[CUNTKIl3U'I'ION
FKOM THE
DEPARTlfEYr O F CHERIISTKI., USIVEKSITY
OF CALIFOKXIA,
l>AVIS]
A Study of the Proximity Effects of Substituents on the Dissociation of Iodobenzene Dichlorides BY I. with gas c\--i,lutioii at roo111 tenipcrnturc t o form ii hrou-n oil. S o attempt \ w s i i ~ x l e It t i ) obtain an equivalent wciglit o i i this iiiatcri:tl. :tl\vays dissolved in acetic acid iminetliately after its prejiit '' IC tion, a n d tiif solutions \vcre analyzed iodometric~illy. 1 other freslily prepared dichltirides generally Iiad equivalciii weights ( a s determinecl ii~tlometric:ill!.) wliich agrcctl 111 within 1.5;; of the tlieorctical v:tluc. Soiiie tlilliculty \ v i 1 5 experienced in prep;tring saiiir if t h e 2-iodci-1 ,~j-dinietIi~~lbenzene derivative whieh had ptable equi\-alcnt ~\-c.iglits. The o-Iodobenzoic Acid Derivative.. mixture of 1 .O g . o f o-iodobenzoic acid aiid 20 i d . of ~iitroiiietliancw i t s hntur a t e d with chlorine. The white solid phase changed t o vellow crystalline inaterial iiverniglit . T h e crystals were filtered, waslied with carhim tetrachloride arid air-dried. In air this dried solid c\nl\-ed a noxious gas rapidly and fatleti t o a light yellow pnwtlcr (later described a s coinpound 11). This inaterial niclteti frmii 168--171°, and the melting poiiit \vas substantial1~-depressed by added o-iodobenzoic acid. T h e equivalent weight, as determined by dissolving a weighed sample in acetic acid, xiding aqueous potassiuni -A\
~~
.I
.
~
~
.
~
~
I I i f b c r , f : , , i . , 43, ???!I 1 i 1 C ' . \ ! ' i l l ~ c , i n ~ c I l , i h r r l , 27, 3 1 1 ( l X ! t t ) , r h j I i' Niclic,l , t i i < l I < l j S . l i i < l i i i 'I i i i y 1 1 (lij
S c l i i i i i i l l i i ~itiiil
\I
fl'i10)
X a y 20, 1039
2873
DISSOCIATIOX OF IODOBENZENE DICHLORIDES
iodide and titrating t h e liberated halogen with standard sodium thiosulfate, was 142.3; calcd. for CiH402ClI: 141.2. T h a t I1 did not contain a free carboxyl group was established by treating a weighed sample with dilute aqueous potassium iodide. T h e material dissolved completely, whereas aromatic carboxylic acids are generally water insoluble. T h e resultant solution was decolorized b y dropwise addition of dilute sodium thiosulfate solution and was then titrated with standard sodium hydroxide solution. The results indicated a n esperimental equivalent weight for the unknown as a carboxylic acid of about 7000. On acidification of the titrated solution o-iodobenzoic acid, m . p . and mixed m . p . with an authentic sample 162-163", was precipitated. X weighed sample of I1 was dissolved in dilute potassium hydroxide solution t o liberate chloride ion. The solution was acidified with dilute nitric acid. T h e white precipitate which formed was filtered and dried. It did riot melt when heated t o 210' and was undoubtedly the compound0
TABLE I ExrINCTIOX COEFPICIENTS O F THE I O D O THE DICHLORIDES ArI"
h,mp
C o M P O U N D S AND
(iLi
o-Iodotoluene 380 0 05 o-Chloroiodobeiizeiie 370 .15 o-Iodobiphenyl 370 34 424 .13 1-Iodonaphthalene 2-Iodonaphthalene 410 .37 2-1odo-1,3-dimethylbenzei1e 380 80 2-Iodo-1,4-diniethylbenzene 380 .oti o-Iodobiplieny15 380 34 Except as noted t h e solvent was acetic acid. vent was nitromethane.
