ANALYTICAL CHEMISTRY
676 levels, or the accurate measurement of weak beta-emitters such as 1‘C and ’S below the 100-mc. level. LITERATURE 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) Bathe, W., 2. 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. ORHL-266 (1949). ( 6 ) Glendenin, L. E., and . l l p t i t ~ lh i t y r a t e I,:t liyl crotonate 1,.t hyl a.6-dihrolnohii tyra te Isoainyl salicylate I'henyl -alicylate ICthyl p-iiydroxyhrnzoete 1,;tIiyl ncetoacetate 1,:thyl trialonate wBiifsl >el)acate 1,; t I is I Iit i t ha1 a t e wl3ut>I i~tithalate I'lirn) I i~titlialate llvtliyl ?,2',6.6'-tetranitro-4,~'iiii~lirnyldicarhoxylate t,-l%iityltartrate ,+13otyI ritrate ikrl7,yl
n-Butyl stearate Methyl henzoate Phenyl benzoate Methyl cinnamate Methyl m-nitrocinnamate E t h y l o,B-dibromo-8-phenylr,royionate E t h v l lactate n-Butyl l a c t a t e Methylsalicylate n-Butyl acetylricinoleate E t h y l glycinate hydrochloride Triacetin Triyropionin Cottonseed oil Linseed oil Coumarin a-Gluconnlactone Polylactic acid Polyvinyl acetate Methyl oxalate E t h y l oxalate E t h y l o.ralproriionate
benzoic, dl-malic, succinic, glutaric, and citric acids all gave yellow solutions by test B. Phenols. Phenols gave yellow solutions by both tests A and B. Aldehydes. Weakly positive tests were often observed with the following aldehyde?: Formaldehyde Benzaldehyde p-~Iydroxybenzaldehs.de
rn-Nitrobenzaldehyde Vanillin Anisaldehyde
Other aldehydes--e.g., isobutyraldehyde, n-butyraldehyde, and n-heptaldehydr --:ilways gave negative tests. Amides. Formamide gave a deep magenta solution by test B. The following amides gave medium magenta tests: Acetainide Formanilide Bensamide
Diacetylhydrazine Phthal hydrazide
Segative tests were given hy urea, butyramide, acetanilide, .I'-berizoyl-p-bromoaniline, .~-heii~oy1-2-naphthylamine,and .Vacetyl-1-naphthylamine. Imides. The following imides gave deep magenta colors by test H : Diacetamide Succini inide
Phthalimide 4-Nitrophthaliinide
hledium t o light magenta tests were given b y the following imides: N-n-Ainyl-3-nitrophthalimide Biuret
Benzoylurea N-.llethyl-N'-acetvl,,rea
A nrgative test was given by diethylbarbituric acid. Nitriles. ..icetonitrile and propionitrile gave light magenta tests by procedure B. Valeronitrile, benzonitrile. and phenylacetonitrile gave yc~llo\vtests. Isocyanates. Phenyl, p-tolyl, arid a-naphthyl isocyanates gavc dcep magenta tests by procedure C but only very weak or iieg:itivc tests by procedure B. p-Nitrophenyl isocyanate gave :i light magenta solution with test C ; it was negative with test. B. Phenyl isothiocyanate wits negative to both tests B and C. Nitro Compounds. The following nitro compounds gave deep red solutions when used in trst B whet,her hydroxylamine hydrocliloritle way added or not : Sitroniethane 2- S i tropropane
Broinot richloroiiiethane Trichloroacetic acid
twt. (yi*llowsolutioiis) were obtained with iodoform, iLchlorirl(~,iind 1,1,2-trichloro-l,2-dibromoethane. Acid Anhydrides. The following acid anhydrides gave soluI I ( I I I S i ) t c l c ~ ~magc~rita p color when used in either test B or C: Siy,:tti\.c.
l.:irt t o 1 1
tt'ti
Phthalic anhydride 3-Nitrophthalic anhydride
Acid Chlorides.
Benzoyl chloride and p-phenylbenzoyl chlo-
i . i r l ( ~ gavt: deep niagcnta solutions with tests B and C. Benzene.ulfonyl chloritle and thionyl chloride gave yellow solutions t o lll,ttl tests.
Formic acid and pht,halic acid gave soluB and C. Lactic (85';) gave a deep magenta color by test B only. Acetic,
Carboxylic Acids. t
ioii'i of medium magenta color with both tests
Hi'i(l
2-Nitro-1-butanol 9-Ni tro- 1-c hlorohutane
Test .Igave yellow solut,ions i n these cases. Sitrobensene and p-nitrotoluene gavr yellow solutions when used in test. B. Sitroaromatic ester> xnct anhydrit1t.s gave normal results (see above). Esters in Mixtures. Methyl benzoate when mixed with an equal amount of each of the following compounds gave solutions of deep magenta color when used in test B: Propionic acid n-Octyl alcohol Propylene glycol Benzaldehyde n-Butyraldehyde
Forma rriide Diethylamline n-Butylamine Ethylanilin?
