INDUSTRIAL AND ENGINEERING CHEMISTRY
1104
freezing of fuming sulfuric acid by the addition of nitric acid, the limits that should be observed. This graph is based on the use of 93 per cent nitric acid as the source of nitric acid, and of three strengths of fuming sulfuric acid, 104.5, 107, and 109 per cent, respectively. The nitric acid plotted along the base line denotes actual per cent of 100 per cent nitric acid present. Summary
Determinations have been made of the freezing points of a number of acid mixtures containing sulfuric and nitric acid in the region where considerable free sulfur trioxide is present, the acid strengths varying between 100 and 109 per cent, calculating the sulfur trioxide present as sulfuric acid. Little information has previously been available covering this range of compositions.
Vol. 23, No. 10
All the data available in the literature and from the present work have been collected and plotted on triangular coordinates, isothermal lines being used to connect points having the same temperatures. A graph on rectangular coordinates is included, plotting the melting points of mixed acids against the nitric content. It will be noted that the most desirable nitric contents for preventing freezing are 1 per cent on the 104.5 per cent curve, 4 per cent on the 107 per cent, and 6 per cent on the 109 per cent curve. Low points occur on all three curves a t 10 per cent nitric acid. Literature Cited (1) Carpenter and Lehrman, Trans. Am. I n s f . Chem. Eng., 17, 35 (1926) (2) Holmes, J. IND.ENG.CHEJI.,12, 781 (1920).
Modification of Hypnotic Action through Changes in Chemical Structure”z Horace A. Shonle LILLYRESEARCH LABORATORIES. ELI LILI.YAND COMPAh‘Y, IXDIAXAPOLIS,
T
HERE are a number of chemical compounds which, in a
given concentration, depress the central nervous system of animals to the extent that both the normal responsiveness and the automatic activity of the living system are temporarily decreased, or even abolished. The general action of all narcotics is similar. KO definite dividing line exists between hypnotic and anesthetic effect. Larger doses of some soporifics give complete anesthesia. It is not the purpose of this article to discuss the various theories proposed to explain the action of narcotics, nor their relative merits (1, 8). There is no doubt but that the dialkyl barbituric acids will contribute in no small measure to the solution of this problem when the final chapter is written. There are various sets of physical-chemical criteria which, in the light of present knowledge, seem essential in a substance having hypnotic action. It must be remembered, however, that not all compounds falling within this classification are hypnotics. Numerous relationships of chemical structure to physiological action have been proposed, but none have stood up under the tests of experience. Chemical structure seems to affect the activity by modifying the physical-chemical properties of the compounds, although specific groups may be responsible for certain side reactions. Such diversified series of aliphatic compounds as the following exhibit sedative properties: R-OH R-CHO
K-0-CO-NHz RR’-C-CO-NH
RR’-CO R-CH( 0R’)n
NH-CO RR-C----CGXH
R-CO-NHz R-NH-CO-NHz R-CO-NH-CO-NH2
CO-NH-CO RR’-C = (S02R”)2
~
I
I
1 Received July 1, 1931. Presented before the joint meeting of the Divisions of Biological, Medicinal, and Organic Chemistry at the 81st Meeting of the American Chemical Society, Indianapolis, Ind., March 30 t o April 3, 1931. 2 In this brief article, it is not possible to give credit to all the investigators whose work may be touched upon. Almost all the dialkyl barbituric acids, for which quantitative data are given, were tested in these laboratories in order that the pharmacological data would be strictly comparable.
IND.
