Formaldehyde, acid catalyzed with aromatic compounds

This reaction was initially studied by von Baeyer in 1872. It is an acid-catalyzed condensation of aromatic compounds with formaldehyde or formaldehyde derivatives. In normal conditions, the reactive benzene derivatives such as phenols and arylamines are applied to condense with formaldehyde however, a small number of less-reactive aromatics have also been used in this reaction, including benzene, toluene, benzyl chloride,biphenyl, iodobenzene, naphthalene, and mesitylene. Although no yields were given in the early studies, it is reasonable to obtain 70-80% yield for this type of reaction. Many other reactions have been developed to synthesize diarylmethanes, including Katritzky s benzotriazole method, Kochi s dealkylative coupling," Fukuzaw s 1,3-propandiol method, and the reduction method. In general, the condensation occurs at the /tflra-position of substituted aromatics. 

The use of silicon-containing phenolic polymers with NDS compounds present as the photoactive polarity switch has been investigated. Formaldehyde condensation polymers with m-trimethyl-silylphenol (19) have been prepared. It is necessary to incorporate phenol as a comonomer in order to decrease the hydrophobicity of these resins so that they are soluble in aqueous base. The maximum silicon content obtainable is around 9% due to the acidolysis of the aromatic carbon-silicon bond during the acid-catalyzed polymerization process. Nevertheless, high resolution images with good oxygen etch resistance are obtained when these resins are formulated into resists with NDS derivatives present. 

Despite its own valuable synthetic potential, the use of [ C2]acetylene as a starting material for various building blocks is of much higher relevance. Mercury(II)-catalyzed hydration, for example, gives [ C2]acetaldehyde (Figure 8.5, Route 1) The same reaction carried out in the presence of ammonium persulfate furnishes [ 2] acetic acid (Route 2). Trapping of its mono- or dianion with formaldehyde or carbon dioxide affords [2,3- C2]propynol, [2,3- C2]butyne-l,4-diol, [2,3- C2]propiolic acid " and [2,3- C2]acetylenedicarboxylic acid, respectively (Routes 3-6). UV irradiation of a mixture of HBr and [ C2]acetylene produces l,2-dibromo[ C2]ethane (Route 8) . Reduction with chromium(II) chloride followed by a two-step epoxidation of the initially formed [ C2]ethylene converts [ 2]acetylene into [ C2]ethylene oxide (Route 7) . Finally, catalytic homotrimerization or co-trimerization with other alkynes provides [ " C ]benzene or substituted [ " C ]benzenes, respectively, the central starting materials for the vast majority of substituted benzenoid aromatic compounds (Route 9). 

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