PHOTOINITIATED ADDITION OF CARBOXYLIC ACIDS T O HIGHER OLEFINS A L F R E D S T E I T Z , JR.,'
A N D T R U M A N P. M O O T E , JR.
Pan American Petroleum Cor#., Tulsa, Okla.
Photoinitiated addition of carboxylic acids to higher olefins is a first-order reaction with respect to acid concentration. Telomeric branched acid products and hydrocarbon polymers are formed. About 75 mole of the acid products are 1 to 1 adducts when normal acids are treated with higher 1-olefins. Power requirements are as low as 1.9 kw.-hr. per pound of product. The addition of propionic acid to 1 -octene requires an activation energy of 2.24 kcal. per gram mole of acid product. A free radical chain mechanism explains the experimental facts.
yo
'
since 1948 that ethylene can be polymerized in the presence of free-radical initiators and oxygenated compounds to form higher molecular weight derivatives (telomers) of the oxygenated compound used (3, 73). More recently, similar studies have been made at lower ethylene pressures to produce lower molecular weight homologs. Thus, C4 to Ca ketones have been prepared from ethylene and acetaldehyde (6, 71, 75) and C4 to Cg acids from ethylene and acetic acid (2). These olefin-oxy addition reactions initiated by free radicals were extended to the preparation of adducts of high molecular weight olefins with oxygenated compounds. Thus, primary and secondary alcohols add to higher olefins, such as 1-octene, in the presence of peroxide or upon radiation with ultraviolet light (72). Similarly high molecular weight ketones can be prepared by addition of aldehydes to olefins (4, 7). T h e purpose of this work was to study the addition of carboxylic acids to higher olefins ( 8 ) . The objectives were to determine the nature of the reaction products and factors controlling their distribution and to study the reaction kinetics so that a n over-all mechanism could be postulated. Since termination reactions become a more important factor when higher olefins are used in place of ethylene, the initiator requirements are comparatively greater. This investigation was carried out by photoinitiation to avoid contamination of products with fragments from radicalproducing chemical initiators. Since completion of this work, a study of free radical addition of monobasic acids to a-olefins using tert-butyl peroxide as initiator has been made in Russia T H A S BEEN KKOWN
(9. Experimental The reagents were commercial materials. Constantboiling heart cuts of the carboxylic acids were used as obtained by fractionation on 4-foot columns packed with Fenske glass helices. Three lamps, one arc and two mercury-resonance (5), were used as sources of ultraviolet light. The arc lamp and one of the mercury resonance lamps were used in the studies of prod-
1 Present address, Research Department, Amoco Chemicals Co., Whiting, Ind.
132
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
uct distribution ; the other mercury-resonance lamp was used in studies of the temperature coefficient of reactivity. The 100-watt arc lamp-G.E. (H 100-A4), high-pressure quartz-emits a broad energy spectrum and considerable heat; the glass envelope was removed to obtain light of less than 3000 A. wave lengths, which is desirable for initiating the reaction. Less than 27, of the radiant energy is at or below 2537 A. wave length. One mercury-resonance lamp-a low-pressure discharge tube-was custom made by Hanovia Chemical and Manufacturing Co. The other is a commercial U-shaped lamp (Hanovia lamp 88A-45), rated a t 35 watts. The first lamp was made from quartz tubing of 5-mm. outside diameter, in 1.5inch diameter spirals, each about 1.5 inches apart. The effective length was about 8 inches; the over-all length, including electrode section but not stem, was 13.5 inches. The lamp required a 3000-volt, 30-ma. ballast and consumed 24 watts per hour. A sketch of the apparatus involving the use of the arc lamp is shown in Figure 1. The quartz lamp was inserted into a quartz well, which was immersed in the reactants in a 1-liter flask. Reactants were added to the flask in the desired ratio, the solution was brought to reflux, and the bulb was turned on. Samples were taken a t convenient intervals by drawing liquid through a condenser into a reservoir with a suction bulb. The reactor used with the spiral resonance lamp was a 3liter resin flask. At the top there were three 24/40 joints and one 34/40 joint. The small joints were used for an ice-water reflux condenser, a glass stirrer, and a sampling device. Through the large center joint. containing a n ice-water condenser, was suspended the ultraviolet lamp, the lead wires of which were protected from boiling acid by a quartz stem connected to the lamp and running through a rubber stopper a t the top of the condenser. T o heat the reacting solution, the resin flask was wrapped with heating wire (35 feet of 20 B and S gage Chrome1 A, 0.629 ohm per foot). The reaction flask was insulated by placing it inside a Dewar flask. The solution was stirred and heated to refluxing temperature before the lamp was turned on, and the reaction time was started. Solution temperature was measured by a thermocouple in a well that extended into the reaction liquid through the reflux condenser. Reactivity of Acid-Olefin Pairs. Ten carboxylic acidolefin pairs (acid to olefin mole ratio of 10 in the charge)
