ANALYTICAL
676
levels, or the accurate measurement of weak beta-emitters such 14C and toS below the 100-mc. level, LITERATURE
as
(10)
CITED
(1) Atomic Energy Commission, Isotopes Division, “Radioisotopes Catalogue,” September 1947. (2) Atomic Energy Commission, Isotopes Division, “Simplified Ionization Chamber,” Isotopes Division, Circ. A-7 (1949). (3) Bothe, W., Z. Naturforsch., 1, 179 (1946). (4) Burnett, W. T., Jr., Tompkins, P. C., and Wish, L., Oak Ridge National Laboratory, Rept. ORNL-263 (1949). (5) Burnett, W. T., Jr., Tompkins, P. C., Wish, L., Beyl, G. E., and Huddleston, M., Oak Ridge National Laboratory, Rept. ORNL-266 (1949). (6) Glendenin, L. E., and Coryell, C. D., Plutonium Project Record, 9B, 7.11.2 (1946). (7) Goldschmidt, B. L., and Morgan, F., Atomic Energy Commission, MC-11 (August 1943). (8) Grummitt, W. E., and Wilkinson, G., Nature, 158, 163 (1946).
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(9)
(11) (12)
(13)
CHEMISTRY
Heitler, W., “Quantum Theory of Radiation,” London, Oxford University Press, 1936. Jones, J. W., and Overman, R. T., “Use and Calibration of a 100% Geometry Ion Chamber,” Oak Ridge National Laboratory, MonC-399 (1948). Nottorf, R. W., Plutonium Project Record, 9B, 7.11.1 (1946). Nuclear Data Committee, Clinton National Laboratory, Nucleonics, 2, Part 2, 111, 133 (May 1948). Overman, R. T., Abstracts of 111th Meeting, Am. Chem. Soc.,
p. 44P, 1947. (14) Plutonium Project, J. Am. Chem. Soc., 68, 2411 (1946). (15) Rasetti, F., “Elements of Nuclear Physics,” Philadelphia, Pa., Prentice-Hall, 1936. (16) Stewart, D. W., Lawson, J. L., and Cork, J. M., Phys. Rev., 52, 901 (1937). (17) Tompkins, P. C., and Wish, L., Oak Ridge National Laboratory, Rept. ORNL-314 (1949). (18) Zumwalt, L. R., personal communication.
Received August 12, 1949. Work done under Contract W-7405-Eng-26 for the Atomic Energy Commission, Oak Ridge, Tenn.
Qualitative Determination of Carboxylic Esters Scope and Limitations
of the Hydroxamic Acid
Test
ROBERT E. BUCKLES and CHARLES J. THELEN State University of Iowa, Iowa City, Ioiva A study of the scope and limitations of the hydroxamic acid test for carboxylic esters has led to the development of three modified test procedures. These procedures make it possible to distinguish between acid derivatives that react with hydroxylamine to form hydroxamic ^cids and compounds that do not. They are used further to distinguish esters from the more reactive acid chlorides and acid anhydrides when limited to compounds which contain no nitrogen. These modified procedures have been especially successful when applied to polymers, plasticizers, fats, and oils. The test can also be used to detect esters in mixtures.
A
NUMBER of the more popular, recent textbooks (6, 8, 9) of qualitative organic analysis give the saponification of an
ester to the alcohol and the salt of the acid as the only reliable, specific classification test for esters. Dependence on this test alone in the qualitative analysis for esters has bien unsatisfactory both in research and in courses in qualitative organic analysis. This article discusses the scope and limitations of the hydroxamic acid test as a specific class reaction for esters. The preparation of a hydroxamic acid by the reaction of hydroxylamine with a suitable derivative of a carboxylic acid has been a well-known reaction for a long time (14)·
RCOOR' + NH2OH
—>-
RCONHOH + R'OH
RCOCI + NH2OH —RCONHOH
(RC0)20 + NH2OH
—»
+ HC1
RCONHOH + RCOOH
Hydroxamic acids can be detected easily and fairly specifically by the addition of ferric chloride solution under conditions acidic enough to keep ferric hydroxide from precipitating. A deep magenta color is observed as a result of this reaction. The reaction that takes place is formulated by Sidgwick (10) as follows:
3RCONHOH + FeCls
—>
L
«VX
0 X
"
X/
NH—O
Fe + 3H+
+ 3C1-
_
Various methods of synthesis of a hydroxamic acid followed by its detection with ferric chloride solution have been used by
Davidson (2) as the bases for classification tests for several types of organic compounds including esters. During the past year this test as applied to esters has been tried out on a considerable number of compounds in order to evaluate it. It has been found necessary to devise modifications. Three useful test procedures have been developed. PROCEDURES
The compounds used in testing these procedures were either samples of commercial products or the more highly purified compounds sold by chemical supply houses. No attempt was made to purify any of these samples further. A. Dissolve a drop or a few crystals of the compound to be tested in 1 ml. of 95% alcohol and add 1 ml. of 1 N hydrochloric acid. Note the color produced when 1 drop of 10% ferric chloride is added to the solution. B. Mix 1 drop or several crystals of the compound with 1 ml. of 0.5 N hydroxylamine hydrochloride in 95% ethyl alcohol. Add 0.2 ml. of 6 N aqueous sodium hydroxide, heat the mixture to boiling, and after the solution has cooled slightly add 2 ml. of 1 N hydrochloric acid. If the solution is cloudy add 2 ml. of 95% ethyl alcohol. Observe the color produced when 1 drop of 10% ferric chloride solution is added. If the color caused by the drop of ferric chloride solution does not remain when it is mixed into the test solution, keep adding the reagent dropwise until the observed color pervades the entire test solution. Usually only 1 drop of the ferric chloride solution is necessary. Compare the color with that produced by test A. A positive test will be a distinct burgundy or magenta color as compared with the yellow observed when the original compound is tested with ferric chloride in the presence of acid. [The color observed in this test is the one listed as magenta (12) in the illustrations under the word “color.”] It is best to observe the color of the test solution within 5 minutes after adding the ferric chloride solution. In
VOLUME
2 2,
NO.
