Vapor acetic anhydride

Homogeneous catalysts. With a homogeneous catalyst, the reaction proceeds entirely in the vapor or liquid phase. The catalyst may modify the reaction mechanism by participation in the reaction but is regenerated in a subsequent step. The catalyst is then free to promote further reaction. An example of such a homogeneous catalytic reaction is the production of acetic anhydride. In the first stage of the process, acetic acid is pyrolyzed to ketene in the gas phase at TOO C ... 

Under sufficient pressure to permit a Hquid phase at 55—56°C, the acetaldehyde monoperoxyacetate decomposes nearly quantitatively into anhydride and water in the presence of copper. Anhydride hydrolysis is unavoidable, however, because of the presence of water. When the product is removed as a vapor, an equiUbrium concentration of anhydride higher than that of acetic acid remains in the reactor. Water is normally quite low. Air entrains the acetic anhydride and water as soon as they form. 

The materials of constmction of the radiant coil are highly heat-resistant steel alloys, such as Sicromal containing 25% Cr, 20% Ni, and 2% Si. Triethyi phosphate [78-40-0] catalyst is injected into the acetic acid vapor. Ammonia [7664-41-7] is added to the gas mixture leaving the furnace to neutralize the catalyst and thus prevent ketene and water from recombining. The cmde ketene obtained from this process contains water, acetic acid, acetic anhydride, and 7 vol % other gases (mainly carbon monoxide [630-08-0][124-38-9] ethylene /74-< 3 -/7, and methane /74-< 2-<7/). The gas mixture is chilled to less than 100°C to remove water, unconverted acetic acid, and the acetic anhydride formed as a Hquid phase (52,53). 

In the fibrous acetylation process, part or all of the acetic acid solvent is replaced with an inert dilutent, such as toluene, benzene, or hexane, to maintain the fibrous stmcture of cellulose throughout the reaction. Perchloric acid is often the catalyst of choice because of its high activity and because it does not react with cellulose to form acid esters. Fibrous acetylation also occurs upon treatment with acetic anhydride vapors after impregnation with a suitable catalyst such as zinc chloride (67). 

Organic Chlorides/Halides — Several organic compounds also are hydrolyzed (or react with water) to produce corrosive materials. Notable inclusions among these compounds are acetic anhydride ([CH3COJ2O), and acetyl chloride (CH3COCI), both of which produce acetic acid upon reaction with water. Both acetic anhydride and acetyl chloride are corrosive in addition, mixtures of the vapors of acetic anhydride and acetic acid are flammable in air, and acetyl chloride itself is flammable. 

In a 3-I. round-bottomed flask provided with a mechanical stirrer and a 90-cm. air-cooled condenser are placed 288 g. (3 moles) of freshly distilled furfural, 460 g. (425 cc., 4.5 moles) of acetic anhydride, and 294 g. (3 moles) of dry, pulverized, freshly fused potassium acetate (Note 1). The ingredients are mixed thoroughly, stirring is started, and the flask is heated in an oil bath at 150° (bath temperature) for four hours, without interruption (Note 2). It is well to make provision for acetic acid vapor which escapes through the air condenser. 

Nishino, Y. (1991). Simplified vapor phase acetylation of small specimens of hinoki (Chamae-cyparis obtusa) wood with acetic anhydride. Mokuzai Gakkaishi, 37(4), 370-374. 

Toxicology. Acetic anhydride vapor is a severe irritant of the eyes, mucous membranes, and skin. 

The dehydrating properties of an acid anhydride can be used to produce another acid anhydride. This is an equilibrium process. By heating the mixture, the more volatile acid vaporizes to shift the equilibrium toward the products. Acetic acid, from acetic anhydride, is useful because it s more volatile than most other carboxylic acids. Figure 12-18 illustrates this reaction. 

The hydrogenation of acetic anhydride was also performed in the vapor phase over a supported palladium catalyst resulting in acetaldehyde and acetic acid in high yields (36). To avoid recycling, the reactor was designed for complete reaction of acetic anhydride. Minor selectivity loss was found in formation of ethyl acetate (0.5-1.5%) and methane (0.5%). Typical reaction conditions were 160-200 C, 30-100 psi, with a hydrogen-anhydride ratio of 3 1 to 10 1. A similar catalyst was used in the liquid phase (37). The simplicity and high selectivity of this process is certainly attractive. 

Vapor Phase Hydrogenation of Acetic Anhydride Acetic anhydride was pumped into an evaporator where it was mixed with hydrogen. The temperature of anhydride-hydrogen mixture was raised to the reaction temperature in a preheater zone, made of a 2 feet bed packed with 2 mm glass beads. The reaction took place in a 2 feet catalyst bed packed with 1 m.m. alpha-alumina coated with 0.5% Pd. The effluent was condensed and analyzed by G.C. 

It was found that a nickel-activated carbon catalyst was effective for vapor phase carbonylation of dimethyl ether and methyl acetate under pressurized conditions in the presence of an iodide promoter. Methyl acetate was formed from dimethyl ether with a yield of 34% and a selectivity of 80% at 250 C and 40 atm, while acetic anhydride was synthesized from methyl acetate with a yield of 12% and a selectivity of 64% at 250 C and 51 atm. In both reactions, high pressure and high CO partial pressure favored the formation of the desired product. In spite of the reaction occurring under water-free conditions, a fairly large amount of acetic acid was formed in the carbonylation of methyl acetate. The route of acetic acid formation is discussed. A molybdenum-activated carbon catalyst was found to catalyze the carbonylation of dimethyl ether and methyl acetate. 

