Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Equilibrium esterification

The effect of adding large quantities of acetic acid to the medium is more complicated. The acceleration of the oxidation rate of isopropanol was ascribed initially to a shift of the esterification equilibrium to the right (reaction 29). However, RoCek found that acceleration by acetic acid occurs for oxidations which cannot involve a pre-equilibrium esterification, e.g. those of aliphatic and alicyclic hydrocarbons. The obvious alternative, i.e. that acetic acid combines with chromic acid, viz. [Pg.306]

Fischer esterification is reversible and the position of equilibrium lies slightly to the side of products when the reactants are simple alcohols and carboxylic acids When the Fis cher esterification is used for preparative purposes the position of equilibrium can be made more favorable by using either the alcohol or the carboxylic acid m excess In the following example m which an excess of the alcohol was employed the yield indicated IS based on the carboxylic acid as the limiting reactant... [Pg.638]

Esterification (Section 15 8) In the pres ence of an acid catalyst carboxylic acids and alcohols react to form esters The reac tion IS an equilibrium process but can be driven to favor the ester by removing the water that is formed... [Pg.810]

Hydrolysis (Sections 20 10 and 20 11) Ester hydrolysis may be catalyzed either by acids or by bases Acid catalyzed hydrolysis is an equilibrium controlled process the reverse of the Fischer esterification Hydrolysis in base IS irreversible and is the method usual ly chosen for preparative purposes... [Pg.849]

Many of the reactions listed at the beginning of this section are acid catalyzed, although a number of basic catalysts are also employed. Esterifications are equilibrium reactions, and the reactions are often carried out at elevated temperatures for favorable rate and equilibrium constants and to shift the equilibrium in favor of the polymer by volatilization of the by-product molecules. An undesired feature of higher polymerization temperatures is the increased probability of side reactions such as the dehydration of the diol or the pyrolysis of the ester. Basic catalysts produce less of the undesirable side reactions. [Pg.300]

The reaction is reversible and reaches equilibrium slowly. Generally, acidic catalysts ate used, such as strong sulfuric acid, hydrochloric acid, boron triduoride, and i)-toluenesulfonic acid (27). Batchwise and continuous processes ate used for the esterification reaction. [Pg.403]

Process Applications The production of esters from alcohols and carboxylic acids illustrates many of the principles of reactive distillation as applied to equilibrium-limited systems. The equilibrium constants for esterification reactions are usually relatively close to unity. Large excesses of alcohols must be used to obtain acceptable yields with large recycles. In a reactive-distiUation scheme, the reac-... [Pg.1321]

If polycondensation is carried out at low temperature, removal of the liberated water is impossible. In this case, reverse hydrolysis must be taken into account unless equilibrium is shifted towards esterification by an excess of one of the reactants. [Pg.58]

The direct biocatalytic esterification of a chiral acid with a simple achiral alcohol in organic media is a reversible process and, in order to bias the equilibrium to the... [Pg.140]

Semibatch or fully continuous operation with continuous removal of a by-product gas is also common. It is an important technique for relieving an equilibrium limitation, e.g., by-product water in an esterification. The pressure in the vapor space can be reduced or a dry, inert gas can be sparged to increase Ai and lower a, thereby increasing mass transfer and lowering u/ so that the forward reaction can proceed. [Pg.389]

One of the most important characteristics of IL is its wide temperature range for the liquid phase with no vapor pressure, so next we tested the lipase-catalyzed reaction under reduced pressure. It is known that usual methyl esters are not suitable for lipase-catalyzed transesterification as acyl donors because reverse reaction with produced methanol takes place. However, we can avoid such difficulty when the reaction is carried out under reduced pressure even if methyl esters are used as the acyl donor, because the produced methanol is removed immediately from the reaction mixture and thus the reaction equilibrium goes through to produce the desired product. To realize this idea, proper choice of the acyl donor ester was very important. The desired reaction was accomplished using methyl phenylth-ioacetate as acyl donor. Various methyl esters can also be used as acyl donor for these reactions methyl nonanoate was also recommended and efficient optical resolution was accomplished. Using our system, we demonstrated the completely recyclable use of lipase. The transesterification took place smoothly under reduced pressure at 10 Torr at 40°C when 0.5 equivalent of methyl phenylthioacetate was used as acyl donor, and we were able to obtain this compound in optically pure form. Five repetitions of this process showed no drop in the reaction rate (Fig. 4). Recently Kato reported nice additional examples of lipase-catalyzed reaction based on the same idea that CAL-B-catalyzed esterification or amidation of carboxylic acid was accomplished under reduced pressure conditions. ... [Pg.7]

