Citric acid esterification

Alcohols typically used in citric acid esterification are methyl, ethyl, butyl, and aHyl alcohols. 

Esterification. Citric acid is easily esterified with many alcohols under a2eotropic conditions in the presence of a catalyst such as sulfuric acid, / -toluenesulfonic acid, or sulfonic acid-type ion-exchange resin. Alcohols boiling above 150°C esterify citric acid without a catalyst (5—8). 

L-ascorbic acid and, 25 751 as chelating agent, 5 731 in cocoa shell from roasted beans, 6 357t Oxalic-acid-catalyzed novolacs, in molding compounds, 75 786 Oxalic acid esterification, 72 652 Oxaloacetic acid, in citric acid cycle, 6 633 Oxalosuccinic acid, in citric acid cycle, 6 633... 

The method is normally performed as follows [32,39] an aqueous solution of suitable oxides or salts is mixed with an a-hydroxycarboxylic acid, such as citric acid, and EG is added to the solution. At heating, an esterification process runs in the system leading to the formation of a stable gel in which the metal ions remain fixed. In the modified Pechini process, ethylenediaminetetraacetic acid (EDTA) has been used to replace citric acid due to its stronger chelating power. 

Subsequent to this breakthrough, the subject was extensively investigated and was subsequently reviewed [390]. The acids most effective are BTCA, tricarballylic acid, and citric acid. Owing to the low cost and wide availability of citric acid, it is undergoing widespread commercial development for esterification cross-linking of cotton and paper products, often with minor amounts of BTCA as an activator, together with suitable catalysts. 

Codeine phosphate in a paracetamol-codeine effervescent tablet was found to react at room temperature with the citric acid constituents to form citrate esters of codeine. The esterification was confirmed in a solid-state reaction at an elevated temperature. Tartaric acid also yielded an ester with codeine phosphate in a similar non-solvolytic reaction. 

Acetyltributyl citrate is prepared by the esterification of citric acid with butanol followed by acylation with acetic anhydride. 

A method of esterification introduced by Meyer807 is to dissolve the carboxylic acid in an excess of concentrated sulfuric acid (if necessary with warming) and to treat the solution cautiously with a small excess of the requisite alcohol when the reaction, which is often violent, ceases—if the mixture does not become warm, it must be heated—the solution is poured on solid sodium carbonate and worked up. This method has been used for esterification of sterically hindered acids and for carboxy derivatives of nitrogenous heterocycles, also for preparation of acetonedicarboxylic esters from citric acid and alcohols.808... 

Finally, the esterification reaction with styrallyl alcohol and acetic acid was carried out under natural reaction conditions using esterification catalysts such as citric acid or by means of bioprocess reactions using commercial esterforming enzymes (5). The catalytic conversion of styrallyl alcohol to styrallyl acetate did not change the stereoisomer ratio. The resulting stereoisomeric mixture of styrallyl acetate was recovered and purified by solvent extraction followed by fractional distillation. 

The 0-protection of A -protected amino acids 55 was achieved by decarboxylative esterification in solvent-free conditions by Colacino et al. (Scheme 4.13). It was found that the use of planetary ball mill was more effective than vibratory mill [8], Commonly used 0-activation reagents (diaUcyl dicarbonate (B0C2O), carbonate (A, A -disuccinimidyl carbonate, DSC), and alkyl chloroformates (ROCOCl, R=Bn, Et, allyl)) were employed in combination with DMAP as base. Reaction parameters had to be optimized for each individual reagent to achieve acceptable yields (selection of results. Table 4.3). Due to high reactivity of benzyloxy chloroformate (Z-Cl), the two-step cycled milling was executed by addition of Z-Cl in 2equiv. portions, so as to consume the chloroformate and reduce the formation of the undesired byproducts. Acidic workup with 10% aqueous citric acid of ether extracts eliminates DMAP and affords the A-protected amino ester derivatives 56 in good yields. 

In the third step, proteins act as amides and react with the free hydroxyl of the citric acid. The hydroxyl of the citric acid reacts like the hydroxyl of an alcohol in a standard esterification process. During the reaction of the amide with the citric acid, the substitution of the amide hydroxyl by an alkoxy radical (-OR) takes place. At the end of the process, the oxygen in the -OH group of the citric acid remains in the chain whereas the hydroxyl oxygen in the amino acids is eliminated in the form of water. This mechanism results in long chains containing metal cations tightly bond and evenly distributed. 

Organic titanates are used as catalysts in the synthesis of citric acid esters. The production steps for the citric acid esters include low temperature esterification at 140°C or below, removal of any excess alcohol and thereafter, alkoxylation Conventional neutralization and finishing steps are then carried out. The alkoxylation step is carried out at a temperature less than approximately 110°C. ... 

Esters of monoglycerides with organic acids such as acetic acid, lactic acid, diacetyltartaric acid, succinic acid and citric acid are widely used as food emulsifiers. The esters are produced in standard batch reactors normally by reacting monoglycerides with the organic acid or its anhydride. A direct esterification of fatty acids, glycerol and the organic acid is also possible for some products. 

Citric acid esters of monoglycerides (CMG) are manufactured by esterification of monoglycerides with citric acid, and the resulting product is often partially neutralized by alkali (Na salts). 

Kolah, A. K., Asthana, N. S., Vu, D. T., Lira, C. T., Miller, D. J. (2007). Reaction kinetics of the catalytic esterification of citric acid with ethanol. Industrial Engineering Chemistry Research, 46, 3180—3187. 

The properties of monoglycerides can also be modified by esterification of one of the hydroxyl groups with acetic, lactic, fumaric, tartaric or citric acids. Similar emulsifiers are synthesised by reacting propylene glycol with saturated fatty acids to give a mixture of mono- and diacyl esters, which can be molecularly distilled to prepare concentrates containing about 90% propylene-glycol monostearate. 

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