Studies on the Kinetics of the Addition of Acetic Acid to Isobutene Citation Showell, John Sheldon (1949) Studies on the Kinetics of the Addition of Acetic Acid to Isobutene. Master's thesis, California Institute of Technology. doi:10.7907/5kmx-0d09. https://resolver.caltech.edu/CaltechTHESIS:09172025-021803490 Abstract The kinetics of the addition of acetic acid to isobutene with anhydrous and water-containing acetic acid as the solvent were studied. The rate was determined by following the changing unsaturation with bromine. The reaction was found to be sensitive to the presence of water, tertiary butyl alcohol being the principal product, when water was present and no polymerization was observed. Under anhydrous conditions the tertiary butyl acetate was formed and the isobutene was observed to polymerize. The kinetics of the anhydrous reaction were theoretically treated quantitatively and the rate step was shown to be the addition of the proton to the isobutene. The water containing conditions were studied, but could not be quantitatively interpreted due to the complex equilibrium system set up, the results were however interpreted qualitatively. The concept of the carbonium ion intermediate of Whitmore was shown to be consistent with the esterification and t he polymerization reaction. Item Type: Thesis (Master's thesis) Subject Keywords: (Chemistry) Degree Grantor: California Institute of Technology Division: Chemistry and Chemical Engineering Major Option: Chemistry Thesis Availability: Public (worldwide access) Research Advisor(s): Lucas, Howard J. Thesis Committee: Unknown, Unknown Defense Date: 1949 Record Number: CaltechTHESIS:09172025-021803490 Persistent URL: https://resolver.caltech.edu/CaltechTHESIS:09172025-021803490 DOI: 10.7907/5kmx-0d09 Default Usage Policy: No commercial reproduction, distribution, display or performance rights in this work are provided. ID Code: 17683 Collection: CaltechTHESIS Deposited By: Ben Maggio Deposited On: 04 Oct 2025 13:11 Last Modified: 04 Oct 2025 13:22 Thesis Files PDF - Final Version See Usage Policy. 10MB Repository Staff Only: item control page

STUDIES ON THE KINETICS OF THE ADDITION OF ACETIC ACID TO ISOBUTENE Thesis by John Sheldon Showell In Partial Fulfillment of the Requirements For the Degree of Master of Science in Science California Institute of Technology Pasadena, California 1949 ACKNCMLEDGEMENTS The author gratefully acknowledges the advice and patient guidance of Professor H. J. Lucas and hopes that he will prove worthy of his interest. To Mr. and Mrs. Harry A. Fee, the author expresses an overwhelming debt of gratitude for making his education possible and for the friendship he has enjoyed. To them the work is dedi- cated, it being a symbol of the author's wish to justify their faith in his future. ABSTRACT The kinetics of the addition of acetic acid to isobutene with anhydrous and water-containing acetic acid as the solvent were studied. The rate was determined by following changing unsaturation wlth bromine. the The reaction was found to be sensitive to the presence of water, tertiary butyl alcohol being the principal product, when water was present and no polymerization was observed. Under anhydrous conditions the tertiary butyl acetate was formed and the isobutene was observed to polymerize. The kinetics of the anhydrous reaction were the'oretically treated quantitatively and the rate step was shown to be the addition of the proton to the isobutene. The water- containing conditions ·were studied, but could not be quantitatively interpreted due to the complex equilibrium system set up, the results were however interpreted qualitatively. The concept of the carbonium ion intermediate of Whitmore was shown to be consistent with the esterification and t he polymerization reaction. -1- INTRODUCTION The study of the addition of acetic acid to isobutene to give t-butyl acetate CHfOOH + (CH ) 2c : CH 2 ¢ 3 ( CH3) 3cOCOCH3 is analogous to the hydration of isobutene. ( CH ) 2o : OH2 + H20 ~ ( CH ) coH 3 3 3 whose acid catalyzed reaction was studied by Lucas and Eber~;. (1) The acetic acid-isobutene, water-isobutene analogy suggested that the acetic acid molecule would give a "larger handle" for the stud7 or the hydration mechanism as both reactions appear to involve the same type of mechanism. Thus both reactions have been found to be bimolecular (1,2,3,4) and acid catal7sed. (1,4) Altschul {4) has recently made a study of the addition or benzoic acid, p-nitrobenzoio acid and acetic acid to isobutene using sulfuric acid as catalyst and dioxane as a solvent. This work