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Vol. 18, No. 3
Detection of Methanol in Alcoholic Beverages’ By F. R. Georgia and Rita Morales CORNBLLUNIVERSITY, ITHACA, N. Y.
Chapin’s modification of the DenigZs method, although superior to the other methods that are now available for the detection of methanol in alcoholic beverages, yields results which cannot always be accepted as proof of the presence of methanol. A negative reaction, in which no precipitate formed upon oxidation with potassium permanganate owing to the formation of condensation products of the aldehydes formed with phenol radicals and which are not dissolved by the oxalic acid, will always be a true indication of the absence of methanol. However, a positive test may be obtained in the absence of methanol.
Procedures for the removal of most of the interfering materials are outlined. In some cases no satisfactory method has been found. The reaction of substances not removed may be due either to the oxidation of a methyl group or to the oxidation of methanol obtained from the decomposition of pectinous material. This decomposition may be brought about in the ripening of fruit or through the application of heat in the manufacture of brandy. Any sensitive method t h a t depends upon the identification of formaldehyde for the detection of methanol will yield a positive reaction in the presence of these substances.
.NY methods have been proposed and so much has written about the detection of methanol in alcoholic beverages that one is at a loss to know which procedures may be used with reliance. It seemed desirable, therefore, to review the methods and determine if a t least one of them might not be used or so modified as to be reliable. Such a review was made by Gettler2 in 1920, but some important work has appeared since that time and furthermore the procedure proposed by him is open to serious criticism. Ris classification of methods and his bibliography are of considerable use, however. Requirements of Method
Methods in the second group are either unreliable or else require too much time and manipulation. For a summary of these methods reference should be had to the article by Gettler.2 The methods included in the third group have received the most attention and deserve the greater consideration. These methods may be further subdivided according to the methods of oxidation employed as well as the tests applied to the oxidation products. A few tests have been proposed which depend upon oxidation of the alcohols to the corresponding acids, and even to carbon dioxide and water, but they are not very satisfactory. All the other tests attempt to oxidize the alcohols to the aldehydes and then detect the formaldehyde derived from any methanol present. The oxidizing agents most commonly employed are a red-hot oxidized copper spiral, potassium dichromate and sulfuric acid, and potassium permanganate either in alkaline or acid solution. The copper spiral method of oxidation results in the forma-’ tion of appreciable amounts of formaldehyde from ethyl alcohol and thus leads to confusion in the results obtained. Potassium dichromate with sulfuric acid is no better. Repeated trials with this reagent always resulted in positive reactions from ethyl alcohol alone. Gettler uses this method of oxidation, but distils the oxidized solution and discards the first fraction for the purpose of getting rid of most of the acetaldehyde formed from the ethyl alcohol. Some formaldehyde will be lost in this discarded distillate and this may compensate for that formed from ethyl alcohol. Such a method of compensation is, however, rather uncertain and undesirable. The same sort of practice has been employed with the copper spiral method. In addition, Chapin4 states that “bichromate and acid, in comparison yith permanganate and acid, appears to afford a high yield of acetaldehyde from ethyl alcohol but a low yield of formaldehyde from methanol.” He also notes that persulfates may produce notable quantities of formaldehyde from pure ethyl alcohol. Chapin studied the oxidation of the alcohols with permanganate in the presence of both sulfuric and phosphoric acids, and concluded that with phosphoric acid a better yield of formaldehyde was obtained from methanol. Using the procedure proposed by Chapin the writers have never gotten any interference from ethyl alcohol and have always obtained positive reactions with small amounts
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I n order to narrow the field somewhat, methods that did not meet the following requirements in a reasonable manner were eliminated: 1-A positive reaction should be obtained for methanol in the presence of ethyl alcohol or of products formed from it during the course of the test. 2-A false positive reaction should not be obtained from ethyl alcohol or products formed from it during the test. 3-The procedure should be simple and not require expert manipulation in order t o obtain reliable results. 4-The time required for the test should be short. 5-The method should be reasonably sensitive.
Development of Method With these criteria in mind we may proceed to a consideration of the methods listed by Gettler and such as have a p peared since the time of his article. We may classify these methods under three groups, as follows: 1-Methods depending on physical constants. 2-Methods involving chemical reactions other than oxidation. 3-Methods involving oxidation of the alcohols and subsequent detection of a n oxidation product.
The only test in the first group worthy of consideration is that of Leach and L y t h g ~ e which ,~ makes use of the similarity of specific gravities and differences in refractive indices of methanol and ethyl alcohol. This is a satisfactory method if the beverage contains 5 per cent or more of methanol, but it cannot be relied on for small amounts. 1 Presented before the Division of Water, Sewage, and Sanitation a t Ithe 69th Meeting of the American Chemical Society, Baltimore, Md., April i6 to 10, 1925. Received October 28, 1925. 2 J . Bid. Chcm., a, 311 (1920). I J . Am. Chem. S O L ,17, 964 (1905).
