Determination of Small Amounts of Secondary Amine in High Molecular Weight Fatty Primary Amines A.
J. MILUN and J. P. NELSON
Chemical laboratories, General Mills, Inc., Minneapolis 7 3, Minn.
> A rapid, simple, colorimetric method
ured at 627 nip against isopropyl alcohol. -4bsorbance was converted into per cent secondary amine using a previously prepared calibration curve.
is presented for determining secondary amine in high molecular weight fatty primary amines in the 0 to 1% range. After reaction of the primary amine with salicylaldehyde in isopropyl alcohol, the color formed by the reaction between secondary amine and bromocresol green is measured spectrophotometrically at 627 mp. Per cent secondary amine is obtained from a calibration curve previously prepared with known mixtures of primary and secondary amines.
D
fatty primary amines, of high molecular weight produced commercially by the reduction of nitriles, usually contain less than 1% of the corresponding difatty secondary amine. Available titration procedures for secondary amine (1, 2, 6, 9) were not sensitive enough for determining such small quantities. Sensitive colorimetric methods were available for the analysis of secondary amines (3, 5, 7); however, they are not directly applicable to the determination of high molecular weight secondary amines in the presence of a preponderance of primary amine. The use of salicylaldehyde to remove primary amine interference appeared attractive in the development of a colorimetric procedure for secondary amine. Broniocresol green in isopropyl alcohol gave a blue-green color of intensity proportional to secondary amine concentration after the primary amine had reacted with salicylaldehyde. This approach was used as the basis for a rapid determination of small amounts of fatty secondary amine in fatty primary amines.
CALIBRATION CURVE
ISTILLED
0 1
2
3
4
5
6
7
8
.
9
P E R C E N T SECONDARY AMINE
Figure 1. 1. 2.
Calibration curves
Didodecylamine in dodecylamine Dioctodecylamine in octadecylamine
propyl alcohol and 0.40 ml. of 0.1000N (or its equivalent) aqueous sodium hydroxide was added. This was transferred quantitatively t o a 200-ml. volumetric flask and diluted to volume with isopropyl alcohol. A fresh solution was prepared every 5 days. Isopropyl Alcohol, -4nalytical Reagent grade. Spectrophotometer, Recknian Model DU with 1-cni. cells. PROCEDURE
For dodecylamine and octadecylamine, 0.625 gram of sample was dissolved in 25 ml. of isopropyl alcohol and a 2-ml. aliquot was pipetted into a 10REAGENTS A N D APPARATUS ml. volumetric flask. T o this was SALICYLALDEHYDE SOLUTION. Exadded 2 ml. of the salicylaldehyde soluactly 5 ml. of freshly distilled salicyltion; any sample solution was washed aldehyde was diluted t o the mark with down in the flask neck. The stoppered isopropyl alcohol in a 50-ml. voluflask was swirled and let stand for 10 to metric flask. Fresh solutions were 30 minutes. Then 2 ml. of the bromoprepared every 5 days. Salicylaldecresol green solution was added, the hyde was distilled in 100-nil. batches solution was made up t o volume with through a Claison head. A 10-ml. isopropyl alcohol, and the flask was forerun was ‘discarded and 70 rnl. colthoroughly shaken. The spectrolected in a brown glass bottle. photometer cell, after two rinses ivith BROMOCRESOL GREEN SOLUTION. the solution, was filled and let stand for Bromocresol green, 0.0300 gram, was 5 minutes to equilibrate with the room mixed with approximately 10 ml, of isotemperature. Absorbance was nieas-
