Ammonolysis mechanism

Lewis acid-base mechanism, 233, 234 Lewis acid catalysts, 13, 546 Lewis-acid-catalyzed ammonolysis, of nylon, 571 Lewis acids, 224 catalysis by, 68-69 Lewis bases, 338... 

The presence of alkoxide ion would enhance the rate of ammonolysis, and the formation of bis(amido) derivatives by an ortho-ester mechanism (see Section VI, p. 110) would be partially suppressed in the competitive set of reactions. Thus, ammonolysis of penta-O-benzoyl-D-glucose in the presence of 5 mmolar proportions of sodium meth-oxide showed a decrease of 11% in the yield of the bis(benzamido)-glucitol derivative as compared with the same reaction conducted without added methoxide ion.47... 

The Hines64 showed that, as acids, ethanol, isopropyl alcohol, and tert-butyl alcohol are weaker than water, whereas methanol is stronger. The influence of the solvent could thus be interpreted in terms of equation 1. In methanol, the equilibrium would be more displaced to the right, and the rate of simple ammonolysis and transesterification would be enhanced, with concomitant decrease in the yields of amido sugars. In water (for the ammonolysis of sugar acetates) and in alcohols other than methanol, the equilibrium would be displaced to the left and this would allow operation of the orthoester mechanism a better chance. The isolation, from the reaction in isopropyl alcohol, of mono-O-benzoylated bis(benzamido)alditols, could also be explained on this basis. 

Compound 5 (see p. 82) was allowed to react83 with ethanolic ammonia-15N in the presence of an excess of acetamide-14N, and compound 6 containing a percentage of 15N similar to that of the ammonia employed was obtained, showing that, actually, the reaction occurs by an intramolecular mechanism. Were the mechanism intermolecular, in accordance with Wohl s views, the percentage of 15N in 6 would have been lower. Likewise, ammonolysis of D-glucose pentabenzo-... 

DFT was employed to study the mechanism of ammonolysis of phenyl formate in the gas phase, and the effect of various solvents on the title reaction was assessed by the polarizable continuum model (PCM). The calculated results show that the neutral concerted pathway is the most favourable one in the gas phase and in solution.24 The structure and stability of putative zwitterionic complexes in the ammonolysis of phenyl acetate were examined using DFT and ab initio methods by applying the explicit, up to 7H20, and implicit PCM solvation models. The stability of the zwitterionic tetrahedral intermediate required an explicit solvation by at least five water molecules with stabilization energy of approximately 35 kcalmol-1 25... 

Since 1950, ammonolysis reactions of many dichlorosilanes have been studied. Usually cyclic trimers and tetramers were formed. But very little was known about the reaction mechanisms.14... 

Mechanism 21-7 Conversion of an Ester to an Amide (Ammonolysis of an Ester) 1003 21-6 Transesterification 1006... 

The mechanism of ammonolysis of phosphorus pentachloride is not completely understood. It has been shown (164) that it proceeds in two steps. Initially, the intermediate [C13PNPC13] + [PC16] is formed, probably via PC14NH2 and PC13NH (48, 380). In the second step, this intermediate reacts with NH4C1 to produce cationic phosphazene chains that undergo cyclization by the elimination of [PC14]+ (164, 256). 

Ammonolysis of alkyl acetoacetates with 15% aqueous ammonia at 25 °C initially led to the formation of alkyl /3-aminocrotonates 372a,b, which slowly converted into the iminodiazocine 53, as the main product. A plausible mechanism is depicted in Scheme 73. Once formed, the aminocrotonates underwent further ammonolysis to give /1-arni nocroton amide, which cyclodimerized to give the diazocinedione 373, which, in the presence of ammonia, finally underwent a transannular Michael addition to give 53 <2002T55>. 

The ammoniation of aflatoxin B i) was studied as a means of possible detoxification of contaminated foodstuffs. Aflatoxin Dj (22) arises through a mechanism whereby the coumarin lactone undergoes ammonolysis with ammonium hydroxide. The resulting ammonium salt is then postulated to decompose to the carboxylic acid, which decarboxylates by virtue of the 0-keto group at C-3, thereby giving the desired structure (22)89,90). 

The ammonolysis of aromatic halides follows a pattern similar to the esters. For example, substituted chloronitrobenzenes containing a la-bilized chlorine atom react in aqueous ammonia at a rate proportional to the concentration of both reactants—indicating that the mechanism is second order. ... 

The vapor-phase ammonolysis of alcohol is much more complicated, because of side reactions. Although much information is available concerning operating conditions, effect of flow rates, and the effects of catalysts, there is little to be found in the literature on actual mechanism. 

Mechanical a tation, which is usually dearable, is necessary when the reactants are immiscible. For example, in the ammonolysis of p-nitro-chlorobenzene u ng aqueous ammonia, the denser molten aromatic compound setti to the bottom if no agitation is provided. Agitation is frequently accomplished by means of high-speed propellers or vaned discs. Less intense a tation is provided by-gate, anchor, and paddle types of a tators. In laboratory shaker tubes, the agitation is accomplished by shaking the entire vessel. 

After ammonolysis, ammonia is evaporated and can be reused after liquefaction, while degradation products of polyurethane hard segments (e.g., amines and chain extenders) and urea are removed by extraction. The pure polyol is left in the reactor. It can be removed mechanically or by extraction with liquid ammonia in which it is soluble. The recovered amines can be converted to the corresponding isocyanates and can be reused, along with polyols, in the same applications as before. A flow scheme of the recycling process is shown in Figure 6.9. 

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