practically colorless, but has a faipt pink tinge. The color with as little as 1 part in 1,000,000 of formaldehyde is easily distinguishable Table I gives the results with various proportions of formaldehyde. The above proportions of acid, water, and milk can be varied a little. Two cubic centimeters of concentrated sulfuric acid can be diluted with 1 cc. of water,and this diluted acid mixed with 1 cc. of the milk to be tested. These proportions will give a stronger purple with very little formaldehyde (1 part in 500,000 or less), but on the other hand the blank then shows a distinct though slight pink color. The faint pinkish color obtained in the blank in this method is probably due to a trace of formaldehyde formed from the carbohydrate of the milk by the action of the strong acid.
The second method is particularly well suited to the detection of formaldehyde in a distillate. Instead of diluting the concentrated sulfuric acid with pure water, dilute it with the distillate to be tested, and then mix with pure milk. All varieties of the Hehner test are spoiled by a large proportion of formaldehyde. This is not a defect of the Hehner test alone, for a number of other formaldehyde tests have the same flaw. However, when enough formaldehyde
Vol. 3, No. 2
is present to interfere seriously with the test, its odor can be distinguished. T a b l e I-Reactions ,FORMALDEHYDE I N
with B r o m i n e Oxidation a n d F o r m a l d e h y d e in Hehner Test BEFOREADDING BROMINE SOLN.
AFTERADDING BROMINE SOLN.
Pam None 1 in 1,000,000 1 in 500,000 1 in 100,000 1 in 50,000 1 in 10,000 1 in 1000 1 in 100
None None None None None Light greenish yellow Greenish yellow, some undissolved material Yellowish white, undissolved material
Whitish faint pink tinge Slight phrple-pink Light pink-purple Deep violet Strong deep violet Intense violet Becomes purplish pink undissolved matter bro&nish Becomes somewhat brown ish; test negative
Literature Cited (1) Assocn. Official Agr. Chem., Methods, p. 132 (1925). (2) Fulton, J . Assocn. Ofinal Agr. Chem., 12, 434 (1929). (3) Leach and Winton, “Food Inspection and Analysis,” p. 165, Wiley, 1920.
The Opium Alkaloids as Reagents for Formaldehyde’
Charles C. Fulton U. S. INDUSTRIAL ALCOHOL BUREAU, OMAHA, NEB. Y.,
Phenolic compounds (phenols and ethers of phenols) HE opium alkaloids, strength sulfuric acid, the rein general, a n d certain of t h e opium alkaloids in parparticularly morphine action is not very sensitive ticular, are useful as reagents for formaldehyde. The and a p o m o r p h i n e , to f o r m a l d e h y d e , and the tests are best made by mixing some of t h e aqueous have had considerable use in color with small amounts of solution t o be tested (preferably a distillate) with condetecting f o r m a l d e h y d e . the aldehyde is &t the brilcentrated sulfuric acid in appropriate proportion, and The r e a c t i o n is that of a liant crimson to:’purple obapplying this solution t o t h e alkaloid. A n oxidizing phenol with an aldehyde in tained with more formaldeagent is also added for t h e more sensitive tests. Morthe presence of strong acid, hyde or more dilute acid, but phine a n d apomorphine give good phenol-aldehyde is a dark blue that develops producing a color. tests. These tests are sensitive t o about 1 part formTests much more sensitive gradually. Hence the test aldehyde in 5000 t o 6000 parts of water. With the made by dissolving morphine both to the phenolic comaddition of t h e oxidizing agent apomorphine, codeine, pound and to the aldehyde in concentrated sulfuric acid pseudomorphine, a n d papaverine give t h e best tests. on a watch glass, and floating can be obtained by the addiThese reactions are n o t specific for formaldehyde, a s tion of an appropriate oxidizthis on the liquid to be exother aldehydes m a y give similar colors, b u t under t h e ing agent to the mixture (4). amined (1, 3) by way of exconditions a n d with t h e precautions given they provide posing the acid solution to the The alkaloids most suitable fairly certain identification, as well as detection of very vapor of formaldehyde, is not for such tests are apomorsmall quantities. They are sensitive t o as little as 1 a good one. It is better to phine, codeine, pseudomorpart formaldehyde in 500,000 or even 1,000,000 parts phine, and p a p a v e r i n e . p r o v e that the reaction is i f aqueous solition. (Phenolic tests in strong acid due to a volatile substance succeed with ethers of phenols by using a distillate from the as well as with true phenols.) The tests with the addition of suspected solution. Mix 1 cc. of the distillate with 2 to 5 an oxidizing agent can