VAPOR PHASE ALDOL REACTION Acrylic Acid by the Reaction of Acetic Acid and Formaldehyde J A M E S F. V l T C H A
A N D V I C T O R A. S I M S
Central Research Laboratories, A i r Reduction Go., Inc., Murray Hill, X. J .
Acrylic acid was synthesized catalytically in the vapor phase from acetic acid and formaldehyde by an aldol-type reaction. Acrylic acid yields of 80 to 100% were obtained at 275" to 385" C., using a mole ratio of 8 to 10 acetic acid to 1 of formaldehyde and a reactant feed rate of 0.1 1 to 0.1 4 mole per hour per liter of catalyst.
studies of the gas phase reaction of formaldehyde and aliphatic acid esters. acetic acid was found to react with formaldehyde to produce acrylic acid in good conversions and high yields. Limited work in our laboratory has indicated the reaction to be general; higher alkanoic acids, such as propionic, isovaleric, caprylic, and lauric, also reacted to give a-alkyl-substituted acrylic acids. The reaction of acetic acid and formaldehyde to form acrylic acid is virtually unreported in the chemical literature. Leathers and Woodward (4) recently reported the reaction of alkanoic acids and formaldehyde to form acrylic acids. The reaction was catalytic and proceeded in the vapor phase a t a preferred temperature of 350" to 400' C., using any alkali metal hydroxide supported on activated alumina. In their examples, they reported a maximum of 11% methacrylic acid and 89% diethyl ketone from the reaction of propionic acid and aqueous formaldehyde. Isikowa (3) in 1939 reported that the reaction of phenylacetic acid and benzaldehyde a t 180' C. gave a,p-diphenylacrylic acid. A French patent ( 2 ) claimed that the condensation of ketones, aldehydes, and acid or derivatives of acids with formaldehyde in the vapor phase using acid catalysts gave unsaturated compounds. Duplication in our laboratory of their experiment on the reaction of acetic acid and formaldehyde resulted in less than a 1% conversion of formaldehyde to acrylic acid (detectable only by vapor phase chromatography). In the Ivork reported in this paper, acrylic acid was obtained by reaction of acetic acid and formaldehyde in yields o conversions of formaldehyde of 50 to 60% of 80 to 1 0 0 ~ with in a single pass. One of the best catalysts was calcium Decalso, a calcium,aluminosilicate made by cation-exchanging Decalso, a synthetic sodium aluminosilicate (Zeolite, Permutit Division, Pfaudler Permutit Co.) with calcium chloride. The reaction is probably a typical aldol-type condensation followed by rapid or almost simultaneous dehydration to form acrylic acid. Although we do not have data to establish the mechanism firmly, the base attack on acetic acid absorbed on the catalyst surface to form a carbanion followed by addition, proton transfer, and dehydration (as shown in Reactions 1, 2, and 3) is plausible.
0
WRING
50
I&EC P R O D U C T RESEARCH A N D DEVELOPMENT
CHs-C
0
/
e
2B:
/
7 CHzC
\
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2BHf
OH 0 e
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H The possibility that the reaction proceeds heterolytically on the catalyst surface rather than homolytically in the vapor state is not incompatible with present thinking ( 7 ) . The equilibrium of Reaction 1 must be largely to the left, because at high acetic acid concentration the conversion of formaldehyde to product is only 50 to 65% and at low concentrations the conversion drops sharply. The competitive reaction of formaldehyde condensation predominates. Malinowski et a / . (5, 6 ) reported aldol condensation reactions on catalytic surfaces in the vapor phase. They reported that a study of the mechanism indicated that dissociation of the CHZgroup and the strength of the base used as a catalyst were the controlling factors. Experimental
Equipment. The reaction system consisted of two 1 x 14 inch cylindrical reactors connected in series and fitted with