€\rlCI2
74.3 10; 193
83.0: 14,5 8h. 1 107.5 138 T h e sol-
centrations, evaluated spectrophotometrically, of solutions which initially contained only the dichloride as a solute. The compounds for which data are reported include several o-substituted iodobenzene dichlorides and the corresponding m- or p isomers as well "iodonaphthalene dichloride and I t was iiot further investigated. The chlorine cnntent of t h e its potentially hindered (by the peri hydrogen atom) original sample was established by gravimetric analysis of thc filtrate. Calcd. for CiH401C11: C1, 12.54. Found: isomer, 1-iodonaphthalene dichloride. The electronic effects of methyl and chloro subc1, 12.49. The Kinetic Measurements.-The general methods for stituents on the stability of iodobenzene dichloride establishing t h e equilibrium and rate constants (equation 1) in acetic acid are opposite. The p-methyl derivaby spectrophotometric methods have been described in detive has a somewhat smaller and the m-chloro derivtail in t h e previous p ~ b l i c a t i o n s . ~ ~A ~ ~modification '0 of ative a considerably larger dissociation constant earlier procedures, which proved useful in determining klvalues in t h e present study, was based on the observation than the parent compound. Since the degree of t h a t pentamethylbenzene reacts very rapidly with free chlodichloride dissociation is enhanced as either p rine in acetic acid solution b u t does not react directly with iodobenzene dichloride.ll Thus, although the degree of dis- methyl or m-chloro substituents are moved to osociation of some of t h e dichlorides under investigation is positions (as is also the case when nitromethane is low in acetic acid solution, in t h e presence of a n excess of the solvent4), it would appear offhand that o-subpentamethylbenzene complete dissociation occurs since the stituents have an unfavorable proximity effect. chlorine is consumed as rapidly as i t is formed. However the differences in K-values for the 0- and For runs in which the dichloride in question and pentainethylbenzene mere the starting materials, rate constants $-methyl derivatives and for the o- and m-chloro ( k , ) were evaluated from optical densities measured during isomers are much smaller than would be anticipated the course of t h e reactions assuming t h e rate law were it essential for maximum stabilization of the -d[CsH(CHa)j]/dt = -d(ArICL)/dt = ki(ArIC12) ( 2 ) dichloride that the linear trihalide grouping lie parI n general these runs were conducted a t concentration levels allel to the aromatic ring plane. d consideration of and at n a v e lengths such t h a t t h e free iodo compounds and molecular models indicates that hindrance to such tlie peiitainethylbenzene did not show appreciable light an arrangement by o-substituents would be intense. allsol-ptiou. T h e reactions were carried t o completion and Furthermore o-iodobiphenyl dichloride in which the t h c measured optical densities were corrected for small final readings, which presumably were characteristic of chlorine- hindrance problem might be acute actually has a containing reaction products, before ratc constants were smaller dissociation constant in acetic acid than the calculated. I n a few cases in which t h e dichloride disso- p-isomer. I n nitroinethane the constants for thc ciated suficiently so t h a t kl-values could be determined with two substances are very similar in magnitude. The rcnsunahle accuracy without addcd pentamethylbenzene, rate constants were obtained both in the presence and ab- differences in IC-values for the 1- and 2-iodonaphsence of t h e :u-ornatic hydrocarbon. T h e values obtained thalene derivatives in acetic acid are also minor. by t h e two procetlures agreed reasonably well with each Perhaps most indicative of the intensity of dichloothcr . ride stability to proximity effects is the fact that .is iii t h c previous iiivcstigatioiis tlic optical measurethe dissociation constants of 2-iodo-lj3-diinethylitleiits to deteriiiinc rate and equilibrium constants were in;tdc a t witve lengths ( : i i i f ) - l X in^ region) in which the dibenzene dichloride and 2-iodo-l,4-diniethylbenzenc chloritlcs :il)sorbed stroiigly. Typical estiiictiori cuclliciciits dichloride in acetic acid are of the same general orfor tlic i i d o c o t i i ~ ~ ~ ~ uatni d sfor tlieir dicliloritlcs it1 acetic der of magnitude. For reactions which are subacid aiid in iiitronietliane wliich wcre found useful and which ject to steric influences of o-substituents the effects have uot been reported earlier are given in Table I . generally are vastly magnified when the reaction Results site is flanked by ring substituents.'? The Equilibrium Constants.-Table I1 sumThe Rate Constants.-There is an abundance of marizes the results of experiments conducted to e ~ i d e n c e ~which , ~ , ' ~ indicates that in a polar medetermine K-values. Except as noted, the reported dium solvent molecules must make a significant constants were calculated from equilibrium con- structural contribution to the activated complex (9) (a) C . Willgerodt, J. Pi'akt. Chetii., 49, -176 (1894); (b) V. Meyer separating an iodobenzene dichloride and its dissoa n d W. W a c h t e r , ibid., 26, 2632 (1892); V. Meyer and P. Askenasy, ciation products. Therefore a substituent neighBe?., 26, 1337 (1893). (11)) 1,. ( 1 !I.%).
