They also thank Mrs. of the department, who cooperated in every way. The preparation of 1-butene was carried out in the following ways: a) the action of zinc diethyl on vinyl bromide, 1 ( b )° the action of zinc dimethyl on e.lyl iodide. In addition, two other methods seem feasible:. e) the action of zinc on 1,2-dibromobutane in a manner similar to the preparation of 2-pentene, 7 and. f) the action of methyl magnesium iodide on allyl bromide, similar to the preparation of higher 1-alkenes.
Purification of hydrocarbons required removal of ether, allyl bromide and methyl iodide. G was now heated with water first at 0 to +5° and later at higher temperatures •. r..s butene was refluxed from the fractionating colu:nn of 5 x 5 mm. glass rings cut into tube I. in dia~ether, supported by hollow glass nipple J.9 Thermometer K graduated to 1/10 degrees recorded the temperature of the gas at the top of the column. The absence of 2-butene in the final product is indicated by the purity of the dibromide obtained by addition of bromine at -5 to -10°.
The latter is superior to method (c) both in product purity and production rate. Iodine and part of the phosphonium iodide were taken up with a saturated solution of calcium iodide3a at 0° in a bubbler, F. During each run a small quantity of reddish powder was formed in the flask for making, an intermediate reduction product of phosphorus pentoxide, which was not.
In the decomposition of the hydroxy acid (equation 3,4,5), the best results were obtained by removing the low-boiling decomposition products from the reaction flask as soon as they were formed. A 75 mm. bead column in the neck of the distillation flask causes a satisfactory separation of the lower boiling unsaturated acids from the higher boiling hydroxy acid and lactide \Equation 5). The hydrogen iodide was formed in a glass apparatus by dripping concentrated hydrogen iodide acid onto phosphorus pentoxide.9 The reaction with tiglic acid proceeded satisfactorily, but the conversion of an-.
Finally, above 60°, the carbon dioxide from the decomposition of the sodium bicarbonate swept the apparatus free of butene. The yields obtained at the various steps and the physical constants for the various products are shown in Table II. Since everything except approx. After 1/4 of the solution had been added, the temperature had risen to 35°.
The mixture was cooled to °0, at which the solubility of cyanohydrin in the salt solution is negligible. The solution was cooled to room temperature and without removing a large amount of a.rru;ionic chloride, 100 g. However, a satisfactory extraction of the hydroxy acid with ether can be carried out by the procedure adopted.
Hydriodides of. Angelic ~ Tiglic Acids.- The addition of hydrogen iodide to the unsaturated acids was carried out in accordance with the general method of Talbot 5• As this operation requires careful manipulation, the details of which are not mentioned by Talbot, it is desirable that the procedure developed for performing this step is described in detail. The chloroform was kept at -15° and the side arm, which formed the outlet tube, was fitted with a drying tube containing Pe05 • The concentration of hydrogen iodide was determined at intervals by titrating 2.00 cc. It was then cooled to -15°C, the side arm opened, the inlet tube removed, and a capillary tube inserted in its place.
Distillation at low temperature was desirable since decomposition of HI and conversion of angelic derivatives to tiglic acid should be kept to a minimum. Isomeric 2-butenes.— The butenes were generated in a 3-liter 3-necked flask equipped with a mechanical stirrer, a dropping funnel, and an outlet tube. A lively evolution of carbon dioxide occurred at 10° in the case of tiglic acid and at 15° in the case of the angelic acid derivative.
Methyl Bromide ~~Methylating agent.- Methyl bromide produced in a two-liter flask, A, (see figure) from 215 grams. 6.7 moles) of methanol, 266 grams (2.6 moles) of sodium bromide, 695 grams (7.0 moles) of 95% sulfuric acid, and 230 grams of water were purified according to Bydgen's instructions,4 by passing it through concentrated sodium. of hydroxide, D, of soda lime, E, of calcium chloride, E', and through a large tube, F, widened at the lower end to a diameter of 22 mm., into a three-necked three-liter flask.