5,
MAY
1950
many cases, however, the colors of test solutions remain unchanged for hours. ('. If test B is positive, repeat it without adding the sodium hydroxide and with only 1 ml. of the hydrochloric acid for acidilicat ion. RESULTS
Carboxylic Esters. The following esters gave solutions of deep magenta color when used in procedure B: Methyl formate Et hyl formate Isuamyl formate //-Amyl formate
Methyl acetate Isohutyl acetate Benzyl acetate lMmnyl acetate
Methyl butyrate
l'lt hyl erotonate
Kthyl a.y-dibromobutyrate Isoamyl salicylate Phenyl salicylate Kthyl p-hydroxybenzoate Kthyl acetoacetate Kthyl malonate //-Butyl sebacate Kthyl phthalate //-Butyl phthalate Phenyl phthalate Methyl 2,2',6,6'-tetranitro-4,4 diphenyldicarVioxylate
/.-Butyl tartrate //-Butyl citrate
n-Butyl stearate Methyl benzoate
Phenyl benzoate Methyl cinnamate Methyl m-nitrocínnamate Ethyl a,/3-dibromo-j9-phenylpropio·
Other aldehydes—e.g., isobutyraldehyde, n-butyraldehyde, and n-heptaldehyde—always gave negative tests. Amides. Formamide gave a deep magenta solution by test B. The following amides gave medium magenta tests:
Negative tests were given by urea, butyramide, acetanilide, ,V-benzoyl-p-bromoaniline, .Y-benzoyl-2-naphthylamine, and N-
Cottonseed oil Linseed oil Coumarin a-Gluconolactone Polylactic acid
Polyvinyl acetate Methyl oxalate Ethyl oxalate Ethyl oxalpropionate
Glyptal resin Polyinethyl methacrylate
Isobutyl acid phthalate and sfr-octtvl acid phthalate usually
oxalpropionate) required more ferric chloride than the average The same behavior was ester in order to give a persistent test. observed with methyl acetate containing oxalic acid. All the esters gave yellow solutions when used in test A. (inly phenyl acetate gave a medium magenta solution when used in test C; all the others gave yellow solutions. Esters of Other Acids. The following esters gave negative
Diacetyl hydrazine Phthalhydrazide
acetyl-l-naphthylamine. Imides. The following imides gave deep magenta colors by test B: Phthalimide 4-Nitrophthalitnide
Diacetamide Succinimide
Medium to light magenta tests imides: .Y-n-Amyl-3-nitrophthalimide Biuret
given by the following
Benzoylurea
-V-Methyl-V'-acetylurea
Isocyanates. Phenyl, -tolyl, and -naphthyl isocyanates gave deep magenta tests by procedure C but only very weak or negative tests by procedure B. p-Nitrophenyl isocyanate gave a light magenta solution with test C: it was negative with test B. Phenyl isothiocyanate was negative to both tests B and C.
