Acetals imidazoles

S—4 shows the pH-rate profile for deacylation. The bifunctional polymers give deddedly hi er (more than one himdied times) deacylation rates. In fact, the rates are greater dian that of acet imidazole (broken line in F 5—4). 

Histidine Acetate Imidazole Rutaceae (in part), Fabaceae (in part)... 

General base catalysis by formate, acetate, imidazole, phosphate, and methoxyamine is also observed in the hydrolysis of ethyl trifluorothiol-acetate the Bronsted exponent j8 is 0 33. In acetate buffers a careful kinetic study demonstrated inhibition by acetic acid. Therefore, the acetate reaction also involves a tetrahedral intermediate according to scheme C. No complex formation of the substrate with acetic acid, which could alternatively cause inhibition, could be found. Scheme C accounts for the acetate catalysis and inhibition by acetic acid. In scheme C, a general base mechanism is written, the same mechanism which unequivocally applies to the water reaction. 

From Hu et al. (2003a). Emulsion prepared with 5 wt% salmon oil, 0.2% protein, and 94.8% 5 mM acetate-imidazole buffer (pH 3.0). Sweet whey contained 12.1 wt% protein whey protein isolate contained 97.6 wt% protein consisting of 55-61% 8-lactoglobulin, 19-22% a-lactalbumin and 6-8% bovine serum albumin. 

From Hu et al. (2004). Emulsions contained 5 wt% algal oil rich in (0-3 PUFA, 95% acetate-imidazole buffer (5 mM each, pH 3) and 0. 2% whey protein isolate. 

From Richards et al. (2002). Emulsions contained 5% lipid, 1 % emulsifier (Brij 700 = polyoxyethylene fatty ether) and 10 mM acetate-imidazole buffer at pH 3.0. Partitioning by centrifugation was followed by analysing the continuous phase for emulsifier by density measurements and for antioxidants by total phenolic concentrations. Oxidations of emulsions were carried out at 32°C. 

The same is true for X=Br, OR, SR, or aryl (39). Recently, both van der Kerk et al. (39) and Ourselves (19S) found a procedure with which trialkyl hydrides can be prepared in situ (X=halogen). In the cases where X is an acetate, imidazole (39), OH (respectively OPbR3), and allyl (198), the equilibrium is shifted more to the side of R3FbH. 

The reaction rate increases with the strength of flie base formate < acetate < imidazol. 

Titrimetric analysis is a classical method for generating concentration-time data, especially in second-order reactions. We illustrate with data on the acetylation of isopropanol (reactant B) by acetic anhydride (reactant A), catalyzed by A-methyl-imidazole. The kinetics were followed by hydrolyzing 5.0-ml samples at known times and titrating with standard base. A blank is carried out with the reagents but no alcohol. The reaction is... 

Nucleophilic catalysis is catalysis by a general base (electron-pair donor) acting by donating its electron pair to an atom (usually carbon) other than hydrogen. Nucleophilic catalysis is exemplified by the imidazole-catalyzed hydrolysis of a phenyl acetate. (The tetrahedral intermediates are not shown.)... 

These Br nsted-type plots often seem to be scatter diagrams until the points are collated into groups related by specific structural features. Thus, p-nitrophenyl acetate gives four separate, but parallel, lines for reactions with pyridines, anilines, imidazoles, and oxygen nucleophiles.Figure 7-4 shows such a plot for the reaction of trans-cmmm c anhydride with primary and secondary aliphatic amines to give substituted cinnamamides.All of the primary amines without substituents on the a carbon (R-CHi-NHi) fall on a line of slope 0.62 cyclopentylamine also lies on this line. If this line is characteristic of normal behavior, most of the deviations become qualitatively explicable. The line drawn through the secondary amines (slope 1.98) connects amines with the structure R-CHi-NH-CHi-R. The different steric requirements in the acylation reaction and in the model process... 

Figure 7-5. Bry4nsted-type plot for nucleophilic reactions of p-nitrophenyl acetate. Key , simple imidazoles in 28.5 ethanol at JO°C. p = 0.80 (data from Ref. 197] O, oxygen anions, in water at 25°, P = 0.95 for linear portion [data from Ref. 119, 198] O, a effect nucleophiles. Several of the nucleophiles are identified.

These data are for the nucleophilic catalysis of the hydrolysis of p-nitrophenyl acetate by imidazoles and benzimidazoles at pH 8.0. Tbe apparent second-order catalytic rate constants are defined by... 

The shapes of the titration curves of weak electrolytes are identical, as Figure 2.13 reveals. Note, however, that the midpoints of the different curves vary in a way that characterizes the particular electrolytes. The pV, for acetic acid is 4.76, the pV, for imidazole is 6.99, and that for ammonium is 9.25. These pV, values are directly related to the dissociation constants of these substances, or, viewed the other way, to the relative affinities of the conjugate bases for protons. NH3 has a high affinity for protons compared to Ac NH4 is a poor acid compared to HAc. 

FIGURE 2.13 The titration curves of several weak electrolytes acetic acid, Imidazole, and ammonlnm. Note that the shape of these different curves Is Identical. Only their position along the pH scale Is displaced. In accordance with their respective affinities for ions, as reflected In their differing values. 

In 1972, van Leusen, Hoogenboom and Siderius introduced the utility of TosMIC for the synthesis of azoles (pyrroles, oxazoles, imidazoles, thiazoles, etc.) by delivering a C-N-C fragment to polarized double bonds. In addition to the synthesis of 5-phenyloxazole, they also described reaction of TosMIC with /7-nitro- and /7-chloro-benzaldehyde (3) to provide analogous oxazoles 4 in 91% and 57% yield, respectively. Reaction of TosMIC with acid chlorides, anhydrides, or esters leads to oxazoles in which the tosyl group is retained. For example, reaction of acetic anhydride and TosMIC furnish oxazole 5 in 73% yield. ... 

Optically active imidazol-4-one-5-acetic acid has been prepared by Kny and Witkop, and therefore it must exist as 108 or 109 rather than as 110. Similarly, Grob and Ankli -- have presented ultraviolet and infrared spectral evidence for compounds of type 111 existing in the 0X0 form. These same investigators considered structure 112 rather than 113 to represent the predominant tautomeric form of the O-methyl derivatives how ever, it would be most surprising if this conclusion were correct. 

Acylation of the common starting 3,4-diaminonitrobenzene with furoyl chloride proceeds on the more basic amino group meta to the nitro group to give 140. This is then cyclized to imidazole 141 by means of acetic anhydride. Reduction of the nitro group (142), followed by condensation with ethyl acetoacetate affords furodazole (143) [26]. 

Trityl Chloride Imidazole Thiophosgene Hydrogen Sulfide Acetic Acid... 

N,N -dimethyloxaldiamide is reacted with PCI5 to give 4-chloro-1-methyl imidazole. This is nitrated with HNO3 to give 5-nitro-1-methyl-4-chloroimidazole. Then, a mixture of 4.6 grams of anhydrous 6-mercaptopurine, 5 grams of 1-methyl-4-chloro-5-nitroimidazole and 2.5 grams of anhydrous sodium acetate in 100 ml of dry dimethyl sulfoxide was heated at 100°C for 7 hours. 

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