!I
QUARTZ T U B E - - - A
1 ~
If\ 1
SAMPLE RESERVOIR
LAMP\
Figure 1 , Apparatus for photoinitiating reaction of organic acid and olefin with an arc lamp
were radiated with the arc lamp. Radiation was continued for 30 hours a t 120' to 140' C . ; the acid product obtained \\as determined by one or more of three methods: water extraction. fractionation, or chromatography. Samples containing acetic or propionic acid as reactants 1% ere extracted. The water-soluble reactant was removed by mater washing, and the water-insoluble material was titrated for high molecular weight product acids. Reactants were removed by fractionation with a 4-foot, 15mm. column, vacuum-jacketed and packed with '8-inch Fenske glass helices. T h e residue was titrated for high molecular weight product acids. This method is probably not so accurate as the other two because the column holdup \+as not recovered for analysis. Low molecular weight reactant acids were separated from the high molecular weight product acids by partition chromatography ( 7 4 ) . T h e immobile phase was methyl Cellosolve adsorbed on silicic acid. The mobile phase was either Skellysolve B for C, and higher acids or Skellysolve B plus nbutyl ether for acids with less than nine carbon atoms. The acid mixture to be analyzed was diluted with Skellysolve B so that 0.25 ml. of diluted acids contained about 0.02 gram of acids. A 0.25-ml. sample was charged to the column. Fractions from the column were titrated with 0.05NN a O H from a buret graduated to 0.001 ml. Effect of Radiation Time, The effect of radiation time on 1 to 1 adduct formation between I-hexene and propionic acid was studied by determining the total acid production and then the product distribution of the isolated acids. After 49 hours of radiation, total acid production was determined by extraction; after 113 hours, it was determined by both extraction and distillation. In a n improved fractionation method, about 3 liters of the crude reaction solution was charged to a 1-inch inside diameter column, packed for 4 feet with Fenske glass helices. Unreacted acid and olefin were taken overhead until the pot temperature reached 200' C. T h e pot residue, still contaminated with unreacted acid, was transferred to a smaller pot fitted to a condenser but having no fractionating section. Vacuum
was applied to keep pot temperature below 200' C., and an overhead temperature cut point was chosen that was about halfway between the boiling points of the unreacted acid and the 1 to 1 olefin-to-acid addition product. The weight and acidity of the pot residue were taken to represent products of the reaction. Because this method required a large sample, only the solution remaining at the end of the reaction was used. Distribution of product acids between 1 to 1 olefin-to-acid adducts and higher ratio adducts was determined by chromatography. The raffinate from water extraction and microfractionation was used as charge sample. I n the microfractionation, a Podbielniak spinning-band microcolumn was charged with about 20 grams of pot residue from the distillation. A vacuum was chosen which would keep pot temperature below 200' C., and the distillate was taken over rapidly using about 20 to 1 reflux ratio. At 7 m m . of Hg pressure, the boiling point of the CSacid adduct of propionic acid and I-hexene is 120' C. The reflux decreased sharply a t the end of the boiling point plateau, and the distillation was shut down. Column and pot were rinsed with heptane. Acid titrations of distillate, bottoms, and heptane wash were made. Column and pot washings were calculated as higher molecular weight products; the distillate, as 1 to 1 adduct. Product Acid Distribution, Both the arc and resonance lamps were used to obtain further data on distribution of product acids between 1 t o 1 olefin-to-acid adducts and higher ratio olefin-to-acid adducts or "higher telomers." Other variables studied were ratio of carboxylic acid to olefin in the feed (10 to 1 and 1 to l ) , radiation time, and variation in structure of reactants. .4simple distillation procedure was used to separate the 1 to 1 adducts from the higher telomers. Excess reactants were removed by distillation a t atmospheric pressure. T h e split between 1 to 1 adducts and higher ratio adducts was made by simple distillation under vacuum-pot temperature was maintained below 200' C.