Substitution reactions hydrolysis

Primary carbocations are so high m energy that their intermediacy m nucleophilic substitution reactions is unlikely When ethyl bromide undergoes hydrolysis m aqueous formic acid substitution probably takes place by an 8 2 like process m which water is the nucleophile... 

Amides are the least reactive caiboxyhc acid deiivative and the only nucleophilic acyl substitution reaction they undeigo is hydrolysis Amides are fanly stable m water but the amide bond is cleaved on heating m the presence of strong acids 01 bases Nomi nally this cleavage produces an amine and a caiboxyhc acid... 

While it may be convenient to use optically active reactants to probe the stereochemistry of substitution reactions, it should be emphasized that the stereochemistry of a reaction is a feature of the mechanism, not the means of determining it. Thus, it is proper to speak of a substitution process such as the hydrolysis of methyl iodide as proceeding... 

If (A i[X ]/A 2[Y ]) is not much smaller than unity, then as the substitution reaction proceeds, the increase in [X ] will increase the denominator of Eq. (8-65), slowing the reaction and causing deviation from simple first-order kinetics. This mass-law or common-ion effect is characteristic of an S l process, although, as already seen, it is not a necessary condition. The common-ion effect (also called external return) occurs only with the common ion and must be distinguished from a general kinetic salt effect, which will operate with any ion. An example is provided by the hydrolysis of triphenylmethyl chloride (trityl chloride) the addition of 0.01 M NaCl decreased the rate by fourfold. The solvolysis rate of diphenylmethyl chloride in 80% aqueous acetone was decreased by LiCl but increased by LiBr. ° The 5 2 mechanism will also yield first-order kinetics in a solvolysis reaction, but it should not be susceptible to a common-ion rate inhibition. 

Chiral oxazolines developed by Albert I. Meyers and coworkers have been employed as activating groups and/or chiral auxiliaries in nucleophilic addition and substitution reactions that lead to the asymmetric construction of carbon-carbon bonds. For example, metalation of chiral oxazoline 1 followed by alkylation and hydrolysis affords enantioenriched carboxylic acid 2. Enantioenriched dihydronaphthalenes are produced via addition of alkyllithium reagents to 1-naphthyloxazoline 3 followed by alkylation of the resulting anion with an alkyl halide to give 4, which is subjected to reductive cleavage of the oxazoline moiety to yield aldehyde 5. Chiral oxazolines have also found numerous applications as ligands in asymmetric catalysis these applications have been recently reviewed, and are not discussed in this chapter. ... 

The reaction of wasabi phytoalexin (109) with excess 15% aqueous NaSMe gives methyl 2-methylthioindole-3-carboxylate (184,70%) and 140 (20%). In this reaction, formation of 2-methylthioindole-3-carboxylic acid (185) is not observed under various reaction conditions. The fact indicates that once 140 is formed, it does not undergo nucleophilic substitution reaction. In addition, hydrolysis of the... 

Hydrolysis of tlie ctioI etliers obtained from tlie substitution reaction witli tlie organocopper reagent yielded diiral -substituted aldehydes witli ees of 62 and 7396 for tlie Su2" and S 2 products, respectively. 

Ester hydrolysis is common in biological chemistry, particularly in the digestion of dietary fats and oils. We ll save a complete discussion of the mechanistic details of fat hydrolysis until Section 29.2 but will note for now that the reaction is catalyzed by various lipase enzymes and involves two sequential nucleophilic acyl substitution reactions. The first is a trcinsesterificatiori reaction in which an alcohol gioup on the lipase adds to an ester linkage in the tat molecule to give a tetrahedral intermediate that expels alcohol and forms an acyl... 

The following reaction involves a hydrolysis followed by an intramolecular nucleophilic acyl substitution reaction. Write both steps, and show their mechanisms. 

