Aldehydes from formic esters

Aldehydes from Formic and Ortho-formic Esters. /0M°X + HC1... 

On the other hand, 1,1,1-trisubstituted alkanes behave similarly to aldehydes, yielding pyrjdium salts (128) with identical substituents in positions 2 and 6. Thus, Dorofeenko and co-workers condensed 2 moles of acetophenone with 1 mole of benzotrichloride in the presence of perchloric acid obtaining 2,4,6-triphenjdpjTylium perchlorate with 1 mole of ethyl orthoformate, they obtained 2,6-diphenyl-pyrylium perchlorate (57) from o-hydroxyacetophenone, ortho-formic ester and perchloric acid, 4-ethoxybenzopyrylium perchlorate was formed. 

The reaction sequence is called the Regitz diazo transfer and requires active methylene compounds as substrates/ Hence it is common to use formic esters to create P-carbonyl compounds from ketones or aldehydes in an aldol reaction. These are used as substrates for deformy-lative diazo transfer reactions in which the diazo group is transferred and the formyl group is removed in one concerted step. The mechanism of the deformylative diazo transfer is shown below. In this case the bulky base NaHMDS ensures deprotonation at the less-hindered a-position of 3, forming the so-called kinetic enolate 13. This enolate is formylated by ethyl formate yielding the P-formyl ketone 14, which is used as substrate in the deformylative diazo transfer. 

It is true that, for instance, one does not find under the keyword aldehyde the preparation of benzaldehyde (a) from toluene by way of benzyl chloride or benzaldehyde dichloride, (b) from benzene and hydrogen cyanide-hydrogen chloride (Gattermann-Koch) or from bromobenzene by way of phenyl-magnesium bromide and formic ester (Grignard), and (c) from stilbene and ozone or from 1,2-diphenyl-1,2-ethanediol and lead tetraacetate but such a collection of syntheses is to be found in the systematic textbooks and reference works of organic chemistry, and the compass of the large reactions remains nevertheless substantially intact in our treatment. 

Aromatic amines, like phenols, are very easily nitrated. However, primary and secondary amines in particular readily undergo oxidative side reactions, so that it is advisable to protect the amino group by acylation or by conversion by an aldehyde into the Schiff base. Even using a large excess of sulfuric acid protects the amino group to a considerable extent, owing to formation of the ammonium salt, but then entry of the nitro group is directed to a considerable extent into the meta-position. The usual A-acyl derivative is the acetyl compound, but benzoyl, /7-toluenesulfonyl, oxalyl, ethoxycarbonyl (from chloro-formic ester), and phthaloyl derivatives are also used. 

The aldehyde (5) can be made in high yield from the amidine (6) via the unisolated 2-dichloromethylimidazole (Scheme 2.2.3). Dichloroacetonitrile is converted into its imidate with methanolic sodium methoxide, and then into the amidine with aminoacetaldehyde dimcthylacetal. When (6) is heated in formic acid it is converted almost quantitatively into the 2-carbaldehyde the use of trifluoroacctic acid at reflux gives around 60% of (5). Using essentially the same method, imidazole-2-carboxylic acid and its ethyl ester can also be made veiy efficiently when trichloroacctonitrilc and the acetal arc used to prepare the amidine [16],... 

From Acetic and Formic Acids.—A fourth method of synthesis from acetic and formic acid esters will be explained in detail in connection with the next acid. All of these syntheses prove the constitution of pyro-racemic acid as an a//>/fa-ketone acid as given. It may be considered as aceto formic acid which is in accord with the fourth method of synthesis. As an acid it forms all acid derivatives and as a ketone it undergoes the characteristic ketone reactions, e.g.y with phenyl hydrazine and hydroxyl amine. On heating to 150° with dilute sulphuric acid in a sealed tube it loses carbon dioxide and yields acet aldehyde. 

The pyrolytic oxidation of the esters generates mainly the esterifying acid and, when the acid has a longer chain, some aldehydes and acids with shorter chain length but which are formed from the esterifying acid. Formaldehyde, formic acid, CO2, CO, etc. are formed from the glucose units. 

The Aldehydic protons of the Formic Acid esters appears as a sharp singlet at low field in the range from 7.9 to 8.10 ppm. 

Carbonyl compounds, carboxylic acids, and esters of a wide variety of types have been isolated from surface waters. Aldehydes and ketones are produced during the photolysis of larger polymers such as humic materials formaldehyde, acetaldehyde, and glyoxal appear to be the most abundant in seawater samples (Kleber and Mopper, 1990). Low molecular weight mono-, di-, and tricarboxylic acids such as acetic, formic, lactic, glycolic, malic, and citric acids have been reported by many investiga-... 

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