INTERACTION OF BROMINE WITH TETRAPHENYLETHYLENES
March 5 , 1952 m
1171
From the theoretical standpoint, the point of attack of the azide ion on styrene oxide is of considerable interest. Attack at the secondary carbon of styrene oxide is clearly indicated. Considering the fact that as a linear structure the azide ion probably possesses only relatively small steric requirements, this fact is in line with the observations of other investigatorsl8 on the position of attack of less bulky anions on styrene oxide. Additional work on this interesting epoxide reaction is now in progress in these laboratories.
IX m
(18) See D. Swern, G. N. Billen a n d H. B. Knight, THISJ O U R N A L , 71, 1152 (1949); C. C. Guss, ibid., 71, 3460 (1949).
X
LAWRENCE, KANSAS
[CONTRIBUTION FROM THE
DEPARTMENT OF
RECEIVED AUGUST8, 1961
CHEMISTRY, STATE UNIVERSITY O F IOWA]
The Interaction of Bromine with Substituted Tetraphenylethylenesl BY ROBERTE. BUCKLESAND NORMAN A. MEINHARDT The electrical conductivities of methylene chloride solutions containing bromine and various substituted tetraphenylethylenes have been measured. A comparison has been made with the conductivity of tetrabutylammonium iodide in the same solvent. Tetraphenylethylenes with methoxyl or dimethylamino groups in at least two of the para positions gave highly colored solutions, which had molar conductances of the same order of magnitude as the ionic ammonium salt. Tetraphenylethylenes substituted with halogen or phenyl groups in the para positions had lower molar conductances on interaction with bromine, but the complexes formed still showed definite ionic character. Lowering the temperature in most case5 increased the conductance of the solutions. This behavior roughly paralleled the qualitative observation of the amount of complex present based on changes in color.
Some sort of ionic complex formed by the interaction of an aromatic compound or an olefin with a halogen is generally considered as an intermediate in aromatic substitution or olefin addition reactions.2 Several recent studies have yielded conclusive spectrophotometric evidence that certain simple aromatic compounds form 1 : 1 complexes with i ~ d i n ebromine4 ,~ and iodine ~ h l o r i d e . ~Possible structures for such complexes as well as those formed by halogens with oxygen-containing solvents known to give brown solutions with iodine have been extensively discussed recently.6 The general structure of the complex appears to involve the aromatic ring (or the oxygen or nitrogen of the “brown” solvents) as a source of electronsa base according to the generalized concept-for bonding to the halogen which is somewhat electron deficient, ;.e., acidic. The two halogen atoms can be represented in equivalent positions with respect to the aromatic compound as in the resonance hybrid (I) or the partial bond structure (11) in which A is a complexing compound
Ai X ‘
scf
A+/
X X-
X
++ A 1
X
b(+)A:,
,y -1 I
‘X6( - ) I1
I Analogous to I and I1 are I11 and IV in which the halogen atoms have assumed non-equivalent positions (1) From the Ph.D. Thesis of Norman A. Meinhardt. (2) C. C. Price, “Mechanisms of Reactions of Carbon-Carbon Double Bonds,” Interscience Publishers, Inc., New York, N. Y., 1946, Chap. 2. (3) J. H. Hildebrand and IT. A. Benesi, Tms J O U R N A L , 7 0 , 2382 (1948): 71, 2703 (1949). (4) R. M. Keefer and L. J. Andrews, ibid., 71, 4677 (1950). ( 5 ) R. M. Keefer and L. J. Andrews, ibid., 71, 5170 (1950). (6) R. S. Mulliken, ibid.. 71, 600 (1950).
A’-XX-
++ A X-X 111
AG(+)----X----XS(-) IV
A third possibility is that the complex formation involves a heteropolar dissociation of the halogen. In the relatively non-polar solvents usually used for the preparation of such complexes the ions formed would be expected to be associated as ion pairs, triple ions and higher ion aggregates.’ AX+
+ X-
AX+X-, etc.
