Acetonitrile acid catalysis with

Interestingly, at very low concentrations of micellised Qi(DS)2, the rate of the reaction of 5.1a with 5.2 was observed to be zero-order in 5.1 a and only depending on the concentration of Cu(DS)2 and 5.2. This is akin to the turn-over and saturation kinetics exhibited by enzymes. The acceleration relative to the reaction in organic media in the absence of catalyst, also approaches enzyme-like magnitudes compared to the process in acetonitrile (Chapter 2), Cu(DS)2 micelles accelerate the Diels-Alder reaction between 5.1a and 5.2 by a factor of 1.8710 . This extremely high catalytic efficiency shows how a combination of a beneficial aqueous solvent effect, Lewis-acid catalysis and micellar catalysis can lead to tremendous accelerations. 

C-Glycosyl derivatives may be prepared by utilizing glycosyl fluorides. Ishido and coworkers reported that the reaction of 2,3,5-tri-O-benzyl-a-(36a) or - -D-ribofuranosyl fluoride (36fi) with isopropenyl trimethylsilyl ether under BF3 catalysis (0.1 -0.05 mol. equiv. for the fluoride, in ether or acetonitrile) gave a mixture of 4,7-anhydro-5,6,8-tri-C)-benzyl-l,3-dideoxy-D-altro- (139, major) and -D-a//o-2-octulose (140) 139 was stated to isomerized to 140 (should be vice versa) under Lewis acid catalysis. Similar... 

It has also been shown that XIII is converted into XIV and vice versa upon contact with triflic acid in acetonitrile, thus strongly suggesting the intermediacy of the bicyclic structure in the route that leads to XIV and III. Its intermediate precursor XII would also be amenable to fragmentation to give carbocation XVI that obviously precedes carbinol XV. Finally, the slow conversion of the latter to XIV under p-toluenesulfonic acid catalysis has also been observed. 

According to Eq. 6, the value becomes larger with decrease in Aa, i.e., the larger pAa value. In general, the pAa value becomes larger in an aprotic solvent such as MeCN as compared with the value in water, since the solvation energy for proton in an aprotic solvent is much less than that in water [85]. Thus, acid catalysis in electron transfer reactions is expected to be much more efficient in acetonitrile... 

A detailed systematic study of the reaction conditions revealed that the ratio of 1,3,4-oxa-diazine imidazole formed is dependent on the solvent, and on the acid or base catalyst employed <90JHC487>. Yields of 1,3,4-oxadiazine are optimal (60-70%) in boiling carbon tetrachloride or in -heptane, whereas in acetonitrile, 1,2-dimethoxyethane, or toluene only the isomeric imidazoles (200) and (201) are produced. Acid catalysis (p-TSA or acetic acid) in hot carbon tetrachloride favors the 1,3,4-oxadiazine (80%), but with silica in boiling carbon tetrachloride imidazoles are the sole products. 

The l-alkyl-3-aryltriazenes (7.15 see Scheme 7-3) are easily obtained from aromatic diazonium salts and alkylamines. They exist in a tautomeric equilibrium (see Zollinger, 1994, Sect. 13.4) and, under acid catalysis, they dissociate into both possible combinations of amine and diazonium ion. The aliphatic amine and aromatic diazonium ion will, however, react further with each other, whereas in the combination alkanediazonium ion -h aromatic amine the diazonium ion will decompose rapidly into the carbocation and dinitrogen. This system has been used little for mechanistic or preparative deamination studies, obviously because a very complex product pattern is inherent in it. The carbocation may react with the aromatic and the aliphatic amine at the amino group. A modified method was described by Southam and Whiting (1982) using anhydrous acetonitrile as medium at —10 to -5°C. ... 

Regenerable, ion-supported (diacetoxyiodo)benzenes promoted the formation of 5-aryl-2-methyl oxazoles from acetophenones and acetonitrile in the presence of CF3SO3H with excellent yields and purity (13T2961). A procedure for the synthesis of oxa(thia)zol-3-yl methyl alcohols 135 started from 3-oxetanone 133 and (thio)amides 134.The reaction proceeds under microwave irradiation and acid catalysis (13CEJ9655). 

