Acid Catalyzed Reaction

Markovnikov addition of thiols to olefins is observed, if acids are applied as catalysts according to the following mechanism  

Molar masses of M = 8900 g moP were determined by GPC and end group analysis, assuming OCH3 end groups. These end groups are a clear indication that does not only function as catalyst for polymer forming but also for polymer degradation. 

Until now there is no good explanation for the discrepancy between the GPC value (ETn = 28,000 g mol ) and the H NMR analysis value (M = 6000 g mol ), which is very close to the theoretical value (M = 6300 g mol ). Maybe the calibration of GPC with polystyrene standards is not suitable in this particular case. 

7 Stoichiometric Organic Reactions and Acid-Catalyzed Reactions in Ionic Liquids 

A novel use of the salt [BMIM][PFg] is to enhance microwave absorption and hence accelerate the rate of a reaction. Ley found that [BMIM][PFg] enhanced the rate of the microwave-promoted thionation of amides by a polymer-supported thionating agent [64]. 

Hardacre et al. have developed a procedure for the synthesis of deuterated imidazoles and imidazolium salts [65]. The procedure involves the platinum- or palladium-catalyzed deuterium exchange of 1-methyl-d -imidazole with D2O to give 1-methylimidazole-d , followed by treatment with a deuterated alkyl halide. 

The pi a shifts observed for these amines are the largest pR, shifts observed in synthetic host molecules and approach those observed in enzymes. 

Nature often exploits large pJQ shifts in enzymes to effect chemical catalysis similarly, we hoped to apply the large shifts in the effective basicities of encapsulated guests to reaction chemistry. Initial studies focused on the hydrolysis of orthoformates, a class of molecules responsible for much ofthe formulation ofthe Bronsted theory of acids almost a century ago [98]. While orthoformates are readily hydrolyzed in acidic solution, they are exceedingly stable in neutral or basic solution [99]. However, in the presence of a catalytic amount of 1 in basic solution, small orthoformates are quickly hydrolyzed to the corresponding formate ester [38]. Addition of NEt4 to the reaction inhibited the catalysis but did not affect the hydrolysis rate measured in the absence of 1. With a limited volume in the cavity of 1, substantial size selectivity was observed in the orthoformate hydrolysis. Orthoformates smaller than tripentyl 

Having established that 1 catalyzes the hydrolysis of orthoformates in basic solution, the reaction mechanism was probed. Mechanistic studies were performed using triethyl orthoformate (70) as the substrate at pH 11.0 and 50 °C. First-order substrate consumption was observed under stoichiometric conditions. Working under saturation conditions (pseudo-0 order in substrate), kinetic studies revealed that the reaction is also first order in [H+] and in [1]. When combined, these mechanistic studies establish that the rate law for this catalytic hydrolysis of ortho-formates by host 1 obeys the overall termolecular rate law rate = k[H+][Substrate][l], which reduces to rate = k [H ][l] at saturation. 

Lineweaver-Burk analysis using the substrate saturation curves afforded the corresponding Michaelis-Menten kinetic parameters of the reaction V max=l-79 xIO- Ms , KM=21.5mM, kcat = 8.06x 10 s for 69, and Knax = 9.22x 10 

Assuming a fast pre-equilibrium with respect to k -at, Km is essentially the dissociation constant of the encapsulated neutral substrate. The specificity factor k JKj can be used to compare the efficiency of hydrolysis by 1 for the two substrates. This constant corresponds to the second-order proportionality constant for the rate of conversion of the pre-formed host-guest complex to the product. Interestingly, 69 and 72 have specificity factors of 0.37 and 0.50 m s, respectively, showing that the more hydrophobic 72 is more efficiently hydrolyzed by 1. 

Since the research on the large calixarenes has been carried out in the laboratories of Gutsche and coworkers in the big state of Texas, these compounds have been colloquially designated as Texarenes . 

