Solvents, acidic equation

Many palladium-catalyzed reactions are initiated by the reaction of a palladium(O) complex with an acidic derivative.367 The catalytic cycle is considered to be induced by a hydridopalladium complex. When the acidic derivatives are strong acids (e.g., HBF4, HC1, CF3C02H, HOTs), the hydridopalladium formation may be regarded as the protonation of basic Pd° to afford complexes HPdL3 +368-374 or IIPdL2.S +,375 in which S = solvent (see Equation (1)) ... 

The first studies of chlorine addition to the simplest diene, 1,3-butadiene, carried out in solvents of various polarity, showed58 that the reaction always led to mixtures of 1,2- and 1,4-addition products, in ratios almost independent of the solvent polarity. Furthermore, the addition of CI2 in acetic acid gave, besides the 1,2- and 1,4-dichlorides, 3-acetoxy-4-chloro-l-butene and l-acetoxy-4-chloro-2-butene arising from solvent incorporation (equation 27). By comparison of these data with those related to Br2 addition... 

Dimethyl tricyclo[4.2.2.02 -5]deca-3,7-diene-9,10-dicarboxylate adds bromine and iodine only to the less hindered double bond to give the syn 1,2-addition product of the cyclobutene moiety79. The product composition from this compound depends on the temperature and the solvent. At high temperatures, the 1,2-addition predominates over the transannular reaction, but this predominance is small in a solvent like chloroform and is lost in a protic solvent such as acetic acid (equation 47). 

Certain expressions describing a solvent acidity function, where S is a base that is protonated by an aqueous mineral acid solution. The equations describe a linear free-energy relationship between log([SH+]/[S]) + Ho and Ho + log[H ], where Ho is Hammett s acidity function and where Ho + log[H+] represents the activity function log(7s7H+/ysH ) for the nitroaniline reference bases to build Ho. Thus, log([SH+]/[S]) log[H+] = ( 1)... 

A modification of the Bunnett-Olsen equation concerned with solvent acidity in which log([SH+]/[S]) - log[H+] = m X -h p/ sH where [S] and [SH+] are the solvent and protonated solvent concentrations, and X is the activity function log[(7s7H+/ysH+)] for an arbitrary reference base. In practice, X = - (Ho + log[H+]), called the excess acidity (where Ho is the Hammett acidity function, m = 1- (f), and 4> represents the response of the S + H+ SH+ equilibrium to changes in the acid concentration). See Acidity Function Bunnett-Olsen Equation... 

In 2001, Albrecht Berkessel and Nadine Vogl reported on the Baeyer-Villiger oxidation with hydrogen peroxide in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) as solvent in the presence of Brpnsted acid catalysts such as para-toluenesulfonic acid (equation 85) . Under these conditions cyclohexanone could be selectively transformed into the corresponding lactone within 40 min at 60 °C with a yield of 92%. Mechanistic investigations of Berkessel and coworkers revealed that this reaction in HFIP proceeds by a new mechanism, via spiro-bisperoxide 234 as intermediate, which then rearranges to form the lactone. The study illustrates the importance of HFIP as solvent for the reaction, which presumably allows the cationic rearrangement of the tetroxane intermediates. 

Reaction with ammonia and primary and secondary amines can also give two types of products, 0-hydroxyamides or amino acids (equation 49). The amide is obtained from the reaction of 0-propiolactone with ammonia in water, while the amino acid is obtained from the reaction in acetonitrile, both in good yield. 0-Lactones react very generally with both aliphatic and aromatic amines, but the type of product does not correlate with polarity of solvent or basicity of amine. Fortunately, conditions can usually be found for the formation of the desired product. 

Similarily, styrene and 4-isobutylstyrene were converted to the corresponding carboxylic acids (Equations 4 and 5) by reaction with CO and H20 in the presence of Pd(tppts)3 and p-CH3C6H4S03H (no organic solvent) at 65°C and 50-140 bar CO (the relatively low temperature is required to suppress polymerization of the substrate). The major products were the branched acids in both cases 90% and 74% with styrene and 4-isobutylstyrene, respectively. In the case of 4-isobutylstyrene the branched acid product is the anti-inflammatory drug ibuprofen. 

Carbonylation of Alcohols - Pd(tppts)3 catalyses the carbonylation of benzylic alcohols to the corresponding phenylacetic acids, in the presence of a Bronsted acid cocatalyst such as H2S04 or p-CH3C6H4S03H in biphasic aqueous/organic media (no organic solvent).305,451 For example, benzyl alcohol was converted to phenylacetic acid (Equation 6) and l-(4-isobutylphenyl)ethanol (IBPE) to ibuprofen (Figure 9). 