thermocouple wells. Each reactor was heated independently by an electrical furnace. The preheater was packed with 4-mm. borosilicate glass beads; the reactor was packed with the test catalyst. Temperature was controlled independently by Gardsman indicator-controllers. The acetic acid-formaldehyde mixture was metered to the preheater by a C orsonCerveny microbellows pump. The receiver was a roundbottomed flask connected to the reactor by a Y-tube; the exit was fitted to a water condenser connected in series with a dry ice trap and a wet-test meter. Materials. The acetic acid was J. T. Baker Co. 99.8y0 reagent grade. T h e formalin was Matheson's (CB396) 3770 formaldehyde in water with 10 to 15% methanol. The Methyl Formcel was a 55% formaldehyde solution in methanol purchased from Celanese Chemical Co. T h e Decalso was a synthetic sodium aluminosilicate, water softener grade, obtained from the Permutit Division of Pfaudler Permutit, Inc. T h e various forms were prepared by cation exchange. T h e silica gel was Fisher's S-156 or S-135. The chemicals used to prepare the catalyst were ACS grade analyzed. Catalyst Preparation. DECALSO CATALYSTS.A 500-gram sample of Decalso was cation-exchanged in a 48 X 1 inch tube fitted with a stopcock at the bottom and a side a r m a t the top. Six liters of 5 to 776 solution of the replacing cation as a soluble salt-i.e., chloride, nitrate, or acetate-was passed upward through the bed a t a rate of 200 to 250 ml. per hour. T h e converted Decalso was washed with distilled water until free of absorbed salts (8 to 10 liters), and dried in a forceddraft oven a t 375' C. for 4 to 24 hours. The test catalyst was screened to a n average particle size of about 30-mesh, and used. IMPREGNATED CATALYST.The salts used to prepare the catalyst were dissolved in a limited amount of water (150 to 100 ml. for 200 grams of carrier) and added rapidly with stirring to the silica gel support contained in an enameled pan or an evaporating dish. Excess water was removed on a steam bath and the catalyst was finally dried in a forced-draft oven at 375' C. for 8 to 24 hours. In preparing catalysts impregnated with insoluble salts, the soluble form of the cation was first put on the support, the excess water removed, and then the soluble form of the anion added to the cation-impregnated support. The impregnated silica gel was 6- to 16-mesh size. Operating Procedure. T h e catalyst tube was charged with 100 ml. of catalyst and connected to the system, a low flow of nitrogen was started, and the electric furnaces were turned on for both the preheater and the catalyst tube. T h e controlling thermocouple for the reactor, attached to a Gardsman controller-indicator, was located a t a position previously determined to give the best temperature profile in the catalyst bed. \Vhen operating temperature was reached, nitrogen flow was continued for an additional 30 minutes to allow for temperature stabilization. After temperature had stabilized, nitrogen flow was stopped and liquid feed started using premixed feed stock of the desired mole ratio. During a run of 1 to 7 hours' duration, periodic temperature gradients were taken at 1-inch intervals and feed flow was checked. At the end of the run, the flow was stopped. wet-test meter read, and nitrogen flush run for 5 minutes, and the contents of the receiver and trap were combined, weighed, and analyzed. The per cent acrylic acid and impurities were determined by gas chromatography. Formaldehyde was determined by the hydroxylamine hydrochloride method. Conversions and yields were calculated on formaldehyde : conversion yield
=
inoles acrylic acid formed moles formaldehyde fed
x
100
moles acrylic acid formed X 100 i moles formaldehvde fed moles formaldehyde recovered)
= -
Space velocity, expressed as liters per hour per liter, is the total gas volume calculated at room temperature and pressure passed over 100 ml. of catalyst per unit of time. Discussion and Results
Catalysts. A rather large group of catalysts (Table I) exhibited activity to some degree, though the best catalysts were alkaline earth Decalsos. These, as well as other catalysts of this type, were prepared from Decalso, a synthetic sodium aluminosilicate, by cation exchange. Calcium Decalso appeared to be a superior catalyst and was studied more extensively under varied conditions. I t exhibited good catalyst life, showing no decrease in activity after 41 hours of intermittent use (Table 11). In addition it was refractory. When the catalyst, used for 41 hours, was heated in an air oven at 700' F. for 18 hours, it was freed of carbonaceous material and showed activity equal to or greater than the starting catalyst. The physical form of the Decalso catalyst appeared to be important? since Linde 5A Molecular Sieve (a calcium aluminosilicate) was essentially inactive. Similarly, Attapulgite and Filtrol (both magnesium aluminosilicates) and a synthetic barium aluminosilicate prepared in our laboratories were inferior to the Decalso, although they showed catalysis. T h e activity of manganese Decalso, prepared from the manganous salt, was not surprising, since it showed good activity in the reactions of methyl acetate and methyl propionate with formaldehyde (7, 8 ) .
Table I.
