Esterification

4 Key excerpts on "Esterification"

• 

  eBook - ePub

  Solvents as Reagents in Organic Synthesis

  Reactions and Applications

  • Xiao-Feng Wu(Author)
  • 2017(Publication Date)
  • Wiley-VCH

    (Publisher)

  In 1940, Norton et al. [8] investigated the mechanism of Esterification between alcohol and strong carboxylic acid, revealing that the generated water was composed of the hydrogen from the alcohol and the hydroxyl from the acid. Since then, Esterification was deeply investigated and developed not only in the field of basic research but also in the industrialized mass production. However, the inherent attribute of the reaction between alcohol and carboxylic acid lie in its reversibility, which makes the reaction require the use of excess amount of one starting material or the addition of one dehydration reagent. Recently, Yamamoto et al. [9] achieved a breakthrough in this topic. With hafnium (IV) salts, such as hafnium (IV) chloride and hafnium (IV) tert -butoxide, as catalyst, the direct condensation of carboxylic acids and alcohols could be achieved in an equimolar amount. Subsequently, this method was applied to direct polyEsterification and large-scale operations. Following that, all kinds of homogeneous catalysts, such as Brønsted acids, Lewis acids, were developed [10]. In addition, ionic liquids [11] (ILs), one of the most promising new reaction mediums and catalysts, have been introduced to homogeneous catalysis of Esterification between alcohols and carboxylic acids. Meanwhile, solid-like non-volatile Brønsted acids have the advantages of motility, greater effective surface area, and potential activity in liquid phase. Combining sthese characteristics, Forbes and Davis et al. [12] first designed novel Brønsted acidic ILs containing an alkane sulfonic acid group and applied to Esterification between alcohol and carboxylic acids, which provided good product selectivities as well as a balance between a homogeneous acid catalyst and heterogeneous catalyst (ease catalyst/substrate separation)

  Sign up to read

  Learn more about book
• 

  eBook - ePub

  Synthetics, Mineral Oils, and Bio-Based Lubricants

  Chemistry and Technology

  • Leslie R. Rudnick, Leslie R. Rudnick(Authors)
  • 2020(Publication Date)
  • CRC Press

    (Publisher)
• 1. Esterification
• 2. Stripping of excess reactants
• 3. Neutralization
• 4. Filtration
The basic chemical reaction for the Esterification process is shown in Figure 3.1 . Esterification is an equilibrium process, and formation of the ester group is carried out by mixing the acid and alcohol raw material while removing the water of reaction in order to drive the equilibrium to the right-hand side. Ester lubricant basefluids are normally manufactured batchwise, using a stirred reaction vessel equipped with heating, cooling, and overheads capable of condensing and separating water of reaction from volatile organic reactants by fractionation or decantation [13 ].
To facilitate removal of water and accelerate reaction, Esterification processes are normally carried out at a temperature of at least 100°C, and since the products have good thermal stability, higher temperatures up to about 250°C are commonly used. Esterification catalysts may be used; these include strong mineral acids such as sulfuric or p-toluene sulfonic acids for use at lower temperatures and Lewis acid catalysts such as tin and titanium alcoholates at higher temperatures. Azeotroping agents may also be used to assist in removal of water [13 ].
For diester products, the monoalcohol reactants normally have significant volatility, and a 10%–20% molar excess of monoalcohol is frequently used to drive the equilibrium. At the end of reaction, excess volatile reactant is removed by stripping under reduced pressure and recycled to subsequent batches.
Similarly, for polyol esters, excess monoacid reactant may be used and stripped at the end of reaction. Because the excess acid serves to catalyze the reaction, polyol esters are frequently manufactured without use of additional catalyst.
The Esterification and stripping process will typically give a conversion of acid groups of >99% in the crude reaction product. However, because very low acid values are generally required for lubricant basefluids, further reduction of acid concentration is frequently necessary. This can be achieved by treatment of the crude reaction product by addition of a base such as sodium carbonate or calcium hydroxide, which converts residual acid to carboxylate soaps that can be removed by water washing and/or filtration.