Irradiation microwave

Researchers created a new technique for the synthesis of CHT-modified CNT by microwave irradiation. According to this technique, solutions of MWNT in nitric acid were placed under microwave irradiation and dried to produce pure MWNT. A mixture of purified MWNT and CHT solution was reacted in a microwave oven and then centrifuged. The resulting black-coloured solution was adjusted to pH 8 and centrifuged in order to precipitate the CNT/CHT composite. 

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Hydration and Dehydration. Succinic anhydride reacts slowly with cold water and rapidly with hot water to give the acid. For this reason it must be carefully stored in anhydrous conditions. Succinic acid can be dehydrated to the anhydride by heating at 200°C, optionally in the presence of a solvent (31). Dehydration can also be performed with clay catalysis in the presence of isopropenyl acetate under microwave irradiation (32) or with his (trichi oromethyl) carbonate at room temperature (33). 

Microwave irradiation has been used to probe aromatic character in isoxazoles (74JA7394)... 

The use of microwave irradiation as an energy source for chemical reactions and processes has been extensively investigated during recent years and has found wide application in various fields of chemistry and technology. The following presentation focuses on the scope and potential of microwaves in chemical analysis. 

Dimethyl-1,3-dioxolane, microwave irradiation. Montmorillonite KSF, 38-95% yield.""... 

BiCl3, microwave irradiation, 2 min, THF, 70-96% yield. a,/3-Unsaturated systems were not effectively cleaved under these conditons. ... 

Microwave chemistry has been found to be a useful method for accelerating reactions or catalyzing reactions that are difficult to carry out by other methods. A modification of the Hantzsch method to directly obtain pyridines has been communicated. A dry medium using ammonium nitrate bentonitic clay system with microwave irradiation affords pyridines 96 in a single pot within 5 minutes. When the pyridine is not the major product (> 75% yield), the dealkylated pyridine 97 becomes an... 

Variations on this theme have been reported. One example utilized silica gel and urea with 95 and 82 under microwave irradiation to afford dihydropyridines 96 in 3-5 minutes and in 70-90% yield. 

Microwave irradiation generates pyridine 98 from triazine 97 and enamine 67. Again, the new technology reduces reaction time and the alternative conditions provide reaction manifolds not obtainable using traditional methods. ... 

Gupta et al. reported that the Vilsmeier-Haack cyclisation of acetanilides 20 using supported reagents and microwave-irradiation in solvent-free conditions is rapid and efficient. Reaction yields are good, although only a few activated derivatives have been investigated. 

The Pictet-Spengler reaction has been carried out on various solid support materials " and with microwave irradiation activation.Diverse structural analogues of (-)-Saframycin A have been prepared by carrying out the Pictet-Spengler isoquinoline synthesis on substrates attached to a polystyrene support. Amine 20 was condensed with aldehyde 21 followed by cyclization to give predominantly the cis isomer tetrahydroisoquinoline 22 which was further elaborated to (-)-Saframycin A analogues. 

Since the revised Biginelli mechanism was reported in 1997, numerous papers have appeared addressing improvements and variations of this reaction. The improvements include Lewis acid catalysis, protic acid catalysis, non-catalytic conditions, and heterogeneous catalysis. In addition, microwave irradiation (MWI) has been exploited to increase the reaction rates and yields. 

Cyclocondenzation of 2-aminoquinoline and isopropylidene 2-(l-methylthioalkylidene)malonates on Si02 under microwave irradiations afforded 3-substituted (3-methylthio, 3-methyl, 3-ethyl, and 3-phenyl) l//-pyrimido[l, 2-n]quinolin-1-ones (00MI40). 

The reaction of cnol ethers 4 with benzene-1.2-diamine and substituted benzene-1.2-diamines under microwave irradiation gives H- 1,5-benzodiazepines 5 or 6.430... 

Finally, dissolution of non-activated cellulose in LiCl/DMAc, and in ionic liquids has been accelerated by microwave irradiation [72,103,104], although the effect of microwave heating on the DP of the polymer has not been investigated. This last point is relevant in view of the fact that ILs are heated with exceptional efficiency by microwaves [105], so that care must be taken to avoid excessive localized heating that can induce chain degradation of the polymer during its dissolution. 

Decalin unit 121, an intermediate in the total synthesis of compactin, has been prepared by intramolecular cycloaddition reaction [117] of trienone-carboxylic acid 122 carried out under either thermal conditions or microwave irradiation. The desired cxo-adduct 123 was the major stereoisomer (Equation 2.34). Similar results were observed in the cycloadditions of the corresponding esters. 

The investigation on the use of K-10 montmorillonite under free solvent conditions was then extended to inner ring dienes such as furan and its 2,5-dimethyl derivative [9] (Table 4.3). The cycloadditions generally proceed slowly, and Zn(II)-doped clay and microwave irradiation were used to accelerate the reactions. The reaction with maleic anhydride preferentially affords the thermodynamically favored exo adduct. 

