Formaldehyde and its Substituted Derivatives

Formaldehyde and its Substituted Derivatives.—Interest in the inorganic chemistry of formaldehyde and its substituted derivatives appears to be declining. Indeed, very few papers in which their properties are described have been published during the period of this Report. The majority of those abstracted are considered in the following sub-sections studies in which spectroscopic data are reported, however, have been collated in Table 8. 

Ab initio calculations on complexes formed between lithium cations and formaldehyde show that the most stable configuration is characterized by an interaction of 43.2 kcal mol, C symmetry, and an oxygen-lithium distance of r(Li—O) = 1.77 A. Detailed analysis of the electron-density function gives proof of the electrostatic nature of the complex and shows extensive mutual polarization. 

The bonding, energetics, and geometry for the ground and several excited states of thioformaldehyde have also been investigated by cd initio MO calculations. The calculated molecular parameters are in good agreement with the microwave structural results (Table 15). In contrast to formalde- 

Theoretical analysis of the vibrational spectra of FgCO, CI2CO, and BraCO and the electronic spectra of (CN)2CO has been attempted the hyperfine structure on certain rotational transitions in F2CO has been observed using a molecular beam maser spectrometer,  

A number of inorganic reactions involving both formaldehyde and carbonyl fluoride have been reported during the period of this Report. The 

A total of four examinations of the photochemistry of formaldehyde have been described. A detailed analysis of the photochemical decomposition of gaseous HgCO has been carried out over a wide range of experimental conditions. The proposed reaction mechanism, which gives reasonable agreement with the experimental results, is based on the two primary processes (16) and (17) together with the secondary reactions (18)—(23). Predissocia- 

---

Formaldehyde and its Substituted Derivatives.—Formaldehyde, Carbonyl Halides, etc. Despite the general decrease in the number of publications in this field, the high proportion describing the spectroscopic properties of these molecules has been maintained these, together with the corresponding publications for formic acid and formates, are collected in Table 9. The... 

Table 9 Spectroscopic studies of formaldehyde and its substituted derivatives...

Since 1994, pyridinium and its substituted derivatives have been identified as effective and stable homogeneous electrocatalysts for the aqueous multiple-electron, multiple-proton reduction of CO2 to various products, such as formic acid, formaldehyde and methanol. Particularly high Faradaic yields were reached in the reduction of CO2 to methanol in both electrochemical and photoelectrochemical systems under energetically advantageous conditions [149]. 

The Eschweiler reaction (formaldehyde and formic acid) has been used for the pyr-A-methylation of l-methyl-l,2,3,4-tetrahydro-j8-carboline, as has formaldehyde and hydrogen in the presence of Raney nickel. Tetrahydroharmine has been reported to react with benzaldehyde to yield a condensation product, C33H36N403, which is presumably a pyr-iV-substituted derivative (318). It is not known whether a similar condensation product of benzaldehyde with harm-aline is a C- or V-substituted derivative of harmaline. Conden-... 

Resole syntheses entail substitution of formaldehyde (or formaldehyde derivatives) on phenolic ortho and para positions followed by methylol condensation reactions which form dimers and oligomers. Under basic conditions, pheno-late rings are the reactive species for electrophilic aromatic substitution reactions. A simplified mechanism is generally used to depict the formaldehyde substitution on the phenol rings (Fig. 7.21). It should be noted that this mechanism does not account for pH effects, the type of catalyst, or the formation of hemiformals. Mixtures of mono-, di-, and trihydroxymethyl-substituted phenols are produced. 

Pr)4, " borohydride-exchange resin,and formic acid. When the last is used, the process is called the Wallach reaction. Conjugated aldehydes are converted to alkenyl-amines with the amine/silica gel followed by reduction with zinc borohydride.In the particular case where primary or secondary amines are reductively methylated with formaldehyde and formic acid, the method is called the Esch-weiler-Clarke procedure. It is possible to use ammonium (or amine) salts of formic acid, " or formamides, as a substitute for the Wallach conditions. This method is called the Leuckart reaction,and in this case the products obtained are often the N-formyl derivatives of the amines instead of the free amines. Primary and secondary amines can be iV-ethylated (e.g., ArNHR ArNREt) by treatment with NaBH4 in acetic acid. Aldehydes react with aniline in the presence of Mont-morillonite KIO clay and microwaves to give the amine. Formaldehyde with formic acid converts secondary amines to the N-methyl derivative with microwave irradiation. 

Hydroxypyridine reacts with formaldehyde and base to give the 2-hydroxymethyl derivative which reacts further, ultimately to yield the 2,6-disubstituted product. No 4-substitution is detected in this case or with 3-hydroxy-2,6-dimethylpyridine when it is treated under the same conditions (75RCR823). 3-Hydroxypyridine readily undergoes bis-aminomethylation at the 2- and 6-positions. 

Most pyrogallol derivatives did not precipitate either (Table III). A small precipitation occurred with pyrogallol (which may be considered as a hydroxyresorcinol) and it reacts with vanillin/HCl also (7). However, any additional substitution eliminates this reactivity, e.g., gallic acid (Table IV). Purpurogallin did precipitate with formaldehyde. It is not very soluble in the reaction mixture, and it is a tropolone. Structures of this type might interfere, but in tea and probably in wine the known tropolone derivatives are flavonoids (I, 25). 

Chloromethylation of selenophene, like other electrophilic substitutions, occurs at the a position, and 2-chloromethylselenophene is formed together with small amounts of the 2,5-bischloromethyl derivative. Selenophene and its homologs have been chloromethyl-ated by diverse reagents formalin and hydrogen chloride, a mixture of mono- and bischloromethyl ether, or formaldehyde bischloro-methylacetal. A mixture of mono- and bischloromethyl ether is the most convenient reagent. 

Substituted diarylmethanes have been prepared from formaldehyde and a variety of its derivatives. Sulfuric acid is a common catalyst. The procedure described is based on the general method of Gordon, May, and Lee. Formic acid is preferable to sulfuric acid as a catalyst because it is capable of acting as a solvent as well, thus eliminating troublesome emulsions. Side reactions such as sulfonation are avoided. 

The related Mannich reaction is not common. Under the usual acidic reaction conditions TV-substitution occurs, but this is a reversible reaction in the presence of base. Therefore, in basic medium, C- substituted products accumulate, and all positions can be substituted. 2-Methylimidazole gives 1,4,5-tri, 4,5-di- and 4-mono-substituted products. The observation that with formaldehyde and hydrochloric acid histamine gave (98) is at variance with the apparent requirement for basic medium. Since 1-substituted imidazoles do not react it is likely that the imidazole conjugate base is the reactive species. Unless imidazoles contain activating substituents they are not very susceptible to reaction with aldehydes (except HCHO) and ketones. An exception appears to be the product (99) of interaction between imidazole and hexane-2,4-dione. An activated compound such as 4-methylimidazoline-2-thione gives the 5-dimethylamino compound (100) imidazoline-2-thione gave only the (V-hydroxymethyl product under the same reaction conditions. Imidazolin-4-ones with a free 5-position readily form benzylidene derivatives (B-76MI40701). 

The reduction of benzoic acids affords the dienolate (77) which may be alkylated in situ by a variety of electrophiles to afford 1-substituted derivatives. Clearly, the addition of alcohol must be avoided or limited to small quantities. It may also be necessary to remove the ammonia before adding the electrophile. The vast majority of applications have been based on reactions with alkyl halides to form (78), but additions of (77) to formaldehyde, epoxides and a,p-unsaturated esters to form the range of adducts (79) to (81) have also been reported (Scheme 14). 

---