Hydroxyaldehydes phenols

GattermaDD synthesis A method for the synthesis of aromatic hydroxyaldehydes. E.g. AICI3 is used to bring about the condensation of phenol with a mixture of gaseous hydrochloric acid and hydrocyanic acid an aldimine hydrochloride is formed and on hydrolysis gives p-hydroxybenzaldehyde... 

Lemon, H. W. The Effect of Alkali on the Ultraviolet Absorption Spectra of Hydroxyaldehydes, Hydroxyketones and other Phenolic Compounds. J. Amer. chem. Soc. 69, 2998 (1947). 

Accordingly, where possible (for the p-hydroxybenzaldehydes), the aluminium chloride method (Reaction XXVIII.) should be used. The yields are better, the reactions go more smoothly, little resin being formed, while pyrogallols and naphthols, etc., also react. Unfortunately, though the non-formation of other than p-hydroxyaldehydes is often an advantage, it limits the scope of the reaction and necessitates the use of the Reimer method in many cases. It should be noted that the nitro-phenols do not condense with chloroform (B., 9, 423, 824 10, 1562 15, 2685). 

Phenols are smoothly converted into phenolic aldehydes by reaction with chloroform in the presence of base (the Reimer-Tiemann reaction). This overall formylation reaction is of interest in that it involves the generation from chloroform and alkali of the reactive intermediate, dichlorocarbene (2). This effects electrophilic substitution in the reactive phenolate ions giving the benzylidene dichloride (3) which is hydrolysed by the alkaline medium to the corresponding hydroxyaldehyde. The phenolic aldehyde is isolated from the reaction medium after acidification. 

Today an unequivocal determination of substituent positions on a phenol or naphthol or hydroxyaldehyde by infrared and NMR spectroscopy is usually straightforward and should always be performed routinely the major or most easily isolated product is sometimes not the expected one For example, the most easily isolated product (the first to crystallize) from a Reimer-Tiemann reaction of 3-chlorophenol is 6-chlorosalicylaldehyde, and not the 4-chloro isomer, which is the major product. 

Mannich bases formed from formaldehyde, secondary amines and ort/io-derivatives of phenol and Schiff bases derived from aromatic ort/io-hydroxyaldehydes are treated as rather convenient model systems to study intramolecular proton transfer . 

This list has to be continued by the Dakin rearrangement, which is the oxidation of aromatic ortho- or para-hydroxyaldehydes with H2O2 in the presence of alkali to afford polyhydric phenols (equation 133). 

Hexamethylenetetramine/hydrogen chloride Ar. hydroxyaldehydes from phenols... 

---