Preparation of cyanuric and isocyanic acids in a fluidized bed reactor

Dragalov, V. V.; Karachinsky, S. V.; Peshkova, O. Yu.; Kirpichev, V.P.

doi:10.1016/0165-2370(93)80050-a

Cited by 4 publications

(1 citation statement)

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“…7.4 Redistribution reactions between germanium tetrabromide (44b) and tetrabutyl-or tetraphenylgermanes (45) under the action of MW irradiation [15,16]. The reaction usually used to produce cyanuric acid (48) is the thermolysis of urea (47) between 180 8C and 300 8C (Scheme 7.11) [58]. The reaction occurs with formation of ammonia, which itself can react with 48 to give secondary products.…”

Section: Redistribution Reactions Between Tetraalkyl-or Tetraarylgermmentioning

confidence: 99%

Microwave‐Assisted Reactions on Graphite

Laporterie

Marquié

Dubac

2002

Microwaves in Organic Synthesis

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for the processing of polymers and composites in which carbon black or graphite particles or fibers are included in the material [9].The MW-promoted cracking of organic molecules in the presence of silica-supported graphite [10 a] or activated charcoal [10 b] has also been reported.Graphite, the most stable of the three allotropic forms of carbon, has two structures, a (hexagonal form) and b (rhombohedral form), which interconvert easily [11]. In a graphite layer, each carbon atom is strongly bonded to three other carbon atoms in a planar configuration (sp 2 hybridization), and the remaining p electrons (one per carbon) are delocalized. The resulting carbon±carbon bonds are very strong (477 kJ mol ± 1 ). The interlayer bonds, in contrast, are weak (17 kJ mol ±1 ), giving rise to the mechanical (lubricant) and chemical (intercalation) properties of graphite. Electronically, graphite is a semimetal of high electrical and thermal conductivity [11]. As for other semimetallic materials, the electronic current (s) is the main factor in the graphite±MW interaction [5]. The rate of heating of a MW-irradiated material has been estimated to be DT/t = s|E| 2 /rC, where E is the electric field, r is the density, and C is the specific heat capacity of the material [5]. Compared with other dielectric solids graphite has an unusually high thermal conductivity (a weak C, 0.63 kJ kg ±1 K ±1 at room temp.) [11]. This thermal conductivity, which decreases exponentially with increasing temperature, is a determining factor in the high rate of heating of graphite on MW irradiation, although other types of MW interaction, e. g. the excitation of weak interlayer bonds, and, especially in graphite powder, eddy currents or localized plasma effects, can also lead to very rapid dissipation of energy in graphite [5].Because of its strong coupling with MW, its good adsorbent properties towards organic molecules [12], and its layer structure which enables it to form intercalated compounds [13], graphite has great potential in MW-assisted synthetic applications in organic chemistry, despite its weak fractal dimension (D & 2) [14].Before the works of Laurent et al. [15,16], which described several examples of MWassisted organic syntheses in the presence of graphite other studies were reported in this field. Literature results are, therefore, very recent. They are presented here in two parts. The first concerns reactions in which graphite behaves as an energy converter (or ªsensitizerº) capable of conveying the energy carried by MW radiation to the chemical reagents. The second includes results which reveal surprising catalytic activity of some metal inclusions of graphite. Graphite as a SensitizerThis section covers reactions in which graphite is a sensitizer, without participation of its metal inclusions as possible catalysts, although a catalyst can be added to the graphite. The amount of graphite can be varied. It is generally at least equal to and most often greater than that of the reagents, resulting in a graphite-supported/microwave (GS/M...

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Section: Redistribution Reactions Between Tetraalkyl-or Tetraarylgermmentioning

confidence: 99%