Cisoid retinoids have been isomerized to give the corresponding trans compounds by catalysis with iodine (Cainelli etal, 1973 Reif and Grassner, 1973). Methyl (13Z)-retinoate (176) has been converted to (all- )-retinoic acid (3) by being treated at room temperature with potassium amide in toluene and hydrolysis of the product obtained (Matsui, 1962). Homogeneous catalysis of a mixture of (9Z)-retinyl acetate (366) and (all- )-retinyl acetate (9) in the presence of palladium(II) chloride/acetonitrile adducts gave, by isomerization, a mixture more concentrated in (9), and pure (all- )-retinyl acetate (9) was then isolated in crystalline form from the latter mixture (Stoller and Wagner, 1975 Fischli et al., 1976). 

The aza-Diels-Alder reaction of imines with diene of Danishefsky is an important route to 2,3-dihydro-4-pyridones. A number of Lewis acids have been used to catalyze the reaction in organic solvents. In water the reaction was realized by acid catalysis via iminium salts or by Bronsted acids. The montmorillonite K-10 catalyzed this cycloaddition in water or in aqueous acetonitrile in excellent yield. Recently Kobayashi has performed the reaction in water at room temperature under neutral conditions in two (imine - - diene) or three (aldehyde -b amine -b diene) component versions by using sodium triflate as catalyst. Imine intermediates from the indium-mediated reaction, in aqueous medium at 50° C, between aromatic nitro compounds and 2,3-dihydrofuran undergo aza-Diels-Alder cycloadditions to give tetrahydroquinoline derivatives in good overall yields. ... 

Trimethylsilyl esters can be formed from carboxylic acids in 64—90% yields simply by treating the latter with MeaSiCl in hot 1,2-dichloroethane. Such silyl esters can also be formed directly from the acids by heating with allyltrimethylsilane in acetonitrile s or hexamethyldisiloxane in toluene both processes require acid catalysis. Trimethylsilyl esters (and hence the free acids) can also be prepared from t-butyl esters under non-acidic conditions using trimethylsilyl triflate and EtsN in refluxing dioxan. Benzyl esters and N-benzyloxycarbonyl groups are not attacked under these conditions. 

Nitrosation is almost equally rare. 2-Picoline failed to react with butyl nitrite under either basic or acidic catalysis. The sodium derivative does react247 j and the reaction is mentioned under Section (/) below. 4-Pyridyl-acetonitrile has been nitrosated at the methylene group, but details have not been given . ... 

The reactions of salicylate esters in aprotic solvents are also intra-molecularly catalysed. Thus the reactions of phenyl salicylate and phenyl o-methoxybenzoate with n-butylamine in acetonitrile are both second-order in amine but phenyl salicylate reacts 132 times faster [31]. These reactions are also catalysed by triethylenediamine and the rate constant for the reaction which is first-order in n-butylamine and first-order in triethylenediamine is over one hundred times greater for phenyl salicylate than for phenyl o-methoxybenzoate. The reaction of phenyl o-methoxybenzoate, but not that of phenyl salicylate, is catalysed by n-butylamine hydrochloride, which suggests that the phenolic hydroxyl group of the latter acts as an internal acid catalysis. Since the rate-limiting step in the aminolysis of esters in acetonitrile solutions is the breakdown of tetrahedral intermediate [32], a reasonable mechanism for the reaction of phenyl salicylate is one in which breakdown of the tetrahedral intermediate is catalysed intermolecularly by a second molecule of amine and intramolecularly by the phenolic hydroxyl group as shown in 25. The reaction of... 

Hydration of nitriles providing carboxamides is usually carried out m strongly basic or acidic aqueous media - these reactions require rather bars conditions and suffer from incomplete selectivity to the desired amide product. A few papers in the literature deal with the possibihty of transition metal catalysis of this reaction [28-30]. According to a recent report [30], acetonitrile can be hydrated into acetamide with water-soluble rhodium(I) complexes (such as the one obtained from [ RhCl(COD) 2] and TPPTS) under reasonably mild conditions with unprecedently high rate... 

Ion exchange resins are used widely as heterogeneous catalysts of processes that require acid or base catalysis, for example, hydration of propylene to isopropanol, reaction of isobutylene with acetonitrile, and many others. The same kind of equipment is suitable as for ion exchange, but usually regeneration is not necessary, although some degradation of the resin naturally occurs over a period of time. 

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