The kinetics of the isomerization of cis-and trans-2-butenes, catalyzed by methanol and boron fluoride mixtures, have been studied. T h e rate was found to be proportional to the concentrations of the boron fluoride -methanol complex and of free boron fluoride but independent of the butene concentration.In previous papers (1, 2) we have reported the results of sonle experiments on the isomerization of cis-and trans-2-butenes in ethylene dichloride solution, using boron fluoride -water nlixtures as catalyst. I n order to interpret the results of those experi~nents it was necessary to estimate the positio~l of the equilibriunl between the mono-and di-hydrates of boron fluoride, and this was done from measurements of the vapor pressure of boron fluoride over solutions of water in ethylene dichloride. Fro111 the resulting values for the concentrations of the hydrates it was concluded that the rate expression for the conversion of one butene isomer into the other wasThe equilibrium constant obtained for the monohydrate-dihydrate reaction was a t best an approximate one for, as its measurenleilt was dependent upon small differences between large numbers, a considerable error was possible. With the catalyst system boron fluoride -methanol, however, this uncertainty can be largely avoided because the dialcoholate is very much less stable than the monoalcoholate and one may therefore assume that the concentration of the latter is approxinlately that of the added alcohol. Furthermore, the rates are lnuch slower, and hence more easily measured, than those with water as cocatalyst, the catalyst ~nixtures are completely soluble over a wide range of concentrations, and the higher vapor pressure of the methanol permits more accurate dispensing of the cocatalyst. The present paper reports the results of some studies of the isomerization of the 2-butenes by boron fluoride -inethanol mixtures. EXPERIMENTAL; iflaterials were prepared and handled essentially as previously described. NIethanol was dried with magnesium nlethoxide and measured as the vapor a t pressures well below the saturation vapor pressure a t room tenlperature.Rates were measured in a reaction flask equipped with a manometer and having a total free space of about 215 ml. Ethylene dichloride (35 1111) was used as solvent and the temperature was coiltrolled a t 20' C by water circulating around the flask. Samples were reinoved as previously described and analyzed either by infrared spectroscopy or by gas chromatography. Isomerization of the trans isomer was follo\ved by the appearance
The rates of reaction of halide ions with ethylene oxide in neutral aqueous solution and the rate of hydrolysis of ethylene oxide in acid solution have been measured and the activation energies determined. From these data and from the ratio of glycol to chlorohydrin formed when ethylene oxide reacts with excess aqueous hydrogen halide, the rates of the acid-catalyzed addition of halide ions to ethylene oxide a t 25°C. have been estimated.
Studies of the boron-fluoride-catalyzed reaction of ethylene oxide with simple alcohols and low molecular weight polyglycols indicate three ways in which chain growth could occur, but only one of these is considered to be important after the initial stages of polymerization. The rate of disappearance of monomer reaches a maximum a t a molecular weight of about 400. A mechanism is proposed to account for both polymerization and depolymerization and it is shown how equilibrium between these two reactions could result.The polymerization of ethylene oxide by boron fluoride is a complex process in which the propagation reaction must compete with an appareiltly independent depolymerization reaction. The depolymerization process, as discussed in the previous paper (I), breaks down the polyglycol to dioxane seemingly through a chain reaction propagated by oxonium ions acting upon the ether linkages in the polymer molecule. The polymerization on the other hand appears to occur through a stepwise addition of monomer to the terminal hydroxyls of the polymer chain. A study was therefore undertaken of the reaction of ethylene oxide with alcohols in the presence of boron fluoride in an effort to obtain a mechanism for the propagation and t o observe the transition fro111 propagation to depolymerization. This paper presents the results of these studies.. EXPERIMENTALEthylene chloride, ethylene oxide, and boron fluoride were prepared for use as previously described (2). Volatile alcohols were dried by distillation froill their magnesium alcoholates in the usual way and ethers were dried over sodium metal or calcium hydride, \ZTherever the reactants were sufficiently volatile they were stored on the vacuum system and transferred by distillation. T h e polyglycols were either stirred under high vacuum for several hours or dissolved in dry ethylene chloride and pumped free from solvent before use. Molecular weights were determined by viscosity ineasureme~lts as before, but in a few cases were confirined by freezing point depressions in benzene. Where hydroxyl content of the polynler was important, end group analysis by acetylation with acetyl chloride in pyridine, according to the nlethod of Smith and Bryant (3), was used. All three methods gave satisfactory agreement.Reactions were carried out in ethylene chloride solution a t 20° C. Rates were followed either by the decrease in vapor pressure of ethylene oxide as described in the earlier work, or by a dilatometric method. The dilatometers were so constructed that they could be dried and filled under vacuunl and then transferred to a constant temperature bath while exposing only the capillary tip t o the atmosphere. Absolute contractions were not determined but the contraction per unit of oxide appeared t o be constant over the range of the experiments. The two methods gave good agreement wherever they could be compared. 'Manuscript
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