Hydrolysis reactivity order

The usual order found with halogenonitrobenzenes is F > Cl Br I, the order of Cl and Br being variable, just as in heteroaromatic reactivity. The position of fluorine is of interest the available data indicate that it is usually the same as for nitrobenzene derivatives. Thus, in acid hydrolysis the order F > Cl for 2-halogeno-quinolines can be deduced beyond doubt since the fluoro derivative appears to react in the non-protonated form and the chloro derivative to resist hydrolytic attack even in the protonated form under appropriate conditions (Section II,D, l,d). Furthermore, in the benzo-thiazole ring, fluorine is displaced by the CHgO reagent at a rate 10 times that for chlorine. ... 

The following reactivity order has been found for the basic hydrolysis of p-substituted methyl benzoates ... 

Acyl halides are so reactive that hydrolysis is easily carried out. ° In fact, most simple acyl halides must be stored under anhydrous conditions lest they react with water in the air. Consequently, water is usually a strong enough nucleophile for the reaction, though in difficult cases hydroxide ion may be required. The reaction is seldom synthetically useful, because acyl halides are normally prepared from acids. The reactivity order is F < Cl < Br < If a carboxylic acid is used as the nucleophile, an exchange may take place (see 16-79). The mechanism ° of hydrolysis can be either SnI or tetrahedral, the former occurring in highly polar solvents... 

In addition to Si NMR analysis, one can measure the alcohol of hydrolysis in order to probe the reactivity of the silane moiety. While one cannot determine extent of crosslinking by this method because it does not measure condensation, one should see a good correlation between rate of silane hydrolysis and shelf life of the formulation. 

Generally, the reaction rates of aryl halides follow the order iodides > bromides > chlorides > fluorides. This fact can be used for the selective substimtion in polyhalogenated systems. For instance, 2-bromo -chlorotoluene gives 76% of 5-chloro-2-methylphenol by treatment with sodium hydroxide at 200 °C. Nevertheless, polyhalogenated systems which contain fluorides have a variable behaviour depending on the reaction temperature. At lower temperatures preferential hydrolysis of the fluoride takes place and at >200 °C the usual reactivity order iodides > bromides > chlorides > fluorides is observed. For instance, l,2-dibromo-3,4,5,6-tetrafluorobenzene affords 2,3-dibromo-4,5,6-trifluorophenol in 87% yield by treatment with potassium hydroxide at 85 °C. Under the same conditions, 1,4-dibromo-2,3,5,6-tetrafluorobenzene produces a 78% yield of 2,5-dibromo-3,4,6-trifluorophenol. However, 4-fluorobromobenzene with NaOH at 200 °C gives 4-fluorophenol in 70-79% yield. ... 

Binuclear zinc complexes of pyrazolate-based chelate ligands (Fig. 61) exhibit differing bis(4-nitrophenyl) phosphate hydrolysis reactivity depending on the nature of the supporting chelate ligand.153 Plots of the pseudo first-order rate constant... 

The replacement of an a hydrogen of an alkyl halide by halogen decreases Sn2 reactivity. Chloroform, however, is about one thousandfold more reactive in basic hydrolysis than methylene chloride . Every bromine-containing halo-form studied (Table 7) is at least 600 times as reactive toward hydroxide ions in 66.7% aqueous dioxan as methylene bromide ". Toward weakly basic nucleophiles, such as thiophenoxide ion, the predicted reactivity order is obeyed haloforms have been found to be less reactive than the corresponding methylene halides . The reaction of haloforms with sodium thiophenoxide is strongly accelerated, however, by the presence of hydroxide ions - . These observations are quite unexplainable in terms of scheme (22). 

It is well known that minor substituent changes in P-lactam antibiotics can have a dramatic effect upon antibacterial activity and susceptibility to P-lactamase catalysed hydrolysis. In order to identify the binding energy effects between the P-lactam and enzymes, the effect of substituents on chemical reactivity must be known. 

Additions of acetals and orthoesters to enol ethers probably represent the most intensively studied class of Lewis acid promoted reactions in the chemistry of aliphatic compounds. Since usually catalytic amounts of BFg OEta have been employed, concentration control (rule A) should predominate. Unlike the solvolyses of alkyl halides, the acid catalyzed hydrolyses of acetals and orthoesters do not follow a rate equilibrium relationship so that the corresponding hydrolysis rates cannot be used for the analysis of electrophilic addition reactions. We have, therefore, carried out competition experiments to determine relative reactivities of acetals and orthoesters towards methyl vinyl ether in presence of catalytic amounts of BF3 0Et2 (Figure 11). As the reactivity order towards other ir nucleophiles can be expected to be similar, the krei values of Figure 11 can be used to rationalize or predict the results of acetal and orthoester additions 1 1 Adducts can only be generated selectively if the k ei values of the designed products are smaller than the k Qi values of the reactants. 

---