Catalyst-free method

We have developed a catalyst-free method of biodiesel fuel production by supercritical methanol (10-12), and we found that the process becomes much simpler and that the yield of biodiesel is higher compared with the alkaline-catalyzed method. The aim of the present work was, therefore, to investigate the possibilities of biodiesel fuel production from rapeseed oil with various alcohols by supercritical treatment. In addition, the super-critically prepared biodiesel fuel was studied for its cold properties. 

Chakraborti et have described an efficient catalyst-free method for water-mediated conjugate addition of thiols to a,p-unsaturated carbonyl compounds, providing p-sulfido carbonyl compounds (Scheme 5.16) at room temperature. The reactions were fast and highly chemoselective. Water played a dual role in simultaneously activating the a,p-unsaturated carbonyl compound and the thiol. 

A highly efficient solvent-free and catalyst-free method for the synthesis of a-aminophosphonates is a microwave-assisted three-component Kabachnik-Fields reaction involving aldehyde, amine, and dimethyl H-phosphonate [40]. 

For some examples of the reaction under catalyst and solvent-free, microwave irradiation conditions, see (a) J. F. Zhou, X. G. Gong, H. Q. Zhu, F. X. Zhu, Chin. Chem. Lett. 2009, 20, 1198-1200. Solvent-free and catalyst-free method for the synthesis of 2,4,5-triarylimidazoles under microwave irradiation, (b) J. F. Zhou, G. X. Gong, X. J. Sun, Y. L. Zhu, Synth. Commun. 2010, 40, 1134-1141. Facile method for one-step synthesis of 2,4,5-triarylimidazoles under catalyst-free, sol-vent-free, and microwave-irradiation conditions. 

A multistep microwave-assisted, solvent- and catalyst-free method has been elaborated for the synthesis of dialkyl ethoxycarbonylmethylphos-phonates (619) from diethyl ethoxycarbonyl-methylphosphonate (618) (Scheme 180). ... 

A one-step, high-yielding and catalyst free method was reported for N-arylation of azoles and indoles from unactivated monofluorobenzenes by Diness and Fairlie... 

Several derivatives of cellulose, including cellulose acetate, can be prepared in solution in dimethylacetamide—lithium chloride (65). Reportedly, this combination does not react with the hydroxy groups, thus leaving them free for esterification or etherification reactions. In another homogeneous-solution method, cellulose is treated with dinitrogen tetroxide in DMF to form the soluble cellulose nitrite ester this is then ester-interchanged with acetic anhydride (66). With pyridine as the catalyst, this method yields cellulose acetate with DS < 2.0. 

Masjedizadeh and coworkers have recently described similar microwave-promoted hydrogen-deuterium exchange reactions in a series of heterocydes using mixtures of deuterium oxide and deuteriomethanol (Scheme 6.173 b) [328], The rapid exchange method was applied to the deuteration of the anti-tumor antibiotic bleomycin A under catalyst-free conditions [328],... 

Although beyond the scope of this book, a vast amount of work has been directed to supporting homogeneous catalysts on solid supports including silica, alumina and zeolites, and functionalized dendrimers and polymers [19]. These give rise to so-called solid-liquid biphasic catalysis and in cases where the substrate and product are both liquids or gases then co-solvents are not always required. In many ways solvent-free synthesis represents the ideal method but currently solvent-free methods can only be applied to a limited number of reactions [20],... 

An interesting entry to functionalized dihydropyrans has been intensively studied by Tietze in the 1990s using a three-component domino-Knoevenagel Hetero-Diels-Alder sequence. The overall transformation involves the transient formation of an activated heterodienophile by condensation of simple aldehydes with 1,3-dicarbonyls such as barbituric acids [127], Meldrum s acid [128], or activated carbonyls. In situ cycloaddition with electron-rich alkenes furnished the expected functionalized dihydropyrans. Two recent examples concern the reactivity of 1,4-benzoquinones and pyrazolones as 1,3-dicarbonyl equivalents under microwave irradiation. In the first case, a new three-component catalyst-free efficient one-pot transformation was proposed for the synthesis of pyrano-1,4-benzoquinone scaffolds [129]. In this synthetic method, 2,5-dihydroxy-3-undecyl-1,4-benzoquinone, paraformaldehyde, and alkenes were suspended in ethanol and placed under microwave irradiations to lead regioselectively the corresponding pyrano-l,4-benzoquinone derivatives (Scheme 38). The total regioselectivity was... 

The simplest solvent-free method involves irradiation of neat reactants in an open container. In the absence of reagents or supports, the scope for such processes appears to be limited to relatively straightforward condensations that can be conducted without added catalysts, or to intramolecular thermolytic processes such as rearrangement or elimination. 

A clean, solvent-free method has been developed for the bis-hydroxylation of alkenes by the use of Nafion-based acidic catalysts and 30% H202.655 Nafion NR50 and SAC-13 exhibited high activity in the oxidation of isomeric C alkenes, cyclohexene [Eq. (5.228)], 1,4-cyclohexadiene, and allylic alcohols in the temperature... 

