VAPOR PHASE CHLORINATION OF 2-BUTENE A L F R E D F . M E I N E R S , F . V . M O R R I S S , A N D C . C . C H A P P E L O W , J R . M i d w s t Research Institute, Kansas City, Mo.
Conditions were determined for the preparation of 1,4-dichloro-2-butene in maximum yield b y the vapor phase chlorination of 2-butene using a simple, single-pass system. Maximum yields were 18 to 2 1 % and the only variable which significantly affected the yield was the reactant ratio. Variations in reactor temperature and reactant ratio caused significant deviations in the yields of most of the other products, but preheat temperature and space velocity did not influence the yield of any product. Increasing reactor temperature increased the yields of HCI, 2-chlorobutane, 3-chloro- 1 -butene, 1,3-dichIoro-2-butenes (a- and 0-forms), and dl-2,3-dichlorobutane, but decreased meso-2,3-dichlorobutane. Increasing the chlorinebutene ratio increased the yields of rneso-2,3-dichlorobutane, 3,4-dichloro- 1 -butene, and 0-1,3-dichloro-2butene, but decreased 1,4-dichloro-2-butene. Oxygen increased the yield of substitution products only within a limited reactor temperature range above a certain minimum ( 2 6 0 " C.) and below the optimum ( 3 7 5 " C.), The vapor phase chlorination of 1 -chloro-2-butene under a variety of conditions gave very poor yields of 1,4-dichloro-2-butene, indicating that the 1 -chloro product i s probably not a major precursor for the 1,4-dichloro product.
study of the vapor phase chlorination of 2-butene was made to determine conditions for the preparation of 1,4-dichIoro-2-butenein maximum yield using a simple, single-pass system. Rust and Vaughn ( 7 7) studied this reaction in the temperature range 210' to 260' C. They observed that the amount of chlorine reacting and the ratio of substitution to addition increased rapidly as the temperature was increased from 200' to 255' C. At 255O, 457& of the chlorine had reacted by substitution and 15% had reacted by addition. At 260" and above, these authors observed that the reaction was difficult to control because of ignition. As there was an interest in maximum amounts of substitution, an extensive scries of experiments was begun to determine conditions which would permit operating a t temperatures above 260'. I n the preliminary experiments, the major problems were flame formation a t elevated temperatures and low yields of substitution products at low temperatures. (The organic products were analyzed by gas chromatography and the yield of HC1 was determined by titration of the quench water.)
A
N EXPLORATORY
Table I. Yidds, 1,4-Dichloro2-butene -
M a x . Reactor
Temp., a C. 192 200 224 251 274 305 330 355 382 401 419 428
1 5 4 7 9
11 18 18 17
18 14 15
During these experiments it became apparent that preheating of the gases was desirable to increase the yield of substitution products. Several preheater and reactor designs were investigated. T h e use of a single jet of chlorine in an atmosphere of 2-butene prevented flaming over a wide range of experimental conditions. Using this reactor design, a second series of experiments was performed in which the reactor temperature was gradually increased. The results of these experiments (Table I ) show that, as the reactor temperature was increased from about 200' to 340' C., there was a gradual increase in the yield of substitution products (1,4-dichloro-2-butene. monochlorobutenes, and HC1) and a corresponding decrease in the yield of addition products (di- and trichlorobutanes). At temperatures above about 350', there was no further increase in the yield of organic substitution products and HC1 yields above 10070 indicated product decomposition. In all these experiments, the chlorine was completely consumed and none was detected in the quench water. Thus, the preliminary experiments provided a set of reaction conditions which permitted control of flaming and near-
Preliminary Experimentsa
?$ ~
HCl
3,4-Dichloro1-butene
dl-2.3Dichlorobutane
Relative Yieldsb meso-2,3Dichlorobutane
MonochlorobutenesC
Trichlorobutanes
67
63 59 64 61 77 96 113 106 100 113 113
5 9 6 7 7.5 7 6 7 4 5 2 7 2
6 5
10 6 6 6 6 4 6 6
9
7 0 2 2 9 8 0
9 10 8 5 5 3 3 3
6 4 0 8 1 5 4 3
6 10 19 21 25 27 27
1 0 0 0 0
4 0
5 12 2 82 1 13 0 98 0 68 0 93 0 88
2 - B u t e n e j o w rate 172 ml./min., chlorinrjow rate 22d m l . / m i n . , and r u n times 15 min. Relative yirlds determined by gas chromatography andfigures prrsmtpd are heights ( i n centimeters) of correspondingpraks. 3-Chloro- I-butene and I-chloro-2-butene. a
66
I&EC PROCESS DESIGN A N D DEVELOPMENT
C.) ; preheater temperature (average temperatures, 333', 307', and 273' C.) ; space velocity (combined feed rates of 300,
Figure 1 , study
Design and randomization of statistical
theoretical yields of hydrogen chloride. In addition, approximate conditions were established for the production of relatively high yields of substitution products and relatively low yields of addition products. Statistically Designed Experiment
As in the authors' laboratories, statistically designed experiments have frequently proved useful in synthesis studies (5, 9). Bennett and Franklin ( 3 ) gave a general reference to the method of experimental design. A statistically designed series of 20 experiments was performed to test the effect of four experimental conditions on the yield of 1,4-dichloro-2-butene. These experiments (a complete replicate of a Z4 factorial experiment with center point replicated four times) simultaneously compared high, low, and medium values of reactor temperature (average maximum temperatures, 402', 381', and 354'
Table II. Expt. No.
