Reaction equilibrium ethyl acetate production

Laboratory studies have been carried out to provide design data on the conversion. A stoichiometric mixture of 60 g acetic acid and 45 g ethanol was reacted and held at constant temperature until equilibrium was achieved. The reaction products were analyzed and found to contain 63.62 g ethyl acetate. 

The reaction is reversible and therefore the products should be removed from the reaction zone to improve conversion. The process was catalyzed by a commercially available poly(styrene-divinyl benzene) support, which played the dual role of catalyst and selective sorbent. The affinity of this resin was the highest for water, followed by ethanol, acetic acid, and finally ethyl acetate. The mathematical analysis was based on an equilibrium dispersive model where mass transfer resistances were neglected. Although many experiments were performed at different fed compositions, we will focus here on the one exhibiting the most complex behavior see Fig. 5. 

Many such activated acyl derivatives have been developed, and the field has been reviewed [7-9]. The most commonly used irreversible acyl donors are various types of vinyl esters. During the acylation of the enzyme, vinyl alcohols are liberated, which rapidly tautomerize to non-nucleophilic carbonyl compounds (Scheme 4.5). The acyl-enzyme then reacts with the racemic nucleophile (e.g., an alcohol or amine). Many vinyl esters and isopropenyl acetate are commercially available, and others can be made from vinyl and isopropenyl acetate by Lewis acid- or palladium-catalyzed reactions with acids [10-12] or from transition metal-catalyzed additions to acetylenes [13-15]. If ethoxyacetylene is used in such reactions, R1 in the resulting acyl donor will be OEt (Scheme 4.5), and hence the end product from the acyl donor leaving group will be the innocuous ethyl acetate [16]. Other frequently used acylation agents that act as more or less irreversible acyl donors are the easily prepared 2,2,2-trifluoro- and 2,2,2-trichloro-ethyl esters [17-23]. Less frequently used are oxime esters and cyanomethyl ester [7]. S-ethyl thioesters such as the thiooctanoate has also been used, and here the ethanethiol formed is allowed to evaporate to displace the equilibrium [24, 25]. Some anhydrides can also serve as irreversible acyl donors. 

Example 1.2 on ethyl acetate is useful also in directing attention to an important point concerning reversible reactions in general. A reversible reaction will not normally go to completion, but will slow down as equilibrium is approached. This progress towards equilibrium can, however, sometimes be disturbed by continuously removing one or more of the products as formed. In the actual manufacture of ethyl... 

Ethyl Acetate. The production of ethyl acetate by continuous esterification is an excellent example of the use of azeotropic principles to obtain a high yield of ester (2). The acetic acid, concentrated sulfuric acid, and an excess of 95% ethyl alcohol are mixed in reaction tanks provided with agitators. After esterification equilibrium is reached in the mixture, it is pumped into a receiving tank and through a preheater into the upper section of a bubblecap plate column (Fig. 5). The temperature at the top of this column is maintained at ca 80°C and its vapor (alcohol with the ester formed and ca 10% water) is passed to a condenser. The first recovery column is operated with a top temperature of 70°C, producing a ternary azeotrope of 83% ester, 9% alcohol, and 8% water. The ternary mixture is fed to a static mixer where water is added in order to form two layers and allowed to separate in a decanter. The upper layer contains ca 93% ethyl acetate, 5% water, and 2% alcohol, and is sent to a second recovery or ester-drying column. The overhead from this column is 95—100% ethyl acetate which is sent to a cooler and then to a storage tank. This process also applies to methyl butyrate. 

Ethyl Acetate. The esterification of ethanol by acetic acid was studied in detail over a century ago (357), and considerable literature exists on determinations of the equilibrium constant for the reaction. The usual catalyst for the production of ethyl acetate [141-78-6] is sulfuric acid, but other catalysts have been used, including cation-exchange resins (358), a-fluoronitrites (359), titanium chelates (360), and quinones and their pardy reduced products. 

Countercurrent flow has advantages in reactions that are limited by product inhibition and equilibrium limitations. Structured catalytic packings (Figure 4, right) are commonly used under conditions of countercurrent flow in catalytic distillation. They have been applied for esterification (to form methyl acetate, ethyl acetate, and butyl acetate), acetalization, etherification (to form methyl tertiary-butyl ether), and ester hydrolysis (to form methyl acetate) have been implemented on an industrial scale. 

