?-----Analyses, Empirical Calcd. C H formula 8.36 ClaHnOnBr 47.43 6.07 C,o€I?DiBrr 36.16
C8II;OBr C,HuOBr L''rH6O CoIIiiO
31.81 40.23 73.41
70-
Found C R 47.42 8.53 36.44 6.20 36.56 6.57 4.67 32.10 4.93 6.19 40.34 6.34
10.27 73.19
10.28
genation to t h e corresponding saturated ether and i,y hydrolysis to esters. They polymerize slowly at rooin temperature, but explode when heated in sealed tuhc. Stlater adds more readily than to 1 iiiyl ethers, hut less readily than to ketene acetal. I? thosyacetylene iriay be refluxed with ethyl alSummary I oh01 without reaction, but a t 0" in the presence J bm)n trifluoride-mercuric oxide catalyst Ethoxy- and butoxy-acetylene have been prcpared from the corrcspoiiding broinoalko?cyethyl- mct alcohol the products are diethyl ether and enes. They are ratlier poisonous liquid- M hicli cth3-l acetate. Ethyl orthoacetate gives the same give unstable copper, silver aiitl mercury deli1 a- [JrOdlictS uilticr like conditions. lives. 'Their stnicturcs n t w pri)rz-butyl bromide in boiling alcohol requires from three to four hours lor completion, while the corresponding reactions of sodium thiophenolate and sodium n-butyl mercaptide are. essentially complete i n a few seconds. 'There appears to be no previous quantitative m-ork on these reactions, although similar reactions have been extensively studied The reaction between methyl iodide and sodiun; ethylate was studied by Ilecht, Conracl aad BrLrIiner4 mho observed that the bimolecular rate constant is decreased by increasing iniiial c'once:~ trations of reactants. Seg:~llcr~~ made an extenrlc.r! study o€ the reactions of a scries t i f riciriiinl m J branched-chain alkyl iodides with late and observeil th? effects o f ten ( i ) T h e authors wish t o express their gratitude Reid, research consultant t o t h e d e r u r t m e n t . Fr problem and for his co,uti,uec? i n t e w - t i n t i z i 4 d n t tion. (3) Abstracted from it thesis sbl>r:iitted by G . I,.wl I i o y a ! ~til tli.: Graduate Faculty o f Emory C;niver,ity in partid fulfilllrirtrt rif t l l . requirements for t h e dcgree of .\faster of Science.
~ ~ i i t r a t i o raii d solvent on the bimolecular rate constants. The rate constants were found to decrease n ith increasing initial concentrations of reactants, ani1 no correlation was observed beLwccn rthactivity and dielectric constant of the 5 0 ! 3 ent It was concluded that the reactions are 'iiot icxic ' I h e work of Hecht, Conrad and Hruchiier and that of Segaller on the reaction of propyl iodide with sodium phenolate was repeated by Schroeder and Acree6 as a test of their 'tliial hypothesis," according to which both ionic a i d iriolecular reactions proceed simultaneously aiic! i~idepcndentlv. The observed concentration explained by this hypothesis. Lauer 1 2 ~h a w receiitly studied the kinetics of 1 hc t-i licrification reaction of allyl bromide with iodiuiii phcnolatt with particular interest in conwiitrLiiion aiitl soli ent effects and conclude that ?hr redctioii i q entirely ionic. Concentration effect iy cyhincci a5 due to a \raving degree of solva' i o i i o f the phenolate ion. d>ject of this investigation was to deter>
L~(hroedcrand Acree, i h d , 106, 2682 (1914), and previoii,
Feb., 1942
KINETICSOF ~Z-BUTYL BROMIDE WITH SODIUMPHENOLATE
mine the rate constants for each of the reactions under consideration under comparable conditions as a measure of the relative reactivities of the sulfur and oxygen compounds, to determine the effects of temperature, concentration, solvent and added salts on these rate constants and to use the data so obtained to postulate a mechanism for the reactions.
Experimental Materials.-Pract. n-butyl bromide was purified with concentrated sulfuric acid and was fractionated under reduced pressure; b. p. range 26.8-27.1 ' (42 mm.). U. S. P. phenol was dissolved in dry ether and dried over anhydrous calcium chloride. The ether was evaporated and the phenol distilled at atmospheric pressure; b. p. range 179.0-179.5'. Thiophenol and n-butyl mercaptan were p d e d by dissolving in sodium hydroxide solution, reprecipitating with hydrochloric acid and fractionating under reduced pressure; b. p. thiophenol72.0' (27 mm.); b. p. range n-butyl mercaptan 55.0-56.0' (200 mm.). Methyl and ethyl alcohols were dried by the method of Lund and Bjerrum.8 Benzene was treated with concentrated sulfuric acid until no further coloration was produced, washed with water, dried over anhydrous calcium chloride and sodium and distilled through a short column a t atmospheric pressure. Lithium chloride was of reagent grade and was not further purified, but was dried in an oven a t 100' for several days immediately before use. Procedure.-Rate determinations were carried out in a thermostat maintained at 25.00, 35.00 and 42.40 * 0.01". Solutions of each reactant were made up t o the desired molarity in volumetric flasks at the temperature of the thermostat. Ten-ml. portions of each reactant were pipetted into test-tubes, and the reactions allowed to run for measured time intervals, a t the end of which they were stopped by pouring the contents of the tubes into an excess of standard hydrochloric acid. The tubes were closed with tight-fitting rubber stoppers. Extent of reaction was determined by back-titration with standard sodium hydroxide solution. Indicators used were methyl red-methylene blue for phenolate and n-butyl mercaptide titrations and brom phenol blue for sodium thiophenolate. Volumetric solutions of sodium phenolate were prepared from stock solutions in absolute methyl and ethyl alcohols. Sodium thiophenolate and sodium n-butyl mercaptide solutions were prepared from weighed quantities of the mercaptans and stock solutions of sodium in absolute alcohol. n-Butyl bromide solutions were prepared from weighed quantities of the solute. Initial concentrations were checked by titration of the volumetric solutions of sodium phenolate or mercaptide; one-half the molarity so obtained was taken as the initial concentration. Precaution was taken t o protect all solutions from moisture, and equipment used in rate determinations was dried in a n oven a t 180' for a t least six hours immediately before use. (8) Lund and Bjerrum, Ber., 64, 210 (1931).
