mental difference is the crux of the analytical method described in this paper. It represents a novel masking technique based on kinetic differentiation. The proposed determination of calcium has signal virtues: It can be carried out in the presence of magnesium, obviating a separation. It is automatic and rapid, and it combines the convenience of using a macrosample with the advantage of a microprocedure in the determinative step.
(4) Chatterji, K. K., J . Indian Chern. SOC.
32,366 (1955). (5) Diehl, H.,Ellingboe, J. L., ANAL. CHEM.28,882 (1956). (6) Dumbaugh, Wm., Ibid., 31, 210 (1959). (7) Folke, S., Acta Chem. Scand. 5, 669 (1951). (8)Hasse, R., 2. Elektrochem. 62, 279 (1958). (9) Hillebrand, 1%‘. F., Lundell, G. E. F., “Applied Inorganic Analysis,” 2nd ed., p. 612, Wiley, Sew York, 1953. (10) Jordan, J., Record Chem. Progr. (Kresae-Hooker Sci. Lab.) 19. 193 ji958j. (11) Jordan, J., Alleman, T. G., ANAL. CHEM.29,9 (1957). (12) Kolthoff, I. M.,Sandell, E. B., J. Chem. Phus. 37.‘ 153 (1933). (13) Ibid., p. 428. ‘ (14) Kortum, G., Bockris, J. O’M., “Textbook of Electrochemistry,” Vol: “Textbook. Vol. 11,p. 680, Elsevier, Sew York, 1951. ,
LITERATURE CITED
(1) Born, M.Z.,2. Physik 1,45 (1920). (2) Brescia, F., Lichstein, B., J . Am. Chem. SOC.76, 1591 (1954). (3) Brescia, F.,Peisach, J., Ibid., 76, 5946 (1954).
.
I
I
’
(15) Latimer, W. J., J. Chem. Phys. 23, 90 11965). (16) Lewis, L., Melnick, L. M., ANAL. C H E M . 38 ~ ~(1960). , (17) Lingane:, J. J., “Electroanalytical Chemistry, 2nd ed., p. 488, Interscience. New York. 1958. (18) &fair, C., Fisch, J., 2. anal. Chem. 76,418 (1929). (19) Schwarzenbach, G.,“Die Komplexometrische Titration,” p. 21, Ferdinand Enke Verlag, Stuttgart, 1956. (20) Sprague, R., Clark, G. L., ANAL. CHEM.24,688 (1952). (21) Welcher, F. J., “Analytical Uses of Ethylenediamine Tetraacetic Acid,” p. 79, Van Sostrand, New York, 1958. RECEIVEDfor review April 11, 1960. Accepted August 22, 1960. Based on a doctoral thesis by E. J. Billingham, Jr. Financial support received from the U.S. Atomic Energy Commission under Contract AT (30-1)-2133 with The Pennsylvania State University. \----,-
Determination of Unsaturation in High Molecular Weight Fatty Nitrogen Derivatives Modification of the Wijs Iodine Value Method ALBERT J. MILUN Central Research laboratories, General Mills, Inc., Minneapolis 13, Minn.
b Modifications of the Wijs iodine value method have been worked out for application to certain fatty nitrogen derivatives of high molecular weight. End point difficulties and high apparent iodine values usually encountered with these compounds have been eliminated. The procedure entails a preliminary acetylation of primary and secondary amines, use of acetic acid solvent for tertiary amines, and addition of sodium lauryl sulfate before the titration in the case of quaternary ammonium chlorides.
