THIOCYANATES A N D ISOTHIOCYANATES.
439
I . 7 I ) , have been added, the metal can be quantitatively separated by a current having N.D. ,oo =0.003 ampere, and voltage 3. T h e deposition is complete in twelve to fourteen hours.
SEPARATION OF LEAD FROM MANGANESE.
Phosphate of manganese is readily soluble in an excess of phosphoric acid, With such a solution several trials showed that even strong currents produced no effect other than to develop a pink coloration, suggesting the color of weak permanganate.’ T h e current was allowed to act at ordinary temperatures for seventeen hours. When lead and manganese were in the same solution and electrolyzed with N.D.,, = 0.01I ampere, Voltage = 3, Dilution = I 30 cc., Phosphoric acid = 14 cc. manganese dioxide was thrown out on the anode, while the lead deposit gave tests for both lead and manganese. Further work is now being done to determine whether lead can be separated from manganese in a phosphoric acid solution. WITTENBERG COLLEGE, SPRINGFIELD, O.,
December
26, 1901.
-[CONTRIBUTION FROM THE SHEFFIELD LABORATORY OFYALEUNIVERSITY.]
RESEARCHES ON THIOCYANATES A N D ISOTHIOCYANATES. (THIRD PAPER.)
ny
HENRYI,. WHEELER AND HENRY
F. MERRIAM.
Received February 14,IF*.
1
N our first paper’ we described the results of an examination of rhodanides formed from certain alkylmonohalides and potassium thiocyanate, and showed that it is a simple matter to distinguish normal from isothiocyanates by their behavior with thiol acids. In the case of monothiocyanates, two reactions were observed. Either a direct addition was obtained with the formation of benzoyldithiourethanes, or along with other products, an ester of thiobenzoic acid resulted. The latter reaction was observed only in the case of certain secondary and tertiary thiocyanates : 1 S m i t h : A m . Chem.]., i ~ , N o . 5 . This Journal, a3, 283 (1901).
2
440
H E N R Y ..I
W H E E L E R A N D H E X R T 12. > I E K X I A l I .
+
C,H,CO.SH NCS.CH,R -C,H,CONHCS.SCH,R and C,H,CO.SH ?;CS.CRR’R” = C,H,CO.SCRRfR” + HKCS. On the other hand, isothiocyanates reacted smoothly to form benzamides and carbon disulphide : C,H,CO.SH SCN-R = C,H,COSHR 1CS,. T h e work has now been extended to dirhodanides, arid iticidentally it has been found that not all dihalides yield dirhodanides. T h e dirhodanides which have been obtained from dilialides and potassium thiocyanate have, without exception, proved to be derivatives of normal tliiocyanic acid. W e have found that the action of thiobenzoic acid, in the case of I , 1-dithiocyanates, as represented by methylene thiocyanate, and of I , a-dithiocyan derivatives, ethylene and phenylethylene (styrolrhodanide), is by no means as smooth or simple as that in the cases previously described. In fact, even wlieii the action was moderated by heating in the presence of benzene, thick oils or varnishes were invariably formed in addition to material that could be crystallized. From methylene thiocyanate and thiobenzoic acid, three crystalline products were directly obtained. These, we have concluded, are methylene dithiourethane ( I ) , benzoyldithiocarbaniicnietliylenethiolbenzoate (II), and the methylene derivative of benzoylditliiocarbamic acid (111) : CH, (SCSNH,),, C,H,CO. SCH,S. CS;”U”COC,H,
-+
+
I.
11.
CH,(SCSNHCOC,H,),. 111.
During the reaction, hydrogen cyanide and carbon disulphide were formed, the latter being due to a secondary reaction of thiocyanic acid, HNCS. I n the case of ethylene thiocyanate, we isolated two products. These were ethylene dithiocarbamate (I\-), and the benzoylderivative of imidomethyleneethyleiie disulphide ( T-), while phenylethylene gave the corresponding iniidornethylenephenylethylene disulphide ( V I ) : C,H,CHS CH,SCSSH, ~Hzs>CNCOC6Hj I )CNCOC,H, I CH,S CH,SCSNH, CH,S 1V.
V.
VI.
T H I O C T A N A T E S AND ISOTHIOCYANATES.