Kiiown mixtures of primary and secondary amine covering the range 0 to 1% secondary amine were carried through the procedure. T n o separatr standard solutions in isopropyl alcohol were used, one containing difatt: secondary amine and the other the corresponding fatty primary amine. For example, a standard secondary aminr solution was prepared containing 0.05 gram of didodecylamine in 100 ml. and a standard primary amine solution was prepared containing 0.619 gram of dodecylamine in 25 rnl. T o each of six 10-ml. volumetric flasks was added 2 ml. of the standard dodecylamine solution. Aliquots of 0.2, 0.4, 0.6, 0.8. and 1.0 ml. of the standard didodecvlamine solution were pipetted into ti\ t of these flasks. The sis flasks then corresponded to samples of dodecylamine containing 0, 0.2, 0.4, 0.6, 0.8. and 1.0% didodecylamine. These samples then were carried through the procedure as described above and a calibration curve was prepared by plotting pry cent secondary amine against ahsorbance. Figure 1 shows the calibration curves obtained for mixtures of didodecylaniine and dodecylamine and for mixtures of dioctadecylamine and octadecylamine. DISCUSSION
In preliminary experiments it was found that bromocresol green war acidic enough to neutralize the basicit!. of trace amounts of sccondary aminc.. This was overcome by neutralizing t h bromocresol green with slightly !pss than an equivalent amount of nqueour sodium hydroxide. The ahswption spectrum of hromocresol green without sodium hydroxide is shown in curve 1. Figure 2 , and the spectrum with sodium hydroxide is shown in curve 2 , Figure. 2. T o demonstrate that the bromocresol green solution could be prepared reproducibly, three solutions were prepared in the prescribed manner and each was used to run duplicate determinations on the same sample of primary amine. By employing the same calibration curve, the following prrccntVOL. 31, NO. 10, OCTOBER 1959
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IO,
1
Table 1. Effect of Variations in Bromocresol Green Concentration
Didodecyl- Bromocresol Green Soin., amine", Mg. M1. 1.5 2 0 2 .:i 1.5 2 0 2.5
0.2 0.4
Absorbance at 627 Mr 0.30 n.43
0.50
0 49 0.61 0.80
a Absorbance readings were made on solutions containing indicated amount of didodecylamine and 80 mg. of dodecylamme.
2 50C
400
600
70C
WAVELENGTW rnN
Table li. Time of Reaction of Salicylaldehyde with Primary Amine
Time after Addition of Salicyialdehyde, Miii. 1 .a3 2.25 :i . 5 5.6 8,; io n
Figure 2. 1. 2.
&):hanee
Absorption curves
Bromocresol green in isopropyl alcohol Neutralized bromocresol green in isopropyl alcohol
a t 627 b
... 0.1c 0.1L ...
0.65 ... ...
0.62
..
W
0
z 4
m
U 0 v,
m 4
a Distilled hydrogenatctd tallow primary amine. b Distilled hydrogenated tallow primary amine containing dioctadecylamine.
.
WAVELENGTH
Figure 8 .
Table 111. Effect of Varying Salicylaldehyde Concentration
Secondary
Sat:-yl-
Mk?
a1,lepytle
Soh., R.1:
Ahsorbnnce a t 627 n r p
3c' 0 4
Z Q iE,
0 11 0 68
mine,^
2 0 2 5
0 60 0 58
0 Absorbance readings wyare made on solutions Containing indicated amorint of dioctadecylamine and $0 mg. of hydrogenated tallow primary amine.
Table IV.
Tertiarv Amine" Content,
% 2 . ii 1 .I) 0.5 a
Effect of Tertiary Amine"
Serondary hmine. 7 0 Ad d e d - F X d 0.40 0.50 0.40 0.40
0.44 0.43
Mixtilres were prepared with distilled
tallow primary amine, dioctadecylaminc,
and trioctadccylaaine.
ages bere obtained: 0.15, 0.15; 0.16, 0.12; c.;4, 0.14. The basis tor this determination of secondary ami.r.e is the elimination of ttc. basicity of primsrq. amine by reactior: with s:ii,cylaidrhyde to form a Schiff basl-. This rmction product is not ba& enmgii t o affect tne absorption spectrum, CItiw bromocrcsol green. This is shown In Figure 3, v : h w curve 1 is thi? spectrum of an isoprfipyl alcohol '1 656
e
ANALYTICAL CHENSTRY
2.
