Dicycloheptatrienyl (Ditropyl) Ether .-A
solution of 0.420
g . (0.0025 mole) of cycloheptatrienylium bromide in 2 ml.
of water ivas treated \vith 2 i d . of 2 sodium bicarbonate solutioii. Curbon dioxide vigorously cvolved. The resultirig turbid mixture w t s c s t r x t e d w i t h four 10-1111, portions of pentaue, the peiitaiie extract dried over magnesium sulfate a n d solvent distilled. T h e residue was cvaporatively distilled a t 100-110" a t 0.5 inm. t o give the ether as a11 allnoit colorless oil, 0.103 g. (81yo), i i Y j 1.5735. ~
The ether is stable when stored under nitrogen a t low tcittpcratures but s l o d y clarkeiis O I I stnnriirig a t room tern])c%!turc. A solutioii of 0.030 g . of thc ether ill 0 . 5 inl. of :ibsolute
[COXTRIIWTIOY
ethanol gives an immediate yellow crystalline precipitate of cycloheptatrienylium bromide when treated with dry hl-drogen bromide, 0.060 g. (77%), m.p. 203" dec., 1111changcd i n admixture with the authentic material. 7-Methoxycyclohepta[1,3,5] triene (Tropyl Methyl Ether) .--To a solution of 0.513 g. of cycloheptatricnyl bromide it1 10 i d . of absolute methanol, an cxcess of methariolic sodium methoxide was added. The colorless mixture was diluted with 25 ml. of water and extracted with four IO-m!. portions of pentane. Distillaticti of the sclr nnd ~aporati,Jedistillationof the rrsiduc gave the cthtv :I colorless somewhat mobile liquid. Calcd. for CuNloO: C , 78.6; 1-1, 8 . 3 ; r ~ l ) l l ~ ~ ~ l : c, 11.0; €1, 8.2. KAITIXAII, Nrsn YORK
/rial.
FROM THE CHEMISTRY D R P A R T M E s r , UNIVERSITY O F BIRMINGHAM]
Studies of Trifluoroacetic Acid. Part X.l The Mechanisms of Syntheses Effected by Solutions of Oxyacids in Trifluoroacetic Anhydride2 T:Y
E. J.
BOVRNF,
J. E. 13.
i r . SIW E Y ,
IIANDLES, ITFCEIVED
DFCBMIIER
J. C. TzirI,on. .\ND J 11.TEDDER
'51, i ~ m
It is postuhted t h a t xhcn a cnrbosylic acid ( R ,CO,H) is tiissolved i n trifluoroacetic :tnhytlridc, otic of- the coiiipweiits of the cquilibriutn mixture is the unsymmetric anhydride ( K ~ C O ~ O ~ C O ~ Cwhich F , ) , ionizes to a small extent into t h e acyiiuni cation ( N . C O -) and the trifluoroncetate ailioll. I t is suggcstetl tllat, i n spite of its sins11 concentration, the reactivity of this cation is sufiiciently great for it t o he responsible for the known ability of such a mixture t o promote syntheses of estcrs arid of arotnatic ketones. The reactions of solutions of inorganic oqacitlh i n t ?iitluoroacetic :tnhytlritlc arc csp1:iinctl 4iniI:xrly.
Previous papers in this series"-" have described syntheses which can be effected with mixtures of oxyacids and trifluoroacetic anhydride. The present communication deals with the mechanisms of these reactions, which hitherto have been discussed ctnly briefly.' SVe believe that, when a carboxylic acid is dissolved in trifluoroacetic anhydride, the following inter-related equilibria arc established (X = Ii C O ) s.011 T ( c F : ; . C O ) L O qI?
+
sococr::; + ci'I.co.rI
S ~ O ~ C O ~ C I ; S.0I-I ,
XJO
+ (CF..CO~l,O
S1O
+ CI~;C0.H
(1)
(2)
2s~O.co.cI:., ( 3 )
Rquilibriuni 3 is necessarily contiiixictl in the other two equations. 111addition, a sinal1 degree of ionization of the unsymnietric anhydride into X + and CFa.C02- is postulated. lye coiisider that the formation of an acyl trifluoroacetate is favored by equilibria 1 , 2 and :j and that the acyliuln catioii (I< CO-)is the principd acylnting agent. 'The trifluoroacetic acid liberated prohiibly assists t!ie acylation process. .I
1 1 ) I ' a r i I T . J. 1;. I3 l < : ~ n d l e J~ , C . T a t l o w nncl .T 11. T?ddcr. ( ' l : e , n .YO< , ,436 11 f t h i i 1r:iper \\-:is prevntecl :It t h e X I I t l i I n t e r f Turc, a n d AI>i>lic,dChcini-,try, \ 7 t ~ ~ York, ~ T. \' ,
, \ i S t ; i c e y , 1 i' ' ? : i i l ~ : i l~ i ~ i 1 3r 'l'cd
