Furoic acids, oxidation

Furfural can be oxidized to 2-furoic acid [88-14-2] reduced to 2-furanmethanol [98-00-0] referred to herein as furfuryl alcohol, or converted to furan by decarbonylation over selected catalysts. With concentrated sodium hydroxide, furfural undergoes the Cannizzaro reaction yielding both 2-furfuryl alcohol and sodium 2-furoate [57273-36-6]. 

Therapeutics. Compounds containing the furan or tetrahydrofuran ring are biologically active and are present in a number of pharmaceutical products. Eurfurjdamine [617-89-0] is an intermediate in the diuretic, furosemide. Tetrahydrofurfurylamine [4795-29-3] may also have pharmaceutical applications. 5-(E)imethyiaininomethyi)furfuryi alcohol [15433-79-17 is an intermediate in the preparation of ranitidine, which is used for treating ulcers. 2-Acet5dfuran [1192-62-7] prepared from acetic anhydride and furan is an intermediate in the synthesis of cefuroxime, a penicillin derivative. 2-Euroic acid is prepared by the oxidation of furfural. Both furoic acid [88-14-2] and furoyl chloride [527-69-5] are used as pharmaceutical intermediates. 

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

Putan (Coll. Vol. i, 269) From furoic acid, by an adaptation of the method of Gilman and Louisinian (using quinoline and copper oxide), in 90 per cent yield (crude). Wagner and Simons, J. Chem. Education 13, 27a (1936). 

Furoic acid has been made by oxidation of lactose followed by pyrolysis, by the oxidation of 2-acetylfuran, 2-methylfuran, or furfuryl alcohol using potassium ferricyanide in alkaline medium, and by other methods already listed. ... 

Furoic Acid (Coll. Vol. r, 270) Furfural is oxidized with oxygen in the presence of an activator, consisting mainly of silver, in dilute sodium hydroxide solutions. U. S. pat. 2,041,184 [C. A. 30, 4515 (1936)]. 

Ring contractions of pyran derivatives are occasionally valuable. The contraction of 3-halo-2-pyrones to 2-furoic acids under the influence of alkali has been studied and the conditions defined.58112113 The method is adaptable to the preparation of 3-furoic acid via furan-2,4-dicarboxylic acid58 and of 3,4,5-triphenylfuran-2-carboxylic acid.113 Another ring contraction involving halides is the conversion of 4-chloromethylpyrylium salts into furylmethyl ketones as indicated in Scheme 21.114 Pyridine oxides may be transformed with unexpected ease into furans through treatment with a thiol (Scheme 22).115... 

XXXVI) from this sirup have been unsuccessful. Instead, 2-formyl-5-methyl-3-furoic acid (XLIX) has been obtained. Apparently, oxidation proceeds beyond the stage of glycol cleavage, as with the benzimidazole... 

As an example, a convenient preparation of methyl (E) and (Z)-4,4-dimethoxybutenoa-tes can be performed by anodic oxidation of furfuryl alcohol, furfural or furoic acid via a dimethoxylated dihydrofuran intermediate (Scheme 132) [157]. 

After the autoclaving (100°) of D-glucose solutions, both 5-(hydroxy-methyl)-2-furoic acid and 2,5-furandicarboxylic acid were detected. No attempt was made to remove oxygen from the starting solutions. Although the D-glucose solution was not initially acidic, subsequent experience indicated that the final pH was probably 4. Air exposure (mild oxidation) of the mixtures increased the two furancarboxylic acids at the expense of 11. 

Formylfuran on oxidation gives furoic acid (Scheme 6.32), which shows reactions resembling those of benzoic acid. 

Diloxanide was first prepared by the reaction of 4-hydroxy-A-methyl aniline with sodium cyanide and chloral hydrate in the presence of a base [9]. Furoic acid was prepared by the hypochlorite oxidation of... 

