Acetyls production anhydride process

A process of polymerization has been described that starts with an acid chloride, and a hydroxy acid in xylene as a solvent. After reaction, the hydrogen chloride is neutralized. In the next step, additional diacid and aromatic diol is added, together with acetic anhydride. Thus the acetylated products are created on the fly in the polymerization vessel. Finally, the actual transesterification polycondensation is performed. ... 

Over the next 30 years, wood distillation declined relative to ethanol dehydrogenation and acetylene based processes as a source of acetyls, but all three would contribute to the acetyl supply chain required to generate the acetic anhydride needed to meet the market demands for cellulose acetate as the product grew and matured over the period 1920-1940. However, while cellulose acetate and cellulose ester markets would grow, improvements in technology for the basic acetyl products were limited during this time period. 

The period from 1970 to 1985 saw radical changes in the production of acetic acid and acetic anhydride. By 1985, both products would be generated not from ethylene, but from synthesis gas which in turn could be generated fi om abundant resources such as coal, natural gas, and in the future, biomass. At the end of this period, acetaldehyde became a very small contributor to the total acetyl product stream since it was no longer required to make acetic acid or acetic anhydride and ethylene would only be required to produce vinyl acetate and to meet a much diminished acetaldehyde market. These advances were the result of two significant process breakthroughs - the Monsanto Acetic Acid Process and the Eastman Chemical Company Acetic Anhydride Process which will be discussed below. 

Manufacture of 2-acetylthiophenes involves direct reaction of thiophene or alkylthiophene with acetic anhydride or acetyl chloride. Preferred systems use acetic anhydride and have involved iodine or orthophosphoric acid as catalysts. The former catalyst leads to simpler workup, but has the disadvantage of leading to a higher level of 3-isomer in the product. Processes claiming very low levels of 3-isomer operate with catalysts that are proprietary, though levels of less than 0.5% are not easily attained. 

Recent Developments. A considerable amount of cellulose acetate is manufactured by the batch process, as described previously. In order to reduce production costs, efforts have been made to develop a continuous process that includes continuous activation, acetylation, hydrolysis, and precipitation. In this process, the reaction mixture, ie, cellulose, anhydride, catalyst, and solvent, pass continuously through a number of successive reaction zones, each of which is agitated (92,93). In a similar process, the reaction mass is passed through tubular zones in which the mixture is forced through screens of successively small openings to homogenize the mixture effectively (94). Other similar methods for continuous acetylation of cellulose have been described (95,96). 

The earliest preparation of cellulose acetate is credited to Schiitzenberger in 1865. The method used was to heat the cotton with acetic anhydride in sealed tubes at 130-140°C. The severe reaction conditions led to a white amorphous polymer but the product would have been severely degraded and the process difficult to control. Subsequent studies made by Liebermann, Francimont, Miles, the Bayer Company and by other workers led to techniques for controlled acetylation under less severe conditions. 

The filtrate from this first batch will comprise a solution of 180 to 270 kg of unprecipitated acetylsalicylic acid (1.0 to 1.5 mols), 510 kg of acetic anhydrice (5.0 mols), 600 kg of acetic acid (10.0 mols) (obtained as a by-product in the acetylation step) and 1,200 kg of the diluent toluene. Into this filtrate, at a temperature of 15° to 25°C, ketene gas is now passed through a sparger tube or diffuser plate, with good agitation, until a weight increase of 420.5 kg of ketene (10 mols) occurs. The reaction mixture wiil now contain 180-270 kg of unprecipitated acetylsalicylic acid (1.0-1.5 mols) and 1,532 kg of acetic anhydride (15 mols) in 1,200 kg of toluene. This mother liquor is recycled to the first step of the process for reaction with another batch of 1,382 kg of salicylic acid. On recirculating the mother liquor, the yield of pure acetylsalicylic acid is 1,780 to 1,795 kg per batch. 

Phlein was acetylated by acetic anhydride in pyridine solution. The crude product was purified by dissolving the dry substance in as small an amount of chloroform as possible, centrifuging to separate impurities, and precipitating the acetate by the dropwise addition of alcohol. After the process had been repeated a few times, a constant-rotating product resulted. 

Reaction (9) generates methyl iodide for the oxidative addition, and reaction (10) converts the reductive elimination product acetyl iodide into the product and it regenerates hydrogen iodide. There are, however, a few distinct differences [2,9] between the two processes. The thermodynamics of the acetic anhydride formation are less favourable and the process is operated much closer to equilibrium. (Thus, before studying the catalysis of carbonylations and carboxylations it is always worthwhile to look up the thermodynamic data ) Under standard conditions the AG values are approximately ... 