With a large excess of n-butyraldehyde in the mixture better results were obtained when the test mixture was allowed to stand 5 or 10 minutes before addition of ferric chloride solution. Isoamyl acetate mixed with acetone gave a negative test by procedure B unless two or three times as much hydroxylamine hydrochloride a3 usual was used. Then a positive t e 4 wa.9 observed. Methyl acetate mixed with an equal amount of each of the following compounds gave positive results varying from weak t o medium by procedure B: Formaldelryde Isohiitrraldehyde
n-Heptaldehyde Aldol
618
ANALYTICAL CHEMISTRY
hlixed with the following compounds methyl acetate gave solutions of deep magenta color when used in test B: Acetaldehyde Acetal Methyl ethyl ketone
Diethyl ketone Methyl n-hexyl ketone Acetophenone DISCUSSION
Generally speaking, esters will give hydroxamic acids only when heated x i t h hydroxylamine in the presence of base (test B). This hydroxamic acid test is fairly satisfactory m a specific classification test for carboxylic esters if i t is limited t o compounds which do not contain nitrogen. The weakly positive tests often obtained with aldehydes which have no hydrogen on a-carbon may be due t o ester formation in an accompanying Canizzaro reaction. Generally these tests are very weak and should not be nlistaken for the strong ester tests. Trihalomethyl compounds often simulate esters and give positive tests, presumably by way of orthoacid derivatives as summed up in the following reaction: RCX3
to form hydroxamic acids. Both formic and phthalic acids act like anhydrides in the hydroxamic acid test. This is not unusual, since formic acid in much of its chemical behavior is more like an anhydride than other carboxylic acids are. It is a good formylating agent both for amines and alcohols. The commercial phthalic acid used may well be contaminated by phthalic anhydride and thus give the test as an anhydride. Many of the nitrogen-containing derivatives of carboxylic acids also give positive tests. Imides, which are the nitrogen analogs of anhydrides, give the moat consistent results. Some amides and nitriles also give positive tests, but the results are not consistent enough to make the test useful for these types of compounds. Kit,ro compounds Ivith enolizable hydrogen react with sodium hydroxide t o yield an ion. The action of acid on this ion jields the aci form of the nitro compound immediately. This aci form slowls. reverts to the nornid form on standing ( 7 ) : RCH,SO:! 4- OH- C- jRCHN02)-
+ 3 0 H - + NHZOH + RCOSHOH + 3X- + 2H2O
Most of these trihalomethyl compounds that, would be encountered, however, would be insoluble in cold, concentrated sulfuric acid and would give a negative ferrox test ( 1 ) . Esceptions would be such compounds as chloral hydrate and trichloroacetic 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 coniplex carboxylic esters. Even esters of high molecular kveight such as glycerides of fatty acids and polymeric esters give good results. hlonoest,ers of dicarboxylic acids tend t o saponify so fast that usually only weak tests are observed. Oxalates or any ester which yields oxalic acid on saponification requires more ferric chloride t,han the usual ester t o give a satisfactory positive test. Presumably a complex fornis between ferric chloride and oxalic acid. Lactic acid acts as an ester in this test. This tiehavior is simply further proof of t,he generally accepted view that lactic acid contains a large percentage of lactyllactic acid as well m higher polymeric esters (If ). 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 chloridewith a phenol (IS): 6.4rOH FeC13 F-* Fe(oAr)~.--- 6 H + 3Cl-
+
+
+
Such a dependence on acid concentration has not been observed in the color reaction between ferric chloride and a hydroxamic 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 t o 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 prcssence of bsse. Presumably the hydroxamic acid derived from t h v substituted carbamic acid is saponified. It has also been reportc,(l ( 5 ) that ketenes react with hydroxylamine hydrochloride
+ Hz0
0 (RCHSO2)-
rapid
+ HaO+ e RCH=N slow
(RCHSO2)-
7
+ HzO
‘OH
+ H,O+ + RCHzN02 + Hz0
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 (3). 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 t o Ralph
I,. 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 t o be used as a specific class reaction for carboxylic esters when applied t o compounds that do not contain nitrogen. The hydroxamic acid test was found t o 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. LITERATURE CITED
Davidson, D., IND.ENG.CHEM.,ANAL.ED.,12,40 (1940). Davidson, D., J . Chem. Education, 17,81 (1940). Hantrsch, A , , and Shultze, 0. W., Ba.,29, 699 (1896). Hurd, C. D., J . Am. Chem. Soc., 45,1472 (1923). (5) Jones, L. W., and Hurd, C. D., Ibid., 43,2422 (1921). (6) MoElvain, S. M., “Characterization of Organic Compounds,” New York, Macmillan Co., 1946. (7) Maron, 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 & Sons, 1948. (10) Sidgwick, N. V., “Organic Chemistry of Nitrogen,” p. 198, Kew York, Oxford University Press, 1937. (11) Watson, P. D., I n d . Eng. Chem., 32, 399 (1940). (12) Webster, “New International Dictionary,” 2nd ed., unabridged. (13) Wesp, E. F., and Brode, W. R., J . Am. Chem. Soc., 56, 1037 (1) (2) (3) (4)
(1934). (14) Yale, H. L., Chem. Rea., 33, 209 (1943).
RECEIVED October 23,
1949.