Preheater
325, and 350 ml. per minute); and chlorine-butene molar ratio (2.0, 2.15, and 2.3 to 1 ) . The design and randomization of the statistical study are presented in Figure 1. T h e results are presented in Table 11. Statistical analysis indicated that the only experimental variable Lvhich significantly affected the yield of 1,4-dichloro-2butene was reactant ratio. Thus, decreasing the chlorinebutene ratio (from 2.3 to 2.0) increased the yield of 1,4-dichloro-2-butene. Although the gross effects of preheater and reactor temperatures were established in the preliminary experiments, the design study showed that variation between the chosen limits of these conditions had no significant effect on the yield of 1,4-dichloro-2-butene, These conditions fairly well bracket the possible conditions between those which gave little substitution and those which caused fairly extensive dehydrochlorination. For this reason, i t is felt that, unless rather drastic changes are made in experimental conditions other than those studied, the reported yields of 1,4-dichlor0-2butene are near the maximum. With some of the other produrts highly significant changes in yield with reaction conditions were observed. However, preheater temperature and space velocity were not significant in changing the yield of any prodiict (although, as discussed below, there was an interaction between preheater temperature and reactor temperature in regard to yield of HCl). T h e known by-products and their significant yield changes are summarized graphically in Figures 2 and 3, which show the variation of peak heights (from the gas chromatography data) with the two reaction conditions that were significant (reactor temperature and reactant ratio). High levels are designated These symbols indicate the obby 0 and low levels by -. served differences in peak height for each compound a t both levels. When the difference is statistically significant, this is noted by a single, double, or triple asterisk, indicating, respectively, that the difference is significant, very significant, or highly significant. The difference is termed "significant" a t the 95% confidence level if the probability (P)of a random effect of this size is between 0.01 and 0.05. When the prob-
Results of Designed Experiment
Temperature Profile, C.a Mixing Areac Initial Max.
Yzelds,
%
_____._.
Reactor Center Initial Max.
1,4-DichloroInitial Max. HCI 2-butened 388 358 1 316 318 315 369 106 15.2 2 263 271 267 341 316 338 88 16.3 3 313 328 258 352 302 330 89 17.6 4 325 332 260 362 298 336 105 18.3 3 303 304 285 392 325 353 111 16.2 h 264 267 300 403 355 37 6 118 14 n 7 321 326 260 352 290 320 93 i5 i 8 326 326 260 373 292 325 102 16 1 9 275 276 318 407 369 380 118 11 8 10 274 274 303 41 9 357 378 127 12 9 11 305 305 287 396 327 352 113 13.4 268 273 256 341 12 294 323 76 20.9 350 291 13 270 275 257 ... 88 15 2 251 358 283 272 275 95 364 14 19 2 284 327 31 1 357 341 15 309 83 19 5 290 400 366 276 278 376 16 110 13 5 297 357 342 347 402 375 103 17 17 4 276 322 305 310 18 380 341 97 18 5 309 343 355 342 19 426 315 124 13 8 306 357 20 376 342 348 364 18 2 as Run times 15 min. and near maximum temperatures attained within 5 min. Temperatures measured at point 7 inch hphind mixingjet. Tenqp~ratures measicr~dat point 7 inch in front of mixing jet. d Y i e l d j i g u r ~ srefer to combined yields of cis- and trans-1,4-dichloro-2-Dufene calculat~dfrom ,gas chromal n q a p h peak h q h t s . ~
VOL. 5
NO. 1
JANUARY
1966
67
~
__
Table 111.