-to a boiling point midway between the boiling points of the 1 to 1 adduct and the 2 to 1 olefin-acid adduct. The distillate fraction (1 to 1 olefin-acid adduct) and the bottoms fraction were titrated for acid content. Further Product Analyses. The quantities of hydrocarbon polymers occurring in the distillate and bottoms fraction from the distillation were determined by a n elution chromatographic process. T h e sample was added to silica gel, the hydrocarbons were washed from the gel with pentane, and the residual oxygenated compounds were determined gravimetrically. T h e hydrocarbon polymers were determined by difference. Products from two experiments made a t different feed to olefin ratios in the feed were analyzed in this manner. I n another experiment, the product made by radiation of a 1 to 1 mole ratio of 1-octene for 72 hours a t 130' to 140' C. with an arc lamp was fractionated. Cuts were obtained boiling in the range of the 1 to 1 and 2 to 1 olefin to acid adducts which had neutral equivalents of 338 to 606, indicating the presence of about 45 to 77 wt. % nonacid impurities. Silica gel chromatographic separation indicates that these impurities were hydrocarbon polymers. Fractionation of the product made by radiation of a 10 to 1 mole ratio of propionic acid and 1-hexane for 113 hours with a resonance lamp at 110' to 136' C. \vas made on a Podbielniak spinning band microcolumn. The 1 to 1 adduct of 1-hexane and propionic acid boiled a t 171 ' C. a t 61 mm. of H g pressure and had a neutral equivalent of 158, identical to the theoretical. Caprylic acid boils a t 165.3' C. and pelargonic acid a t 178.8' C. a t 64 mm. of H g (70). VOL. 1
NO. 2
APRIL 1962
133
Table 1.
olefins involves determining the nature of the main products and by-products and experimental conditions influencing their formation. Determination of such kinetic factors as the rate controlling process and activation energy supplements the product data and aids in postulating a mechanism for the overall reactions. Products. T h e total quantities of acid addition product from 10 acid-olefin pairs obtained during 30-hour radiation with the arc lamp a t 130" to 140" C. are shown in Table I. Acids with secondary hydrogens in the a-position are more reactive than acetic acid containing only primary hydrogens; isobutyric acid would be expected to be most reactive. Although it was reactive, the reaction medium darkened during radiation, and the consequent opaqueness interfered with light absorption, preventing valid comparisons of relative reactivities. All samples became opaque upon radiation except those containing acetic or propionic acid. The relative amount of 1 to 1 olefin to acid adduct formed, as compared with higher telomers, was determined as a function of radiation time, type of ultraviolet lamp, molecular weight of olefin, molecular weight and type of carboxylic acid, and reactant ratio. Radiation time does not appreciably affect the ratio of 1 to 1 adduct to higher telomers (Figure 2) within the time and product concentration limits studied. This is confirmed in experiments 1, 2, and 3 shown in Table 11. The experiments also show that substantially the same result is obtained whether an arc or a resonance lamp is used, when 1-octene is substituted for 1-hexene (Table 11, experiment 3) and when n-butyric acid is used instead of propionic acid (Table 11, experiment 7). The relative amount of 1 to 1 adduct formed, as compared with higher telomers, is determined largely by reactant ratio (Table 11, experiments 4 and 5). The formation of 1 to 1 adduct is also favored when reacting an acid having a tertiary hydrogen atom with the higher olefin (Table 11, experiments 6 and 7). Product acids are branched acids because the 1 to 1 adduct of propionic acid and 1-hexene boils midway between the normal CS and C9 acids. Branched acids boil a t lower temperatures than the corresponding normal acid. The main side product of the photoinitiated addition of carboxylic acids to higher olefins is hydrocarbon polymer. High
Comparison of Reactivity of Various Acid-Olefin Pairs Acid/olefin mole ratio = 10
Total Product Acids, Millimoles/30 Hr. Reactants Extrac- Distilla- Chromatogtion tion raphy Acid Olejin Acetic 1-0ctene 7 ... ... Propionic 1-Octene 720 ... 727 Butyric 1-0ctene ... 40 107 Isobutyric 1-0ctene ... 332 350 Valeric 1-0ctene ... 48 87 Caproic 1-0ctene ... 84 66 Acetic 1-Hexenea 3 , . . , . . Propionic 1-Hexene 567 530 410 Isobutyric 1-Hexene ... 80 331 Caproic 1-Hexene ... 130 ... a Run made at 80 C. instead of 730" to 140 C. as in the other runs.