B
many commercial fatty nitrogen derivatives of high molecular weight are manufactured from materials containing yarying degrees of unsaturation, a simple, accurate method for determining unsaturation is highly desirable. These nitrogen derivatives include primary, secondary, and tertiary amines and quaternary ammonium chlorides. The unsaturation encountered in these products is relatively low and is generally made up of nonconjugated, nonterminal double bonds in unbranched alkyl chains. The double bonds are far enough removed from the amino groups so that addition reactions of the double bonds would not be influenced by the nitrogen. The Wijs iodine value method (1) is a relatively simple method widely ECAUSE
used for determining nonconjugated unsaturation in fatty substances. Catalysts such as mercuric acetate (2) may be used to give the so-called rapid Wijs method. However, difficulty is encountered in applying the standard Wijs method to fatty nitrogen derivatives. Nitrogen-containing compounds readily form complexes with iodine ( 3 ) . These prevent the formation of the usual blue starch-iodine complex that is employed for end point detection in the IA‘ijs method. Also, complete titration of all the iodine is difficult because of the apparent affinity of the nitrogen compound for iodine. The net result is a very indistinct end point and often erratic values. Zvejnieks (5) claimed that the addition of palmitic acid improved the Wijs end point with unsaturated fatty primary amines, but reported no details. Smirnov and Bezhentseva (4) reported t h a t the high iodine values for octadecylaniine as obtained by the Wijs procedure could be avoided by conversion of the amine to the hydrochloride prior to analysis. The high values were ascribed to substitution of the nitrogen protons by the reagent. I n our laboratories simple modifications of the Wijs method were developed for application to primary, secondary, and tertiary amines and quaternary ammonium chlorides. The primary and secondary amines were
quickly acetylated with acetic anhydride prior to adding the iodine monochloride and mercuric acetate solutions. The resulting acetamides did not interfere with the formation of the blue starch-iodine complex during subsequent titration of iodine with thiosulfate. Tertiary amines gave accurate results in the rapid Wijs procedure, if the sample size was limited and acetic acid was used as the solvent in place of chloroform. With quaternary ammonium chlorides, the quaternary ammonium cation was tied up as the lauryl sulfate salt, enabling the iodine to be titrated t o a starchiodine end point in the 30-minute Tl7ijs procedure. REAGENTS AND APPARATUS
Wijs iodine monochloride solution (1). Starch indicator solution, 1yo stabilized n5th either 0.005yo of red mercuric iodide or 0.125% of salicylic acid. Sodium thiosulfate, aqueous 0.1N, stabilized with 0.38y0 borax. Potassium iodide solution. Dissolve 15 grams of potassium iodide in water and dilute to 100 ml. Mercuric acetate solution. Dissolve 2.5 grams of mercuric acetate in 97.5 grams of glacial acetic acid. PROCEDURE
Primary a n d Secondary Amines (includes N-alkyl aminopropylVOL. 33, NO. 1, JANUARY 1961
123
Table 1.
Iodine Values
Sample Size, G.
Sample Fatty primary amines Dodecylamine Oleic acid Dodecylamine +4.8% oleic acid 4-11. 6% oleic acid Dodecylamine Octadecylamine
1
0.2 2 2 3 (CHC13) 1
2 CHC13) 4 fCHC13)
Iodine Value 1.3
86. 2a
5 . 4 ( 5 . 6 calcd.) 11.6 (12.6 calcd.) 0.7 3.9b 3.9 3.9
Commercial mixed octadecenyloctadecadienylamine 0.3 107c Difatty secondary amines Dioctadecylamine 1 1.4d Commercial dioctadecylamine 1 0.8 +23.27, oleic acid 1.3 20.6 (calcd. 20.6) Commercial dioctadecylamine 4 (CHCla) 0.7 Commercial dioctadecenylamine 0.3 86.2O Commercial di (mixed octadecenyloctadecadienyl) amine 0.3 105.5 a Standard 30-minute Wijs method gave value of 86.7. Quantitative hydrogenation with Pd catalyst gave iodine values of * 2.6; 0 105; d 1.1; * 81. Table
II.
Iodine Values of Commercial N-Alkyl Aminopropylamines
Alkyl Group of Sample Octadecyl $23.1 % oleic acid Octadecyl (sample 2) coco Sample 2 Octadecenyl Sample 2 Sample 2
Sample Size, G.
Iodine Values Present method 30-min. Wijs 3.1 9.7 3.2 3.2 22.1 (calcd. 22.3) ... 4.0 18.8 5.7 11.3 15.2 6.5 73.1 87.0 59.7 73.9 59.6 73.8
1
3 (CHCla) 4 (CHCla) 1.3 1 1 1
0.3 0.3 0.4
Table 111.
Sample Tridodecylamine Hexyloleate Tridodecylamine 18.7% hexyloleate +43.4% hexyloleate
+
Iodine Values of Tertiary Amines
Present Method 1.1
68.5 13.4 (13.6 calcd.)b 30.5 (30.3 calcd.)) 0.3
Rapid Wijsa 4.8
... ...
