V O L U M E 2 8 , NO. 1 2 , D E C E M B E R 1 9 5 6
1977
Table 111. Chromatographic Separations of p-Phenylphenacyl Ester-2,4-Dinitrophenylhydrazones (S = separated, 0 = not separated)
Acetic Propionic Butyric Isobutyric Valeric Isovaleric Hexanoic Isohexanoic Heptanoic Octanoic Nonanoic Decanoic Undecanoic Dodecanoic Tridecanoic Tetradecanoic Hexadecanoic Octadecanoic
S
.. s
8
s s ..os s 8 ..s s ..os s s . s ..os s s s s s s .. s
E
s s
.. s
. s
.. s
. . s. . s s
.. s
.. s..
colored and differently formed crystals may be obtained from the same preparation of a derivative simply b y changing the solvent used for crystallization. In general, no depression of melting point was obeerved with a mixture of the two crystalline forms of a derivative of a single acid-that is, the melting range was the same as that observed when the lower melting form was melted by itself. The melting points listed in Table I are those of the higher melting, more stable crystal modifications. The greatest value of the 2,4-dinitrophenylhydrazones of the p-phenylphenacyl esters lies in the fact t h a t extremely small amounts of the orange colored derivatives may be chromatographed to give measurable R values which may be helpful in the identification of a particular compound. Table I1 lists the R
values for the 18 derivatives investigated. All the derivatives chromatographed have significantly different R values, with the exception of the three cases of the normal and is0 acid derivatives of the same molecular weight. I t is possible that with a column of greater length the isobutyrate derivative could be separated from the normal butyrate derivative, but the two hexanoate derivatives moved with identical speeds, as nearly as could be determined. The values recorded for relative travel rates are reproducible when the chromatographic columns are carefully prepared. I t was found that a column could be used repeatedly for separations but that variations in the R values occurred as the column aged. Therefore, when a R value TTas desired to assist in the identification of an unknown acid, a freshly prepared chromatographic column was always used. I n Table I11 are recorded the results of experimental chromatographic separations of various combinations of the double derivatives. In every chromatogram three different derivatives were run a t the same time, one of which was always the hexanoate or reference derivative. Examination of Table 111 shows t h a t with the exception of the normal and is0 acid derivatives of the same molecular weight, the separations on the chromatographic column were excellent. I n the case of the structural isomer8 no separation was evident. LITERATURE CITED
H. van, Rec. trav. chim. 73, 78 (1954). (2) Ikeda, R. M., Webb, A. D., Kepner. R. E., (1) Duin,
. ~ Z S ~ LCHEW. . 26,
1228 (1954).
(3) Kirchner, J. G., Prater, h. S . , Haagen-Smit, A. J., IND. Exc. CHEZI.,A s . 4 ~ ED. . 18, 31 (1946). (4) Kramer, P. J. G., D u i n , H. van, Rec. trai.c h i m . 73, 63 (1954). (5) S h i n e r , R. L., Fuson. R. C . , "Systematic Identification of Organic Compounds," 3rd ed., Wiley, S e w York, 1948. RECEIVED for review June 11, 1956. Accepted August 11, 1956. Division of .4nalytical Chemistry, 130th Meeting, ACS, Atlantic City, N. J., September 1956. Taken from master's thesis presented to the Graduate Division. University of California, June 1956, by Hawkins Kg.
Determination of Primary Aliphatic Amines by an Acidimetric Salicylaldehyde Reaction JAMES B. JOHNSON and GREGORY L. FUNK Development Department, Carbide and Carbon Chemicals Co., Division o f Union Carbide and Carbon Corp., South Charleston, W. V a . An acidimetric method for the determination of primary amines uses an indicator end point. A measured excess of salicylaldehyde reacts with a primary amine and the excess reagent is titrated as an acid with sodium methylate in a pyridine medium. Aliphatic secondary and tertiary amines do not interfere. The interference of ammonia, alcoholamines, aniline, heterocyclic amines, and the ethyleneamines is discussed. Data are presented for the determination of 12 primary aliphatic amines. The method is rapid, easy to perform, and applicable over a wide rangeof concentrations.
