Leaving groups sulfonates

These data show that a change from a hard leaving group (sulfonate, sulfate) to a softer leaving group (bromide, iodide) favors carbon alkylation. Another possible factor in C 0 ratios may be the ability of sulfonates to form a six-membered cyclic TS for both modes of reaction, whereas halides can form such structures only for C-alkylation. ... 

Once the alcohol has been activated by being converted into a sulfonate ester, the appropriate nucleophile is added, generally under conditions that favor Sn2 reactions. The reactions take place readily at room temperature because the leaving group is so good. For example, a para-toluenesulfonate ion is about 100 times better than a chloride ion as a leaving group. Sulfonate esters react with a wide variety of nucleophiles, so they can be used to synthesize a wide variety of compounds. 

These data show that a change from a hard leaving group (sulfonate, sulfate) to a softer leaving group (bromide, iodide) favors carbon alkylation. 

Because halides are poorer leaving groups than p toluene sulfonate alkyl p toluene sulfonates can be converted to alkyl halides by 8 2 reactions involving chloride bro mide or iodide as the nucleophile... 

A further measure of improvement has resulted ia a cycHc process for the electrochemical syathesis of NH (196). The catalyst is /n j -W(N2)2(dppe)2 or less effectively its Mo analogue. The choice of acid is important so as to provide a ligand duriag part of the cycle, yet also an effective leaving group when the catalyst is reformed. A sulfonic acid is used. 

All lation. In alkylation, the dialkyl sulfates react much faster than do the alkyl haHdes, because the monoalkyl sulfate anion (ROSO ) is more effective as a leaving group than a haHde ion. The high rate is most apparent with small primary alkyl groups, eg, methyl and ethyl. Some leaving groups, such as the fluorinated sulfonate anion, eg, the triflate anion, CF SO, react even faster in ester form (4). Against phenoxide anion, the reaction rate is methyl triflate [333-27-7] dimethyl sulfate methyl toluenesulfonate [23373-38-8] (5). Dialkyl sulfates, as compared to alkyl chlorides, lack chloride ions in their products chloride corrodes and requires the use of a gas instead of a Hquid. The lower sulfates are much less expensive than lower bromides or iodides, and they also alkylate quickly. 

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 pify of the leaving group and the hydrophobe chain length can dramatically affect the efficiency of the perhydrolysis reaction. Additionally, the stmcture of the acid portion of the precursor can affect the yield and sensitivity of the reaction to pH. The mono-4-hydroxybenzenesulfonic acid ester of a-decylsuccinic acid (13) undergoes extremely efficient perhydrolysis at much lower pHs than other peracid precursors, eg, decanoyloxybenzene sulfonate (14). This may be because of the neighboring group participation of the adjacent carboxylate as shown in Table 2 (115). 

SuIfona.tlon, The sulfonic acid group is used extensively in the dyes industry for its water-solubilizing properties, and for its ability to act as a good leaving group in nucleophilic substitutions. It is used almost exclusively for these purposes since it has only a minor effect on the color of a dye. 

In the anthraquinone series, apart from the special case of the amination of leucoquinizarin, sulfonic acid and nitro are the preferred leaving groups. 1-Aminoanthraquinone is manufactured from anthraquinone-l-sulfonic acid or 1-nitroanthraquinone, and 2-amino anthraquinone (betamine) from anthraquinone-2-sulfonic acid. 

The preparation of esters can be classified into two main categories (1) carboxy-late activation with a good leaving group and (2) nucleophilic displacement of a caiboxylate on an alkyl halide or sulfonate. The latter approach is generally not suitable for the preparation of esters if the halide or tosylate is sterically hindered, but there has been some success with simple secondaiy halides and tosylates (ROTs, DMF, K2CO3, 69-93% yield). ... 

The solvolysis of 2, 35-3-(4-methoxyphenyl)but-2-yl/>-toluensulfonate in acetic acid can be followed by several kinetic measurements (a) rate of decrease of observed rotation (k ) rate of release of the leaving group (k,) and, when 0-labeled sulfonate is used, the rate of equilibration of the sulfonate oxygens (k ). At 25°C, the rate constants are... 

The most common leaving groups are sulfonate esters and halides. For the sake of convenience, the discussion of certain dehalogenation reactions is also included in this section even though they may not involve 8 2 type displacement. Benzylic alcohols are also known to be displaced by hydrides or deuterides, but there is no evidence for the application of these reactions to the steroid field. 

In contrast to phosphorus esters, sulfur esters are usually cleaved at the carbon-oxygen bond with carbon-fluorine bond formation Cleavage of esteri nf methanesulfonic acid, p-toluenesidfonic acid, and especially trifluoromethane-sulfonic acid (tnflic acid) by fluoride ion is the most widely used method for the conversion of hydroxy compounds to fluoro derivatives Potassium fluoride, triethylamine trihydrofluoride, and tetrabutylammonium fluoride are common sources of the fluoride ion For the cleavage of a variety of alkyl mesylates and tosylates with potassium fluoride, polyethylene glycol 400 is a solvent of choice, the yields are limited by solvolysis of the leaving group by the solvent, but this phenomenon is controlled by bulky substituents, either in the sulfonic acid part or in the alcohol part of the ester [42] (equation 29)... 

It is often advantageous to proceed to a desired product through two nucleophilic displacements rather than directly when one can exploit a difference in the reactivity of two leaving groups. An example is the conversion of 4-chloro-2,6-dimethoxypyrimidine (109) (not satisfactorily reactive with sulfanilamide anion) by means of trimethylamine into the more reactive trimethylammonio derivative 110. Conversion of chloro-quinohnes and -pyrimi-dines into nitriles is best accomplished by conversion (with sulfite) into the sulfonic acids before reaction with cyanide. 

R Cu, or litliium or magnesium homocuprates RfCuM fM = Li, MgX), are fre-quently used, but a number of catalytic processes have also been developed. These processes nornnally utilize a catalytic amount of a copper salt CuY and a stoichiometric amount of an organometallic reagent R M IM = Li, MgX, ZnX, etc.). Hie leaving groups used include balides, esters, sulfonates, and epoxides, among others. 

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