Molecular eliminations carboxylic acids

The use of much-neglected bismuth derivatives for the oxidation of organic compounds has been reviewed.74 Bismuth(III) carboxylates, obtained by reaction of Bi2C>3 with pyridine mono- and di-carboxylic acids and with phthalic acid, act as catalysts for the oxidation of styrene oxide to benzoic acid in DM SO in the presence of 02.75 It is proposed that the bismuth may activate both epoxide and oxidant in a solvate, from which dimethyl sulfide evolution and elimination leads to a ketoalkoxide-bismuth complex (and hence to the initial product, 2-hydroxyacetophenone). Further oxidation to tlie ketoaldehyde and acid requires molecular oxygen, but is also found to be catalysed by bismuth. 

The mass spectra of the ethyl esters are dominated by the elimination of ethylene from the molecular ion, and the subsequent fragmentation paths are similar to that of the corresponding carboxylic acid. Only the ethyl esters of /3-ferrocenylpropionate and y-ferrocenylbutyric acid (n = 2, 3) show loss of C5H5 followed by loss of acetaldehyde, and numerous ions in the spectra seem to contain the C6H6 and C7H7 ligands. 

The polymerisation of a-aminoacid A-carboxyanhydride, which is accompanied with the elimination of carbon dioxide, constitutes a convenient method for preparing high molecular weight polypeptide. This polymerisation, with the use of a-aminopropionic acid (alanine) A-carboxylic acid anhydride as a monomer, was also carried out in the presence of coordination catalysts such as group 2 and 3 metal alkyls [168-174] or their combinations with water, secondary amine or alcohol [168,173] and yielded polyalanine (Table 9.2). 

The heterobimetallic complexes [N(n-Bu)4] [Os(N)R2(/u.-0)2Cr02] catalyze the selective oxidation of alcohols with molecular oxygen. A mechanism in which alcohol coordinates to the osmium center and is oxidized by B-hydrogen elimination (see -Hydride Elimination) is consistent with the data. The hydroxide adduct of OSO4, [0s(0H)204], with ferric cyanide and other co-oxidants catalyzes the oxidative dehydrogenation of primary aromatic and aliphatic amines to nitriles, the oxidation of primary alcohols to carboxylic acids, and of secondary alcohols to ketones. Osmium derivatives such as OsCb catalyze the effective oxidation of saturated hydrocarbons in acetonitrile through a radical mechanism. ... 

SCHEME 12.1 Photochemical reactions of diazonaphtoquinone derivatives elimination of molecular nitrogen with formation of a carbene, followed by Wolff rearrangement to give a ketene that reacts with water traces to form a carboxylic acid. 

Superacid DF-SbFs induces protium-deuterium exchange in isobutane [54b]. Strong acids (BF3, BFj-HjO, HF-BFj, CF3SO3H)catalyze carbonylation of alkanes including methane by carbon monoxide [54c], whereas sulfuric acid can induce carbonylation of iso- and cycloalkanes [54e,d]. In both cases, carboxylic acids are obtained. The elimination of molecular hydrogen from alkyl can occur (see a recent theoretical study of the Hz elimination from CzHs [54f]). 

The molecule has undergone an elimination reaction to give a stable product. We have already seen that hexan-3-ol, which has a molecular ion at m/z 102, can lose water to give hexene, which has a molecular ion at m/z 84. Carboxylic acids often lose CO2 (mass 44 Daltons) to give an ion of even m/z ratio loss of HCl (masses 36 and 38 Daltons) and HBr (masses 80 and 82 Daltons) and loss of ethene (mass 28 Daltons) are also observed. Such peaks are often small. 

To that end they converted dichloroacetonitrile to 2-(dichloromethyl)-4-oxazo-line carboxylic acid methyl ester 355 in 88% yield. Treatment of 355 with one equivalent of sodium methoxide produced 356 via an internal transfer of oxidation state through a molecular framework. The synthesis was completed by acid-catalyzed elimination of methanol to afford 357 in 48% overall yield from dichloroacetonitrile. 

Some steroids, such as cholic acid, progesterone and testosterone were already mentioned in the chapters discussing aldehydes, ketones and carboxylic acids. The most common steroid in humans is cholesterol. Although the compound has been discovered in the eighteenth century its complete molecular structure was determined only in the middle of the last century. Cholesterol appears in most of tissues and it has a special role in the regulation of blood circulation. An imbalance of cholesterol in the organism can cause serious health problems similar to arthero-sclerosis. The cholesterol molecule, like other steroids, is formed by a particular biosynthetic pathway from the terpene precursors, squalene and lanosterol. Since cholesterol has 27 carbon atoms, 3 atoms less than the triterpene squalene (which has 30 C-atoms), 3 C-atoms are eliminated during the biosynthetic process. 

The benzyl ester of malolactone was used as the monomer instead of malolactonic acid to eliminate potential problems in the ionic polymerization reactions. The carboxylic acid group, if present, could react with the initiators or cause either chain transfer or termination reactions during the polymerization. The polyester of this pendant ester was readily converted to poly-3-malic acid by hydrogenolysis without change in its molecular weight, according to the following reaction ... 

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