T
HE methods available for the determination of primary
amines have been revien-ed by Critchfield and Johnson ( 2 ) . The reaction of salicylaldehyde with primary amines to form the corresponding imines was used by Wagner, Brown, and Peters (6) as a basis of a method for the analysis of amine mixtures. I n their procedure the unreacted secondary and tertiary amines are titrated in a nonaqueous medium. Primary amine content may be calculated as the difference between a total base and
secondary plus tertiary amine determination. As this method does not employ an indicator end point, it is necessary to determine the entire potentiometric titration curve for each titration. This paper is a presentation of an unpublished method originally cited b y Hillenbrand (6) and more recently by Critchfield and Johnson (8)for the direct determination of primary amines by the salicylaldehyde reaction employing an indicator end point. Moss, Elliott, and Hall (4), Fritz and Keen (S), and others have shown that many phenols may be quantitatively titrated as acids in basic solvents. The method described herein is based upon the fact that in pyridine medium, salicylaldehyde is acidic and can be titrated with sodium methylate. The reaction products of a primary aliphatic amine and salicylaldehyde are imine and water, XThich are neutral in pyridine medium. The amount of salicylaldehyde consumed, determined by titrating the exceas reagent v i t h sodium methylate, is a measure of the primary amine. REAGESTS
Methanol, anhydrous, Carbide and Carbon Chemicals Co. Pyridine, redistilled.
1978
ANALYTICAL CHEMISTRY
Salicylaldehyde, approximately 0.5K. Dilute 5 ml. of reagent grade salicylaldehyde to 100 ml. with redistilled pyridine. Sodium methylate, 0.1X solution in pyridine. Prepare 4 5 sodium methylate by dissolving 21i grams of dry sodium methylate in sufficient methanol to make 1 liter of solution. Transfer 25 ml. of the 4K sodium methylate to a 1-liter reagent bottle containing 75 ml. of methanol and dilute to 1 liter m-ith redistilled pyridine. Standardize this solution against Bureau of Standards benzoic acid, using pyridine as solvent and thymolphthalein indicator. For the change in normality m-ith temperature use LV per O C. = -0.0001. The reagent readily absorbs carbon dioxide from the air and is best preserved in a bottle equipped with a 50-ml. automatic buret. All vents open to the air must have protective Ascarite tubes. Phenolphthalein indicator, l.Oyc solution in pyridine. Thymolphthalein indicator, l.OYc solution in pyridine. PROCEDURE
Pipet exactly 10 ml. of the 0.5N salicylaldehyde into each of two 250-ml. glass-stoppered flasks. If the sample is an aliquot portion of a dilution, add an equivalent volume of the diluent to one of the flasks, stopper, and reserve as a blank. I n the other flask place an amount of sample containing not more than 3 meq. of primary amine. For volatile amines, use a sealed-glass ampoule and add several pieces of 8-mm. glass rod to a pressure bottle. Alternatively an aliquot from a pyridine dilution may be used for volatile amine samples. Cap the bottle and shake to break the ampoule or swirl the flasks to effect adequate mixing of reagent and sample. illlow the sample and blank to stand for 15 minutes a t room temperature. Carefully remove the stopper or cap and v a s h any adhering liquid into the vessel with a few milliliters of redistilled pyridine. To each vessel add 1 ml. of the preferred indicator (phenolphthalein or thymolphthalein; see discussion) and titrate with standard 0.1-V sodium methylate in pyridine to the end point. The difference between a blank and sample titration is a measure of primary amine. DISCUSSION
Reaction Rate. The reaction of primary aliphatic amines with salicylaldehyde goes rapidly to completion a t room temperature. Table I illustrates the rate of reaction of isopropylamine and butylamine with the reagent. I n the determination of all the amines shown in Table 11, the reaction was complete in 15 minutes. The difference between the per cent primary amine obtained by this method and by total base titration is undoubtedly due to the presence of small percentages of the corresponding Fecondary and tertiary amines in the commercial samples. Ammonia Interference. Primary amines cannot be determined in the presence of ammonia by this method. Ammonia reacts with salicylaldehyde to give an apparent primary amine value. However, the reaction is not stoichiometric under these conditions. All attempts either to obtain a quantitative reaction of salicylaldehyde with ammonia or to prevent reaction have been unsuccessful. Effect of Alcoholamines. Ethanolamine does not react quantitatively under the conditions employed and, as in the case of ammonia, the reaction could not be forced to completion. Furthermore, diethanolamine also reacts with salicylaldehyde. For example, a sample of refined diethanolamine (total base as diethanolamine 99.9%) reacted to the extent of 67% in 15 minutes a t room temperature. A sample of ethanolamine (total base as ethanolamine 99.3%) analyzed 86% in the same time. The explanation of the phenomenon has been adequately discussed by Wagner, Brown, and Peters ( 6 ) . Effect of Aromatic Amines. Attempts to obtain quantitative results with aniline also were unsuccessful. A highly refined sample gave a reaction of 70% in 1 hour. Presumably other aromatic amines also fail to react completely under the specified conditions. Other Interferences. Amine salts interfere quantitatively and a correction must be applied if they are present. Inasmuch as some amine carbonates form readily, care must be exercised to prevent atmospheric contamination of the samples. Heterocyclic secondary amines such as piperidine, piperazine, and mor-
Table I.
