original weak formic acid. These are formamide types, which result when numerous primary and secondary amines are distilled with aqueous formic acids. Thus, Tobias (4) proved that various aromatic amines react with formic acid to produce these types. I n particular, Kallach and Wusten (6) showed that formanilide can easily be prepared in quantitative yield by the simple distillation of equiyalent parts of aniline and an aqueous formic acid. They found that this distillation removed the water in the aqueous acid and also that lost from the aniline formate in anilide formation, and left the formanilide as a residual oil of high boiling point, Because of the ready availability and relative cheapness of aniline, it n a s decided to choose formanilide among the various possible formamide types for study in its applicability to the problem on hand. Any of these formamide types, however, will undergo extensive hydrolysis only if a strong base or mineral acid is also present in the system (2, 3 ) . T h e addition of formanilide to an aqueous formic acid is not enough. Hydrolysis of the formanilide must be induced by the subsequent addition of a strong mineral acid. 66" B6. sulfuric acid was found to be satisfactory for use in the present system.
High-Concentration Formic Acid A Method for Its Production from Aqueous Acids FRANK 0. RITTER Washington Square College, New York University,
New York, N. Y.
General Process Formanilide is made by refluxing and then distilling a n equimolecular mixture of the original aqueous formic acid and aniline. To the cooled, weighed sample of formanilide, more of the original aqueous acid is added and an amount of 66 O BB. sulfuric equivalent to the formanilide is then introduced. The amount of aqueous formic acid added to the formanilide is carefully regulated, however, so that the sum of the water in this acid and that in the equivalent of 66" BB. sulfuric acid is a t most just sufficient to take care of the hydrolysis of the weighed sample of formanilide. On standing, the clear mixture becomes semi-solid, because of the separation of aniline sulfate crystals which are bathed by the fortified acid. The following reaction has taken place:
Formic acid (99 to 100 per cent) can readily be prepared in good yields from aqueous acids by the addition of formanilide or analogous compounds in such quantity that the water in the aqueous acid is completely consumed in hydrolyzing the formanilide to yield more formic acid. Hydrolysis is induced by the addition of the equivalent of 66' BG. sulfuric acid. Formanilide itself can readily be made from an aqueous acid by a simple distillation of aniline and the acid. The aniline sulfate by-product can be reconverted to aniline and thrown back into the process.
T
HE problem of removing the residual water from aqueous formic acid is difficult because of the ease with which the formic acid molecule breaks down to produce carbon monoxide and mater. All methods so far proposed strive to solve it by accomplishing a n actual separation of water and acid. With this end in view, various mild dehydrating agents, such as anhydrous magnesium sulfate, copper sulfate, or oxalic acid, have been added to the weaker acid in order to cause the water to combine with these agents and to leave a strong acid as a residue (6). There is another approach to the problem which has not received consideration. If we could add to the weaker acid a substance which would react with the water by a hydrolytic reaction t o produce more formic acid, then we should again produce a stronger acid but by a method whose basic idea is quite different from those already proposed. The water in the original weaker acid would be transformed to a n equivalent of formic acid, and such a process might appropriately be called one of fortification of the original acid. The present investigation has shown that this idea is easily realized. Substances which produce formic acid on hydrolysis, and which are a t the same time suitable for the present use, are well known. They can also be readily prepared from the
The fortified acid is removed from the aniline sulfate by distillation, and the latter is treated with milk of lime to recover the aniline for the next run. The aniline sulfate residue is always transformed to aniline and then used again for the next run; aniline recovered averages 95 per cent. Both the sulfuric and formic acids should be carefully titrated before use; either excess water or sulfuric acid leaves residual Fvater in the fortified acid. If the formanilide stands overnight, it sets to a solid mass of crystals, thus rendering solution in formic acid more troublesome.