D-glucose or D-fructose into 5-(hydroxymethyl)-2-furaldehyde in solution in acidified deuterium oxide.17 The 2-furaldehyde was isolated as 5-(hydroxymethyl)-2-furoic acid, and thus this experiment did not permit an evaluation of reversible equilibration of 1,2-enediols with the parent sugars. However, the 2-furoic acid was devoid of measurable carbon-bound deuterium, which indicated the absence of 3-deoxyglycosulose intermediates. It is also noteworthy that 3-deoxy-D-en/fhro-hexosulose is converted, in acidified deuterium oxide, into 5-(hydroxymethyl)-2-furaldehyde with no solvent exchange84 this result lends further support to the conclusion that 45 does not participate in the reaction as an intermediate. 

Nitrofuvan, OCH=CH—C(NOa)=CH mw 113-075, N 12.39% crysts, mp 27°. Prepd by heating 3-nitro-2-furoic acid, which was prepd by oxidizing 3-nitro-2-methylfuran with K3Fe(CN)6/KAc at 100°... 

Methyl-2-furoic acid has been prepared by the oxidation of 3-methyl-2-furaldehyde 4 and by the degradation of 3-methyl-2-isovalerylfuran (Elsholtzia ketone).5 3-Methylfuran has been prepared by the present method 6 and more recently by a three-step method starting with methallyl chloride and ethyl orthoformate.7 Circuitous routes from citric acid 8 and malic acid 9 have also been used. 

Acetyl furan [1192-62-7], prepared from acetic anhydride and furan is an intermediate in the synthesis of cefuroxime, a penicillin derivative. 2-Furoic acid is prepared by the oxidation of furfural. Both furoic acid [88-14-2] and furoyl chloride [527-69-5] are used as pharmaceutical intermediates. 

Furoic acid (furan-2-carboxylic acid, or pyromucic acid) is used as a bactericide, and the furoate esters are used as flavoring agents, as antibiotic and corticosteroid intermediates. It is obtained by the enzymatic or chemical/catalytic aerobial oxidation of furfural (2-furalaldehyde) the latter is the only unsaturated large-volume organic chemical prepared from carbohydrates today. D-Xylose and L-ara-binose, the pentoses contained in the xylan-rich portion of hemicelluloses from agricultural and forestry wastes, under the conditions used for hydrolysis undergo dehydration to furfural. 

The oxidation of furans has often been used to express the latent functionality present within this heterocyclic framework, and it results particularly attractive for the synthesis of the widespread butenolides [8c,56]. Dye-sensitized photo-oxygenation of furfural, furoic acid and a- or a,a -unsubstituted furans leads directly to butenolides [8c,56,60d,63]. The presence of a silyl group in a-position enhances the rate of endoperoxide formation and controls the regiochemical outcome of the second-step leading to the related butenolide via a rapid intramolecular silatropic shift [64]. An application of this reaction is shown in Sch. 39 as a step in the synthesis of spongianolide A, an antitumoral natural sestertepenoid [65],... 

The furoic acid may be obtained from furfural by means of the Cannizzaro reaction 2 or by oxidation with alkaline potassium permanganate.3 It is important to purify the furoic acid to a melting point of 131-132°. 

Furan carboxylic acids usually decarboxylate readily, and this method is often used in the laboratory for the preparation of furans. Furan itself can be obtained in good yield from 2-furoic acid in quinoline, with a copper catalyst, while industrial methods employ the catalytic decarbonylation of furfural. Copper powder, copper oxide or copper bronze, or heavy metal oxides,22 are the best catalysts, in combination with quinoline as solvent and weak base.23-28 Dann et al,2fl decarboxylated 2,5-dimethyl-3-furoic acid in 50% yield using barium hydroxide. 3-Furoic acid, which is difficult to obtain in large quantities, is best prepared by controlled decarboxylation of the easily prepared furan tetracarboxylic acid. 

The well-known conversion of certain furans into lactones has been further studied recently. 2-Furoic acid, which was labeled in the carboxyl group, gave radioactive C02 when oxidized by bromine water to mucobromic acid.341... 

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