__
mp
3. Absorption curves
Octadecylamine, salicylaldehyde, and neutralized brarnacreso! green Octadecylamine, dioctadecylarnine, salicylaldehyde, and neutralized bromocresol green
solution containing primary amine, salicylaldehyde, and neutralized bromocresol green. Curve 2 in Figure 3 was obtained by application of the proposed procedure to a sample of octadecylamine containing 0.5% dioctadecylamine. The influence of indicator concentration, time of reaction, and salicylaldehyde concentration on results was investigated. Table I shows the effect produced by changing the amount of bromocresol green. The reaction between the salicylaldehyde arid the fattv primary amine is complete within 3 minutes, as shown in Table 11. In this experiment absorbance was read at various times after the addition of sa:icylaldehydc and bromocresol green to two different sample solutions. Tabie III snows t h a t small variations in the concent,ration of salicylaldehyde do not affect the results appreciably. VariationE in results obtained using undistilled salicylaldehyde from. diiferent sources were eliminated bb- iie tilling the wlisyhldehyde. Distillxi salicylaldehyde stored in brown botties has been used for as long as 2 months without signs of deterioration. The dodecylnmine used as a standard in this work was tested for the pxse:icc of seeondaF amine in the foliowing rzianner. Mixtures were prepared, each
containing the same amount L : dodecylamine b u t different am the dodecylamine, and were T ried through the procedure. Thi was a n increase of only 0.06 in &swtance in going from 80 to 13: u g . o' dodecylamine. This increase in oS5cr' ,ante is equivalent to what wo" ' be aldehyde concentration c a u s d
I,
i
fore, indicated t h a t thew was amine. The octadec)u' m i n p WP' I L used as a standard gave the VJL), > * sorbance value as the dodecylaa was considered to be at the S L L I ~ . L ! of purity. The didodecylamine and h L L d ylamine standards were found h- : < tion (6, 8) "Lc contain 99 2nd Pt ondnry amice, respectively. Because trace amounts c, tertiary amines might be p r w , i f i fatty p r i a a r y amines, the F t e r t i a v amine on the second:^ analysis R as icvestigated !liiatirc, containicq primary, s e c w d a v , F n r f e r t i a v arnir.es were e n a I y 7 4 hy EL proposed method. Tnble 11-s h w s tha, less than :yo ai' krtidil- amine ha5 little effect This rplatively w i i L LD.terference x d d be due to t w pLez m -
enon observed b y Davis and Schuhmann (Q), who found that tertiary amines give colors different from secondary amines in nonaqueous solutions containing bromophthalein magenta. They noted that the wave length of maximum absorption with tertiary amines was approximately 40 mp lower than that with secondary amines. The molar absorbance was less for the tertiary amines than for secondary amines. Table V lists the rcsults obtained with the proposed method on known mixtures and commercial samples. The reproducibility of the outlined procedure is estimated a t 50.05% absolute. The method should also be applicable to low molecular weight amines, if equivalently smaller sample sizes are used. The method was applied to a sample of n-butylamine of unknown purity and to mixtures containing this amine and di-la-butylamine. The re-
suits indicated thRt di-la-butylamine gives absorbance vaiues close to those obtained with the same equivalents of didodecylamine. On the other hand, aromatic secondary amines are apparently too weakly basic to be de-
Table
V.
Analysis of Purified and Commercial Amines
Samp1ea Dodecylamine 0.727’ didodecylamine Dodecylamine 0.29% Didodecylamine Dodecylamine Dodecylamine Octadecylamine Tallow primary amine Tallow primary amine Tallow primary amine
+ +
1.
2. 3. 4. 5. 6. 7. 8.
Secondary Amine Found, yo 0.66 0.28 0.10 0.50 0.30 0.80 0.10 0.48
1 and 2, purified amines; 3 through 8, commercial distilled amines. a
tectra :his method. l\ilixttriws containing slethybniline and aniline gave no m o r . LITERATURE CITED
( I ) Ilritchiield, F. E., Johnson, J. A N A L .CHEM.28, 430 (1956). (2) [bid., 2 9 , 957 (1957). (3) Crilles, E. C.. Waddington, D. . -4naI. Chim. Acta 15, 158 (1956). (4) Davis, M. M., Schuhmann, P. J. Research Natl. Bur. Shndarda
B.. J., J., 39,
221 (19471. ( 5 ) Hershenson, H., Hume, D., ANAL. CHEM.29, 16 (195i). (6)Jackson, J., Ibid., 25, 1764 (1953).