indicates that the reaction is bimolecular with respect to the acid and the isobutene at constant catalyst concentrations. In the reac- tion, no polymerization was observed to occur contrasting to the results obtained here when acetic acid was the solvent. This anomaly is explainable on the basis of the recent work or Weith, Hobbs, and l Gross {5) who from absorption itudies postulated l o~CH2-0H2,; i=- c1l 'CH2•CHz ·J ~ toH2-cH2,o H-c11 'cH2-CH2/ which would stabilize the dioxane hydrogen ion complex with respect to isobutene -2- thus eliminating the polymerization reaction + C1H.3 Ci13 Clf3 ( CH3) 3C + Cli2= C-CH3 ~ -JcH,i-OH = o;;.cH3 + H CH) In this work the sulfuric acid catalyzed addition or acetic acid to isobutene using acetic acid as a solvent was studied. The consumption or isobutene by the reaction )f : (CH 3 CH 2 + CHfOOH ~ (CH ) 3 cooocH 3 3 was measured by the method or Lucas and Pressman (6) slightly modified, using the sampling technique of Eberz and Lucas. (7) EXPERIMENTAL Materials: Carbon Tetrachloride. Technical cc14 was purified by saturating it with chlorine and exposing to sunlight for two days. The solu- tion was then washed with C.P. dilute NaOH, dried over CaC12 and distilled to give carbon tetrachloride, b.p. 75.8-76.0° at 71.2, nm. t-Butyl Acetate It was prepared by the method or Norris and 5 = 1,3865. Rigby, (8) b.p. 97.0-97.1°C at 748 m., n: Cyelohexene Reagent cyclohexene was redistilled through a 40 oa Vigreux column, b.p. 82.0-82.2°0 at 749m.. Acetic Acid c.P. Baker's glacial acetic acid was made anhyd~ous by refluxing it for two hours with acetic anhydride, the amount of acetic anhydride being calculated from the freezing point depression of the glacial acetic acid. -3100% Sulfuric Acid Smal amounts or c.P. oleum of unknown strength were mixed with varying quantities or c.P. concentrated sulfuric acid in order to adjust the composition by means of melting point determination to give a product m.p. 10.3°c. Isobutene The isobutene was prepared using c.P. t-butyl alcohol, m.p. 24.5°0 and oxalic acid dihydrate as the dehydrating agent. (9) The isobutene, as it was generated, was scrubbed in water, dried by passing through anhydrite, condensed and sealed in large ampoules. The isobutene was dispensed as needed into the stock isobuteneacetic acid solution. Sodium Thiosulfate Standard Solutions In 1 liter of freshly boiled, cooled water 25 gm of Na.~~r 5H,20 and O.l gm N92C03 were dissolved. The solution was then allowed to set for a day and standardized with K3Fe(ON)6, following the procedure of Kolthoff and Sandell. (10) • ·The solution was frequently restandardized, no change in concentration being observed. Potassium Brom.ate-Bromide Standard Solution To 1 liter or distilled water were added 2.5 gm c.P. KBr03 and 25 gm c.P. KBr. This was standardized against newly standardized Na~20.3 solution, following the procedure of Kolthoff and Sandell. (10) The solutit>n was restandardized frequently, complete stability being ob.s erved. Equipment The reaction vas carried out on a thermostatt, set at 25.00 fo.05°0 and checked with a Bureau or Standards thermometer, constant stirring being provided. by a 1/4 horsepower stirring motor. Special reaction bulbs (Fig. 1) were designed with a pressure sampling head to prevent the loss of isobutene from the system, and absorption of -4- l---lr-+---11 ~<-- C Figure 1 Reaction Bulb A. Sampling head outlet c. Volume calibration mark B. Nitrogen inlet D. 300 ml. bulb -6oxygen from the atmosphere. The reaction bulb was provided with a long neck, so that the reaction mixture would be completely submerged in the thermostat and to keep to a minim.um. the free volume in the system, thus making the isobutene volatilization negligible and the amount or oxygen present initially minimal. The calibration mark was made on each reaction bulb, so that a known volume of isobutene solution could be added. All burets and pipets were calibrated gravimetrically using water at room temperature. The sampling pipets of Eberg and Lucas (7) were calibrated using redistilled mercury. The standard potassium bromate-bromide and thiosulfate solutions were prepared and standardized b7 the usual analytical procedures, the values being rechecked frequently. The isobutene solutions were prepared by bubbling isobutene into the acetic acid, using a special head that permitted the system to be sealed from the atmosphere (Fig. 2). The iso- butene was bubbled through valve 1 with valve 2 open until the isobutene concentration approximated the desired value. cocks 3 and 4 were then closed. Stop- The