Acetaldehyde catalysts

Peracetic Acm-AcErALDEHYDE Reaction. The cobalt- and manganese-catalyzed reactions of peracetic acid with acetaldehyde were studied by a continuous flow technique (9). Peracetic acid (0.15M in acetic acid) and acetaldehyde-catalyst solutions were metered through rotameters to a mixing T (standard 0.25-inch stainless steel Swagelok T) and... 

In the polymerization system, the catalyst reacts with acetaldehyde to form the acetaldehyde-catalyst complex. The equilibrium existing between monomeric [XVIII] and dimeric forms [XIX] of the complex is conceivably shifted far to the monomeric form in the polymerizing system than in benzene solution referred to earlier, due to the large difference in dielectric constants. The electron accepting site in the monomeric complex molecule is an aluminum atom and the electron... 

In this mechanism, the stereoregulation in the propagation reaction is realized faithfully by the steric effect acting between the incoming monomer and the growing end monomeric unit, both of which have interactions with an aluminum atom. The penta-coordinate aluminum atom of the catalyst, which is similar to that shown in the dimeric acetaldehyde-catalyst complex, plays an important role as an intermediate compound or as a transition state. In principle, an identical mechanism may be applied to the polymerization by the dialkyl-aluminum monoalkoxide catalyst. 

List of Copper Compounds Copper (I) acetaldehyde Catalysts. See Vol 1,... 

The industrially important acetoxylation consists of the aerobic oxidation of ethylene into vinyl acetate in the presence of acetic acid and acetate. The catalytic cycle can be closed in the same way as with the homogeneous Wacker acetaldehyde catalyst, at least in the older liquid-phase processes (320). Current gas-phase processes invariably use promoted supported palladium particles. Related fundamental work describes the use of palladium with additional activators on a wide variety of supports, such as silica, alumina, aluminosilicates, or activated carbon (321-324). In the presence of promotors, the catalysts are stable for several years (320), but they deactivate when the palladium particles sinter and gradually lose their metal surface area. To compensate for the loss of acetate, it is continuously added to the feed. The commercially used catalysts are Pd/Cd on acid-treated bentonite (montmorillonite) and Pd/Au on silica (320). 

Actual Au loading. PO propene oxide, PA propionaldehyde, AT acetone, AA acetaldehyde. Catalyst, 0.5 g feed gas, CjH6/02/H2/Ar = 10/10/10/70 space velocity, 4000h" mlgca,". ... 

Technically, acetaldehyde is mainly made by the oxidation of ethylene using a CuCl2/PdCl2 catalyst system.. Although some acetic acid is still prepared by the catalytic oxidation of acetaldehyde, the main process is the catalytic oxidation of paraffins, usually -butane. 

Much of the acetaldehyde of commerce is obtained by the hydration of acetylene in hot dilute sulphuric acid solution in the presence of mercuric sulphate as catalyst ... 

Acetaldehyde, b.p. 21°, undergoes rapid pol5unerisation under the influence of a little sulphuric acid as catalyst to give the trimeride paraldehyde, a liquid b.p. 124°, which is sparingly soluble in water. The reaction is reversible, but attains equilibrium when the conversion is about 95 per cent, complete the unreacted acetaldehyde and the acid catalyst may be removed by washing with water ... 

Acetaldehyde (and other aldehydes containing at least one hydrogen atom in the a position) when treated with a small quantity of dilute sodium hydr oxide solution or other basic catalyst gives a good yield of aldol (p hydroxy-n-but3Taldehyde) (I), which readily loses water, either by heating the isolated aldol alone or with a trace of mineral acid, to form crotonaldehyde (II) ... 

Acetaldehyde condenses in the presence of a little sodium sulphite or sodium hydroxide solution to aldol. The latter ehminates water upon distUlation at atmospheric pressure, but more efficiently in the presence of a trace of iodine, which acts as a catalyst, to yield crotonaldehyde ... 

Although Pd is cheaper than Rh and Pt, it is still expensive. In Pd(0)- or Pd(ll)-catalyzed reactions, particularly in commercial processes, repeated use of Pd catalysts is required. When the products are low-boiling, they can be separated from the catalyst by distillation. The Wacker process for the production of acetaldehyde is an example. For less volatile products, there are several approaches to the economical uses of Pd catalysts. As one method, an alkyldi-phenylphosphine 9, in which the alkyl group is a polyethylene chain, is prepared as shown. The Pd complex of this phosphine has low solubility in some organic solvents such as toluene at room temperature, and is soluble at higher temperature[28]. Pd(0)-catalyzed reactions such as an allylation reaction of nucleophiles using this complex as a catalyst proceed smoothly at higher temperatures. After the reaction, the Pd complex precipitates and is recovered when the reaction mixture is cooled. 

