REACTIONS OF KETENE HUGH.J. HAGEMEYER, JR. Tennessee Eastman Corporation, Kingsport, Tenn. Ketene and carbonyl compounds can react to form either enol acetates or p-lactones and products thereof, depending on the choice of catalyst and reaction conditions. Enol acetates are formed by reaction of enolizable carbonyl compounds-that is, a carbonyl compound containing a t least one available hydrogen atom on a carbon atom adjacent to the carbonyl group-with ketene in the presence of acid esterification catalysts. Acetylsulfoacetic acid is a preferred enol acetylation catalyst and temperatures in the range 50" to 90" C. are usually employed. Ketene and carbonyl compounds react to form p-lactones and products thereof in the presence of suitable condensation catalysts. The optimum conditions, catalysts, and catalyst concentrations vary for individual carbonyl comqounds. The choice of the catalyst and catalyst concentration should be such that maximum rate of reaction is obtained with a minimum formation of diketene. If 0-lactones or decarboxylation products thereof are the desired compounds, the reaction should be conducted a t low temperatures, 0' to 10" C., to minimize the linear polymerization of the p-lactone. Where the unsaturated acid is the desired product, the reaction is conducted a t 40" t o 60" C., to ensure the gradual formation of the linear polyester of the p-lactone, which is then depolymerized by distillation.
HC-CH H e b-CHO
6'
CeHsCHO
+(CeHJz C=C(CoHs)z
+ COa
CH-C(OH)CHs
+ CH2=C=O/EI2SOd
+
With the advent of the work of Degering ( 4 ) and Kung (IO)B renewed interest has been taken in the utilization of ketene in the synthesis of organic compounds. I n the author's laboratories the condensation of ketene with itself and with carbonyl *compounds-aldehydes, ketones, diketones, keto esters, aromatic aldehydes and ketones, and unsaturated aldehydes and ketones-has been investigated. Other catalysts have also been found which are suitable for the condensation and in some instances they are superior to the FriedelCrafts type catalysts for the formation and isolation of p-lactones. Aldehydes and a,p-unsaturated aldehydes and ketones were also enol acetylated.
+ GO1
DIKETENE
The dimerization of ketene should be considered in a study of the condensation of ketene with carbonyl groups. Of the three structures commonly assigned to diketene, p-vinylacetolactone has been chosen as representing the product of the condensation of the carbon-to-carbon double bond of one ketene molecule with the carbonyl group of a second ketene molecule to form a p-lactone.
+ CHZO/ZnCl%--+CH2CH2C=0 LOJ
+ CH&HO/ZnClZ
CaH6CHCHZC=O + KOAC -0.J 60" C. CsHsCH=CHs
CHFC(CH~)OCOCH~
CHz=C=O
and CHZ=C=.O
+ CHa=C=O
CHsCOCHa
More recently Kung (10)described the condensation of ketene, CHz=C=O, with formaldehyde and acetaldehyde in the presence of Friedel-Crafts type catalysts to form propionolactone and pbutyrolactone, respectively. CH*=C==O
---t
0
Hurd used anhydrous potassium acetate as a catalyst and in addition to the decarboxylation products he isolated furacrylic acid and cinnamic acid which probably resulted from the depolymerization of linear polyesters of the corresponding p-lactones upon distillation. Staudinger in 1911 ( 1 6 ) reported diphenylacetylation of the enol of acetophenone with diphenylketene. Vinyl diphenylacetate was also prepared by the reaction of diphenylketene with acetaldehyde. The enol esters were identified by hydrolysis and isolation of diphenylacetic acid. Gwynn and Degering ( 4 ) in 1942 discovered that enol acetylation with ketene was accomplished in good yields by using acid esterification catalysts. Acetone and ketene reacted in the presence of sulfuric acid catalyst to form isopropenyl acetate.
ETENE, the inner anhydride of acetic acid,ismanufactured by the pyrolysis of acetic acid and acetone. Commercially it is used principally in the production of acetic anhydride and, to a lesser extent, diketene. The discovery and development of new catalysts for reactions with ketene have now led to the manufacture of p-lactones and enol acetates from carbonyl compounds and ketene. Staudinger (17)first described the formation of @-lactonesby condensing diphenylketene with quinone. I n condensations with diphenyllietene, Staudinger used compounds containing highly active carbonyl groups such as dibenzyl ketone, quinone, and benzophenone. The condensation reaction was carried out in the absence of catalysts and required elevated temperatures such that the decarboxylation products of the plactones rather than the p-lactones themselves were isolated-for example, benzophenone and diphenylketene give tetraphenylethylene and carbon dioxide.