441
As a n example of a I ,g-dithiocyanate, trimethylene rhodanide was examined. This reacted in the normal manner for a primary thiocyanate, and a bisdithiourethane was snloothly formed. A property which appears to be unique for normal thiocyanates was observed in the case of trimethylene and phenylethylene thiocyanates. These compounds combine directly with one molecular proportion of aniline, probably to form seven- and eightmembered rings, the behavior being somewhat similar to that when pseudothiohydantoi’ns are formed by the action of bases on ethylphenylthiocyanacetate,etc. The compounds may be viewed as cyclopseudophenyldithiobiurets. If tautomeric forms are excluded, two isomers are possible in the case of trimethylene thiocyanate, while from phenylethylene there are three. I n the latter case, the end nitrogen atoms have different positions in respect to the phenyl group (VII). Since the trimethylene compound was not obtained from phenyldithiobiuret, C,H,NHCSNHCSNH,, trimethylene bromide, and alkali or ammonia, it appears that the followiug formulas best represent the structure of these compounds : C,H,C H,-S-C= NH C II,-S-C =N H
I
)NC,H, CH,-S-C-NH
I I
CH,
I
NC,H,
I
CH,-S-C=NH VII.
VIII.
There seenis to be no mention in the literature of dithiocyanates derived from 2,3 dihalides, and it is a noteworthy fact that such dihalides of this type, as we have examined, react with alcoholic solutiolis of potassium thiocyanate in a peculiar manner. In each case, with the exception of isoeugenolmethpletherdibromide, the yellow, amorphous material or mixture called pseudocyanogen sulphide’ was formed in more or less amount. I n these cases, the halides act like free bromine on potassium thiocyanate. I n addition to pseudocyanogen sulphide, 2,3-dibrombutane, CH,CHBr-CHHr-CH,. gave a yellow oil. This was found to decompose on di>t lling under reduced pressure. T h e oil was, therefore, simply washed atid then dried in a vacuum. A nitrogen determination gave I 2 . 2 per cent., while the calculated for butylene dithiocyanate is I 6.2 per cent. nitrogen. These figures 1
Goldberg: J. prakt. Chem., 6 4 , 166
(iyx).
432
H E N R Y L. W H E E L E R A N D H E N R Y F. 31ERRIA3I.
are given here merely to show that, in all probability, a dithiocyanate is formed in this case. Pinacone dibroniide (CH,),CBr CBr(CH,), and allylbenzene dibroniide, C,,H,CHBrCHBrCH,, behaved in a similar manner. 2,4-Dinitrostilbene dibromide C,H,( NO,)?CHBrCHBrC,H,, dibronimethylhydrocinnamate, C,H,CHBr-CHBrCO,CH,, and the dibroniide from the nitrile of phenylcinnamic acid, CtiH5CHBrCBr (CN) C,H,, when warmed with alcoholic potassium thiocyanate gave abundant precipitates of pseudocyanogen sulphide. I n these cases, the bromine was simply removed and the conipounds were converted into the corresponding unsaturated products from which the bromides were prepared. T h e property of forming pseudocyanogen sulphide is not confined to z,3-dihalides, since it has been found that certain tertiary halides behave in like manner. W e have found that I , 2-dibromisobutane, (CH,),CBrCH,Br, gives pseudocyanogen sulphide. Monobrombenzylcyanide and hroincyanethyl acetate react in the same manner. Eugenol tetrabromide, C,,H(OH.OCH,,Br,)CH,CHBrCII,Br, gave no pseudocyanogen sulphide, nor did isoeugenol methyl ether dibromide, C,H,( OCH,),CHBr-CHBrCH,, a z ,3-dibroinide. 'I'he exceptional behavior of the latter compound shows that the formation of pseudocyanogen sulphide is not general in the case of 2,3-dibroinides. T h a t this dibroniide has the structure assigned to it, and that isoeugenol methyl ether does not add bromine in the I,# position, i. e., part in the nucleus and part in the sidechain, has been proved by us by oxidation with potassium permanganate, whereupon veratric acid and dimethoxyphenylglyoxylic acid' were obtained. EXPERIMENTAL PART.
iVethyLeelze, Thiocyanate a i d Thiobenzoic Acid.-Nineteen grams of the thiocyanate and 35 grams of the acid were dissoltied in about two volumes of benzene and the mixture was heated on the steam-bath. After five or six hours it was found that yellow crystals had separated. Ten cc. of the benzene was then distilled off and found to contain hydrogen cyanide and carbon disulphide. T h e insoluble material, after washing with benzene, was crystallized from glacial acetic acid, whereupon, on slowly cooling, it separated in the form of small, slender, pointed, pale 1
Ciamician and Silber : Be>-.d. chem. Grs., a3, 1164 IS^).
