HIGH TEMPERATURE CHLORINATION OF a-METHYLSTYRENE KARL
E.
FUGER
A N D
D O N A L D
1. D E V R I E S
Atlantic Richfield Co., Harvey, I l l . 60426
The! major processing variables of the chlorination of a-methylstyrene were studied. Selectivities of a-methylstyrene to 2-phenylallyl chloride of 90% at 30% conversion were achieved by operating a t 50OoC. and 0.025-second reaction time. High temperatures and short reaction times followed by immediate quenching of the reaction product are the most important factors governing the formation of :?-phenylallyl chloride in high selectivities.
A ,REACTIVE bifunctional product, 2-phenylallyl chloride, is obtained by the chlorination of a-methylstyrene and
a precursor to a series of potentially interesting monomers. While the chlorination of propylene a t elevated temperatures had been known for a long time (Groll and Hearne, 1939; Hearne et al., 1953) and is used in a commercial process for the manufacture of allyl alcohol (Fairbairn et al., 1947), little information was available in the literature on the synthesis of 2-phenylallyl chloride (Hatch and Patton, 1954; Reed, 1965). The present work was undertaken to study the factors leading to high selectivities of 2-phenylallyl chloride by chlorination of a-methylstyrene. Initial experiments had shown that chlorination in the liquid phase formed substantial amounts of 1-chloro-2-phenyl-1-propene among other by-products (Keith and Zmitrovis, 1963). Separation of the allylic and vinylic chlorides is very difficult because of close boiling points and similar physical properties. Chlorination of a-methylstyrene in the vapor phase a t elevated temperatures resulted in an almost complete suppression of 1-chloro-2-phenyl-1-propeneformation. Hydrolysis of 2-phenylallyl chloride to alcohol is reported by Fuger and DeVries (1969).
of a tube (17% inches long, K inch x 16 gage) with concentric thermowell ( % inch x 16 gage trimmed to 0.208-inch 0.d.). The reactor volume was 4.65 cc. and the difference between the diameters of the reactor tube (i.d.) and the thermowell (0.d.) was only 1.2 mm. At the end of one feed line and a t the upper end of the reaction zone 1-mm. i.d. capillaries led to pressure gages. A small bleed of nitrogen was used to avoid condensation of product in these capillaries. Preheaters and reactor were made of Inconel tubing. A stainless steel valve with an extended stem was welded to the exit of the reactor and the valve connected to a %-inch stainless IS
Experimental
a-Methylstyrene used was supplied partly by Matheson, Coleman & Bell and partly by Allied Chemical. Chlorine was obtained from the Matheson Co. and prepurified nitrogen from Airco was used. The apparatus is shown in the flowsheet in Figure 1 and Figure 2. 0-Methylstyrene was fed with a Zenith pump, 9, from a 250-ml. buret with 1-ml. calibrations, 8, into a preheating coil, 11. Chlorine from a cylinder, 2, was dried with Drierite, 3, and fed through a rotameter, 6, into another preheating coil. The nitrogen used as diluent was fed from a cylinder, 1, in two equal streams through rotameters 4 and 5 into the two preheating coils. Two thermowells a t the end of the preheaters permitted measurement of the temperature of the two feed streams which maintained salt-bath temperatures in all runs. The feed lines were connected to the reactor through short pieces of capillary tubing to avoid backmixing. The reaction zone consisted
I
I
22
Figure 1. Flowsheet of chlorination apparatus 1 . NPcylinder 2. CIPcylinder 3. Dryer 4 , 5 . N2 rotameter 6. CIProtameter 7. Check valve
8. a-Methylstyrene feed 9. Zenith pump 10. Therrnostated salt bath 1 1 . Feed preheaters ~ncone~ 12. Reaction zone 13. Pressure gages for pressure
]
14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24.
Thermowells with thermocouples Water quench
25.