T. hnilrews
;tti
T.4BLE Iv THERMODYNAMIC CONSTAXTS FOR FORMATION AND D~ssocrA T I O S PROCESSES
Iodo compound
ARC,
ASO.
kcal./mole
e u.
El, kcal. / mole
-AS',*, e .u .
Acetic acid solvent Iodobenzenen p-Iodotoiuene o-Iodotoluene %Iodo-l,-l.dimethyiben-
7 0 11 8 . 1 = 0 . 5 13 i 2 lj 2 i 1 . 3 7 I j
10.ii 12 20 4 zt 0 . 1 8 . 3 i 1 . 7 I ! J . 5 =t . 5 I l . i i i 1 7
Lene
2 - Iodo-1,8-rlimethglbenzene p-~odobip~ieny~~~ u-iodobiphenyl 9-Iodonaphthalene 1-Iodonaphthalene iib-Chluroi~dw benzene" o-Chloroiodubenzene
Nitroinethane solvent lodubenzene' !I. 8 p-Iodobiphenyl" 10.3 i 1 2 u-Iodobiphenyl 8 5 zt 0 t i
1T 18 i 3 1:3 = 2
12,;
........ . , . . . ...
10
........ . .. .
From ref. 4. From ref. 3 . The values i)f E l aiiti are estimated from kl-valucs tlcterrnined from the known values of K and k,,. \-alucs calculated usitie tlic equilibrium constant a t 25:Oo reported in ref. 4 .11itl t l k t 'it 45.6' reported in Table 111. a
ASl+
tives in nitromethane occurs rather rapidly a t 45', rate constants for reactions of these compounds a t this temperature are q'ot reported in Table 111; however, crude estimates of the kz-values a t 45" were made. Comparison of these values with those a t 25" leads to the conclusion that in nitroinethane the activation energies for the reactions of of the two iodobiphenyls, like those for other iodo compounds, are much smaller than in acetic acid. The Product of Reaction of o-Iodobenzoic Acid and Chlorine.-In connection with the current investigation an attempt to prepare o-iodobenzoic :tcid dichloride was made. The product of reaction of the iodo acid with chlorine in nitromethane
hlay 20, 1959
STEREOISOMERS OF
(presumed to be the dichloride) rapidly evolved a gas in the dry state and changed in crystalline character to form a product which, although it oxidized iodide ion, had a lower iodometric equivalent weight than the theoretical value for iodobenzoic acid dichloride. Because of the instability of the dichloride, plans to study its equilibration with its components were abandoned.
2x79
IO-~IET€IYL-~-DECA\LOL
chloride evolved hydrogen chloride to produce 11.Ya Confirmation of this lactone structure has been obtained through study of the reactions, described below, of I1 in dilute solutions of potassium iodide and sodium hydroxide. Complete details are Ho-l-o, b C = O
c1-1-0
- ,+ w I
i)H- I1
I
coo-
I-
&
y
O
H
\
given in the Experimental section.
O;;&'
Acknowledgment.-The authors are indebted t o ~ 1 behavior , ~ which has been described was the National Science Foundation for a grant in supnoted many years ago and explained without con- port Of this research* firming evidence, on the assumption that the di- DAVIS,CALIF. [CONTRIUUTIOS FROM THE CHEMIC.4L
LABORATORIES O F NORTHIVESTERN
L-NIVERSITT]
The Stereoisomers of lO-Methyl-2-de~alol~~~ BY ROBERTH. BAKER,L. S . MINCKLER AND ALLENS.HUSSEY RECEIVED h-OVEMBER
8, 1958
h n improved synthesis of cis-l0-meth~-l-2-trans-decalol( I ) and the synthesis of the trans-trans isomer (11) of the cis-cis isomer (111) and of the traizs-cis isomer ( 1 x 7 ) by procedures which permit assignment of configuration are reported. -Absorption bands in the infrared spectra of these and related compounds appear t o be diagnostic of the nature of the ring fusion geometry.