T h e study of product acid formation rate at various ratios of propionic acid to 1-octene in the feed was made with the apparatus shown in Figure 1 ; 50-ml. samples were withdrawn a t convenient intervals. Analyses of samples were made by extracting the unreacted propionic acid from the hydrocarbon layer with water and then titrating the product acid left in the raffinate hydrocarbon layer. When olefin content of the mixture was low-i.e., when the ratio of acid to olefin was greater than 1-the sample was diluted with heptane before the extraction. The samples were extracted five to seven times with 50-ml. portions of water. The final washes were titrated to be sure that no further acid was being extracted. When 0.05 meq. or less of acid was removed per extraction, the extraction was stopped. Data on the temperature coefficient of reactivity with a resonance lamp were obtained using the commercial U-shaped lamp. Two thirds of its effective length was immersed into the reactants.
Discussion of Results Extending knowledge of olefin-oxy addition reactions to a study of the photoinitiated addition of carboxylic acids to higher
Table II. Distribution of Product Acids between 1 / 1 Adducts and Higher Ratio Adducts Experiment 1 2 3 4 5 6
Reactants Acid Olefin Mole ratio acid/olefin Conditions Lamp Radiation time, hr. Temp., C. Produci analysis 1/1 adduct (distillate) Wt. % hydrocarbon Neutral equiv. Theoretical neutral equiv. 1/1 adduct, mole % of product acids Higher adducts (residue) Wt. yc hydrocarbon Neutral equiv. Theoretical neutral equiv.* Higher adducts, mole 70of product acids a
134
Hydrocarbon-free basis.
b
Propionic 1-Hexene
Propionic I-Hexene 10.6
10.0
Arc 30 116-130
Propionic 1-Octene 9.9
Propionic 1-Octene 1.o
Resonance Resonance Resonance 98 100 113 130-140 130-140 110-136
...
158 158 74
...
470 242 26
For 2/7 olefin-acid telomer.
l & E C PROCESS D E S I G N A N D D E V E L O P M E N T
158 158 72 2dB 242 28
9
192" 186 75 46 312a 298
25
70 260a 186 27 69 368" 298 73
7
Propionic 1-Octene 1. o
Dbutyric -0ctene 10.0
n-Butyric 1-0ctene
Arc
Arc 30 30-1 48
Resonance 30 130-1 59
72
130-140
9.9
...
186 32
...
...
298 68
71 222a
312 11
650' 312 24
z
1800-
W
a
2 700
3
si 600
w -
A
H
2
- 1000-
6 500 w
E
cc 400
El 0 300 2 y
62 50 REACTION TIME, HOURS Figure 2. Radiation time does not appreciably affect ratio of 1 to 1 adduct to higher telomers Addition of propionic acid to 1-hexene: 32.6 moles acid/3.08 moles olefin at stort; reaction temperature, 1 10-1 36OC.j 24-watt resonance lamp 0 Total product acids 0 Cg acids A C1bL ecids
ratios of olefin to acid favor formation of hydrocarbons (see Table 11). Kinetics. T h e photoinitiated addition of carboxylic acids to higher olefins to produce higher molecular weight acids was studied by determining the quantity of product acid formed a t various radiation times a t 130' C. Several such curves determined a t different reactant ratios are shown in Figure 3. These curves are similar in that the rate of product formation is low. There is no evidence of induction periods. During the initial radiation period in which acid production is linear with time, the reactant concentrations change insufficiently to affect the rate of product formation. Thus: during the early stages of the radiation, the higher acid production is zero order-dependent only on quantity of photons of ultraviolet radiation absorbed. The tendency of the curves to level out with time may be caused by products of the reaction inhibiting the reaction-that is, the over-all reaction appears to be "auto-inhibited."