Nitro Compounds. The following nitro compounds gave deep red solutions when used in test B whether hydroxylamine hydrochloride was added or not:
procedure B:
hyl oirt.unatc
Kthyl carbamate
hr hyl chlnrofurmate
Mm by! µ-1 .'luene^iilfimatv
Metliy] sulfate Ethyl sulfate Ethyl nitrate Butyl phosphate
Trihalomethyl Compounds. Solutions of deep magenta color obtained when benzotrichloride and chloral hydrate were u-ed in test B. The following compounds gave solutions of were
medium magenta color:
acetic acid. The hydroxamic acid test does not give positive results with carbonates, urethans, chloroformates, sulfonates, and esters of inorganic acids. This, of course, is a limitation on its use as a general ester test. The test is strongly positive with both simple and complex carboxylic esters. Even esters of high molecular weight such as glycerides of fatty acids and polymeric esters give good results. Monoesters of dicarboxylic acids tend to saponify so fast that usually only weak tests are observed. Oxalates or any ester which yields oxalic acid on saponification requires more ferric chloride than the usual ester to give a satisfactory positive test. Presumably a complex forms between ferric chloride and oxalic acid. Lactic acid acts as an ester in this test. This behavior is simply further proof of the generally accepted view that lactic acid contains a large percentage of lactyilactic acid as well as higher polymeric esters (11). A phenolic group either in the original compound or formed as a result of the hydroxylaminolysis of the ester group does not hinder the test with ferric chloride solution. The presence of acid in the solution would depress the formation of the colored ion expected from the reaction of ferric chloride with a phenol (IS): 6ArOH + FeCls s=t Fe(OAr),— + 6H + + 3C1Such a dependence on acid concentration has not been observed in the color reaction between ferric chloride and a hydroxamic
(RCHNOj)- + H30
rapid s=t
RCH=N
\
+ H20 OH
slow
(RCHN02)- + H30+
RCH2N02 + H20
—>
If the solution is tested with ferric chloride while an appreciable amount of the aci form is still present, a deep red color will be observed (S). Hence these nitro compounds give color reactions when test B is applied to them even when no hydroxylamine hydrochloride is used. ACKNOWLEDGMENT
The authors would like to express their appreciation to Ralph L. Shriner for the many suggestions which aided this work. SUMMARY
The scope and limitations of the hydroxamic acid test for carboxylic esters have been investigated. Three procedures have been developed to enable the hydroxamic acid test to be used as a specific class reaction for carboxylic esters when applied to compounds that do not contain nitrogen. The hydroxamic acid test was found to give satisfactory results not only with simple carboxylic esters, but also with polymeric esters and with glycerides of fatty acids. It was also satisfactory for testing esters in mixtures. Positive tests (misleading from the standpoint of the application of the test to esters) with nitrogen-containing compounds, trihalomethyl compounds, and aldehydes have also been investigated and discussed.
acid.
The use of the hydroxamic acid test for esters as a preliminary test on both water-soluble mixtures and water-insoluble mixtures is feasible. Most types of compounds accompanying esters in mixtures do not interfere with the test. Aldehydes and ketones may compete successfully for the hydroxylamine and make the test weak or negative, but the addition of more hydroxylamine hydrochloride solution than called for in the procedure will correct this deficiency. The formation of hydroxamic acids from anhydrides and chlorides of carboxylic acids when they react with hydroxylamine hydrochloride even in the absence of base serves as a test to distinguish these compounds from the less reactive esters as well as from the nitrogen-containing acid derivatives which give positive tests according to procedure B only. Isocyanates give positive results by test C (4), but they give negative tests in the presence of base. Presumably the hydroxamic acid derived from the substituted carbamic acid is saponified. It has also been reported (5) that ketenes react with hydroxylamine hydrochloride
+
LITERATURE
CITED
Davidson, D., Ind. Eng. Chem., Anal. Ed., 12, 40 (1940). Davidson, D., J. Chem. Education, 17, 81 (1940). Hantzsch, A., and Shultze, O. W., Ber., 29, 699 (1896). Hurd, C. D., J. Am. Chem. Soc., 45, 1472 (1923). Jones, L. W., and Hurd, C. D., Ibid., 43, 2422 (1921). MoElvain, S. M., “Characterization of Organic Compounds,” New York, Macmillan Co., 1946. (7) Marón, S. H., and La Mer, V. K„ Ibid., 61, 692 (1939). (8) Schneider, F., “Qualitative Organic Microanalysis,” New York, John Wiley & Sons, 1946. (9) Shriner, R. L., and Fuson, R. C., “Systematic Identification of Organic Compounds,” 3rd ed., New York, John Wiley &
(1) (2) (3) (4) (5) (6)
Sons, 1948. (10) Sidgwick, N. V., “Organic Chemistry of Nitrogen,” p. 198, New York, Oxford University Press, 1937. (11) Watson, P. D., Ind. Eng. Chem., 32, 399 (1940). (12) Webster, “New International Dictionary,” 2nd ed., unabridged. (13) Wesp, E. F., and Erode, W. R., J. Am. Chem. Soc., 56, 1037 (1934). (14) Yale, H. L„ Chem. Rev., 33, 209 (1943). Received
October 23, 1949.
