Degradation dehydration reaction

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. 

Recently several pubhcations have examined replacing aqueous solvents with ionic liquids. Since simple and complex sugars are soluble in many imidazolium hahdes, water is not required as a co-solvent and degradation of HMF is minimal. Lansalot-Matras et al. reported on the dehydration of fmctose in imidazolium ionic liquids using acid catalyst (6). Moreau et al. reported that l-H-3-methylimidazolium chloride has sufficient acidity to operate without added acid (7). And we reported that a 0.5 wt% loading (6 mole% compared to substrate) of many metal halides in 1-ethyl-3-methylimidazohum chloride ([EMIM]C1) result in catalytically active materials particularly useful for dehydration reactions (8). 

Other degradation products of the cytosine moiety were isolated and characterized. These include 5-hydroxy-2 -deoxycytidine (5-OHdCyd) (22) and 5-hydroxy-2 -deoxyuridine (5-OHdUrd) (23) that are produced from dehydration reactions of 5,6-dihydroxy-5,6-dihydro-2 -deoxycytidine (20) and 5,6-dihydroxy-5,6-dihydro-2 -deoxyuridine (21), respectively. MQ-photosen-sitized oxidation of dCyd also results in the formation of six minor nucleoside photoproducts, which include the two trans diastereomers of AT-(2-de-oxy-/j-D-eryf/iro-pentofuranosyl)-l-carbamoyl-4 5-dihydroxy-imidazolidin-2-one, h/1-(2-deoxy-J8-D-crythro-pentofuranosyl)-N4-ureidocarboxylic acid and the a and [5 anomers of N-(2-deoxy-D-eryfhro-pentosyl)-biuret [32, 53]. In contrast, formation of the latter compounds predominates in OH radical-mediated oxidation of the pyrimidine ring of dCyd, which involves preferential addition of OH radicals at C-5 followed by intramolecular cyclization of 6-hydroperoxy-5-hydroxy-5,6-dihydro-2 -deoxycytidine and subsequent generation of the 4,6-endoperoxides [53]. 

Decene complexes with gold, 12 348 Deformation density, 27 29-33 Degradation reactions, heteronuclear gold cluster compounds, 39 336-337 Dehydration reactions, osmium(II), 37 351 Delocalization, see also Valence delocalization added electron, reduced dimer, 38 447, 449 optical centers, interaction with surroundings, 35 380 Density... 

When allowed to react in an almost anhydrous medium (the only water being that produced during the dehydration reaction), compound 51 was found to form maltol (52) and isomaltol (16) in proportions varying with the reagents.88 In aqueous acidic solution, these products and acetylformoin (53) would all be expected from 50 or 51, dependent on whether or not the ring opened and the manner in which the opening occurred. The presence of 49 accounts for compounds 51, 52, 53, and 16, that are frequently detected as products of the degradation of D-fructose, particularly when amines are present. 

Initially, ethylene was obtained by the dehydration reaction of ethanol. Nowadays, ethylene is obtained by steam cracking from naphtha as a basic chemical. Steam cracking degrades longer aliphatic chains and introduces the double bond. Steam cracking is done at temperatures up to 900°C and leaves a wide variety of products behind. Ethylene is recovered by distillation processes. 

The Reduction Reactions. The object of the next three reactions (steps 4 to 6 in fig. 18.12a) is to reduce the 3-carbonyl group to a methylene group. The carbonyl is first reduced to a hydroxyl by 3-ketoacyl-ACP reductase. Next, the hydroxyl is removed by a dehydration reaction catalyzed by 3-hydroxyacyl-ACP dehydrase with the formation of a trans double bond. This double bond is reduced by NADPH catalyzed by 2,3-trans-enoyl-ACP reductase. Chemically, these reactions are nearly the same as the reverse of three steps in the j6-oxidation pathway except that the hydroxyl group is in the D-configuration for fatty acid synthesis and in the L-configuration for /3 oxidation (compare figs. 18.4a and 18.12a). Also remember that different cofactors, enzymes and cellular compartments are used in the reactions of fatty acid biosynthesis and degradation. 

The addition of a Lewis acid, i.e., ZnC significantly decreases the production of tar and enhances the production of char due to the enhanced dehydration reactions. At higher temperatures the glycosyl units and the random condensation products are further degraded to a variety of volatile products, as shown in Table V (9). Comparison of this table with the high temperature pyrolysis products listed for cellulose in Table III shows that the products of both fractions are basically similar. The significant increase in the yields of 2-furaldehyde, water and char and decrease in the yield of tar by the addition of ZnCl verifies the enhanced dehydration and is similar to observed effects in cellulose pyrolysis. 