In general, the effectiveness of this series increases with the complexity of the molecule. Since these structures have so little in common, the hypnotic action must depend on some property of the molecule as a whole and, more specifically, on its physical-chemical properties. The fact remains that hypnotic compounds almost invariably consist of lipo-soluble alkyl radicals attached to water-soluble groups, or polar groups, which are capable of forming associated molecules in aqueous solvents, and which may or may not possess similarity to shuctures occurring in the body. The only common chemical characteristic that can be ascribed to this varied group of compounds is a degree of chemical stability which prevents a too rapid destruction in the body before they exert their effect, yet permits a certain necessary degree of degradation, since compounds excreted unchanged exert little or no effect. None of these compounds have pronounced acid or basic properties. The most effective-the barbituric acids-lean toward the acid side. Thus the variations in the degree of alkalinity of the body fluids and of the cell itself must exert a more pronounced influence on this series of hypnotics than in others which lack this pseudo acid structure. Hypnotic Effect of Different Amounts of Compounds
Since degrees of sleep cannot be measured very satisfactorily in laboratory animals, the amount of the compound necessary to cause the disappearance of certain reflexes is usually used as a measure of relative hypnotic value. This value is then compared to the amount necessary to cause death. Although it may be argued that this quantitative relationship may not be a true measure of hypnotic effect, it affords a most useful, as well as the only, means of studying the effects of chemical changes in these molecules. Because the ratio of the lethal dose to the narcotic dose is larger in cold-blooded animals, warm-blooded animals must be used, if the therapeutic value of the compound is the goal. A study of the alcohols might be expected t o give relationships of the hypnotic action of the alkyl groups which might be used to advantage in preparing other series of hypnotics containing these groups. Richardson (16),over half a century ago, noted that, as the alcohols increase in molecular weight,
INDUSTRIAL AND ENGINEERING CHEMISTRY
October, 1931
their action becomes more intense and prolonged. The effectiveness of the straight-chain alcohols increases approximately in the molar ratio of 1:3:32,etc. The work of Munch and Schwartze (19) on rabbits shows that the secondary alcohols are less narcotic than the normal primary, but more narcotic than the isoprimary or the tertiary. As the molecular weight increases the narcotic properties of tlie alcohols increase more rapidly than the toxic properties; that is, the larger molecules are safer hypnotics. The secondary alcohols show the greatest ranges between their narcotic and toxic doses. The introduction of bromine or chlorine into the alcohol increases the effect, provided three halogens are attached to one carbon atom as, for example, tribromoethylalcohol. Iodine and fluorine are of no value in augmenting the hypnotic effect of alkyl groups. In the alkyl or acyl ureas, the acid amides, and the urethans, the effectiveness likewise increases with increase in molecular weight, but the tertiary radical is more effective than either the secondary or primary. As the molecular weight increases, the physiological response increases, reaches a maximum, and then decreases, so that compounds of high molecular m-eight are inert. The relative effectiveness of some of the previously mentioned compounds can be seen in the study of the derivatkes related to phenylethylbarbituric acid given in Table I. The formation of a ring structure increases the effectiveness in this series. Table I-Relative Effectiveness of Certain Compoundsa (Milligrams given rat subcutaneously per kg. of weight1 MIN. LETH.4L DOSE MIN. *MAX. MIN. hlrx. EFFECTIVE TOLERATED LETHAL EFFECTIVE DOSE CouPocnu DOSE DOSE DOSE CsHo COzH ‘C
/’\
CYHr
H
CsH,
COtH
C ‘’
hH,
CiHf CsHs
800
900
1.00
Noneffective
Nontoxic
...
,.
300
300
400
1.33
600
600
700
1.16
165
190
200
1.21
175
220
240
1.3
CONHI
‘,. c
CIH!
900
H‘
C ~ H L CO-P~II-CO-NHI \C/
C r H f \H CsHi
CONH
\/ I
CiH!
‘XHCO
CsHr
\d
CONH
co
CsH!
\ONH a The minimum amount necessary to abolish response to external stimuli is compared to the maximum tolerated and the minimum lethal dose.