Acid-catalyzed condensation of resorcinols and aldehydes, on the other hand, provides the method of choice for the synthesis of the calixresorcarenes. An interesting variation on this theme has been discovered by Botta and coworkers in which the starting materials are 2,4-dimethoxycinnamates Botta, B. DiGiovanni, M. C. Monache, G. D. De Rosa, M. C. Gacs-Baitz, E. Botta, M. Corelli, F. Tafi, A. Santini, A. Benedetti, E. Pedone, C. Misiti, D. J. Org. Chem. 1994, 59, 1532 Botta, B. Delle Monache, G. De Rosa, M. C. Carbonetti, A. Gacs-Baitz, 

In a reaction similar in some respects to those described above, 3,4,5-trimethoxytoluene (22) reacts with paraformaldehyde under acidic conditions to yield a mixture of cyclooligomers 23 with n = 4-13. Calix[4]arenes carrying substituents on the bridge methylene groups (25) have been prepared by the acid-catalyzed reaction of triphenylmethanes 24 with paraformaldehyde and obtained in 18-30% yields. 

Hydroxymethylphenols yield oxacalixarenes under mild conditions of acid 

Schatz, R. Weber, C. Schilling, G. Oeser, T. Huber-Patz, U. Irngartinger, H. von der Lieth, C.-W. Pipkorn, R. Liebigs Ann. Ghent. 1995,1401. 

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Alkylation combines lower-molecular-weight saturated and unsaturated hydrocarbons (alkanes and alkenes) to produce high-octane gasoline and other hydrocarbon products. Conventional paraffin-olefin (alkane-alkene) alkylation is an acid-catalyzed reaction, such as combining isobutylene and isobutane to isooctane. 

Because of the mentioned leveling effect of the solvent (or excess acid itself acting as such) the acidity cannot exceed that of its conjugate acid. In the case of water the limiting acidity is that of HsO. Proton-ated water, H30 (hydronium ion), was first postulated in 1907, and its preeminent role in acid-catalyzed reactions in aqueous media was first realized in the acid-base theory of Bronsted and Lowry. Direct experimental evidence for the hydronium ion in solution and in the... 

Steps 4-5 Conversion of hemiacetal to carbocation These steps are analogous to the formation of carbocations m acid catalyzed reactions of alcohols... 

In an extension of the work described m the preceding section Bender showed that basic ester hydrolysis was not concerted and like acid hydrolysis took place by way of a tetrahedral intermediate The nature of the experiment was the same and the results were similar to those observed m the acid catalyzed reaction Ethyl benzoate enriched m 0 at the carbonyl oxygen was subjected to hydrolysis m base and samples were isolated before saponification was complete The recovered ethyl benzoate was found to have lost a por tion of Its isotopic label consistent with the formation of a tetrahedral intermediate... 

Acid-C t lyzed Chemistry. Acid-catalyzed reactions form the basis for essentially all chemically amplified resist systems for microlithography appHcations (61). These reactions can be generally classified as either cross-linking (photopolymerization) or deprotection reactions. The latter are used to unmask acidic functionality such as phenohc or pendent carboxyhc acid groups, and thus lend themselves to positive tone resist apphcations. Acid-catalyzed polymer cross-linking and photopolymerization reactions, on the other hand, find appHcation in negative tone resist systems. Representative examples of each type of chemistry are Hsted below. 

Transparent, homogeneous hybrids using a 50 50 PVAc-to-TEOS mixture and an acid-catalyzed reaction have been produced and characterized by dsc and dms (46). Dsc indicated only a slight increase in the T of the hybrid with incorporation of sihca. Dynamic mechanical tan 8 responses indicate a strong interaction between the organic and inorganic phases and, hence, weU-dispersed phases that lead to high modulus mbbery plateaus. 

Transparent, homogeneous hybrids using a 50 50 PVP-to-TEOS mixture and an acid-catalyzed reaction have been reported, but only tga data were presented in the way of characterization (46). 

G-All lation. Siace para-alkylated derivatives of DPA are widely used ia large volumes as antioxidants (qv), the most important reaction of DPA is the acid catalyzed reaction with olefins (2,3). Alkylation is carried out by adding the olefin to a mixture of DPA and an acid catalyst, such as AIQ. ... 

