Leaving group conjugate acids

Leaving group Relative rate leaving group conjugate acid... 

Starting material Leaving group Conjugate acid pICa... 

Carbonyl compound Leaving group Conjugate acid of the leaving group ... 

Apparent dehydration reactions, thus, appears to require certain well-defined conditions, namely conjugation of the OH group to make it a good leaving group, and acidity of the vicinal proton. Such conditions are seldom met simultaneously, offering a possible explanation for why the reaction occurs so rarely. 

Notice too that strongly basic leaving groups are absent from Table 8 8 In gen eral any species that has greater than about 2 for its conjugate acid cannot be a... 

R can be a variety of stmctures. Z is a leaving group and typically the conjugate base of a weak acid whose piC can range from 5 to 20 (86). The hydrogen peroxide is typically incorporated into the bath by a dding a soHd source of peroxide such as sodium percarbonate or the mono- or tetrahydrate of sodium perborate (86). 

The perhydrolysis reaction could theoretically continue to give four moles of peracid per mole of TAED but stops at this stoichiometry because of the substantial increase in the conjugate acid pify of the leaving group going from an amide (p-R = 17) to an amine (pif = 35) (94,95). Nonanoyloxybenzene sulfonate (NOBS) [101482-85-3] is used in detergent products in the United States and Japan. The NOBS perhydrolysis reaction is shown in equation 20 (96). 

The configuration at C-10 of 2 and the ratio of SN2 /SN2 depended on the leaving group (OR). There appears to be a correlation between the acidity of the conjugate acid of the leaving... 

The alkoxyl group OR is not a leaving group, so these compounds must be converted to the conjugate acids before they can be hydrolyzed. Although 100% sulfuric acid and other concentrated strong acids readily cleave simple ethers, the only acids used preparatively for this purpose are HBr and HI (10-71). However, acetals, ketals, and ortho esters are easily cleaved by dilute acids. These compounds are... 

Note that these mechanisms are the reverse of those involved in the acid-catalyzed hydration of double bonds (15-3), in accord with the principle of microscopic reversibility. With anhydrides (e.g., P2O5, phthalic anhydride) as well as with some other reagents such as HMPA, it is likely that an ester is formed, and the leaving group is the conjugate base of the corresponding acid. In these cases, the mechanism can be El or E2. The mechanism with AI2O3 and other solid catalysts has been studied extensively but is poorly understood. 

An important group of acylation reactions involves esters, in which case the leaving group is alkoxy or aryloxy. The self-condensation of esters is known as the Claisen condensation.216 Ethyl acetoacetate, for example, is prepared by Claisen condensation of ethyl acetate. All of the steps in the mechanism are reversible, and a full equivalent of base is needed to bring the reaction to completion. Ethyl acetoacetate is more acidic than any of the other species present and is converted to its conjugate base in the final step. The (3-ketoester product is obtained after neutralization. 

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