Alcoholysis mechanism

In addition, REX processing was used to chemically modify PLA via an alcoholysis mechanism for blown film applications. In this case, intensive alcoholysis reactions from a diol solution or from functionalized alcohol promoted by titanium tetrapropoxide were carried out to tune the PLA chain length and rheology. It was found that under certain alcoholysis conditions, the resulting PLA blends were suitable for melt-blown non-woven processing. 

Fatty Acid Process. When free fatty acids are used instead of oil as the starting component, the alcoholysis step is avoided. AH of the ingredients can therefore be charged into the reactor to start a batch. The reactants are heated together, under agitation and an inert gas blanket, until the desired endpoint is reached. Alkyds prepared by the fatty acid process have narrower molecular weight distribution and give films with better dynamic mechanical properties (34). 

Aromatic ethers and furans undergo alkoxylation by addition upon electrolysis in an alcohol containing a suitable electrolyte.Other compounds such as aromatic hydrocarbons, alkenes, A -alkyl amides, and ethers lead to alkoxylated products by substitution. Two mechanisms for these electrochemical alkoxylations are currently discussed. The first one consists of direct oxidation of the substrate to give the radical cation which reacts with the alcohol, followed by reoxidation of the intermediate radical and either alcoholysis or elimination of a proton to the final product. In the second mechanism the primary step is the oxidation of the alcoholate to give an alkoxyl radical which then reacts with the substrate, the consequent steps then being the same as above. The formation of quinone acetals in particular seems to proceed via the second mechanism. ... 

The mechanism of hydrolysis and alcoholysis has been described, and the greater reactivity of the 4-position over the 2-position is attributed to the greater stability of the transition complex (20) with respect to (21), hence its greater ease of formation. The hydrolysis... 

B. Studies of Equilibria and Reactions.—N.m.r. spectroscopy is being increasingly employed to study the mode and course of reactions. Thus n.m.r. has been used to unravel the mechanism of the reaction of phosphorus trichloride and ammonium chloride to give phosphazenes, and to follow the kinetics of alcoholysis of phosphoramidites. Its use in the study of the interaction of nucleotides and enzymes has obtained valuable information on binding sites and conformations and work on the line-widths of the P resonance has enabled the calculation of dissociation rate-constants and activation energies to be performed. 

Mechanistic Studies.- The kinetics and mechanism of alcoholysis of some cyclic phosphoramidites (126)-(129) has been studied in... 

Although hydrolysis as well as other nucleophilic reactions of A-acylazoles (alcoholysis, aminolysis etc.) most likely follow the addition-elimination (AE) mechanism, there are indications that more complex mechanisms must be taken into account for hydrolysis under specific structural conditions. For example, for neutral hydrolysis of imidazolides with increasing steric shielding of the carbonyl group by one, two, and three... 

For the mechanism of azolide hydrolysis under specific conditions like, for example, in micelles,[24] in the presence of cycloamyloses,[25] or transition metals,[26] see the references noted and the literature cited therein. Thorough investigation of the hydrolysis of azolides is certainly important for studying the reactivity of those compounds in chemical and biochemical systems.[27] On the other hand, from the point of view of synthetic chemistry, interest is centred instead on die potential for chemical transformations e.g., alcoholysis to esters, aminolysis to amides or peptides, acylation of carboxylic acids to anhydrides and of peroxides to peroxycarboxylic acids, as well as certain C-acylations and a variety of other preparative applications. 

Imidazolides of aromatic sulfonic acids react much more slowly in alcoholysis reactions than the carboxylic acid imidazolides. Although the reaction with phenols is quantitative when a melt is heated to 100 °C for several hours, with alcohols under these conditions only very slight alcoholysis is observed. In the presence of 0.05 equivalents (catalytic amount) of sodium ethoxide, imidazole sodium, of NaNH2, however, imidazolides of sulfonic acids react with alcohols almost quantitatively and exothermically at room temperature in a very short time to form sulfonic acid esters (sulfonates). (If the ratio of sulfonic acid imidazolide to alcoholate is 1 2, ethers are formed see Chapter 17). The mechanism of catalysis by base corresponds to that operative in the synthesis of carboxylic esters by the imidazolide method. Because of the more pronounced nucleophilic character of alkoxide ions, sulfonates can also be prepared in good yield by alcoholysis of their imidazolides in the presence of hydroxide ions i.e., with alcoholic sodium hydroxide. 45 Examples of syntheses of sulfonates are presented below. 

Induction of elimination by nucleophilic attack of a solvent molecule on phosphorus (SN2(P)) would represent a mechanistic alternative. However, since not only ethanol but also sterically demanding alcohols such as cyclohexanol and tert-butanol are phosphorylated on alcoholysis of 2-chlorodecyl-l-phosphonic acid, this mechanism appears unlikely. Neither alcohol is a suitable nucleophile. 

The mechanisms of the hydroxycarbonylation and methoxycarbonylation reactions are closely related and both mechanisms can be discussed in parallel (see Section 9.3.6).631 This last reaction has been extensively studied. Two possibilities have been proposed. The first starts the cycle with a hydrido-metal complex.670 In this cycle, an alkene inserts into a Pd—H bond, and then migratory insertion of CO into an alkyl-metal bond produces an acyl-metal complex. Alcoholysis of the acyl-metal species reproduces the palladium hydride and yields the ester. In the second mechanism the crucial intermediate is a carbalkoxymetal complex. Here, the insertion of the alkene into a Pd—C bond of the carbalkoxymetal species is followed by alcoholysis to produce the ester and the alkoxymetal complex. The insertion of CO into the alkoxymetal species reproduces the carbalkoxymetal complex.630 Both proposed cycles have been depicted in Scheme 11. 

