Hydrolysis in acid

FIGURE 20 7 The mecha nism of amide hydrolysis in acid solution Steps 1 through 3 show the for mation of the tetrahedral intermediate Dissociation of the tetrahedral inter mediate is shown in steps 4 through 6... 

Ha.logena.tlon, 3-Chloroindole can be obtained by chlorination with either hypochlorite ion or with sulfuryl chloride. In the former case the reaction proceeds through a 1-chloroindole intermediate (13). 3-Chloroindole [16863-96-0] is quite unstable to acidic aqueous solution, in which it is hydroly2ed to oxindole. 3-Bromoindole [1484-27-1] has been obtained from indole using pytidinium tribromide as the source of electrophilic bromine. Indole reacts with iodine to give 3-iodoindole [26340-47-6]. Both the 3-bromo and 3-iodo compounds are susceptible to hydrolysis in acid but are relatively stable in base. 

The influence of boron-bonded ligands on the kinetics and mechanistic pathways of hydrolysis of amine boranes has been examined (37,38). The stoichiometry of trimetbyl amine azidoborane [61652-29-7] hydrolysis in acidic solution is given in equation 10. It is suggested that protonation occurs at the azide ligand enabling its departure as the relatively labile HN species. 

Mechanistically, amide hydrolysis is similar to the hydrolysis of other carboxylic acid derivatives. The mechanism of the hydrolysis in acid is presented in Figure 20.7. It proceeds in two stages a tetrahedral intermediate is formed in the first stage and dissociates in the second. 

On the basis of the general mechanism for amide hydrolysis in acidic solution shown in Figure 20.7, write an analogous sequence of steps for the... 

Subsequent steps of the process involve the decomposition of ammonium peroxometalates, (NH4)3Ta08 and (NH4)3Ta08, which takes place according to a hydrolytic mechanism. Belov et al. [512] presents the following interactions as occurring by different mechanisms in different media. Hydrolysis in acidic media at pH < 3 appears to occur with the separation of oxygen, as shown in Equation (152) ... 

As esters of sulfuric acid, the hydrophilic group of alcohol sulfates and alcohol ether sulfates is the sulfate ion, which is linked to the hydrophobic tail through a C-O-S bond. This bond gives the molecule a relative instability as this linkage is prone to hydrolysis in acidic media. This establishes a basic difference from other key anionic surfactants such as alkyl and alkylbenzene-sulfonates, which have a C-S bond, completely stable in all normal conditions of use. The chemical structure of these sulfate molecules partially limits their conditions of use and their application areas but nevertheless they are found undoubtedly in the widest range of application types among anionic surfactants. 

Alcohol and alcohol ether sulfates are commonly considered as extremely rapid in primary biodegradation. The ester linkage in the molecule of these substances, prone to chemical hydrolysis in acid media, was considered the main reason for the rapid degradation. The hydrolysis of linear primary alcohol sulfates by bacterial enzymes is very easy and has been demonstrated in vitro. Since the direct consequence of this hydrolysis is the loss of surfactant properties, the primary biodegradation, determined by the methylene blue active substance analysis (MBAS), appears to be very rapid. However, the biodegradation of alcohol sulfates cannot be explained by this theory alone as it was proven by Hammerton in 1955 that other alcohol sulfates were highly resistant [386,387]. 

There are many parallels between phosphates and sulfates of aliphatic alcohols. Both types of surfactants contain ester bonds undergoing hydrolysis in acid solutions. In that case the starting materials are received once more. By dry heating of the salts above a temperature of 140°C destruction will occur forming the corresponding alkenes and an inorganic acid salt. In the same way as sulfonic and sulfinic acids are formed by C-S bonds, C-P bonds lead to phosphonic and phosphinic acids. 

For amide hydrolysis in acid, proton transfer to give a cationic intermediate is easy, and breakdown to products is favored over reversion to starting material process b is hopelessly bad, but process b is better than a. 

Decomposition Pyrolysis occurs at 170°C after prolonged periods yielding CO, COz, benzophenone, and benzhydrol appreciable hydrolysis in acidic or basic solutions occurs yielding 3-quinuclidinol and benzilic acid BZ is oxidized by hypochlorite at a pH of 1-13. 

These coordinated heterocycles are not very sensitive towards atmospheric moisture. Upon hydrolysis in acidic medium diketonates, (e.g., acetylcyclo-... 