solution was then dispensed, when desired, into the reaction bulbs, using nitrogen pressure at 2. In this manner it was possible to dispense solutions of the same initial isobutene concentration. Initially, difficulty was experienced in controlling the sulfuric acid concentration in the reaction mixture. This was overcome by preparing standard sulfuric acid solutions from 100% C.P. H2S04 and acetic acid, containing acetic anhydride, in a volu- -7- 1 3 2 Figure 2 Storage Bulb -8metrie flask. The sulfuric acid concentration in the reaction mix- ture was then controlled by the volume pipeted in from a sulfuricacetic acid standard solution. From the volume of isobutene solu- tion and the volume of sulfuric acid catalyst added, allowing a correction for volume changes, the sulfuric acid and isobutme concentrations in the reaction mixture were calculated. The correction for volume changes due to the non-ideal behavior of sulfuric ac id and acetic solutions, was obtained from a series of dilution experiments with sulfuric and acetic acids. The reaction mixt.ure was sampled by using the sampling pipets of Eberz and Lucas (7) shown in Fig. 3. The reaction solu- tion was forced into the pipette by attaching the pipette to A (Fig. 1) using a rubber tube as a connector to the special reaction bulb head described previously. The N2 -used in displacing the solution was dried by passing it through anhydrite. The solution was permitted to rise into 2 (Fig. 3) so as to clean out the pipette and to insure that the solutions came from the main part of the reaction bulb D (Fig. 1). The reaction was then analyzed using the technique of Lucas and Pressman (6), and their special bromination flasks. The sampling pipet was then allowed to drain with liquid in 2 (Fig.)), being permitted to replace the wash acetic acid on the pipette surface. This minimized the possibility and effect of dilution when the sampling procedure was repeated. Analytical Procedure The analytical procedure of Lucas and Pressman was modified slightly when it was found that the mercuric sulfate and sodium chloride could be eliminated from the reaction mixture. The potassium -9- Figure 3 Sampling Pipette -10bromate-bromide solution was made up with 15% excess of KBr over that required for generating the bromine. The substitutive bromination of isobutene was fowid to increase when the bromination time was increased, however, the three minute period used in these experiments gave negligible substitution. To avoid an excess of bromine greater than 10-15%, it was necessary to vary the amounts of standard bromate bromide solution. This was accomplished by using only one sampling pipet and varying the volume of standard bromate bromide solution that was pipeted into the analyzing nasks, this being accomplished by using a series of calibrated pipets (±· 0.1%). This permitted the preparation of the brominating solutions prior to the reaction rate experiment and greatly facilitated the analyses. It was found that there was a negligible blank so no correction was made for it· in the computations. This procedure was checked against standard cyclohexene solutions and was found to give an accuracy of 0.5%. Typical Run Prior to each reaction rate study, the reaction bulb (Fig. 1) containing the acetic acid-isobutene solution was placed in the thermostat and allowed to come to equilibrium at 25.00°c. Then it was taken from the thermostat and the volume reduced to the calibration mark. The catalyst solution was then accurately pipeted into the isobutene solution, the reaction head replaced and the reaction bulb shaken vigorously to insure complete mixing. stat. The bulb was returned to the thermo- The zero time is chosen as the instant when the catalyst was added, the entire time being about forty-five seconds before the reaction bulb was returned to the thermostat. Sampling was begun immediately -11- so as to obtain as many initial observations as possible, the frequency being deper.ident upon the initial concentrations. The time for each reading was ta.ken as the instant of addition to the brominating mixture, the indeterminacy being fiv-e seconds. The sampling was con- tinued until the solution was exhausted. The data obtained experimentally in this manner are tabulated in Table I. The isobutene concentration was calculated from a knowledge of reactions involved in the analysis: ( CH ) c 3 2 =CH2 + Br2 ~ ( CH3) 2cBr CH 2Br excess Br2 + 31- ---=--- Ij + 2Br- I3 + 28203 ~ S406+ 31Identification of Reaction Mixture Products In some preliminary experiments, it was observed that water had a marked