Feb. 20, 1938
HYDROLYSIS AND DEUTERIUM EXCHANGE OF CHBrzFAND CHFIz
methanol (about 24 hours a t low concentrations of methanol). Tests on Reliability of Extraction Procedure.-Three 10ml. samples of kinetic solution containing 0.1015 M trityl chloride, 0.0984 M pyridine and 0.00884 M methanol were extracted with 10 ml. of water each. The first was extracted once, the second twice successively, and the third three times. The activities of the remaining organic phases were the same within 1.7%, with the highest activity in the third. This test demonstrates the sufficiency of only one extraction when equal volumes of water and sample are used. Single extractions of this same kinetic solution were made using 15-ml. samples with 10- and 5-ml. volumes of water, respectively. The activity of the aqueous phase of the
[COXTRIBUTION FROM
THE SCHOOL O F
s19
second was twice that of the f i s t within experimental error (less than 2%). Methanol, a t a concentration higher than any used kinetically, was shown not to increase the solubility of trityl methyl ether in water. Two samples from run 111 which had been left for 16 days and was calculated t o contain 0.057 M trityl methyl ether were extracted with water alone and with water containing 0.08 11.1methanol. There was no difference in activity between the two aqueous phases: the first gave 15.7 counts per second and the second. 15.3 counts per second. The equivalent initial methanol activity for this run was 3780 counts per second. CAMBRIDGE 39, ~IASSACHUSETTS
CHEMISTRY
O F THE
GEORGIA INSTITUTE O F
TECHNOLOGY]
The Hydrolysis and Deuterium Exchange of Dibromofluoromethane and Fluorodiiodomethane BY JACK HINE,RICHARD BUTTERWORTH AND PAUL B. LANGFORD RECEIVED AUGUST26, 1957 Rate constants and heats and entropies of activation have been determined for the basic hydrolysis and the deuterium exchange of dibromofluoromethane and fluorodiiodomethane in aqueous solution. The hydrolysis of bromodichloromethane and dibromochloromethane also was studied. For all four haloforms the data support the hydrolysis mechanism in which trihalomethyl anions, formed reversibly from haloform and base, decompose to dihalomethylenes, reactive intermediates that react quickly, either with halide ions t o regenerate haloform or with water and alkali to give carbon monoxide or formate ions. The effect of added salts on the rate of the hydrolysis of dibromofluoromethane is compared with their effect on bromodichloromethane and dibromochloromethane in order t o learn how variations in the structure of dihalomethylenes affect the efficiency with which the dihalomethylenes may be captured by halide ions. The intermediates, dichloromethylene and bromochloromethylene, are captured with roughly equal efficiency, while bromofluoromethylene is captured with much less efficiency, if a t all. While the rate of exchange of deuterodibromofluorometliane was about that expected from data on other haloforms, deuterofluorodiiodomethane exchanged more rapidly than anticipated.
I n earlier articles2 evidence was presented to show that the basic hydrolysis of several haloforms involves the intermediate formation first of a trihalomethyl anion and then a dihalomethylene. I n order to investigate the generality of this reaction mechanism for haloforms as well as to learn more about the effect of structure on reactivity in trihalomethyl anion and dihalomethylene formation, we have studied the hydrolysis and deuterium exchange of dibromofluoromethane and fluoro-
The rate constants were calculated from the equation used previously*
diiodomethane. We also have studied briefly the effect of the structure of dihalomethylenes on their ease of capture by halide ions.
TABLE I BASIC HYDROLYSISOF DIBROMOFLUOROMETHANE AKD FLCORODIIODOMETHASE I N . ~ Q U E O U SSOLUTION
k =
2.303 4a13
+ fl
(1) P a r t X in t h e series "hlethylene Derivatives a s Intermediates in Polar Reactions." Fur part IX, see ref. 21. This work was supported in p a r t b y t h e Office of Ordnance Research, U. S. Army. (2) J. Hine, A. M . Dowel!, Jr., and J. E. Singley, THISJOURNAL, 78, 479 (195G). and references cited therein. (3) 0. Ruff, 0. Bretschneider, W. Luchsinger and G. Xiltschitzky, Ber., 69B,299 (1936). (4) R. N. Haszeldine, J . Chebiz. Soc.. 4259 (1952). ( 5 ) J. Hine a n d S. J Ebrenson, .I Our. Chrm.. '21, 819 (iYs5G!.
b(a - x ) log _____ a ( b - [3 +flz)
(1)
where a [CHX31c~ ?I = [OH-]0- = a .- ICHC131t, = time, S = fraction of haloform that hYdrolYzes to formate (the rest gives carbon manoxide), and k is expressed in liters/mole of haloform x seconds* In I are listed these data and
Results and Discussion Hydrolysis.-Although the fluorodiiodomethane prepared by the reaction of iodoform with mercuric fluoride boiled higher than that reported by Ruff and co-workers3or by H a ~ z e l d i n ethe , ~ agreement of the boiling point with that predicted from an empirical equation for correlating the boiling points of halo me thane^^ as well as the agreement of the molar refractivity and iodine analysis with the calculated values support the assignment of the CHFI2 structure. IVe have studied the hydrolysis of fluorodiiodomethane in aqueous solution a t 0 and 20.85".
- b)
CHBrzF
103k a t 0" 103K a t 20.85" AH*, kcal./mole AS+,e.u. At 19.6".
