Reaction, acid catalyzed Summarized

To optimize the alkylation conditions, ferrocene was reacted with allyldimethyl-chlorosilane (2) in the presence of various Lewis acids such as aluminum halides and Group lO metal chlorides. Saturated hydrocarbons and polychloromethanes such as hexane and methylene chloride or chloroform were used as solvents because of the stability of the compounds in the Lewis acid catalyzed Friedel-Crafts reactions. The results obtained from various reaction conditions are summarized in Table IV. 

The majority of reactions of aziridines deal with acid-catalyzed ring opening with various nucleophiles. In this review only reactions with aziridine-2-car-boxylic esters are summarized (for other types of aziridines, see ref. [3]). 

If ri = rate of reaction of SA and r2 = rate of formation of DES, then rate of formation of MES = r2 - ri. The equilibrium constant for each of the esterification reactions was determined by allowing the reaction to proceed until no further reaction was observed. For the quantities of resin used, the rate of resin-catalyzed esterification is much slower than that for sulfuric acid-catalyzed reaction. All results are summarized in Table 1. 

Lewis-acid-catalyzed reactions often occur with unique reactivity and selectivity, and the reactions proceed under mild conditions. Many Lewis-acid-mediated reactions are now used not only in laboratories but also in industry. This chapter summarizes these Lewis acid-mediated reactions successfully used in organic synthesis they are organized mainly by the element of the Lewis-acid catalyst. Due to limitations of space, the focus is on more recent publications.1-3... 

The main features of the copper catalyzed autoxidation of ascorbic acid were summarized in detail in Section III. Recently, Strizhak and coworkers demonstrated that in a continuously stirred tank reactor (CSTR) as well as in a batch reactor, the reaction shows various non-linear phenomena, such as bi-stability, oscillations and stochastic resonance (161). The results from the batch experiments can be suitably illustrated with a two-dimensional parameter diagram shown in Pig. 5. 

Table III summarizes the parameters that affect Brrfnsted acid-catalyzed surface reactions. The range of reaction conditions investigated varies widely, from extreme dehydration at high temperatures in studies on the use of clay minerals as industrial catalysts, to fully saturated at ambient temperatures. Table IV lists reactions that have been shown or suggested to be promoted by Br nsted acidity of clay mineral surfaces along with representative examples. Studies have been concerned with the hydrolysis of organophosphate pesticides (70-72), triazines (73), or chemicals which specifically probe neutral, acid-, and base-catalyzed hydrolysis (74). Other reactions have been studied in the context of diagenesis or catagenesis of biological markers (22-24) or of chemical synthesis using clays as the catalysts (34, 36). Mechanistic interpretations of such reactions can be found in the comprehensive review by Solomon and Hawthorne (37).

Carbohydrates have found widespread use as chiral auxiliaries in asymmetric Diels-Al-der reactions156. A recent example is a study conducted by Ferreira and colleagues157 who used carbohydrate based chiral auxiliaries in the Lewis acid catalyzed Diels-Alder reactions of their acrylate esters 235 with cyclopentadiene (equation 66). Some representative results of their findings, including the ratios of products 236 and 237, have been summarized in Table 9. The formation of 236 as the main product when diethylaluminum chloride was used in dichloromethane (entry 3) was considered to be the result of an equilibrium between a bidentate and monodentate catalyst-dienophile complex. The bidentate complex would, upon attack by the diene, lead to 236, whereas the monodentate complex would afford 236 and 237 in approximately equal amounts. The reversal of selectivity on changing the solvent from dichloromethane to toluene (entry 2 vs 3) remained unexplained by the authors. 

A robust and highly active catalyst for water-phase, acid-catalyzed THs of carbonyl compounds at pH 2.0-3.0 at 70 °C was disclosed by Ogo and coworkers [60]. The water-soluble hydride complex [Cp lr(bipy)H] (72, Cp = Tl -CsMes, bipy = 2,2 -bipyridine) was synthesized from the reaction of [Cp lr(bipy)(H20)] (73) with HCOOX (X = H or Na) in H2O under controlled pH conditions (2.0 < pH < 6.0, 25 °C). The pH control is pivotal in avoiding protonation of the hydrido ligand of 72 below pH ca. 1.0 and deprotonation of the aquo ligand of 73 above pH ca. 6.0. The rate of the reaction is heavily dependent on the pH of the solution, the reaction temperature, and the concentration of HCOOH. High TOFs of the acid-catalyzed transfer hydrogenations at pH 2.0-3.0, ranging from 150 to 525 h, were observed for a variety of linear and cyclic ketones, as summarized in Table 4.5. 