The equilibrium of the enzyme acylation reaction can be shifted towards the synthesis of the amide by precipitation of the acylated product formed (Fig. 6). The racemic ethyl 3-amino-5-(trimethylsilyl)-4-pentynoate 3 is an insoluble liquid, whereas the (R)-phenylacetamide 10 is an insoluble solid. The racemic ethyl 3-amino-5-(trimethylsilyl)-4-pentynoate 3 was added to dilute hydrochloric acid. The pH of the reaction medium was then adjusted to 6. Phenylacetic acid (2 equiv.) was added and the pH of the medium was readjusted to 6. Soluble PGA (50 units/100 mg of racemic amine) was added, and the reaction was stirred at room temperature. After completion of the reaction, the pH of the reaction mixture was adjusted to 4. Filtration of the reaction mixture gave (R)-amide 10 in quantitative yield. Chiral HPLC analysis of this isolated amide showed the absence of (S)-amide. The pH of the filtrate was raised to 8, and the filtrate was extracted with ethyl acetate to obtain (S)-amine 11 (yield 90%) (Fig. 6). The chiral HPLC analysis indicated an R S ratio of 2 98. 

The product, ethyl acetate, is called an ester, so the reaction as a whole is known as an esterification reaction. By combining various amounts of acetic acid and ethanol, different amounts of products were obtained once the reaction came to equilibrium (it takes about an hour of boiling in the presence of HC1, which acts as a catalyst.)... 

The equilibrium constant for the reverse, esterification, reaction has been measured by Berthelot and P6an de St. Gilles and found to be 3.96, corresponding to 66.57 per cent esterification. The forward reaction would thus reach equilibrium at 33.43 per cent hydrolysis with K equal to 0.253. The equilibrium position was shown to be independent of the temperature. A calculation of the heat of reaction by the method of bond energies gives a value of zero, since the bonds broken are of the same type as the bonds formed. From the van t Hoff equation (see later section) the condition for a zero temperature coefficient of equilibrium is that 6H be zero. The heat of reaction for the hydrolysis of ethyl acetate, therefore, is n ligible. At a temperature of 60°C and a pressure of 5,000 atm, the equilibrium position remained at approximately 33 per cent hydrolysis. This is to be expected, since an equal number of molecules appears in reactants and products. 

CH3COOCH2CH3(so/v) + H20(so1v) where (solv) indicates that aU reactants and products are in solution but not an aqueous solution. The equilibrium constant for this reaction at 55 °C is 6.68. A pharmaceutical chemist makes up 15.0 L of a solution that is initially 0.275 M in acetic acid and 3.85 M in ethanol. At equilibrium, how many grams of ethyl acetate ar e formed ... 

Ma, Xu, Liu, and Sun (2010) used perfluorosulfonic acid-poly(vinyl alcohol)-Si02/ poly(vinyl alcohol)/polyacrylonitrile (PFSA-PVA-Si02/PVA/PAN) bifunctional hollow-fiber composite membranes. The catalytic and the selective layer of the membrane were independently optimized. These membranes were synthesized by dipcoating. The performance of these bifunctional membranes was evaluated by dehydrating the ternary azeotropic composed of a water, ethanol, and ethyl acetate system (top product of a reactive distillation process of esterification of acetic acid with ethanol), obtaining separation factors of water/ethanol up to 379. An extensive assessment on the esterification reaction of ethanol-acetic acid was later published (Lu, Xu, Ma, Cao, 2013). In this case, the reaction equilibrium was broken in less than 5 h, and a 90% conversion of acetic acid was achieved after 55 h. 

To make a reaction irreversible, it can be performed in neat acyl donor, for instance, in ethyl acetate, which otherwise is reversible (Fig. 12, entry 9). Acylation with S-ethyl thiooctanoate has allowed successful kinetic resolution of secondary alcohols, because evaporation of the formed thioethanol easily shifts the equilibrium to the product side (entry 3) (18). However, acid anhydrides and especially activated esters, which liberate a low nucleophilic (entry 8) or unstable (entries 1, 5, and 6) alcohol, are usually more appropriate. When acid... 

Hanika et al. (2003) investigated the esterification of acetic acid and butanol in a trickle bed reactor, packed with a strong acid ion- exchange resin (Purolite 151) at 343 K - 393 K. Experimental data illustrate the benefit of simultaneous esterification and partial evaporation of the reaction products in the multi-functional trickle bed reactor. In case of total wetting of the catalyst bed, contact of vaporized products (ester and water) with catalyst was naturally limited and thus, the backward reaction i.e. ester hydrolysis was suppressed. This phenomenon shifted the chemical equilibrium conversion to high values. Saletan (1952) obtained quantitative reaction rate data for the formation of ethyl acetate from ethanol and acetic acid in fixed beds of cation exchange resin catalyst. The complex interaction of diffusion and reaction kinetics within the resin, which determine over-all esterification rate, has been resolved mathematically. 

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