be so made as to be sensitive to 1 part cc. of concentrated sulfuric acid, while cooling; then apply to morphine on a spot plate. A purple-red to purple color of formaldehyde in 1,000,000 parts of aqueous solution. denotes formaldehyde. The color appears practically at; Phenol-Aldehyde Reactions once down to about 1 part of formaldehyde in 6000 of water. MORPHINE-The test with morphine is usually made by The test can be carried out as a zone reaction if desired. APOMORPHINE-The above remarks in regard to mordissolving the alkaloid in concentrated sulfuric acid and adding a drop or two of the solution to be tested. It is better phine apply in large part to apomorphine also. With the to dilute the sulfuric acid with the aqueous formaldehyde latter, the color in concentrated acid is purple, rapidly darksolution and then apply the mixture to the morphine, but the ening to blue-black and then changing to dark green; with texts do not state what proportion of acid and aqueous solu- only a little formaldehyde the color develops as dark green. tion should be used for such a test. There is a too-prevalent With acid of 75 to 85 per cent sulfuric acid, the purple to violet assumption that phenol-aldehyde reactions take place best color is better and more persistent. Gettler recommended in full-strength, concentrated sulfuric acid, but this assump- apomorphine over morphine. He mixed 5 cc. concentrated tion is often erroneous. The morphine reaction is best in sulfuric acid with 2 cc. of distillate from the suspected solusulfuric acid of 75 to 85 per cent sulfuric acid. With full- tion, then added the alkaloid (5). “Allen’s” misrepresents him as recommending apomorphine for Bonnet’s test (3). I Received January 21, 1931.
INDUSTRIAL A N D ENGINEERING CHEMISTRY
April 15, 1931
The simple phenol-aldehyde reaction is probably as well obtained with morphine as with apomorphine, but with the addition of an oxidizing agent, even in the merest trace, apomorphine gives a far more sensitive test. This phenomenon is often noticed when no oxidizing agent is intentionally added. In fact, it probably takes place to a slight extent under the action of the air. Moreover, the color developed is similar to that of the simple phenol-aldehyde reaction. This probably accounts for the recommendation of a number of different investigators that apomorphine rather than morphine be used in the phenol-aldehyde test for formaldehyde. Phenol-Aldehyde-Oxidant Reactions
Mix concentrated sulfuric acid, while cooling, with some of the suspected solution, or better with a distillate from the suspected solution, in a proportion suitable to the alkaloid used for the test. Also mix one of the two oxidizing solutions given below with concentrated sulfuric acid in the same proportion. Then add about 0.4 cc. of the acid solution believed to contain the aldehyde to a little of the alkaloid on the spot plate, and stir with a glass rod. The color of the simple phenol-aldehyde reaction will be noticed a t thispoint with apomorphine or codeine, if the formaldehyde exceeds about 1 part in 5000 of aqueous solution. Next add a single drop of the sulfuric acid solution of the oxidizing agent and stir it in. The color of the phenol-aldehyde-oxidant reaction then develops. The test is unmistakably sensitive to 1 part formaldehyde-in 500,000 of water with apomorphine, codeine, or pseudomorphine, and to 1 part in 100,000 with papaverine. The results are given in Tables I. 11,and 111. T a b l e I-Color R e a c t i o n s of A o o m o r o h i n e in T e s t for F o r m a l d e h v d e 2 cc. concd. HzSO4 with 1 cc. aqueous formaldehyde soh. Ferric oxidizing agent
FORMALDEHYDE BEFOREADDING I N AQUEOUS OXIDIZING SOLN. AGENT
Parts None 1 in 1,000,000 1 in 500,000 1 in 100,000
AFTERADDING OXIDIZING AGENT
None None or a very -light pink None’ or a very slight pink None: or a very slight pink
Light salmon Weak (dull) pink Quickly purplish pink Good purplish pink, gradually purplish red None, or a very slight pink Purpjish pink, soon purplish rea Faint yellowish; purplish if Purple changing to strong allowed t o stand deep purple-red Slight yellowish changing t o Strong violet, changing to strong purple, changing to light purple strong red-purple, then to deep purple-red; gradually dark red Light violet rapidly darken- Deep blue, changing t o strong 1% violet a t once; to strong red-purple soon: gradually dark red
1 in 50,000
1 in 10,000 1 in 1000
1 in 100
R e a c t i o n s of Codeine in T e s t for F o r m a l d e h y d e
2 CC. CONCD. H2S04 3 CC. CONCD. &So4 WITH 1 CC AQUEOUSFORMALDEHYDE SOLN. WITE 1 cc. AQUHOUS FORMALDEFERRIC OXIDIZING AGENT FORMALDEHYDE SOLN.
