Hydrolytic conditions

J lie decarboxylation is frequently the most troublesome step in this sequence. Attempts at simple thermal decarboxylation frequently lead to recycliz-ation to the lactam. The original investigators carried out decarboxylation by acidic hydrolysis and noted that rings with ER substituents were most easily decarboxylated[2]. It appears that ring protonation is involved in the decarboxylation under hydrolytic conditions. Quinoline-copper decarboxylation has been used successfully after protecting the exocyclic nitrogen with a phthaloyl, acetyl or benzoyl group[3]. 

Acylaminothiazoles easily regenerate their 2-aminothiazole counterparts under acidic hydrolytic conditions (120). 

Tribromoacetic acid [75-96-7] (Br CCOOH), mol wt 296.74, C2HBr302, mp 135°C bp 245°C (decomposition), is soluble in water, ethyl alcohol, and diethyl ether. This acid is relatively unstable to hydrolytic conditions and can be decomposed to bromoform in boiling water. Tribromoacetic acid can be prepared by the oxidation of bromal [115-17-3] or perbromoethene [79-28-7] with fuming nitric acid and by treating an aqueous solution of malonic acid with bromine. 

Hydrolysis of Peroxycarboxylic Systems. Peroxyacetic acid [79-21-0] is produced commercially by the controlled autoxidation of acetaldehyde (qv). Under hydrolytic conditions, it forms an equiHbrium mixture with acetic acid and hydrogen peroxide. The hydrogen peroxide can be recovered from the mixture by extractive distillation (89) or by precipitating as the calcium salt followed by carbonating with carbon dioxide. These methods are not practiced on a commercial scale. Alternatively, the peroxycarboxyHc acid and alcohols can be treated with an estetifying catalyst to form H2O2 and the corresponding ester (90,91) (see Peroxides and peroxy compounds). 

C-17 protecting group e.g., cycloethylene ketal) is usually favored when selective hydrolytic conditions are employed. ... 

The hydrazinolysis is usually conducted in refluxing ethanol, and is a fast process in many cases. Functional groups, that would be affected under hydrolytic conditions, may be stable under hydrazinolysis conditions. The primary amine is often obtained in high yield. The Gabriel synthesis is for example recommended for the synthesis of isotopically labeled amines and amino acids. a-Amino acids 9 can be prepared by the Gabriel route, if a halomalonic ester—e.g. diethyl bromomalonate 7—is employed as the starting material instead of the alkyl halide ... 

These phosphorus-containing PAN derivatives are unstable under hydrolytic conditions, and the phosphoryl groups are easily split off under the action of boiling water. If, however, the modified PAN is treated with dimethyl phosphite solution in toluene in the presence of dimethylamine, a modified PAN, stable towards hydrolysis, is obtained. Its composition seems to be the following ... 

An interesting rearrangement was found by Davies and Kirby (1967) in the diazo-tization of 7-amino-benzothiazole (6.68). As Scheme 6-45 shows, the diazonium ion formed initially rearranges under hydrolytic conditions into 7-amino-l,2,3-benzo-thiadiazole (6.69). 

Comparison of these results for plutonium with those for other tetravalent metals reveals some interesting facts. Thor-ium(IV), uranium(IV) and neptunium(IV) sulfates have been investigated under hydrothermal hydrolytic conditions. For uranium, the stable phases which have been reported include U(0H)2S0i (2), U60i, (OH)i, (SO.,) 6 (2). U (SOi,) 2 4H20 (23) and IKSO (24). 

Pyrazolo[3,4-/>]quinoxalines can undergo ring fission under reductive or hydrolytic conditions to give different types of quinoxalme. The following examples illustrate these possibilities. 

Phosphazene polymers can act as biomaterials in several different ways [401, 402,407]. What is important in the consideration of skeletal properties is that the -P=N- backbone can be considered as an extremely stable substrate when fluorinated alcohols [399,457] or phenoxy [172] substituents are used in the substitution process of the chlorine atoms of (NPCl2)n> but it becomes highly hydrolytically unstable when simple amino acid [464] or imidazole [405-407] derivatives are attached to the phosphorus. In this case, an extraordinary demolition reaction of the polymer chain takes place under mild hydrolytic conditions transforming skeletal nitrogen and phosphorus into ammonium salts and phosphates, respectively [405-407,464]. This opens wide perspectives in biomedical sciences for the utilization of these materials, for instance, as drug delivery systems [213,401,405,406,464] and bioerodible substrates [403,404]. 

