ON THE FOIiMATION O F ANTHRAQUINONE UNDER PECULIA K. C:ONIIIT 10N S. --
B Y L. H. FKIEUBURG, 1”. I). -(Read before tlie A M E R I C ACHEMICAL ~ SOCIETY, E’eby. 7 , 1890.)
Both the indophenin reactioii, formerly used as a test for benzol’, and the phenanthraqninone reaction of Laubenheimerz, effected with toluol, have been shown by Victor hIeyer3 to be due, ,)hot to benzol and toluol, but to thiophene and niethylthiophene respectively. l!he first suggestion of an experiment looking towards the isolation of thiophene was the fact that some benzol, obtained by distillation of benzoi’c acid4 witli lime, did m t show the inciophenin reaction5. This reaction consists in treating coal tar benzol with isatin and concentrated sulptiuric acid, when deep blue indoplienin C, ,H,?JOS results. But benzol and toluol, after proper treatment with concentrated sulphuric acid, will not show t h e indopheriin or the phenanthraquinone re:iction respectively6. This latter reaction, also called tlic Laubenheimer reaction, was described 1~s its discoverer in 15’75 ( 1 7 0 ~ . cit.) as follows : “ A few drops of toluol are added to ii dilute solution of “ plienantliraquinone in glacial acetic ticid. The mixture is (‘cooled continually and drops of concentrated sulphuric acid are I ’ allowed to run into it, After a few minutes water is added. ‘’ A coloring substance is precipitated, which, on shaking with ‘(ether, dissolves with a beautiful purple tint.”
a.r o n Raeyer, Ber. 12, 1311 ;
16, 1477 ; 16, 2637 Ber. 8, 294. Die Thiopliengruppe ; Vieweg, 1888. From urine, from resin or from toluol. V. Meyer, (Zoc. cit.) pp. 1 e t seq. ‘ Bey. 17. 1338.
ON T H E FORMATION O F ANTHRAQUINONE.
27
The indophenin reaction is caused by the presence of thiophene (C,H,S) which exists in all coal tar benzol, while correspondingly, the Laubenheimer reaction is occasioned by a-methylthiophene, called a-thiotolene, C,H,S CH,, contained in all coal tar toluol. T h e pure thiophene and thiotolene show the two described reacti ons most d isti nc tl y. The analysis of the coloring matter prepared from phenanthraquinone, tu-thiotolene and conc. sulphuric acid, shows approximately the formula, C,gH,,OS, so that V. Meyer' writes the following equation for the formation of this body, which is precipitated in the shape of indigo blue flocks :
C,,H,02 +C,H,S=CC,,H,,OS
+ H,O.
It is a dark blue powder which, on pressure, assumes a copper lustre. It is easily soluble in alcohol, benzol, chloroform and carbon disulphide, but insoluble in water. Heated alone, i t does not show any charticteristic behavior. A remarkable result was shown, however, on combustion of the substance with lead chromate. At a comparatively low heat a yelloia wnpor was formed, whicli sublimed in the colder part of the tube (outside of the combustion furnace), in the shape of large golden yellow ncedles. These were free froni sulphur, did ?bot give the phenanthraquinone rtxaction, showed on resublimation the melting point of 27'4"C. and exhibited every other property of antIwrtpzciiao~ze. The characteristic reaction of Claus 2 for anthraquinone was niso obtained and finally the body was transformed into nliznrine. The phenanthraquinone that was used for the preparation of the above mentioned coloring substance had been newly prepared * Die Tliiophengruppe, p. 40.
' Mix 1 nig. anthraquinone with some sodium amalgam, add absolute ethep (free fisom alcohol) and shake. On now adding a few drops of water a red coloration ensues, which disappears again on shaking, in consequence of the admission of air. On adding absolute alcohol to t h e mixture of anthraquinone and sodium amalgam a green coloration sets in, disappearing on agitation with air. Both colors reappear on standing. (Claus, Ber. 10,937.)