Reaction Rate of Primary Amines with Salicylaldehyde
Aminen 1 Isopropylamine 9 5 . 6 Butylamine , , , a
5 97.7 ...
Time, Rlinutes 15 30 98.2 98 2 97.2 97.3
45 98 2 . .
120 ... 97.3
-411 values are per cent by weight.
Table 11. Determination of Primary Amines by Acidimetric Salicylaldehyde Reaction .Imine0 n-Butyl Isopropyl tert-Butyl Isoamyl n-Amyl n-Hexyl Isobutyl Propyl, aqueous 2-Ethylhexyl Diethylaminoethyl Ethyl Methyl, aqueous
This Method* 97.3 i 0 2 98.6 0.2 96 8 0.0 91.0 0.4 84.6 97.6 0.2 97.2 + 0 . 3 44.7 i 0 . 2 96 4 i. 0 . 2 96.2 0.3 98.3 0 1 28.8 i 0 . 0
*++ + + +
Total Basec 89.2 99.2 97.6 92.4
85.8 99.1 98.8 45.4 99.5
i0i:g 29.7
Prim. plus Sec. -4mined 99.2 ,..
... ... ...
98 9 99.3 100: 1
...
... , . .
Commercial grade materials containing small percentages of corresponding secondary amines. Average of at least 2 determinations; all values are per cent by weight. c B y titration in water with 0.5S hydrochloric acid using bromocresol green-methyl red indicator. d B y carbon disulfide procedure of Critchfield a n d Johnson ( I ) . Calculated as primary amine. a
*
Table 111. Determination of Ethylamine in Refined Diethylamine Ethylamine, Wt. % Present Sample 1
Sample 1 plus 0.2747,
0 299
Sample 1 plus 0.599%
0 624
Found Salicylaldehyde Van Sly& reaction methoda
0 0 0 0 Av. 0 0 0 0 Av. 0 0 0 0 Ar. 0
033 027 014 027 025 287 294 287 289 596 609 623 609
0 017
0 330
0 594
Sample 2
Av. 0 286 a
Modified T a n Slyke nitrogen-evolution method ( 7 ) .
pholine react partially under the specified reaction conditions and therefore must be absent from the sample. Alcohols and water do not interfere and have been used in certain cases to prepare dilutions of amines for analysis. Indicators. I n most cases phenolphthalein and thymolphthalein indicators may be used interchangeably. The proper selection of indicator seems to be a matter of individual preference. I n some cases the color of reaction products may dictate the ultimate choice. Accuracy. An indication of the accuracy of the method is given by the analysis of a synthetic sample of the following composition: ethylamine, 2.4%; diethylamine, 22.6%; triethylamine, 2.3%; ethyl alcohol, o.9yO; and water, il.8$Z0. The procedure described herein gave duplicate results of 2.370 for ethylamine.
1979
V O L U M E 28, NO. 12, D E C E M B E R 1 9 5 6 ACKNOWLEDGXIENT
Low Concentrations. The salicylaldehyde procedure has been slightly modified for the determination of low concentrations of ethylamine in diethylamine and presumably is adaptable to other amine combinations.
The authors gratefully acknowledge the work of R. L. Anderson and 0. R. Trimble, who obtained some of the data presented in this paper.
For this determination pipet 25 ml. of 0.1A- salicylaldehyde in pyridine into a suitable glass-stoppered flask. Add 75 ml. of pyridine and introduce a 10-ml. sample of known specific gravity. Allo~v to react 15 minutes a t room temperature and titrate with standard 0.1-V sodium methylate reagent to a phenolphthalein end point which should last 15 seconds. The use of a blanket of nitrogen above the liquid helps to prevent fading of the end point thereby increasing the precision. Diethylamine and salicylaldehyde produce an orange color in this determination, which obscures the thymolphthalein end point.