227
Where reactions were run in the presence of salts, the desired quantity of salt was added t o the volumetric solution of sodium mercaptide. Reactions in mixtures of methyl alcohol and benzene were run by adding the desired volume of benzene t o the volumetric solutions of reactants.
Calculations Rate constants were obtained graphically by plotting the function x/a(a - x ) against time, since initial concentrations of both reactants were the same in all reactions studied. Straight lines were obtained as shown by the data for a typical reaction in Table I. TABLE I REACTION OF PhSNa WITH n-BuBr a - x
Time, min.
5 5 10 10 15 a = 0.1013 molar.
AT 25.00' x/o(a x)
0.0741 .0746 .0575 .0576 .0475
-
3.624 3.533 7.520 7.490 11.18
Energies of activation were obtained graphically by plotting log k against the reciprocals of the absolute temperatures. Rate constants were reproducible to about 5%) and energies of activation may be considered as accurate to about f1OOO calories. Mole fractions of benzene were calculated on the assumption of no volume change on mixing.
. Results and Discussion The rate constants obtained for the reactions of n-butyl bromide with the sodium salts of phenol, thiophenol and n-butyl mercaptan under various conditions of initial concentration, temperature and solvent and the energies of activation and the ratios of calculated to observed rate constants are TABLE I1 REACTIONS OF SODIUM n-BuTYL BROMIDE
RATE CONSTANTS FOR
SALTS WITH
Energy of activation 25.0' 36.0' 42.4" cal. k X 106 1.31 3.90 8.10 19,530 0.992 3.18 8.07 21,990 .871 2.82 6.67 21,120 .401 1.32 3.48 22,940
koalod.
Reactant
Init. concn.
Solvent
PhONa PhONa PhONa PhONa
0.05 .10 .20 .10
CzHsOH CzHsOH
PhSNa PhSNa PhSNa PhSNa
.05 .10 .20 .10
k X lo* CzHsOH 1.28 3.42 CzHrOH 1.25 3.12 CzHrOH 1.24 2.84 C H I O H 0.450 1.10
6.57 5.54 4.75 2.25
17,400 15,720 14,060 17,840
66.7 76.9 83.3 4.8
BuSNa BuSNa BuSNa BuSNa
.05 .10 .20 .10
k X 102 CzHrOH 2.00 5.10 CIH~OH1.81 4.84 CZHIOH1.83 4.50 CHiOH 0.443 1.11
8.94 8.84 7.58 2.00
16,800 17,540 15,900 17,140
8.7 9.1 9.7 20.4
CzHsOH
CHIOH
Rate constant
kobs.
14.5 17.2 20.0 1.4
given in Table 11. Calculated values were ob tained from the expression k = 2.8 X 10" xt.p-"'' by substitution of average experimental ralues of E . The value 2.8 X 10" is an average value of theoretical collision frequencies for a iiuniber oi solution reactions Comparison of Sulfur-Oxygen Reactivity.--The order of rea&\ ity of the three sodium, salts R ith n-butyl bromide is butyl mercaptan, sodium thiophenylate, sodium phenolate. The differenct i n reactivity of the two sulfur compounds is small, rate constants in methyl alcohol solution are thc ?auie withiti experimental error, while those i t 1 ethyl alcohol solution differ by a factor of about ) significant difference in activation enersics is apparent Assuming constancv of s. a facR' t ( r of 1 in the rate exprvsstoti k = re ( ort csporids to a change in I. of roughly :300 caloI IC'\ ' i i i r h a (1ii-u eiicc i q nithin the evperi i!icntal (rr6)r (if the present ttwarcii I'lie rate constdnts characteristic of sorliurii phenolate and sodium t hiophenolate differ tre triendously. 'I'he sulfur compound is approxi mately 1000 titiiri as reactive toward n-butyl brornidc as is thc analogous oxygen compound III both methyl atid ethyl alcohol solutions, thc t1ifferenc.r i i i ac'tii-ation energies IS almut ,50(]0 t*alorie I'hc agreement between calculated and oh strverl rate constants is within the normal range to be expected considering the approximate na ture oi the calculations Thiy indicated that despite the great diff ercnce in reactivity betweer! analogous oxygen and sulfur compounds, thr same mechanism obtains in both cases. The Effect of Initial Concentration.---In general, there is a'rjoul a 1.5 to 20(> decrease in rate constant as the initial concentration is increased from 0 Kj to il.20 molar A concentration effect ot this iiature i s custon~ari1~taken as evidence that the reaction urider consideration is ionic in nature m d that the rate cotistant is dependent upon thc degree of ioiii7atio.n. 'The 'dual hypothesis" of Schroeder and .%Creefihas offered the most suit nl,le arid generally acceptedL"niechatiism ot ether ricatiori reactions yet proposed Legitimate 011 Irctions to this hypothesis, however. have been raised7 on the basis thdt sodiuiii salts of phenols arc strong eltctrolyte5 in alcoholic solution and that, coiiseyueiitiy. the degree oi ioriimtion