28
ON THE FORMATION OF ANTHRAQUINOKE.
from its pure bisulpliite compound and did not contain any anthraquinone. V. Meyer’ says : ‘(It will be difficult t o find a n explanation for this peculiar pyrogenous reaction. It seems almost as if the methyl group of the thiotolene has to d o with this formation of anthraquinone. The faci that the p e e n coloring substance obtained from tiiiophe?i.e,* and pliena~ntliraquino~ieunder t h e same treatment did m t lead to anthritquiiioue. favor this assumption. In the following pages I ofTer an explanation of this peculiar formation of anthraquinone, and I shall also propose some experiments which will decide whether my theory is right or not. A careful study of V. Meyer’s work 011 thiophene and its derivatives and a11 extended acquaintance with the behavior of aromatic compounds, particularly of those formed by contlcnsation from the fatty series, lead me to regard this explanation :is liiglily probable. Before considering the main object of this paper, it may be well to glance briefly a t the mode of preparation arid the constitutional formula of thiophene, also to mentioii sonic of its properties. iT. Meyer, 3 i’olhard and Erdmann, 4 P a d , 5 idso I’aal and Tafel, ‘I‘iernann and Haarmann, 7 have contributed nietliods for the synthesis of thiophene. According to these researdies8 many substances which contain t h e group ; -C
I
co
C as For instance,
I
oc
succinic acid, pyro-tartaric acid, acetonyl-acetone, laevulinic acid, Die Tliiopliengruppe, page 41. See pp. 30 and 43 of this paper.. Ber. 16, 2176. 4 Ib. 18, 454. 5 Ib. 18, 367 and 2251. e Ib. 18, 436 and 688. 7 Ib. 19, 1237. E V. Mejer, die Thiophengruppe, p. 249.
ON THE FORMATION OF ABTHRAQUIKONE.
29
etc., when treated with phosphorus trisulphide, * yield thiophenes,
a complex group C
- - -.c
being formed from the two CO
\/ 5
groups. T h e best synthetical preparation of thiophene, one of practical value, is t h a t of Volhard and Erdmann &G. cit.), pnblished i n 1884. It consists in the treatment of sodium succinate with a dozcble quantity of phosphorus trisniphide. This method, which has since been improved, yields fifty per cent. of the thcoretical quantity. Thiophene t h u s prepared is sold at 130 marks per kilo. V. Meyerz gives a discussion of the structural formula of thiophene, which leads him tocompare it to.ficrfurn?ze and pyrro2. Furfurane :
Thiophene :
H H //c-c HC
+
E
H
Pyrrol :
E
H
4c-c \\ Hc
\,/CH
Which is not to be considered a real chemical combination, but afused niixture of the components in the proportion of P, to S,. In order t o understand this formation, we must assume t h a t five molecules of sodium succinate would be acted upon by a mixture of P,S,, (very nearly 4P,S,). Because one molecule of sodium succinate would have to lose 0, and Nal, while one atom of sulphur would take the place of these. The reaction could then most sinmlv be exDressed :
."
+
+
5NaBS. P,S, = 5C,H,S -t 4P,O, CH, -COO Na The molecular weight of sodium succinate and of P,S, are very nearly t h e same, being as 162 t o 158. Since phosphoric anhydride cannot easily be supposed t o exist under these conditions along with either sodium succinate or sodium sulphide, a more complicated reaction will take place, leading to sulphur compounds higher than thiophene. To avoid this may be the reason for the practical prescription of using 2% times t h e amount of P, S,, indicated by t h e equation. L. H. F. Die Thiophengruppe, p. 30, et seq.
T o facilitate the sttidy of the substitnted t h i o p h ~ n c s .he uses the
abbreviated formulE :
01
T h u s the methyl thiophene above rnentiolied as t v - m e t l ~ y l t h i o plbeae or a-thiotolene, has the constitution :
while t h e corresponding thiophenaldehydc, whicli will be referred to later, would be :
c G . 0 .