Such a complex in the case of the action of iodine on pyridine has been shown to be ionic by electrical conductance,8 to involve the PyI + ion by comparison of its absorption spectrum with those of other PyI+ and to be formed by a rapid equilibrium from iodine and pyridine by the rapid exchange of radioactive iodine with various PyIf salts in pyridine. lo In the case of the more complex aroniaticolefin systems of highly arylated ethylenes evidence for ionic complexes with halogens has been presented.” A number of such compounds both substituted tetraphenylethy1enes1la and substituted unsym-diphenylethylenes,llblC interacted with halogen to give highly colored, salt-like solids containing varying amounts of halogen depending on the nature of the ethylene and the identity of the halogen. The structures suggested” for the saltlike complexes were stable carbonium ions associ(7) R. M. Fuoss, Chem. R e v s , 17, 27 (1935). (8) L. F. Audrieth and E. J. Birr, THIS J O U R N A L , 16, 668 (1933). (9) R. A. Zingaro, C. A. VanderWerf and J. Kleinberg, ibid., 7.3, 88 (1951). (10) J. Kleinberg. ibid.. 7.3, 1865 (1951). (11) (a) R. Wizinger a n d J. Fontaine. Bcr., 60, 1377 (1927): (b) P. Pfeiffer and R. Wizinger, A n n . , 461, 132 (1928); (c) P. Pfeiffer a n d P. Schneider, J . 9rakt. Chem., 119, 129 (1931).
KOBERTE. BUCKLESAND NORMAN A. MEINHARDT
1172
VOl. 74
showed that interaction with excess bromine gave rise to complexes of varying composition. In carbon tetrachloride a t room temperature a light (Ar2C-CAr2)++2Br3 atid (ArX -CH,Br) +Brred, granular solid, which appeared to contain three Compounds which gave stable complexes of these bromine atoms per molecule of ethylene, was obtypes had groups, such as the dimethylamino tained. At 10' a n orange-red precipitate with five group, which are capable of assuming the positive bromine atoms per ethylene was isolated. Both charge or of complexing with halogens themselves, of these products gave blood red aqueous solutions substituted in some of the para positions. which had molar conductance-concentration relaA different point of view was presented12 con- tionships characteristic of strong electrolytes. cerning complexes formed in the reactions between Treatment of solid V with bromine vapor gave a bromine and tetraphenylethylenes substituted in black liquid which on standing lost bromine to give the para positions with phenyl groups or halogens. a brittle, black solid containing from ten to eleven I n these cases, complex formation was observed bromine atoms per olefin molecule. This solid only by color changes as the solution was cooled to was water insoluble but gave moderately stable, Dry Ice-bath temperature. It was found that red solutions in aqueous acetone which had elec6 s ; and trans isomers underwent no isomerization trical conductivity behavior characteristic of a as a result of the reversible reaction of complex strong electrolyte. formation. On the basis of these results the ionic Pursuant to the results of Bockemiiller and types of structures were discounted but no clearly JanssenI2 conductance measurements were carried defined alternatives were presented. out on eight tetraphenylethylenes in methylene The present work is concerned with establishing chloride containing bromine. Methylene chloride the ionic character of the complexes formed when though not very polar in character was a suitable tetraphenylethylenes, substituted in the para posi- solvent for the complexes. The dielectric constant tion with methoxyl, dimethylamino, halogen and of the solvent is sufficiently high (8.3 a t 17-19°),13 phenyl groups, interacted with bromine. to give appreciable conductance values with electrolytes. The relatively low m.p. (-96.7") of Discussion of Results methylene chloride also made i t particularly suitPreliminary experiments with 1,?