Products wifh Commercial Possibilities from
Reactions of 'Crotonaldehyde OTTO HORN -Y
Farbwerke Hoechst, FrankfortlMain, Germany
- INITIALLY,
ALIPHATIC chemistry was based almost entirely on acetylene. In the United States, the first carbide furnace was set up in 1894, but acetylene chemistry did not reach an industrial scale until 20 years later. In 1912, Duden of Farbwerke Hoechst delegated to Ernst who was head of his laboratory. the task of developing a commercial process for making acetaldehyde and its derivatives. Wunderlich and Grunstein had worked on a eimilar problem in the Griesheim laboratories. Thus. a t the beginning of World War I, aldehyde synthesis was discovered almost simultaneously in three places--in Canada a t Shawinigan Chemicals. and in Germany a t Alexander Wacker and Farbwerke Hoechst.
When acetaldehyde reacts with itself in the presence of dilute alkali, a bimolecular product, acetaldol is formed. In the industrial process, only about 50% of the acetaldehyde reacts. T h e crude aldol is slightly acidified with acetic acid and on heating to 100' C., it yields crotonaldehyde.
Hydrogenation of crotonaldehyde gives n-butanol. Formerly, hydrogenation was done using active copper (violet copper) which was applied to a carrier such as pumice stone. However, differences in pumice stone caused difficulty in reproducibility which increased as more active catalysts such as copper-kieselguhr activated with magnesium were used (German Patent 833,801). But with the new catalysts, even after many hours of reaction, butanol thus obtained was practically free of byproducts. The reaction was conducted in a furnace where contact and temperature-regulation zones were close together-e.g., the furnace used by Fischer in the Fischer-Tropsch synthesis. Thus, heat of reaction was removed so that temperature variation could be kept to a minimum. This resulted in higher yield and longer catalyst life. Because Europe does not have a large petrochemical industry, most of the n-butanol produced there is used to make n-butyl acetate. Ester solvents rather than ketones are used for lacquers, paints, and varnishes far more extensively than in the United States.
When acetals are made from unsaturated aldehydes, the alcohol used is also added to the double bond, thus giving alkoxy acetals. Primary alcohols may be added to crotonaldehyde to form alkoxyaldehydes (German Patent 554,949)-e.g., in the presence of sodium hydroxide a t a temperature below 10' C. with subsequent neutralization and distillation, methanol gives 3-methoxy-n-butyraldehyde in 90y0 yield. This is then oxidized to the acid or hydrogenated to the alcohol, methoxybutanol, which boils a t 158' C. Because of its low volatility, this alcohol is an excellent additive for spraying and brushing lacquers. especially because it does not corrode rubber. I t is also used as a breaking liquid. The acetic ester of methoxybutanol (Butoxyl) which boils at 167" to 171' C. is a desirable high boiling solvent-it resists saponification, promotes gloss, and has a great dilution capacity.
When crotonaldehyde is hydrogenated so that hydrogen is added only to the
double bond, butyraldehyde is formed. Crotonaldehyde may be hydrogenated in both the liquid and vapor state. Ullman's Encyclopaedia of Technical Chemistry (1956 edition) correctly describes the state of the art thus, "In practice, it is scarcely possible to direct the reaction so that hydrogen is added only to the double bond of crotonaldehyde because the reaction always proceeds further, and butanol also is formed in addition to butyraldehyde." Formerly. butyraldehyde was made on a large scale by hydrogenating gaseous crotonaldehyde in the presence of a copper catalyst which, because it had been used in making butanol, had lost much of its activity. With this catalyst, a temperature of 180' to 200' C., and hydrogen diluted up to 807, with nitrogen, a mixture could be obtained from crotonaldehyde-initially 45 to 50% butyraldehyde in butanol, and later about 6070 butyraldehyde with a residue of butanol. Because of the high yield of butanol obtained by this method, separation by distillation resulted in partial acetal formation and consequent loss of butyraldehyde. h-ickel-chromium catalysts on asbestos have been suggested. They are said to have a more se!ective action, hociever, this view has not been confirmed in these laboratories. Also, it has been suggested that crotonaldehyde be diluted with butanol, but this is no solution to the problem either. According to patent