The biomedical uses of polyphosphazenes mentioned earlier involve chemistry that could in principle be carried out on a classical petrochemical-based polymer. However, in their bioerosion reactions, polyphosphazenes display a uniqueness that sets them apart. This uniqueness stems from the presence of the inorganic backbone, which in the presence of appropriate side groups is capable of undergoing facile hydrolysis to phosphate and ammonia. Phosphate can be metabolized, and ammonia is excreted. If the side groups released in this process are also metabolizable or excretable, the polymer can be eroded under hydrolytic conditions without the danger of a toxic response. Thus, poljnners of this tjT are candidates for use as erodible biostructural materials or sutures, or as matrices for the controlled delivery of drugs. Four examples will be given to illustrate the opportunities that exist. 

Various classes of additives may undergo chemical reaction in hydrolytic conditions. For example, hydrolysis of aromatic phosphites forms phenolic compounds [645]. Additives may also undergo reaction with the polymer chain, which causes extraction difficulties. 

The identification of L-iduronic acid as the major glycuronic acid constituent of heparin proved to be a much slower process than the identification of the amino sugar residue. Although this compound was detected in acid hydrolyzates of heparin116117 and heparin oligosaccharides,118 its yield was usually poor, because of the drastic conditions used for the acid hydrolysis (which are known to lead to extensive destruction of uronic acid).119120 Also, L-iduronic acid escaped detection as L-idose in the hydrolyzates of carboxyl-reduced heparin, probably because L-idose is readily converted into 1,6-anhydro-L-idose under the usual hydrolytic conditions. 

Since 2-deoxy-2-fluoro derivatives of aldopyranoses and furanoses are far more stable towards hydrolytic conditions than their 2-deoxy counterparts, the synthesis of the former entails primary preparation of the anomeric phosphotriesters 31, which are chromatographically separated into individual diastereomers and subsequently deprotected on phosphorus... 

The platelet hist UIline release assay demonstrated that cotton mill dust extract, cotton bract extract, cotton leaf extract, dialyzed CMD extract, polyphenols, compound 48/80, rutin, trimethylamine HCl, quercetin, catechin, tannic acid, ellagic acid and sodium metasilicate all release histamine directly (48). Thus not only do tannin compounds induce histamine release, but they may also form higher molecular weight polymers and contain components that survive acid hydrolytic conditions (48). Tannins are widely distributed in the plant kingdom. 

Honda and coworkers used 4 M hydrochloric acid for 6 h at 100° for the hydrolysis of nondialyzable glycoconjugates when determining amino monosaccharides, but preferred 2 M CF3CO2H for 6 h at 100° when determining the neutral monosaccharides and uronic acids, as these compounds are subject to more-severe degradation by 4 M hydrochloric acid. They obtained complete hydrolysis (with >90% recovery of monosaccharides added prior to hydrolysis) by using these two sets of hydrolytic conditions. 

The methods described in this section are of great significance because of the essentially neutral non-hydrolytic conditions employed. 

In aqueous solution, both glucose (hemiacetal) and frnctose (hemiketal) exist as equilibrium mixtures of cyclic and open-chain carbonyl forms. Sucrose, however, is a single stable substance (acetal and ketal), and conversion back to glucose and frnctose requires more rigorous hydrolytic conditions, such as heating with aqueous acid. 

Proteins are fundamentally polymers of a-amino acids linked by amide linkages (see Section 13.1). It is a pity that biochemists refer to these amide linkages as peptide bonds remember, a peptide is a small protein (less than about 40 amino acid residues), whereas a peptide bond is an amide. Therefore, peptides and proteins may be hydrolysed to their constituent amino acids by either acid or base hydrolysis. The amide bond is quite resistant to hydrolytic conditions (see above), an important feature for natural proteins. 

The amino groups are replaced with oxygen. Although here a biochemical reaction, the same can be achieved under acid-catalysed hydrolytic conditions, and resembles the nucleophilic substitution on pyrimidines (see Section 11.6.1). The first-formed hydroxy derivative would then tautomerize to the carbonyl structure. In the case of guanine, the product is xanthine, whereas adenine leads to hypoxanthine. The latter compound is also converted into xanthine by an oxidizing enzyme, xanthine oxidase. This enzyme also oxidizes xanthine at C-8, giving uric acid. 

Tamariz et al. reported the synthesis of mukonine (11) based on a regioselective Diels-Alder reaction of N-phenyl-4,5-dimethylidene-2-oxazolidinone (634) with methyl propiolate (635). The diene 634 was prepared in moderate yield from the condensation reaction of 2,3-butanedione (632) with phenyl isocyanate (633). In an optimized reaction procedure using drastic basic hydrolytic conditions (KOH/ MeOH), followed by methylation with dimethyl sulfate, the adduct 636, was... 

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