-bis-ip-di- able for measurements down to Dry Ice-bath (V) temperatures. methylaminophenyl) -1 ,?-diphenylethylene The presence of either bromine or one of the tetraphenylethylenes in solution did not appreciably increase the specific conductance of the pure ohm-'). Measursolvent (less than 2.98 X able conductances were observed when both bromine and one of the ethylenes were present in 60 solution. The effect on the.molar conductance of the number of bromine atoms per ethylene molecule i v is shown in Fig. 1. Up to a point increasing the * relative amount of bromine increased the concentray tion of the conducting species. I n each case a =' 4.0 bromine-ethylene ratio was reached beyond which 3 J the molar conductance remained relatively cona stant or was actually decreased. From the results C shown in Fig. 1 convenient bromine-ethylene 2 ratios were chosen for measurements of conductances a t various temperatures and a t various 2.0 concentrations. The relative amount of bromine which leads to a maximum conductance value in any given case is that amount which gives the most favorable formation of conducting species by way of the several equilibria of complex formation and of ion apgregate dissociation.7 Any attempt to interpret the 10 20 data in terms of composition of the complex or Bromine atoms per molecule of olefin complexes is not warranted without more data, e.g. Fig 1 -The dependence of the molar conductaiicc of the tetraphenylethylenes in methylene chloride on the rela- a spectroscopic study of the complex formation. The dependence of molar conductance on temtive amount of bromine present a t -78". 0, 0 01 Itf transperature is shown in Fig. 2 for those ethylenes which 1,2-bis-(4-biphe1iyly1)-1,2-diphenylethyle11e (\'HI), 9, 0 0026 M and @, 0 01 df 1,2-bis-(p-dimethylaminophenyl)- formed complexes with conductivities of the same 1,2-diphenylethylene ( V ) , @, 0 0025 Af 1,2-bis-(p-dimethyl- order of magnitude as that of tetrabutylamnionium ~rninophenyl)-1,2-his-(p-methouyphenyl)-ethyIene ( V I ) ; 0 , iodide, ;I strong electrolyte in polar solvents. i~OV2.5 A 4 1,2-bis (p-rriethoxyphenyl)-l,2-diphetlylethylet~e'Those complexes with conductivities of somewhat (1'11) lower values are given in Fig. 3. In all cases, the ated with chloride, triiodide or tribromide ions such as
i
#
12) \'i
U ~ ~ ~ L ~ I I i~l l cUl IKI Ui,rllS5ell
IW
5.41, I M , i ( w )
:,';! 1'
\\':al,IC==)2 (VII) Bromine red Deep blue temperature (as shown by the quaternary ammonium salt) is counteracted by the increase, in the p-CsHsCsH4 amount of ionic complex a t the lower temperaC= 2 (VIII) Bromine red Olive green tures. GH) The variation of molar conductance with the P-ClCsHa square root of the concentration is shown in Figs. 4 (IX) Bromine red Red violet and 5 and in Table 11. I n Fig. 4 and Table I1 C.H)C=)' the complexes with higher conductances are compared with tetrabutylammonium iodide P-C1CsH4>C=)2 (X) Bromine red Red violet while in Fig. 5 those with lower conductances are P-BrCsHa
(
( ( ( (
)
ICOUEKT
E. BVCKLES
AND
NORMAN A. ME1NHARL)T
VOI. 74
5
10
di x