specifications, hydrogenation of liquid crotonaldehyde should form only butyraldehyde, but larger-scale manufacture still yields butanol as a byproduct. The first attempts to hydrogenate liquid crotonaldehyde to butyraldehyde were carried out a t Hoechst as early as the twenties, but the results icere not satisfactory. Later attempts, using noble metals as catalysts was likewise unsuccessful. However, when the importance of acid-binding and oxidationinhibiting agents was recognized, success was achieved. The crotonaldehyde used must be as fresh as possible-Le., free from oxygencontaining products such as crotonic acid which poison the nickel catalyst. Also, it should be stabilized with 1% hydroquinone. Chalk is the most suitable acid-binder; compounds of stronger alkalinity cause condensation (German Patent 856,147). When allowed to remain in the flow pipe for 1 hour in the presence of 0.1% chalk, 0.3% nickel catalyst on pumice powder, and small amounts of emulsifier a t about 25 atm. and 65" to 70' C., crotonaldehyde produces 80% butyraldehyde, 0.67, crotonaldehyde, 4.47* Imtanol, 4.2y0 ethylhexanal. and 3.67, high boiling products. However. in this method, the catalyst must be removed from the liquid butyraldehyde by filtering through presses, and a bad odor is developed. At this point development of a shaped catalyst was begun in these laboratories. The object was to define the catalyst and to produce butyraldehyde in the existing hydrogenation equipment (Fischer furnace) without using pressure. Also, formation of butanol had to be minimized so that no butyraldehyde would be lost from acetal formation. T h e first successful results were obtained, using an iron catalyst activated with nickel in a ratio of 8 parts of nickel, 2 of iron, and 100 of kieselguhr, prepared by precipitating the nitrite solution with soda. The catalyst was washed and reduced with hydrogen at 300' C. At 200' C., using 100 cc. per hour of crotonaldehyde (SO:%) per liter of catalyst, a mixture of about 74.87, of butyraldehyde, 14.3yc crotonaldehyde, and 0.3% butyric acid was obtained, together with water and a little butanol. The butyraldehyde could be easily removed from about 2% higher boiling substances by distillation. ,4n iron-copper-nickel-kieselguhr catalyst (8 : 1 : 4: 100) behaved in principle similarly. By adding copper, the reduction temperature could be lowered to about 200' C. The principal fact recognized here was the possibility of activating iron with nickel. Finally a simple useful catalyst was found (German Patent 950,908). Commercial nickel monoxide (10YG),prepared by roasting the nitrate, was kneaded VOL. 51, NO. 5
M A Y 1959
655
AceMdehyd
I
[11
Figure 1. Acetaldehyde forms acetaldol which in turn yields crotonaldehyde Adolisator, aldol reactor; 10% Essigs, 10% acetic acid; Aldehyd zuidck, aldehyde back; Abtreibkolonne, strip column; Kuhler, cooler; Warsertrenngefass, water separator; Zur kolonne, to column; Sumpf, residue
into a paste with kieselguhr, shaped, dried, and reduced in a hydrogen current at 190' C. At 180' C., 1 liter of catalyst could convert 120 grams per hour of crotonaldehyde (90%) into about 84 to 87% butyraldehyde, 3.5y0 crotonaldehyde, 2% butanol, and 0.3% butyric acid. h-ickel monoxide obtained by roasting cannot be completely reduced a t 420' C. and definitely not at 180' to 200' C. For example, a fresh catalyst consisted of 25.1570 nickel monoxide, 4.137, nickel sesquioxide and no metallic nickel, but a reduced catalyst removed with precaution consisted of 25.57, 0: and ?1.587~of these substances, respectively. Under these conditions only the nickel sesquioxide is reduced. Thus, a few active centers on the surface of the catalyst are probably responsible for selective hydrogenation. Therefore, surfaces of various samples were loaded with argon according to the gas adsorption m e t h o d 4 . e , the starting material (nickel monoxide) and the catalyst when it was fresh, just reduced, and after it had been used. I n many instances, the surface greatly decreased after a prolonged opera tion, but no definite conclusions can be drawn from this. Therefore, u p to about 5% copper sulfate was added to the catalyst paste of nickel monoxide and kieselguhr (German Patent 1,022,208). In this way, catalysts having an excellent uniform activity and long life were obtained. The fresh catalyst contained 26.1 1% nickel monoxide, 3.40% nickel sesquioxide. and 4.7770 copper sulfate; the used catalyst contained 22.91, 0, and 5.02% of these substances, respectively, together with 3.88% metallic nic!