Detailed Description of a Run A 97.5-gram portion of aniline saturated with water at 25" C. and containing, therefore, 4.98 per cent water ( 1 ) (obtained after a steam distillation of aniline) was treated with 54.0 grams of 85.3 per cent formic acid. The mixture was refluxed for 30 minutes and then distilled over an open flame. During distillation a slow stream of air was drawn over the mixture t o assist in the removal of water vapor. After 30 to 45 minutes the temperature within the liquid had mounted to 160" C., and ebullition had ceased. The mixture was then allowed t o cool t o 100' C. with the air current still floB-ing. The formanilide residue 15-as a light brown viscous liquid weighing 113.2 grams. A 71.5-gram portion of 85.3 per cent formic acid was added to the warm formanilide and the whole was gently agitated. The resulting homogeneous mixture was cooled to 15" C., and a total of 98.0 grams of 93.6 per cent sulfuric acid was added in several small portions, shaking and cooling after each addition to keep the temperature between 15" and 20' C. The clear liquid was then allowed to stand for 15 hours at room tempera1224
OCTOBER, 1933
ISDUSTRIAL A S D ENGINEERISG CHEMISTRY
ture. By this time the reaction mixture had set to a semi-solid mass of aniline sulfate and the fortified acid. The mixture was then distilled by sinking the flask in water at 70” C. while maintaining a vacuum of 60 to 65 mm. in the system. The receiver consisted of two flasks in series, each surrounded by chipped ice. In this way 95 grams of a colorless liquid was obtained. 9 test for the presence of sulfuric acid by means of barium chloride solution was negative. Titration of a weighed sample with standard sodium hydroxide solution proved it to contain 99.1 per cent formic acid (melting point, 6.0” C.). Recovery was approximately 90 per cent calculated on the total amount of formic acid introduced into the system. The water flowing from the aspirator in the final distillation was slight’ly acid to litmus; therefore, the recovery would have been higher if all traces of acid could be condensed. .1 small amount of oil (approximately 3 grams) came over when the aniline-formic acid mixture was dist,illed to produce formanilide. It could not be crystallized and probably con-
1225
sisted of a mixture of aniline and formanilide. I t was saved and thrown in with the aniline sulfate when the latter was converted to aniline.
Literature Cited -Uexejeff, IT., Ber., 10, 708 (1877). Gasiorowski, K., a n d Merz, T’., I h i d . , 18, 1001 (1885). Gerhardt, Ann., 60, 311 (1846). Tobias, G., Ber., 15, 2443 (1882). Lllmann, “EnzyklopRdie der technischen Chemie,” 2nd ed., T’ol. I, pp. 342-3, Berlin a n d Vienna, Urban & Schwartzenberg (1928). (6) Wallach, O., a n d W‘iisten, M., Ber., 16, 145 (1883).
(1) (2) (3) (4) (5)
RECEIVED March 20, 1933. Presented before the Division of Industrial and Engineering Chemistry at the 89th Meeting of the American Chemical Society, New York. N. Y., April 22 t o 26, 1933.
Seeking a Working Language for Odors and Flavors E. C. CROCKER Arthur D. Little, Inc., Cambridge, Mass.
A
IXSTRUJIEST that can detect a millionth of a milligram, and in some cases less than a billionth of a milligram, of the vapor of hundreds of kinds of organic substances should inspire our admiration. That instrument, with its spectroscopic sensitivity and great convenience of operation, is the human nose. Difficulties of experimentation have tended t o make investigators avoid working on smell and smelling, so that today entirely too little is known concerning them. There should be both commercial and scientific value in a better understanding of the nature of odor and of the mechanism of smelling, as well as in an adequate, logically founded language for odor description. It does not take much argument to convince an organic chemist that his sense of smell is of great value in his work. But very few chemists, without a careful appraisal of the matter, give this lowly and despised sense even a portion of its proper credit. By its means, for example, leakages, toxic vapors, or fires may usually be discovered in time for action leading to safety. A sniff of the vapor when the stopper is removed from a bottle gives assurance that the label is correct, K i t h a deeper and more searching type of smelling, supplemented by judicious tasting, the food chemist judges the quality and even the history of a questioned article of food. The perfume chemist goes still further in his nasal analysis, and to meet his approval a natural or synthetic material must either be very pure or skillfully disguised. During the past few years the public has become increasingly more odor-conscious and is gradually demanding a perfection in the odors of consumer goods comparable with the great improvements that have recently taken place in their physical qualities and appearance. Whatever commercial products cannot be made strictly odorless must a t least be made to smell pleasantly. Several perfume material houses are now specializing in producing odorizing or deodorizing S
compoqitions for a wide range of industrial and consumer products including rubber, linoleum, paints, inks, paper, and oils. “Sell-by-smell” is becoming a potent sales consideration. In spite of the importance of odor, industrially as well as esthetically, there is no competent, universally accepted method for its characterization. The odor descriptions given in chemical handbooks are pitifully inadequate. To find the odor of a chemical described as peculiar, nauseating, foul, characteristic, or pleasant, gives but a trace of the help reasonably expected. Such rough comparisons as spicy, tarry, anisic, musty, or aromatic a t least specify the class, even though much more information is usually desirable, especially where an odor may have the qualities of several such classes simultaneously, only one of which is mentioned. Among perfumers the situation is not so helpless, for a rigid nasal
The human nose is a detecting agent of extraordinary sensitivity, giving indications in some instances with less than a billionth of a milligram of material, in vapor form. It is very convenient to apply for analytical or comparative purposes, yet its actual usefulness is seriously limited by lack of an adequate language for expression and especially for record. Chemists are little helped by the customary textbook descriptions of odor as “peculiar,” “characteristic,” etc. This article summarizes what is now known about odor and the sense of smell, draws analogies from work on the other senses as to what may be expected of accomplishment, and makes a strong plea for more workers of various types to develop an adequate method of odor expression.