2 . 7 7 zk 0 . 0 3 7 0 . 8 i 2.9" 25.7 0.5 24.1 + 2.0
CHFIz
0.153 + 0.003 6 . 1 5 Z!C .13 27.7 i . 3 25.6 + 1 . 2
heats and entropies of activation calculated from the absolute rate equation6 k = kT - -- e - A H : / R T clS:/K h
Preliminary tests showed that dibromofluoromethane was the most reactive haloform that we have studied. The rate constants obtained in the first runs a t 0" fell considerably as the reaction proceeded. This was found to be due t o the temperature of the reaction solution being significantly above 0" for the first few minutes of the reaction. (6) S. Glasstone, K . J. Laidler a n d H . Eyring. "The Theory of Rate Processes," McGraw-Hill Book Co., Inc., New York, N. Y . , 1941, p. 14.
820
JACK
HINE,RICHARD BUTTER\VOKTII
Although the pipets used t o introduce the base that initiated the reaction were chilled before use, they and their contents warmed several degrees during the process of transferring the solutions. The necessity of shaking the reaction flask and the exothermic nature of the reaction added to this effect. I n previous runs with less reactive compounds, it had been possible t o ignore the first few minutes of reaction and calculate k's from data on the part of the reaction occurring after that time. In tlic present case, however, too much of the reaction took place during the first few minutes. i1-e therefore calculated our rate constaiits by use o f the following corrections. The instantaneous rate constant a t the higher teniperatures occurring in our reactioii ( k t ) is related to the v:tlue at 0" ( k ) by the expression kt = k
CELT
- ria)/'L'i3T
where 1' is the absolute temperature of the reaction solution a t the time t and E is the Arrhenius activation energy. Substitution into the differential form of eq. 1 and rearrangement gives
Since the integral of the left side of this equxtioti is simply kun, t where kunc is the uncorrected [falling, rate constant that we had calculated from eq. 1
.IND P A U L
B. LANGFORD
Yol. 80
pounds fits satisfactorily into a quantitative correlation of halofonn reactivities based on the proposed xiicchanisiii.l 2 Capture of Dihalomethylenes by Halide Ions.From the observed relative reactivities of haloforms i t appears that, relative to chlorine, fluorine stabilizes dihalorriethylenes and bromine destabilizes theiii.2,12 We thought it of interest to tletermine how the presence of the various halogens affects the ease oi capture of dihalomethylenes by such iiueleuphilic reagents as halide ions. I t has 1,eeii reported earlier that the additiori of cliloritlc ioii s l o w the basic liylrolysis of chloroforiri, clue t ( J re\,ersal oi the secorid step of the reaction (see triechanisni I i .i Eroriiide and iodide bring aliout ii larger "apparelit" decreases in reactioii rate (they decrease the rate a t which alkali disappears), by combining siniilarly with tlichloroniethyleii~to yield halofornis. P.:. CCl: f i -- +CClsl - .
ir,o -+
CIIClJ
\\*e tlierefore studied the effect of various sodium salts a t concentrations around 0.08 Jf on the rate oi the basic hydrolysis of dibroIiiofluororiiethane, tlibroriioehloroInethane and broniodichloroinethane (as nieasuretl by the rate of disappearance of alkali), 'Thc rate constants obtaiiied are sliown in Table 11. TAijLE
11
a plot of T e's. t was made, antl from this plot and :t value of E the integral in ey. 2 could be evaluated for any t. -1sa check on the validity of the method it was found that the value of E t h a t resulted in k ' s having the least average deviation froiri the mean in five different runs was 27.7 -C 1..5 kc:il.,; mole, in reasonable agreement with the value determined experimentally (26.2). The cxpcriiiieiital value was the one used in calculating the k ' s listed in Table I. The rate constants were determined a t an ionic strength of about 0.10, but data on broniodichlororiiethane ('Table I1 1 arid chloroform7 show that haloform hydrolysis rates :ire i i o t very sensitive to changes in ionic strength. In addition to argument by analogy, there is much direct experimental evidence that tliioclofluoromethane and dibrorriofluoroiiiethane hydrolyze by the mechanism CHSl - O € Y
-z. + CSj-
H?O
(I)
cs3- +cs, - s
a [OR-]3 -0.036 .li for CI-I13rlT:antl -0.020 for other 1i:tloforms. 'i .it 0". - i t 40". Falling rate cvnstants cstrapohted to zern time.
followed by rapid reactions of the inteniiediate It TT;E found earlier with chlorofonri that with CX2. Both compounds are reported herein to undergo base-catalyzed deuterium exchange rnorc such salts as sodium fluoride, nitrate and perchlorapidly than they hydrolyze. Both are much rate, which \rould iiot he expected to be effective a t more reactive than would be expected for t h e S X ~ c:t~)turitigdilialoiiietli~lctieintcniiediates, the reacmechanis~n.~The reactivity of each of the ~0111- tion rate is essentially indcpeiideiit of the exact iiature o f the anion a t conceiitrations below O . l ( i ( 7 ) J. Hiue and A . M. I)owell, J r . , TH!SJ O C K N A L . 7 6 , 2fjS8 (1954). Alf.: I'liis obscr\-atioii, which w;ts substaiitiated (8) T h e compounds are the a-fluoro derivatives of nicthylenc b r w mide a n d methylene iodide, respectively. T h e n-fluorc auliititiicnt by iiie:isureiiieiits o r 1 tlil~romofluuroiri~tli~~iie aiid tliappears tu decrease thc Ss9 reactivity i n t h e cases t h a t have Lren l~rc,ii:ocliloroiiic.tliati~~, shoivs that the spccific salt studied.8 10 T h e reactivith- o f alk5-I halides toward sodimn Iiydroxide in water appears to be about the same as toward sodium methiwide i i i methaaal.!' I)il,r,,mi,lluoronicth;*ne i. therefore & h i i t i i ni!lliori times as reactive a s methylene bl-inni