OF MIXTURES OF THE NORMAL BUTENES
Mixtures of dibromides gave reaction constants which were essentially the value calculated on the assumption that. The values seem to deviate slightly from the calculated values, but always in the same direction, possibly indicating that. Since there was only a very limited supply of pure 2,3-dibromides available, a mixture of these two isomers completely separated by fractional distillation was used.
ABLE XI
Mixtures of dibromides gave reaction constants that were essentially the values as calculated assuming that. rate is an additive function. Table XII gives the densities of pure dibromides and mixtures. Density of pure dibromobut and their mixtures. Specific reaction rates of 1,2-dibromobuta.ne and. racemic and mesa 2,3-dibromobuta.ne with potassium iodide in M!eel~te methanol at 75 °C proved second order.
Since there is a marked difference in the specific rates of reaction as well as in the densities, these properties have been used as the basis for a method of analyzing mixtures of these three dibromobutanes. The method is also applicable to mixtures of 1-butene, cis-2-butene and trans-2-butene, hydrocarbons that can be quantitatively converted into the respective dibromides. In studying the reaction rates of 1,2-dibromobutane and meso- and racemic 2,3-dibromobutanes with potassium iodide1 at about 75° in 99.0"fi methanol, it was found that the reaction proceeds at a second order rate, being first order with respect to both the.
However, none of these results is in agreement with the observations of Van Duin3, who has criticized Bülmann's work as well. Van Duin has argued that the reactions of potassium iodide with o(-f'3-dibromopropionic acid and many other alkylene bromides, conducted at 25°C in 75%, are third order, first order with respect to the diromide and second order with related to potassium iodide.
Although the conditions under which the reaction rates were carried out in these various studies were exactly the same, there is sufficient similarity in some of the experiments to warrant. Now van Duin was wrong in concluding that his reactions were third order, since the constant he obtained for different concentrations of potassium iodide was not the same. He assumed that the order was proven simply because these third-order values remained constant during a single run.
In this paper, it is shown that when recalculating van Duin's data, second-order constants are obtained, which are in agreement with the Biilma.nn and Dillon and Young constants.
CHI-
R!CHI c
In the latter case, the overall rate changes during the course of the reaction and will therefore not be a simple second- or third-order rate. In any case, experimental evidence shows that the rate is constant in the first half of the course, so the first assumption is considered correct. Van Duin has recently criticized Biilmann's method of determining the order of reaction by van't Hoff's method and found it to be third order.
Note.- The concentrations given in this and a.11 of the following losses correspond to the weighed amounts of 1materials that are mixed together for the velocity measurements and are slightly greater than the values of (a) and (b) corresponding to t = 0 in the expression for k3 , as the reaction is measurable at 25° and cannot be taken into account from the time of mixing. The conversion of third-order constants as calculated by van Duin to second-order constants can easily be done in an approximate manner. Furthermore, the values of the second-order constant that will be calculated do not correspond to the likely mechanism.
Second Order Constants calculated from Van Duin's Third Order Values and a Comparison of the Value of k2 and k3. This is easily accounted for when the reaction of potassium iodide with iodine in ac- is taken. In alcoholic solutions the same conditions would be expected to apply and so in these experiments the iodine liberated in the reaction as well as that added at the beginning of the experiment would lead to a decrease of potassium iodide equal to these two values .
While the results are not very good, they are sufficiently satisfactory to justify the assumption that three molecules of potassium iodide enter into the reaction instead of two, and that there is no delayed effect of iodine. Despite the convincing evidence given in Slater's work on the decomposition of ethylene iodide and ethylene bromiodide in the presence of potassium iodide, that a diiodide would not be formed as an intermediate in the reaction of alkylene bromides with potassium iodide, van Duin prefers to assume that they are formed. However, this is to be expected as it is perhaps a necessary consequence of the conclusion that the reaction is third order.
Based on this calculation and his rate measurement results, the conclusion is entirely valid1 but it clearly ignores Slator's considerations entirely. That the possible reaction mechanism of potassium iodide with alkylene bromides is expressed by the following equations.