influence on the course of the reaction. This indicated that water was forming t-butyl aloohol, in addition to the t-butyl acetate. Using an acetic acid solution, containing 5% water, 2.5 gm of isobutene were bubbled into 300 ml acetic acid and 19 ml of concentrated c. P. Sulfuric acid were added. The solution was shaken for 3 minutes then placed in a separatory runnel and added dropi,rise, with stirring, to an ice-water solution of 450 gm Na2co •H2o. Upon 3 neutralizing the acid solution, the basic solution was steam distilled, no second phase being obtained. A portion of the distillate was poured into an excess of concentrated HCl to obtain a cloudy solution. Another part of the distillate was fr~ctionally distilled, the f.irst #14 #13 #12 #11 #10 #9 t = 1.s4 .00984 3.15 6.45 7.72 .02510 .02430 .01878 .01521 1.50 .00217 175.07 .02910 2.46 .02643 5.56 .,0282.3 3.96 .325 7.56 .01952 .567 .01651 .475 .583 .7/+2. .01425 076 .958 .01175 1.25 lo75 .00887 .00665 .00432 1.02 .138 .0743 3.95 .00560 .058 .0818 3.38 .00645 t (B) .00499 4.48 .0614 .413 000488 5.08 .04742 .04217 .03121 .02420 1.25 1.78 .01940 .Ol.365 1.;2 000182 .00182 .00182 [B] : 0.09333 (H2SOi1 .: 0.0849 (H20] : 0.100 •889 .175 .J42 .468 .600 • 750 1.00 2.22 4.1e .04379 .01165 .00954 .00679 .00556 .00400 .00442 .00442 .004.37 (BJ, =o.09345 lH2s041 = 0.0110 (H20]= 0.100 .083 .0.33 .00170 000163 .00163 [Bl 0 =o.oJ300 [H~O.iJ = 0.0172 I}!~]= 0.0616 46.28 73.62 169.15 .0029.3 000241 .00207 .00193 000217 .00217 .0020.3 .00212 .00217 ~] 0 =0.03304 [H~OJ = 0.0288 [H20]= o.0616 .029 .075 .217 .437 .629 .791 1.00 1.34 1.61 .02611 .02440 .01770 .01110 .00731 .00546 .00.385 .00268 .00225 2.83 7.79 19.76 = = [:al 0 -o.o.3320 1iii,S04] = 011000494 (H2d o.0616 .038 11092 .242 .508 1.25 1.50 .03210 .03205 .0.3186 .03134 .03072 .0.3053 12.18 13.SJ 26.4.3 29.75 32.62 75.17 .02012 .01887 .01312 .01110 .om:, 000477 li3] 0 =0.03322 ~ 2soj] 0.00556 [H2o] 0.0616 .46 .184 .392 • 5.34 .850 1.02 .03139 .0'2961 .02896 .02685 .02310 .02144 s.1g 10.22 12.37 J6.64 40.11 43.09 t {B} (BJ t [B] t [BJ [B] t t IBJ [B] rmtt ml t t [B] Rate Studz , (concentrations on moles/liter of solution•time in hours) Rate Study Data Table I 2.20 .01157 2.96 .00219 .00167 2.24 .00417 265.35 .00217 6.25 .02190 10.12 ~ ~ #2JJ #19 #18 #17 #15 Wl (B) t t t (B) t (B) {Bl t t (B] [B] t [B) t t (B] t [B] t [B) Rs.t~ S_'tudz .097 .0862 4.56 .02625 = = = = = = 0.00580 [H20} = 0.100 • .319 .467 .621 .842 1.07 .0821 .0752 .0746 .0701 • •0660 6.78 8 • .38 7.48 25.77 .01543 .01.346 .onoo .00437 [BJo=o.08425 (H2S0.t) o.0087.3 (CH3C0)20] :t o.380 .050 .125 • 502 .659 .85.3 1.15 1.48 .0132 .o695 .o643 .06295 .o6080 .057/;J .05445 5.08 7.06 27.95 5.99 .03055 .02685 .0166o .00990 {BJ o=0.08695 (H~04} o.00898 [(CH3C0)20] : 0.0995 .042 .142 .396 .;92 .s2; 1.07 1.s, .07290 .07170 .06785 .06608 .06.355 .o6o95 .05.355 ;.65 76.31 83.14 95.59 110.«, .03015 .01180 .01255 .01252 .01280 [Ii o=0.08420 (H2S0,4) 0.0228 [(CH3C0)20] • o.0963 .042 • .317 .550 .775 1•.30 1.85 3.00 .05895 .0;045 .04680 .04275 .0.3485 .02890 .02470 72.01 87.30 .02395 .02610 [B) 0 :0.07590 (H2so.tJ o.022JJ fi CH3CO) 20) 0.096.3 .0.39 .084 .192 .359 .;25 1.05 1.69 .0;400 .05.325 .05015 .04650 .04.325 .035.35 .0281; 4.18 7.77 9.22 5.09 19.98 27.68 33.42 .01430 .01225 .01000 .0100; .01195 .01435 .01560 89052 .021a; .0.34 .0877 4.10 .02913 (B] 0 ::0.09385 (H2S04l Table I (con'd.) .04685 2.29 2.21 .023.30 54.83 .01900 .019.35 .01870 67.30 3.00 40.90 .0142; .02u; 26.90 2.56 3.69 .04780 .0.3990 2.13 3.05 .04795 .04240 1.44 .0;74 002025 79.45 .3.62 .01610 59.00 .02255 .0.356o 4.51 .0350.3 4o25 2.77 .04079 I ~ \J.) #25 #24 #23 #22 #21 [Bl t [B] t t (B] t [B] [B] t (B] t (B) t t fB1 {B) t (Bl t Rate Stud.z [B] 0 =o.03296 {H2soJ = 0.0224 ((cH!co) 2o] = 0.151 .047 .117 .217 .342 • .38 .680 1.034 .01176 .01082 .01082 .01042 .0098.3 .00928 .00842 6.27 5.28 7.42 8.57 .9• .30 19.87 32.42 .00576 .00585 .00580 .00621 .0066o .01000 .01236 {Bl o:0.0.3172 (H2S04"\ = 0.00452 {(c~00)20] : 0.426 .067 .100 .267 .4.33 • 2 1.500 2.308 • 02745 • 02781 .02718 .02668 .02577 .02414 .02.305 7.150 8.150 19.00 22.02 26.66 .30.93 43.12 .01545 .01485 .00824 .00724 .00674 .00572 .005.30 (B)o=o.033.34 (H2SO~ :: 0.00996 [!cHiC0)20] = 0.150 . 