conducted by the U. S. Geological Survey on behalf of the Division of Raw Alaterials, U. s. Atomic Energy Commission. LITERATURE CITED
auger,
\-.,
647 (1912).
Compt.
rerid.
155,
Cooke, 1%‘.D., Hazel, F., hIcYabb, JrT. Af., A N h L . CHEM. 2 2 , 654 (1950).
Furman, S . H., Bricker, C. E., Dilts, R. V., Zbid., 2 5 , 482 (1953). Furman. S . H.. Mason. W. B.. Pekol;, J. S.; Ibid., ’21, 1325 (1949).
(5) Jones, C
Il’raris a 4 v ~I.n s t . .timing Enyis. 17, 411 (1888-89). ~
( 6 ) Newton, H. D., Hughes, J. L., J.Ani. Chenz Soc. 37, 1711 (1915). ( 7 ) Rodden, C. J., ed., “Analytical Chemistry of the Manhattan Proj-
ect,” Sational Nuclear Energy Series, Div, VIII, Vol. 1, pp. 64-5, Atomic Energy Commission, and AIcGraw-Hill, S e w York,
1950. (8) Rodden, C. J., Tregoning, J. J., “Manual of Analytical Methods for Determination of Uranium and Thorium in Their Ores,” p. 4, Atomic Energy Commission, Sew Brunsm-ick Laboratory, 19.55.
( 9 ) Sill, C. S . , Peterson, H. E,, -4\.\1,, CHEM.2 4 , 1175, 1455 (1952). (10) Smith, G. F., Anal. Chim. A c t a 5 , 397-421 (1953). ( 1 1 ) Smith, G. F., “Cerate Oxidimetrj-,” p. 77, G. Frederick Smith Chemical Co., Columbus, Ohio, 1942. (12) Someya, Kinichi, Tohoku I m p . r-nrc., Sci. Repts. Ser. 1, 15, 411 (1926); Z . anorg. u . allgem. Chew/. 152, 368-381 (1926).
RECLIVEI)for review August 27, 195G. Accepted January 12, 1957. Pittsburgh Conference on Analytical Chemistry and iipplied Spectroscopy, Pittsburgh, P:t., February 1956
Determination of Aliphatic Primary and Secondary Plus Tertiary Amines A Modified Salicylaldehyde Method FRANK E. CRITCHFIELD and JAMES B. JOHNSON Development Department, Carbide and Carbon Chemicals Co., A Division o f Union Carbide and Carbon Corp., Sooth Charleston, W. Va.
b In a modified salicylaldehyde method for the determination of secondary and tertiary amines a chemical indicator is used to detect the equivalence point. The reaction of primary amines with salicylaldehyde to form the salicylaldehyde-imine is conducted in chloroform medium. The unreacted secondary and tertiary amines are titrated with standard perchloric acid in dioxane using bromocresol green indicator. After neutralization of the sample to bromocresol green indicator, the salicylaldehyde-imine, therefore the primary amine, is titrated with the same titrant using Congo red indicator.
method requires a potentiometric titration because of the buffering effect of the weakly basic imines formed by reaction of primary amines with salicylaldehyde. As shown in Figure 1, in the presence of large amounts of primary amines, the titration of t h e unreacted secondary amine is affected b y the basicity and concentration of the imine formed. Therefore, the sharpness of the potentiometric break is a function of t h e primary amine content of the sample. Attempts have been made to find a solvent system in which the imine does not exhibit appreciahle baqicity. DEVELOPMENT OF METHOD
P
the most versatile procedure yet developed for the determination of secondary and tertiary amines is the salicylaldehyde procedure of Wagner, Rronn, and Peters ( 5 ) . Salicylaldehyde reacts with primary amines to form imines. Most secondary and tertiary amines do not react and may be determined b y titration in methanol medium with alcoholic hydrochloric acid. Siggia, Hanna, and Keri-enski ($) modified this method for application to aromatic amines. From the standpoint of control of plant processes, these procedures suffer the disadvantage of requiring a complete potentiometric titration for detecting the equivalence point. The Wagner, Brown, and Peters ObSIBLY
T o find a n indicator for use in conjunction with salicylaldehyde i t was necessary first to find a solvent system in which imines can be distinctly differentiated from secondary amines by direct titration. Fritz ( 3 ) recommended acetonitrile medium and perchloric acid in acetonitrile as the titrant for this differentiation. -4lthough acetonitrile is a better medium than methanol for this system, the millivolt reading a t the equivalence point for the titration of secondary amines is affected to some extent by the concentration of the primary amine. Freeman (2) used chloroform medium and perchloric acid in dioxane as the titrant. T h e titrant used for Figure 2 was perfluorobutyric arid in benzene and the