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March, 1926
of methanol. This method of oxidation therefore appears to be the most satisfactory one available. The next problem was the choice of a reliable reagent for testing for formaldehyde in the presence of acetaldehyde. Such a reagent should admit of easy preparation and be stable as well as sensitive. Reagents that produce precipitates with formaldehyde were discarded in favor of those producing color reactions, since the latter were believed to be more sensitive. Tests depending on the use of alkaloids were also discarded b e cause of the difficulty in obtaining reagents such as morphine or codeine. Of the remaining reagents that have not been noted as being unreliable a reduced fuchsin (Schiff reagent) seemed to be best suited to the purpose. DenigW first, proposed a procedure using this reagent in which interference from acetaldehyde is eliminated. His method of oxidation is, however, inferior to that proposed by Chapin and the reagent that he used is quite unstable. Many modifications of the reagent have been used, but that employed by Elvove6 and later used by Chapin seems to be satisfactory. I n this laboratory the writers have prepared their reagent according to Elvove’s procedure except that they substituted rosaniline hydrochloride for fuchsin. This reagent has been kept in small amber bottles that were nearly full for over two years without serious loss of sensitivity. Procedure
The procedure was essentially that outlined by Chapin for qualitative work. The method was made somewhat simpler by combining certain of the reagents and was as follows: Five cubic centimeters of the alcohol solution previously diluted t o 5 per cent by volume total alcohol were oxidized for 10 minutes with 2 cc. of a solution containing 3 grams of potassium permanganate and 15 cc. of 85 per cent phosphoric acid per 100 cc. The excess potassium permanganate was then destroyed by the addition of 2 cc. of a solution containing 5 grams of oxalic acid dissolved in 100 cc. of 1:l sulfuric acid. As soon as the potassium permanganate was decolorized 5 cc. of the modified Schiff reagent were added, the solution mixed and the tube observed for the development of the characteristic color produced by formaldehyde after standing 10 minutes. The reagent was prepared by dissolving 0.2 gram of Kahlbaum’s rosaniline hydrochloride in 120 cc. of hot water, allowing this to cool and then adding 2 grams of anhydrous sodium sulfite dissolved in 20 cc. of water, followed by 2 cc. concentrated hydrochloric acid. The solution was diluted to 200 cc. and stored in well-filled glassstoppered amber bottles.
Blanks were always run on pure ethyl alcohol and on ethyl alcohol containing a small amount of methanol as checks on the procedure. The investigation had to do, then, with the substances that might cause interference and their elimination. D e t e r m i n a t i o n of I n t e r f e r i n g Substances
According to Chapin, other workers have listed carbohydrates, glycerol, formic and acetic acids, formaldehyde, terpenes, phenol, fusel oil, and acetone as causing interference. Chapin himself found no interference with acetic and formic acids, amyl alcohol, and acetone in solutions of 10 per cent strength using the above procedure. Gettler also notes that ciders may give reactions for formaldehyde when oxidized before distillation, but says that such interference was eliminated if distilled before oxidation. The writers have attempted to study the action of such materials as might be normally present in all sorts of alcoholic beverages or which are used in the denaturing of industrial alcohol with the exception of some materials that would be removed by ordinary distillation. ‘:Compt. rend., 150, 823 (1910). ‘ , T ~ I sJOURNAL, 9, 205 (1917).
