[CONTRIBUTIONS
FROM T H E
SHEFFIE1.D
LABOR.4TORY 01: T A L E
UNl-
VERSITY.]
RESEARCHES
ON
THIOCYANATES ANATES. (FOURTH PAPER. I,.
ISOTHIOCY-
)
BY HENKYL. WHEELER A S D TREATB. Keceived . \ p i 1
AND
JOHSSOS.
1902.
THE work described in this paper was undertaken with the object of investigating the behavior of some tertiary halides towards alcoholic solutions of potassium thiocyanate. U p to the present time no tertiary alkyl halide has been found to give an isothiocyanate or mustard oil. This property has only been observed in the case of the primary allyl halides and the secondary diphenylmethyl bromide. In fact this subject has hitherto received little attention. Of the three tertiary halides that have been examined triphenylmethyl bromide and a-bromisobutyric ethyl ester gave normal. thiocyanates while tricarbethoxymethane failed to react.' The tertiary halides which we now discuss comprise all the possible compounds formed by substituting the positive group methyl, and the negative radicals, phenyl and carbethoxyl, -CO.OC,H,, for hydrogen in methyl bromide.* There are ten combinations to be coiisidered ; and among these, it will be noticed, are the above three tertiary forms that have already been exaniined : I. BrC(CH,), 11. BrC(CH,),C,H, 111. BrCCH,(C,H,), IV. BrC( C6H5), V. BrC(CH,),CO,C,H,
\'I. BrCCH,(CO,C,H,), VII. t'III. IX. X.
BrC.CH,.C,H,.CO,CH, BrC( C02C2HS)S BrCC,H,( CO,C,H,), ClC(C,H,),CO,C,H,
The investigation has shown that six of these compounds give normal thiocyanates, while the remaining four give neither normal or isothiocyanates. Tertiary butyl bromide ( I ) reacted smoothly with alcoholic 1 Since the above was written Crocker has found that picryl chloride gives a n isothiocyanate. Jour. Chon. Soc. (London), 81,436 (192). 2 I n one case (VII) the methyl ester was used a n d in another (X)the chloride instead of the bromide was employed ; experience has shown that the bromides react more readily than the chlorides.
THIOCYANATES Ah'D ISOTHIOCYANATES.
68 I
potassium thiocyanate, and the product was shown to be a normal thiocyanate by combining it with thioacetic acid, whereupon acetyl dithioisobutyl urethane, CH,CONHCSSC,H,, was obtained. r '-Gromisopropyl benzene (11) , I'-brom-I ,I-diphenylethane, (111) , 1'-bromhydratropicmethyl ester (V11) , and tricarbethoxymethyl bromide (1-111) reacted readily with, or were decomposed by, potassium thiocyanate, and a bright yellow, amorphous precipitate separated which had the properties of the so-called pseudocyanogen sulphide. These bromides therefore act like free bromine on potassium thiocyanate. The behavior of tricarbethoxymethyl bromide, in reacting immediately in the cold, is in strong contrast to that of the chloride, which showed little tendency to react even on heating for a number of hours. Triphenylniethyl bromide (IT-), as previously stated, gave a normal thiocyanate. In this case the rhodanide formed thiol esters with thioacetic and thiobenzoic acids. a-Bromisobutyric ethyl ester ( V ) also gave a normal thiocyanate. This was shown by boiling the product with hydrochloric acid, whereupon u-pu-diketo-/3-diniethyltetrahydrothiazoleI was obtained. hiethylbrommalonic ester (1-1) readily reacted with potassium thiocyanate, while ethyl chlormalonic ester remained unaltered even when heated with potassium thiocyanate to 14oO-145~ for a number of hours. \Yhen the product, in the case of methylbrommalonic ester was warmed with thioacetic acid, a thick oil was obtained which, on dissolving in alkali and precipitating with hydrochloric acid, gave a-keto-p sulpho-/3-methylthiazolidine, the so-called cY-rhodaninpropionic acid.' T h e structure of this is represented by formula XI. That the rhodanide is a normal thiocyanate is shown by the fact that the reaction took place as follows : CH,CONHCSSCCH,(CO,C,Hj), 4- NaOH H 2 0= C,H,ONS, CH,COONa 4-CO, + 2C,H,OH. CH,CH-S C,H,CH-S I 1 I '
+
co cs \ / NH XI.
+
co cs \ / NH
XII.
682
HESKT I.. "HEELER
A X D TREAT E. JOHNSON.
Croniphenylmalonic ester (TX) reacted smoothly with potassium thiocyanate, and the product with thioacetic acid and alkali behaved in a similar manner, inasmuch as a-keto-p-sulpho-Pphenylthiazolidine ( X I I ) n-as obtained. Diphenj.lchlorethy1 acetate ( X ) gave the first and only rhodanide that has failed to react with thio acids. I t reacted, however, with aniline, yielding triphenylpseudothiohydantoiii ( X I I I ) . On warming the latter with alcoholic hydrochloric acid, a-p-diketo-P-diphenyltetrahydrothiazole was obtained X I V ) . (C,H,),C--S
l
i
CO C =- NC,,H?
\/
NH
XI11
-
(C,>H.,), C -- S
I
co co \/
"
XIY.
The behavior of this hydantoin with hydrochloric acid differs from that of the pseudothiohydantoin from phenylthiocyanethyl acetate,l inasmuch as the latter, under certain conditions, gives up ammonia and not aniline on boiling with hydrochloric acid : generally, however, a mixture is obtained. The behavior of phenylpseudotliioliy~aiitoin with h! drochloric acid has lieen supposed to show that the conipouiid has the structure represented by formula XVII. L\-e have found that this long-known phenylpseudothioh! dantoin which, according to Meyer,* Liebermann,3 and Dixon,' gives a,p-diketo-N-phenyltetrah ydrothioazole ( 'phenylsenfoelglycolid"), formula XXI, with hydrochloric acid, also gives a , p diketotetrahydrothiazole ( X X ) . It follows from this that the reaction with hydrochloric acid can not he used to decide the structure of these thiohpdantoins. Both of the theoretically possible isonieric phen? lpseudothiohydantoins, (XI-11) and ( X1711T) , for example, can give phenylthiohydantoic acid (XIX) , ant1 this can be decomposed into the tn-o tetrah! drothiazoles that are actually o1)tained Ani
Clwiii J , 2 6 , 353 (1901) RPY d clreiri GPS 14, 1661 (rS8Ii 3 A u n C/rem (Liebig). 207, 129 ( i R S r +] C/IPIIISoc (London) 71. 620 (rS51
1
653
THIOCYANATES A N D ISOTHIOCYANATES.
CH,-S
I
co
I C=NH
\ /
NC,H,
CH,-S I C=NC,H,
CO
/\ /
\
J
XVII.
NH
XVIII.
HOCOCH,SC( NH)NHC,H, XIX.
co co
do co
\ /
\ /
NH
N C" X"
xx.
XXI.
Dixon found that the hydantoln in question gave a-keto-p-sulphotetrahydrothiazole ( "rhodanininsaure" ) ,formula, X X I I below, when heated with carbon disulphide, and he therefore assigned to the compound the structure represented above by formula XVIII. This is undoubtedly correct since by the action of benzyl chloride and alkali, a benzyl derivative is obtained from this hydantoin, which is identical with that from benzylphenylthiourea, C,H, (C,H,CH,) NCSSH,, ethylchloracetate and alkali. This benzyl derivative must have the structure represented by formula XXIII : CH, - S
I
i
co cs
CH,-
co I
S C-"