+ (CeHJ2 C=C=O
\/
KOAc 60°C.
CH-CH
K
(CeH5)aCO
H:-~~CHCH.C=O L-OJ H
$ CH2=C=O --+
+ CH,=C=O
50" C.
CHz=$Xf;C=O f
No catalyst
-3 CH,CHCH-C=O
CHaCOCH=C=O
L-0-J
A similar condensation with ketene and furfural and ketene and benzaldehyde was reported by Hurd in 1933 (6) in which the plactone decarboxylation products, a-vinylfuran and styrene, respectively, were isolated.
I
CHz=CCH&=O LO-1
I1
CHaC=CHC=O LO--]
I11
Although many investigators show a preference for either Pvinylacetolactone (11) or 0-crotonolactone (111) as representing
765
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
766
the structure of diketene, it is interesting t o note that diketene does not form @-alkoxy compounds with alcohols which is characteristic of the 0-lactones. Diketene ( 2 5 ) is manufactured in 90 to 95% yields simply by passing ketene in through a dispersion plate in the bottom of a tower (Figure 1, omit formaldehyde and catalyst feed lines) filled with diketene and overflows continuously at the top of the tower. The rate of addition is controlled so that the liquid overflowing at the top of the tower is substantially free of dissolved ketene. Temperature is the important factor in controlling the dimerization of ketene and at 40"to 50" C. a smooth rapid rate of dimerization is obtained. The diketene is fed continuously to a still at reduced pressure, 30 mm., for final purification. Catalysts should never be used in the production of diketene. Commercially ketene is produced by the pyrolysis of acetic acid at reduced pressure, 40 t o 100 mm. Where diketene is the desired product it is prepared by inserting one or more scrubbers in series in the reduced pressure system. Ketene is fed into the scrubber (Figure 2, omit formaldehyde and catalyst feed lines) below the packing support and scrubbed with diketene. Referring to the diagram, 1 indicates a primary scrubber which may be cooled with water or other cooling agent through the cooling coil, 2. T h e scrubber is packed with Raschig rings and ketene is metered through rotameter, 7, and enters the scrubber through the nozzle, 17, below a packing support. Diketene is circulated by a pump, 16, from the reserve tank, 5, through a cooled line, 13. The rate of flow of diketene through the scrubber is gaged by the rotameter, 15. The off-gas is led out at 22 and passes through a condenser, 9, and a liquid gas separator, 10, to the jet in the reduced pressure system, Where a high throughput is desired two or more scrubbers are usually connected in series. A copper scrubber 6 feet high and 8 inches in inside diameter packed with 0.5-inch Raschig rings was used to produce 3 to 4 pounds of diketene per hour in 97% yield. Diketene is cycled through the scrubber at the rate of approximately 1 to 2 gallons per minute at 30" to 35' C. and is overflowed at 25 to the reduced pressure still. 0-Butyrolactone is produced by the hydrogenation of diLetene with Raney nickel catalyst at 60 to 70' C. and 300 to 500 pounds per square inch in the presence of an equal or larger volume of diluent. @-Butyrolactone, benzene, and other inert hydrocarbon solvents are suitable as diluents. I n the absence of diluents the hydrogenation cannot be controlled and the diketene decomposes with violence.
CH2=CCH&=0 L-OJ
+ Hz
diluent CH3CHCH&=0 -01 Ni(R) GO" to 70' C. 500 pounds per square inch
-+
On increasing the hydrogenation temperature to 120 O to 160 * C. @-butyrolactoneundergoes hydrogenolysis to n-butyric acid. CH,CHCHzC=O LO-_I
+ HZ -+ Ni(R)
CH3CHzCHzCOOH
120Oto 150" C.