443
T H I O C Y A N A T E S A N D ISOTHIOCYANATES.
yellow prisms. It melted, not sharply and with effervescence, at 166'. T h e yield was about 4 grams, and on analysis the following results were obtained: Found.
Calculated for CzHcN&.
Nitrogen Sulphur
................... 14.1 .................... 64.6
I.
11.
14.2 65.5
'3.9
...
T h e nitrogen determinations agree with the calculated for inethyZene dithiocarbamate, H,NCS.SCH,SCSNH,, and this structure is confirmed by the fact that the compound dissolves iu alkali and undergoes decomposition into methylene mercaptan and thiocyanic acid. T h e benzene filtrate from the above was evaporated in a vacuum, and the thick oil thus obtained was stirred with ether containing a little alcohol. T h e solid material, thus produced, was crystallized from alcohol and benzene, whereupon yellow elongated plates melting at 138'-139' were obtained. T h e yield was about 4 to 5 grams, and analysis gave the following results : Calculated for Cl6H1,O?NS3.
Nitrogen Sulphur
................ 4.03 ................ 27.66
I.
Found.
4.33 28.46
11.
4.56 27.65
Since the material is soluble in alkali with decomposition and has a yellow color, the assumption that it contains a dithiourethane grouping seems justified. In view of the above analyses, this would then permit of the following structural formula: C,H,CONHCS.SCH,SCOC,H,. T h e substance is, therefore, a methylene ester .f thiobenzoic and ben zoyldiihiocn rba nzic acids. The ether solution from the above was shaken with alkali and precipitated with carbon dioxide. T h e resulting oily solid was crystallized from benzene and ligroi'n, whereupon bright yellow crystals melting at 13oO-131~were obtained. T h e yield, owing to decomposition by alkali, was less than a gram and a nitrogen determination gave : Nitrogen.. .............................
Calculated for C~~H~IOIN?S+
6.89
Found.
7.14
This corresponds to the calculated for, the methylene ester of benzoyldithiocarbamic acid, ( C,H,CONHCS.S),CH,. Methylene Thiolbenzoate, ( C,H,COS) ,CH,, -The possibility
444
HENKI' L. WHEB1,ER AND HENRY F . M E K R I A n I .
suggested itself that the solubility of the above compounds in alkali might be due to tlie presence of two negative groups attached to methylene and not to a dithiourethane group. I n order to decide this point, we have prepared tlie iiietliylene ester of tl~iolbenzoic acid by treating potassium tliiolbeiizoatc \vitli methylene iodide. Tlie mixture in alcoliolic solution reacted at once, and the product foriiied long, snow-whiten e d l e s iiieltiiig at 120'. I t is insoluble in, aud remains unaffected by dilute alkali. A sulphur determination gave : Sulp11lir. ..............
CI3HIL'O1.S?.
....... 2 2 . 2 2
Folllld.
22.,;1
Efhyleiie Thiocyaiza te n 12d Thiobeu zoic A cid. -T h i r t y gram s of ethylene thiocyanate were heated on the steam.batli, for six to eight hours with j 6 grams of thiobenzoic acid, diluted with 1 2 j cc. of benzene, whereupon it was found that a crystalline precipitate had separated. About I O cc. of the benzene were then distilled off, and this gave the reactions for carbon disulphide and hydrogen cyanide. T h e insoluble niaterial was crystallized from gl,tcial acetic acid and, on slowly cooling, it came down in aggregations of flattened prisms, of a very pale cream color. Thirteeti grains of this material were o5taiiied melting, not sharply, at I 8s"- 89". T h e analytical results were a i fo1low.i : Carbon ................................ Hydrogen. ........................... Nitrogen .............................
~