0.042 .108 .292 .533 .7 7 1.008 1.400 .02495 .02482 .02364 .02278 .02164 .02084 .01979 5.617 7.796 9.267 21.86 .01124 .00923 .00824 .00589 {B] 0 =o.o.3.334 {H2s041 = 0.0136 kcH~C0)20] = 0.150 .442 . •167 .217 .508 • 92 1.22; 2.616 .01852 .01843 .01707 .01630 .01527 .01372 .01046 18.1.3 21.s.3 29.37 4.3.27 66.97 90.08 116.05 .00662 .00773 .00896 .01059 .01314 .01368 .014.32 [B) 0 =0.04426 {H2soi = o.00572 [(o~co) 2o] = 0.1.33 .043 .104 • 38 .60; .9 1.238 1.925 .03978 003991 .0.3837 .0.3733 .036.38 .0.3538 .0.3.365 4.758 5.442 6.267 7.425 9.100 10.02 10.68 .02640 .02524 .02350 .02152 .01943 .01852 .01721 Table I (oon 1 d) 511-.65 2.595 .0.3171 11~91 .01648 3.104 .0.3026 12.58 .01522 4.017 5.892 .oo86o .00671 4.100 4.88.3 .01993 .01866 53.12 .00552 . 2.042 2.667 .01767 .01689 .01535 .or,os 44.60 1.717 2.64 .007.33 .00626 3.808 .02917 7.675 .00611 .01259 4.458 6.284 1101689 J.73 .00590 69.03 .01825 f I #.30 #29 #28 #27 #26 (B) t t lB] [!3] [B] t t 1}3] t t l:S] @l t [B] t t [B] t [B) Rate Stud,;t .su = 2.028 .0lll0 1.695 .01227 2.942 .3.58.3 .01612 .OU].3 .00706 2.3.17 2.704 [B] 0 =0.1328 lH2SO/) = 0.0275 {{ cH3co) 2g :s o.159 .038 .150 .400 .625 .855 1.044 1.275 lo725 2.167 .1156 .1102 .09985 .09095 .08260 .07715 .07060 .06030 .05085 3.258 3.675 4.984 6.088 7.392 8.58.3 9.567 .0.3608 .03246 .02443 .02041 001685 .01527 .01530 2.542 0.4624 .01046 2.501 3.8.33 .02564 .02291 .01943 1.909 .00907 .00824 [B]o:0.1368 {H2S0iJ = 0.00560 tcH3C0)2oJ = o.163 .038 .221 .550 .892 1.188 1.521 1.988 2.437 .3.042 0.1358 0.1322 0.1288 0.1258 0.1220 0.1182 0.1136 0.1046 0.1052 3.535 4.050 5.096 6.821 7.933 9.225 10.42 11.42 0.1005 o.0958 o.oss3 0.0780 .0123 .06650 .06150 .05630 = = (B]8=o.04412 [H2s0J o.ouo [(cH3C0)20] = o.133 • 34 .119 .275 .529 .825 1.171 1.521 .03525 .0.3460 .OJ.356 .03229 .0.3062 .02840 .02750 5.5.34 6.500 7.588 8.6;4 9.6.3.3 10.52 21.88 .0155.3 .Ol.381 .01227 .01110 .01050 .00982 .00702 (B] 0 =o.04406 (H2so;J 0.0167 RcH3co) 2o] 0.1.32 .042 .04.3 ~80 .6.34 .972 1 • .329 2• .300 .0.3053 .02935 .02894 .02654 .02414 .02260 .01812 4.567 5.428 6.296 7.213 .01221 .0101s .009;5 .00878 [B] 0 :0.04268 [H2soa = 0.0280 f.{CH3C0)20] = 0.1.32 .0.38 .104 .256 .483 1.001 1.285 .02142 .02101 .01952 .01768 .01621 .01513 .01.377 .3.000 .3.582 'l'~ble_I (con 1d.) '{' I I-' -16two milliliters being separated and KOH pellets were added to it. A second, lighter than water phase, separated. Using microtechnique, the upper layer was dried with K2C03 and an ester test was made by the Davidson test (11), negative results being obtained. point by the Emich method was 80°c. The boiling This corresponds tot-butyl alcohol, b.p. 83°c. The above procedure was repeated using a 1% water solution in acetic acid as solvent. The basic solution upon distillation gave 0.5 ml. of a second phase. This gave an Emich boiling point of 92°c and a positive Davidson ester test, corresponding tot-butyl acetate. The water phase from the steam distillation gave an immediate second phase on pouring into concentrated HCl. Using acetic acid, that .was made anhydrous by refluxing with an excess of C.P. redistilled acetic anhydride, as a solvent the above procedure was duplicated to obtain 1.6 ml. of a second phase on steam distillation. This gave A positive Davidson ester test. These results indicate that there are two competing reactions; hydration and esterification, the hydration reaction overwhelming the esterification as the concentration of water is increased. ANALYZING DATA AND DISCUSSION Introduction The reaction of isobutene and acetic acid was studied under two conditions, one in which water was present and the second -17in which an excess of acetic anhydride was present. It was found that both gave smooth curves when the unsaturation was plotted against the time. Graphs No.land No. 2 are representative of the two groups respectively. noted: However, two distinct differences were 1) In the solution containing some water a smooth curve was obtained, starting at the initial isobutene concentration; in anhydrous acetic acid a smooth curve was obtained, but it started at a value much below the initial isobutene concentration; 2) the water containing acetic acid solution showed a continual drop in unsaturation (after the initial drop) to a final constant value of the unsaturation; the anhydrous acetic acid solution showed a drop to a minimum unsaturation and then an increase. Analysis of Data Using the method of Lucas and Pressman (12), the unsaturUnsaturation - {B] 8 ation was plotted in the form of logio Initial Unsaturatio~ - [B]e l 1 against time, the constant (B]e being chosen to give the best straight line through the data points. The following symbols were used in the computations: [B] - concentration of isobutene in moles/liter or solution [B] 0 - concentration of isobutene at t = o, calculated from the B determined before the catalyst added, by allow- ing for the dilution of the reaction mixture by the catalyst and assuming no reaction has taken place: moles/liter of solution [B1 1 - the concentration of isobutene obtained by extrapolating tot= o, using the best straight line for the data points: moles/liter or solution 0.2000 -18Graph #1 Rate Study #14 0.1600 [H20] = 0.100 - < (I) (I) 'ci 0 . 