I n continuous hydrogenation diketene can be hydrogenated directly to butyric acid. REACTIONS OF KETENE WITH ALDEHYDES A h D KETONES
Ketene and aliphatic aldehydes such as acetaldehyde, propionaldehyde, and butyraldehyde react in the absence of catalyst t o form a,p-unsaturated ketones. 2CHz=C=0
+ RCHzCHO
RCH&H=CHCOCHj
+ COz
Actually the ketene dimerizes to diketene and as such reacts with the aldehyde to form a 0-lactone which decarboxylates upon heating to form the a,P-unsaturated methyl ketone (1). CH,COCH=C=O
+ RCHnCHO +CH3COCH--C=O
Vol. 41, No. 4
then CH,COC€I-C=O
' b
+RCHzCH=CHCOCH3
+ CO2
RCHz-CHJ17ith acetaldehyde the product is 3-pentene-2-one; with propionaldehyde 3-hexen-2-one; and with butyraldehyde 3-hepten2-one. The reaction is conducted by passing ketene into a solution of the aldehyde a t room temperature. Conversions t o unsaturated ketones average between 50 and 65%, A similar condensation reaction is not observed with ketones. Ketene and acet,onedo react, however, in the absence of a catalyst a t elevated temperatures, to form small amounts of isopropenyl acetate in addition to diketene. CHz=C=O+CH,COCH,/BO
O
C. --+CHz=C(CHJ-OCOCHI
ENOL ACETYLATIONS
With catalysts such as sulfuric acid ( 5 ) ,p-toluencsulfonic acid, and particularly with acetylsulfoacetic acid in concentrations of 0.01 to 0.1% and a t 40Oto 80" C., the corresponding enol acetates are formed. Acetylsulfoacetic acid is prepared b y the reaction of acetic anhydride with sulfuric acid: the acetic acid is distilled off at reduced pressure ( 8 ) .
+ 2( CHsCO) ~ O + C H S C O ~ S O ~ . ~ I € ~ C Of2CHyCOOH OH + CH3CHO/Hd304 +CHFCHOCOCH~ CHFC=O CI€?=C=O + CHaCOCIla/I12304 --+ CH2=C(CH3)0COCHa H2S04
In the case of the aldehydes, the a,@-unsaturatedkelones \yvliich result froni the condensation of diketene with the aldehydes are formed in increasing amounts as me ascend in the aldehyde series.
TABLE I. ESOLXCXTYLATIOK Enol Acetate Conversion, C. % 72 21
$.P.,
Carbonyl Compound Acetaldehyde Propionaldehyde Butyraldehydo -4oetone RIethyl ethyl ketone
99 128 96
45
18
118
31
7
Unsaturated Ketone, Conversion,
% 17 34 51
None None
The conversions are bnsed on the ketene added. Sulfuric acid was used as the catalyst. With acetylsulfoacetic acid as a cntalyst, greatly increased conversions to the enol acetates are obtained-e.g., with acetone the conversion to isopropenj-1 acetate is 75 t o 8570 as compared with 35 t o 45% for sulfuric acid catalyst. Anhydrous sodium acetate is also a catalyst for the enol acetylation of acetone with ketene. p-LACTOhES
I n the presence of suitable condensation catalysts, aldehydes and ketones condense with ketene t o form @-lactones. Some of the better catalyst materials include boric acid, triacetyl borate, mercuric chloride, zinc chloride, zinc thiocyanate, magnesium pel chlorate, and boron trifluoride etherate. Catalysts suitable for use In the condensation of ketene with carbonyl compounds generally fall within the classification of a group of salts which are strongly acid in concentrated aqueous solutions ( I d ) . The compounds are capable of forming coordination complexes with hydroxy groups and also have a strong catalytic activity towards carbonyl derivatives These compounds include the borates, aluminates, halides, thiocyanates, nitrates, chlorates, and perchlorates of zinc, tin, mercury, aluminum, lithium, boron, iron, manganese, and cobalt. The inactivity of some salts of this group is generally due to their insolubility in the reaction solution. Although this list includes the Friedel-Crafts type of catalyst, most of the compounds are not Friedel-Crafts catalysts. The cata-
April 1949
INDUSTRIAL AND ENGINEERING CHEMISTRY
polyoxymethylene acetates due to the prepence of water in the 95% paraformaldehyde which is vaporized in the depolymerization and enters the reactor. Under anhydrous conditions yields of propionolactone as high as 96% have been obtained. The reduced pressure reactor (Figure 2) used in the manufacture of diketene was also used in the production of lactones.
CONDENSER
PUMP
Figure 1. Condensation Reactor
*
767
lyst activity depends on the solubility of the metal salt as well as the degree of diwociation in organic media, With aldehydes and ketones the effective metal salts Can be thought of as forming an oxonium'type complex with the carbonyl group. The choice of a catalyst is important if a high yield of @-lactone is to be obtained. This choice of a catalyst depends on the react i d y of the particular carbonyl compound to be condensed with ketene. For example, with aldehydes (particularly the lower aliphatic aldehydes, formaldehyde and acetaldehyde, and aromatic aldehydes) the preferred catalysts are boric acid, triacetyl borate, zinc thiocyanate, and zinc chloride. Acetone, methyl ethyl ketone, methyl pyruvate, and diacetyl require strong condensation catalysts such as boron trifluoride etherate or acetic acid complex to obtain maximum yields. Zinc chloride acetic acid complex and the metal fluoborates of zinc, iron, and tin can also be included in this group. In carrying out the condensation of ketene with aldehydes continuously, it is preferred to add the ketene and aldehyde in equimolar amounts to a solution of the catalyst in the corresponding lactone. Other solvents such as ethers, alkyl halides, and ketones are also suitable and are preferred in batchwise operation because of the polymerization tendency of the @-lactones.