Two of the four isomers of 10-methyl-2-decal01 reduction with lithium aluminum hydride. In have been described p r e v i ~ u s l y . ~ - Both ~ of these spite of the nine steps involved, the over-all yield isomers melt in the region of 65-70' a t very nearly of I is 3 5 4 0 % and the product is much less subject the same temperature. The p-nitrobenzoate of to contamination by isomeric impurities. one has been reported to melt a t G5-G7°,5,7 the IVhen compound I, prepared in this way, was 3,5dinitrobenzoates to melt a t 110.G-111.2" and a t converted to its p-toluenesulfonate and the latter 07.5-98.5°.4 The isomer which forms the higher was refluxed with potassium acetate in acetic acid melting 3,5-dinitrobenzoate has been synthesized -acetic anhydride solvent, the epimeric acetate was from a 10-carboxy-2-decal01which forms a l a ~ t o n e . ~formed in 25-30y0 yield. Considerable (ca. 30y0) Also, when oxidized with chromic anhydride, this elimination accompanied the displacement reaction. isomer has furnished 10-rnethyl-2-trans-de~alone.~ Saponification and a chromatographic procedure on It is therefore cis-10-methyl-2-trans-decalol( I j . alumina led to the isolation of trans-10-methyl-2We have found the p-nitrobenzoate derivative trans-decalol (11) m.p. 59.5-90.5". The p-nitroto melt a t 71-73'; hence it would appear to be benzoate and the 3,5-dinitrobenzoate of I1 melted identical with that described by Yanagita and co- a t 153-154" and 122-123", respectively. Thereworker~.~,~ fore the second isomer previously reported4 is While compound I can be prepared in three not the trans-trans isomer 11. steps from 2-methylcyclohexanone by way of 10The synthesis of cis-10-methyl-2-cis-decalol (111) methyl-A1~9-octal-2-one,3~4~7~8 we have come to pre- and of trans-l0-methyl-2-cis-decalol (IVj involved fer the synthetic sequence to 10-methyl-2-trans- the common starting material, 10-hydroxymethyl-2 decalone, as developed by D r e i d i ~ ~followed g,~ by cis-decalone (V)lo as follows: V was converted to its p-toluenesulfonate V I and the latter was (1) Presented, in p a r t , before t h e Division of Organic Chemistry, 129th Meeting of t h e American Chemical Society, Dallas, Texas, reduced with sodium borohydride to a mixture of April 8-13, 1 9 X . the epimeric 10- [p-toluenesulfonoxyniethyl]-2-cis(2) A grant from the Iiezearch Corporation assisted t h e carrying decalol isomers. By way of a fractional crystalo u t of this research. lization procedure, the epimeric p-nitrobenzoates (3) E;. C. d u Feu, F J. hIcQuillen and R . Robinson, J . Cheriz. Sac., 53 (1'337). were separated to furnish 177, of the cis-cis (4) A. S. Husscy, H. P. Liao and R . H. Baker, THISJ O U R N A L , 76, isomer V I 1 and 71% of the trans-cis isomer V I I I . 4727 (1953). See footnote 3 ior t h e naming convention used t o desigThe former melted a t 114-116" and showed no nate t h e geometry of these isomers. depression of melting point when mixed with an ( 5 ) R?. Yanagita and A. T a h a r a , J . Org. Chein., 18: 792 (1953). (6) A. S. Dreiding and .4. J . Tomasewski, THIS JOWKFAI,,77, 168 authentic sample cf V I I , 1n.p. 115-116', from czs(1'355). 10-hydroxymethyl-2-cis-decalol. lo Similarly V I I I , ( 7 ) .\I. Yanngita, I;. Kiamakawa and .4.T a h a r a , J . O r e . Chem., 20, m.p. 161-162", did not depress the melting point 17fi7 (195.5). ( 8 ) See F. D . Gunstune and I