30-hlin. Wijsa 23.1
34.3 Tridec ylamine 9.1 Trioctylamine 0.0 ... Methyldihydrogenated-tallow amine 2.0 5.4 Methyldioctadecylaminne 0.5 ... Dimet hyldodecylamine 0.4 1.5 Dimethylcocoamine 7.5 9.6 Chloroform solvent and 0.3-gram sample. Quantitative hydrogenation with Pd catalyst gave iodine values of b 14.4 and
amines). Accurately weigh t h e sample into a 250-ml. iodine flask. Weigh 3 t o 4 grams for iodine values close t o zero and 0.3 gram for values in the neighborhood of 100, interpolating for intermediate values. Add 5 ml. of acetic anhydride from a graduated cylinder. Place the flask on a steam b a t h for a t least 5 minutes; however, this acetylation time may be extended for as long as 1 hour. The sample should be in solution during the acetylation. Add 15 ml. of acetic acid and cool the solution t o room temperature. With high molecular weight saturated fatty amines use 15 ml. of chloroform in
124
ANALYTICAL CHEMISTRY
...
...
solution, to the complete disappearance of the blue starch-iodine color. Carry a blank through exactly the same procedure used for the sample. Tertiary Amines. Weigh 0.3 gram of sample into a n iodine flask. Add 20 ml. of acetic acid and, if necessary, warm to dissolve t h e sample. Follow the procedure outlined above, omitting t h e acetylation step. Continue titration until t h e solution changes from brown t o a n off-white. Carry a blank through exactly t h e same procedure, b u t titrate t o t h e complete disappearance of the blue starchiodine color. Quaternary Ammonium Chlorides. Cse 1-, 0.6-, or 0.3-gram samples for iodine values of 0 t o 30, 30 t o 50, and 50 to 100, respectively. (Samples containing approximately 25% isopropyl alcohol have been r u n with and without evaporation of t h e solvent. No significant difference in results was obtained. However, i t is recommended t h a t larger amounts of solvent be removed prior to analysis.) Add 20 ml. of chloroform to dissolve the sample, heating gently if necessary, but then cooling to room temperature. Pipet in 25 ml. of the iodine monochloride solution. Swirl the flask to ensure intimate mixing of contents. Store the flask in the dark for 30 minutes. Add 30 ml. of potassium iodide solution followed by 50 ml. of water. Add 2 to 2.5 grams of sodium lauryl sulfate and shake vigorously for approximately 10 seconds. Titrate to a light brown color with the standard thiosulfate solution. Add 3 ml. of starch indicator and shake. Continue the titration dropwise while vigorously shaking the stoppered flask between drops until the well shaken contents are white and further addition of a drop of titrant causes no change in color, The color change is from a brownish purple to white. Carry a blank through exactly the same procedure used for the sample.
...
27.4 28.8 17.7
Iodine value
=
(ml. of blank - ml. of sample) X N X 12.69 nt. of sample
...
10.6 19.8 30.3.
place of the acetic acid in order to keep the sample in solution. Pipet in 25 ml. of the iodine monochloride solution. Add 10 ml. of mercuric acetate solution from a graduated cylinder. Stopper the flask, swirl, and allow to stand for 3 to 5 minutes. Add 30 ml. of potassium iodide solution followed b y 50 ml. of water, pouring around the stopper in order to rinse in any reagent in the neck of the flask. Add 10 ml. of carbon tetrachloride. Titrate to a light yellow color with the standard thiosulfate solution. Add 2 ml. of the starch indicator solution. Continue the titration slowly while vigorously shaking the
DISCUSSION
Table I shows results obtained with the acetylation procedure on various saturated and unsaturated primary and secondary amines. The mixtures of amines and oleic acid represent samples with known amounts of unsaturation. Constant iodine values were obtained over a wide range of sample sizes with compounds of low unsaturation. Chloroform can be added to help in dissolving the larger samples which are used with the more saturated amines. More complex interferences were encountered with the #-alkyl aminopropylamines when the standard 30minute Wijs procedure was applied. End points were extremely poor and unusually high iodine values were obtained on samples known to contain
very little unsaturation. Table I1 lists comparative results b y the 30minute Wijs method and b y the acetylation procedure in which the end points were satisfactory. A sample of commercial diethylenetriamine, which had an apparent iodine value of about 40 by the 30-minute Wijs, gave a value of 0.6 with the acetylation procedure. Trifatty tertiary amines, besides interfering with the starch-iodine end point, gave high results in the rapid Wijs method and especially in the 30minute Wijs procedure. However, by limiting the sample size and employing acetic acid as a solvent, reasonable values and a satisfactory end point n-ere obtained with the rapid Wijs procedure. Table I11 lists comparative results obtained with the three different methods. High molecular weight quaternary ammonium chlorides also gave very poor end points in the 30-minute Wijs procedure. Their behavior was similar to that of the primary and secondary amines, and apparently for similar reasons. Sodium lauryl sulfate was used in the Wijs method to tie u p the quaternary ammonium cation as the lauryl sulfate salt. This appears to prevent the formation of the quaternary-iodine complex which causes the obscure end points during the titration of iodine with thiosulfate. With the recommended sample sizes, the indicated
Table IV.