The metabolic breakdown of triacylglycerols begins with their hydrolysis to yield glycerol plus fatty acids. The reaction is catalyzed by a lipase, whose mechanism of action is shown in Figure 29.2. The active site of the enzyme contains a catalytic triad of aspartic acid, histidine, and serine residues, which act cooperatively to provide the necessary acid and base catalysis for the individual steps. Hydrolysis is accomplished by two sequential nucleophilic acyl substitution reactions, one that covalently binds an acyl group to the side chain -OH of a serine residue on the enzyme and a second that frees the fatty acid from the enzyme. 

Michael reaction, 894-895 mutarotation. 986 nitrile hydrolysis, 768-769 nucleophilic acyl substitution reaction. 790... 

No electrophilic aromatic substitution reactions of toluene, ethylbenzene, and cumene occur with BBrj in the dark the electrophile is too weak for these reactions. The photochemical reactions followed by hydrolysis give the p-isomers of the corresponding boronic acids as the major products (delocalization band in Scheme 9) [44]. 

When 35 was heated in acetic acid containing hydrogen bromide, the tribromide 46 was obtained as a single product in 74% yield. Debromina-tion of 46 with zinc dust in acetic acid furnished the cyclohexene derivative 47, which was converted into compound 48 by osmium tetraoxide hydroxyl-ation and acetylation. The substitution reaction of 48 with acetate ions provided carba-a-DL-glucopyranose pentaacetate (49), which gave the carba-sugar 50 on hydrolysis. ... 

The water-soluble calix[n]arenes 6.3 (n = 4, 6 and 8) containing trimethylammonium groups act as efficient inverse phase-transfer catalysts in the nucleophilic substitution reaction of alkyl and arylalkyl halides with nucleophiles in water (Eq. 6.19).40 In the presence of various surfactants (cationic, zwitterionic and anionic), the reactions of different halides and ketones show that the amount of ketone alkylation is much higher and that the reactions are faster in the presence than in the absence of surfactant aggregates.41 The hydrolysis of the halide is minimized in the presence of cationic or zwitterionic surfactants. 

Hydrolysis of diphenyl phosphorochloridate (DPPC) in 2.0 M aqueous sodium carbonate is also believed to be a two-phase process. DPPC is quite insoluble in water and forms an insoluble second phase at the concentration employed (i.e. 0.10 M). It seems highly significant that the hydrophobic silicon-substituted pyridine 1-oxides (4,6,7) are much more effective catalysts than hydrophilic 8 and 9. In fact, 4 is clearly the most effective catalyst we have examined for this reaction (ti/2 < 10 min). Since derivatives of phosphoric acids are known to undergo substitution reactions via nucleophilic addition-elimination sequences 1201 (Equation 5), we believe that the initial step in hydrolysis of DPPC occurs in the organic phase. Moreover, the... 

Summary Several lithium l,3-diphospha-2-sila-allyl complexes 3a-f and the diphosphino-dichlorosilane 2 have been prepared and characterized. The hydrolysis and substitution reactions of these compounds are described yielding a number of phosphino- and diphosphino-silaphosphenes 5a-d, 4a,b and 6. The compounds have been characterized by NMR and by X-ray analyses in the cases of 2, 3a-c and 4a. 

The reaction of cyclohexaamylose with a series of p-carboxyphenyl esters is an example of a decelerating effect which may be clearly attributed to nonproductive binding. Rate effects imposed by cyclohexaamylose on the hydrolyses of three such esters are summarized in Table IX. As the hydrophobicity of the ester function is increased by alkyl substitution, the hydrolysis is inhibited the stability of the inclusion complex, on the other... 

Other electrophilic substitution reactions on aromatic and heteroaromatic systems are summarized in Scheme 6.143. Friedel-Crafts alkylation of N,N-dimethyl-aniline with squaric acid dichloride was accomplished by heating the two components in dichloromethane at 120 °C in the absence of a Lewis acid catalyst to provide a 23% yield of the 2-aryl-l-chlorocydobut-l-ene-3,4-dione product (Scheme 6.143 a) [281]. Hydrolysis of the monochloride provided a 2-aryl-l-hydroxycyclobut-l-ene-3,4-dione, an inhibitor of protein tyrosine phosphatases [281], Formylation of 4-chloro-3-nitrophenol with hexamethylenetetramine and trifluoroacetic acid (TFA) at 115 °C for 5 h furnished the corresponding benzaldehyde in 43% yield, which was further manipulated into a benzofuran derivative (Scheme 6.143b) [282]. 4-Chloro-5-bromo-pyrazolopyrimidine is an important intermediate in the synthesis of pyrazolopyrimi-dine derivatives showing activity against multiple kinase subfamilies (see also Scheme 6.20) and can be rapidly prepared from 4-chloropyrazolopyrimidine and N-bromosuccinimide (NBS) by microwave irradiation in acetonitrile (Scheme... 