102. Fig. 5.-The dependence of molar conductance (based I I on the olefin) on the concentration of bromine-olefin com10 '0 plex in methylene chloride a t -78" (mole ratio of bromine to dc x 102. olefin = 11): 0, cis-1,2-bis-(p-chlorophenyl)-l,2-diphenylFig 4.-The dependence of molar conductance (based ethylene (IX);@, trans-l,2-bis-(~-chlorophenyl)-1,2-diphenyl011 the olefin) on the concentration of bromine-olefin comethylene (IX); a, 1,2-bis-(p-chlorophenyl)-l,Z-bis-(pplexes in methylene chloride at 78' (mole ratio of bromine bromophenyl)-ethylene ( X ); e, cis- 1 ,Z-bis-(4-biphenylylj- 1, to olefin = 2.5): 9, 1,2-bis-(p-dimethylaminophenyl)-1,2-diphenylethylene ( V I I I ) ; 8 , Irans-1,2-bis-(4-biphenylyl)diphenylethylene (V); e , l,2-bis-( p-dimethylaminopheny1)- 1,2-diphenylethylene (V I1I ) , 1,2-bis-(p-methoxypheny1)-ethylene (VI); 0 , 1,2-bis-(p:nethoxqphenyl)-1,2-diphenylethylene (VII). The results are compared with 0, tetrabutylammoniurn iodide. TABLE 11 7
-
given. The results show the characteristic behavior of electrolytes in solvents of low dielectric constant.14 Association into ion pairs would be important even a t the lowest concentrations represented. The Ostwald dilution function (equations (1) and (2)) would apply only approximately to these lowest concentrations. In fact, most of the points on the curves were obtained a t concentrations above the critical concentration (about JI in methylene chloride a t 25') where the conductance equation corrected for long range interionic interactions (equation (3)) would not hold.' ,4t higher concentrations ion aggregates such as triple ions and quadrupoles would become increasingly important and be responsible for the presence o f iiiinirna arid maxima in some of the curves.
.
.i = a(AO
- /-)
(3)'j
(14) I t has been pointed o u t b y the referee t h a t t h e f a r t t h a t c o t ~ pound V I 1 behaves differently from Compounds V a n d V I hoth when concentration is varied (Fig. 4) a n d when temperature is varied (Fig. 2) might conceivably be related t o t h e fact t h a t t h e bromine-olefin ratio i n thc case of VI1 is significantly lowpr than t h a t shown to give maxiw u n i Cwnductance i n I:lg 1. 13) A-is t h e rIis>oci;rtiun constant of ion pairs going irito ions, A is tlic equivalent conductmicc, .io is the eqiiivalent coiidnctance a t intinitr ililutioii, c is the coiiceritratioii. n is t h c rlcgree of dissociation and A is thc Onsager coefficient
I)ILUTION DATAFOR FIG 4 hlolar Conductance i
t' C
x
102
(?t-BU),N
...
V
VI
VI1
...
4.05
...
.. 4 , 43
17.1 14.1
3.84
1.88 1.93
12.2
...
21.3
...
10.0 8.66 7.10 6.13
4.71 ... 3. :j9
...
2.73
..
2.66 ,.. 3.40
...
6.30
5 . 00
6.52
,..
4 33 3.54
...
3.90 ... 5.12
, . .
s.52
2 . 79
...
...
5.8,i
3.99 ... 4 . 90
3.12
...
2.30
10.4
...
... li.50
2.16 1 .i 7 1. 5-i 1 .53 1 . ox
...
6.52
...
13.3 ...
8.01
1G.9
...
...
8.35 ...
9.95
10.1 ...
...
12.9
11.8
..
21.3
...
14.8
...
14.6
...
...
22.6 ..
0.88
19 , 3
,77 '63 .51
...
44
...
.:Is . :i 1
...
,27 .I9
...
)..
18.3 20.7
, . .
...
. . .
..
. . ... . .
..
.
6.22 .. 4.3s ...
3.72 ... 4.06 ...
4 . 73 ..
3.32 ... .. 7.R ... GO
!7.
14.6
March 5, 1952
INTERACTION OF
BROMINE WITH TETRAPHENYLETHYLENES
Even a t the lowest concentrations the application7vl6of such equations to the calculation of dissociation constants cannot be applied in the present case. The equilibria of complex formation must first be studied separately, and the relationship of molar conductance to equivalent conductance of the complex must be determined.
1175
biphenylyl-(dich1oro)-phenylmethane with copper.22 The separation of isomers was effected by crystallization. The isomer, presumed t o be trans, had m.p. 252', that presumed t o be cis, 219'.