Table 111.
200 100
0 0
IO
70
20 30 40 50 6Q REACTION TIME, HOURS
80
Figure 3. Radiation time and reactant ratio affect quantity of product acid formed Reaction temperature, 130' C.; 1 00-watt arc lamp Starting mole ratio of propionic acid to 1 -octene: 0 0.4914.9 3.1/3.1 0 10.4/0.93
Slopes of the curves in Figure 3 show that the rate of acid production is proportional to the concentration of the propionic acid. Thus, the over-all reaction is first order with respect to propionic acid concentration at 130' C. under the conditions of radiation used. Photochemical activation of propionic acid must therefore be the rate determining step in the over-all reaction. The effect of temperature on reaction rate of propionic acid and 1-octene with ultraviolet light is shobvn in Figure 4. Although the different lamps vary in their efficiency of initiating the reaction, the effect of temperature on acid production is the same for each lamp. .4rise of 1 " C. within the range of 60" to 140' C. will increase product acid formation by 0.22 meq. per hour of radiation time. The activation energy may be calculated from the Arrhenius equation by knowing the temperature coefficient of reactivity in the range 60" to 140" C. for the addition of propionic acid and I-octene for a 10 to 1 molar ratio of reactants. ,4 value
Comparison of Power Requirements for Higher Acid:Production 10/1 propionic a d d to olefin mole ratio
Conditions Lamp Wattage Olefin Acid Temp., " C . Higher acid production rate, meq./hr Powrr requirement Kw.-hr./gram mole Kw.-hr./lb. producte a Data from Fi'ure 4. 6 Data from
Resonance
Resonance
Resonance
.4rc
24
24
24
100
1-Octene Propionic
1-0ctene Propionic
1-Hexene Propionic
110 3 0 . Sa
60
19.0a
0.79
1.92 Figure 3.
c
120-1 40 18.4*
1-0ctene
Propionic I30 21.14
1.27 1.31 4.7 3.2 11.6 3.1 In all cases molecular weight of product assumed to be 186 ((211 acid).
VOL.
1
Arc 100 1-0ctene Propionic 80 10.7O 9.4 27.8
NO. 2 A P R I L
1962
135
hv
CH3CHzCOOH + CH3CHCOOH CH CH3CHCOOH
(1 1
1
+ RCHzCH = CHZ
-P
RCHCHZCHCOOH (2)
CH 3
1
RCHCHzCHCOOH
+ RCHzCH=CHz
-+
R
I
CH3
I
RCHCHiCHCHzCHCOOH
(3)
CH 3
I
RCHCHzCHCOOH
+ CH3CHzCOOH
+
CHI
CH3CHCOOH
I + RCH,CH,CHCOOH
(4)
CH3
I
RCHCH2CHCOOH j-RCHzCH=CHz CH3
I
RCHzCH2CHCOOH
= CH2
RCH-CH
= CH2
I
RCHCH = CHz
Arc lamp, 130'C. Resonance lamp, 6OoC. 0 Arc lamp, 8OoC.
of 2.24 kcal. per gram mole of product acid is obtained. This comparatively low value is typical of photochemical-activated processes involving breaking and forming chemical bonds by free radical mechanisms. Product rates obtained a t different temperatures with the various lamps are summarized in Table 111. For the same power input the resonance lamp is much more efficient at initiating the reaction than the arc lamp. T h e superior performance of the resonance lamp is due to the fact that a larger percentage of the radiated energy is below 3000 A. The arc lamp loses most of the applied power as heat (5).