1200 s S:J () •r- j +> al f-, ~ o. 0800 a.> (.) i:: 0 0 0.0400 0.000Qa......_,___.____...__---1_ ___.,_--'-_ ___.__ _,__....._--'-_......__..,__..,_---' 0 1 2 6 3 4 7 5 Time (hr.) 0.0800 Graph #2 Rate ~.tudy #20 IH2S04] =0.0220 [( CH3co) 20] =0.0963 [B] =0.07590 0 ,,..... 0.0600 ~ CJ) Cl) r-l ~ ...._.. 0.0200 0.00001------1......--__,__._ _ _ _--'-_ _ _........_..._ _ ____,. 20 0 10 15 25 5 Time (hr.) -19[B] e - t he constant that gives the best straight line plot of the data points by the use of the formula [B] - [B] e \ loglO ( [B]i - [B]e 1 = -kt where tis the time in hours and k is t he slope of the best straight line: moles/liter of solution The values so obtained are tabulated in Table II. These values again illustrate the marked difference in the reactions which take place with and without water. When water is present there are apparently two competing reactions, viz. hydration and esterification: In the absence of water, the reactions are apparently esterification and polymerization: ( CH ) 2 c: CH -1- CH co H ~ ( CH ) cOCOCH 2 3 3 3 3 2 3 (cH ) 2 C : CH2 ~ 3 polymer Theoretical Development and Discussion The marked difference in behavior between the water-containing and anhydrous acetic solutions is best understood in terms of the simpler anhydrous reaction conditions due to the complex set reactions that take place when water is present. For this reason the anhydrous system will be discussed kinetically and the results qualitatively applied to the water-containing reaction studies. The following symbols are to be used in addition to those already defined: .0543 .0118 .07590 .03296 .0355 . 04412 .1162 .061328 30 29 .136s · .0061 .0052 .0070 .0070 .0060 .oo6o .0200 .0132 .oo41 .oo42 .ooso .0532 .0100 .0050 .1160 .1030 ~0249 .0157 .0285 .0326 .0138 .0192 .0237 .0077 .o455 .07695 .07755 .os905 .08945 .03105 .03141 .03137 .08975 .oos75 .00lf40 .00355 .00li4o .00263 .00263 .00217 -- - .1000 .1000 .1000 .0616 .0616 .0616 .159 .163 .132 .132 .133 .133 .150 .150 .426 .J.51 .0963 .0963 .0995 .380 -- - .00898 .0228 .0220 .0224 .00452 .00996 .0136 .00572 .0110 .0167 .0280 .0056o .0275 .005so .oos73 .0172 .0849 .0170 .00556 .0288 .- 46.2 .0166 .0086 .0132 .0210 .0008 .oo47 .0143 .ooso .0212 .003g .0260 .0216 •0137 .ooso 61.3 2.65 9.84 2.62 5.80 4.07 4.15 4.66 5.64 3.15 1.2s 5.27 10.60 6.32 22.5 7.71 22.5 28.2 61.3 E1 could be assumed to be 1 then K = k1 k-2L3 [HOA~) It is not possible to calcule.te the reverse rEi,te constant k..1 because theory has shown that _ Ke.= k1k?19 [BO.le] so that as on:t.y KE., k1, [HO.Ac] a.re known k..1 cannot be cal.cu"!' k.. 1k..2lr..3 lated unless some v~lue for -~ could be determined, thus, is not possible het'e . (lt .0217 .1360 .o44o6 .04268 .0309 .0396 .0190 .04426 .03334 .0253 .0279 .0582 .03172 .03334 .0732 .0763 --- .'2Sl-l-25 ~ 08695 .08420 .09385 .09333 .09345 .03300 .033o4 .03322 26 27 28 25 24 23 18 19 20 21 22 i7 15 14 13 11 12 10 130 18,7 1i;.6 13.9 17.9 16.0 14.s lS.8 27.9 27.3 19.2 19.5 23.5 1s.7 ~ -0 c.v•~ 144 112 1g7 176 181 [B]o [B]1 [B] [(CH3)3COOOCH.Jl (12"] (0H3C0)20] [H2 so4) [B] 0 -[:s1. XE l.;1 Rate Concentration Extrapolated Equilibrium Equilibrium _ _ _ Equil• Forward Study of Isobutene initial con- Concentration concentration Mole/1 Mole/l Mole/l Mole/l ibrium Ra-toentration I sobutene t-butyl acetate . Constant Oon1tiant at t = o of isobuten& .0616 .00217 .03103 .000494 1+6.2 .03320 186 9 fable II Rate Study Data in moles/! 1 ti on at 25.00 ± 0.05°0 • .sou ? I -21- concentration of isobutene at time tin moles . /liter of solution - - carbonium ion - - acetic acid (AcOH;] --acetic acid-proton complex [BHOAc] - - t-butyl acetate }rn2oAct°] -t-butyl acetate proton complex k1k2k3 specific rate constants of the forward reaction k_1k-2 k~3 reverse In the anhydrous reaction mixture the following reactions are occurring: k2 -t- BH + AcOH + ~ k_2 + BH OAc + HOAc 2 th us but -dd~B] {BH20Ac•] BH 20Ac k3 ~ k-3 = k1 [B] + BHOAc + AcOH 2 [AcOH~] - k_1 {mf] {AcOH) k2 {B~] (Acori] = £°1 but [BHOA~ = [B11 - {B] assuming [BH-+] is very small, it being the reactive intermediate, andlB] 1 , the initial isobutene concentration : k [B] [AcOH+]+ k1k2k-3 l 2 k2k3 [B] [AcOH2] _ k_1k_ 2k_3 fi3] 1 (AcoH-;J [HOAc] k k [HOAc) 2 3 -22Let KE= 1½_k2k3 ~1 !s2 ~3 [HoAc] be the equilibrium constant for the addition reaction _._ -di~] : k1 [B] [AcOH~] + ~ [ B] [ AcoH;] E =(B] ( k1 [ Acmi;J + ~ (AcOH!