Esterifications phenols

Fischer esterification m which a phenol and a carboxylic acid condense m the pres ence of an acid catalyst is not used to prepare aryl esters... 

Because vanillin is a phenol aldehyde, it is stable to autooxidation and does not undergo the Cannizzarro reaction. Numerous derivatives can be prepared by etherification or esterification of the hydroxy group and by aldol condensation at the aldehyde group. AH three functional groups in vanillin are... 

The hydrolysis of phosphites is retarded by the addition of a small amount of a base such as triethanolamine. A more effective approach is the use of hindered phenols for esterification. Relatively good resistance to hydrolysis is shown by two esters derived from hindered phenols tris(2,4-di-/ / butylphenyl)phosphite [31570-04-4] (25) and tetrakis(2,4-di-/ /f-butylphenyl)4,4 -biphenylenediphosphonite [38613-77-3] (26). The hindered fluorophosphite [118337-09-0] (27) has excellent resistance to hydrolysis. 

From Boric Acid. The most common method for the preparation of trialkoxy- and triaryloxyboranes is the esterification of boric acid using three moles of an alcohol or phenol. 

The esterification of -butyl alcohol and oleic acid with a phenol—formaldehydesulfonic acid resin (similar to amberHte IR-100) is essentially second order after an initial slow period (52). The velocity constant is directiy proportional to the surface area of the catalyst per unit weight of reactants. 

Inter and Intramolecular nucleophiKc displacement o< alcohols wHh inversion by means of cHethyi azo cartMxylate (DEAD)-triphenylphosphine and a nucleophile. Also dehydration, esterification of alcohols or alkylallon of phenols,... 

Laminating resins have been offered by Akzo (Diacryl 101), Dow (Derakane Vinyl Esters) and Showa (Spilac). Typical of these is Diacryl 101, which is manufactured by esterification of the addition product of ethylene oxide to bis-phenol A with methacrylic acid. They exhibit lower curing shrinkage than the polyester laminating resins during cure. The structure of Diacryl 101 is... 

A variety of nucleophiles can be employed—e.g. carboxylic acids, phenols, imides, thiols, thioamides, and even /3-ketoesters as carbon nucleophiles. Of major importance however is the esterification as outlined above, and its use for the clean inversion of configuration of a chiral alcohol. 

The esterification of the phenolic hydroxyl group in salicylic acid with acetic acid results not only in an... 

This procedure provides a convenient method for the esterification ol a wide variety of carboxylic acids. The reaction proceeds smoothly with sterically hindered acids6 and with acids which contain various functional groups. Esters are obtained in high purity using Kugelrohr distillation as the sole purification technique. In cases where traces of dichloromethane present no problems, the crude product is usually pure enough to be used directly in subsequent reactions. Methyl and ethyl ethers of phenols may also be prepared by this procedure (see Note 8). 

Whilst the addition of a chiral NHC to a ketene generates a chiral azolium enolate directly, a number of alternative strategies have been developed that allow asymmetric reactions to proceed via an enol or enolate intermediate. For example, Rovis and co-workers have shown that chiral azolium enolate species 225 can be generated from a,a-dihaloaldehydes 222, with enantioselective protonation and subsequent esterification generating a-chloroesters 224 in excellent ee (84-93% ee). Notably, in this process a bulky acidic phenol 223 is used as a buffer alongside an excess of an altemativephenoliccomponentto minimise productepimerisation (Scheme 12.48). An extension of this approach allows the synthesis of enantiomericaUy emiched a-chloro-amides (80% ee) [87]. 

The second step, nucleophilic attack of an alcohol or phenol on the activated carboxylic acid RCOIm (carboxylic acid imidazolide), is usually slow (several hours), but it can be accelerated by heating[7] or by adding a base[8] [9] such as NaH, NaNH2, imidazole sodium (ImNa), NaOR, triethylamine, diazabicyclononene (DBN), diazabicycloimdecene (DBU), or /7-dimethylaminopyridine to the reaction mixture (see Tables 3—1 and 3—2). This causes the alcohol to become more nucleophilic. Sodium alcoholate applied in catalytic amounts accelerates the ester synthesis to such an extent that even at room temperature esterification is complete after a short time, usually within a few minutes.[7H9] This catalysis is a result of the fact that alcoholate reacts with the imidazolide very rapidly, forming the ester and imidazole sodium. 

Since the imidazolide method proceeds almost quantitatively, it has been used for the synthesis of isotopically labeled esters (see also Section 3.2), and it is always useful for the esterification of sensitive carboxylic acids, alcohols, and phenols under mild conditions. This advantage has been utilized in biochemistry for the study of transacylating enzymes. A number of enzymatic transacylations (e.g., those catalyzed by oc-chymo-trypsin) have been shown to proceed in two steps an acyl group is first transferred from the substrate to the enzyme to form an acyl enzyme, which is then deacylated in a second step. In this context it has been shown[21] that oc-chymotrypsin is rapidly and quantitatively acylated by Af-fraw.s-cinnamoylimidazole to give /ra/w-cinnamoyl-a-chymotrypsin, which can be isolated in preparative quantities and retains its enzymatic activity (see also Chapter 6). 

One of the mainstays in the treatment of tuberculosis is paraaminosalicylic acid (PAS). It is not, however, a pleasant drug to take. Phenyl aminosalicylate (20) was synthesized from 4-nitrosalicylic acid (18) by esterification of its acid chloride with phenol to give 19, which is converted to the desired... 

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. 

Acids are well known as efficient catalysts of various heterolytic reactions (hydrolysis, esterification, enolyzation, etc. [225,226]). They catalyze the heterolytic decay of hydroperoxides formed during oxidation. For example, they catalyze the decomposition of cumyl hydroperoxide into phenol and acetone (important technological reaction) [5]. 

Another method is based on the same principle,112 in which the [14C]labelled methyl ester of D-galacturonan is prepared by esterification of pectic acid with [,4C]diazomethane. In the course of the enzymic de-esterification, aliquots are removed, and the unreacted substrate is precipitated with acidified ethanol or 1-propanol. After centrifugation, the labelled methanol in the supernatant liquor is determined in a liquid scintillation counter. An advantage of this method lies in the possibility of using, as substrates, short-chain oligo-D-galactosiduronates partially esterified with [14C]methanol. These substrates, beginning with the trisaccharide, are not soluble in 1 4 80% phenol-diethyl ether, which is used for the extraction of enzymically released, labelled methanol. 

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