Increasingly, biochemical transformations are used to modify renewable resources into useful materials (see Microbial transformations). Fermentation (qv) to ethanol is the oldest of such conversions. Another example is the ceU-free enzyme catalyzed isomerization of glucose to fmctose for use as sweeteners (qv). The enzymatic hydrolysis of cellulose is a biochemical competitor for the acid catalyzed reaction. 

Crotonylidene Diurea. (CDU). Crotonjlidene [1129 2-6] is produced by the acid catalyzed reaction of urea with either crotonaldehyde or acetaldehyde. The condensation reaction produces a ring-stmctured compound. Table 4 hsts select properties. 

Little information is available about 5,6-dihydropteridines, of which various 6,7-diphenyl-5,6-dihydropterins (65HCA764, 69HCA306) and -lumazines (68HCA1029, 70HCA789) have been synthesized and characterized. As noticed already (51BSF521), this type of compound isomer-izes in an acid-catalyzed reaction to the 7,8-dihydro derivative (77HCA922) or oxidizes to... 

Although imidazolinones are usually resistant to hydrolysis, oxazolinone rings are often easily opened. In acid-catalyzed reactions of this type, water converts azlactones (181) into a-acylamino-a,/3-uhsaturated acids (182) (77AHC(21)175). 1,3,4-Oxadiazolinones are readily opened by hot water to give hydrazine carboxylic acids which undergo decarboxylation. 

Benzodiazepines as antianxiety agents, 1, 170 as anticonvulsants, 1, 166 organometallic complexes, 7, 604 as sedatives, 1, 166 IH- 1,2-Benzodiazepines conversion to 3H-1,2-benzodiazepines, 7, 604 synthesis, 7, 597, 598, 604 3H-1,2-Benzodiazepines acid-catalyzed reactions, 7, 601 nucleophilic reactions, 7, 604 oxidation, 7, 603 synthesis, 7, 596 thermal reactions, 7, 600 5H-1,2-Benzodiazepines photochemical reactions, 7, 599 synthesis, 7, 603... 

Acid catalyzed reaction at nilnles with aikenes or alcohola to afford amides... 

As chemists proceeded to synthesize more complicated stmctures, they developed more satisfactory protective groups and more effective methods for the formation and cleavage of protected compounds. At first a tetrahydropyranyl acetal was prepared, by an acid-catalyzed reaction with dihydropyran, to protect a hydroxyl group. The acetal is readily cleaved by mild acid hydrolysis, but formation of this acetal introduces a new stereogenic center. Formation of the 4-methoxytetrahy-dropyranyl ketal eliminates this problem. 

Me2C(OMe)2, DMF, pyridinium p-toluenesulfonate (PPTS). The use of PPTS for acid-catalyzed reactions has been quite successful and is particularly useful when TsOH acid is too strong an acid for the functionality in a given molecule. TBDMS groups are stable under these conditions. 

Compounds i, ii, and iii can be prepared by an acid-catalyzed reaction of a diol and the cycloalkanone in the presence of ethyl orthoformate and mesitylenesul-fonic acid. The relative ease of acid-catalyzed hydrolysis [0.53 M H2SO4, H2O, PrOH (65 35), 20°] for compounds i, iii, acetonide, and ii is C5 C7 > ace-... 

Ethoxy-2-cyclohexenone has been prepared by reaction of the silver salt of dihydroresorcinol with ethyl iodide and by the reaction of dihydroresorcinol with ethyl orthoformate, ethanol and sulfuric acid." The acid-catalyzed reaction of dihydroresorcinol with ethanol in benzene solution utilized in this preparation is patterned after the procedure of Frank and Hall. ... 

There has been little study of the stereoselectivity of the reaction under acidic conditions. In the absence of a coordinating Lewis acid, there is no preference for a cyclic transition state. When regioisomeric enols are possible, acid-catalyzed reactions tend to proceed through the more substituted of the enols. This reflects the predominance of this enol. (See Section 7.2.)... 