Wet test meter
Water cooler Product receiver Product separator Recycle pump Wash bottle Dry ice traps Dry ice trap with dernister p a d Activated carbon towers Wash bottle
drop in reaction zone
VOL. 8 N O . 2 JUNE 1 9 6 9
163
recovered in this manner. As shown by blank tests, a standard amount of 8 grams was added to the total weight of product because of unrecoverable losses with the amount of quench water used. The reaction product was then dried by shaking with Drierite. After each experiment air was passed through the reactor a t 550" C. for 20 to 30 minutes to burn out any coke that might have formed. Analysis
R e a c t i o n z o n e >_
I
4'
Figure 2. Chlorination reactor
steel tube used as the quench zone. At ?4 inch from the valve, another %-inch stainless steel tube was attached to the quench zone to introduce the quench water. Preheaters, reaction zone, and initial part of the quench zone were all submerged in a well stirred salt bath kept a t constant temperature. The quenched reaction product was then cooled, 16, to room temperature and collected in a product receiver, 17. The aqueous phase (-3500 to 4000 ml.) was recycled, 19, as quench water (-270 ml. per minute). The gas phase containing reaction product in the form of white fumes was passed successively through a wash bottle with water, 20, through three large traps in dry ice, the last one, 22, containing "demister" pad, and through two towers, each containing approximately 200 grams of activated carbon. The exit gas was then saturated with water and its volume measured. A few check tests showed that the organic material in the traps had the same composition as the main product. I t was therefore assumed that this is also the case for the vapors absorbed in the carbon towers. A total of approximately 2 to 3% of product was collected in traps and towers. A prerun of approximately 200 ml. of a-methylstyrene feed was made to equilibrate the reaction system, followed by a run of 210 to 220 ml. of feed. At the end of the run a temperature profile within the reaction zone was taken by pulling the thermocouple stepwise out of the thermowell. I n most runs a temperature maximum was observed 2 to 3 inches from the beginning of the reaction zone. Another minor temperature maximum was sometimes observed, depending on the reaction conditions, further on along the reaction zone. The first maximum temperature zone was considered as the true reaction temperature. The separated hazy aqueous layer was heated to 40" to 5O"C., 4 to 5 grams of sodium chloride were added, and the layer was again cooled to room temperature. An additional 4 to 15 grams of product were 164
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
The reaction product was analyzed by gas chromatography. A 5-foot length of %-inch tubing column was used, containing in the order of gas flow: 1.8 grams of 25% polypropylene glycol adipate (Reoplex 400) on Chromosorb W and 10.7 grams of 10% Sinclair 9150 oil (solvent-refined lubricating oil with a viscosity index of 90 and a viscosity of 150 Saybolt seconds) on Silicladtreated Chromosorb W. H e flow was 150 cc. per minute; column temperature, 154"C. The following compounds were analyzed quantitatively: a-methylstyrene, 6-chloroO-methylstyrene (2-chloro-l-phenyl-l-propene), l-chloro-2phenyl-1-propene, and 2-phenylallyl chloride. p-tertButyltoluene was used as internal standard with help of calibration charts. 1,2-Dichloro-2-phenylpropane was determined quantitatively by the difference between the total amount of chlorine fed and the degree of reaction by substitution. Although a larger degree of uncertainty may be attached to these values, the general trends are defined. Less certain is the accuracy of the determination of 1,3-dichloro-2-phenyl-l-propene found from the difference between the total hydrochloric acid titrated in the quench water and the sum of the monochlorides found by gas chromatography. The determined values are included, as they indicate the trend of its formation with respect to reaction conditions. d-Chloro-8methylstyrene was not isolated in such purity as to permit an unequivocal identification, but all available evidence points to this compound. Results
The five major processing variables studied were temperature, molar per cent chlorination, dilution (ratio Nz/ a-MS + C12),total pressure, and reaction time. The levels of these variables were chosen as far apart as thought necessary, based on initial exploratory runs to obtain as complete an insight as possible into the reactions taking place. The levels of dilution and degree of chlorination were taken such that rapid coking would be avoided. T o reduce the number of experiments, the program was carried out in two parts (Figure 3 ) . Experimental conditions are given in Table I and in Figures 4 to 8. Effect of Dilution. Dilution of the reactants with nitrogen was necessary to avoid coking in the reaction zone, particularly toward the end and around the exit valve. Within the limits chosen for this experimental program, the degree of dilution had only a minor effect on the selectivity of the reaction of wmethylstyrene, particularly a t 500" C. At 350" C. a slight decreasing tendency was observed in the formation of 2-phenylallyl chloride and 1,2-dichloro2-phenylpropane, while the formation of 1-chloro-2-phenyl1-propene (vinylic chloride), (3-chloro-6-methylstyrene,and 1,3-dichloro-2-phenyl-l-propene was slightly favored as dilution increased. Effect of Temperature. Temperature is the dominant processing variable, since it affects the distribution of reaction products most significantly, At 30% molar chlorina-
Te m pera t ure 1001
tion
I
I
500°C -
J.