Effect of Oxygen on Chlorination of 2-Butene“ Temperature Profile, C. _._._____ . . _. Preheater M i x i n g Area Rcactor __ Center- Initial Max. Initial 1Max. Initial Max. ~
Run No.
Oxygen
Concn. 0 0
1 2 3
1
4 5 6 7 8 9 10
2 3 3b 0
3 0 3
260 260 260 260 260 260 175 175 251 256
265 265 265 265 265 265 180 180 283 277
246 258 252 251 253 247 150 148 226 215
360 356 355 355 366 394 163 159 302 302
4 R u n time 30 min., combined feed rate 350 m l , / m i n . , and mole ratio (chlorine-butene) 2.0. oxygen introduced into chlorine stream.
ability is between 0,001 and 0.01, the differrnce is significant a t the 99% confidence level or very significant. When the probability is less than 0.001, the difference is significant a t the 99.9% level or highly significant. Hydrogen Chloride. An increase in reactor temperature significantly increased the yield of HC1 and, although not quite significant, HC1 yields increased with increased chlorinebutene ratio. Also, for HCl there was a n interaction between reactor temperature and preheat temperature. Thus, a t low reactor temperatures, an increase in preheat temperature increased the yield of HCl. (This fact explains the earlier observation that preheating was desirable.) At high reactor temperatures, the yield of HC1 was not increased by increased preheat temperature. 2-Chlorobutane was formed in the reaction mixture by the addition of HCl to 2-butene. Increased reactor temperatures caused highly significant increases in the yield of this product, probably because of the increased yield of HC1 at high temperatures. 1-Chloro-2-butene and 3-Chloro-1-butene are products of monosubstitution. Yields of both were increased by increases in reactor temperature. However, the yield increases were highly significant for 3-chloro-I-butene but not significant for 1-chloro-2-butene. This result may be explained by the subsequent observation that the latter compound is extensively isomerized to the former under the conditions of the experiment. Increased chlorine-butene ratio caused highly significant decreases in the yield of both products. 2,3-Dichlorobutanes are formed by the addition of chlorine to 2-butene. Stereospecific trans addition of chlorine to trans2-butene would produce the meso isomer and this is by far the major product a t lower reactor temperatures where addition reactions predominate (see Table I). At conditions where substitution is the major reaction, the dl and the meso products
Table IV.
M o l e Ratio (Chlorine/ Chloro butene 1
Combined Gaseous Feed Rate, Ml./Min.
0.29 0.31 0.34 0.27 0 . 34c
319 351 348 320 361
233 223 231 222 226 238 143 148 239 231
HCl 121 102
233 231 231 230 232 238 172 157 260 250
Yields, yo 7,4-Dichloro2-butene
17.5 16.3
114 ..
9 4
112 113 117
13 6 16 7 13 3
0 0 75 88
0
0 8.7 11.4
Oxygen introduced into 2-butene stream.
In all others;
were formed in almost equal amounts. However, higher reactor temperatures caused highly significant increases in the yield of the dl isomer and very significant decreases in the yield of the meso isomer. Decreased chlorine-butene ratio also caused very significant increases in the yield of the dl isomer and significant decreases in the yield of the meso isomer. Therefore, a t higher temperatures and a t increased chlorinebutene ratios, it appears that the trans addition of chlorine proceeds to a lesser extent. Although the trans addition of chlorine to cis-2-butene would explain the yield increases of the dl isomer, it is not likely that trans-2-butene would be converted to cis-2-bu~eneunder the conditions of the experiment. At 417’ for 305 minutes, trans-2-butene yielded only 8.1% of the cis isomer ( 7 ) . Thus, the apparent nonstereospecific addition a t elevated temperatures is probably best explained by the free radical addition of chlorine in a manner analogous to the addition of HRr to noncyclic olefins a t temperatures above room temperature (6). 3,4-Dichloro-l-butene may be formed by the rearrangement of its closely related isomer, 1,4-dichloro-2-butene. Reactor temperature did not significantly influence the yield of this product, but yields were lowered by increased chlorine-butene ratios (the opposite chlorine-butene ratio effect was observed for 1,4-dichloro-2-butene). 1,3-Dichloro-Z-butene. Hatch and Perry (7) demonstrated that the a-form of 1,3-dichloro-2-butene had the same carbon framework a s trans-2-chloro-2-butene. T h e @-form was shown to be similarly related to cis-2-chloro-2-butene. Both the a- and @-formswere present in the reaction mixtures. The formation of these products probably involved a dehydrochlorination step and a number of reaction sequences arr possible. Yields of both the a- and @-formswere significantly increased reactor temperature. Yield of a-form was also very significantly increased by increased chlorine-butene ratio.