The first mechanism was proposed by Baird et al. [189]. The carbocationic species is schematically shown in Scheme IX. The attack of monomer, well known on the carbocationic center of a metal-ion-activated olefin, proceeded in the normal manner for carbocationic polymerization. This mechanism is based on the following two evidences. Alcoholysis of the polymerization system, TiMe3Cp /B(C6F5)3, resulted in the presence of an alkoxy group at an end group, and vinyl ethers and iV-vinylcarbazole were polymerized by using the same system. 

Fahey (16) suggests that intermediate 3 dissociates formaldehyde he finds supportive evidence in the rhodium-based system by observation of minor yields of 1,3-dioxolane, the ethylene glycol trapped acetal of formaldehyde. For reasons to be discussed later, we believe the formation of free formaldehyde is not on the principal reaction pathway. (c) We have also rejected two aspects of the reaction mechanism proposed by Keim, Berger, and Schlupp (15a) (i) the production of formates via alcoholysis of a formyl-cobalt bond, and (ii) the production of ethylene glycol via the cooperation of two cobalt centers. Neither of these proposals accords with the observed kinetic orders and the time invariant ratios of primary products. 

Mechanism of alcoholysis of carboxylate esters 288 Mechanism of alcoholysis of neutral phosphate esters 294... 

While the above indicates that Ln3 + and transition metal ions in the presence of at least 1 equi. of OR promote the alcoholysis of carboxylate and phosphate esters, sometimes by spectacular amounts, we have not presented evidence about the mechanism for the catalytic reactions. So far, the underlying theme is that the most active forms of the lanthanide ions are the Ln3 + ( OR) forms, either as a monomer (as in the case of Eu3 + ( OCH3)) or as a dimer (as in the case of La2+( OCH3)2). For the transition metal ions the most active forms are those where one face of the... 

C. K. Ingold and E. D. Hughes, "Dynamics and Mechanism of Aliphatic Substitutions," Nature 132 (1933) 933934 C. K. Ingold, E. D. Hughes, and S. Masterman, "Reaction Kinetics and the Walden Inversion. Pt. I. Homogeneous Hydrolysis and Alcoholysis of beta-n-Octyl Halides," JCS 140 (1937) 11961201 and subsequent articles. 

Toniolo reported the carbonylation of aromatic aldehydes containing electron-donating substituents with a Pd/PPh3 catalyst system in the presence of HC1 to give phenylacetic acid derivatives [64]. No activity was observed in the absence of PPI13 or HC1, and high yields could be achieved with alkanols as solvent (e.g., EtOH). It is believed that the mechanism involves HC1 addition to the aldehyde, with the resultant chlorohydrin being subject to oxidative addition to Pd, CO insertion, and alcoholysis. Upon Cl -o- OR substitution with the formed mandelic acid derivative, a second carbonylation takes place,... 

Otton, J., Ratton, S., Vasnev, V. A., Markova, G. D., Nametov, K. M., Bakhmutov, V. I., Komarova, L. I. Vinogradova, S. V. and Korshak, V. V., Investigation of the formation of poly(ethylene terephthalate) with model molecules Kinetics and mechanisms of the catalytic esterification and alcoholysis reactions II. Catalysis by metallic derivatives (monofunctional reactants), J. Polym. Sci., Polym. Chem. Ed., 26, 2199-2224 (1988). 

The influence of temperature on the ortho effect has been evaluated in the alkaline hydrolysis in aqueous DMSO solutions of ortho-, meta- and para-substituted phenyl benzoates (26). The alcoholysis of phthalic anhydride (27) to monoalkyl phthalates (28) occurs through an A-2 mechanism via rate-determining attack of the alcohol on a carbonyl carbon of the anhydride (Scheme 4). Evidence adduced for this proposal included highly negative A 5 values and a p value of 4-2.1. In the same study, titanium tetra-n-butoxide and tri-n-butyltin ethanoxide were shown to act as effective catalysts of the half-ester formation from (27), the mechanism involving alkoxy ligand exchange at the metal as an initial step. ... 

The tetrazole-catalysed alcoholysis of simple dialkylphosphoramidates (267) in THE to yield trialkylphosphites (268) occurs via nucleophilic catalysis (Scheme 29). The proposed mechanism sees tetrazole acting first as an acid catalyst to give the protonated intermediate (269), which then reacts with tetrazolide anion to yield the tetrazolylphosphite (270) alcoholysis of the latter (270) then yields the final product, the trialkylphosphite (268). ... 

The syn addition of the adducts suggests a mechanism different from that observed in rhodium-catalyzed alcoholysis and aminolysis reactions. Mechanistic investigations from the Tautens laboratory have revealed that the most likely mechanism involves an enantioselective carbopalladation followed by a (3-alkoxide elimination to afford the ring-opened product." ... 

The percentage of diester, keto-ester and diketone end groups in the copolymers depends on the relative rates of alcoholysis and protonolysis. For example, when these two termination processes occur at a comparable rate, the diester, keto-ester and diketone end groups are in a 1 2 1 ratio, respectively [11], The use of oxidant co-reagents may increase the amount of ester end groups [lb], while the chain-transfer mechanism controls the nature of the termination metal product (Pd-OR, Pd-OH and Pd-H). 

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