The Influence of Catalyst upon Conversion and Yield of Acrylic Acid
Conditions. 385" C . ; mole ratio AcOH:H2CO = 1 0 ; 377, Formalin; S.V. = 400 to 450 liters/hr./liter
70
Acrylic" Acid in
~
Based on HICOa __
70
5%
T y p e of Catalyst
Soh.
conver
yield
Sodium Decalso Potassium Decalso Rubidium Decalso Magnesium Decalso Calcium Decalso Strontium Decalso Barium Decalso Manganese Decalso Nickel Decalsob Zinc Decalso Aluminum Decalso* 3YGsodium silicate on silica gel 177, calcium silicate on silica gel Linde 5A Molecular Sieves Barium aluminosilicate 1 YGNaOH on silica gel 1 ye K O H on silica gel 1 ye RbOH on silica.ge1 1 TGRbOH on silica gelc 1yGCsOH on silica gel 1OTOBa( OH)z on silica gel 107, sodium acetate on silica gel lOYGbarium acetate on silica gel Attapulgited Filtrol 62E .i\luminab,J .4lumina-Alcoa F20, 8-14 mesh0 .L\l(OH)aon silica gelb 10% H3POa on silica gel lOy0 H3P04 on silica gel
4.1 4.4 3.5 4.9 5.9 5.5 5.3 5.6 0.7 5.0 4.0
38 41 32 46 54 50 49 50 45 34
92 83 59 84 98 99 86 86 6 72 35
2.9
28
55
4.2 0.7 4.4 3.5 4.2 5.2 2.5 4.2 2.7
37 5 39 32 39 48 23 38 25
62
1.6
14
16
2.4 3.9 3.7
22 35 34 10
35 75 47 12
1.1
1.8 3.2 2.3 0.4
6
..
60 64 56 94 100
66 53
3 29
21 3
30
a Based on analysisfor acrylic acid and H2CO. Large amount of offDauison grade 42 CoCl2 indicating silica gel. A l l other Fisher gas. S- 755 6- to 16-mesh silica gel. Minerals and Chemicals P h i l i j p Corp. e Filtrol Corp. J Filtrol Cor). grade 86 3 / ~ , - i n c h pellets. Ratio AcOH to HzSO = 1f o r this run. Q
Some reaction variables ivere studied and the following effects Lvere observed
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The silica gel-supported catalysts, except for 1yo rubidium hydroxide on silica gel, were less active than the Decalsos. Activity of the alkali metal hydroxide on silica gel catalysts reached an optimum with rubidium hydroxide. Malinowski (5) reported a progressive improvement in yield up through cesium for the vapor phase catalytic reaction of formaldehyde with aldehydes, ketones, and nitriles. The impregnation of silica gel with different inorganic acetates also failed to produce an active catalyst. Leathers and Woodward (4)claimed alkali metal salts of carboxylic acids supported on alumina to be effective catalysts. Limited studies by the authors indicated alumina to be an inferior catalyst support. Temperature. The optimum temperature was 375' to 385' C. At lower temperatures conversion of formaldehyde dropped, although yields were high, while at higher temperatures conversions and yields were lower. At 400' and higher, decomposition was evidenced by increased gas formation. Ratio of Acetic Acid to Formaldehyde. The conversion and yield of acrylic acid as a function of mole ratio of acetic acid to formaldehyde are shown in Figure 1. As the ratio of acetic acid to formaldehyde decreased, the competitive reaction of formaldehyde with itself to form polymers predominated, as a result both conversion and yield dropped. The preferred ratio was 8 to 10 (Figure 1). At this condition a
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desirable concentration of acrylic acid in solution was obtained, and the conversion and yield were high. At higher ratios the yield approached 100% ; however, the concentration of acrylic acid in solution was low. Feed Rates. Feed rates or space velocities were dependent to some extent on the temperature. As the temperature was lowered, a decreased feed rate maintained the highest conversion and yield. Conversely. as the temperature was raised, increased feed rates tended to maintain yield and conversion. Optimum space velocities with the calcium Decalso catalyst were 275 to 325 liters (RTP) of reactants ( H 2 C 0 , HOAc, H20) per hour per liter of catalyst, which corresponded to a total reactant feed of 0.11 to 0.14 mole per hour per liter of catalyst. Formaldehyde Source. Formalin, a 37% aqueous solution of formaldehyde stabilized with 12 to 15% methanol, was the best source of formaldehyde. The effect of different formaldehydes on the conversion and yield at two temperatures is shown in Table 111. The higher yields with Formalin us. nonaqueous formaldehyde were not entirely anticipated in view of previous work. Nonhomogeneity of the feed solution was not a factor. since paraldehyde, trioxane, and Methyl Formcel (a 55% formaldehyde in methanol solution, Celanese Chemical Co.) were soluble in glacial acetic acid. Sulfuric acid (0.25 to 0.50%) was added to the trioxane feed stock to facilitate depolymerization of the trimer. Methanol in Methyl Formcel repressed the reaction of formaldehyde and acetic acid, which was contrary to results (7, 8) obtained with formaldehyde and alkanoic acid esters. With Methyl Formcel only 2y0 of the formaldehyde, which reacted to form acrylic acid, was found as methyl acrylate. Reaction By-products. The decomposition of either reactants or products a t the optimum conditions with calcium Decalso was minimal. Degradation was 2% or less based on gas formation and after 41 hours' operation the catalyst weight had increased only 0.2%. There was no loss of acid and no evidence of acetic anhydride formation when pure glacial acetic acid was passed over calcium Decalso. Very little formaldehyde by-product was formed, because the yields of acrylic acid based on formaldehyde were high (80 to 100yo). The formaldehyde which did not react to form acrylic acid, or was not recovered, was believed to be converted to polyols. The formation of methanol or formic acid by Cannizzaro condensation of formaldehyde was not evident.