titration was conducted in chloroforin medium. B y comparing curves 1 and 2 i t can be seen that the presence of the imine has very little effect upon the titration curve. The indicator end point is independent of the amine concentration. This is not the case in methanolic medium, as 4ioir n in Figure 1. Khile perfluorobutyrir acid is sufficiently strong to titrate most amines n i t h ionization constants greater than 1 x lo+, it is too venk to be used for the titration of the s:ilicylaldehyde-imines. This, coupled with the fact t h a t cliloroform is a good differentiating medium, no doubt causes the shape of the titration curve to he independent of the imine concentration. T h e high cost of perfluorobutyric acid prohibits its use in control work. An attempt \\as made to substitute trifluoroacetic acid but a stablc reagent could not he m:de from this compound. Figure 3, curve 1, shows the titi‘‘1 t’ion of 2-eth~lhexylaiiiinesusing 0.5A- perchloric acid in dioxane as the titrant. The initial reaction and titration of the first equivalence point were conducted in chloroform medium. Then dioxane was added and the imine was titrated. The bromocresol green indicator end point. P , corresponds to the titration of di(2-ethyl1iexyl)amine. The difference betneen T, the Congo red indicator end point, and P corresponds t o the titration of the imine. Figure 3, curve 2, is the titration of pure di(2VOL. 29, N O . 6, JUNE 1957
957
ethylhexj-1)amine under the same conditions. Although the presence of the imine has a marked effect upon the first equivalence point, the indicator end point coincides with the potentiometric equivalence point. Besides being inexpensive, perchloric acid offers a further advantage in that the second equivalence point is sharp and can be detected by means of an indicator. APPARATUS A N D REAGENTS
1
1
0 1 0 4
1
18
1
22
'
,b
i
l
26 ~T-36 ml. 0 5N ALCOHOLIC HCI
l
42
1
46
1
50
A11 potentiometric titrations were perFigure 1. Titration of 2-ethylhexylamines by method formed using a Leeds &- S o r t h r u p lineof Wagner, Brown, and Peters (5) operated pH meter. A sleeve-type calomel electrode with saturatpd potassium 1. Mixture containing 33.7% 2-ethylhexylamine and 65.1 % chloride in methanol ( I ) and a glass elecdi(2-ethylhexy1)amine 2. Di(2-ethylhexyl)amine trode were used in conjunction iTith this P. Bromocresol green indicator end point inrtrument. SALICYLALDEHYDE, reagent grade. L~IOXANE,commercial grade, Carbide and Carbon Chemicals Co. DISCUSSION quantitatively. I n Table I11 are listed CHLOROFORM, Mallinckrodt Chemical data for known mixtures of primary Salicylaldehyde reacts quantitatively K o r k s analytical reagent. and secondary or tertiary amines, I'CRCHLORICACID, 0.5N solution in with most of the primary aliphatic obtained as described. I n general, the dioxane. Shake the dioxane used to preamines investigated. The reagent tends pare this solution overnight with Smberto react with certain secondary amines, lite IRA-100 ion exchange resin (6). such as diethanolamine and diisopropaPrepare the solution by diluting 70 nolamine (6). Listed in Table I are the grams of 70 to 727, perchloric acid to 1 amines whose corresponding secondary liter n i t h the special dioxane. Standamines do not react with this reagent ardize against potassium acid phthalate. under the conditions of the method. BROVOCRESOLGREEX INDICATOR, In the method of Wagner, Brown, and 0.5% solution in methanol. CONGORED INDICATOR, 0.1% soluPeters ( 5 ) only the secondary alcohol tion in methanol. amines caused serious interference n-hile in the present method many more secondary amines caused interference. PROCEDURE Evidently these side reactions proceed, a greater extent in solvents of low to Add the volume of chloroform specidielectric constant-for example, the fied in Table I to a 250-ml. glass-stopsecondary amino nitrogen of diethylenepered Erlenmeyer flask followed by triamine reacts n-ith salicylalclehj-de in addition of the specified volume of salichloroform but not in methanol mecylaldehyde. Add 4 to 6 drops of the bromocresol green indicator and neutraldium-and, have a greater tendency to ize just to the end point with perchloric take place in dioxane than in chloro0 acid in dioxane or alcoholic potassium 10 14 18 22 26 form. m l 0 5 N PERFLUOROBUTYRIC A C I D