In aqueous solutions, aldehydes [RHC=0] undergo general acid-catalyzed addition of water to yield the hydrate [RHC(0H)2], and the equilibrium position lies in favor of the hydrate. Jencks summarized the most likely mechanism for the hydration reaction. 

As summarized recently [61], a large scope of Brpnsted and Lewis acids catalyze this multicomponent reaction to promote the DHPM formation. The heterocyclic Biginelli scaffold has also been obtained under eco-Mendly conditions, as illustrated... 

This chapter deals mainly with the 1,3-dipolar cycloaddition reactions of three 1,3-dipoles azomethine ylides, nitrile oxides, and nitrones. These three have been relatively well investigated, and examples of external reagent-mediated stereocontrolled cycloadditions of other 1,3-dipoles are quite limited. Both nitrile oxides and nitrones are 1,3-dipoles whose cycloaddition reactions with alkene dipolarophiles produce 2-isoxazolines and isoxazolidines, their dihydro derivatives. These two heterocycles have long been used as intermediates in a variety of synthetic applications because their rich functionality. When subjected to reductive cleavage of the N—O bonds of these heterocycles, for example, important building blocks such as p-hydroxy ketones (aldols), a,p-unsaturated ketones, y-amino alcohols, and so on are produced (7-12). Stereocontrolled and/or enantiocontrolled cycloadditions of nitrones are the most widely developed (6,13). Examples of enantioselective Lewis acid catalyzed 1,3-dipolar cycloadditions are summarized by J0rgensen in Chapter 12 of this book, and will not be discussed further here. 

In general, acid catalyzed reactions are performed at high alcohol-to-oil molar ratios, low-to-moderate temperatures and pressures, and high acid catalyst concentrations. Table 9 summarizes reactions conditions proposed by Zhang et al. to prepare biodiesel from waste cooking oil using sulfuric acid as the catalyst. A simplified BFD of the acid process is shown in Figure 9. 

The alcoholysis of sulfites such as dimethyl sulfite offers a convenient method for the preparation of high-boiling dialkyl sulfites [33]. Earlier, Voos and Blanke [8a] reported that dimethyl sulfite is converted to diethyl sulfite in 44 % yield. The reaction was shown to be acid-catalyzed and failed when barium carbonate was present. However, a patent refers to the use of lithium hydride in the transalcoholysis of 2,2-(4,4 -dihydroxyphenyl)propane with diphenyl sulfite or di-o-cresyl sulfite [32]. Recently Mehrotra and Mathur [34] reported that the alcoholysis reaction proceeds in the absence of catalysts. Their results are summarized in Eqs. (21)—(23) and Table VII. Tertiary butanol did not... 

Although the quantitative theory of reactions in moderately concentrated solutions of strong acids is unsatisfactory, we do have a good qualitative idea of the processes involved in the acid-catalyzed hydrolysis and formation of esters. Under conditions where the degree of protonation of the substrate is small it is not possible to separate with confidence the factors which affect the solvolytic process and those which affect the preliminary protonation equilibrium. But there have been a number of recent studies of t ie behaviour of carboxylic acids and esters in very strongly acidic media, in. which they are essentially completely protonated. Under these conditions it is possible to observe the behaviour of the protonated species directly. It is appropriate to summarize the results of this research before discussing the reactions under more normal solvolytic conditions. 

Fromm12 proposed that l,3-diazetidine-2-thiones were the products of the reaction between dithiobiurets and aldehydes or ketones, which he called aldurets and keturets, respectively. These structures were subsequently shown to be hexahydrotriazines by Fairfull and Peak.13 Kurzer,3 in his review of dithiobiurets, summarized the structural work on aldurets and keturets. Dixon and Taylor14 claimed that 1,3-diazeti-dine-2-thiones wrere the products of the acid-catalyzed treatment of... 

In 2007, Wiles et al. (2007c) demonstrated the ability to employ solid-supported catalysts in series within an EOF-based microreactor. As summarized in Scheme 39, the model reaction sequence involved combining a previously investigated acid-catalyzed deprotection with a base-catalyzed condensation reaction to enable the synthesis of a,(3-unsaturated carbonyl compounds from dimethyl acetals. 

About 10 years have passed since this study began to be seriously undertaken, but the usage of solid superacids as catalysts is still limited. Table IX summarizes the acid-catalyzed reactions on sulfated metal oxides, i.e., cracking, isomerization, alkylation, acylation, esterification,... 

The following box summarizes the base-catalyzed and acid-catalyzed mechanisms for nucleophilic addition, together with their reverse reactions. 

---