LITERATURE CITED
(1) Critchfield, F. E., Johnson, J. B., A N ~ LCHEM. . 2 8 , 430 (1956). (2) I b i d . , p. 436. Keen, R. T.,Zbid.;25, l i 9 (1953). (3) Fritz, J. S., ( 4 ) Moss, 11. L., Elliott, J. H., Hall, R. T., I b i d , 20, i 8 4 (1948). (5) Riddick, J. A , Fritz, J. S.,Davis, XI. AI., Hillenbrand, E. F., Jr., Markunas, P. C., Ibid., 24, 310 (1952). (6) Kagner, C. D., Brown, R. H., Peters, E. D., J . Am. C h e m . SOC. 69, 2609 (1947). (T) Wilson, H. S . ,Heron, A. E., Analyst 7 0 , 38 (1945).
9 sample of refined diethylamine was carefully fractionated, and samples of known ethylamine content were prepared and analyzed. Table I11 shows the results obtained.
R E C L I V Efor D review Janua:.y 11, l % G .
. i c c e p t c d . i u g u s t 7 , 1956.
Detection of Surface-Active Alkylaryl Sulfonates by Alkaline Fusion and Formation of an Azo Dye MILTON J. ROSEN and GERALD C. GOLDFINGER Department o f Chemistry, Brooklyn College, Brooklyn, N. Surface-active agents containing the alkylaryl sulfonate group may be detected by the purple, red, or orange color produced when the phenol obtained from their fusion with potassium hydroxide reacts with diazotized dianisidine. Compounds containing nitro or halo substituents on the benzene ring give false negatives.
Y.
The phenol produced is then detected by reaction with diazotized dianisidine to form an azo dye.
A
LTHOlTGH the alkylar! 1 sulfonate group is the functional group most commonly found in surface-active agents (I), the literature contains no simple, convenient, and definitive test for the qualitative detection of this grouping. Published tests for this group are based on formation of a precipitate with 10% cupric sulfate solution ( 5 ) ; nitration of the aromatic nucleus, reduction of the product, and detection of the resulting aromatic amine ( 4 ) ; or alkaline fusion of the aromatic sulfonate and detection of the resulting phenol (6, 7 ) . The first type of test (cupric sulfate precipitation) is unsatisfactory, as a number of types of surfactants which do not contain this functional group are also precipitated by cupric sulfate (S), n hile certain alkylaryl sulfonates are unaffected by the reagent. The second IL-pe also suffers from lack of specificity, because it is given by all aromatic nuclei, sulfonated or unsulfonated. For example, it gives positive results with all alkylphenol-ethylene oxide condensates. The third test seems to have the greatest potential spwificity; the fact that it is given by all phenols, sulfonated or not, is not considered a serious disadvantage, as unsulfonated phenols are not ordinarily used as surface-active agents and phenol--ethylene oxide condensates n-ould give negative results. Honever, the published procedures (6, 7 ) for performing the alkaline fusion type of test are inconvenient, require a good deal of experience, or are not specific to aryl sulfonates. The test as outlined by Muller (6) suffers from a lack of specificity, as it gives false positive results n i t h many easily oxidized compounds, 1% hile the fusion devised by Kurzschmitt ( 7 ) must be done under carefully controlled conditions and, according to the author, needs experience to be performed correctl?. The procedure outlined below has been devised to remedy these deficiencies. The aryl sulfonate first reacts with molten potassium hydroxide in the usual fashion to give a phenol, according to thp equation
I
L
1-c3-o
i
-I
Diazotized dianisidine was chosen for this purpose because, under the conditions of the test, it forms azo dyes that are more intensely colored than those of any other amine tested. Because diazotized amines produce colors not only with the phenols produced by the fusion with molten alkali, but also with the by-products formed during the fusion, it was necessary to remove these by-products by solvent extraction before the coupling reaction. For this purpose, the reaction mixture was first extracted with benzene, while still alkaline, to remove benzene-soluble by-products and unreacted sulfonate and then, after acidification, extracted with petroleum ether to remove the phenol from the remaining by-products. Ethyl ether, which is used to extract the phenol in other tests of a similar nature (6), was found to dissolve by-products of the fusion reaction as well as the phenol and thereby give false positive results in a number of cases. PROCEDURE
Preparation of Diazonium Salt Solution. Dissolve 20 mg. of dianisidine in 10 ml. of 1 to 4 (by volume) hydrochloric acid.