Effect of Group Substitution in Compounds
There are a number of groups which modify or destroy the value of 5,s-dialkyl barbituric acids. The introduction of hydroxyl, ethoxy, carbonyl, amino, or carboxyl groups in one of the alkyl groups destroys the narcotic effect. Through the introduction of these polar groups, the tendency of the alkyl groups to impart lipo-solubility to the molecule has been lessened. Replacing one of the alkyl groups by a physiologically active group, such as ether or acetone, results in inert barbituric acid derivatives (4, 6 , 9). The introduction of amino, nitro, or hydroxy groups in the phenyl
1105
radical of phenylethyl barbituric acid causes a loss of activity, while bromine or chlorine only increases the toxicity (2). Mono-substituted barbituric acids, which are very watersoluble and acidic, are inert. If a group which is very reactive chemically, as is the benzyl or propargyl group, is introduced, the resulting barbituric acid has a convulsive action. Replacing both alkyl radicals by the benzal group or making the methylene carbon atom a member of a cyclic hydrocarbon or cyclic ether results in inert compounds, as has been shown by other investigators. Two methyl, benzyl, or amyl groups give practically useless products. Replacing the oxygen of’the carbon atom in the 2 position by S, NH, or H2 results either in toxic or inert compounds, while increasing the ring to eight members, as in malonyl malonamide, destroys the activity. Replacing one or both hydrogens on the nitrogen by an aliphatic or an aromatic radical has not resulted in products of therapeutic value ( 5 ) . It is a simple matter to introduce two similar alkyl groups into the barbituric acid molecule. Consequently, for two decades, with the exception of phenobarbital, there were available only symmetrically dialkyl-substituted barbituric acids. In 1920 it occurred to workers in these laboratories that barbituric acids possessing dissimilar alkyl groups should possess decided clinical advantages. Thus, if one of the ethyl groups of barbital were replaced by a larger alkyl group, one should expect to incorporate into the barbituric acid molecule the increased hypnotic effect which the larger alkyl group possessed, and perhaps other qualities, such as a more rapid action, quicker elimination, and a wider margin of safety between the effective and lethal dose. An extensive number of unsymmetrical dialkyl barbituric acids have been prepared and tested in these laboratories, following the early observation that, in the more effective compounds, the sum of the carbon atoms in the two substituent alkyl groups was seven (3, 17, 18, 20, 21). With the exception of the alkylmethyl derivatives, the most effective numbers had the greatest dissimilarity in the two groups, as, for example, the amyl and the ethyl group. It is usually advisable to introduce the two groups into the malonic ester before it is condensed with urea to form the barbituric acid. Graphs I and I1 show the quantitative relationships of the alkyl groups in several series of alkylethyl barbituric acids with respect to the narcotic and lethal doses when freshly prepared solutions of the sodium salts of the barbituric acids were injected intraperitoneally into white rats. The narcotic dose is that amount which causes the animal to fail to respond to external stimuli, such as tickling the inner ear with a splint (15). To consider that these quantitative differences give the complete picture is to ignore available pharmacological literature on barbituric acids (7, 11, 19). Such qualitative differences as rapidity of action, duration, rate of elimination, cumulative action, effect on circulation, etc., must be considered in the selection of the better therapeutic agent. Effect of Change in Molecular Weight of Alkyl Substituent
In the alkylethyl barbituric acid series, as the molecular weight of the alkyl substituent increases, an increase in the toxic and narcotic action occurs with the maximum effect a t about the amyl group. With a further increase in molecular weight, the effect diminishes. The margin between the effective and the lethal dose increases t o a maximum which is reached a t the amylethyl barbituric acids. At the point of maximum effect, the onset is more rapid and the duration is less prolonged than in the members with higher or lower mo-
IC6
I,VDcSTRIAL A N D ESGINEERING CHEMISTRY
I-01. 23,
KO.
