Chemistry
Esterification
Esterification is a chemical reaction in which an alcohol and a carboxylic acid react to form an ester and water. This process typically requires the presence of an acid catalyst, such as sulfuric acid. Esterification is commonly used in the production of fragrances, flavorings, and as a method for synthesizing organic compounds.
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eBook - ePubSynthetics, Mineral Oils, and Bio-Based Lubricants
Chemistry and Technology
- Leslie R. Rudnick(Author)
- 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.
eBook - PDF- Mark Crocker, Eduardo Santillan-Jimenez, Mark Crocker, Eduardo Santillan-Jimenez(Authors)
- 2019(Publication Date)
- Wiley-VCH(Publisher)
Esterification can effectively remove the majority of the acids (not all due to the reaction equi-librium of Esterification reactions), which alleviates the corrosiveness of bio-oil. Nevertheless, from a survey of the current literature, the Esterification of bio-oil involves far more than just Esterification reactions between the carboxylic acids and the alcohols. A number of other reactions take place in parallel, including the conversion and transformation of sugars, aldehydes, furans, and aromatics. The Esterification of bio-oil is more accurately described as the acid-catalyzed con-version of the organics in an alcohol-rich medium. Many reactions, which are catalyzed by an acid catalyst, can take place. Indeed, as the reaction medium is 102 4 Stabilization of Bio-oil via Esterification alcohol-rich, many components of the bio-oil undergo reactions with the alcohol. As a consequence, the reaction network under Esterification conditions is very complex. The composition of bio-oil changes significantly during Esterification, contributing to the bio-oil stabilization. In the Sections 4.2 and 4.3, the detailed reaction routes of the major bio-oil components during Esterification and the effect on bio-oil stability are discussed in detail. 4.2 Reactions of the Main Components of Bio-Oil Under Esterification Conditions 4.2.1 Sugars Sugars, including sugar monomers and oligomers, are one of the major com-ponents of bio-oil and are produced from the degradation of cellulose and hemicellulose during biomass pyrolysis [38, 39]. In general, levoglucosan is one of the most abundant detectable anhydrate sugars in bio-oil, while other sugars such as glucose, galactose, xylose, etc. are also present. The reactivity of sugars under the conditions of acid treatment is broadly similar to that in acid-catalyzed conversion of model sugars [40, 41]. Nevertheless, bio-oil is a very complex reaction medium.
eBook - PDFPolyester and Alkyd Resins
Technical Basics and Applications
- Ulrich Poth(Author)
- 2020(Publication Date)
- Vincentz Network(Publisher)
From the point of view of the distillation process, this is an example of “residue recovery”. R 2 C OH O O H R 1 R 2 C O R 1 O H OH + + carboxylic acid alcohol ester water Figure 3.2: Overall equilibrium equation for Esterification and saponification Reactions that produce polyesters 19 3.1.1.2 TransEsterification As the saponification reaction shows, the ester group can be polarised by water. But it can also be polarised by alcohols. Thus, ester groups can react with mobile hydrogen atoms from alcohols to form an intermediate structure. This intermediate structure can decom-pose into its reactants, but it can also decompose into the ester formed with alcohol 2 and into the free alcohol of ester 1 (see Figure 3.3 and overall equation in Figure 3.4). The chemical equilibrium involved in transEsterification is also subject to the law of mass action. Equation 3.2 Here, again, the equilibrium state is influenced by the “R”-groups in the carboxylic acid as well as the alco-hol. Naturally, it is also influenced by the concentration of reactants and by the temperature. If the goal is to prepare one of the esters in high yield, the reaction equilibrium needs to be shifted to the correct side. This is usually ac-complished by removing one of the products through distillation. This means that polyesters can be pro-duced from polycarboxylic esters of lower alcohols. Full transesterifica -tion with polyols is then achieved by distilling off all the low boiling alco -hol from the starting product. TransEsterification also plays a role in the preparation of alkyd re-sins. Starting products are then na-tural oils or fats (triglycerides) which are transesterified with poly -ols.
- Kenneth Williamson, Katherine Masters(Authors)
- 2016(Publication Date)
- Cengage Learning EMEA(Publisher)
Esterification and Hydrolysis PRE-LAB EXERCISE: Write the detailed mechanism for the acid-catalyzed hydrolysis of methyl benzoate. The ester group is an important functional group that can be synthesized in a variety of ways. The low molecular weight esters have very pleasant odors and indeed comprise the major flavor and odor components of a number of fruits. Although a natural flavor may contain nearly 100 different compounds, single esters approximate natural odors and are often used in the food industry for artificial flavors and fragrances (Table 40.1). Esters can be prepared by the reaction of a carboxylic acid with an alcohol in the presence of a catalyst such as concentrated sulfuric acid, hydrogen chloride, p -toluenesulfonic acid, or the acid form of an ion exchange resin. For example, methyl acetate can be prepared as follows: H + The Fischer Esterification reaction reaches equilibrium after a few hours of refluxing. The position of the equilibrium can be shifted by adding more of the acid or of the alcohol, depending on cost or availability. The mechanism of the reaction involves initial protonation of the carboxyl group, attack by the nucleophilic hydroxyl, a proton transfer, and loss of water followed by loss of the catalyzing proton to give the ester. Each of these steps is completely reversible, so this process is also, in reverse, the mechanism for the hydrolysis of an ester. Flavors and fragrances Fischer Esterification When you see this icon, sign in at this book’s premium website at www.cengage.com/login to access videos, Pre-Lab Exercises, and other online resources. w 517 CHAPTER 40 The ester group Copyright 2017 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience.
