Degradation Dehydration

At the other end of the reaction, deviations from idealized rate laws are attributed to secondary reactions such as degradations of acids, alcohols, and amines through decarboxylation, dehydration, and deamination, respectively. The step-growth polymers which have been most widely studied are simple... 

Pyridazinecarboxamides are prepared from the corresponding esters or acid chlorides with ammonia or amines or by partial hydrolysis of cyanopyridazines. Pyridazinecarboxamides with a variety of substituents are easily dehydrated to nitriles with phosphorus oxychloride and are converted into the corresponding acids by acid or alkaline hydrolysis. They undergo Hofmann degradation to give the corresponding amines, while in the case of two ortho carboxamide groups pyrimidopyridazines are formed. 

The reactions of amides fall into hydrolysis, dehydration and degradation (to amines) acid hydrazides and acid azides undergo additional reactions. 

Pyrimidine-5-carboxamide, 4-amino-purine synthesis from, 5, 582 Pyrimidine-5-carboxamide, 4-amino- N- pheny synthesis, 3, 122 Pyrimidinecarboxamides Curtius degradation, 3, 82 dehydration, 3, 82 Hofmann degradation, 3, 82 hydrolysis, 3, 81 reactions, 3, 81 synthesis, 3, 127 Pyrimidinecarboxamides, thio-synthesis, 3, 128... 

Silica gel and aluminium oxide layers are highly active stationary phases with large surface areas which can, for example, — on heating — directly dehydrate, degrade and, in the presence of oxygen, oxidize substances in the layer This effect is brought about by acidic silanol groups [93] or is based on the adsorption forces (proton acceptor or donor effects, dipole interactions etc) The traces of iron in the adsorbent can also catalyze some reactions In the case of testosterone and other d -3-ketosteroids stable and quantifiable fluorescent products are formed on layers of basic aluminium oxide [176,195]... 

The next three steps—reduction of the /3-carbonyl group to form a /3-alcohol, followed by dehydration and reduction to saturate the chain (Figure 25.7) — look very similar to the fatty acid degradation pathway in reverse. However, there are two crucial differences between fatty acid biosynthesis and fatty acid oxidation (besides the fact that different enzymes are involved) First, the alcohol formed in the first step has the D configuration rather than the L form seen in catabolism, and, second, the reducing coenzyme is NADPH, although NAD and FAD are the oxidants in the catabolic pathway. 

In any form of analysis it is important to determine the integrity of the system and confirm that artefacts are not produced as a by-product of the analytical procedure. This is particularly important in enantiomeric analysis, where problems such as the degradation of lactone and furanon species in transfer lines has been reported (40). As chromatography unions, injectors, splitters, etc. become more stable and greater degrees of deactivation are possible, problems of this kind will hopefully be reduced. Some species, however, such as methyl butenol generated from natural emissions, still remain a problem, undergoing dehydration to yield isoprene on some GC columns. 

Conversion of the aldehyde into a nitrile is accomplished by treatment of an aldose with hydroxvlamine to give an oxime (Section 19.8), followed by dehydration of the oxJme with acetic anhydride. The Wohl degradation does not give particularly high yields of chain-shortened aldoses, but the reaction is general for all aldopentoses and aldohexoses. For example, D-galactose is converted by Wohl degradation into n-lyxose. 

Phenolic networks are well known for their excellent thermal and thermo-oxidative stabilities. The mechanisms for high-temperature phenolic degradation include dehydration, thermal crosslinking, and oxidation, which eventually lead to char. 

Aldoximes are prepared from aldehydes and hydroxylamine by condensation reaction, and the dehydration reaction of aldoxime is one of the most important methods of nitrile synthesis in organic chemistry." We speculated that it would become one of the most important examples in Green Chemistry if the dehydration reaction could be realized by an enzymatic method, and started studies on a new enzyme, aldoxime dehydratase, and its use in enzymatic nitrile synthesis. Furthermore, we clarified the relationship between aldoxime dehydratase and nitrile-degrading enzymes in the genome of the microorganisms and the physiological role of the enzyme. 

The dehydration reaction of aldoxime to form nitriles using the resting cells of Rhodococcus sp. YH3-3 was optimized. We found that the enzyme was induced by aldoxime and catalyzed the stoichiometric synthesis of nitriles from aldoximes at pH 7.0 and 30°C. Phenylacetonitrile once synthesized from phenylacetaldoxime was hydrolyzed to phenylacetic acid, since the strain has nitrile degradation enzymes such as nitrile hydratase and amidase. We have been successful in synthesizing phenylacetonitrile and other nitriles stoichiometrically by a selective inactivation of nitrile hydratase by heating the cells at 40°C for 1 h. Various nitriles were synthesized under optimized conditions from aldoximes in good yields. 

Hydrolysis to the diol followed by dehydration to the aldehyde and oxidation to the carboxylic acid is used by a propene-utilizing species of Nocardia (de Bont et al. 1982). Although an ethene-utilizing strain of Mycobacterium sp. strain E44 degrades ethane-l,2-diol by this route, the diol is not an intermediate in the metabolism of the epoxide (Wiegant and de Bont 1980). 

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