I
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30 35 5 IO 15 20 25 MOLE RATIO OF ACETIC ACID TO FORMALDEHYDE Figure 1 . Effect of mole ratio of acetic acid to formaldehyde on conversion and yield of acrylic acid calculated on formaldehyde A A 0
Conversion at 400'C. and 4 0 0 liters/hr./liter Yield at 40OoC. and 4 0 0 liters/hr./liter Conversion at 375OC. and 250 liters/hr./liter Yield at 375OC. and 250 liters/hr./liter
Table 111. Table II. Catalyst Activity on Extended Intermittent Use Conditions. 385" C.; mole ratio Ac0H:HzCO = 10; 37y0 Formalin; S.V.a = 275 to 300 liters/hr./liter
yo ~ R u n No.
64-1
Time. Hr. 6 7
64-2 64-3 64-4 64-5 64-6 64-7" S.V . = liters of
7 7 7 7 7
~
Calculated ~ ~ on Hl z C O i
7%
70
Acidb in Solution
conuer.
yieldb
5.8 4.5 4.9 4.7 4.2 4.6 5.5
50 43 45 44 40 43 52
93 87 93 88 97 80 82
a total gaseous feed calculated at 20' C. and 1 atm. D a t a after Average of 2 to 4 analytical samples taken during each run. heating catalyst in air oven at 700" F. f o r 18 hr. Catalyst black before; light gray after.
h
52
I&EC P R O D U C T RESEARCH A N D D E V E L O P M E N T
Effect of Formaldehyde Source on Conversion and Yield of Acrylic Acid
Formaldehyde Source
Reaction Conditions" S.V.,c AcOH: Temp.. HlCO liters/ C. ratio hr./liter
Result on H & O b
72
72
conver.
yield
~
37y0 Formalin Paraformaldehyde Trioxane 3793 Formalin Paraformaldehyde Trioxane Methyl Formceld
375
10
270
58
98
375 375 385
10 10
220 255 350
54 47 58
62 62 90
385 ~. 385 385
10
330 385 400
52 51 42
68
~
10
10 10
70 67
Calcium Decalso catalyst. Analyses based on formaldehyde and SV = liters of reactantslhourlliter calcd. at 20" C. and acrylic acid. 1 atm. d 5.573 formaldehyde in methanol. Celanese Chemical Co.
Acknowledgment
The authors are indebted to Lucien Barnes and his analytical associates for analytical support. They also Fatefully acknowledge the helpful suggestions of R . C . Terrell and F. E. McKenna in preparation of this manuscript.
(3) Isikowa, S., Takenty, H., Sci. Reps., Tokyo R u m k a Daigaku A3. 231-7 (1939). (4) Leathers, 'J. M., W'oodward, G. F. (to Dow Chemical Co.); U. S. Patent 3,051,747 (August 1962).
(5) Malinowski, S., Jedrzejewski, H., Basinski, S., Benbenek, S.; Chirn. Ind. (Party) 85, 885-96 (1961) ; C. A . 56, 2321g. (6) Malinowski, S., Jedrzejewski, H., Basinski, S., Benbenek, S., Rev. Chim.. Acad. Reb. Roumaine 6. 5-19 (19611 : C. A . ' Pobulatre ' 57, 11003i. (7) Vitcha, J . F., Russell. J. P. (to Air Reduction Co., Inc.), U. S.Patent 3,089,898 (May 1963). (8) Vitcha, J. F., Sims, V. A. (to Air Reduction Co., Inc.), Ibzd., 3,089,899 (May 1963). \
literature Cited
(1) Gzuld. E. S., "Mechanism and Structure in Organic Chemistry, pp. 504-7. Henry Holt, New York, 1959. (2) I. G. Farbenindustrie A. G., French Patent 847,370 (June 1939).