Chlorination of I-Chloro-2-butene
Reactor Ternpwature, __O C. Mixing Reactor area center
259 146 152 132 137
303 239 195 186 21 3
.-
HC1 101 23 28 25 36
Yields, yG _______ 7 ,CDichloro2-butene
0
7 7 9 3
“Addition Product”a Ob
8 6 8 3
79 83
84 85
.Vo volatile or anic product rrcovered f r o m this experiment. Extensiue a “Addition product” not identified, but presumed to be 7,2,3-trtchlorobutune, Oxygen ( 7.6% of total port$ zntroduced into 7-chlorn-2-butene stream during this run. decomposition z5a.r apparent and a tarry product ioas formed in reactor.
68
l&EC P R O C E S S DESIGN A N D DEVELOPMENT
60
I II
**#
El
Q
HIGH TEMPERATURE RANGE T LOW TEMPERATURE RANGE
1
v)
t z
+
SEN SlTIVlTY 112 1/8 8
3
I-
a a
-5
i
0 5 > P a .01 9 5 % CONFIDENCE LEVEL SIGNIFICANT .OI > D > ,001 9 9 % CONFIDENCE LEVEL: VERY SIGNIFICANT ,001r Q 99.9% CONFlDENCE LEVEL ; HIGHLY SIGNIFICANT
40 I
U
U
2 a U
=. a c
I
Y
I
52 w
l i
20
Y
4
w n
1 1
Figure 2.
RETENTION
I
TIME (MIN.)
Effect of reactor temperature on chlorination of 2-butene
Unidentified Products. There wt're several uiiidentified products in the reaction mixtures. Kecausc. of their re1,itively long retention times (10.6, 26.1, and 33.4 minutes): three were presumed to be trichlorobutanes. The yirlds of these materials decreased with increased reactor temperature. Products Not Formed in Reaction. Shown t o be absent from the reaction mixtures were 1.l-dichloio-7-butene, 2,2dichlorobutane, and 1,3-dichlorohutane. The absence of the latt.er compound probably indicates that the addition of HC1 to 1-chloro-2-butene produces exclusively 1.2-dichlorobutane. However5 the preserici: of 1,2-dichlorobiitane in thc reaction mixtures could not definitely he cstahlished, har:ause h i s product had the same retentioil time as 3.4-dichloro-1-butene. Effect of Oxygen
Rust and Vaughn (10) observed that, at temprraturcs helow 260' C., the over-all chlorination of 2-burene (substitution and addition) is strongly inhibitc.d by oxygtm (3°10 ir; the gas stream). However, ac this temperature and nbovo: they notcd that the reaction is acceleratcd by the presence of oxygen. Cnfortunately, in the high temperaturt expcrirnents these inbestigators were not able to drtermine the rat.io or siibstitution to addition. Comparable rfft=cts of oxygen 1w.d also bern noted by other iiivestigators. For example, Egloff a n d Alexander (1) in an extensive review state that "above certain tcmperarurts, \vhich vary somcwhat with the alkene usrd, small amounts of oxyg,'n actually catalyze tha total chlorination. increaLr the per ccnt substitution, and almost totally siip!)rrss addition." 'Thus. i t was of interest to detrrminc the rffects of oxygen c;n the chlorination of 2-butene undrr conditions previoiisly s h o w n to be optimum. This was donr (7-able 111. run5 1 to 6) and i t was sho\vn that the presence of oxygen did Iioi incrcase the yield of 1,4-dichloro-2-butene. Since lower temperatures result in increased amounts of addition products, exparimcnts were also pcrformcd at Iowcr temperattlras LO determine whethr r oxygen would promote
