Carboxylic acids and phenols

Fig. 23. Representative protecting groups for phenolic and carboxylic acid-based systems, (a) The polymer-based protecting groups are fisted in order of increasing activation energy for acid-catalyzed deprotection, (b) Acid-labile monomeric dissolution inhibitors, a bifunctional system based on protected bisphenol A. (c) Another system that combines the function of dissolution inhibitor and PAG in a single unit.

Me3SiCH2CH=CH2i TsOH, CH3CN, 70-80°, 1-2 h, 90-95% yield. This silylating reagent is stable to moisture. Allylsilanes can be used to protect alcohols, phenols, and carboxylic acids there is no reaction with thiophenol except when CF3S03H is used as a catalyst. The method is also applicable to the formation of r-butyldimethylsilyl derivatives the silyl ether of cyclohexanol was prepared in 95% yield from allyl-/-butyldi-methylsilane. Iodine, bromine, trimethylsilyl bromide, and trimethylsilyl iodide have also been used as catalysts. Nafion-H has been shown to be an effective catalyst. 

Trimethylsilyl cyanide. This reagent readily silylates alcohols, phenols, and carboxylic acids, and more slowly, thiols and amines. Amides and related compounds do not react with this reagent. The reagent has the advantage that a volatile gas (HCN is highly toxic) is the only byproduct. 

Me3Si0C(0)NMe2. This reagent produces volatile byproducts and autocatalytically silylates alcohols, phenols, and carboxylic acids. 

Hydrogens on carbon next to a carbonyl group are acidic. In general, a /3-dicarbonyl compound is most acidic, a ketone or aldehyde is next most acidic, and a carboxylic acid derivative is least acidic. Remember that alcohols, phenols, and carboxylic acids are also acidic because of their -OH hydrogens. 

The breakdown of organic contaminants present in the MU water to produce ammonia (from nitrogenous contaminants), phenols and carboxylic acids (from humic and fulvic acids), and tri-halomethanes (from the by-products of chlorination)... 

Kinetic data17 with both phenols and carboxylic acids used as catalysts in reaction (10-27) are summarized in Table 10-6. The Brpnsted plot is shown in Fig. 10-6. The slope of the line gives a, which is 0.54. 

Kulikov, A. Arumugam, S. Popik, V. V. Photolabile protection of alcohols, phenols, and carboxylic acids with 3-hydroxy-2-naphthalenemethanol. J. Org. Chem. 2008. 73, 7611-7615. 

Saarikoski, J., Lindstrom, R., Tyynela, M. and Viluksela, M. (1986). Factors affecting the absorption of phenolics and carboxylic acids in the guppy (Poecilia reticulata), Ecotoxicol. Environ. Saf., 11, 158-173. 

Chau and Terry [146] reported the formation of penta-fluorobenzyl derivatives of ten herbicidal acids including 4-chloro-2-methyl-phenoxy acetic acid [145]. They found that 5h was an optimum reaction time at room temperature with pentafluorobenzyl bromide in the presence of potassium carbonate solution. Agemian and Chau [147] studied the residue analysis of 4-chloro-2-methyl phenoxy acetic acid and 4-chloro-2-methyl phenoxy butyric acid from water samples by making the pentafluorobenzyl derivatives. Bromination [148], nitrification [149] and esterification with halogenated alcohol [145] have also been used to study the residue analysis of 4-chloro-2-methyl phenoxy acetic acid and 4-chloro-2-methyl phenoxybutyric acid. Recently pentafluorobenzyl derivatives of phenols and carboxylic acids were prepared for detection by electron capture at very low levels [150, 151]. Pentafluorobenzyl bromide has also been used for the analytical determination of organophosphorus pesticides [152],... 

It is true that the acid character of phenol itself is not very pronounced, but the acidity increases as negative substituents such as NOa and halogen are introduced into the ring. The alkali salts of phenol are to a great extent hydrolysed in aqueous solution and they are completely decomposed by carbonic acid. Phenols and carboxylic acids can hence be separated by the action of carbon dioxide. 