~ Let C= 1'i and D : [AcOH2] +- :~ ( AcOH;) = k1 [ AcOH;J l ~ H ! l [B] 1 [AcOHt] If it is assumed that [AcOH 2] is a constant, that is the acidity does 11 not change during the reaction ,; . - dd~B] = C [B] -D • "• dlB] - C B] -D -dt - or J but Jc [B -D - ln (C [B] -D) J = + d fB] _ C (B] -D - f d ~] or C (B] -D Now [B] _ !f constant dln (C [B] -D) = ~ ln (C [B] -D) = -ct+ Constant x C = Constant x e-8t = [B} 1 at t• 0 ln (C [B] -D) ln -t -dt Constant= or } ln (C [B]1 -D) C = -ct C [B] -D [;, = C BJi -D -ct C [ru -D _ -Ct C [B] -D - e 1 ln (C [B i -D) 11 -23.• C tB] -D : or (C [B]i -D)e-Ct C [B] = (C IBJ1 -D)e-C\ D r, } _ LB - ( [ :i D -Ct D BJi - C ) e --t C . B =c~ -ct+ ~ e .. • ~ (1-e -ct) ' 1 C thus since D = ~ [BJ 1 [Ac0H;] KE: and C = kl [AcOH~] (1 +- ½ ) (; D ; 1 c- ~ [B] i [ AcoHt] {B] . - --1 - k1 [ AcoH;](l-t fr;') - l + KE. Thus substituting back in when tis large e.nd thus Now since the initial reaction of H so is with the isobutene to give 2 4 irreversibly (essentially) which then ionizes completely since it is a dilute solution and the solvent is a strong base, thus ( CH ) coso 2oH 3 3 Thus [AcoH;] + AcOH --3. ( CHJ) = [ H2SOJ - + coso2o -t- AcOH2 3 Now after equilibrium (a steady state actually) is attained, the unsaturation increases due to the reaction BH+ + B J..4 aJ!-1- k_4 ++ B2H AcOH ~ B2 -4- AcOH2+ where k , k_4 , k 5 are specific rate constants 4 and [B2] is the dimer concentration, which is irreversible and goes initially only to the dimer (because of decreased ' reactivity does not add HOAc or further polymerize_ rapidly), thus -25- dt d [B, .. =~ LI3H4--] LI.com lB ] [AcOHi] However - -2-~J dt k_ 1 k k k l 4 5 [B] 2 [AcOH k_1k_ 4 2] , the polymerization constant so that [ [B]2 = l( [B]i - (B]E )e -k1 [AcOH.._] (1.f- 1 ) 2 KE + [B]2 E:: But since the polymerization rate is low, at large t (near equilibrium) : rB-.2 lB,2 'J l!>JE :. thus d [B2] : dt K e ----3. o fB]2 [AcOH+] 2 d [B2] : Jt ~ 2 t 0 where t K~ Pr lB2] J -k1 [AcoH;] (1 + ~ )t as [B](: (AcoH;] dt E is time at which equilibrium is attained l = Kp [B]: (AcoH;] (t - tE) :. {B2 Thus the measured unsaturation will be for large t [unsaturation]t = [B\ -1- [B2] · =[B\_ + ~[B]: [AcoHt] (t-tE) Since • •• [AcOH2]= [H2S041 K = [Unsaturation]t -[B]~ p [B]! [H2S041 (t-tE) t -26The theory indicates that the relation between[B]and t should be (IB] - lB]~ \ = loglO \[B]i - [B]f:) which, when compared with l [B] - LB]£) loglO fBl i - [B]~ Kt =- that was used in the analysis of the data, shows that and predicts that l _ K _ K -[H2S04] - should be a constant as was experimentally found. The mechanism presented also permits the polymerization to be studied semi·quantitatively. Thus, since which predicts that KP = (B] - [B]E [B]2 [H2S04] (t - tE) E. should be a constant. This is indeed found to be true as shown by Table III. The presence of excess acetic anhydride has no effect upon the equilibrium constant, KE, or the forward rate constant k1 . This is shown on Table II by Rate Studies #17 and #18 where a fourfold variation in its concentration did not effect KE or k1• There seems to be no trend in the values of KE and k1 with respect to the initial isobutene concentration and the sulfuric acid concentration. The average values of the equilibrium and the -27- Table III Rate Study #20 t - tE 9 .. 9 17.7 23.4 44.8 57.3 69.4 79.5 [B]-[Bl.. .0064 ,.0112 .0137 .0205 .0212 .. 0230 .0260 Rate Study #21 [Hj= Oa0220 moles;1 lBJ~= 0.0088 lBl-lBlE fB]-l.slt: IW'J [H+] [~ ~ .291 .. 510 .623 .923 .963 1.046· 1,.181 950 1670 2040 3050 3150 3420 3860 96 94 87 68 55 49 48 E [It]= 0,.0224 moles;1 [Bf .0041 t - t£ rn~ -[Bl ~1-tBJ, ~1-JBk H.. J f t + tit 5.9 5.7 2.3.2 36.7 47.9 57.9 72.3 .0042 .0050 .0119 _. 0175 .0245 ,.0259 . 0283 .188 .223 • 52.3 .782 1.093 1.156 1 .. 262 Rate Study #24 t - tE. 8.1 11.8 19.4 33.3 57.0 80.l 106 [B]-[B]E .0028 .0051 .0075 ,.0112 .0158 .0169 ,.0182 ~ E ~ H+] .206 .375 .551 .824 1.160 1. 242 1• .339 tsl:;fl~ lH [BJ2 (t-t > «: E 2900 3310 7900 11600 16300 17200 18800 [H]= o.0136 moles;1 (t-tE-) 490 490 340 320 340 300 260 [B]= .0285 I: ts)-lBJE [H-1-] lB] 2 ~ 2060 3610 5300 7930 11200 12000 12900 ~?