I
RECEIVED for rekiew July 9, 1965 ACCEPTED October 15. 1965
REACTION OF ACETIC ACID WITH T R I S (2-METHYL-1-AZIRIDINYL) PHOSPHINE OXIDE A Kinetic Study D . E. JOHNSON, R . S.BRUENNER, AND A. J .
D I M I L O
Aerojet-General Corp., Sacramento, Calif.
The rate of reaction of acetic acid with tris-(2-methyl-l -aziridinyl) phosphine oxide in dioxane and in toluene was studied a t 60" to 100" C. The rate was third-order to about Soy0 reaction, then deviated rapidly. The reaction is complicated by homopolymerization of the aziridine functions and by P-N cleavage and rearrangement in the product. The third-order rate constants in dioxane and toluene a t 80" C. were 0.053 and 0 . 4 4 I.'/eq.' hr., respectively. In both solvents the activation energy was 19 kcal./eq. a t 60" to 80" C. and the activation entropies a t 80" C. were - 28.0 and - 2 4 . 8 e.u., respectively. The third order con1.095 Ka stant depends upon the ionization constant of the acid; in dioxane the relation log ka = 3.79 I.'/eq.' hr. was derived. The effect of p-toluenesulfonic acid, lithium perchlorate, lithium linoleate, phenols, aryl- and alkylphosphites, and water on the rate of reaction was studied.
+
use of a,w-dicarboxylic acid derivatives, of polybutadiene imine derivatives is assuming increased importance for the preparation of elastomers, some of which are finding use in solid rocket propellants. Of the possible polyfunctional imines capable of crosslinking diacid resins, tris-(2-methyl-l -azirdinyl) phosphine oxide (MAPO) is highly favored. This study was initiated to investigate some characteristics of the reaction between M A P O and carboxylic acid. T o avoid problems introduced by polymer formation, acetic acid was used as a model acid. T h e kinetic method employed was considered sensitive enough to detect very subtle aspects of the reaction chemistry of M A P 0 and carboxylic acids. The use of a model compound with well defined properties sharpened the sensitivity of the kinetic studies to aberrations in the chemistry of the system. While acetic acid differs in many ways from CTPBD, the results obtained with acetic acid are generally related to what occurs in the CTPBD-MAP0 system. Rate studies were made in several solvents, although most runs were made in purified dioxane or toluene. Acetic acid was used in the majority of studies, but a few other acids were also investigated. HE
T (CTPBD) cured with polyfunctional
Experimental
Kinetic Studies. Into separate 50-ml. volumetric flasks were weighed samples of acetic acid and MAPO. These
were diluted to volume with the proper solvent and shaken. The solutions were then mixed in a 250-ml. stoppered flask and placed in a constant temperature bath. Aliquots were taken with a calibrated pipet, and both the acid and imine were determined in duplicate by methods discussed below. Later, the procedure was modified to make it easier to take samples and to eliminate evaporation. The samples were sealed in ampoules and placed in a constant temperature bath. When removed from the bath, samples were frozen in dry ice and opened. Aliquots were taken as previously. Analyses of Samples. DETERMINATION O F ACID. Onemilliliter aliquots were placed in 125-ml. Erlenmeyer flasks. Duplicates were titrated for acid with standard sodium hydroxide to a phenolphthalein end point. These data were used to determine the amount of acetic acid remaining. An accurate value for acid was obtained only if the titration was carried out quickly, since on standing the phenolphthalein again became colorless. Continuing titration of such a solution would give an acid value equal to the initially added acetic acid rather than the acetic acid unreacted. Several aliquots were taken from one reaction which contained 23 meq. of acid, or 23% of the initial acid concentration. By adding small increments of base over a 2-day period, 100 meq. of acid were titrated. With some samples, allowed to stand 3 days, titration indicated 110 meq. of acid or 10% more than the initial acetic acid in the mixture. DETERMINATION O F MAPO. In the initial stages of this research, M A P 0 was determined by the sodium thiosulfate method. Later, this determination was done by the potassium VOL. 5
NO. 1
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1966
53