10
tain differences are noted. In the primary aeries the maximum effect and toxicity lie between the propyl and the butyl groups, but in this secondary ETHn, AZXYL, BARBI’I’lJRIC ACIDS series between the butyl and the amyl groups. At CC.!76o SOLUTION TO PRODUCE NARCOSIS AND these points the values are almost identical with DEAm W RATS I N W P S R I T O N E U Y those of the ethyl series. In comparing the amyl groups of this series, the isoprimary is considerably more effective than the sow n-primary, a n d t h e c y c l o p e n t y l is more effecKG tive than either, but less effective than the secondary. Thus the r e l a t i o n s h i p s between isomers are affected by a change of the second group from ethyl to allyl. I n the ethyl and allylalkyl barbituric acids the therapeutic ratios f o r r a t s r e a c h a m a x i m u m of about 2.5. In general this ratio drops with the increasing molecular weight. Replacing one of the ethyl groups of barbital by an amyl group results in products which have five to ten times the effectiveness of barbital, mole for mole, in producing narcosis in rats. The onset of narcosis is more rapid, the recovery more prompt. The toxicity does not increase in this ratio. In contrast to the alcohols, the secondary radical is more effective than the primary. I n Graph IV, the alkyl groups in alcohols are compared with the same alkyl group in alkylethyl barGraph I bituric acids. The effectiveness of the alkyl group has been increased fifty times through its introduction lecular weight. The secondary alkyl groups are approximately into the barbituric acid molecule. The isomeric alkyl groups twice as effective as the primary or isoprimary isomers. The do not show similar relationships in the alcohols and barpropylmethylcarbinylethyl and the diethylcarbinylethyl bar- bituric acids and, as was noted above, may even vary in the bituric acids have the same degree of effectiveness. S o marked ethyl and allyl barbituric acids. The variations in solubility which exist in homologous series difference exists between the n-amyl, isoamyl, or active amyl (Bmethylbutyl) ethyl barbituric acids. Cyclopentylethyl containing alkyl groups, are far greater in the alcohols than barbituric acid, which contains a cyclic secondary group, has in the alkyl ureas or the dialkyl barbituric acids. For this the activity of the primary rather than of the secondary series. reason the relationships found for the alkyl groups in alWhen the molecular weight is large, the animals show mus- cohols might not be the same as obtained for the corresponding alkyl groups in dialkyl barbituric acids, cular incoordination as with diamyl barbituric acid. If t h e e t h y l g r o u p i s r e p l a c e d b y a larger group, as, for example, the propyl group, the effectiveness is lessened. secButyl-n-propyl barbituric acid is less toxic and less narcotic than is the sec-butylethyl b a r b i t u r i c acid, although the former has t h e s a m e m o l e c u l a r w e i g h t as the secamylethyl. The mere presence of a secondary group is not enough; a certain balance must exist between the molecular weights of the two substituent radicals. Thus, the molecular weight as well as the isomeric structure of the alkyl substituents are factors of importance. T h e i n c r e a s e d effect of the sec-butyl and the sec-amyl groups has been stated to be due to the presence of a group hav- 15 ing optical activity. However, since the dZ-2-methylbutyl (active amyl) derivative has almost the same effectiveness as the l - m e t h y l b u t y l ( i s o a m y l ) , and since the Z-ethylpropyl (diethylcarbinyl) derivative does not differ widely from the dl-l-methylbutyl (propylmethylcarbinyl) d e r i v a t i v e , the enhanced effect of the secondary groups would seem due to causes other than the presence of a group having optical activity. c CS 190 When the ethyl group is replaced by the Graph I1 a l l y l g r o u p , as shown in Graph 111, cer-
2
I
October, 1931
ISDUSTRIA L AiYD ESGINEERING CHEMISTRY
Effect of Unsaturation
1107
-