Since alcohols and ketones generally possess high oxidation potentials, the indirect method is often applied to those compounds, while phenols and carboxylic acids are mainly oxidized by... 

One of the most important phase II conjugation reactions is that catalyzed by the glucuronyl transferases. A number of functional groups have the potential to be glu-curonidated as shown in Table 7.3, but phenol and carboxylic acid functions are of prime importance to the medicinal chemist. 

The main fluorescent pH indicator probes are based on fluorescein and therefore it is important to understand the pH-dependent ionic equilibria of it and its derivatives, hi aqueous solutions above pH 9 the phenolic and carboxylic acid functional groups in the molecule are almost totally ionised (Figure 3.14). Upon acidification of the dianion, firstly, protonation of the phenolic group occurs (pK 6.4) to yield the monoanion followed by the carboxylic acid (pA < 5), giving the neutral species of fluorescein. On further acidification the fluorescein cation pK 2.1) is generated. In strongly acidic environments fluorescein is non-fluorescent, only the mono-anion and di-anions are fluorescent, with quantum yields of 0.37 and 0.93, respectively. The pH-dependent absorption spectrum of fluorescein exhibits a blue-shift and... 

Nafion-H has been shown to be effective in a variety of protection-deprotection reactions including (9-trialkylsilylation of alcohols, phenols, and carboxylic acids, as well as the preparation and methanolysis of tetrahydropyranyl (THP) ethers.672 However, when compared, for example, with HBF4-silica or Nafion nanocomposites,... 

A simple process for the trimethylsilylation of alcohols, phenols, and carboxylic acids in refluxing CH2C12 over Nafion-H has been reported by Olah et al.672 [Eq. (5.240)]. The transformation of phenols and carboxylic acids requires higher temperature (CCI4 reflux). 

Extraction by chemically active solvents. Not infrequently the crude organic product from a reaction may contain a mixture of acidic (phenols and carboxylic acids), basic and neutral components in various combinations. Some of these components may of course be impurities, but none the less, whether as a preliminary purification stage or as a means of separating the mixture, a carefully planned solvent extraction procedure may be adopted using acidic and basic reagents which react chemically with the basic and acidic components of the mixture respectively. The following full account of a typical procedure may be abbreviated in practice according to the complexity of the mixture to be handled. 

Silylation of acidic compounds.2 The combination of ethyl trimethylsilylacetate and 2-5 mole % of tetra-n-butylammonium fluoride (TBAF) is a markedly efficient reagent for transfer of trimethylsilyl groups to relatively acidic substrates such as ketones, alcohols, thiols, phenols, and carboxylic acids, and even 1-alkynes. KOCH3/ (18-crown-6) and Triton B are also effective catalysts. 

There has been a summary of the use of insertion reactions of arynes into a-bonds to prepare nrt/io-disubs tituted arenes. A key to the success of these processes is the ability to generate benzyne under mild conditions by the reaction of readily available o-(trimethylsilyl)phenyl triflate with fluoride ions.61 Reaction of amines and their derivatives with benzynes generated in this way has been shown to be an efficient method for the production of N-arylated derivatives, as illustrated in Scheme 8. The method also works well in the O-arylation reactions of phenols and carboxylic acids 62... 

As a result of investigating the nonhalide phenol and carboxylic acid compounds as potential new hosts, it was found out that three types of phenol compound and seven types of carboxylic acid compound will form inclusion complexes with Cl-MIT (Tables 2-4). 

PhsPAuOTf has been shown to catalyse the intermolecular addition of phenols and carboxylic acids to terminal alkenes, RCH2CH=CH2, at 85 °C in toluene with Markovnikov selectivity to produce RCH2CH(OR)Me.131 AUCI3 triggers the electrophilic 6(0)ir n-endo-dig cyclization of 2-(alk-l-ynyl)alk-2-en-l-ones to produce highly substituted furans in analogy with other electrophiles (see above Scheme 3).40... 

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