substitution reactions at the expense of addition reactions. Lower reactor temperatures were dificult to maintain because of the exothermic reaction that occurred near the point of mixing. With initial temperatiires as low as 150' C., an easily controlled reaction was observed (runs 7 and 8), but the yiclds of HC1 and 1,4-dichloro-2-butene were zero (the major product was meso-2,3-dichlorobutane). OxygeTi also had no signific;rnt effect on these results. At intermediate starting temperatures of 21 5' to 225', the temperature increases were rather large, but these experiments (runs 9 and 10) provided reaction conditions intermediate between those which resulted predominantly in addition products and those in which maximum substitution occ:irred. In these experiments at intermediate temperatures, oxygen caused a marked increase in SI Ibsritution products and a proportional decrease in addition products. 'This observation is consistent with the results of Rust and Vaughn (70). Howevt.r, the yields of 1,4-dichloro2-butene were less than those obtained previously at optimum remptratii;es in the absence of oxy;en. Thus, it appears that oxygen will increase the yield of substitution products only if the reactor temperature is above a minimum (260') and below the optimum (350' to 375'). Vapor Phase Chlorinatian of I-Chloro-2-butene
Since the st.atisLica1study indicated that lowering the reactant ratio caused highly significant increases in the yield of monosubstituted products (1-chloro-2-butene and 3-chloro-lbutene), the ftasibility of a step-wise route to 1,4-dichloro-2butcne was investigated. This involved a study of the chlorination of 1 -chloro-2-butene. Using fourfold excesses of 1-chloro. 2-butme a d reactor tempcra tures which were opriinum for the chlorination of 2butme caused cxtcnsive decomposition, and little or no product other than tar could be recovered. I-Chloro-2-butene was isornrriyed rxtansively to 3-chloro-1 -butene under these conditions. When 1-chloro-2-butene was p a s s d through the reactor VOL. 5
NO. 1
JANUARY
1966
69
*
0 5 > P > .01
.oi
*a =*a
60
9 5 % CONFIDENCE LEVEL. SIGNIFICANT LEVEL: V E R Y SIGNIFICANT 9 9 . 9 % CONFIDENCE LEVEL; HIGHLY SIGNIFICANT
> P > ,001 9 9 % CONFIDENCE
.OOI>P
9 HIGH CHLOR1NE:BUTENE RATIO ( 2 . 3 : l )
-
T
LOW CHLOR1NE:BUTENE RATIO ( 2 , O : l )
SENSITIVITY
v)
t z
3
t-
a
a
3 40
I
W (3
a a W
5 I-
S
I1
P w
Q
20
I
9
Y
a w n
44
11 '
20 RETENTION
30
Figure 3.
Effect of chlorine-butene ratio on chlorination of 2-butene
alone (temperature range 121' to 186'), the product was isomerized to 3-chloro-1-butene (9% conversion). At higher reactor temperatures (233" to 246"), the conversion to isomerized product was increased to 24y0. Lower reactor temperatures permitted fair recovery of unchanged 1-chloro-2-butene and several chlorination experiments were performed a t these temperatures (initial reactor temperature approximately 140" at point of mixing to approximately 200' maximum). Careful determination of the conversion and yield indicated that 2 to 394 conversions and 3 to 10% yields were the maximum obtainable. The use of oxygen to suppress addition and the use of increased chlorine ratios did not increase the yield of 1,4-dichloro-2-butene. The results of these experiments are summarized in Table
IV. Experimental
Reactor Design. The reactor (Figure 4) consisted of a ,-inch horizontal borosilicate glass tube about 20 inches in length Preheated 2-butene was allowed to enter one end and preheated chlorine was introduced into the 2-butene atmosphere by means of a single jet located at the point a t which the glass tube entered the tube oven. The tube oven was 10 inches long and consisted of a 1000-watt cylindrical heating element controlled by a thermostat located a t the middle of the heating element near the glass reactor tube. The pre-
\,
r M l X l N G JET
I
Lz-BUTENE
- CHLORINE
THERMOCOUPLE W E L L
1
Figure 4. Schematic diagram of reactor and preheaters 70
10
TIME (MIN.)