A series of publications appeared regarding the transformation of corynanthe-type alkaloids to yohimbane derivatives (285-287). The saponification of cory-nantheine (52) in methanol yielded a complex mixture of corynantheic acid (588), two C-16-epimer acetal acids (589), and demethoxycarbonylcory-nantheine (590). All four compounds upon hydrolysis in acid resulted in cory-... 

Protection of Alcohols. Trimethylsilyl ethers, readily prepared from alcohols by treatment with a variety of silylating agents have found considerable use for the protection of alcohols. They are thermally stable and reasonably stable to many organometallic reagents and they are easily cleaved by hydrolysis in acid or base or by treatment with fluoride ion. t, Butyl dimethylsilyl ethers have considerably greater hydrolytic stability and are easier to work with than trimethylsilyl ethers. They are prepared from alcohols by treatment with t. butyl dimethylsilyl chloride. 

First, acetamenaphthone (I) undergoes hydrolysis in acidic medium to yield the corresponding phenol and secondly, this phenol is oxidised quantitatively with ammonium ceric sulphate to give the resulting 1, 4-dione derivative (II). 

Polyacrylate and polyhydroxylate polymers with pendent aspirin moieties were recently prepared for aspirin delivery [454]. The homogeneous and heterogeneous hydrolysis in acidic and alkali media of poly(acetylsalicylyloxy ethyl... 

Acid-Catalyzed Hydrolysis. In acid-catalyzed ester hydrolysis the species that undergoes the rate-determining step is the protonated ester (Fig. 13.10). When the molecule is in this protonated form, the enhanced depletion of electrons near the central carbon promotes the approach of an electron-rich oxygen of a water molecule. Hence, the hydrolysis rate depends on the fraction of compound molecules that are protonated. This fraction, in turn, depends on how strong a base the ester function is. If we define an acidity constant (see Chapter 8) for the protonated species... 

The hydrolysis in acid or base of five-membered cyclic esters of phosphoric acid proceed some 10 times faster than their acyclic analogs or the six- and seven-membered cyclic phosphates 55 56. Unlike that of dimethyl phosphate, the hydrolysis of hydrogen ethylene phosphate is accompanied by rapid oxygen exchange into the unreacted substrate57, viz-... 

For the three reactions represented in Fig. 12 the maximum rate of hydrolysis in acid represents only a mpdest acceleration, compared with the rate in initially neutral solution. Bunton and Hadwick89,90 explained the maximum for methyl and phenyl trifluoroacetate in terms of negative salt effects on both acid-catalyzed and neutral reactions. Consistent with this interpretation, it was demonstrated directly that the rate of neutral hydrolysis is decreased by added salts. The effect of added salt should be to decrease the activity of water, and perhaps also to salt in the ester. 

Hydrolysis in acid of compounds assigned the a-cyanoazoacetophenone structures (681) affords arylglyoxal semicarbazones (682). These can be cyclized in hot sodium hydroxide to 5-aryl-l,2,4-triazin-3-ones (683) <02LA(325)129). 

A very different result has been reported by El-Awady and Hugus, who studied the hydrolysis in acidic and basic solutions by spectrophotometry and by pH-stat measurements, respectively. According to these authors, the spectral changes occurring during the acid hydrolysis ([H+] = 10-3-10-1 M) are best interpreted in terms of two consecutive first-order reactions (359). 

Sulfation is the generation of an oxygen sulfur(IV) bond, where the oxygen is attached to the carbon backbone, in the most controlled manner possible, using some form of sulfur dioxide moiety. When sulfating alcohols, the reaction is strongly exothermic, Examples of feedstocks for such a process include alkenes, alcohols, or phenols. Unlike the sulfonates, which exhibit excellent stability to hydrolysis, the alcohol sulfates are readily susceptible to hydrolysis in acidic media, The sulfation of fatty alcohols and fatty polyalkoxylates has produced a substantial body of commercial detergents and emulsifiers. 

The 1,4-benzodiazepinones, exemplified by diazepam (53), undergo hydrolysis in acid and base to yield the corresponding o-aminobenzophenones (54). However, unusual byproducts were observed when diazepam (53) or 2-((V-methyl)amino-5-chlorobenzophenone (54) was hydrolysed in aqueous methanolic hydrochloric acid, and now a mechanism involving a nitrene has been proposed to account for the... 

A more reactive equivalent for ketone synthesis is a nitrile 28. Addition of a Grignard reagent gives an intermediate 29, stable under the reaction conditions, rather like 21. Hydrolysis in acid solution releases the ketone 2. The exactly analogous reagent to DMF would be a tertiary amide... 

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