Nucleophilic aliphatic kinetic studies

Kinetics of the transformations of the N-F class of fluorinating agents in water, acetonitrile, alcohols, and aqueous solutions of alkali metal hydroxides have been studied.159 Other kinetic studies include die reactions of triphenylphosphine with 3-methoxy- or 3-acctoxy-4,4,5,5-tetrasubstitutcd-1,2-dioxolanes,160 the reactions of 2-amino-5-chlorobenzophenone witii HC1 in MeOH-H20 (die aspect of nucleophilic aliphatic substitution lies in certain products arising from attack of AH2 on CH3OH there are six products in all, and rate constants are evaluated for die formation of each of them),161 and the hydrolysis of derivatives of diazidophenyhnethane.162... 

Kinetic studies of the nucleophilic reactions of azolides have demonstrated that the aminolyses and alcoholyses proceed via a bimolecular addition-elimination reaction mechanism, as does the neutral hydrolysis of azolides of aromatic carboxylic acids. Aliphatic carboxylic acid azolides which are subject to steric hindrance can be hydrolyzed in aqueous medium by an 5n1 process. There have been many studies of these reactions, and evidence supporting both 5n1 and 5n2 processes leaves the impression that there are features of individual olysis reactions which favour either an initial ionization or a bimolecular process involving a tetrahedral intermediate (80AHC(27)241, B-76MI40701). 

K. Okamoto, S. Fukui, I. Nitta, and H. Shingu, Bull. Chem. Soc. Jpn., 40, 2354 (1967). Kinetic Studies of Bimolecular Nucleophilic Substitution. VIll. The Effect of Hydroxylic Solvents on the Nucleophilicity of Aliphatic Amines in the Menschutkin Reaction. 

There are various reports in the literature concerning kinetic studies of the Upase-catalyzed hydrolysis or synthesis of esters in microemulsions [8,9,49,83,84]. A simple MichaeUs-Menten kinetic model was proposed for the hydrolysis of triglycerides [85,86], while the esterifications of aliphatic alcohols with fatty acids follow a ping-pong bi-bi mechanism [87]. According to this mechanism the lipase reacts with the fatty acid to form a noncovalent enzyme-fatty acid complex, which is then transformed to an acyl-enzyme intermediate, while water, the first product, is released this is followed by a nucleophile attack (by the alcoholic substrate) to form another binary complex that finally yields the ester and the free enzyme. The kinetic parameters and determined in these studies represent apparent... 

The following studies, some involving kinetics, are also of interest for nucleophilic aliphatic substitution. 

Most of the kinetic measures of solvent effects have been developed for the study of nucleophilic substitution (Sn) at saturated carbon, solvolytic reactions in particular. It may, therefore, be helpful to give a brief review of aliphatic nucleophilic substitution. Two mechanistic routes have been clearly identified. One of these is shown by... 

Because EHOMO is a measure of the ability of a compound to donate electrons (i.e., act as a nucleophilic species or undergo oxidation), the increase in kinetic rate leads to increasing destruction efficiency. In the case of activation energy, activation energy increases as EHOMO decreases therefore, EHOmo is 311 indicator of the ability of the aliphatic compound to donate electrons. Muller and Klein (1991) studied a set of 63 aliphatic compounds, and they stated that the reaction rate was significantly correlated with the Ehomo-... 

Competitive effects for the interactions of cisplatin with various active sites in the cellular environment are discussed in papers of Deubel.55,56 In the earlier paper, energetic and structural data of complexes with the different substituted ligands were explored. The more recent work deals with kinetic factors in the relation to the transition state (TS) for water replacement of the semihydrated cisplatin complex (cis-[Pt(NH3)2(H20)Cl]+ ) with either an N- or S-containing ligand (thiopheneimidazol, dimethyl sulphide, or methanethiolate which serve as amino acid models). Deubel concluded the kinetic preference of N-sites over S-nucleophiles where the important role is played by the electrostatic terms. In addition, the aliphatic/aromatic character of the substituent as well as the influence of different dielectric constants of the environment are very important. A more realistic model for the aqua-ligand replacement with adenine and guanine was studied in works of Chval et al.53,57 and Eriksson and coworkers.58 They performed independently the estimation of the thermodynamic and kinetic parameters of this process. 

From the results summarized in Table I, apparently the Brpnsted relationship will hold for all combinations of nucleophiles and electrophiles. Because, as pointed out previously, the Hammett equation is really a special case of the Brpnsted relationship, all the legion of nucleophile-electrophile, rate-equilibrium Hammett correlations that have been studied also fall under the scope of the Brpnsted relationship. For example, nucleophilicities of ArO , ArS , ArC(CN)2 , and the other families listed in footnote c of Table I have generally been correlated by the Hammett equation, where the acidities of benzoic acids in water are used as a model for substituent interactions with the reaction site (a), and the variable parameter p is used to define the sensitivity of the rate constants to these substituent effects. The Brpnsted equation (equation 3) offers a much more precise relationship of the same kind, because this equation does not depend on an arbitrary model and allows rate and equilibrium constants to be measured in the same solvent. Furthermore, the Brpnsted relationship is also applicable to families of aliphatic bases such as carboxylate ions (GCH2C02 ), alkoxide ions (GCH20 ), and amines (GCH2NH2). In addition, other correlations of a kinetic parameter (log fc, AGf, Ea, etc.) can be included with various thermodynamic parameters (pKfl, AG°, Eox, etc.) under the Brpnsted label. 

The first kinetic investigation of a nucleophilic substitution reaction was that of Werner et who studied the reaction of 11 with several primary aliphatic... 

In addition, the same group has studied the ability to use aliphatic alcohols as competent nucleophiles in the Pd-catalysed dynamic kinetic asymmetric transformation of Baylis Hillman adducts. The corresponding substituted pyran products were obtained in high yields and enantioselectivities, as shown in Scheme 2.55. The utility of this method was further demonstrated in the context of concise total syntheses of the gastrulation inhibitor, (-l-)-hippo-spongic acid A, and the antibiotics, furaquinocins A, B and E. 

This general scheme is valid for both aliphatic and aromatic polyimides. Since this is the route preferably used for aromatic, aliphatic and cycloaliphatic polyimides of technical importance, it has been the subject of numerous studies, and the main aspects of the meehanisms and kinetics are fairly well known [16]. It is a two-step reaction. In the first step the nucleophilic attack of the amine groups to the carbonyl groups of the dianhydride gives rise to the opening of the rings yielding an intermediate poly(amic acid) (Scheme 2). 

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