Iodine Values of Quaternary Ammonium Chlorides
Quaternary Ammonium Chloride Iodine Value Trimethylhexadecyl 0.2 Dimethyldidodecyl 0.1 Methyltrioctadecyl 0.2 Dimethyldihydrogenated tallow 2.7 5 . 4 (calcd. 5 . 9 ) + 3 . 7 % oleic acid 8 . 9 (calcd. 9 . 0 ) 7 . 1yo oleic acid 13.9 (calcd. 14.3) 13,377, oleic acid 2 5 . 3 (calcd. 24.6) $25.07, oleic acid Dimethyldihydrogenated tallow Sample 2 l.lG Sample 3 4.2b Sample 4 11.4~ Dimethyldisoya 57. I d Trimethyltallow 27.8 Quantitative hydrogenation with palladium catalyst gave iodine values of
++
1;
*
3;
52.
quantity of sodium lauryl sulfate was sufficient to give satisfactory end points with starch indicator. Similar results were obtained either by adding the sodium lauryl sulfate initially to the sample in the iodine monochloride or by adding i t after the reaction just before the titration. Table IV gives iodine values obtained with various purified and commercial grade quaternary ammonium chlorides. The mixtures of quaternary chloride with oleic acid simulated various levels of unsaturation.
Analytical Services Department who carried out the analyses reported herein.
ACKNOWLEDGMENT
RECEIVEDfor review May 20, 1960. Accepted September 26, 1960. Paper No. 249 Journal Series, Central Research Laboratories, General Mills, Inc.
The author gratefully acknon-ledges the work of Eileen Smith of the
LITERATURE CITED
(1) Am. Oil Chemists’ Society, “Official and Tentative Methods,” 2nd ed., 1947-1959, E. M. Sallee, ed., Method NO. Cd 1-25. 1956. (2) Hoffman, H. D., Green, C. E., Oil & Soap 16, 236 (1939). (3) Nagakura, S., J. Am. Chem. SOC.80, 520 (1958). (4) Smirnov, 0. K., Bexhentseva, V. M., Zavodskaya Lab. 21, 414 (1955). (5) Zvejnieks, A., Svensk Kem. Tidskr. 66, 316 (1954).
Extraction of Zirconium with Di-n-butyl Phosphate and Direct Determination in the Organic Phase with 1-(2- Pyridy Ia z 0)- 2- na pht ho I Application to Fluoride Solutions R. F. ROLF The Dow Chemical Co., Midland, Mich.
b A sensitive and selective method for separation and determination of microgram quantities of zirconium in aluminum-magnesium alloys consists of dissolving the alloy in a mixture of mineral acids and fluoboric acid. Aluminum nitrate is used to complex the fluoride and the zirconium is quantitatively extracted with a solution of di-n-butyl phosphate in chloroform. The addition of an alcoholic solution of 1-(2-pyridylazo)-2-naphthol to the zirconium extract yields an intense red color. The system obeys Beer’s law over the concentration range of
10 to 65 fig. of zirconium per 25 ml. The molecular absorptivity is about 32,000. The extraction of zirconium by di-n-butyl phosphate was studied using zirconium-95 tracer. A study of the effect of diverse ions showed the method to b e highly selective. A standard magnesium alloy containing mischmetall was analyzed by the proposed method with an average This method offers precision to f2%, the advantage over existing literature methods that fluoride can b e used to ensure complete dissolution, but does not interfere in the determination.
S
on the solubility of zirconium in aluminum-magnesium alloys required determining microgram quantities of zirconium. Low concentrations of zirconium in aluminum-magnesium alloys are commonly determined by a spectrophotometric procedure employing sodium alizar in sulfonate (Alizarin Red S) as the chromogenic reagent. A more sensitive method was needed, since the amounts of zirconium were found to be below the range of the Alizarin Red S method (I?’). A number of reagents have been proposed for the spectrophotometric TUDIES
VOL. 33, NO. 1, JANUARY 1961
125