Whereas the majority of reactions of acetic anhydride with wood are thermally assisted, there has been some interest in using other methods for delivering energy. Larsson Brelid (2002), Larsson Brelid and Simonson (1999) and Larsson Brelid etal. (1999) studied the use of microwave heating to acetylate wood in order to reduce reaction times, improve the distribution of bonded reagent within the wood and achieve more efficient removal of process chemicals and by-products. 

The partial rate factors for the substitution reactions of biphenyl, with the exception of a few observations, are on a firm experimental basis. The chlorination of biphenyl was examined on several occasions (de la Mare et al., 1958a Beaven et al., 1961 Mason, 1959 Dewar and Mole, 1957). There are significant differences in the reported values for the rate relative to benzene. A recent careful examination of the products (Beaven et al., 1961) indicated the formation of 2- and 4-chloro-biphenyl in 76.5% yield with 17.5% of the residual chlorine consumed via addition processes. The partial rate factors presented in the table are corrected on this basis. Two early studies of the nitration of biphenyl with acetyl nitrate in acetic anhydride yield rate data in poor agreement (Dewar et al., 1956 Simamura and Mizuno, 1957). A recent re-examination of the problem (Billings and Norman, 1961) yielded partial rate factors (ofh = 36.4 = 32.6) confirming the results... 

Acetic anhydride is also produced by the Rh-catalyzed carbonylation of methyl acetate. The method is called the Eastman process (Scheme 3.11). The Rh-catalysed production of acetic anhydride from methyl acetate can be understood by the formation of Mel and acetic acid by the reaction of methyl acetate with HI. Finally, attack of AcOH on the acetylrhodium affords the anhydride and HI, or acetyl iodide reacts with AcOH to give acetic anhydride and HI. 

Fig. 31 shows a diagram of the preparation of triacetoxymethylsilane with acetic anhydride. The acetylation of methyltrichlorosilane can be carried out in reactor 6, a steel enameled cylindrical apparatus with an agitato-rand, a water vapour jacket and rectification tower 3 filled with Raschig rings. The reactor is loaded with necessary amounts of methyltrichlorosilane and acetic anhydride from the batch boxes, the agitator is switched on and the jacket is filled with vapour. The process ends with the complete distillation of the fraction which boils below 58 °C. The reactor is still filled with triacetoxymethylsilane with an impurity of unreacted acetic anhydride. The product is collected in receptacle 7. 

Cellulose acetate is usually produced by the so-called solution process with exception of the fully acetylated end product (triacetate). In the solution process the pulp is first pretreated with acetic acid in the presence of a catalyst, usually sulfuric acid. The purpose of this activation step is to swell the fibers and increase their reactivity as well as to decrease the DP to a suitable level. Acetylation is then performed after addition of acetic anhydride and catalytic amounts of sulfuric acid in the presence of acetic acid. After full acetylation the final triacetate obtained is dissolved. This "primary" acetate is usually partially deacetylated in aqueous acetic acid solution to obtain a "secondary" acetate with a lower DS of about 2 to 2.5. 

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. 

Aromatic ketones are important intermediates in the production of fine chemicals and pharmaceuticals1,2. Thus, the anti-rheumatic Naproxen is produced by the Friedel-Crafts acetylation of 2-methoxynaphthalene into 2-acetyl-6-methoxynaphthalene and subsequent Willgerodt-Kindler reaction. Commercial acylation processes involve over-stoechiometric amounts of metal chlorides (e g. AICI3) as catalysts and acid chlorides as acylating agents, which results in a substantial formation of by-products and in corrosion problems. This is why the substitution of these corrosive catalysts by solid acid catalysts and of acid chlorides by anhydrides or acids is particularly desirable. 

Over HBEA zeolites, acetylation of 2-methoxynaphthalene with acetic anhydride leads mainly to l-acetyl-2-methoxynaphthalene. However, the desired product, i.e. 2-acetyl-6-methoxynaphthalene, precursor of Naproxen is obtained at long reaction time by an intermolecular irreversible isomerization process. A very selective production of II (83%) can be obtained by acetylation of 2-methoxynaphthalene over a commercial HBEA zeolite (Si/Al = 15) at 170°C, with nitrobenzene as a solvent. With dealuminated HBEA samples (framework Si/Al ratio between 20 and 40), better results could be expected. Furthermore, preliminary experiments showed that this selective synthesis of 2-methoxynaphthalene can be carried out in a flow reactor system. 

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