Not so for synthesis in the chemical industry where a compound must be prepared not only on a large scale but at low cost There is a pronounced bias toward reactants and reagents that are both abundant and inexpensive The oxidizing agent of choice for example in the chemical industry is O2 and extensive research has been devoted to develop mg catalysts for preparing various compounds by air oxidation of readily available starting materials To illustrate air and ethylene are the reactants for the industrial preparation of both acetaldehyde and ethylene oxide Which of the two products is ob tamed depends on the catalyst employed... 

Oxidation. Acetaldehyde is readily oxidised with oxygen or air to acetic acid, acetic anhydride, and peracetic acid (see Acetic acid and derivatives). The principal product depends on the reaction conditions. Acetic acid [64-19-7] may be produced commercially by the Hquid-phase oxidation of acetaldehyde at 65°C using cobalt or manganese acetate dissolved in acetic acid as a catalyst (34). Liquid-phase oxidation in the presence of mixed acetates of copper and cobalt yields acetic anhydride [108-24-7] (35). Peroxyacetic acid or a perester is beheved to be the precursor in both syntheses. There are two commercial processes for the production of peracetic acid [79-21 -0]. Low temperature oxidation of acetaldehyde in the presence of metal salts, ultraviolet irradiation, or osone yields acetaldehyde monoperacetate, which can be decomposed to peracetic acid and acetaldehyde (36). Peracetic acid can also be formed directiy by Hquid-phase oxidation at 5—50°C with a cobalt salt catalyst (37) (see Peroxides and peroxy compounds). Nitric acid oxidation of acetaldehyde yields glyoxal [107-22-2] (38,39). Oxidations of /)-xylene to terephthaHc acid [100-21-0] and of ethanol to acetic acid are activated by acetaldehyde (40,41). 

Reduction. Acetaldehyde is readily reduced to ethanol (qv). Suitable catalysts for vapor-phase hydrogenation of acetaldehyde are supported nickel (42) and copper oxide (43). The kinetics of the hydrogenation of acetaldehyde over a commercial nickel catalyst have been studied (44). 

Polymerization. Paraldehyde, 2,4,6-trimethyl-1,3-5-trioxane [123-63-7] a cycHc trimer of acetaldehyde, is formed when a mineral acid, such as sulfuric, phosphoric, or hydrochloric acid, is added to acetaldehyde (45). Paraldehyde can also be formed continuously by feeding Hquid acetaldehyde at 15—20°C over an acid ion-exchange resin (46). Depolymerization of paraldehyde occurs in the presence of acid catalysts (47) after neutralization with sodium acetate, acetaldehyde and paraldehyde are recovered by distillation. Paraldehyde is a colorless Hquid, boiling at 125.35°C at 101 kPa (1 atm). 

Reactions with Aldehydes and Ketones. The base-catalyzed self-addition of acetaldehyde leads to formation of the dimer, acetaldol [107-89-1/, which can be hydrogenated to form 1,3-butanediol [107-88-0] or dehydrated to form crotonaldehyde [4170-30-3]. Crotonaldehyde can also be made directiy by the vapor-phase condensation of acetaldehyde over a catalyst (53). 

The base-catalyzed reaction of acetaldehyde with excess formaldehyde [50-00-0] is the commercial route to pentaerythritol [115-77-5]. The aldol condensation of three moles of formaldehyde with one mole of acetaldehyde is foUowed by a crossed Cannizzaro reaction between pentaerythrose, the intermediate product, and formaldehyde to give pentaerythritol (57). The process proceeds to completion without isolation of the intermediate. Pentaerythrose [3818-32-4] has also been made by condensing acetaldehyde and formaldehyde at 45°C using magnesium oxide as a catalyst (58). The vapor-phase reaction of acetaldehyde and formaldehyde at 475°C over a catalyst composed of lanthanum oxide on siHca gel gives acrolein [107-02-8] (59). 

Ethyl acetate [141-78-6] is produced commercially by the Tischenko condensation of acetaldehyde using an aluminum ethoxide catalyst (60). The Tischenko reaction of acetaldehyde with isobutyraldehyde [78-84-2] yields a mixture of ethyl acetate, isobutyl acetate [110-19-0] and isobutyl isobutyrate [97-85-8] (61). 

Reactions with Ammonia and Amines. Acetaldehyde readily adds ammonia to form acetaldehyde—ammonia. Diethyl amine [109-87-7] is obtained when acetaldehyde is added to a saturated aqueous or alcohoHc solution of ammonia and the mixture is heated to 50—75°C in the presence of a nickel catalyst and hydrogen at 1.2 MPa (12 atm). Pyridine [110-86-1] and pyridine derivatives are made from paraldehyde and aqueous ammonia in the presence of a catalyst at elevated temperatures (62) acetaldehyde may also be used but the yields of pyridine are generally lower than when paraldehyde is the starting material. The vapor-phase reaction of formaldehyde, acetaldehyde, and ammonia at 360°C over oxide catalyst was studied a 49% yield of pyridine and picolines was obtained using an activated siHca—alumina catalyst (63). Brown polymers result when acetaldehyde reacts with ammonia or amines at a pH of 6—7 and temperature of 3—25°C (64). Primary amines and acetaldehyde condense to give Schiff bases CH2CH=NR. The Schiff base reverts to the starting materials in the presence of acids. 