In a faster, selective and cleaner applications of the microwave-accelerated reactions, Stone-Elander et al. have synthesized a variety of radiolabeled (with 3H, 11C, and 19F) organic compounds via the nucleophilic aromatic and aliphatic substitution reactions, esterifications, condensations, hydrolysis and complexation reactions using monomodal MW cavities on microscale [121]. A substantially reduced level of radioactive waste is generated in these procedures that are discussed, at length, in Chapt. 13 [122]. 

Bob s research interests and knowledge across chemistry were great. Throughout his career he retained an interest in biomimetic chemistry, specifically the study of metal ion-promoted reactions and reactions of molecules activated by metal ion coordination. His early interests in carbohydrate chemistry inspired him to study metal ion catalysis of both peptide formation and hydrolysis as well as studies in inorganic reaction mechanisms. He was particularly interested in the mechanisms of base-catalyzed hydrolysis within metal complexes and the development of the so-called dissociative conjugate-base (DCB) mechanism for base-catalyzed substitution reactions at inert d6 metal ions such as Co(III). 

Because the carbon-halogen bond is polar the OH attacks the S+ carbon atom and so the reaction is classified as a nucleophilic substitution. Reactions in which an -OH group replaces a halogen atom are also called hydrolysis reactions. 

Ring opening reactions are the main feature of a brief review (though with 69 references) of kinetics and mechanisms of hydrolysis and substitution reactions of platinum(II) complexes (219). 

Sequential hydrolysis, 10 536 Sequential modular approach, 20 730 Sequential polymerization, 24 704 Sequential proportioning, 26 249 Sequential substitution reactions, 16 361 Sequential synthesis film fabricatior, 17 447... 

Substituted thioindigoid dyes are usually obtained via the appropriate benzenethiol in a Heumann-type synthesis. The final cyclisation of the phenylthioglycolic acid derivative can often be achieved in concentrated sulphuric acid or by using chlorosulphonic acid. Several routes make use of the Herz reaction (Scheme 6.22), in which a substituted aniline is converted into the corresponding o-aminothiophenol by reaction with sulphur monochloride followed by hydrolysis of the intermediate dithiazolium salt [47]. After reaction between the thiol and chloroacetic acid, the amino group is converted into a nitrile group by a Sandmeyer reaction. Hydrolysis of the nitrile leads to the formation of the required thioindoxyl derivative. 

Ionisation of the hydroxy groups in cellulose is essential for the nucleophilic substitution reaction to take place. At neutral pH virtually no nucleophilic ionised groups are present and dye-fibre reaction does not occur. When satisfactory exhaustion of the reactive dye has taken place, alkali is added to raise the pH to 10-11, causing adequate ionisation of the cellulose hydroxy groups. The attacking nucleophile ( X ) can be either a cellulosate anion or a hydroxide ion (Scheme 7.8), the former resulting in fixation to the fibre and the latter in hydrolysis of the reactive dye. The fact that the cellulosic substrate competes effectively with water for the reactive dye can be attributed to three features of the reactive dye/ cellulosic fibre system ... 

Steric hindrance is well known to slow down the rates of ligand substitution reactions in square-planar metal complexes. An example for which steric hindrance controls the aquation rate is complex 9. The effect of 2-picoline on the rate of hydrolysis of CP trans to NH3 (cis to 2-picoline) is dramatic, being about 5 times as slow as the analogous CP ligand in the nonsterically hindered 3-picoline complex (Table I) (44). 

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