S I h e properties of thiophene arc t h c fullowing : I t is a colorless,
r i
clear liquid, boiling a t 84" C. (Benzol boils a t 80.5' C?.) It has a feeble and not very characteristic odor. I t is iiot miscible with water. It does ?tot solidify in ;t mixtnrc of ice mil salt. Concentrated sulphuric acid dissolves it in the" cold with dark brown coloration ; later the mixture evolves hydrogen sulphide, thcn sulphur dioxide, finall? tlic mass thickens, and when water is added it thick, gray, amorphous precipitate is formed, which is insoluble in all liquids. l ' h e r ~ a c t i o nbetweeii tliioplienc, isatin and conc. sulpliuric acid, forming by condcns~ttion,according t o A. v. Bseyer (Zoc. cit.), the beautifully bluc dyestuff iiidophenin, is the most delicatc reaction, indicatiiig tlie presence of the smallest traces of thiophenc. According to A. Y, Iheyer, the reaction takes place t h u s : It i dop ?L e 12 i 11. [C,H,NO, C,II,S] - 1120 :--= C,,Il,P;OS. Thiophene and plienaiit,liiarjuiiioiie show the Laiibenheimer reaction, when ether is replaced by c h l o ~ o f o m i , ,tlie dye formed dissolving in the latter with. deep emerald green color. 1
+
* V. Meye]., die Thiophengruppe, pp. 24 and 23. See also pp. 28 a n d 43. of this paper.
O N T H E FO11)1IhTIOh- O F ANTHRAQUINONE.
81
Thiophene is not attacked when didtilled over metallic sodium. I n physiological action i t differs from benzol.' Approaching now the main object of our discussion, which is, t o explain the formation of anthraquinone froin the dye C, , H I ,OS,2 when this latter is heated with lead chromate, we find, n priori, three possible cases of decomposition. I.-The anthraquinone is exclusiwly formed out of the phenanthraquinoue residue, by rearrangement of the atoms within the molecule and oxidation. II.--13oth, the phenanthraqninone residue aiid the thiotolene residue participate in building u p anthraquinone. 111.-The thiotoleite residiie o d y is transformed into anthraquinone, being a t first and intermediately oxidized to thiophene aldehyde. I shall only consider the third case, which also implies the formation of anthraquinone out of a - ~ n e t l ~ y l t l ~ i o p l ~ e ~ ~ e . The following two equations express the supposed formation :
+
+
+ [GO] minus [CO, 3H,S 2H,O]= C H, 0,. Anthraquinone 2. [3C,H40S] minus [COS f?H,S] = C,,H,O,. In constructing these two equations I have, of course, recognized the fact that we do not find a d u d e molecule of methylthiophene in the blue dye obtained from phenanthraquinone plus methylthiophene minus water, but probably the residue C,H,S very closely linked to one oxygen atom, which binds the carbon of the methyl group to the phenanthraqninone, while a second valency of this same carbon atom is directly linked to the phenanthraquinone residue, according t o the following formula : , 1. [SC,H,S]
+
-Die Thiophengruppe, p. 26 ; and A. Heffter, Archiv ftii. die gesammte
Physiologic, 39,420. a
From a-thiotolene, phenanthraquinone and conc. sulphuric u i d .
32
OK THE POKXATION O F AKTHRAQUINON E.
T h e splitting off of thiopliene aldehyde is then indicated by the dotted line. Further, it will bo snown how anthraquinone may be formed from thiophenalileliytc, tr:insitorily existing in our reaction as the formula indicates. 1 will only point o u t lierc, t h a t s i w d l n u e o u s l y with such ii formation: tJliephenanthreiie rc4tlne (I, ?I18 also might suffer a rearraiigement of its ~iuclt?usiLIl(1 then be osidizcd by the lead cliroinato to anthraqtiirioiie, so that a formation of this latter 111. and c:tse I. together. might take 1~l:ice:~ccorcliiigto B u t t h e main interest bcirig attitciied to cas(! 111., since it slioms t h e poseibil ity of a trausition f r o m i i tliioplienc deriwitive to an anthracene deriviitivc, I will consider it csclusively. Let us then look iit the irinclr nieclianism, :LS indicated by equation '2. To this end I arrange 011 t h c paper the formulE* of three tliiophenaldehyde molecules in sucli i~ manner that the supposed formation of anthraquinone may be more easily foreseen. I
FIB. 1
I
H
\
1
'
,
H
HCO ' \
\
C
H
\ \
\
\
COH1 .~-
L a d e n b w g , Theorie der aromatischen Verbindungen (Vieweg, 1876), page 23, sags : In rnoqern chemistry the formula of a substance is a n expression which gives not only a n account of the composition and the true molecular weight of that substance, but which a k o indicates a definite view of the manner in which t h e atoms, forming t h a t molecule, are linked together. I
33
ON T H E FORMATION O F ANTHRAQUINONE.