Mercaptals, CH2CH(SR)2, are formed in a like manner by the addition of mercaptans. The formation of acetals by noncatalytic vapor-phase reactions of acetaldehyde and various alcohols at 35°C has been reported (67). Butadiene [106-99-0] can be made by the reaction of acetaldehyde and ethyl alcohol at temperatures above 300°C over a tantala—siUca catalyst (68). Aldol and crotonaldehyde are beheved to be intermediates. Butyl acetate [123-86-4] has been prepared by the catalytic reaction of acetaldehyde with 1-butanol [71-36-3] at 300°C (69). 

Reaction of one mole of acetaldehyde and excess phenol in the presence of a mineral acid catalyst gives l,l-bis(p-hydroxyphenyl)ethane [2081-08-5], acid catalysts, acetaldehyde, and three moles or less of phenol yield soluble resins. Hardenable resins are difficult to produce by alkaline condensation of acetaldehyde and phenol because the acetaldehyde tends to undergo aldol condensation and self-resinification (see Phenolic resins). 

Miscellaneous Reactions. Sodium bisulfite adds to acetaldehyde to form a white crystalline addition compound, insoluble in ethyl alcohol and ether. This bisulfite addition compound is frequendy used to isolate and purify acetaldehyde, which may be regenerated with dilute acid. Hydrocyanic acid adds to acetaldehyde in the presence of an alkaU catalyst to form cyanohydrin the cyanohydrin may also be prepared from sodium cyanide and the bisulfite addition compound. Acrylonittile [107-13-1] (qv) can be made from acetaldehyde and hydrocyanic acid by heating the cyanohydrin that is formed to 600—700°C (77). Alanine [302-72-7] can be prepared by the reaction of an ammonium salt and an alkaU metal cyanide with acetaldehyde this is a general method for the preparation of a-amino acids called the Strecker amino acids synthesis. Grignard reagents add readily to acetaldehyde, the final product being a secondary alcohol. Thioacetaldehyde [2765-04-0] is formed by reaction of acetaldehyde with hydrogen sulfide thioacetaldehyde polymerizes readily to the trimer. 

Acetic anhydride adds to acetaldehyde in the presence of dilute acid to form ethyUdene diacetate [542-10-9], boron fluoride also catalyzes the reaction (78). Ethyfldene diacetate decomposes to the anhydride and aldehyde at temperatures of 220—268°C and initial pressures of 14.6—21.3 kPa (110—160 mm Hg) (79), or upon heating to 150°C in the presence of a zinc chloride catalyst (80). Acetone (qv) [67-64-1] has been prepared in 90% yield by heating an aqueous solution of acetaldehyde to 410°C in the presence of a catalyst (81). Active methylene groups condense acetaldehyde. The reaction of isobutfyene/715-11-7] and aqueous solutions of acetaldehyde in the presence of 1—2% sulfuric acid yields alkyl-y -dioxanes 2,4,4,6-tetramethyl-y -dioxane [5182-37-6] is produced in yields up to 90% (82). 

In the one-stage process (Fig. 2), ethylene, oxygen, and recycle gas are directed to a vertical reactor for contact with the catalyst solution under slight pressure. The water evaporated during the reaction absorbs the heat evolved, and make-up water is fed as necessary to maintain the desired catalyst concentration. The gases are water-scmbbed and the resulting acetaldehyde solution is fed to a distUlation column. The tad-gas from the scmbber is recycled to the reactor. Inert materials are eliminated from the recycle gas in a bleed-stream which flows to an auxdiary reactor for additional ethylene conversion. 

This oxidation process for olefins has been exploited commercially principally for the production of acetaldehyde, but the reaction can also be apphed to the production of acetone from propylene and methyl ethyl ketone [78-93-3] from butenes (87,88). Careflil control of the potential of the catalyst with the oxygen stream in the regenerator minimises the formation of chloroketones (94). Vinyl acetate can also be produced commercially by a variation of this reaction (96,97). 

From Ethyl Alcohol. Some acetaldehyde is produced commercially by the catalytic oxidation of ethyl alcohol. The oxidation is carried out by passing alcohol vapors and preheated air over a silver catalyst at 480°C (98). 

From Acetylene. Although acetaldehyde has been produced commercially by the hydration of acetylene since 1916, this procedure has been almost completely replaced by the direct oxidation of ethylene. In the hydration process, high purity acetylene under a pressure of 103.4 kPa (15 psi) is passed into a vertical reactor containing a mercury catalyst dissolved in 18—25% sulfuric acid at 70—90°C (see Acetylene-DERIVED chemicals). 

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