The apparatus shown is charged with 50 grams of zinc chloride in 5 gallons of propionolactone which is circulated through the scrubber, 1, at 1.5 to 2 gallons per minute. Paraformaldehyde is depolymerized at 19, metered through a heated rotameter, 8, and mixed with gaseous ketene immediately before entering the scrubber through the nozzle, 17, which is centered below the screen supporting the packing. The reaction temperature is held a t 5' to 10' C. by cooling. There are two factors on which the choice of a reaction temperature depends: (1) to obtain a fast rate of reaction between ketene and formaldehyde so as to minimize the amount of homo condensations due to the presence of high concentrations of the monomers in solutions, and (2) to minimize the formation of linear polyesters of the @-lactone. In a 48-hour run 3.5 grams of ketene per minute and 2.5 grams of formaldehyde per minute were mixed immediately before entering the scrubber. Catalyst make-up was added intermittently a t 4 and a concentration of 0.05 to 0.25% was maintained. Propionolactone was taken off continuously a t 25, fed to a flash heater, and then redistilled. A yield of 88% propionolactone, 3% acrylic acid, and 9% residue was obtained.
TABLE11. PROPIONOLACTONE
Run 15 16
Conversion To di- To Ketene, CHIO, ZnCh, T, To lac- ketene acrylio RedGrams Grams % ' C. tone acid acid due 7 15 3050 2142 3 0 78 3 3360 2023 3 10 60 4 12 24 12 6 .2 14 10 1990 1422 0.3 10 84 . 11 5 1095 760 .., 0 3 23 71 1440 1031 . , 40 7 21 . 62
ix :;;i :gig !:: ii !i 20
22 23
I
.
Mole Ratio Keten$/ CHzO 1.10/1 1 19/1 1.03/1 1 05/1 1 02/1 1.02/1 0.97/1
PROPIONOLACTONE
Ketene and formaldehyde are metered separately and passed into a solution of zinc chloride in propionolactone. The solution is cycled through the column concurrent with the flow of incoming gases and is maintained a t approximately 10' C. by cooling. The lactone is overflowed continuously through a rotameter to a small flash heater at reduced pressure. The crude lactone is then redistilled to remove acrylic acid. Typical results are reported in Table 11. It was found that some propionolactone is formed even in the absence of any catalyst. Although the temperature was 40" C. in run 23 and 7% propionolactone was obtained, no acrylic acid was isolated by destructive distillation of the residue. The residue formed in the presence of catalysts is comprised largely of
Figure 2.
Reduced Pressure Reactor for Ketene Reactions
768
INDUSTRIAL
AND ENGINEERING CHEMISTRY
Vol. 41, No. 4
Table 111. Products from Aliphatic Aldehydes and Ketones Carbonyl Compound Formaldehyde Acetaldehyde Acetone Methyl ethyl ketone
Lactone Propionolactone P-Butyrolactone 0-Methyl-8-butyrolactone 8-Ethyl-B-butyrolactone
Butyraldehyde
8-Propylpropionolactone
Reduction Propionic acid Butyric acid Isovaleric acid 3-Methylpentanoic acid Caproic acid
Polymerization and Pyrolysis Acrylic acid Crotonic acid P,8-Dimethylacrylic acid 8-Methyl-p-ethylacrylic acid 8-Propylacrylic acid
Propionolactone can be purified by redistillation at 28" C. and 3 mm. to give a product showing no unsaturation on the infrared spectrometer. The pure lactone has the constants: n"," 1,4135, dEo 1.1489, melting point -31.2" C., boiling point 51" C. at 10 mm. Acetaldehyde and ketene reacted similarly, using a solution of 0.25% zinc chloride in p-butyrolactone. An 85% yield of P-butyrolactone r a s obtained. Diketene and methyl propenyl ketone are by-products. With ketones such as acetone and methyl ethyl ketone the reaction is carried out in the presence of excess ketone, which is recovered and recycled. CHaCOCHa
+ C H e C = O --+
UNSATURATED ALDEHYDES AND KETONES
1
+ CHt=C=O/ZnCl2
RCH=CR-CR-CHz
1
O--C=O
and
+ CHz=C=O
AHz---C=O
I
O
As the molecular weight increases the problem of isolating the lactone becomes more difficult because of a tendency to decarboxylation. However, once the p-lactones are isolated in the pure state, they are stable compounds a t rooin temperature. If an unsaturated acid is desired as the final product, the reaction between ketene and the carbonyl compound is carried out a t 40 O to G O o C. to give a low molecular weight linear polyester of the @-lactonedirectly. This linear polyester is then depolymerized b y distillation t o form the a,p-unsaturated acid ( b , l f ).