Consider an equilibrium-limited esterification reaction. One way to drive the reaction to completion is to remove the water formed by the reaction selectively through a membrane. This can be an attractive strategy when higher temperatures are undesirable due to factors like colouration of the materials and formation of undesirable products even though these may be present at a low level. As another example, consider the air oxidation of cyclohexane or cyclododecane to cyclohexanone/-ol or cyclododecanone/-ol, where the product can undergo more facile oxidation to unwanted or much lower value products. Consequently, industrial processes operate at a level of less than 5% conversion. If a membrane can selectively remove cyclohexanone as it is formed, the problems mentioned above can be thwarted. However, selective polymeric membranes, which can work at oxidation temperature, have not yet been proved. [Pg.171]

Example 5.4.2.1. Equilibrium in esterification of acetic acid with ethanol (after Smith and van Ness, 1988)... [Pg.272]

Equilibrium Constants in a Reversible Esterification Reaction Using ESLand SIMUSOLV... [Pg.116]

SA conversion increases with increasing residence time, and with increasing MeOH SA to a maximum of about 98%. It appears that the maximum conversion increases to 99% for the highest MeOH SA studied (30), consistent with an equilibrium limited reaction. The esterification reaction rate was strongly suppressed by lowering MeOH/SA ratio below 10%. [Pg.286]

This is an equilibrium process and two techniques are used to drive the reaction to completion. One is to use a large excess of the alcohol, which is feasible for simple and inexpensive alcohols. The second method is to drive the reaction forward by irreversible removal of water, and azeotropic distillation is one way to accomplish this. Entries 1 to 4 in Scheme 3.5 are examples of acid-catalyzed esterifications. Entry 5 is the preparation of a diester starting with an anhydride. The initial opening of the anhydride ring is followed by an acid-catalyzed esterification. [Pg.252]

Such esterifications and acetal formations are achieved through enzyme catalyses. However, such reactions are relatively rare in aqueous conditions chemically. This is because the reversed reactions, hydrolysis, are much more favorable entropically. Kobayashi and co-workers found that the same surfactant (DBSA) that can catalyze the ether formation in water (5.2 above) can also catalyze the esterification and acetal formations reactions in water.52 Thus, various alkanecarboxylic acids can be converted to the esters with alcohols under the DBSA-catalyzed conditions in water (Eq. 5.6). Carboxylic acid with a longer alkyl chain afforded the corresponding ester better than one with a shorter chain at equilibrium. Selective esterification between two carboxylic acids with different alkyl chain lengths is therefore possible. [Pg.157]

The equilibrium conversion of lactic acid was measured by allowing reaction to proceed until no further changes were observed. We then used the data to calculate the equilibrium constant for the esterification reaction as a function of temperature. The final form of the equilibrium constant is given by the following equation. [Pg.376]

If ri = rate of reaction of SA and r2 = rate of formation of DES, then rate of formation of MES = r2 - ri. The equilibrium constant for each of the esterification reactions was determined by allowing the reaction to proceed until no further reaction was observed. For the quantities of resin used, the rate of resin-catalyzed esterification is much slower than that for sulfuric acid-catalyzed reaction. All results are summarized in Table 1. [Pg.377]


See other pages where Equilibrium esterification is mentioned: [Pg.583]    [Pg.35]    [Pg.379]    [Pg.302]    [Pg.380]    [Pg.91]    [Pg.61]    [Pg.83]    [Pg.132]    [Pg.484]    [Pg.216]    [Pg.303]    [Pg.874]    [Pg.91]    [Pg.275]    [Pg.379]    [Pg.117]    [Pg.287]    [Pg.298]    [Pg.299]    [Pg.303]    [Pg.286]    [Pg.241]   
See also in sourсe #XX -- [ Pg.146 ]




SEARCH



© 2024 chempedia.info