Hydrolysis-dehydration

In the reaction of ethylene with sulfuric acid, several side reactions can lead to yield losses. These involve oxidation, hydrolysis—dehydration, and polymerization, especially at sulfuric acid concentrations >98 wt % the sulfur thoxide can oxidize by cycHc addition processes (99). 

The steps involved in formation of the metal oxoalkoxide are hydrolysis, dehydration, and dealkoxylation ... 

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

Abstract Polyfunctionality of carbohydrates and their low solubility in conventional organic solvents make rather complex their conversion to higher value added chemicals. Therefore, innovative processes are now strongly needed in order to increase the selectivity of these reactions. Here, we report an overview of the different heterogeneously-catalyzed processes described in the literature. In particular, hydrolysis, dehydration, oxidation, esterification, and etherification of carbohydrates are presented. We shall discuss the main structural parameters that need to be controlled and that permit the conversion of carbohydrates to bioproducts with good selectivity. The conversion of monosaccharides and disaccharides over solid catalysts, as well as recent advances in the heterogeneously-catalyzed conversion of cellulose, will be presented. 

Here we report an overview of the different heterogeneously-catalyzed pathways designed for the selective conversion of carbohydrates. On the basis of these results, we shall try to determine the key parameters allowing a better control of the reaction selectivity. Water being commonly used as solvent in carbohydrate chemistry, we will also discuss the stability of solid catalysts in the aqueous phase. In this review, heterogeneously-catalyzed hydrolysis, dehydration, oxidation, esterification, and etherification of monosaccharides and polysaccharides are reported. 

Silica gel is produced by the hydrolysis, dehydration, and polymerization (gelation) of TEOS in solution according to the following reactions ... 

The polymer of methyl methacrylate (MMA) is known as Perspex. It is a clear transparent glasslike material with high hardness, resistance to fracture, and chemical stability. The conventional route, as shown by reaction 4.10, involves the reaction between acetone and hydrocyanic acid, followed by sequential hydrolysis, dehydration, and esterification. This process generates large quantities of solid wastes. An alternative route based on a homogeneous palladium catalyst has recently been developed by Shell. In this process a palladium complex catalyzes the reaction between propyne (methyl acetylene), methanol, and carbon monoxide. This is shown by reaction 4.11. The desired product is formed with a regioselectivity that could be as high as 99.95%. 

Surface Activation. Acid Activation. Acid treatment of cellulose and hemicelluloses generally leads to hydrolysis to monosaccharides, which can subsequently dehydrate and condense to form furan-type compounds such as furfural and its 5-hydroxymethyl adduct. Further reactions lead to polymeric materials of dark color as well as to monomers such as levulinic acid, formic acid, and angelica lactones. Various condensation and solvolysis reactions also accompany the acid treatment of lignin 123). The hydrolysis, dehydration, and condensation reactions have been used to explain formation of covalent bonds between surfaces (85), increase in water resistance (85, 124), and weakening of wood (75) in nonconventional plywood or particle board production. However, very little factual information is available on how far, in terms of the consecutive reactions mentioned, and in what direction, in terms of the parallel reactions mentioned, does the surface of lignocellulosic materials actually change... 

As expected, octasilacubane possesses high reactivity toward electrophiles. As shown in Scheme 3, mCPBA oxidation of silyl-substituted 1 resulted in a hi -yield formation of octasilsesquioxane (3) (Tg). Silsesquioxanes are well studied, but were previously only prepared by the hydrolysis-dehydration of halo- or alkoxysilanes. When the substituents are bulky, the reaction proceeds no further than the silanol stage, and silsesquioxanes are not obtained. For example, hydrolytic condensation of t-butyldimethylsilyltrichlorosilane gave only partly hydrolyzed silanols. Thus, 3 is the octasilsesquioxane with the bulkiest substituents, and the only silyl-substituted one ever reported. The structure was determined by X-ray ciystallography [7], and the bond lengths and angles are similar to those of known octasilsesquioxanes. 

Hydrolysis of monoorganotin compounds can give rise to a wider variety of hydroxides and oxides through a combination of hydrolysis, dehydration, and aggregation reactions,116 but less work has been done in this field. In moist air, ethyl-, butyl- and octyl-tin trichloride are hydrolysed as far as the hydrated hydroxide dichlorides, RSnCl2(OH)... 

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. 

In these reactions, hydrolysis of diphenyl and triaryl phosphites to monoaryl phosphites and phenol was coupled by dehydration between carboxylic acids and amines or alcohols to the corresponding amides and esters. Therefore, the reaction can be generalized as a hydrolysis-dehydration reaction (Scheme 2). The concept of the hydrolysis-dehydration reaction using phosphites has been drown to be applicable also to reactions with other phosphorus compounds such as phosphinites, phos-phonites and phosphorates s Aryl esters of these phosphorus compounds are effective as condensing agents in the production of carboxylic amides and esters (from carboxylic acids and amines or alcohols, respectively) whereas alkyl esters are ineffective (Eqs. (1-3)) ... 

In addition, we have applied successfully the concept of hydrolysis-dehydration reaction with phosphorus compounds to the reaction with sulfur compounds such as sulfites7- as shown below ... 

Recently, we have found other types of the hydrolysis-dehydration reactions between carboxylic acids and amines or alcohols promoted by triphenyl phosphite and alkyl halides (Eq. (6)) 8> and metal salts like LiCl (Eq. (7))9 ... 

Drug substances used as pharmaceuticals have diverse molecular structures and are, therefore, susceptible to many and variable degradation pathways. Possible degradation pathways include hydrolysis, dehydration, isomerization and racemization, elimination, oxidation, photodegradation, and complex interactions with excipients and other drugs. It would be very useful if we could predict the chemical instability of a drug based on its molecular structure. This would help both in the design of stability studies and, at the earliest... 

Dedsuksophon W, Faungnawakij K, Champreda V, Laosiripojana N (2011) Hydrolysis/ dehydration/aldol-condensation/hydrogenation of lignocellulosic biomass and biomass-derived carbohydrates in the presence of Pd/W03-Zr02 in a single reactor. Bioresour Technol 102 2040-2046... 

Soft-chemistry routes, which the French call chimie douce, are indeed desirable because they lead to novel prodncts, many of which are metastable and cannot otherwise be prepared. Soft-chemistry rentes essentially make nse of simple reactions such as intercalation, ion exchange, hydrolysis, dehydration and rednction that can be carried out at relatively low temperatures. The topochemical nature of certain... 

It is most useful as acid-catalyst reaction such as esterification/condensation/acetylation/polymerization/alkylation s/ hydrolysis/dehydration. As a hardening agent of furan resin which is applied in foundry Industry (Sand Casting)... 

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