I&EC PROCESS DESIGN A N D DEVELOPMENT
heaters consisted of 6-mm. glass tubes (about 30 inches long) wrapped with resistance wire and asbestos. In the area where the preheater tubes entered the reactor tube, the reactor tube was also wrapped with resistance wire and asbestos. Both preheaters and the junction area were heated by means of separate Variacs. A thermocouple tube was inserted from the opposite end of the reactor and extended from the far end of the reactor to within 1 inch of the chlorine jet. At any given time, a temperature profile of the reactor could be obtained by moving a thermocouple down the length of this tube. The temperatures throughout the length of the preheaters were measured prior to reaction by means of a thermocouple and correlated to Variac settings. An additional thermocouple was placed in the junction area about 1 inch behind the mixing jet. Temperatures a t this point were monitored continuously during the reactions. At the exit of the reactor, a spray of water was directed downward into the gas stream emerging from the reactor. The water provided a quench for the reaction and absorbed chlorine and hydrogen chloride. For the chlorination of l-chloro-2-butene, the reactor was very similar. A metering pump was used to deliver liquid 1-chloro-2-butene (2.5 ml. per minute) to a hypodermic needle which was inserted into the junction area of the reactor tube at a point about 3 inches behind the chlorine jet. Nitrogen was swept through the system during the runs (5.0 minutes a t 85 ml. per minute) and for 3 minutes after the flow of l-chloro-2butene had been stopped. In these experiments, the receiver consisted of a single vapor trap containing about 20 ml. of water. Operating Procedure. Flow rates were measured by rotameters which were calibrated by making triplicate determinations a t three different flow rates. trans-2-Butene (Matheson Co., 99.97, minimum purity) and chlorine (Matheson Co., 99.85% minimum purity) were metered from lecture bottles and the cylinder weight losses (2 to 6 grams) were measured using a torsion balance. Oxygen and nitrogen flow rates were determined volumetrically by water displacement. Prior to reaction, the reactor and preheaters were heated to the desired initial temperatures. After the system was swept out with nitrogen, the flow of 2-butene and chlorine was begun almost simultaneously. An electric timer was started and the run was continued for a preselected time. During the runs, the temperature profile of the reactor was observed a t various
times. Usual run times were 15 to 20 minutes and nearmaximum temperatures were attained within 5 minutes. After the reactant gases were shut off, the reactor was swept out with nitrogen. The liquid reactor products were separated from the quench water, dried over sodium sulfate, and analyzed by gas chromatography. The quench water was extracted with carbon tetrachloride and titrated to determine the hydrochloric acid content. Chlorine was determined by treating the carbon tetrachloride extract with aqueous potassium iodide and titrating the liberated iodine with thiosulfate. Product Identification and Analysis. Gas chromatography provided a quantitative analysis for 1,4-dichloro-2-butene. Calibration curves were obtained (peak height us. weight) and used to calculate yields. Other components were analyzed qualitatively by this procedure. For a series of experiments, a comparison of corresponding peak heights provided a means of determining the relative yields of each component. The chromatograph was a Perkin-Elmer Model 154-B (column A, helium carrier gas, 125” C., 20 p.s.i.g.). 2-CHLOROBUTANE (Eastman Chemical Co.) was a 99 mole yomixture of the dl isomers. Retention time, 2.0 minutes. ~ - C H L O R O - ~ - B U T(Columbia ENE Organic Chemicals Co.) was a 99 mole yo mixture of the dl isomers. Retention time, 2.2 minutes. ~ - C H L O R O - ~ - R U T(Columbia ENE Organic Chemicals Co.) was a 99 mole % mixture of the cis-trans isomers. Retention time, 2.7 minutes. 1,1-DICHLORO-2-BUTENE was prepared from crotonaldehyde (Eastman Chemical Co.) and phosphorus pentachloride according to the method of Andrews (2). Andrews demonstrated that the product was 90% 1,3-dichloro-l-butene and about 10% 1,l-dichloro-2-butene. Gas chromatography of this reaction mixture showed two peaks (area ratio approximately 9 to 1) and the assignments were made accordingly. Retention times, l,l-dichloro-2-butene, 5.7 minutes; 1,3dichloro-1-butene, 6.8 minutes. T h e absence of 1,l-dichloro2-butene from the reaction mixtures from the 2-butene chlorinations was confirmed by gas chromatographic analysis a t lower temperature (85’ C . ) . 