eBook - ePub- Raymond D. Harbison, Marie M. Bourgeois, Giffe T. Johnson(Authors)
- 2015(Publication Date)
- Wiley(Publisher)
57 Esters Raymond D. Harbison and C. Clifford ConawayEsters are compounds that result from the reaction of an alcohol or phenol with acids or derivatives of acids. Almost all the aliphatic esters are prepared by the reaction between carboxylic acids and alcohols. The subclasses of esters presented in this chapter include the aliphatic esters, halogenated acid esters, alkyl esters of sulfuric acid, important phosphate esters, nitrate esters, and esters of phthalic acid. Some esters, such as aliphatics esters, may present human health hazards (USEPA, 2007), if exposure occurs via the respiratory or dermal routes.Many organic esters are used extensively in the plastic industry, either as resins or as plasticizers, and as solvents for lacquers. The group of esters, including succinate, adipate, azelate, sebacate, citrate, and phthalate is generally used as plasticizers. Esters of inorganic acids, such as esters of sulfuric acid and phosphate esters, may have prominent corrosive or pharmacological properties. See Table 57.1
eBook - ePub- (Author)
- 2009(Publication Date)
- Academic Press(Publisher)
The recent discovery of chloroformate-induced Esterification of carboxylic acids is a good example of this. Over time, many derivatization methods have become more or less obsolete as their original usefulness was determined by a lack of alternative methods for the determination of minute amounts of some analytes, especially those in biological fluids. Until the discovery of immunoassay (radioimmunoassay, RIA, and enzyme immunoassay, EIA) and the development of specific and sensitive HPLC detectors, the electron-capture detector (ECD) in GC was the only way to reach picomole concentration levels. At that time, therefore, there was considerable interest in the conversion of analytes into perhalo-genated products with a correspondingly high ECD response. Some of these methods or principles still persist; others do not. A comprehensive list of various chemical treatments can be found in the Handbook of Derivatives for Chromatography by Blau and Halket (see Further Reading). Some of the older useful methods and recent novel discoveries will be discussed in more detail below (see also the reviews by Hušek and Wells listed in the Further Reading section). Esterification Carboxylic acid groups usually require treatment with a group-oriented reagent that will not react in most cases with any other protonic groups that may be present. The choice of treatment depends on what class of acidic compounds – with or without extra reactive groups in the molecule – is to be esterified and what kind of detection (ECD or flame ionization detection, FID) is required. Esterification with Acidified Alcohols For analytical work, Esterification with methanol through to isoamyl alcohol is best done in the presence of a volatile catalyst such as hydrogen chloride, thionyl chloride or acetyl chloride, which can be readily removed together with any excess alcohol
- Jean-Marc Campagne, Timothy J. Donohoe, Xuefeng Jiang, Ming Wang(Authors)
- 2024(Publication Date)
- Thieme Chemistry(Publisher)
[52] Catalytic direct Esterification of carboxylic acids with secondary alcohols (e.g., 1-ary- lalkyl alcohols) under solvent-free conditions takes place in the presence of phosphoro- fluoridic acid 21 (5 mol%) bearing an L-menthyl group. The ester products are obtained in moderate to good yields (entry 13). [53] On the other hand, the combination of a catalytic amount of trifluoromethanesulfonic acid with the fluorous organic hybrid solvent 1,1,1,3,3-pentafluorobutane (Solkane 365mfc) is proposed for direct Esterification of equi- molar ratios of acid and alcohol substrates under quite simple reaction conditions. For ex- ample, this reaction affords octyl pivalate in 97% yield (entry 14). [54] Another possibility is the use of Brønsted acidic ionic liquids as both an efficient recyclable catalyst and solvent for direct Esterification. Efficient approaches in this context are the use of either 1-meth- ylimidazolium tetrafluoroborate (22) [55] or N-methyl-2-pyrrolidonium methylsulfonate (23). [56] Whereas the first one requires high reaction temperatures (110 8 8C), the latter ionic liquid provides condensation reactions under milder conditions (room temperature or 273 20.5.1 Alkyl Alkanoates 60 8C). The esters formed [e.g., butyl 2-hydroxypropanoate (24, R 1 = CHMeOH; R 2 = Bu)] are insoluble in the ionic liquid and can be removed by decantation, without the use of vola- tile organic solvents (entries 15 and 16). Moreover, both the Brønsted acidic ionic liquids 22 and 23 can be reused several times after removal of water under reduced pressure, with catalytic activity retained.
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