Phenyl acetates, reaction with imidazole

Bruice and Sturtevant, 1959. The EM s are complicated by a mechanism change for the substituted compounds (see footnote 6) and are based on the reaction of the phenyl acetate with imidazole... 

Structure-reactivity relationships in these reactions have been studied by several authors. Bruice and Schmir299 found that a series of substituted imidazoles react with / -nitrophenyl acetate at rates which depend on their basicity, and are correlated by the Bronsted equation with a/3-value of 0.8 although the simple relationship is complicated by the increasing importance of reaction with the anion of more acidic imidazoles. The reaction of imidazole itself with a series of substituted phenyl acetates is correlated by the Hammett equation withp = 1.90296. 

Fig. 11.6 (A) Spectroscopic detection of acetylimidazole in the imidazole-catalysed hydrolysis of 4-nitro-phenyl acetate at pH 5 (D) and at pH 6 (E) curves are calculated from data in reference [12] and the curve for the acetate ion product (C) is for pH 5. (B) Reaction of imidazole with 4-nitrophenyl acetate (k) and the hydrolysis of acetyl imidazole (k2) curves constructed from data in references [13] and [12].

It is a general rule that imidazoles and benzimidazoles are resistant to Friedel-Crafts reactions. This is not surprising since such basic compounds must be markedly deactivated in the presence of Lewis acids. Imidazolin-2-ones appear to be an exception and apparently possess sufficient activation to react. Reactions between imidazoles and Af-methylfor-manilide and phosphoryl chloride are also unproductive. With 4,5-diphenylimidazole, phenyl isocyanate at 80 °C gives products of both N- and C-substitution, but in boiling nitrobenzene only the latter (86) is formed. 2-Methyl-4-phenylimidazole gives (87) under the same conditions, and 1,3-diphenylimidazolium perchlorate is transformed by potassium t-butoxide into a ylide which reacts at C-2 with phenyl isothiocyanate. Sufficient activation is present in l-methyl-2-phenyl-4-phenylaminoimidazole for it to react by substitution at C-5 with acetic anhydride (71JOC3368). 

Reactions of amines with substituted phenyl acetates are subject to a change in pathway as a function of basicity of the leaving phenoxide group. In the ammonolysis, hydrazinolysis, and imidazole-catalyzed hydrolysis of substituted phenyl acetates, both first- and second-order terms in amine are observed (Bruice and Mayahi, 1960 Bruice and Benkovic, 1964). Out of five phenyl acetate derivatives (p-NOg, m-N02, p-H, p-Cl, and p-CHs) the general-base term kz is observed with only the least acidic leaving groups, that is p-CHs, p-H, and p-Cl in the case of ammonolysis and hydrazinolysis, and p-CHj in the case of the imidazole reaction. Uncatalyzed k terms are observed with all... 

The value of Peq for the reaction of substituted phenyl acetates with imidazole (Equation 10) was first measured from kinetic data. In this case the standard equilibrium is the dissociation of substituted phenols (Equation 11). 

Neuvonen H. Kinetics and mechanisms of reactions of pyridines and imidazole with phenyl acetates and trifluoroacetates in aqueous acetonitrile with low content of water nucleophilic and general base catalysis in ester hydrolysis. J Chem Soc Perkin Trans II 1987 266 159-67. 

This paper reports that we synthesized amino-6-CD to compare catalytic activity with 3-CD-histamine and it was clear that an imidazole group acted as an active site in the hydrolysis of p-nitro-phenyl acetate. And it also shows that in the hydrolytic reactions, 3-CD-histamine has a structural selectivity for substrates which are structurally different to each other. 

To prepare model compounds representing the polymers structures two model compounds were prepared by reacting imidazole-blocked phenyl isocyanate (T STC) with PMDA and BPDA (coded PMDA-M and BPDA-M, respectively) under the same conditions as polymerization reaction. However, from the same reaction with NTDA we could not obtain pure compound NTDA-M and the yield was low(27 %). Tlie product obtained always revealed some incomplete cyclization, and it needed be additionally cyclized by reflux in acetic anhydj ide for prolonged time. More conveniently and in higher yield, it could be prepared by direct condensation with aniline in cyclohexane/DMAc mixture at reflux temperature. 

Fox, J.P., Jencks, W.P. General acid and general base catalysis of the methoxyami-nolysis of 1-acetyl-l,2,4-triazole. J. Am. Chem. Soc. 1974, 96(5), 1436-1449. Bruice, T.C., Donzel, A., Huffman, R.W., Butler, A.R. Aminolysis of phenyl acetates in aqueous solutions. VII. Observations on the influence of salts, amine structure, and base strength. J. Am. Chem. Soc. 1967, 89(9), 2106-2121. Williams, A., Jencks, W.P. Acid and base catalysis of urea synthesis nonlinear Bronsted plots consistent with a diffusion-controlled proton-transfer mechanism and the reactions of imidazole and N-methylimidazole with cyanic acid. J. Chem. Soc. Perkin Trans. 2. 1974, 1760-1768. 

Data for the reactions of several cyclic tertiary amines with phenyl, 4-nitro-phenyl and 2,4-dinitrophenyl acetates, at 25°C and ionic strength 1.0, appear in Table 40, and as a Bronsted plot in Fig. 20. The usual irregularities of such plots for nucleophilic attack are evident. Linear relationships between log k and pKa are generally found for groups of compounds of closely similar structure, as for the substituted pyridines in Fig. 20. The data for the two tricyclic amines fall on separate curves, and the points for imidazole clearly fall on neither of the first two sets of lines. The separate lines for the reactions of particular classes of nucleophile are approximately parallel, as is usually found. 

A somewhat similar biomimetic acetyl transfer reaction has been reported. Thus reaction of mono-n-butyl thiolmalonate (4) with phenyl thiolacetate (5) in the presence of imidazole and magnesium acetate in THF at room temperature gives n -butyl acetothiolacetate (6) in 60% yield. 

Reactions and Properties of l,A-Diazepines. 2-Amino-5-phenyl-3//-l,4-benzodiazepines were converted into their 1-oxides, e.g. (Ill), by m-chloroper-oxybenzoic acid when these oxides reacted with phosgene in the presence of imidazoles they underwent an interesting rearrangement to give the 3-imidazolyl derivatives, e.g. (113), apparently via primary formation of the unstable compound (112). Treatment of (111) with acetic anhydride gave the 2-acetamido-3-oxo-derivative. ... 

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