125. The Reimer–Tiemann reaction

Preparation and characterization of PbO/carboxymethyl cellulose/polyvinylpyrrolidone nanocomposite films

“…Figure a–d reveals the dependence of the dielectric constant ( ) of pure CMC, CMC/PVP blend, 2 and 4 wt%PbO/CMC/PVP nanocomposite films on the frequency ( f ) at different temperatures. The dielectric constant has higher values at low f due to the charge carrier's accumulation near the electrodes . As f increases, decreases, i.e., the polarization decreases or the number of dipoles decreases.…”

“…The values of E a for the investigated films are presented in Table 3. These values depend [52]. As f increases, E 0 decreases, i.e., the polarization decreases or the number of dipoles decreases.…”

Acid catalyzes the synthesis of aromatic gem-dihalides from their corresponding aromatic aldehydes

“…Replacing acetyl chloride with acetyl bromide and its addition to benzaldehyde (entry 4) and p-tolualdehyde (entry 6) yielded only benzal bromide and 4-methylbenzal bromide instead of benzal chloride and 4-methylbenzal chloride. The exclusive formation of the corresponding gam-dibromides when acetyl bromide was used in the presence of AlCl 3 indicates that the Lewis acid acts as a catalyst and not as a chlorinating reagent as other inorganic chlorides [15][16][17], as concluded from the blank reaction with AlCl 3 (entry 1). For both substrates, the detected product yields, which were calculated based on a benzal bromide commercial standard, were higher than the yields obtained with acid chlorides, probably due to the higher activation of acid bromides in the presence of an acid catalyst.…”

“…The reaction proceeded in two representative solvents, dichlorobenzene (DCB), which was chosen as a solvent since it dose not react in the presence of acid catalyst, and excess of benzaldehyde as a self solvent. Inorganic chlorides such as PCl 5 and BCl 3 react with benzaldehyde to form benzal chloride [15][16][17] but can also act as Lewis acids. Therefore, the blank reaction of benzaldehyde with AlCl 3 was initially tested to determine if there is any dihalo-de-oxo-bisubstitution between benzaldehyde and AlCl 3 .…”

“…Generally, ␣,␣-dihalotoluenes can be produced by catalytic or non-catalytic halogenation of toluene or halomethylation of benzene [14], however benzyl chloride is mostly the main product and trichlorobenzene is also formed. Alternatively, benzaldehyde can be reacted with several inorganic chlorinated reagents such as PCl 5 [15], BCl 3 [16] and SOCl 2 [17] to form the corresponding gem-dihalides by dihalo-de-oxobisubstitution. Yet, when PCl 5 is replaced by PBr 5 it does not give good yields of gem-dibromide.…”