1
.
8
1
310
4.0
"
5.0
6.0 Dilution
I
350@J'u
65
30
I
350°C
100% M o l a r Chlorination h
50
c
'5 .c
Reaction Time Sec.1
40.
-0-
L
30.
-CL
3.0
4.0
5.0
Figure 4. Effect of dilution a-methylstyrene to products
ACI 1.2 DiCl
6.0 D i l u t i o n on
of
selectivity
500" to 350" C., 30% chlorination, 0.05-second reaction time,
0.025 20
40
4P
40-p.s.i.g. pressure
*
YOpsig Pressure
ACI. 2-Phenylallyl chloride VCI. 1-Chloro-2-phenyl-1-propene 1, 2 DiCI. 1, 2-Dichloro-2-phenylpropane 1, 3 DiCI. 1, 3-Dichloro-2-phenyl-1-propene
Figure 3. Reaction conditions
6-CI-d-MS. $-Chloro-d-rnethylstyrene
tion the selectivity of a-methylstyrene to 2-phenylallyl chloride increases rapidly from 41% a t 350°C. to 85% at 500°C. and appears to level off or decrease a t higher temperatures (Figure 6). An experiment a t 580"C., 30% chlorination, dilution 3.0, 0.05-second reaction time, and 40-p.s.i.g. pressure led to immediate carbonization and plugging of the reaction zone as soon as the chlorine
feed was started. The formation of by-products is significantly reduced with increased reaction temperatures, except for the formation of 1,3-dichloro-2-phenyl-lpropene, which shows a tendency to higher values. A similar product distribution pattern was observed a t 100% chlorination. The selectivity of a-methylstyrene to by-products, particularly 1,2-dichloro-2-phenylpropane at
Table 1. Experimental Conditions
Temp.,
No.
c.
Molar R Chlorination
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
510 501 352 495 430 342 495 354 421 496 499 499 360 435 542 544 498 497 496 501 503
102.7 31.8 31.1 65.9 100 98.9 31.0 31.6 30.9 30.3 65.3 103 102 66.9 31.2 34.3 29.4 30.6 30.2 32.5 31.0
Run
Dilution, N2/a-MS+ ClP
Reaction Time, Sec.