1,2-Bis-(p-chlorophenyl)-1,2-bis-(p-bromophenyl)-ethyl-
ene (X).-The compound was prepared by the reaction of p bromophenyl-(P-chloropheny1)-dichloromethane with copper.'* The m.p. was 231.5'. As previously found only one isomer was isolated. Methylene Chloride.-Commercial methylene chloride Experimental was waihed with aqueous sodium thiosulfate followed by 1,P-Bis-(p-dimethylaminopheny1)- 1,2-diphenylethylene aqueous sodium carbonate and then dried over phosphorus pentoxide. The liquid was distilled from fresh phosphorus (IV).-The bimolecular reduction of p-dimethylaminobenpentoxide through an efficient fractionating column. The zophenone17~with tin and hydrochloric acid in the c0ld"b gave rise t o a product very difficult t o purify. Adsorption product used had b.p. 39.5' (730 mm.). Solid Complexes of Bromine with 1,2-Bis-(p-dimethylon activated alumina was used as the method of removing impurities from the chloroform solution of the ethylene. aminophenyl)-l,2-diphenylethylene(V).-A solution of 2.0 The crystallization of the product was brought about by the g. of V in 1100 ml. of carbon tetrachloride containing 2.0 g. washed free addition of absolute alcohol to the chloroform solution. of bromine gave a black precipitate which was The result was After several such adsorption-crystallization treatments a of excess bromine by carbon tetrachloride. sample of the ethylene V of m.p. 225018 was obtained. 3.27 g. of light red, granular product. It gave stable, bloodred aqueous solutions. In acetone, chloroform or acetoThe only contaminating compound isolated was the glycol, nitrile the blood-red solutions obtained quickly decolorized 1,2-bis-(p-dim~thylaminophenyl)-l,2-diphenyl-l,2-ethanediol, m.p. 253 No geometric isomer of V could be to light yellow. Anal. Calcd. for CooHaoNzBr~:Br, 36.5. Found: Br, found. 1,2-Bis-(p-dimethylaminophenyl)-l,2-bis-(p-methoxy- 36.9. phenyl)-ethylene (VI).-In a method entirely analogous t o In a similar preparation carried out a t 10'C. 3.61 g. of an the synthesis of V above, 21 g. of P-methoxy-p'-dimethylorange-red product was obtained. Its solubility behavior aminobenz~phenone~~ was reduced to give 1.0 g. (5%) of was similar to that of the first preparation. the hitherto unreported ethylene VI of m.p. 217-218". Anal. Calcd. for CsoH~oNBr~:Br, 48.9. Found: Br, Only one isomer was obtained. 48.9. Anal. Calcd. for C ~ Z H ~ ~ N C, ~ O80.1; Z: H , 7.16; N, When 1.0 g. of V was kept in the presence of excess bro5.85. Found: C, 79.6; H , 7.07; N, 5.67. mine vapor for five hours, a black liquid was obtained. This 1,2-Bis-(p-methoxyphenyl)-l,2-diphenylethylene(VII).-liquid was subjected t o evaporation under reduced pressure A solution of 76 g. (0.36 mole) of p-methoxybenzophenone20 to remove excess bromine. A brittle, black solid resulted. and 75 g. of phosphorus pentachloride in 200 ml. of benzene The powdered solid was kept over solid potassium hydroxide was boiled under reflux for eight hours. All of the volatile and it gradually lightened to a red-brown color. Except solvent and by-products were removed by distillation under that it was insoluble in water this product behaved as the reduced pressure. The residue was dissolved in 200 ml. of others in solution. benzene and 200 g. of copper powder was added. The Anal. ,Calcd. for C~HaoN2Brlo: Br, 65.6. Calcd. for mixture was boiled under reflux for 12 hours. The reaction C80HaoN2Brll: Br, 67.7. Found: Br, 66.9. mixture was filtered and the filter cake washed with hot The fist two preparations in water and the third in 50% benzene. After evaporation of the benzene solution t o dryness the residue was crystallized from 95% alcohol to give aqueous acetone gave solutions for which the plots of molar 22 g. (31%) of impure product, m.p. 153-173'. Crystalli- conductance vs. the square root of the concentration were zation from chloroform-alcohol followed by crystallization essentially linear with negative slopes. Conductance Measurements.