French researchers [38c] have investigated the /zetero-Diels-Alder reaction of methylglyoxylate and glyoxal monoacetal with 2-methyl-1,3-pentadiene in a microwave oven under various reaction conditions (Table 4.9). The microwave (MW) irradiation does not affect the diastereoisomeric ratio of adducts trans/cis = 70 30) but dramatically reduces the reaction time. The glyoxal monoacetal, for instance, gives 82 % adducts after 5 minutes when submitted to irradiation with an incident power (IP) of 600 W in PhH and in the presence of ZnCL (Table 4.9, entry 1), while no reaction occurs if carried out for 4h at 140 °C in sole PhH. Similarly, methylgloxylate in water at 140 °C gives 82% adducts after 3h, whereas microwave irradiation reduces the reaction time to 8 minutes (Table 4.9, entry 5). 

Almena I., Carrillo J. R., De la Cruz P., Diaz-Ortiz A., Gomez-Escalonilla M. J., De la Hoz A., Langa F., Prieto P., Sanchez-Migallon A. Application of Microwave Irradiation to Heterocyclic Chemistry Targets Heterocyclic Systems-Chemistry and Properties 1998 2 281-308, Eds. Attanasi O. A. and Spinelli D., Pb. Soc. Chim. Ital. Keywords Diels-Alder reactions, [60]-fullerene... 

Metallocenes Mg(II)-catalyzed Microwave irradiation MO calculation Montmorillonite Moraceous plants Morphinadienes Mulberry tree Multifunctional catalysis Multi-step... 

Benzenediamine (185) and benzoin (186) gave a separable mixture of 2,3-diphenyl-1,2-dihydroquinoxaline (187, R = Ph) and 2,3-diphenylquinoxaline (188, R = Ph) (dry mixture, microwave irradiation under reflux, 4 min 21% and 67%, respectively) in contrast, similar treatment with m,m -dichloro-benzoin gave only the aromatized product, 2,3-bis(m-chlorophenyl)quinoxa-line (188, R = C6H4Cl-m) (94%). ... 

Like oxalic acid, oxalic esters and o-phenyldiamines give 2,3(l//,477)-quinox-alinediones that bear substituents according to those on the substrate such condensations appear to be assisted substantially by microwave irradiation. 

In a less straightforward way, D-glucose (393) underwent a Maillard-type reaction with an excess of glycine (394) under microwave irradiation to afford 5-hydroxy-l,3-dimethyl-2(l/f)-quinoxahnone (395) as a major product, Repetition with labeled reactants suggested that the product contained six carbon atoms from the sugar and four from the amino acid on this evidence, a detailed mechanism has been postulated. 

There is sfill some dispufe about how microwave irradiation accelerates reactions. Besides the generally accepted thermal effects, one beheves that there are some specific (but also thermal) microwave effects, such as the formation of hot spots . There is still some controversy about the existence of non-thermal (athermal) microwave effects. At the present time, new techniques such as coohng while heating are being investigated and the problem of upscahng... 

In the 1990s the technique of solid-phase organic synthesis (SPOS) became generally popular, but especially in the medicinal chemistry community, for lead detection and lead optimization via combinatorial techniques. The combination with microwave irradiation brought an elegant solution for the problem of the notoriously slower reactions compared to those in solution phase. 

Scheme 11 Chloro dehydroxylation of 4-hydroxy-2-qninolones under microwave irradiation...

The use of microwave irradiation for this reaction, compared to conventional thermal heating, was investigated. Chloroform used as solvent under the conventional heating did only allow a temperature of 60 °C and a direct comparison between the two methods is therefore somewhat unfair imder these circumstances. Nevertheless, the microwave-assisted method is attractive and proved useful for both primary and secondary amines resulting in highly substituted pyrazolo ring-fused pyridones 40 in 68-86% yields within only 10 min. 

Scheme 12 Bromination of 2-quinolones using NBS and microwave irradiation...

When position 6 on the 2-quinolone is blocked, bromination takes place selectively at the 3-position. Thus, microwave irradiation of 45 in acetonitrile at 150 °C for 50 min afforded the 3-bromo-quinolin-2(lff)-one 46 in 87% yield (Scheme 12). 

The Suzuki reaction has been successfully used to introduce new C - C bonds into 2-pyridones [75,83,84]. The use of microwave irradiation in transition-metal-catalyzed transformations is reported to decrease reaction times [52]. Still, there is, to our knowledge, only one example where a microwave-assisted Suzuki reaction has been performed on a quinolin-2(lH)-one or any other 2-pyridone containing heterocycle. Glasnov et al. described a Suzuki reaction of 4-chloro-quinolin-2(lff)-one with phenylboronic acid in presence of a palladium-catalyst under microwave irradiation (Scheme 13) [53]. After screening different conditions to improve the conversion and isolated yield of the desired aryl substituted quinolin-2( lff)-one 47, they found that a combination of palladium acetate and triphenylphosphine as catalyst (0.5 mol %), a 3 1 mixture of 1,2-dimethoxyethane (DME) and water as solvent, triethyl-amine as base, and irradiation for 30 min at 150 °C gave the best result. Crucial for the reaction was the temperature and the amount of water in the... 

Hydrolysis of nitriles normally requires quite harsh conditions and long reaction times [101,102]. Applying microwave irradiation for this type of re-... 

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