(7) Stanley, E. I,., Rmim, H., Gove, J. L., Ibid., 23, 1779 (1951). (8) Wagner, C. D., Brown, R. H., Peters, E. D., J. Am. Chem. SOC.69,
2609 (1947). (9) Wagner, C.
D., Brown, R. H., Peters, E. D., Ibid., 69, 2611 (1947).
RECEIVEDfor review .4pril 10, 1959. Accepted June 22, 1959. Paper 236 Journal Series, Research Laboratories, General Mills, Inc.
Steam Distillation of Fluorine from Perchloric Acid Solutions of Aluminiferous Ores E. J. FOX and W. A. JACKSON Fertilizer Investigations Research Branch, Soil and Water Conservafion Research Division, U. S. Department of Agriculture, Beltsville, Md.
b An all-glass multiple-unit fluorine distilling apparatus equipped with automatic temperature controls was developed in a study of factors affecting the volatilization of fluorine during the acidulation of phosphate rock. Results obtained with this equipment indicate that the interference of aluminum in the steam distillation of fluorine from perchloric acid solutions of aluminum-bearing rocks is caused by the formation of acid-soluble complex ions of aluminum, fluorine, and possibly other elements that greatly reduce the partial pressure of fluorine compounds in the gas phase above the distilling acid solution. A procedure for simultaneous double distillation to speed up the operation is described.
T
HE interference of aluminum and
silicon in the determination of the fluorine content of rock b y distillation from perchloric acid solution and in the titration of the distillate with thorium nitrate has long been recognized (25). The exact nature of the interference, however, is not apparent from a perusal of the several procedures that have been suggested to overcome the di5culties
engendered by the presence of these elements in fluorine-bearing materials. Dahle and Wichmann (3) found that aluminum salts retard the rate of fluorine distillation, while Reynolds (16) found that hydrous silica adhering to the walls of distilling flasks above the level of the acid solution retains fluorine during distillation from fluorine-rich samples, only t o give i t up during the distillation from fluorine-poor samples, thus vitiating the results of both. Willard and Winter (25) attributed interference in the titration with thorium nitrate to the precipitation of a nondissociakd aluminum salt. Hoskins and Ferris (9) determined the permissible limits of concentration of such ions in solution in which fluorine was 50 be titrated. The use of a multiple-unit distilling apparatus such as that described by Reynolds, Kershaw, and Jacob (18) made control of the temperature of the distilling acid difficult, while the use of rubber stoppers and hose connections with perchloric acid was recognized as potentially dangerous ( 1 7 ) and a possible source of error due to their sorption and desorption of hydrogen fluoride. Some of the more recently proposed
procedures for the determination of fluorine in rocks that require fusion prior to distillation are reviewed by Hollingsworth (8) and a high ternperature pyrohydrolysis method especially designed for the assay of aluminum fluoride is described by Haff, Butler, and Bisso (6). A procedure applicable to the analysis of aluminifwous ores decomposed by acid digPstion is described ip. this article. The influcnce of the s l u ~ i n u mion on the distillation cf fluorine from materials decomposed by alkali fusion is also indicated. EXPERIMENTAL PROCEDURE
Improved Bluorine Distillation Apparatus. A sectional drawing of one of t h e units comprising a multipleunit still is shown in Figure I . .h arrangement for mounting the several unit,s i s likewise suqgc,stcd by the cross-sectional outline of t h e wooden framework of the apparatus in this figure. Castalloy clamps were used to fasten the steam-generator flasks to the frame. The distilling flasks 5 cm. in diameter were blown from the female sections of 29/42 standard-taper borosilicate glass ;oink to F,t 50-ml. Mas-Col heating mantles. The 7-mm. outside diYOL. 31, NO. 10, OCTOBER 1959
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