BF3 reacts smoothly, in inert solvents, with alkali metal sulfates and phosphates to give stable 2 1 and 3 1 complexes (Table 9), whereas the intermediate complexes that form with NOT, SO and COl- decompose to [BF4] and B203.55 Brownstein et al. have established114 that BF3 reacts easily with alkylammonium salts in CH2C12 or liquid S02. [BF3A]- complex anions are formed with the salts of strong acids (equation 17) whereas complexes with salts of weak acids easily undergo disproportionation (equation 18) and/or conversion into a 2 1... 

On the other hand, the ionization of a cationic acid (equation 5.39) is insensitive to solvent polarity, since there is no change of charge in the equilibrium. 

The major equilibrium process controlling the solvent acidity is given by equation (1),... 

The synthesis of dialkyl hex-3-ene-l,6-dioate from the dioxycarboxylation of butadiene in an alcoholic solvent, and in the presence of a dehydrating agent such as trimethyl orthoformate444 or 1,1-dimethoxycyclohexane,445 provides an economically attractive route for the synthesis of adipic acid (equation 175). 

Substituted silatrane-3,7,10-triones 143-147 are formed in high yield (80-95%) from tetrachlorosilane or organyloxytrichlorosilanes and tris(trialkylstannyl) esters of aminotriacetic acid (equation 161). CCI4, pentane or petroleum ether can be used as a solvent. Tetraethoxy- and tetraacetoxysilanes are ineffective under the same conditions384. 

Solvent D KIE in the acid-catalysed hydrolysis of some iV-phenyl-4-substituted-benzohydroxamic acids (equation 276), using either H2SO4 or D2SO4 in 20/80 dioxane-water medium, have been observed to be equal (Table 4)536. 

DMF (and its adduct with HC1, DMF HCl) is an effective catalyst (and solvent) in the oxidation-chlorination of primary alcohols to a,a-dichloroaldehydes, which can be smoothly oxidized to the corresponding a,a-dichlorocarboxylic acids (equation 158)1054. 

Such an equilibrium system is termed a conjugate (or corresponding) acid-base system. A and B are termed a conjugate acid-base pair. It is important to realize that the symbol H+ in this definition represents the bare proton (unsolvated hydrogen ion), and hence the new definition is in no way connected to any solvent. The equation expresses a hypothetical scheme for defining the acid and base - it can be regarded as a half reaction which takes place only if the proton, released by the acid, is taken up by another base. 

Propionic acid is a significant intermediate in the production of a number of plastics, textiles, solvents, fragrances, pharmaceuticals and pesticides. Several transition metals (e.g. Ni, Pd, Rh, Ir, Ru, Mo) can catalyze the conversion of ethylene into propionic acid (Equation 22), and it is made by BASF by a nickel catalyzed hydroxycarbonylation of ethylene (100-300 bar 250-320°C) ... 

Decarboxylation of alkanoic acids means of LTA in benzene as solvent is hindered by die formation of all lbenzenes as by-products. This side reaction is especially pronounced widi radicals derived from primary acids or odier acids from which the radical is not easily oxidized LTA. In some cases, such as that of apocamphane-l-carboxylic acid (equation 54), good yields of alkylbenzene can be obtained. Intramolecular versions of this reaction in which the radical cyclizes onto an aromatic nucleus at the appropriate position in the chain have also been observed. 

In an analogous manner, the generation of alkyl radicals in benzene solution by the O-acyl oxime method results in the formation of alkylbenzenes with moderate to good yields for simple acids (equation 55). Use of pyridine as solvent leads to the formation of alkylpyridines as mixtures of ortho, meta and para isomers in which the para isomer predominates. The 0-acyI benzophenone oxime chemistry can also be applied to aryl acids in benzene or pyridine, resulting in the formation of mixed biaryls. A closely related method involves photolysis of mixed anhydrides of arenecarboxylic acids with the hydrox-amic acid A -hydroxy-Z-pyridone in benzene solution (equation 56). 

In aqueous solvents chlorine and bromine react with thiols to give sulfonyl halides or sulfonic acids (equations 8 and 9), while under anhydrous conditions various reactions occur to give sulfonyl halides (RSX), RSX3 and/or disulfides.On the contrary, oxidation with iodine is prone to give disulfides (equation 10) typically using a solution of I2 in acetic acid, alcohol, ether or aqueous Under... 

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