Unsaturation usually increases the effectiveness, provided the groups hare like numbers of carbon atoms. If in sec-butylpropyl barbituric acid, the propyl group is replaced by the allyl group, the effectiveness and toxicity are increased in the same order. Replacing the allyl group by the p r o p a r g y l g r o u p does not affect the toxicity but decreases the n a r c o t i c effect and gives a product which produces c o n v u l s i o n s . 10 The introduction of bromine in the beta carbon atom of the allyl group increases the toxicity but does not increase the narcotic action. If the bromine is removed to the gamma carbon atom, 0 the narcotic action is decreased. Three series of hypnotics containing aromatic groups were studied, the arylethyl barbituric acids, arylmethyl hydantoins, and arylethyl hydantoins. From Graph V it is seen that the sequence of phenyl, b e n z y l , and phenylethyl groups differ in the barbituric acids and hydantoins. In addition, in neither series is the benzyl group in its homologous position. This might be expected, since in chemical reactivity it does not lie between the phenyl and phenylethyl groups. I n t h e b a r b i t u r i c a c i d s , t h e benzyl group is the most toxic, in the hydantoins, it is the least. I n no instance does the benzyl group give a satisfactory hypnotic effect. The benzyl and propargyl groups, which are the most chemically reactive groups, though quite unlike in structure, produce like effects-tremors and conrulsions. This is the only actual instance of a correlation of chemical reactivity and effect which has been found in this laboratory. The alternating order of reactivity of alkyl groups, shown by Norris ( I d ) , is not in evidence. h'either does the relationship found by him for the isomeric amyl radicals obtain in the barbituric acids. Sorris ( I S ) has recently shown that in
Graph IV
monoalkyl-substituted malonic acids, as the molecular weight of the substituent increases, the acids split off COZmore easily. There is some evidence that, with increase of molecular weight, the alkylethyl barbituric acids break down more rapidly. The evidence which points to a physical rather than to a chemical cause of effect is strengthened by the fact that, in optically active barbituric acids, Hsueh and Marvel have shown that the d-, the 1-, and the dl-mixtures have a like action ( I O ) . The m-ater-solubilitv of the sec-amylethyl barbituric acid is t&x that of isoamylethyl. The differences which exist in the partition coefficients of the barbituric acids between oil and water are factors which must be considered in the ALIX ALKYL B A R J 3 I m C ACID transportation of the barbituric acids in the CC %o SOLUTION TO PRODUCE NARCOSIS A N D D U I " body. IN RATS INTRPSERITONEPiLLY The surface-tension depression and the I oil-water interfacial tensions of equal molar solutions of sec-amylethyl and isoamylethyl barbituric acids appear to be identical, yet their effects differ by almost 100 per cent. The mere fact that, as the molecular weight of the barbituric acid increases, the surface tension effect i n c r e a s e s , does not give a measure of activity as ha. been proposed.
m
cc
!!A; SOLI
KG
2c
15
1c
5
C
'i Ii
Conclusions
Prccise laws by which the physical properties, requisite for the ideal hypnotic, may be foretold, hare not yet been formulated. The t h e r a p e u t i c properties of new substances cannot at the present time be foretold from their physical properties. il survey of the chemical s t r u c t u r e s of the families of organic compounds which show hypnotic activity does not permit a t present the sketching of a structure containing the essentials of the ideal hypnotic. The struc-
INDUSTRIAL AND ENGINEERING CHEMISTRY
1108
Vol. 23, No. 10
pharmacologist, apply the knowledge gained from the study of barbituric acids to the development of the ideal hypnotic and anesthetic. Acknowledgment
The author wishes to express his appreciation to G. H. A. Clowes for his suggestions, and to E. E. Swanson for his pharmacological evaluations of the barbituric acids. The compounds listed in Table I and the hydantoins used were prepared in T. B. Johnson's laboratory by Robert Herbst, and tested by C. L. Rose of the Lilly Research Laboratories.