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The substances studied and the results obtained are given in the accompanying tables. For this purpose 2 per cent solutions of the materials in 5 per cent,ethyl alcohol by volume were used. Five-cubic centimeter portions of these solutions were acidified with 1 cc. concentrated sulfuric acid and tested with the modified Schiff reagent. They were also tested after oxidation as outlined above. S u b s t a n c e s G i v i n g No R e a c t i o n E i t h e r b e f o r e or a f t e r O x i d a t i o n Acetone Formic acid Oil of sweet birch Ammonium iodide Fluid extract of quassia Oil of wintergreen Amyl alcohol Furfural o-Nitrotoluene Potassium iodide Benzene Glucose Propyl alcohol Benzoic acid Kerosene Pyridine Brucine Malic acid Salicylic acid Butyl alcohol Menthol Shellac Camphor Nicotine Sodium salicylate Chloroform Nitrobenzene Citric acid Oil of almond Spanish saffron Sucrose Dextrose Oil of cinnamon ~-.. .. Diethylphthalate (Caosia) Tetrachloroethane Enanthic ether Oil of cinnamon (Cey- Thymol Erythrosine lon) Zinc chloride Ethyl acetate Oil of cloves Eucalyptol Oil of spearmint ~
Formaldehyde was the only substance tested to give a positive reaction with Schiff reagent in the presence of sulfuric acid without oxidation. Although the acetaldehyde formed during the oxidation of a 5 per cent ethyl alcohol never causes any interference, a color reaction was obtained in a solution of acetaldehyde of 2 per cent concentration. This color could not be called a positive test, for the reddish purple color develops immediately upon the addition of the Schiff reagent, increases to a maximum, and then gradually fades. At the end of 10 minutes this decrease in color is quite noticeable. S u b s t a n c e s G i v i n g Positive R e a c t i o n s after O x i d a t i o n Oil of nutmeg -Acetaldehyde Oil of calamus Oil of capsicum Oil of orange (bitter) Benzaldehyde Oil of citronella Oil of orange (sweet) Cinchonine Oil of pine Fluid extract of arnica Oil of coriander Oil of rosemary Fluid extract of ipecac Oil of curaCao Oil of fennel Oil of sage Formaldehyde Oil of safrol Glycerol Oil of ginger Licorice Oil of peppermint Oil of sassafras (artificial) Methyl acetate Oil of hyssop Oil of sassafras (true) Oil of angelica Oil of juniper Oil of sweet flag Oil of thyme Oil of anise seed (Rus- Oil of lavender Oil of lemon Oil of turpentine sian) Oil of wormwood Oil of balm mint Oil of mace Quinine sulfate Oil of bay Oil of marjoram Oil of bergamot Oil of mustard Strychnine sulfate
The following gave precipitates when oxidized either in the presence of ethyl alcohol or methanol, owing to condensation with the aldehydes formed. Unless such materials are removed they will prevent the detection of methanol. PREXIPITATB Aniline Methyl violet Phenol Resorcinol Tannic acid
Green Blue Brown Orange Yellow
L
Different samples of the same oils gave different intensities of color. This may be due either to the age of the samples or to differences in the composition of the oil. However, the concentrations used were far greater than would be found in liquors, cordials, or gins, and interferences from such materials would not as a rule be important from a practical standpoint. Synthetic preparations of these beverages in general failed to cause any interference. The procedure was further tested by applying it to grape juice, “near” beer, cider, and vinegar, both with and without the addition of alcohol. Grape juice and cider were further tested both before and after fermentation. Negative results were obtained except with the apple products. With apple products positive reactions were obtained even on the freshly expressed juice. ,411 samples were distilled before tests were made.
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-4few samples of authentic pre-var wines were also examined. Some gave positive and some negative results. Brandies made from these wines might be expected to react in the same manner. Positive reactions were obtained from commercial pectins. Since these pectins contain methyl groups, it is quite possible that they are split off and oxidized to formaldehyde, thus accounting for the reactions obtained on apple products snd some but not all grape products. The writers have not been able to remove such materials either by distillation or extraction. From the foregoing tables it can be seen that the work of the writers agrees with that of Chapin on the reaction of acetone, amyl alcohol, and formic acid. However, the writers failed to experience any interference from carbohydrates. Removal of Interfering Substances
Having determined that interference with the method occurred under certain conditions or when certain substances were known to be present, the next problem was to eliminate such interferences. Formaldehyde. The following methods have been proposed for the removal of formaldehyde in the presence of methanol:
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in 10 minutes. Although resorcinol and phloroglucinol may be used to remove formaldehyde, pyrogallol has the advantage of producing a color change if the aldehyde has not been completely removed. That is, if sufficient pyrogallol has been added to remove the formaldehyde, a white flocculent precipitate will form upon the addition of the acid provided sufficient formaldehyde is present, the solution remaining colorless or assuming a slight green color. However, if an excess of formaldehyde is present, a white precipitate will form and the solution assumes a bright red color, indicating that more reagent must be added to remove the formaldehyde before distillation. The green color has been reported by Buraczevski and Matejko" to be produced when formaldehyde is added to a mixture of concentrated sulfuric acid and alcohol, and this coloration is increased by heat. One gram of pyrogallol will remove approximately 0.2 gram of formaldehyde. The procedure may be outlined as follows : One gram of pyrogallol is dissolved in 10 cc. of water, 10 cc. of the unknown, which has been diluted t o 5 per cent alcohol by volume, is added and followed by 5 cc. of concentrated sulfuric acid. The flask is tightly stoppered, the solution mixed and allowed t o stand for 10 minutes. The heat developed upon the addition of the acid is great enough t o cause the reaction t o proceed. Ten cubic centimeters are distilled and 5 cc. used for the test for methanol.