-Measurements were made from glacial acetic acid yielded VI1 of m.p. 185187'. in a glass cell with square platinum electrodes separated by Only one isomer was isolated. glass rods fused to the platinum. The electrodes were Anal. Calcd. for Cz8H24Og: C, 85.6; H , 6.16. Found: carefully platinized. The cell constant was determined t," C, 85.0; H , 5.97. be 0.268 with 0.1 N aqueous potassium chloride a t 20 . The only synthesis reporteds' for this compound was the A Leeds and Northrup Wheatstone bridge was used with a acid-catalyzed rearrangement of 2,2-bis-(p-methoxyphenyl)- General Radio, type 13, 1000 cycle audio oscillator. The 1,a-diphenylethanol. , No proof of structure was given. cell was cooled in Dry Ice-acetone-bath in a dewar flask. The m.p. was 191-192'. The ethylene dissolved in methylene chloride was introcis- and trans- 1,2-Bis-(p-chlorophenyl)-l,2-diphenylethyl- duced into a volumetric flask. The flask was cooled to ene (IX).-Dichloro-(p-chloropheny1)-phenylmethane was -78' and the desired amount of standard bromine in methtreated with copper to give a mixture of the two isomers of ylene chloride was added. The solution was made up to IX." Separation by crystallization alone was not satis- volume with additional methylene chloride. The cold factory. A combination of adsorption on active alumina and solution was transferred to the cell and conductance meascrystallization from chloroform-alcohol yielded the high urements were carried out at -78' in the Dry Ice-bath. m.p. isomer, presumably trans, of m.p. 205'. The low Determinations a t other temperatures were carried out in m.p. isomer was obtained with m.p. 157-158' which does baths of intermediate temperatures. Above -55' the temnot agree with the reported m.p. of 179°.*2 perature was measured with an alcohol thermometer. The A&. Calcd. for C26Hl8C12: C, 78.0; H , 4.52. Found: concentrations were corrected for the expansion accompanying the increase in temperature of the solution. The reC, 77.9; H , 4.48. cis- and trans-l,2-Bjs-(4-biphenyl)-I,2-diphenylethylene versibility of the temperature effect was demonstrated by (VIII).-The isomers were prepared by the reaction of 4- the fact that the same curves were obtained on cooling down Conductancet o -78' as on warming up from -78". (16) C. A. Kraus and W. C. Bray, THISJOURNAL, 36, 1315 concentration measurements were run in duplicate to insure the reproducibility of the curves. (1913). The specific conductance of pure methylene chloride was (17) (a) C. D. Hurd and C. N. Webb, "Organic Syntheses," Coll. No appreVol. 1, John Wiley and Sons, Inc., New York, N. Y.,1941, p. 217; determined to be less than 2.95 X 10-8 ohm-1. ciable change was noted when either one of the ethylenes or (b) R.Willstiitter and M.Goldmann, Bcr., 89,3765 (1906). bromine was dissolved in the solvent. (18) All m.p.'s corrected. (19) German Patent 295,495,Chcm. Zcnlr., 88,I, 150 (1917). IOWA CITY,IOWA RECEIVED AUGUST24, 1951
.
(20) C.Hell and H. Stockmayer, Ber.. 31, 225 (1904). (21) J. Levy, Bull. SUC. chim.. 141 19, 895 (1921).
(22) W.Schlenk and E. Bergmann, A n n . , CSS, 119 (1928).