The irradiation of 2-methoxytropone (A) leads to methyl 4-oxo-2-cyclopentenyl-acetate (D). The reaction can be followed by analytical gas chromatography and two intermediates are observed. These have the structures B and C. Indicate a mechanism by which each of the three successive reactions might occur. The first two steps are photochemical, while the third is probably an acid-catalyzed reaction which occurs under the photolysis conditions. 

As a preparative route to A -3-ketones, the anhydrous reaction in benzene at room temperature gives 40-55 % of product after chromatography and is inferior to a stepwise conversion (via A -3-ketone). The principal side reaction (which also occurs in the acid catalyzed reaction of A -3-ketones with two moles of DDQ) appears to be addition of the hydroquinone ... 

Thioketals are readily formed by acid-catalyzed reaction with ethane-dithiol. Selective thioketal formation is achieved at C-3 in the presence of a 6-ketone by carrying out the boron trifluoride catalyzed reaction in diluted medium. Selective protection of the 3-carbonyl group as a thioketal has been effected in high yield with A" -3,17-diketones, A" -3,20-diketones and A" -3,l 1,17-triones in acetic acid at room temperature in the presence of p-toluenesulfonic acid. In the case of thioketals the double bond remains in the 4,5-position. This result is attributed to the greater nucleophilicity of sulfur as compared to oxygen, which promotes closure of intermediate (66) to the protonated cyclic mercaptal (67) rather than elimination to the 3,5-diene [cf. ketal (70) via intermediates (68) and (69)]." " ... 

A -3-Ketones readily form A -dien-3-ol ethers by acid-catalyzed reaction with orthoformates. Under these conditions A" -3-ketones can be selectively protected in the presence of 17- and 20-ketones (72) (73)]. 

A -Dieiiol ethers are also formed by acid-catalyzed reaction of the steroid directly with benzyl alcohol with azeotropic removal of water/ Use of isooctane as azeotropic carrier may improve yields/ ... 

A"" -3-Ketones are more reactive than cross-conjugated A ""-3-ketones. A"" -3,3-CycIoethylenedioxy compounds can be easily prepared by acid-catalyzed reaction with ethylene glycol or by exchange dioxolanation. 3,3-Cycloethylenedioxy-A -dienes can be prepared from 3,3-cycloethy-lenedioxy-A -enes by allylic bromination and dehydrobromination. Acid hydrolysis yields A"" -3-ketosteroids. ... 

Unsubstituted 20-ketones undergo exchange dioxolanation nearly with the same ease as saturated 3-ketones although preferential ketalization at C-3 can be achieved under these conditions. " 20,20-Cycloethylenedioxy derivatives are readily prepared by acid-catalyzed reaction with ethylene glycol. The presence of a 12-ketone inhibits formation of 20-ketals. Selective removal of 20-ketals in the presence of a 3-ketal is effected with boron trifluoride at room temperature. Hemithioketals and thioketals " are obtained by conventional procedures. However, the 20-thioketal does not form under mild conditions (dilution technique). ... 

A -20-Dien-20-ol acetates are prepared by acid-catalyzed reaction with isopropenyl acetate.A -20-Semicarbazones can be prepared in the usual manner. ... 

B-Homosteroids have also been prepared by acid-catalyzed reaction of diazomethane with a,/5-unsaturated ketones. 3/ -Hydroxycholest-5-en-7-one acetate (57) reacts with diazomethane in the presence of concentrated fluoroboric acid, boron trifluoride etherate or aluminum chloride to give 3yS-hydroxy-B-homo-cholest-5-en-7a-one acetate (67). The 7a-keto group is reported to be chemically less reactive than an 11-keto group. 

Parallel reactions give rate equations having sums of rate terms. Each term provides the transition state composition for a reaction path. Eor example, some acid-catalyzed reactions have the rate equation... 

We suppose that the molar concentration scale is used brackets signify concentration, and parentheses signify conventional activity as determined by pH measurements. First, consider an acid-catalyzed reaction having the rate equation... 

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