(1) Refluxing for at least 2 hours with aniline and phosA m y l alcohol, essential oils (except oil of angelica), $uid phoric acid.7 extracts of arnica and of ipecac. These substances are re( 2 ) Refluxing for 4 hours with ammoniacal silver nitrate.8 (3) Allowing the solution t o stand in t h e presence of silver moved by a modsed method of Thorpe and Holmes.18 nitrate and sodium hydroxide for 2 h0urs.O To 10 cc. of the distillate which has been diluted t o contain (4) Heating in a water bath (70" t o 80' C.) for 2 hours in a 5 per cent alcohol hy volume, 40 cc. of water and 14 grams of glass-stoppered bottle with resorcinol and concentrated sulfuric sodium chloride are added. The mixture is shaken with 25 cc. acid.1° of petroleum ether in a separatory funnel for 5 minutes, or until ( 5 ) Simple distillation with an excess of potassium cyanide." the alcohol-water layer becomes clear, when the lower layer is (6) Allowing the solution t o stand for 1.5 t o 2 hours at 30' drawn off into a round-bottom flask. The ether is washed with t o 40" C . in t h e presence of sodium sulfoanilate.l* two 10-cc. portions of saturated salt solution, which is added to (7) Formation of urotropine by digesting with a n excess of the main solution. The salt solution is distilled and the first ammonia in a glass-stoppered bottle in a heated water bath 10 cc., containing the alcohol, is used in making the test for (70' to 80' C.) for 4 t o 5 hours.ls methanol. At times it becomes necessary t o resort t o a second (8) Treating in the cold with a n excess of sodium bisu1fite.l' ether extraction. (9) Treating in the cold with a n excess of sodium ~u1fite.l~ (10) Digesting with hydrazine sulfate.l6 While the intensity of the color due to oil of angelica may
I n each of these methods it is necessary to test for the com- be reduced by extracting in this manner, complete removal plete removal of the formaldehyde before testing for methanol. was not secured, owing to the greater solubility of some of the Methods 1, 2, 3, 4, 7, 8, and 9 were tested; Method 6 was interfering material in the dilute alcohol solution than in omitted since the time required by the method was equal to ether. Cinchonine, glycerol, licorice, methyl violet, quinine sulthat of several others already tested, and Method 5 because fate, resorcinol, strychnine sulfate, and tannic acid. By disof the toxicity of the hydrocyanic acid given off. Method 1 removed the formaldehyde in 2.5 hours, but was also found tillation. Aniline. Distillation from a sulfuric acid solution. to remove small amounts of methanol. Method 4 gave Phenols. Distillation from sodium hydroxide solution. satisfactory results, but, as in the case of aniline and phosAcetaldehyde, benzaldehyde. Addition of sulfuric acid bephoric acid, the time required for the removal of the formaldefore the addition of Schiff-Elvove reagent. hyde was long. Interfering substances not removed. Methyl acetate, oil of Since the larger the number of hydroxyl groups the greater angelica, and pectinous material. the reactivity of the phenols, pyrogallol, a trihydroxy1 phenol, was substituted for resorcinol. It was found that if the 17 J . Chcm. SOL.(London), 108, 654 (1915). 18 I b i d . , 83, 314 (1903). amount of sulfuric acid was increased and pyrogallol employed formaldehyde could be removed without any loss of alcohol Allen and Chattaway, Analyst, 16, 102 (1891). Orchard, Ibid., 22, 4 (1897). 9 Vanino, I b i d . , 27, 93 (1902). 10 Mulliken and Scudder, A m . Chcm. J . , 34, 444 (1900). 11 Leffman, Chcm. Ztg., 39, 1086 (1905); J . Chcm. SOC.(London), 88, 7
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864 (1905). 1 2 Gnehm and Kaufler, 2. ongcw. Chcm., 17, 673 (1904); J . Chcm. SOL. (London), 86, 520 (1904). laLeglu, Be?., 16, 1333 (1883); J . Chcm. SOL. (London), 44, 1035 (1883). 14 Banberger, 2. angcw. Chcm., 17, 1246 (1904); J . Chcm. SOC.(London), 86, 786 (1904). n Lernme, Chcm. Ztg., 37, 896 (1903); J. Chcm. SOC.(London), 84, 768 (1903). 18 Pfap, Chcm. Ztg., 36, 701 (1902).
Production of Rubber on American Soil Experiments made by the Intercontinental Rubber Company in growing rlbber in t h e Southwest and West indicate t h a t ultimately the product may be raised within the United States in quantities great enough t o supply a large measure of domestic needs. This company is engaged in growing rubber in an experimental way in twenty localities in the western and southwestern states, and already has expended $1,000,000 in this work of experimentation. G. H. Carnahan, president of the company, stated t h a t the work is about t o be changed from an experimental t o a commercial phase, and t h a t he is convinced rubber can be produced on American soil a t costs that will enable i t t o be sold "under normal prices for competitive rubbers."