ous S O ~ N Before . add-
ing oxidizing agent
After adding oxidizing agent
1 in 500,000
Slight blue quickly becomes light blue
1 in 100,000 1 in 50,000 1 in 10,000
None None Practically none Soon purple
Good blue Good blue Blue
1 in 1000
1 in 100
After adding nitric acid oxidizing agent I
None Slight blue, become light blue
Color changed to lighter blue-green, gray-blue, then dark blue; gradually dark hrowan __. ... Color changed t o light green, light brownish gray, then violet-gray; gradually h 1 u e - b 1 a c k , gradually dark brown
T a b l e 111-Color Reactions of P s u e d o m o r p h i n e a n d Papaverine in Test for F o r m a l d e h y d e a f t e r Adding Oxidizing Solution I
- IN . .-
Light yellow Light blue-green, changing t o light ereen: rrraduallv ereenkilow . Q&kly light blue, changing gradually t o weak dull green Deep blue Strong deep blue Strong deep blue ~
Light gray, changing to weak gray-green, then to dull grayblue Color changed to light gray, then to brown
2 cc. concd. H B O t with 1 cc. 4 cc. concd. HzSO4 with 1 cc. aqueous formaldehyde s o h . aqueous formaldehyde soln. Ferric oxidizing agent Nitric acid oxidizing agent
1 in 1,000,000 Light green, slightly bluish
Greenish yellow, fading to slight yellowish Greenish yellow fading to slight yellowish Light green, gradually fading to yellowish Blue. eraduallv fadinc somewha? Blue
1 in 500,000
1 in 100,000
Greenish blue. soon becoming good blue-green Blue, slightly greenish changing to deep blue-green Blue, very slightly greenish, Intense deep blue changing to deep blue-green Blue, very sliahtly greenish, Intense deer, blue changing t i d e e p blue-green Blue, changing t o deep blue- Intense deep blue ereen
1 in 50,000
1 in 10,000
The tests with the addition of an oxidizing agent are carried out as follows:
1 in 1000 1 in 100
The two oxidizing solutions are as follows: ferric, a 10 per cent solution of ferric sulfate in water; nitric acid, 5 drops of concentrated nitric acid in 50 cc. water. These solutions are mixed with concentrated sulfuric acid in appropriate proportion before use. The tests are not specific for formaldehyde, as other aldehydes may give similar colors. However, if they are performed as described, using a distillate from the suspected solution, and two or three different alkaloids, the identification is fairly certain. APOMORPHINE AND CODEINE-codeine has been previously recommended for a test of this kind, but apparently the reaction was not understood (a). Both codeine and apomorphine give the simple phenolaldehyde reaction if the formaldehyde exceeds about 1 part in 5000 in the aqueous solution, and the test with the addition of the oxidizing agent is changed or even spoiled if this much formaldehyde is present. The color is best developed in acid as weak as can well be used, since the oxidizing agent by itself produces too much color in stronger acid. PSEUDOMORPHINE AND PAPAVERINE-The more formaldehyde present, the better the reactions with these two alkaloids succeed. Neither gives the simple phenol-aldehyde reaction in diluted sulfuric acid. With pseudomorphine, however, so little oxidizing action is required that a slight green almost invariably develops when the formaldehyde exceeds 1 part in 10,000, even though no oxidizing agent is intentionally added. With papaverine no color appears until the addition of the oxidizing agent. The pseudomorphine test gives the least proof that formaldehyde is present, as most aldehydes give either a blue or a green color with it, under appropriate conditions. The ferric oxidizing agent by itself gives a dull green color with pseudomorphine in concentrated acid, but not in the weakened acid used for the aldehyde test. Papaverine requires stronger acid and a stronger oxidizing action than is necessary with the other alkaloids, and the test is somewhat less sensitive. On the other hand, it gives the most nearly specific test for formaldehyde. Probably there are very few other aldehydes combining readily enough with papaverine to give the blue color under the conditions of this test. Literature Cited (1) “Allen’s Commercial Organic Analysis,” Vol. 1 , p. 327. Blakkton, 1923. (2) Aloy and Valdiguie, J. fibarm. chim., 4,390 (1926). (3) Bonnet, J . Am. Ckem. S O L ,27, 601 (1906). (4) Fulton. J. Assocn. O f i c d Agr. Chem., la, 434 (1929). (5) Gettler, J. Biol. Chem.. 4S, 311 (1920).