Alcoholic hydroxyl esterification

In addition to the esterification and etherification studies, the presence of three alcoholic hydroxyl groups has been shown by the action of metallic sodium in liquid ammonia on cellulosic materials. - For each D-glucose unit, one atom of sodium reacts readily while the two other atoms enter more slowly. 

Polyesters can be prepared by the direct esterification of carboxyl groups with alcoholic hydroxyl groups in the same or different compounds. Similarly, polyesters can be prepared from the reaction of carboxylic esters and alcoholic hydroxyl groups in the same or different... 

Esterification of an alcoholic hydroxyl with dialkylglycine or its analogs is a very popular mode of solubilization of... 

Esterification of an alcoholic hydroxyl with dialkylglycine or its analogues is a very popular mode of solubilization of alcohols. It is illustrated (Fig. 36.15) by soluble esters of forskolin/ of allopurinol and of metronidazole. This mode of solubilization can also be applied to phenols such as paracetamol (see Chapter 31). 

Total hydroxyl can be determined by reaction with acetic anhydride in pyridine this process may require prolonged periods (several days) at 90°C (195°F). Alcoholic hydroxyl can be determined by esterification with phthalic anhydride and this reaction also requires several days at 90°C (195°F) to ensure completion. 

Chemically, all alkyds are polyesters and are derived from a polycondensation reaction of polyhydric alcohols and polybasic acids with a certain degree of modification by some kind of oil or fatty acid. Among the important chemical reactions involved in alkyd resin technology are direct esterification of carboxylic acids with alcoholic hydroxyl groups, transesterification reactions, and reaction of an alcoholic hydroxyl with an acid anhydride. These reactions are shown in Figure 2.7. 

Esters. Most acryhc acid is used in the form of its methyl, ethyl, and butyl esters. Specialty monomeric esters with a hydroxyl, amino, or other functional group are used to provide adhesion, latent cross-linking capabihty, or different solubihty characteristics. The principal routes to esters are direct esterification with alcohols in the presence of a strong acid catalyst such as sulfuric acid, a soluble sulfonic acid, or sulfonic acid resins addition to alkylene oxides to give hydroxyalkyl acryhc esters and addition to the double bond of olefins in the presence of strong acid catalyst (19,20) to give ethyl or secondary alkyl acrylates. 

The synthesis of 2,4-dihydroxyacetophenone [89-84-9] (21) by acylation reactions of resorcinol has been extensively studied. The reaction is performed using acetic anhydride (104), acetyl chloride (105), or acetic acid (106). The esterification of resorcinol by acetic anhydride followed by the isomerization of the diacetate intermediate has also been described in the presence of zinc chloride (107). Alkylation of resorcinol can be carried out using ethers (108), olefins (109), or alcohols (110). The catalysts which are generally used include sulfuric acid, phosphoric and polyphosphoric acids, acidic resins, or aluminum and iron derivatives. 2-Chlororesorcinol [6201-65-1] (22) is obtained by a sulfonation—chloration—desulfonation technique (111). 1,2,4-Trihydroxybenzene [533-73-3] (23) is obtained by hydroxylation of resorcinol using hydrogen peroxide (112) or peracids (113). 

Esterification. The hydroxyl groups of sugars can react with organic and inorganic acids just as other alcohols do. Both natural and synthetic carbohydrate esters are important in various apphcations (1,13). Phosphate monoesters of sugars are important in metabohc reactions. An example is the enzyme-catalyzed, reversible aldol addition between dibydroxyacetone phosphate [57-04-51 and D-ylyceraldehyde 3-phosphate [591-57-1 / to form D-fmctose 1,6-bisphosphate [488-69-7],... 

The chemistry of ethyl alcohol is largely that of the hydroxyl group, namely, reactions of dehydration, dehydrogenation, oxidation, and esterification. The hydrogen atom of the hydroxyl group can be replaced by an active metal, such as sodium, potassium, and calcium, to form a metal ethoxide (ethylate) with the evolution of hydrogen gas (see Alkoxides, metal). 

As has been mentioned, preparation of esters of the C-17 hydroxyl group of selected progestins affords compounds with prolonged action. Similar chemical treatment of a corticoid would almost certainly lead to an ester of the sterically more accessible primary alcohol at C-21. In an interesting method for achieving esterification of the more hindered and less reactive tertiary 17-hydroxyl, prednisolone... 

Exactly the same considerations apply to the esterification of hindered acids (182) in the reverse direction. It will be noticed that this mechanism requires protonation on the less favoured (cf. p. 240) hydroxyl oxygen atom (185) to allow the formation of the acyl carbocationic intermediate (184). Apart from a number of R3C types, a very well known example is 2,4,6-trimethylbenzoic (mesitoic) acid (186), which will not esterify under ordinary acid-catalysis conditions—and nor will its esters (187) hydrolyse. Dissolving acid or ester in cone. H2S04 and pouring this solution into told alcohol or water, respectively, is. found to effect essentially quantitative esterification or hydrolysis as required the reaction proceeds via the acyl cation (188) ... 

How the aliphatic monomers are incorporated into the suberin polymer is not known. Presumably, activated co-hydroxy acids and dicarboxylic acids are ester-ified to the hydroxyl groups as found in cutin biosynthesis. The long chain fatty alcohols might be incorporated into suberin via esterification with phenylpro-panoic acids such as ferulic acid, followed by peroxidase-catalyzed polymerization of the phenolic derivative. This suggestion is based on the finding that ferulic acid esters of very long chain fatty alcohols are frequently found in sub-erin-associated waxes. The recently cloned hydroxycinnamoyl-CoA tyramine N-(hydroxycinnamoyl) transferase [77] may produce a tyramide derivative of the phenolic compound that may then be incorporated into the polymer by a peroxidase. The glycerol triester composed of a fatty acid, caffeic acid and a>-hydroxy acid found in the suberin associated wax [40] may also be incorporated into the polymer by a peroxidase. 

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