A Semimicro Qualitative Test for the Nitro Group in Organic Compounds W. M. HEARON AND R. G. GUSTAVSON University of Denver, Denver, Colo.
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known is added. Then 0.5 ml. of the base solution is added and a stream of natural gas (or any inert gas) is assed through the tube to remove any air. The tube is uicily stoppered and shaken. A positive test is indicated by &e formation of a redbrown to brown precipitate of ferric hydroxide. Negative tests in many cases gave a very light green recipitate. However, in some cases the precipitate became d a r i due to slight oxidation.
EVERAL qualitative tests for the nitro group have been reported.
Vortmann (18) suggests three: reduction to amino group and subsequent indentification, formation of chloropicrin which may be recognized by its odor, and the red or yellow coloration produced by boiling solutions of alkaline hydroxides. Mulliken and Barker (13) have shown these to be inadequate and present two additional tests. The first involves the reduction with zinc and alcohol to a substituted hydroxylamine which in turn is identified by its reducing action on ammoniacal silver nitrate. The second test utilizes the oxidizing power of the nitro group to change “aniline oil” (equal parts of 0- and p-toluidine, and aniline) to the highly colored magenta red. Mulliken does not quote this last test in his “Identification of Pure Organic Compounds” (12). Janovsky (9) found that aromatic dinitro compounds in acetone gave colorations with aqueous potassium hydroxide. This work was extended and its limitations observed by Bitto (31, Reitzenstein and Stamm (15), and Rudolph (17). Bost and Nicholson (6) have confirmed this test and find that, in general, mononitro aromatic compounds give no colorations, dinitro compounds give a purple, and trinitro compounds produce a blood red coloration. The presence of amino or hydroxyl groups in the nucleus, however, interfere. Konowalow (11) tested for primary and secondary nitro groups by treating their sodium salts with ferric chloride and extracting the colors in suitable organic solvents. Dimethylaniline (19) gives colors with many nitro compounds. Anhydrous aluminum bromide in benzene (14) has also been reported to give a red color with aromatic nitro compounds. Rosenthaler (16) states that nitromethane when treated with ammonium hydroxide and vanillin and heated gives a red color which disappears on cooling. If sodium nitroprusside is used in place of vanillin, he states that an indigo blue coloring appears, which gradually changes to green and then to yellow. The higher homologs were found to give a brick red coloration. Bose (4)has found that all except mononitro aromatic compounds will split off potassium nitrite with strong potassium hydroxide which in turn is identified with Griess-Ilosvay’s reagent. Kamm (IO)has described a test which involves the reduction of the group to various colored compounds by means of sodium amalgam and alcohol.
Discussion and Conclusion In the aromatic series, forty-five nitro compounds were tested and all gave a positive test in less than 30 seconds. Unfortunately nitromethane was the only representative of the aliphatic series available, and it gave a positive test only after a minute. The speed with which the iron is oxidized was seen to be a function of the solubility of t h e nitro compound. Thus p-nitrobenzoic acid gave a positive result almost immediately, while nitronaphthalene required 25 seconds. Obviously any organic oxidizing agent powerful enough will oxidize the ferrous hydroxide, and it is seen that nitroso compounds, aliphatic nitrates and nitrites, quinones, and hydroxylamine will also show a positive test. As in any color test, highly colored compounds cannot be successfully
TABLE I. RESULTSO F TESTS Compound
Color of Ppt.
Compounds Containing the Nitro Group Brown Nitromethane Brown Mononitrobenzene Brown m-Dinitrobenzene Brown Nitrona hthalene Brown p-Nitrol?enzoic acid Brown p-Nitrophenylacetic acid Brown p-NitSoacetanilide Brown 2,4-Dinitroqhenol m-Nitronmlinn Brown . . ..-. ._._ ~~. .. Brown o-Nitroanisole Brown m-Nitrobenzaldehyde Brown p-Nitrobennylcyanide Brown m-Nitrobenzhydradde m-Nitrophenylhydrazine Brown
The presented test is dependent upon the oxidation of a suspension of ferrous hydroxide by the nitro compound. Ferrous hydroxide has been used many times in the past for preparing amino compounds from nitro compounds For example, (m-aminopheny1)-gloxylic acid ( B ) , o-aminophenylpropiolic acid (1), o-aminobenzaldehyde ( 2 ) , and o-aminocinnamic acid (7) have been prepared by the reduction of the corresponding nitro compounds by means of ferrous hydroxide. Jacobs and Heidelberger (8) have prepared a niimber of amino acids, amides, and ureas by reducing the nitro compound with ferrous hydroxide and ammonia. The authors have been unable, however, to find any reference to the use of this reagent in a qualitative test.
2,4,6-Trinitro-1,3-dimethyl-5-tertbutylbenzene
Brown
Time Sec. 60 2
10
25 2 2 10 3 3 2 1 5 5 2 25
Compounds Not Containing the Nitro Group Ethyl alcohol n-Amyl alcohol Benzaldehyde Acetone Benzoic acid Benzoin Aenavl
Benzidine Dimethylaniline Benzaldehyde-phenylhydrazone Glucosazone Acetamide
Procedure Two solutions are required. 1. IRON SOLUTION. A 500-ml. portion of distilled water is boiled for 15 minutes to remove any dissolved air. After cooling, 25 grams of ferrous ammonium sulfate and 2 ml. of concentrated
sulfuric acid are added. An iron nail may be added to retard oxidation by the air. 2. BASE SOLUTION. 30 grams of stick potassium hydroxide are dissolved in 30 ml. of distilled water and then added to 200 ml. of 95 per cent ethyl alcohol. A 0.7-ml. ortion of the iron solution is pi etted into a 4-ml. test tube, anXa small quantity (10 mg.) of the inely powdered un-
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Light green Light green Light green Light green Light green Dark green Dark green Gray green Light green Light green Yellow green Light green
Ethyl nitrite Ethyl nitrate 1,4-Naphthoquinone Benzoquinone
Brown Brown Dark brown Brown
Benzoyl peroxide
Light green
o-Nitr oso-m-cresol Tetrachloroquinone
Brown Brown
Anthraquinone Dimethyl sulfate Resorcinol Diphenyl sulfone Sodium benzene sulfonate Triphenyl phosphate
Red solution Light green Light green Light green Light green Light green
Hydroxylamine hydrochloride
Brown
Benzophenone
Light green
Min. 5
5 5
5 5 5 5 5 5 5 5 5 See. 5 30 30 5
Mzn. 5 See. 3
7 Mzn. 5
5 5
5 5 5
Sec. 2
Min. 5
JULY..lS, 1937
ANALYTICAL EDITION
tested. Seventy-five compounds not containing the nitro group were tested and were all found to be negative with the exceptions noted above. The test as outlined, when used in correlation with other accepted tests, will be a decided aid in the detection of the nitro group in organic compounds.
