Subject hydroxyl-substituted

The effect substitution on the phenolic ring has on activity has been the subject of several studies (11—13). Hindering the phenolic hydroxyl group with at least one bulky alkyl group ia the ortho position appears necessary for high antioxidant activity. Neatly all commercial antioxidants are hindered ia this manner. Steric hindrance decreases the ability of a phenoxyl radical to abstract a hydrogen atom from the substrate and thus produces an alkyl radical (14) capable of initiating oxidation (eq. 18). 

Hydroxyl Group. The OH group of cyanohydrins is subject to displacement with other electronegative groups. Cyanohydrins react with ammonia to yield amino nitriles. This is a step in the Strecker synthesis of amino acids. A one-step synthesis of a-amino acids involves treatment of cyanohydrins with ammonia and ammonium carbonate under pressure. Thus acetone cyanohydrin, when heated at 160°C with ammonia and ammonium carbonate for 6 h, gives a-aminoisobutyric acid [62-57-7] in 86% yield (7). Primary and secondary amines can also be used to displace the hydroxyl group to obtain A/-substituted and Ai,A/-disubstituted a-amino nitriles. The Strecker synthesis can also be appHed to aromatic ketones. Similarly, hydrazine reacts with two molecules of cyanohydrin to give the disubstituted hydrazine. 

The dangerous reactions of alcohols, apart from the ones that involve the carbon chain, are linked either to the exothermicity of the reactions whose consequences are often aggravated by poor temperature monitoring, or the instability of the intermediate or final compounds formed. The first case often happens with oxidation reactions, the second especially with substitutions of active hydrogen or hydroxyl. Nitric acid will be the subject of special consideration since it can have both characters, without knowing which one played a role during accidents that have involved this compound. 

Aldol addition and related reactions of enolates and enolate equivalents are the subject of the first part of Chapter 2. These reactions provide powerful methods for controlling the stereochemistry in reactions that form hydroxyl- and methyl-substituted structures, such as those found in many antibiotics. We will see how the choice of the nucleophile, the other reagents (such as Lewis acids), and adjustment of reaction conditions can be used to control stereochemistry. We discuss the role of open, cyclic, and chelated transition structures in determining stereochemistry, and will also see how chiral auxiliaries and chiral catalysts can control the enantiose-lectivity of these reactions. Intramolecular aldol reactions, including the Robinson annulation are discussed. Other reactions included in Chapter 2 include Mannich, carbon acylation, and olefination reactions. The reactivity of other carbon nucleophiles including phosphonium ylides, phosphonate carbanions, sulfone anions, sulfonium ylides, and sulfoxonium ylides are also considered. 

The reactions of the six-membered chlorocyclophosphazene were studied with a number of aliphatic diamines (169 175), aromatic diamines (176), aliphatic diols (177-179), aromatic diols (180,181) and compounds containing amino and hydroxyl functional groups (169,170,182). This subject has been reviewed (11,16,20). There are at least five different reaction products that are possible (Fig. 19). Replacement of two chlorine atoms from the same phosphorus atom produces a spirocyclic product. Replacement of two chlorine atoms from two different phosphorus atoms in the same molecule produces an ansa product. Reaction of only one end of the difunctional reagent, resulting in the substitution of only one chlorine atom, leads to an open-chain compound. Intermolecular bridged compounds are formed when the difunc-... 

Methyl-substituted indole has been the subject of an investigation and the degradation metabolites were identified [346], An indole-degrading methanogenic consortium induced a two-step reaction on 3-methylindole, through a hydroxylation pathway that... 

Chlordane is subject to hydrolysis via the nucleophilic substitution of chlorine by hydroxyl ions to yield 2,4,5,6,7,8,8-heptachloro-3a,4,7,7a-tetrahydro-4,7-methano-l//-indene which is resistant to hydrolysis (Kollig, 1993). The hydrolysis half-life at pH 7 and 25 °C was estimated to be >197,000 yr (Ellington et ah, 1988). 

In the epoxidation of acyclic allylic alcohols (Scheme 6), the diastereoselectivity depends significantly on the substitution pattern of the substrate. The control of the threo selectivity is subject to the hydroxyl-group directivity, in which conformational preference on account of the steric interactions and the hydrogen bonding between the dioxirane oxygen atoms and the hydroxy functionality of the allylic substrate steer the favored 7r-facial... 

The subject of relative reactivities of hydroxyl groups in carbohydrates has been discussed previously in this Series.1,2 In these articles, emphasis was placed on the selective introduction of substituents into carbohydrates. A much less exploited approach for the preparation of partially substituted carbohydrates involves the selective removal of hydroxyl-protecting groups from carbohydrate derivatives. The purpose of the present article is to draw attention to this relatively neglected aspect of synthesis in the belief that the greater use of de-... 

Although significant improvements have been made in the synthesis of phenol from benzene, the practical utility of direct radical hydroxylation of substituted arenes remains very low. A mixture of ortho-, meta- and para-substituted phenols is typically formed. Alkyl substituents are subject to radical H-atom abstraction, giving benzyl alcohol, benzaldehyde, and benzoic acid in addition to the mixture of cresols. Hydroxylation of phenylacetic acid leads to decarboxylation and gives benzyl alcohol along with phenolic products [2], A mixture of naphthols is produced in radical oxidations of naphthalene, in addition to diols and hydroxyketones [19]. 

The question of which lattice components to include in the interpretive analysis reduces to the experimental problem of comparing systems of similar geometry but which contain different species in the lattice—e.g., Ge or Th in substitution for Si (1) S or F in substitution for O or OH, and say 2Na+ for lCa+2. The effect of change of cation is well known. In limiting cases it modifies the Molecular Sieve effect in zeolites. For host substituents, the availability of suitable systems is limited. The present work offers a comparison between a normal aluminosilicate and the same species after subjection to a substitution of halogen for oxygen and hydroxyl. 

The details of the reaction conditions used in this study have been described elsewhere (Dershem, S. M., et al., Holzforschung Fisher, T. H., et al., J. Org. CAem., in press). To test the importance of a p-hydroxyl substituent, the kinetics of oxidation of three benzyl alcohols p-hydroxybenzyl alcohol, (1), m-hydroxybenzyl alcohol, (2), and 4-hydroxy-3-methoxybenzyl alcohol, (3), were examined under alkaline nitrobenzene oxidation conditions. Some l-(4-hydroxyphenyl)-2-(4 -substituted phenyl)ethanols, (4), were synthesized as / -l lignin model compounds and subjected to alkaline nitrobenzene oxidation at 120 °C to study substituent effects. For controls, some of these compounds were reacted with or without nitrobenzene, alkaline catalyst, or water. In an effort to determine the effects of substituents on the oxidative-cleavage reaction of 4-hydroxystilbenes (5), a series of competitive rate experiments using both nitrobenzene and copper(II) as the oxidants in 2N NaOH was performed (Dershem, S. M., et al., Holzforschung, in press). 

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