hydroxide. Usually the latter step can When salicyaldehyde reacts with priI N BENZENE be omitted, because the blank on the mary amines in chloroform medium, reagent is very small. Weigh into the Figure 2. Titration of 2-ethylhexylITater is formed and separates from soluflask a n amount of'sample calculated to amines in presence of salicylaldehyde tion. When this occurs dioxane can be contain no more than 12.5 meq. of using perfluorobutyric acid used as a cosolvent to obtain a homoprimary amine and 12.3 meq. of secongeneous solution, and to solubilize aquedary plus tertiary amine. If the solu1 , Mixture containing 43.970 2-ethylhexyltion becomes turbid because of the ous samples in the reaction medium. amine and 55.270 di(2-ethy1hexyl)arnine separation of the miter of reaction, add Listed in Table I1 are purity data 2. Di(2-ethylhexyl)amine the minimum quantity of dioxane necesP. Bromocresol green indicator end point for amines t h a t can be determined sary to effect solution. Allom the sample to react 15 minutes at room temperature before titrating it Ii-ith standard perchloric acid in dioxane just to the disReaction Conditions for Determination of Primary, Secondary, and/or Table 1. appearance of the green color. Record Tertiary Amines this titration and level the buret a t zero. Add the volume of dioxane specified in Reagent and Solvent Systems Table I and 8 to 10 drops of the Congo Chloroform, Salicylaldehyde, Dioxane, red indicator. Titrate the sample with Amine Mixtures ml. ml. m1.5 the perchloric acid solution to the np75 5 25 Butylamines -pearance of a pure green color. 13 5 25 Ethylamines 75 5 25 2-Ethylhexylamines 50 10 The amount of perchloric acid re50 Isopropylamines 75 5 25 Hexylamines quired for the first titration is a measure I3 5 25 Methylamines of the secondary plus tertiary amine 75 5 25 Propylamines content of the sample. The amount required for the second titration is a a Add dioxane after titration to bromocresol green indicator end point. measure of the primary amine content.
--
958
ANALYTICAL CHEMISTRY
Table II. Determination of Purity of Primary, Secondary, and Tertiary Amines
Average Purity, Wt. % Salicylaldehyde method5 Otherb
Compound 9 7 . 5 =!Z 0 . 1 ( 2 ) 97.1 Butylamine Dibutylamine 9 9 . 1 f 0 . 2 ( 2 ) 99.6 Diethylamine 98.6 f 0 . 0 ( 2 ) 99.1 Di(2-ethylhexy1)amine 9 9 . 2 f O . l ( 2 ) 99.6 Dihexylamine 9 2 . 4 1 0 . 0 ( 2 ) 9 2 . 6 Diisopropylamine 9 8 . 8 =k 0 . 1 (4) 99.4 Dimethylamine 3 7 . 7 10 . 1 ( 2 ) c 3 7 . 8 7 0 . 0 =k 0 . 1 ( 4 ) c 70.2 Ethylamine 2-Ethylhexylamine 98 2 f 0 l ( 2 ) 98 0 99 2 10 2(2’1 99 1 Hexylamine Isopropylamine 98 8 f 0 l ( 3 ) 99 1 37 5 f 0 3 (2)c 37 5 Illethylamine Triethylamine 99 6 10 l ( 2 ) 99 4 Tripropylamine 96 7 10 l ( 2 ) 96 9 a Figures in parentheses represent number of determinations. By titration with aqueous hydrochloric acid. c ilqueous samples.
Figure 3. Titration of 2-ethylhexylamines in presence of salicylaldehyde using perchloric acid 1. 2.
P. A. T.
Mixture containing 48.6% 2-ethylhexylamine and 49.5% di(2-ethylhexyllamine Di(2-ethylhexy1)amine Bromocresol green indicator end point Addition of dioxane Congo red indicator end point
RTerage deviation for the determination of both the primary and the secondary :imine is +0.37,. Because both primary and secondary or tertiary amines are determined by using a single sample, the lower limit of detection of each is limited b y the total volume of titrant required. Therefore, for small amounts of primary or secondary amines the accuracy of the method is limited by the small net titration. However, fair results can be obtained for concentrations of primary and secondary or tertiary aniine a s low as 1.0%. Ammonia does not react quantitatively with the reagent and must be separated before analysis. Heterocyclic qecondary amines, such as morpholine, and secondary alcohol amines interfere if present. The method cannot be used for determining the primary and secondary amine content of polyethylene:imines such as diethylenetriamine and triethylenetetramine. However, as indicated in Table 111, it is applicable to the determination of mixtures of ethylenediamine and secondary or tertiary :mines. I n general, i t cannot be used for the determination of compounds t h a t contain both primary and seconclary or tertiary amino nitrogens in the