In a 5-I. flask, provided with a two-hole stopper fitted with a 90-cm. fractionating column uand a dropping funnel, are placed 1500 g. of benzoic acid, 1500 g. of acetic anhydride, and 1 cc. of syrupy phosphoric acid. The mixture is very slowly distilled, at such a rate that the temperature of the vapor at the head of the column does not exceed 120° (Note 1). When 250 cc. of distillate has been collected, 250 g. of acetic anhydride is added, and distillation is continued. This process is again repeated, so that in all 2000 g. of acetic anhydride has been taken. Fractionation is then continued, fractions which distil respectively below 1200, at 120-130°, and at 130-140° being collected. Heating is continued until the temperature of the reaction mixture in the flask reaches 270°. 

The buckets were returned to the acetylation apparatus, sealed, and re-evacuated, usually overnight. Three to four more hours evacuation with the diffusion pump was followed by admission of the acetic anhydride vapor. The amount of acetylation was controlled by varying the temperature of the liquid acetic anhydride and the time of contact of the vapor with the coal. The acetylation apparatus was then evacuated for three days including 12-15 hours with the diffusion pump. This amount of evacuation was sufficient to remove all traces of acetic acid and acetic anhydride. After evacuation dry air was admitted, the cap removed, and the samples were withdrawn and reweighed. The difference in weight before and after acetylation was taken as the amount of acetylation. 

Dr. Mitchell No, surface area measurements were not compared in this way. However, in view of the extremely mild acetylation conditions used (brief exposure to acetic anhydride vapor), it is difficult to believe that any material change in physical structure resulted. 

Data on the influence of solvents as sensitizers in the vapor phase were collected for water, benzene, carbon tetrachloride, methanol, ethanol, formaldehyde, acetone, acetic add, acetic anhydride and methyl propionate (157). 

Stull Mimmun/cs the data available on the vapor pressures of acetic anhydride and ethyl formate from the melting point to tile critical point, and for propionic anhydride and isopropyl acetate up to the boiling point 1 The vapor pressures ubove the boiling point were estnriuccd by a previously described method ... 

Synonyms ethanal, acetic aldehyde Formula CH3CHO MW 44.05 CAS [75-07-0] used in the production of acetic acid, acetic anhydride, and many synthetic derivatives found in water stored in plastic containers colorless mobil liquid fruity odor when diluted boils at 20.8°C solidifies at -121°C highly volatile vapor pressure 740 torr at 20°C density 0.78 g/mL at 20°C soluble in water, alcohol, acetone, ether, and benzene highly flammable... 

Acetylation of cellulose to the triacetate has been carried out without breaking down of the structure with acetic anhydride containing pyridine to help open up the cell wall structure and to act as a catalyst (71). This led Stamm and Tarkow (72) to test the liquid phase reaction on wood. High dimensional stabilization without break down of the structure was obtained, but excessive amounts of chemical were used. They hence devised a vapor phase method at atmospheric pressure that proved suitable for treating veneer up to thicknesses of 1/8 inch. Acetic anhydride pyridine vapors generated by heating an 80-20% mixture of the liquids were circulated around sheets of veneer suspended in a box lined with sheet stainless steel. Hardwood veneer,... 

A large number of catalysts and swelling agents have been studied for the acetylation reaction. The best acetylation conditions have been reported in vapor phase treatment with uncatalysed acetic anhydride in xylene solutions at 100-130 C (28). Acetylation reaction between wood and acetic anhydride proceeds as follows 0... 

Figure 1. Vapor phase acetylation assembly. Key 1, reaction chamber 2, wood samples 3, thioacetic acid 4, thermometer 5, water condenser 6, heating mantle 7, magnetic stirrer with heater and 8, acetic anhydride and catalysts.

Benzo[c]thiophene may be prepared by low-pressure (20 mm) vapor-phase catalytic dehydrogenation of l,3-dihydrobenzo[c]thio-phene (Section III,A) at 330° under nitrogen,5,8 by decarboxylation of benzo[c]thiophene-1 -carboxylic acid (Section III,C) with copper in quinoline16,38 or by dehydration of l,3-dihydrobenzo[c]thiophene 2-oxide (Section VI,A) in acetic anhydride or over aluminum oxide at 20 mm Hg and 100°-125° in a sublimation tube.52 A trace of water appears to be beneficial to the first reaction, and it has been suggested53... 

The fibrous acetylation process is performed in the presence of a suitable liquid, such as benzene, in which the reaction product is insoluble and which thereby retains the fiber form. For fibrous acetylation vapor-phase treatment with acetic anhydride can also be used. Besides sulfuric acid, perchloric acid and zinc chloride have been used as catalysts. 

Of several anhydrides studied, acetic anhydride reacted the most readily. Reactions were carried out by refluxing the wood in a xylene/acetic anhydride solution or with acetic anhydride vapors alone at 120°C. With this system, for each mole of acetate bonded onto the wood a mole of acetic acid is generated as a byproduct. Although this byproduct generation is a disadvantage of the process, the chemical system does penetrate and react quickly with wood, without a catalyst. It is not... 

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