Potentiometric Titration of Long Chain Amine Oxides Using Alkyl Halide to Remove Tertiary Amine Interference SIR: Long chain amine oxides are finding increasing use in detergent formulations as wetting agents and in textile treatments. These long chain amine oxides are basic compounds made b y oxidizing such tertiary amines as dimethylalkylamines (alkyl = CpC,,) (2). I n the manufacture of these compounds i t is desirable to have a rapid method for determination of amine osides and parent amines in mixtures. Recently, several titrimetric methods for determining lower molecular weight amine oxides and heterocyclic N-oxide.. have been described ( I , 4) using perchloric acid as the titrant and acetic anhydride as the solvent. A qualitative colorimetric method for long chain amine oxides which utilizes Fehlings bolution has also been described (3). I n our laboratory we attempted to use gab chromatography for separating and estimating amine oxides and tertiary amines in mixtures. HoIvever, on some Column> there is decomposition a t the high operating temperatures required. The long chain amine oxides are le>basic than the corresponding tertiary amines and can be titrated potentiometrically in isopropyl alcohol using alcoholic hydrochloric acid as the titrant. The main impurity, the parent tertiary amine, will also titrate under these conditions ivithout any discernible differences in end point. Consequently, it is necessary to remove the interfering parent tertiary amine before this method is of any practical value. Methyl iodide can be added to the amine oxide-ter tiwy amine mixture to form the neutral quaternary ammonium iodide of the tertiary amine. TT’hen this is done, only the amine o\;ide will titrate in the above isoproprl alcohol system. Thus, if the sample is also titrated without the addition of methyl iodide, the difference between the two titration, i- a measure of the tertiary amine present in the sample. The use of alkyl halides as a reagent to neutralize tertiary amines has not apprared in the analytical literature for differential titration systems because tertiary amines usually are determined in the presence of primary and secondary amine which also react with alkyl halidei. However, in systems in which
tertiary amines are to be determined in the presence of other titratable compounds, the quaternization of the amine should be a valuable analytical device. EXPERIMENTAL
Apparatus and Reagents. A Radiometer Titrator TTT-1 with glass and calomel electrodes was used in all titrations. Two pure amine oxides were prepared in our laboratory from high purity distilled tertiary amines. A commercial dimethylcetyl amine oxide (ilmmonyx CO, Onyx Chemical Corp., Jersey City, N. J.) was also tested. T h e infrared spectra were r u n on t h e first two samples t o verify their structure.
Table I.
RESULTS AND DISCUSSION
A number of long chain amine oxides were analyzed b y the method described. To these samples were added known amounts of the parent tertiary amine. These mixtures 1%-erethen used t o determine the accuracy and precision of the analytical procedure. Table I gives a summary of the results obtained on these samples, which agree reasonably well with the calculated values. I n controlling the production of amine oxide from tertiary amine, it is nwessary to use only the titration that utilizes methyl iodide. With this single titration, the concentration of amine oxide in the reaction mixture can he followed easily.
Titration of Amine Oxides and Tertiary Amines Mixtures after Reaction with Methyl Iodide
System Dimethyldodecyl amine oxide and dimethyldodecyl amine
Dimethyloctadecylamine oxide and dimethyl octadecylamine Ammonyx CO
Amine oxide, 70 Found
Calc.
Tertiary amine, 76 Calc. Found
0.0 99.8 91.3 84.0 71.2
0.0 99.4 90.1 83.4 70.5
99. fi 0.0
15.8 28.6
59.3 0.0 9.7 16.4 29.3
0.0 98.5 93.5 78.9 20.0
0.0 98.6 93.8 77.5 20.6
98.5 0.0 5.0 20,6 0.0
98.6 0.0 4.7 21.0 0.0
Procedure. Two samples of approximately 0.007 mole are weighed into 150-ml. beakers. T h e samples are dissolved in 50 ml. of isopropyl alcohol One sample is titrated potentiometrically with t h e 0 . 2 5 alcoholic hydrochloric acid (titration A). Methyl iodide (3 ml.) is added to t h e second sample, and t h e mixture, are allowed t o stand for 15 minutes a t 50’ C. This sample is then titrated potentiometrically with the alcoholic HC1 (titration B). The difference between titrations A and B is a measure of the tertiary amine content. Titration B isIa measure of the amine oxide content.
-
8,s
LITERATURE CITED
(1) Muth, C. W., Darlak, R. S., English,
W. H., Hamner, A. T., A N . ~ L CHEM. . 34,1163 (1962). (2) Ralston, A. W.,“Fatty Acids and Their Derivatives,” p. 675, TT’iley, Sew York, 1947. (3) Rosen, M. J., “Systematic Analysis of Surface ’4ctive Agents,” p. 132, Interscience, New York, 1960. (4) Wimer. D. C.. AWL. CHEM.34, 873 (1962).
L. D. METCALFE
Research Laboratories Armour Industrial Chemical Co McCook, 111.
VOL. 34, NO. 13, DECEMBER 1962
1849