Mechanism Any mechanism for the photoinitiated addition of acids to higher olefins must account for six experimental findings: T h e kinetics indicate that the reaction is photochemically activated by a process that is first order with respect to acid concentration. T h e activation energy is low. Telomeric products are formed. Branched acid products are formed. T h e over-all reaction is auto-inhibited. Reactants and reactant ratios control the relative amount of 1 to 1 adduct formed as compared to higher telomers. Evidence for a free-radical chain mechanism for addition of carboxylic acids to higher olefins is provided by the kinetics, low activation energy, and product distribution. This distribution is determined by chain growth, transfer, and termination processes. T h e mechanism suggested is similar to that proposed for alcohol addition (12) to higher olefins except for variation in functionality of the radical that adds to the olefin and for the nature of the termination reactions. 136
I b E C PROCESS D E S I G N A N D D E V E L O P M E N T
+ CHaCHCOOH
(ja)
(5b)
-+
R CH,
I 1
CH, = CHCHCHCOOH ( 5 ~ )
8 Resonance lamp, 1 1 O°C.
A
+ RCHCH = CH,
2 RCHCH = CH2 + RCH-CH
REACTION TIME 9 HOURS Figure 4. Effect of temperature on acid production is the same for each type of lamp, although lamps vary in efficiency of initiating the reaction
-+
RCHCH=CH*
+ RCHZCH=CH2
+
RCHCH = CHz I
RCH,CHCH~
Equations 1 to 5 represent the chain initiation, addition, propagation, transfer, and termination reactions, respectively. Presumably initiation occurs by absorption of trace quantities of radiation in the far-ultraviolet range known to be emitted by these lamps. Without speculating on the nature of the excited state of the initiating molecule, it is proposed that acid radicals depicted in Equation 1 are formed by a firstorder photon-activated process initiating the over-all reaction in harmony with the experimental kinetic data. The main reaction resulting in formation of 1 to 1 adduct is shown in Equation 2. The formation of telomeric acid products is presented in Equation 3, and chain transfer to acid radical initiator completing a chain reaction is shown in Equation 4. The relative amount of 1 to 1 olefin-to-acid adduct formed in relation to higher ratios of olefin-to-acid products is determined by the relative rates of chain transfer (Equation 4) and chain growth (Equation 3). These equations show that the relative rate of chain transfer to chain growth is proportional to the ratio of the concentrations of carboxylic acid and olefin, as shown experimentally. There is no reason to expect from the mechanism that chain transfer would be affected by type of ultraviolet lamp, radiation time, or molecular weight of normal acid. The ease with which a hydrogen atom may be removed from the a-position of a carboxylic acid would be expected to decrease in the following order: tertiary hydrogen (e.g., isobutyric acid) > secondary hydrogen (e.g., propionic acid) > primary hydrogen (acetic acid). T h e rate of the over-all reaction and the relative amount of chain transfer should decrease in the same order. This was indicated experimentally. The principal termination reaction, particularly in the absence of chemical initiators, is believed to be chain transfer to olefin, forming resonance-stabilized allylic radicals of low reactivity, as shown in Equation 5. Such a process has been
(3) Joyce, R. M., Hanford, \V. E., Harmon, J., J . Am. Chem. SOC. 70, 2529 (1948). (4) Kharasch, M. S., Urry, I V . H., Kuderna, B M., J . Org. Chem. 14,248 (1949). (51 Koller. I,. R.. “Ultraviolet Radiation.” DD. 44-65, IVilev, ,. New Yoik. 1952.’ (6) Ladd, E. C. (to U. S. Rubber C o ) , Brit. Patent 640,479 (July 19, 1950). (7) . , Ladd, E. C. (to U. S. Rubber Co.), U. S. Patent 2,517,684 (Aug. 8, 1950). (8) Moote, T. P., Steitz, A. (to Pan American Petroleum Corp.), Zbzd., 2,823,216 (Feb. 11, 1958). (9) Petrov, A. D., Nikishin, G. I., Ogibin, Yu. N., Doklady Akad. NaukS.S.S.R. 131,580-3 (1960). (10) Pool, W. O., Ralston, .4. LV., IXD. ENG. CIIEM.34, 1104 (1942). (11) Stiteler, C. H., Little, J. R. (to U. S. Rubber Co.), U. S. Patent 2,517,732 (Aug. 8, 1950). (12) Urry, W. H., Stacey, F. W., Huyser, E. S., Juveland, 0. O., J . Am. Chem. SOC. 76,450 (1954). (13) Walling, C., “Free Radicals in Solution,” p. 245, Wiley, New York, 1957. (14) Zbinovsky, V., Anal. Chem 27, 764 (1955). (15) Ziegler, K., Brennstoff Chem. 30, 181 (1949).
