Benzal bromide

XfjT Conversion m-nitro toluene Conversion bromine Selectivity benzyl bromide Selectivity benzal bromide Selectivity side product... 

Fig. 6 High p,T operation for the radical side-chain bromination of m-nitro toluene in a micro-mixer-reactor setup. The large increase in operational temperature increases conversion at good selectivities, which tend to decline slightly with temperature. The two-fold substituted product, m-nitro toluene benzal bromide, is formed in larger amounts at temperatures above 200°C (IMM, unpublished results)...

Molar ratios of bromine to m-nitrotoluene ranging from 0.25 to 1.00 were applied. The reactants were contacted in an interdigital micro mixer followed by a capillary reactor. At temperatures of about 200°C nearly complete conversion is achieved (see Fig. 6). The selectivity to the target product benzyl bromide is reasonably high (at best being 85% at 200°C and higher being 80%). The main sideproduct formed is the nitro-substituted benzal bromide, i.e. the two-fold brominated side-chain product. 

Behenyl alcohol, d817 Benzal bromide, dl32 Benzal chloride, d273 Benzalphthalide, bl05 Benzeneacetaldehyde, p77... 

Moss and Pilkiewicz (1974) used crown ethers to determine the freeness of carbenic species by comparing the relative reactivities of various alkenes towards phenylbromocarbene [192], generated either by treatment of benzal bromide [194] with t-BuOK or by photolysis of phenylbromodiazirine [193]. The results (Table 48) show that the reactive species produced by these... 

Benzal bromide, dl02 Benzalphthalide, blOl Benzanthrone, b8 Benzeneacetaldehyde, p76a... 

The reaction can be operated as a two-phase system in this case the process can be employed at the reflux temperature of the solvent. It should be noted that in some cases, no solvent need be used296 and this is especially efficacious where mono-brominated products are the target. An example of the system s versatility in solvent-free mode can be seen in Table 3.7. Here we see that at a molar ratio of 1 1.1 1 (hydrogen peroxide/hydrogen bromide/2-nitrotoluene) over 90% selectivity to the benzyl bromide is observed at a conversion of 76%. However, increasing the oxidant ratio to 3 3.2 1 (hydrogen peroxide/hydrogen bromide/2-nitrotoluene), a selectivity of 98% to the benzal bromide is afforded. Diphenylmethane can be fully converted to oxidized products with 96% selectivity to the benzophenone compound.297... 

Demethylation of methoxybenzaldehydes. BI3 is more reactive than BCI3 (2, 34-35 4, 43) and cleaves methoxyl groups of aromatic aldehydes regardless of the position. BBr, is also effective but this reagent can convert benzaldehydes into benzal bromides. ... 

A carbenoid is formed when potassium t-butoxide reacts with benzal bromide in benzene. The reactivity of the carbenoid, 4-31, is similar to that of phenylbromocarbene. The exact nature of the interaction between the carbenoid carbon and the metal halide, in this case potassium bromide, is not known. 

Arylcyclopropanes from Benzal Bromides, Alkenes and Alkyllithium General Procedure ... 

In a 25-mL round-bottom flask, equipped with an addition funnel and magnetic stirrer bar, was placed cyclohexene (10 mL). The flask was cooled to — 20 C in an ethene glycol/dry-ice slush bath, and then benzal bromide (0.50 mL, 0.75 g, 3.0 mmol, 1 equiv) was added. The solution was stirred and 1.6 M BuLi... 

The reaction of an alkene with bromo(phenyl)carbene (or carbenoid), generated from di-bromo(phenyl)methane (benzal bromide) and potassium ter -butoxide, afforded 1-bromo-l-phenylcyclopropanes (Houben-Weyl, Vol. 4/3, pp232-233, and Vol. E19b, p998). The reactions were carried out by shaking all components (10- 12 equivalents of an alkene) in a sealed tube at ca. 25°C for 50-70 hours. ... 

Under SbCls catalysis oxygen-bromine exchange between benzaldehyde and o-chlorobenzal bromide proceeds at 100 °C to give benzal bromide and o-chlorobenzaldehyde in moderate yields [88]. Isomeric transformation of perfluorinated epoxides to the corresponding carbonyl compounds occurs in the presence of SbFs [89]. Isomerization of polyfluorinated olefins, cyclohexadienes, and cyclopropanes is also promoted by the action of SbFs [90]. 

Bamford-Stevens reaction, 109 Beckmann fragmentation, 133 Beckmann rearrangement, 230-231 Benzalacetone, 240, 241 Benzalacetophenone, 106, 206 Benzalaniline, 106, 205, 206 Benzal bromide, 67... 

The sulfonamide method has been used to prepare aza-crowns with a methylene unit between nitrogen atoms or nitrogen and oxygen atoms. The bis-sulfonamide was reacted with dibromomethane, benzal bromide, or methylene ditosylate (Krakowiak and Kotelko, 1982, 1983a, 1983b, Krakowiak et al., 1983) or with bis-chloromethyl ether (Krakowiak et al., 1984). Unfortunately, the macrocydes were not stable after the Af-tosyl groups were removed. 

Table 8.4. Transition Metal Catalyzed Coupling of Phenylmagnesium Bromide and Benzal Bromide...

The method developed by Garegg et al. [14] to form benzylidene acetals was modified by Oscarson et al. [5], who treated compound 9 with benzal bromide and N-(methylpolystyrene)-4-(methylamino)pyridine (PS-DMAP) in acetonitrile under microwave irradiation conditions to form the 4,6-O-benzylidene derivative 20 (83%) after 5 min (Scheme 12.9). 

The synlanti ratios are always greater in pentane as compared to ether, and differ slightly with benzal bromide and benzal iodide as starting materials. Clearly, the transition state of the carbenoid addition involves lithium halide. The relative rate data, on the other hand, show relatively minor variations with the degree of olefin substitution in both reaction types (Table 19). 

Phenylbromocarbene, generated by diazirine photolysis, is apparently more selective than the corresponding carbenoid from benzal bromide and potassium -butoxide. The electrophilic behavior of the carbenoid may be obscured by steric factors in the reaction with highly substituted olefins, as discussed above. In principle, however, complexation of a singlet carbene may increase or decrease its electrophilicity, depending on whether the com-plexing agent supplies electrons to the vacant p orbital (Lewis base) or withdraws electrons from the occupied sp orbital (Lewis acid). More data on this problem is clearly warranted. 

An interesting chemical proof of the symmetry of this cation was provided by preparing it from C-labelled benzal bromide and then ring-opening the derived triphenylcyclopropenium cation [33] ... 

For example, a ratio of 1.0 1.1 1.0 H202 HBr o-nitrotoluene gives over 90% selectivity to the benzyl bromide at 76% conversion, whereas increasing oxidant ratios to 3.0 3.2 1.0 gives about the same selectivity to the benzal bromide at 100% conversion. Diphenylmethane is oxidised to benzophenone at 96% selectivity, 100% conversion using a ratio of 3.0 3.2 1.0 H202 HBr substrate. 

Benzyl and benzal bromides can be hydrolysed to the corresponding alcohol or aldehyde using a variety of known methods, depending on the substrate. The simplest, allowing ready recycle of HBr, is steam hydrolysis. This is not, however, effective for deactivated substrates, for which more forcing hydrolysis conditions must be applied [143]. Carboxylic acids can be produced by this method via the aldehyde, using methods described in section 9.5.1.4.1. In the case of diphenylmethane or ethylbenzene oxidation, where the product is a ketone, hydrolysis is usually spontaneous under the reaction conditions, and a sub-stoichiometric amount of HBr can be employed [144]. 

---