We may now remove from these three molecules of thiophenaldehyde, two of hydrogen sulphide and one molecule of carbon oxysulphide in the following manner .
FIB, e , . I .
H
:
n
H
CH
... ...... . ,
..... .
.
.
.
a
.
T h e remaining residues, in which the unsaturated valencies are indicated by dotted lines, would then face each other thus :
FIB. 8 H
/c HC
:
HC
\c ‘ H
Now in order to do justice, in a manner, to Kekulir’s repeatedly expressed demand 1 (“in imagining the construction of such forSee page 35 of this paper, foot note.
m u h , care should bc taken to unite :L; f ; ~ as r possible those carbon atoms with eitch other, wliicli (optfkcr have furnished the ele" ments for the eliminatt~d (wmpounds,") wc may mutually saturate thc free valt,iic:ies :is indicateti i i i Fig. 3 , i i i the manner shown in Fig. 4 . l[aintaiiiing tlic sequence of n u m li
"
F16,4
..............&. i3
A:
CH
"T
l
CH
..............................................................
i
H
bers of the carbon atoms, this Fig. 4, as will be easily seen, is a plLenal2thrcir/uino?~e,as shown i n Fig. 5. I t is not
FIB.6 H
B
'I
f
"
lo
c;*/
Hc';2.ja- /
=
C
\14
13
C-C I I O."""O
necessary a t this point to give a correct picture of anthraquinone, this will be done later. I restrict myself here to showing merely that a similar ring can easily be formed out of thiophenaldehyde. T h e forms which would correspond to equation 1, are quite
ON THE FORMATION OF ANTHRAQUINONE.
analogous to the ones given just now, only wc have to start from methylthiophene under oxidizing conditions. I n relation to the arbitrary abstraction of H,S and of COS, we must not forget that we work in the presence of lead and of available oxygen, and that 1 only assume, that the elements which can form those two compounds are taken away, so as to form finally water, carbon dioxide and lead sulphate. The decisive experiment which I propose, is to condnct thiophenaldehyde (or methylthiophene) over fused lead or lead oxide, a t it gentle heat, perhaps also over mercuric oxide, and only if that experiment should not produce anthraquinone, to take lead chromate. But here I must suggest an important consideration. 17aterniediate products have always been of great weight in the study of t h e formation of aromatic nuclei. I merely instance phorone and mesityloxide in the formation of mesitylene from acetone, as one example.' I have thought, that it might lead more easily to the point, if the possibility of formation of intermediate products were considered also in this case. One such product for example, could be formed from t w o molecules of thiophenaldehyde, from which the elements of one mol. H9S and of one mol. COS would be eliminated. Fig. 6 indicates, in a 1
Mesityloxide Two mols. of acetone minus one mol. of water = --___ C,H,oO HHH HHH HH HH c, C
cI o I
I
co I
-
7'/7 C
I
co I
C C C C H8 H* H* H* One mol. of mesityloxide plus one mol. of acetone minus one mol. of Phorone water = -- (see also KekulB, Ber. 2, 368). C,H,,O
36
OS THE
FORMIATICIX O F A X T H R A Q U I S O N E .
manner perfectly malogous to that of Fig. *? how this eliniination might be supposed to take effect.
FI0.6 H
The remaining rcsidues ;ire showii 111 Fig. 7 w i t h the free valencies indicated b y dotted lines, ~vliilc in Fig. S those yalencies are mutually saturated :
FIB. 8
F10.7
H
"P
H
/c
,;
C H
,
Hc\;
'
C
Ha,.
I
II
1I
'
rC II
H C/\c
c-,,
*
co
Hc\
:
C
/"\ /CH co
H
4
hIe\itylene One mol. of Phorone minus one mol. of ~ \ n t e r=C,H,(CH,), H II H H H HH H 4' c /c c __
11
c" I
L
, c / / cco I
1
=
cI1 I
J/I
(
