Aldehydes aromatic compounds

Saturated ketones Of,/ -Unsaturated ketones Aromatic ketones and aldehydes Aromatic compounds... 

From ehloromethyl or bromomethyl aromatic compounds by heating with hexamethylenetetramine (hexamine) in aqueous alcohol or aqueous acetic acid. A quaternary ammonium compound is formed, which yields the aldehyde upon treatment with water in the presence of hexamine for example... 

The catalyst is inactive for the hydrogenation of the (isolated) benzene nucleus and so may bo used for the hydrogenation of aromatic compounds containing aldehyde, keto, carbalkoxy or amide groups to the corresponding alcohols, amines, etc., e.g., ethyl benzoate to benzyl alcohol methyl p-toluate to p-methylbenzyl alcohol ethyl cinnamate to 3 phenyl 1-propanol. 

Aldehyde Synthesis. Formylation would be expected to take place when formyl chloride or formic anhydride reacts with an aromatic compound ia the presence of aluminum chloride or other Friedel-Crafts catalysts. However, the acid chloride and anhydride of formic acid are both too unstable to be of preparative iaterest. 

High reactivity contaminants phenols, aldehydes, aromatics, amines, some sulfur compounds. 

Heterocyclic enamines A -pyrroline and A -piperideine are the precursors of compounds containing the pyrrolidine or piperidine rings in the molecule. Such compounds and their N-methylated analogs are believed to originate from arginine and lysine (291) by metabolic conversion. Under cellular conditions the proper reaction with an active methylene compound proceeds via an aldehyde ammonia, which is in equilibrium with other possible tautomeric forms. It is necessary to admit the involvement of the corresponding a-ketoacid (12,292) instead of an enamine. The a-ketoacid constitutes an intermediate state in the degradation of an amino acid to an aldehyde. a-Ketoacids or suitably substituted aromatic compounds may function as components in active methylene reactions (Scheme 17). 

The Pictet-Spengler reaction is one of the key methods for construction of the isoquinoline skeleton, an important heterocyclic motif found in numerous bioactive natural products. This reaction involves the condensation of a P-arylethyl amine 1 with an aldehyde, ketone, or 1,2-dicarbonyl compound 2 to give the corresponding tetrahydroisoquinoline 3. These reactions are generally catalyzed by protic or Lewis acids, although numerous thermally-mediated examples are found in the literature. Aromatic compounds containing electron-donating substituents are the most reactive substrates for this reaction. 

II) = which contain no aldehyde group. This is a B band, which occurs in the spectra of all aromatic compounds. 

An important side reaction is the formation of diaryl methane derivatives ArCHaAr. Moreover poly substituted products may be obtained as minor products. Aromatic compounds have been treated with formaldehyde and hydrogen bromide or hydrogen iodide instead of hydrogen chloride. The formaldehyde may be replaced by another aldehyde the term Blanc reaction however stands for the chloromethylation only. 

While the Friedel-Crafts acylation is a general method for the preparation of aryl ketones, and of wide scope, there is no equivalently versatile reaction for the preparation of aryl aldehydes. There are various formylation procedures known, each of limited scope. In addition to the reactions outlined above, there is the Vdsmeier reaction, the Reimer-Tiemann reaction, and the Rieche formylation reaction The latter is the reaction of aromatic compounds with 1,1-dichloromethyl ether as formylating agent in the presence of a Lewis acid catalyst. This procedure has recently gained much importance. 

The reaction of electron-rich aromatic compounds with yV,A -dimethylformamide 2 and phosphorus oxychloride to yield an aromatic aldehyde—e.g. 3 from the substituted benzene 1—is called the Vilsmeier reaction or sometimes the Vilsmeier-Haack reaction. It belongs to a class of formylation reactions that are each of limited scope (see also Gattermann reaction). 

Solution The spectrum shows an intense absorption at 1725 cm- due to a carbonyl group (perhaps an aldehyde, -CHO), a series of weak absorptions from 1800 to 2000 cm-1, characteristic of aromatic compounds, and a C—H absorption near 3030 cm-1, also characteristic of aromatic compounds. In fact, the compound is phenylacetaldehyde. 

Infrared radiation, electromagnetic spectrum and, 419, 422 energy of. 422 frequencies of, 422 wavelengths of, 422 Infrared spectroscopy, 422-431 acid anhydrides, 822-823 acid chlorides, 822-823 alcohols. 428, 632-633 aldehydes, 428. 730-731 alkanes, 426-427 alkenes, 427 alkynes, 427 amides. 822-823 amines, 428, 952 ammonium salts, 952-953 aromatic compound, 427-428, 534 bond stretching in, 422... 

Rearrangement reaction, 138 Reducing sugar, 992 Reduction, 229. 348 acid chlorides, 804 aldehydes, 609-610. 709 aldoses, 992 alkene, 229-232 alkyne, 268-270 amides, 815-816 arenediazonium salt, 943 aromatic compounds and, 579-580... 

The preparation of mesitaldehyde is an example of a generally applicable method for the preparation of aromatic aldehydes by treatment of aromatic compounds with dichloromethyl methyl... 

The mass spectrum of 2-methylbenzaldehyde suggests an aromatic compound because of the intensity of the molecular ion and peaks at m/z 39, 51, and 65 (see Figure 6.2). The loss of hydrogen atoms and loss of 29 Daltons from the molecular ion indicate that this is an aromatic aldehyde. Looking up m/z 91 in Part III suggests the following structure ... 

In Figure 13.2, the intensity of the ion at m/z 170 represents a molecular ion of an aromatic compound. The characteristic losses from the molecular ion (M - 1, M - 28, and M - 29) suggest an aromatic aldehyde, phenol, or aryl ether. The molecular formula of Ci2H 0O is suggested by the molecular ion at m/z 170, which can be either a biphenyl ether or a phenylphenol. The simplest test to confirm the structure is to prepare a TMS derivative, even though m/z 11 strongly indicates the diaryl ether. 

The condensation of aromatic rings with aldehydes or ketones is called hydroxy-alkylation. The reaction can be used to prepare alcohols, though more often the alcohol initially produced reacts with another molecule of aromatic compound (11-12) to give diarylation. For this the reaction is quite useful, an example being the preparation of l,l,l-trichloro-2, 2-bis (p-Chlorophenyl) ethane (DDT) ... 

Apparently, the initial step involves reaction of the aromatic compound with the aldehyde to form the hydroxyalkyl compound, exactly as in 11-22, and then the HCl converts this to the chloroalkyl compound. The acceleration of the reaction by ZnCl2 has been attributed to the raising of the acidity of the medium, causing an increase in the concentration of HOCHj ions. 

Phenols, secondary and tertiary aromatic amines, pyrroles, and indoles can be aminomethylated by treatment with formaldehyde and a secondary amine. Other aldehydes have sometimes been employed. Aminoalkylation is a special case of the Mannich reaction (16-15). When phenols and other activated aromatic compounds are treated withA-hydroxymethylchloroacetamide, amidomethylation takes place " ... 

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