[CONTRIBUTION FROM
THE
RESEARCHLABORATORY OF ARMOURAND COMPANY, CHICAGO, ILLINOIS]
THE PREPARATION AND PROPERTIES OF HIGH-MOLECULARWEIGHT ALIPHATIC THIOAMIDES A. W. RALSTON, R. J. VANDER WAL AND M. R. McCORKLE Received January $3, 1939
Investigations of the preparation and properties of thioamides have been confined to aromatic and low-molecular-weight aliphatic thioamides. Two general methods for the preparation of thioamides have been described: the thiohydrolysis of nitriles and the action of phosphorus pentasulfide upon amides. Bernthsen' described the preparation of thiobenzamide and thioacetamide by the action of an alcoholic ammonium solution of hydrogen sulfide upon benzonitrile and acetonitrile, respectively. Hofmann? prepared thiobenzamide and thioacetamide by the action of phosphorus pentasulfide upon the corresponding amides. More recently Kindle? has shown that the presence of an ammonium or alkali hydrosulfide catalyzes the thiohydrolysis of nitriles. High-molecular-weight aliphatic thioamides, such as thiostearamide, have not been previously prepared. The authors have prepared such thioamides by heating the nitriles with alcoholic solutions of ammonium hydrosulfide under pressure in a steel bomb at 150" to 160" for several hours. The reaction is represented by the following equation:
'S
The amount of ammonium hydrosulfide used was greatly in excess of that employed by Kir~dler.~By this method we obtained substantial yields of several long-chain aliphatic thioamides. A few of their characteristic reactions have been investigated. In general, the high-molecular-weight thioamides are characterized by reactions similar to those reported for the other members of the series. An exception is the formation of amines by reduction with sodium and alcohol. Bernthsen' reported that thiobenzaldehyde resulted from the BERNTHSEN, Ber., 10, 36 (1877). (1878). * KINDLER,Ann., 4 1 , 187 (1923). 1
* HOFMANN,{bid., 11, 34.0
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HIGH-MOLECULAR-WEIGHT ALIPHATIC THIOAMIDES
action of sodium amalgam upon an alcoholic solution of thiobenzamide. The behavior of the high-molecular-weight thioamides is somewhat similar to that of the corresponding amides. Pyrolysis produced the corresponding nitriles with the loss of hydrogen sulfide. Pyrolysis into the nitrile and hydrogen sulfide takes place a t a somewhat lower temperature than is necessary for the analogous reaction with the amides. The hydrogen sulfide formed does not react with the remaining thioamide. Ralston, Hanvood, and Pool4report the pyrolysis of stearamide to yield both stearonitrile and stearic acid. Hydrolysis with concentrated acids, aqueous or alcoholic alkali solutions gave carboxylic acids and not thio acids. EXPERIMENTAL
Thiostearamide.-One hundred cubic centimeters of absolute ethyl alcohol was saturated with dry ammonia and dry hydrogen sulfide a t 0". This solution was then added to 10 g. of stearonitrile previously placed in a steel bomb. The steel bomb had a capacity of 80 cc. and was equipped with a valve for the release of gas. This valve was kept tightly closed during the reaction period. After the addition of the reactants the bomb was closed quickly and placed in an oil bath. The temperature of the bomb was then raised over a period of two hours t o 160°, and kept a t this temperature for two hours. Heating was then discontinued, and the bomb was allowed t o cool for ten hours. The reaction product was filtered and washed with cold alcohol. The product melted a t 94-95", and, after three recrystallizations from ethyl alcohol, 7.5 g. of thioamide melting at 96-97' was obtained. Anal. Calc'd for CI8HIINS:S, 10.7; N, 4.7. Found: S, 10.6; N, 4.8. The following thioamides were also prepared by the above-described procedure : ANALTBII, COMPOUND
Y.P.,
%
N
S
OC.
Cala'd
I
Found
Calc'd
I
Found
Thiolauramide ......................... Thiomyristamide ...................... Thiopalmitamide ...................... Reduction of thiostearamide.-One gram of thiostearamide was reduced with metallic sodium in n-butyl alcohol. The butyl alcohol solution was then washed with water, and the butyl alcohol was removed by distillation. The residue was dissolved in ether, washed with water, and the ether was then removed by distillation. The product was dissolved in alcohol, from which i t was precipitated as the hydrochloride by the addition of concentrated hydrochloric acid. It was immediately acylated with acetic anhydride and crystallized from water and alcohol and from alcohol. The product melted a t 78-80'. A mixture with N-acetyloctadecylamine prepared by another method* showed no depression in melting point.
RALSTON,HARWOOD, AND POOL,J . Am. Chem. SOC.,69, 986 (1937). stearonitrile by sodium in n-butyl alcohol, followed by acetylation. This product melted at 78-80".
* Reduction of
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RALSTON, R. J. VANDER WAL AND M. R. MCCORKLE
Hydrolysis of thiostearamide by 16% alcoholic potassium hydroxide.-Thiostearamide (0.5 9.) was refluxed for thirteen hours with 20 cc. of a 15% solution of potassium hydroxide in ethyl alcohol. The stearic acid obtained weighed 0.28 g. and melted at 66-8". The melting point of a mixture with known stearic acid showed no depression. A benzimidazole' prepared from this product melted a t 93-94.5" and showed no melting point depression when mixed with known 2-heptadecylbenzimidazole. Hydrolysis of thiostearamide by 80% sulfuric acid.-Thiostearamide (0.5 9.) was refluxed for one hour with an 80% solution of sulfuric acid. Hydrogen sulfide was evolved, and 0.25 g. of stearic acid was obtained. This melted a t 68-69"and showed no depression in melting point when mixed with known stearic acid. The benzimidazole melted at 93-94". Pyrolysis of thi0stearamide.-Thiostearamide (0.5008 9.) was heated in a testtube immersed in an oil bath, and the gaseous products were swept out with dry nitrogen into a slightly acidic 20% cadmium sulfate solution. Initial decomposition was observed at 150" and was rapid a t 175-180". The sample was heated a t 175-200" for twenty-four hours. The residue melted a t 38.5-43". The melting point of a mixture with known stearonitrile was 38.5-39.5". Hydrolysis of 0.086g. of this product with concentrated sulfuric acid at room temperature for one and one-half hours gave stearamide melting a t 104-106". A mixture with known stearamide melted a t 106-107.5". A portion was distilled under high vacuum and gave a distillate melting a t 106-107.5". The same procedure applied t o thiopalmitamide gave approximately a theoretical yield of hydrogen sulfide and a product identified as palmitonitrile. SUMMARY
The thioamides of lauric, myristic, palmitic, and stearic acids have been prepared from the nitriles by thiohydrolysis of the corresponding nitriles. Several characteristic reactions have been investigated. 6
POOL,HARWOOD, AND RALSTON, J . Am. Chem. Soc., 69, 178 (1937).