6.1 6.3 3.1 3.0 3.0 6.0 3.0 6.3 6.2 4.5 6.0 4.6 4.6 4.6 3.1 5.0 3.0 3.1 3.0 3.0 3.1
0.049 0.05 0.048 0.05 0.05 0.05 0.05 0.05 0.05 0.05 0.045 0.057 0.05 0.05 0.05 0.05 0.073 0.076 0.076 0.05 0.025
Quench a-MS sc Pressure, Water, Concersion Feed Rate, P.S.I.G. MolesiMin. Moles Min. of a-MS 39 40 37.7 40.2 40 40 40 40 40 40 40 40.5 40 40 40 40 20 40 60 60 60
15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 15 21 30
1.36 2.03 4.5 2.93 2.69 1.72 1.70 2.52 2.305 2.72 1.88 1.71 2.16 2.32 3.41 2.26 1.65 2.46 3.41 5.08 9.79
76.3 32.2 34.9 55.1 87.0 94.5 30.1 27.8 30.8 28.2 58.4 78.7 99.7 64.7 27.8 28.1 25.2 28.1 27.8 28.4 30.9
C/c
Conversion of
c12
100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
VOL. 8 NO. 2 JUNE 1 9 6 9
165
IO0 loo
80 )r
.-
c
.,> 60 c
0
40
o\"
0- 1.3 DiCl
I
K l . 2 DiCl
fI
I.2DiCI
20
4
~
*r'
20
"
,
40
60"
,
V ,
80
C
,A
I 8-CI.SMS
IOOo/,Chlorination
35OOC
Tem per a t u r e Figure 5 . Effect of temperature on selectivity of a-methylstyrene to products 30% chlorination, 0.05-second reaction time, 40-p.s.i.g. pressure
,, 1.3DiCl 8.CI.B-MS
20
40
60
80
IOOgbChlorination
Figure 7. Effect of per cent chlorination on selectivity of a-methylstyrene to products 500"C. and 350" C., 0.05-second reaction time, 40-p.s.i.g. pressure
Temperot ure Figure 6. Effect of temperature on selectivity of a-methylstyrene to products
,\." 20
100% chlorination, 0.05-second reaction time, 40-p.s.i.g. pressure
lower temperatures and 1,3-dichloro-2-phenyl-l-propene a t higher temperatures, was increased a t the expense of 2-phenylallyl chloride (Figure 6). Effect of Degree of Chlorination. 2-Phenylallyl chloride is obtained with a higher selectivity a t lower degrees of chlorination. Figure 7 depicts how a t 500" C. the selectivity of a-methylstyrene to 2-phenylallyl chloride is decreased from 86.4 to 66.0% by increasing the degree of chlorination from 30 to 102%. T h e main increase in by-product formation is that of l,3-dichloro-2-phenyl-l-propene. At 350" C. the product distribution is such that an increase in degree of chlorination from 30 to 100% does not alter it to a large degree. A slight increase in the selectivity of l-chloro2-phenyl-1-propene was observed, while those of 2-phenylallyl chloride and 1,2-dichlor0-2-phenylpropanewere reduced. Effect of Reaction Time. The reaction time was varied by changing the feed rates of starting materials and calculated under the assumption of validity of the ideal gas laws. The only reaction products affected by varying the reaction time between 0.025 and 0.076 second are 2-phenylallyl chloride and 1,3-dichloro-2-phenyl-lpropene. As the contact time is reduced, the selectivity diminishes. With the to 1,3-dichloro-2-phenyl-1-propene 166
I&EC PRODUCT RESEARCH A N D DEVELOPMENT
I 2 DiCl A-CI-A.
MS
Reaction Time Figure 8. Effect of reaction time on selectivity of a-methylstyrene to products 500" C., 30% chlorination, 3.0 dilution, 60-p.s.i.g. pressure
reactor used for this program, the feed rates could not be increased to reaction times much below 0.025 second (Figure 8). Pilot Plant
To provide larger quantities of 2-phenylallyl chloride for the study of the hydrolysis and derivatives, a pilot plant was constructed (scale-up factor 8). The design was basically the same as the apparatus used in this work. The feed streams were heated to the desired temperature by individual electric heaters and the reactants allowed to react in a noninsulated tubular reactor and quenched with water. Results obtained a t this larger scale chlorination indicated a good reproducibility of bench scale experiments. Coke formation was no major problem, if optimum reaction conditions were chosen and closely observed.
Discussion
Toxicity Studies
High temperature chlorination of a-methylstyrene leads to reaction products of type similar to those obtained by chlorination of propylene (Groll and Hearne, 1939). The main product, 2-phenylallyl chloride, is probably formed by chlorination via an allylic radical intermediate and predominantly favored a t reaction temperatures of 500" to 550°C. and a low degree of chlorination. Under these conditions the rate of reaction is very fast and chlorine conversion is complete a t reaction times of 0.025 second or less. As the degree of chlorination is increased, a t the high temperature 2-phenylallyl chloride reacts further, conceivably in a manner similar to that reported for allyl chloride (Hearne et al., 1953), to give mainly 1,3-dichloro-2-phenyl-l-propene.At low temperatures, 1,2-dichloro-2-phenylpropene is formed in a substantial degree by addition of chlorine across the double bond of cy-methylstyrene. Reaction conditions favoring the formation of 1,2-dichlor0-2-phenylpropanewere the same for the vinylic chloride, 1-chloro-2-phenyl-1-propene. We assume therefore that the vinylic chloride is formed either by dehydrochlorination of 1,2-dichloro-2-phenylpropane or from an intermediate species in the formation of the latter. To which extent such a path also contributes to the formation of allylic chloride is uncertain. I n this respect the chlorination of a-methylstyrene differs from that of propylene (Groll and Hearne, 1939) and of ar-methylstyrene (Hoffenberg, 1964), which have hydrogen substituents in the 2-position. Similarly, but to a much smaller degree, d-chloro-d-methylstyrene is believed to be present and formed by a phenyl shift. The structure identification is somewhat tentative but supported by the observation that the compound exhibited a high degree of stability under hydrolysis conditions.