1,3-Dichloro-l-butene could not be distinguished from 3,4-dichloro-1-butene because of nearly identical retention times, even a t lower temperature. ~,~-DICHLOROBUT (Columbia A N E S Organic Chemicals Co.) were purchased as a 99 mole % mixture of the dl and the meso isomers. Assignment of appropriate retention times was based on a fractional distillation of the mixture using a vacuumjacketed, concentric-tube column. The difference in boiling points ( d l , 117.1O0C.,/746rnm.; meso, 113.14’C./746mm.)(&) permitted almost complete separation of the stereoisomers. Retention times, meso, 5.5 minutes; dl, 6.2 minutes. 3, ~ - D I C H L O R 1-BUTENE O(Peninsular ChemResearch, Inc .) !vas a 99 mole % mixture of dl isomers. I t was also identified
as a by-product in commercial 1,4-dichloro-2-butene. Retention time, 6.8 minutes. Two other compounds, 1>3dichloro-1-butene and 1,2-dichlorobutane (Chemicals Procurement Laboratories, Inc.), had nearly identical retention times and were indistinguishable from 3,4-dichloro-l-butene. 1,3-DICHLORO-2-BUTENE (Eastman Chemical c o . ) was a mixture of the a- and @-isomers. The predominant isomer in the authors’ reaction mixtures was assigned the a-configuration because this configuration is identical to that of the starting material, trans-2-butene (7). Retention times, a-isomer, 7.8 minutes; @-isomer,9.9 minutes. ~,~-DICHLOROBUTANE(Chemicals Procurement Laboratories, Inc.) was not found in any reaction mixture. Retention time, 8.9 minutes. 1,4-DICHLORO-2-BUTENE (Peninsular ChemResearch, Inc.) was 98 mole Yo the trans isomer. Another sample (E. I. du Pont de Semours &r Co.) was 93 mole yo trans isomer, 6 mole 7 0 cis isomer, and 0.3 mole 7o 3,4-dichloro-l-butene. Retention times, cis isomer, 14.8 minutes; trans isomer. 17.8 minutes. Acknowledgment
The authors are indebted to Calvin Bolze, who formulated the experimental design and performed the statistical analyses, and to Robert N. Clark and Dayton A. Saunders, who assisted in the chlorination experiments. Literature Cited
(1) Anderson, W. F., Bell, J. A., Diamond, J . lM., \$‘ikon. K. R., J . A m . Chem. SOG.80, 2384 (1958). (2) Andrews, L. J., Ibid., 68, 2584 (1946). (3) Bennett, C. A , , Franklin, N. L.: “Statistical Analyses in Chemistry and the Chemical Industry,” \Viley, New York, 1954. (4) Egloff, G., Alexander, M., 011 Gas J.41, 39 (1942). (5) Franz, R. X., Xpplegath, F., Baiocchi, F., Morriss, F. V., J . Org. Chem. 26, 3309 (1961). (6) Gzuld, E. S.,“Mechanism and Structure in Organic Chemistry, p. 734, Holt, New York, 1959. (7) Hatch, L. F., Perry, R. H., J . A m . Chem. SOC. 7 7 , 1136 (1955). (8) Lucas, H. J., Gould, C. W., Jr., Ibid., 63, 2541 (1941). (9) Meiners. A. F., Bolze, C.: Scherer, A. L., Morriss. F. V., J . Org. Chem. 23, 1122 (1958). (10) Rust, F. F., Vaughn, W. E., Ibid.,5 , 481-2 (1940). (11) Ibid.,pp. 486-7. RECEIVED for review March 12>1965 ACCEPTED September 1, 1965 Work supported by the Texas Butadiene and Chemical Corp. (now part of Sinclair Petrochemicals, Inc.).
EFFECT OF ADDITIVES ON OXIDATION OF BENZOIC ACID IN T H E TOLUENE-TOPHENOL PROCESS DENTON M. A L B R I G H T , CHARLES P E R L A K Y , AND P H I L I P X . M A S C I A N T O N I O dpplted Research Lahoratoiy, United States Steel Corp., Monroeville, Pa.
years, a new synthetic phenol process has become This is a two-stage process involving (1) the liquid-phase oxidation of toluene to benzoic acid, and (2) the subsequent conversion of benzoic acid to phenol. This paper is concerned with the second process stage, and more particularly with the effect of selected antioxidants on the amount of phenol produced and on the formation of by-product tar. Y RECEST
I-commercially available.
The conversion of benzoic acid to phenol involves oxidation of benzoic acid at elevated temperature with small amounts of a cupric benzoate catalyst promoted with magnesium benzoate ( 7 , 4-77, 75-18). T o maintain the cupric benzoate catalyst in the active state, oxygen (or air) is continuously introduced to the reaction mixture. Steam is simultaneously introduced to hasten the decomposition of intermediate reaction products, such as phenyl benzoate, to give phenol. VOL: 5
NO. 1
JANUARY
1966
71