cc. M A 0
x1w
m 4
Literature Cited
3c 2c
lo
Graph V
ture of naturally occurring alkaloids, having sedative effect, has not contributed much to the development of hypnotics. Work must still be done in a rather empirical fashion. If there is any special group that can be called the hypnophore or pharmacophor group in hypnotics, it is the alkyl group, the hypnotic effect of which can be varied by attachment to different polar groups. Many hundred variations of barbituric acids are possible through changes of the two aliphatic substituents. Although less than 10 per cent of these have been made, this field can be considered as quite thoroughly explored. The synthetic chemist must now, in cooperation with the
(11) (12) (13) (14)
(15) (16) (17)
(18) (19) (20) (21)
(1) Bancroft. \\'. D . , and Richter, G . H . , Colloid Symposium Monograph, p. 215, Chemical Catalog, 1931; J. Phys. Chem., 36, 215 (1931). (2) Bousquet, E. W., and Adams, R . , J. A m . Chem. Soc., 62, 224 (1930). (3) Carnot, P . , and Tiffeneau, M., Compl. rend., 176, 242 (1922). (4) Dox, A. W., and Hjort, A. M., J. A m . Chem. Soc., 46,-252 (1924). (5) Dox, A. Itr.,and Hjort, J . Pharmacol., 31, 455 (1927). (6) Dox, A. W., and Yoder, L.,J. A m . Chem. Soc., 45, 1757 (1923). (7) Eddy, S . B . , J. Pharmacol., 33, 43 (1928). (8) Henderson, V. E . , Physiol. Re%, 10, 171 (1930). (9) Hill, A. J., and Keach, D. T., J. A m . Chem. SOC.,48, 257 (1926). (10) Hseuh, C. M . , and Marvel, C. S., Ibid., 50, 855 (192s). Koppanyi, T., and Lieberson, A,, J. Pharmacol., 39, 177 (1930). Munch, J . C., and Schwartze, E. W., Jr., J. Lab. Clin. Med., 10, 985 (1925). Nielson, C., Higgens, J. A . , and Spruth, H . C., J. Pharm. Erpll. Med., 26, 371 (1926). Norris, J. F., "Contemporary Developments in Chemistry," Colorado Univ. Press, 1927. Norris, J. F., and Young, R . C., J. A m . Chem. Soc., 62, 5066 (1930). Richardson, B. W.. Med. Times and GQZ.,18, 703-6 (1869). Shonle, H . A , , Keltch, A. K . , and Swanson, E. E., J. A m Chem Soc. 52, 2440 (1930). Shonle. H . A , , and Moment, A., Ibid.,45, 243 (1923). Vogt, M., Arch. e x p f l . Pafh. Pharmakot., 152, 341 (1930). Volwiler, E. H., J . Am. Chem. Soc., 47, 2236 (1925). Volwiler, E . H., and Tabern, D . L , Ibid.,62, 1676 (1930)
Preparation of Vinegar from Coffee Fruit Pulp' F. W. Freise VILLAN. S.
DA
POMPEIA, 3
6 SIR., ~ ~No. 15. RIC. DE ALBUQUERQVE, FED. DIST..BRAZIL
T
HE raw material is the pulp which covers the two
seeds or beans of the cherry-like coffee fruit and which is freed from the seeds in the so-called "wet process of coffee preparation." The ripe pulp is of a bright scarlet color and amounts to 40 per cent of the weight of the entire berry. The average composition of the pulp may be figured as follows: %
Moisture. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42.660 Volatile o i l s . .. . . . . . . . . . . . . . . . . . . . . . . . . . . 0 . 1 1 2 Waxes, fats, resins.. . . . . . . . . . . . . . . . . . . . 1 . 1 8 4 Tannins., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.557 Raw fiber.. . . . . . . . . . . . . . . . . . . . . . . . . . . 2 7 . 4 4 5 Sugars.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 . 4 5 5 Mineral substances. . . . . . . . . . . . . . . . . . . . . . 3 . 7 7 2 6.815 Notspedfied . . . . . . . . . . . . . . . . . . . . . . . . . . .
The maximum amount of sugar, 12.553 per cent, was found in a sample of Botucatu coffee in complete state of ripeness. Among the sugars, glucose and sucrose may be identified; the highest amount of the latter was found to be 1.25 per cent. 1
Received April 28, 1931.
To secure a rapid and uniform fermentation, the pulp must be reduced to a mash. When this mash is pasteurized a t 75" C. during 45-55 minutes and then inoculated with a culture-e. g., of Saccharomyces octoporus, a good fennentation sets in within 24 hours (temperature being held a t 23-25' C.) and reaches its climax on the fourth day. After 12 days the fermentation is complete and clarification must follow. Calculated on 100 grams of sugar, an average of 43.5 grams of alcohol is present. The specific gravity of the liquid is about 1.006, and the acetic acid contents, 0.25 gram per 100 cc. When this liquid is acidified in barrels filled with wood chips slaked in previously prepared strong vinegar, the temperature of the acidification room being held a t 35" C., the vinegar which results is of a clear Rhine-wine color, has a smell like pear oil and a taste resembling old whisky. The taste disappears within 3 or 4 weeks of storage and the color clears up somewhat. The vinegar has a specific gravity of 1.0154, a total acid
