068 0,020
Formaldehyde-Propionaldehyde Solutions 0.0040 16 25 0.0043 20 25 0.0033 0.0031
-7.0 -6.0
450
INDUSTRIAL AND ENGINEERING CHEMISTRY
proximate calculation of the unknown is made first. If the two solutions differ by more than 5 per cent, one or the other is diluted sufficiently to satisfy this requirement and a nex colorimetric comparison is made. Sometimes a third comparison is necessary. The concentration range for the most satisfactory colorimetric comparison is from 0.001 to 0.005 per cent formddehyde. Aqueous solutions of pure formaldehyde may be analyzed to a degree of accuracy dependent upon the colorimeter-i. e., within 2 or 3 per cent. However, other aldehydes tend to change the color and solutions containing appreciable quantities of other aldehydes may not be accurately compared with pure formaldehyde standards. In such cases the standard should be made up to contain the higher aldehydes in concentrations approximating those considered to be in the unknown. For example, in solutions containing acetaldehyde and formaldehyde, if the ratio of acetaldehyde to formaldehyde is between 10 and 100 the standard should be made up with a ratio near 50; if between 1 and 10 the standard ratio should be about 5 ; and if the ratio is less than 1 a pure formaldehyde standard may be used.
Vol. 13, No. 7
The method has been tested on mixtures of formaldehyde with acetaldehyde, propionaldehyde, glyoxal, methylglyoxal, biacetyl, and their polymers. It has been used satisfactorily in photochemical studies of acetaldehyde (2) and propionaldehyde. Table I contains a few typical analytical results obtained on unknown solutions. In addition to the results described above, the Deniges qualitative method works very well in colorimetric capillaries (1). In such experiments t h e limit of sensitivity is about 0.02 microgram in 5 cu. mm. of solution.
Literature Cited (1) Benedetti-Pichler and Spikes, “Introduction to the Microtechnique of Inorganic Qualitative Bnalysis”, p. 93, Douglaston, N. Y., Microchemical Service, 1935. (2) Blacet and Blaedel, J . Am. Chem. SOC.,62, 3374 (1940). (3) DenigQs,Compt. rend., 150, 529 (1910).
Determination of Sulfur in Organic Compounds Oxidation of Sulfur of Cystine and Methionine, Combination of Parr Oxygen Bomb and Acidimetric Benzidine Method, and Determination of Small Amounts of Sulfur Compound Present as Contaminant in Organic Material T. P. CALLAN AND G. TOENNIES, The Lankenau Hospital Research Institute, Philadelphia, Penna.
I
N CONNECTIOS with investigations concerned with the sulfur-containing amino acids and their derivatives, data pertaining t o various analytical problems have accumulated in this laboratory. The material set forth below deals chiefly with the behavior of the sulfur present in the structure of cystine and methionine on oxidation by alkaline permanganate and by other \yet-oxidation methods, the development of a practical analytical procedure in which combustion of the organic substance in the Parr oxygen bomb is followed by precipitation of sulfate as the benzidine salt and acidimetric determination of the latter, the effect of certain inorganic substances in this procedure and a n investigation of its accuracy when applied to the determination of small amounts of organic sulfur in the presence of large amounts of sulfur-free material.
Alkaline Permanganate Method T h e method as used by the authors is based on that reported by Blix (6),who shovied that the sulfur of cystine mas recovered with a n accuracy of 98.9 * 0.6 per cent when t h e substance was oxidized b y an alkaline permanganate solution, the excess permanganate was reduced to manganous ion by hydrochloric acid, and the sulfate was determined as barium sulfate. The aut’hors have compared this procedure with the alternate possibility of reducing the permanganate to manganese dioxide which is filtered off before precipitation of barium sulfate. Twenty-five cubic centimeter portions of a solution of 1.6132 grams of 1-cystine [which optical rotation (18) showed to be a t least 99.7 per cent pure] and 50 millimoles of hydrochloric acid in a total volume of 250 cc. \rere analyzed as follows. a. The sample of solution was heated for 2 hours on the steam bath with 30 cc. of 2 -21 sodium hydroxide and 1.50 grams of potassium permanganate (both of reagent grade) in a total volume of 150 cc. Excess permanganate was then decom osed by addition of 25 cc. of 7 Jf hydrochloric acid and gentle goiling. After partial neutralization (just acid to methyl orange) with sodium
hydroxide, sulfate was precipitated by 35 cc. of a 0.05 llf barium chloride solution and, after leaving on the warm steam bath overnight, filtered, ignited, and weighed. b. After oxidation as under ( a ) a few cubic centimeters of methanol were carefully added to the hot solution, causing the formation of manganese dioxide and a colorless solution. After addition of 20 cc. of 2 -If hydrochloric acid, which causes conversion of the manganese dioxide into a more easily filterable condition, the manganese dioxide was a t once filtered and washed with hot water (containing about 1 per cent ammonium acetate to prevent colloidal passage of manganese dioxide) until a sample of the filtrate showed absence of chloride ion (about 8 washings). In the combined filtrate and washings sulfate was determined, after adjustment of the acidity, as under (a). c. The determination n-as carried out as under ( b ) except that 4.5 grams of potassium Permanganate were used. In the determination of the sulfate blank attributable to the potassium permanganate the procedure was similar to ( b ) , except that cystine was omitted and 10.0 grams of potassium permanganate were used. The results were as follon-s: sulfur found in potassium permanganate, 0.0176 and 0.0163 per cent. The sulfur content of the cystine was found, after deduction of the corresponding permanganate blanks, as 2i.01 and 26.61 per cent according to procedure ( a ) , 26.41 and 26.50 according t o ( b ) , and 26.51 and 26.71 accordin to ( c ) . The theoretical value is 26.67 per cent. The mean vafue of procedures ( b ) and (c) corresponds to 99.5 * 0.3 per cent of the theoretical, irhile procedure ( a ) gave 100.5 * 0.S per cent. In further work the procedure involving filtration of manganese dioxide was adopted because of its higher precision and accuracy, and because the color of the barium sulfate obtained in procedure ( a ) indicated the presence of manganese. d. A semimicromodification (about 50 mg. of substance, 100 mg. of barium sulfate) ~ ~ h i cthe h authors have frequently used for the determination of sulfur in certain oxidation products of cystine (15) is as follow: A 50-mg. sample of the substance, weighed into a 125-cc. Erlenmeyer flask to the nearest 0.05 mg., is dissolved in about 50 cc. of a solution containing 10 millimoles of sodium hydroxide and 0.50 gram of potassium permanganate. After heatsing the solution for 2 hours on the steam bath, 1.5 cc. of methanol are added, followed by 10 cc. of 2 31 hydrochloric acid when reduction of the permanganate is completed. The precipitate is a t once filtered and washed until free of chloride. In this case, where filtration is carried out at ai? acid reaction, addition of ammonium acetate to the Trash water :see ( b ) , above] proved to be unneces-