A chloride-free catalyst, Fe(BF4)2-6H20, was used for the reaction of P-oxo ester 24a with MVK (41a) in the ionic liquid [bmim][NTf2] [89]. Product 42a was obtained in about the same yield (95%) as for the solvent-free protocol with Fe(C104)3-9H20 (99% yield) (Scheme 8.27). Both protocols with ionic liquids are, however, operationally less simple than the solvent-free methods reported before, because of the use significant amounts of Et20 for workup and purification of the products. 

Aliphatic aldehydes typically provide only moderate yields in the Biginelli reaction unless special reaction conditions are employed, such as Lewis-acid catalysts or solvent-free methods, or the aldehydes are used in protected form [96]. The C4-unsubstituted DHPM can be prepared in a similar manner employing suitable formaldehyde synthons [96]. Of particular interest are reactions where the aldehyde component is derived from a carbohydrate. In such transformations, DHPMs having a sugar-like moiety in position 4 (C-nucleoside analogues) are obtained (see Section 4.7) [97-106]. Also of interest is the use of masked amino acids as building blocks [107, 108]. In a few cases, bisaldehydes have been used as synthons in Biginelli reactions [89, 109, 110]. 

By a similar but solvent-free method Plaquevent et al. produced the Michael adduct 30 from 2-pentyl-2-cyclopentenone in 91% yield and with 90% ee, by use of the quinine-derived catalyst 31 (Scheme 4.10) [16], When the quinidine-derived ammonium salt 32 was employed, 80% of the enantiomeric product ent-30 was ob-... 

In the metal-free epoxidation of enones and enoates, practically useful yields and enantioselectivity have been achieved by using catalysts based on chiral electrophilic ketones, peptides, and chiral phase-transfer agents. (E)-configured acyclic enones are comparatively easy substrates that can be converted to enantiomeri-cally highly enriched epoxides by all three methods. Currently, chiral ketones/ dioxiranes constitute the only catalyst system that enables asymmetric and metal-free epoxidation of (E)-enoates. There seems to be no metal-free method for efficient asymmetric epoxidation of achiral (Z)-enones. Exocyclic (E)-enones have been epoxidized with excellent ee using either phase-transfer catalysis or polyamino acids. In contrast, generation of enantiopure epoxides from normal endocyclic... 

A catalyst-free supercritical methanol method for biodiesel fuel production was proposed with the optimum conditions of 350°C, 20 MPa, a molar ratio of 42 in methanol, and a 4-min treatment period (12-13). This method has been proved to produce a high yield, because of simultaneous reactions of transesterification of triglycerides and methyl esterification of free fatty acids (10). The only shortcoming of this one-step method is that it requires a severe reaction condition compared with the conventional commercial method with acid or alkaline catalyst. Consequently, our method would require a special alloy to cover the high temperature and high pressure of the reaction system. 

A variety of other environmentally friendly strategies for the synthesis of quinolines were also reported. Goswami et al. developed a one-pot approach for the synthesis of quinolines from aromatic amines and P-aryl vinyl ketones under solvent and catalyst free conditions <07JHC1191>. In another solvent free one-pot method, Nagarajan et al. synthesized 3-quinolylcarbazoles from P-nitrovinylcarbazole and 2-amino acetophenone in moderate yields <07TL2489>. 

An azo-free method for preparing the ruthenium metathesis catalysts was developed by Nolan [6]. 

The reductive carbonylation of nitroarenes with transition metal catalysts is a very important process in industry, as the development of a phosgene-free method for preparing isocyanate is required. Ruthenium, rhodium, and palladium complex catalysts have all been well studied, and ruthenium catalysts have been shown to be both highly active and attractive. The reduction of nitroarene with CO in the presence of alcohol and amine gives urethanes and ureas [95], respectively, both of which can be easily converted into isocyanates [3,96]. 

Microwave irradiation of a mixture of an acid anhydride, an amine adsorbed on silica gel, and TaCl5/Si02 is a solvent-free method for the synthesis of A-alkyl and A-aryl-imides [47]. Ni(II) promotes the conversion of an acrylamide to ethyl acrylate via a Diels-Alder adduct with (2-pyridyl)anthracene [48], Aromatic carboxylic acids [49] and mandelic acid [50] are efficiently esterified with Fc2(S04)3 XH2O as catalyst. Co(II) perchlorate in MeOH catalyzes the methanolysis of acetyl imidazole and acetyl pyrazole [51]. Hiyama et al. used FeCb as a catalyst for the acylation of a silylated cyanohydrin. The resulting ester was then cyclized to 4-amino-2(5H)-furanones (Sch. 5) [52]. 

A number of different types of classic Raney nickel catalysts with varying activities have been prepared by the addition of the commercially available alloy to sodium hydroxide solutions. These catalysts have been designated as Wl, W2, W3, W4, W5, W6, W7 and W8. The procedures utilized to prepare these catalysts differ in the amount of sodium hydroxide used, the temperature at which the alloy is added to the basic solution, the temperature and duration of alloy digestion after addition to the base and the method used to wash the catalyst free from the sodium aliuninate and the excess base. These differences are listed in Table 12.1. 

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