T h e results of oral ingestion and inhalation exposure on rats indicate that 2-phenylallyl chloride is relatively toxic. Skin and eye irritation tests on rabbits show that excessive exposure can result in inflammation of the exposed area. Acute Oral
Acute Vapor
LD,o (Rats), G &
LC )(Rats), Mg L
1.5
> 3.2
Irritation (Rabbits) Es e Skin Moderate
Moderate
Literature Cited
Fairbairn, A. W., Cheney, H. A., Cherniavsky, A. J., Chem. Eng. Progr. 43, 280 (1947). Fuger, K. E., DeVries, D. L., IND. ENG.CHEM.PROD. RES. DEVELOP. 8, 167 (1969). Groll, H . P. A., Hearne, G., I n d . Eng. Chem. 31, 1530 (1939). Hatch, L. F., Patton, T. L., J . A m . Chem. SOC.76, 2705 (1954). Hearne, G. W., Evans, T. W., Yale, H. L., Hoff, M. C., J . A m . Chem. SOC.75, 1392 (1953). Hoffenberg, D. S., IND.ENG.CHEM.PROD. RES. DEVELOP. 3, 113 (1964). Keith, W. C., Zmitrovis, R. P. (to Sinclair Research), U. S. Patent 3,100,232 (1963). Reed, S. F., J . Org. Chem. 30, 3258 (1965).
RECEIVED for review July 19, 1968 ACCEPTED January 29, 1969
HYDROLYSIS OF 2-PHENYLALLYL CHLORIDE KARL
E.
FUGER
A N D
Atlantic Richfield Co., Harvey, Ill.
D O N A L D
1.
D E V R I E S
60426
The m8ajorprocessing variables of batch and continuous hydrolysis of 2-phenylallyl chloride with aqueous sodium hydroxide were studied. Yields of 2-phenylallyl alcohol greater than 90% were obtained with 20% molar excess of 6% sodium hydroxide solution at 150" to 180" C. Substantial isomerization of 2-phenylallyl alcohol to 2-phenylpropionaldehyde occurred if the aqueous phase became acidic.
A MONO ME^ of potential interest is 2-phenylallyl alcohol, since it is readily available by hydrolysis of 2-phenylallyl chloride. A number of useful applications can be found, particularly in thermosetting resins of the methyl methacrylate type and thermosetting acrylics used in materials such as paints, as well as to produce allyl phosphonates which are effective flame retardants. As is the case with 2-phenylallyl chloride, very little information on 2-phenylallyl alcohol is reported in the literature. Butler (1953 ) prepared the alcohol by hydrolysis of 2-phenylallyl acetate obtained by selenium dioxide oxidation of a-methylstyrene. Hatch and Patton (1954)
hydrolyzed 2-phenylallyl bromide made by the reaction of N-bromosuccinimide with a-methylstyrene. The present work describes the batch and continuous hydrolysis of purified 2-phenylallyl chloride as well as the crude reaction product of the high temperature chlorination of a-methylstyrene. Experimental
The hydrolysis feed was obtained by high temperature chlorination of a-methylstyrene as described by Fuger and DeVries (1969). Crude chlorination product as well as 2-phenylallyl chloride purified by vacuum distillation VOL. 8 N O . 2 JUNE 1 9 6 9
167