Literature Cited (1) Baeyer and Bloem, Ber., 15, 2147 (1882). (2) Bamberger and Demuth, Ibid.. 34. 1330 (1901). (3) Bitto. Ann.. 269. 377 (1892). (4j Bose,’AnaZyst, 56, 504 (1931). (5) Bast and Nicholson, IND.ENG.CHEM., Anal. E d . , 7, 190 (1935). (6) Claison and Thompson, Ber., 12, 1946 (1879). (7) Gabriel, Ibid., 15, 2294 (1882). (8) Jacobs and Heidelberger, J. Am. Chem. Soc., 39, 1435 (1917).
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(9) Janovsky, Ber., 24, 971 (1891). (10) Kamm, Oliver, “Qualitative Organic Analysis,” p. 161, S e w York, John Wiley & Sons, 1932. (11) Konowalow, Ber., 28, 1850 (1895). (12) Mulliken, S. P . , “Method for Identification of Pure Organic Compounds,” Val. 2, p. 32, New York, John Wiley & Sons, 1916. (13) Mulliken and Barker, Am. Chem. S., 21, 271 (1899). Olivier, Rec. trav. chim., 37, 241-4 (1918). Reitaenstein and Stamm, S. prakt. Chem., 81, 167 (1910). Rosenthaler, L., “Der Nachweis organischer Verbindungen,” p. 68, Stuttgart, Verlag von Ferdinand Enke, 1923. (17) Rudolph, Z . anal. Chem., 60, 239 (1921). (18) Vortmann, “Anleitung zur chemisches Analyse organisehea Stoff e,” (19) Walter, Z. Farbenind., 10, 49 (1911). RECEIVED April 19, 1937
An Improved Reaction Microapparatus D. S. BINNINGTON Grain Research Laboratory, Board of Grain Commissioners for Canada, Winnipeg, Canada
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tion. The main a b s o r b e r is charged with 3 cc. of 10 per cent p o t a s s i u m iodide solution containing 3 to 4 drops of 0.6 per cent s t a r c h s o l u t i o n prepared according to the method of Nichols ( 1 ) and the secondary absorbing trap with 1 cc. of the above potassium iodide solution. Air is then aspirated through the system at a rate of approximately o n e b u b b l e per second, for 5 hours. At the end of this period the absorption unit is d i s c o n n e c t e d , t h e upper stopper is loosened, and the contents of the trap are blown into the main absorber which is then washed with two successive 1-cc. portions of the 10 per cent potassium iodide solution. Titration is carried out in the main absorber with 0.001 N sodium thiosulfate.
UMEROUS micromethods
involve t h e e v o l u t i o n and quantitative a b s o r p t i o n of v a r i o u s gases and vapors. The usual setup for this type of analysis is frequently cumbersome and inefficient because of the use of rubber stoppers and connections. The all-glass apparatus described here obviates these difficulties, is very comp a c t , a n d titrations may be carried out directly in the apparatus. It was originally designed for the microdetermination of bromine by evolution and absorption in potassium iodide solution, b u t m a y b e employed without modification for a wide range of analyses. D e t a i 1s of construction are shown in Figure 1, Pyrex glass a n d s t a n d a r d t a p e r ground joints being used throughout. The use of the apparatus is illustrated by the technic employed in carrying out bromine determinations by a modification of the Yates (2) method developed in this laboratory, The sample, equivalent to not more than 500 gamma of bromine, is transferred to the reaction flask with 7 cc. of water, and 2.5 cc. of concentrated sulfuric acid are added through the tap funnel over a period of 10 minutes, cooling the flask in ice water during this addition. This is followed by 4 cc. of chromic acid solution (20 grams of CrOs, 40 cc. of concentrated sulfuric acid, and 120 CC. of water). The inlet to the tap funnel is then connected to a wash bottle containing 20 per cent potassium hydroxide solu-
Prior to the development of this reaction vessel, the perc e n t a g e recovery of bromine was in the order of 95 to 96 per cent, while with its use the recovery ranges between 98 and 100 per cent with greatly reduced variability between replicates.
Literature Cited (1) Nichols, M. S.,I N D .E N G . C H E M . Anal. , Ed., 1, 215 (1929). (2) Ya’tes, E. D . , Biochem. J., 27, 1762 (1933).
SCALE
- Cm.
FIGURE 1. DIAGRAM OF APPARATUS
RECEIVEDApril 14, 1937. Contribution from the Grain Research Laboratory, Board of Grain Commissioners, Winnipeg, Manitoba, with financial assistance from the National Research Council of Canada. Published as paper No. 119 of the Associate Committee on Grain Research, National Research Council of Canada and Dominion D e partment of Agriculture.