+ CHZO/ZnCl2
1
0 t o 10 O 0.
+
$. R C H C R c C R O
I
40" to 60" C.
+
-OCHzCH2CO-
[OCHZCI~ZCO] -OCH&IIzCO
-CO [OCH~CH~CO],O/CU(OAC)~ A CHz-CHCOOH
--+
I n this particular case a small amount of copper acetate is added as an inhibitor t o vinyl polymerization prior t o the distillation. Some of the products which are obtained from aliphatic aldehydes and ketones with ketene via the p-lactones are listed in Table 111.
I c=o
CH2
I
+CHaCHzC(CHa)-0
b.p. 60" to 61 C. at 10 min.
CHa=C=O
I-Pentene
Unsaturated aldehydes and ketones can react with lret m e to give a variety of products. I n the presence of suitable condensation catalysts ketene adds both 1,2 and 1,4 to form p(1)- and a( 11)-lactones.
b.p. 54" C. at 10 rnm.
CHsCHzCOCHs
Decarboxylation Ethylene Propylene Isobutylene 2-Methvl-1-butene
Furfural gave only tars and uncontrollable reactions with zinc chloride and similar catalysts. Furacrylic acid and cinnamic acid were prepared by the reaction of ketene with furfural and benxaldehyde, respectively, a t GOo C. using sodium acetate catalyst followed b y destructive distillation. Yields were 40 to 60%.
4 3 2 RCH=CR-CR=O
CHs-C(CH8)-0 0°C. I BF3etherate CH2----&=0
Alcoholysis ( 9 ) 8-Alkoxypvopionic acid P-Alkoxybutyric acid 8-Alkoxyisovaleric acid 2-Alkoxv-2-methvl _ uentanoic . acid P-Alkoxycaproic acid
I1
R can be hydrogen, alkyl, or aryl. The &lactones are decarboxylated b y pyrolyzing 0.r heating at temperatures above 100" to 120" C. to form diene derivatives. &Lactones decarboxylate a t slightly higher temperatures and also form diene derivatives. RCH=CR-CR-CH2
1 0-Lo
RCHCR=CRO
I
CHz-----C=O
I
RCH=CR--CR=CH2
A
+
Cod
--f
A
+
CHz=CR--CR=CHR
+ COz
P-Lactones are usually formed in the ratio of 10 to 1 of the delta lactones as calculated from the yield of olefinic decomposition products obtained from the condensation of crotonaldehyde with ketene (Table IV). If a doubly unsaturated acid is the desired product, the condensation is carried out a t 40' t o 50" C. and a product is obtained comprising largely the linear polyesters of the lactones. Destructive distillation a t reduced pressure result5 in the formation of the doubly unsaturated acid. Sorbic acid is manufactured in 70 to 80% yields in this may from crotonaldchyde and ketene. With enol esterification catalysts, and a t 50" to 80" C., the wrresponding acetoxy dienes are formed. For example, 1-ace1oxy-
AROMATIC ALDEHYDES AND KETONES
Benzaldehyde and acetophenone reacted with ketene; boric acid and zinc chloride were used as catalysts at, 0 O to 10' C. Decarboxylation gave good yields of styrene and a-methylstyrene, respectively. CsI15CHO
+ CH-C=O
--+ CeHsCHCHzC=O L-0-J
Acetone was uaed as diluent in the benzaldehyde reactioii. The yield of styrene was approximately three times as much with boric acid catalyst as with sodium acetate. The aromatic ketones gave no reaction with sodium acetate catalyst. CsH&HCHzC=O '-02
A CBH~CH=CHZ KaOA4c12%, &BO3 34%
+
TABLE IT'.
U S S A T U R A T E D -4LDEHYDES AND l