(t-t ) E 255 306 274 2.38 197 150 121 ~ -28rate constants are The high deviation in KE comes from K ~ = ~CH3) 3COCOCH3] [ (CH3) 2C : CH2] = [B)1 -LB]E [B]~ where {B] 1 depends on [B)~, a quantity that is chosen to give the best straight line. The equilibrium isobutene concentration,[B]E, can have a relatively large effect since it is small and sensitive to errors. The relatively low deviation of k1 comes from kl= [H~~J(l+ 1 )2.303 KE:. where K is the slope of the straight line obtained with the best [B] . E Since K is comparatively insensitive to moderate variations in [B~ 1 and k1 depends on (1+ K ), any slight variation in K will have a E small influence on k1 • The treatment of the very complex equilibrium m:ixture that exists with water present was not possible due to the lack of information as to the final concentration oft-butyl alcohol and the distribution constant of the proton between water and acetic acid: + BH + AcOH -+ B0H3 BH+ + AcOH BOH3 + H20 ......,__ ~ ~ BHOH + H3o+ BOH3 +- AcOH ~ BHOH +- AcOH; BH 20~-+ +H 20 BH20At * BHOAc + H o+ 3 + AcOH ~ BHOAc+ AcoH; -29Qualitatively it is possible to predict that the hydration reaction should be much more rapid due to the greater basicity of water relative to acetic acido This is indeed reflected in the larger values of the forward rate constant for Rate Studies #9 to #15 on Table II. The "equilibrium constants" also show a larger value which is understandable in terms of the greater stability of tertiary butyl alcohol. There are no observable systematic trends on the data, thus K~ = 41.2 ~ 10.0, for Rate Studies #9 to #15 as compared with KE. Studies #17 to t¥30. = 5.3 '! 2.0 for Rate The K(., k1, and [BJ£ values for the two sets of conditions show no correlation with [H2SOJ, tB) 0 , lH20l or [( CH3CO) 20]. The KE values for #9 to #15 (water con- taining) were not reproducible from experiment to experiment whereas the KE for #17 to #30 (anhydrous) gave values that were more duplicatable, although being as sensitive to experimental errors. This lack of reprodubibility reflects the extreme complexity of the reaction system when water is present and is understandable in terms of the equations given above, CONCLUSIONS Using Whitmore 1 s (13) concept of the carbonium ion as an intermediate in acid catalyzed reactions, it has been possible to treat in a quantitative manner the kinetics of the addition of ac~tic acid to isobutene and to semi-quantitatively treat the polymerization. When water is present the reaction -30kinetics become very complicated and were only treated qualitatively. The successful quantitative treatment of the reaction, assuming the following mechanism CHJ'-. / C CH3 /OH = CH2 + CH3-C~ ~ ~PH -+ (CH3) c + CH3 co 2H 3 ~ ~ CH3) 3CO COCH3J+ H 00 co ~ ( CH3 ) 3 cOCOCH.3 + CH.3c( t,"H ( CH ) c-t + CH co 2H 3 3 3 ~ ~ CH.3) .3COHCOCH.31 CH3 2H + and putting in the assumption that (CH3).3C+is present only in small concentrations, leads to (B] - IBlt )- k1 loglO ( {B]i -[BJ~ - -2°303 l H2S041 (1 + Kj 1 t and [B2] = Kp [BJ: [H2soJ (t - t~) where k1 = 19.5 ± 3.1, KE = 5.3 ~ 2o0 and Kp ~ 200,. The semiquantitative results obtained in treating the polymerization on the basis of Whitmore's carbonium ion, further strengthens the evidence for its existance. -31REFERENCES 1. H. J. Lucas, W. Ferdinand Eberz J .A.c.s. (1934) 22, 460; J.A.c.s. (1934) 22, 1230 2. Y. P. Liu, T. C. Wei J. Chinese Chem. Soc. (1936) ~, 297; British Chem. AbstractA(l936) 1210 3. G. Timofejew, L. Andreassaw Journ. chimique de 1 1 Ukraine l, 107-10; Chem. Zentr. 96II, 1652 4. R. Altschul J.A.c.s. (1946) 68, 2605 5. A. J. Weith, M. E. Hobbs, Paul M. Gross J.A.c.s. (1948) 70, 805 6. H. J. Lucas, D. Pressman Ind. Eng. Chem. Anal. Ed. (1938) 1Q, 140 7. w. F. Eberz, H. J. Lucas 8. Norris, .R.igby J.A.c.s. (1932) 2ft, 2088 9. Hu.rd, Spence J.A.c.s. (1929) .2!, 2561 10. Kolthoff and Sandell, Textbook of Quantitative Inorganic Analysis, 621-3 J.A.c.s. (1934) .22, 1230 11. D. Davidson J. Chem. Ed. (1940) 11, 81-4 12. H. J. Lucas, D. Pressman J.A.c.s. (1940) ~' 2069 13~ F. Whitmore J.A.c.s. (1932) 2ft, 3274 t lJ2M ?n ss0'1 L1.t c.<1 s 1 i "'~ T Wn) emdl,s~j ifu 0'11all'iJ (l/{\d _ 1•1 canbd") co~ -ifus1S - T 1,n&,;,lo~ aQ.Q tho SltGf5UO!ls ~olt MQd.o. b !'<\.Q It<\ ~cw-, QQSi /ktTun lr'l -Wio f l)Y)O.O d.nf", j_ he ie --i9i td "I ha.ue. d()/IQ ~ CO'!n_Q ~ - T ~Cl\Kl 'SQ. ~en aP oi:,lQ s MUI ) O'W. b.w>G f<Yi ~au os a-s T ~® w~ihm ilu:s wf)g b o.c.D'.f<th0i 01) . 'IE ~ SQJiiJ R=. T s 0'1=% h:i{'e i:hJ- e.umdihlftl~ ls U") CJ') clvi l!S er Q ~ <?__ U 1 ) 1 r " ' 1 ['<\C'lQ C So(Jf) tin~ ~ To f ~1?1Md OJ<ld cii1C1u1bn~s ~ , T ho?< io ~an -fnorn r Q r n d (i:nof LtU$ (lJY) , as 5o<)() Q.S poss Iha QS \I i , sho\#dans b f i:lwn~s aimpGi_T.ad, T L) I~~ . U,'<),S wtW bi "'- 6 R°"d (% hQ\f'~ b h.u.an a.OOctl- ffi(lf() k lM~~~ Noto GI\ hts tiXY1k ~ a.ds01~UoY) ~ ( ~ ~\'\~ News) 1 it ~i-dcc_~Q.Q f'eO.Omls 4 , ooci: Q ~ kst '(c, ~011 t'r ifsse1 Luc.Qs 1 i~ i <U1.J,WJ Q/Yl cl \-{ € N l ) " ( d (111\ d tfe <t-