termed “degradative chain transfer” by Altschul and Bartlett ( I ) , since the allylic radicals are incapable of continuing the main chain reaction. This mechanism accounts for the observation that addition rates are decreased by high ratios of olefin to acid in the feed. The fate of the allyl radicals is not known, but it is possible that they couple (Equation 5b) or codimerize with a propionic acid radical (Equation 5c) to form a n unsaturated ac’d adduct. ‘The quantity of hydrocarbon polymers found in the product suggests that the main termination reaction is a chain polymerization of the olefin initiated by a n allylic radical (Equation 5d). Increasing concentrations of allylic radicals as the overall reaction proceeds could account for the auto-inhibiting effects noted.
\
literature Cited
(1) Altschul, R., Bartlett, P. D., J . Am. Chem. SOC.67, 816 (1945). (2) Banes, F. W., Fitzgerald, W. P., Nelson, J. F. (to Standard Oil Development Co.), U. S. Patent 2,585,723 (Feb. 12, 1952).
I
I
I .
RECEIVED for review March 14, 1961 ACCEPTED August 24, 1961
LIQUID PHASE PROCESS FOR ACETYLENE REACTIONS J0 HN J
.
N E DW I C K
,
Rohm 3 Haas Co., Philadelphia, Pa.
A liquid phase technique for carrying out acetylene reactions under high pressure has been developed. The operation of the process is described and its advantages with respect to safety, economy, productivity, and versatility are discussed. It has been applied successfully to the vinylation of alcohols, diols, mercaptans, and lactams and to other base-catalyzed reactions of acetylene. N A N Y ACETYLESE
PROCESS
whether it be a t low or high
I pressure, there always exists the possibility of a n explosion or detonation, though the dangers are more acute a t the higher pressures. The usual practice for safely carrying out acetylene reactions under pressure employs a dilution of acetylene with gaseous diluents ( 7 , 2, 17, 74). In these processes, the rate of reaction is controlled primarily by the solubility of acetylene in the liquid phase in which the reaction takes place. The solubility is lowered by the use of high (reaction) temperature and by the use of diluents. As a result, the reactions are slow, space-time yields are low, reactor volumes must be large, and the resultant long contact times foster side reactions. I n contrast, it is possible to carry out acetylene reactions under pressure by operating in the liquid phase in the complete absence of a gas phase. Acetylene is dissolved in the reactants at a low temperature under pressure, catalyst is added, and the reaction mixture is passed through a heated tubular reactor under pressure high enough to prevent desorption of acetylene. The pressure is then lowered to atmospheric, and the product and unreacted starting materials are recovered bv distillation.
In the liquid phase mode of operation, the transfer of acetylene from the gas to liquid phase is accomplished at a low temperature. Systems may be used which are good solvents for acetylene and the rate of solution of acetylene in the reaction mixture can be very rapid. T h e liquid reaction mixture which is introduced into the heated reaction zone then contains all of the acetylene necessary to reach the desired conversion. Since there is no gas phase present a t any time ivhile the reaction mixture is being heated, the possibility of a n acetylene explosion in the gas phase is eliminated. ‘The purpose of this article is to describe a liquid phase system developed by this company, to discuss the critical role of acetylene solvents, to illustrate the scope of the system by means of several concrete examples, and to summarize the advantages which accrue as a result of this mode of operaton. Apparatus The major components of the laboratory liquid phase process are described here together with a flow diagram (Figure 1). Absorber. A jacketed 1-liter stirred autoclave (Pressure Products Industries, No. D-281) with a n internal cooling coil served as the absorber. T h e hollow shaft stirrer was specifically VOL. 1
NO. 2 A P R I L 1 9 6 2 137