Quantitatively, the major path of degradation of the Amadori or Heyns Intermediate 1s a dehydration reaction which yields furfural and hydroxymethylfurfural. Of greater flavor significance are the minor pathways which can result in both aromatic products as well as reactive Intermediates. These Intermediates can undergo a retro-aldollzatlon reaction to produce alpha dicarbonyl compounds, such as pyruvaldehyde and diacetyl as well as reactive monocarbonyls, such as glycolaldehyde and glyceraldehyde. 

With acid degradation, the first step appears to involve the formation of 1,2-enols from the aldose or ketose (7), followed by a series of dehydration reactions resulting in the formation of 5-hydroxymethyl-2-furfuraldehyde. If the initial sugar is a pentose, the final product is 2-furfuraldehyde. 

Fire retardancy of wood involves a complex series of simultaneous chemical reactions, the products of which take part in subsequent reactions. Most FRs used for wood increase the dehydration reactions that occur during thermal degradation so that more char and fewer combustible volatiles are produced. The mechanism by which this happens depends on the particular FR and the thermal-physical environment. The effectiveness of a FR treatment depends upon the performance rating of the treated material when tested in accordance with ASTM E84 (no greater flame spread than 25). 

Aldehydes result from the decomposition of certain ozonides. The technique is similar to that used for the preparation of ketones (method 182). High yields are obtained by catalytic hydrogenation of the ozonides. This step coupled with Grignard and dehydration reactions has been used as a procedure for the degradation of an aldehyde to its next lower homolog, viz.,... 

In the presence of acid additives thermal degradation of cellulose is intensified at lower temperatures, due to the occunence of the dehydration reactions [3], Condensation reactions result in the decrease of volatile products at 450"C combined... 

Chemical Stability Chemical degradation of the drug includes reactions such as hydrolysis, dehydration, oxidation, photochemical degradation, or reaction with excipients. The constant presence of water and oxygen in our environment means that exposure to moisture or oxygen can affect the chemical stability of a compound. Chemical stability is very important, not only because a sufficient amount of the dmg is needed at the time of administration for therapeutic purposes, but also because chemical degradation products may adversely affect the properties of the formulated product and may even be toxic. 

Dehydration reactions are another common degradation pathway. Ring closures are a fairly common type of dehydration, as is seen for both lactose18,19 and glucose.20 22 Both of these compounds dehydrate to form 5-(hydroxymethyl)-2-fur-fural. Batanopride is another example of a compound which can undergo a dehydration reaction.23... 

Isoleucine and valine. The first four reactions in the degradation of isoleucine and valine are identical. Initially, both amino acids undergo transamination reactions to form a-keto-/T methyl valerate and a-ketoiso valerate, respectively. This is followed by the formation of CoA derivatives, and oxidative decarboxylation, oxidation, and dehydration reactions. The product of the isoleucine pathway is then hydrated, dehydrogenated, and cleaved to form acetyl-CoA and propionyl-CoA. In the valine degradative pathway the a-keto acid intermediate is converted into propionyl-CoA after a double bond is hydrated and CoA is removed by hydrolysis. After the formation of an aldehyde by the oxidation of the hydroxyl group, propionyl-CoA is produced as a new thioester is formed during an oxidative decarboxylation. 

The fourteen alkaloids discussed in this section constitute a remarkable series of structurally and stereochemically interrelated substances. Superficially, all the alkaloids contain the same basic ring system, 5,10b-ethanophenanthridine (145), but alkaloids are elaborated from both enantiomorphs of this basic nucleus. Further variations are produced by differences in aromatic substitution and the functional groups attached to rings C.and D. It has been possible to interrelate all the alkaloids of this section through a combination of simple oxidation, reduction, and dehydration reactions coupled with four rather specific degradative techniques. These reactions are (1) aromatic demethoxylation by sodium and amyl alcohol (82), (2) replacement of OH by H via the action of lithium aluminum hydride on an intermediate chloro compound (146), (3) acid hydrolysis of ally lie methyl ethers to alcohols (147, 148), and (4) 0-methylation of hydroxylic alkaloids with... 

Aromatization of ring C is actually a chemical instability occurring as a dehydration reaction under acidic conditions and, of course, accelerated by elevated temperatures (Fig. 6-20). The elements of H20 derive from the 6-OH and 5a-H atom affording a 5a-6 DB. The 1 la-12 DB spontaneously isomerizes to the 11-1 la position yielding anhy-drotetracycline (ATC). This inactive degradation product is therefore formed in aging TC-containing products, and its rate of formation is increased if improperly stored (e.g.,... 

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