2-Furaldehyde preparation

It is not necessary that the intermediate be separated from the reaction medium in the preparation of the end product. Instead, the reaction mixture, after cooling, is treated with 200 ml of water acidified with 42 ml 10% hydrochloric acid solution, and filtered. To the clear, light yellow filtrate is added dropwise a solution of 9.B g (0.07 mol) 5-nltro-2-furaldehyde in 100 ml ethyl alcohol. An orange solution of the hydrochloride results. The free base is precipitated asyellow plates by making the solution basic with saturated sodium carbonate solution. 14 g of the compound is filtered off by suction, washed with alcohol, and dried. The yield, MP 204°C to 205°C (dec.), is 53% of theoretical based on 3-(N-morpholinyl)-1,2-epoxy-propane. Recrystallization from 95% alcohol (75% recovery) raises the melting point to 206°C (dec.). 

Furaldehyde is a classical example of such thermodynamically unfavoured monomers . Its strong conjugation with the ring is well represented by a carbonyl frequency at about 1670 cm-1 and the best indication of its reluctance to polymerize is simply the fact that, despite many attempts and some claims of success, no one has in reality been able to prepare a polyacetal with the structure given below ... 

A more general reaction between kojic acid and aldehydes is a trimolecu-lar condensation discovered by Barham and Reed." By a process of elimination, they arrived at the conclusion that C6 of kojic acid was most probably the point of attack two molecules of kojic acid reacted with one molecule of the aldehyde, with the elimination of one molecule of water, giving a product of structure LXXV. Such compounds were prepared from kojic acid and the following aldehydes the normal alkanals from formaldehyde to heptanal, benzaldehyde, cinnamaldehyde, hydrocinnamaldehyde, 2-furaldehyde, and acrolein. The compound derived from kojic acid and benzaldehyde (LXXV, R = phenyl) was also obtained by treating LXXII (R = phenyl) with hot, aqueous sodium carbonate.92... 

All of the possibilities mentioned are credible perhaps each participates to some extent in the reaction. No studies similar to those with aldoses have been made of substituted uronic acids, and no intermediates have been isolated. Aso,96 who first suggested 72 as a precursor for 2-furaldehyde and reductic acid,92 has prepared 72, but its significance in the decarboxylation reactions has not been fully examined.123... 

Aso98 first proposed 5-hydroxy-2-oxo-3-pentenal (94) as an intermediate in the conversion of uronic acids to reductic acid,190 191 but this proposal does not appear to have been experimentally tested, although the intermediate was prepared.190 Isbell121 suggested a mechanism in which the formation of reductic acid and 2-furaldehyde from pentoses and uronic acids results from the reaction of different tautomers of 94. Although other mechanisms have been suggested,100 102 115 Isbell s original scheme seems adequate to explain the experimental facts. 

The 2(/ )-tetrahydro-2-furaldehyde (112) is reduced115 by sodium borohydride to the corresponding alcohol (114). 2,5-Dihydrofurfuryl alcohol can be prepared, starting from 2,5-anhydro-l-0-benzoyl-3,4-di-O-p-tolylsulfonyl-D-ribitol, by using the Tipson-Cohen112 method for introducing the 3,4-double bond, with subsequent saponification of the ester.116... 

The study of Mateos and Fuente Blanco on the aldol condensation between magnesium enolate of 2,2,6-trimethylcyclohexanone and 3-furaldehyde is in accord with the preceding stereochemical results. Application to the preparation of model compounds of limonoid, such as pyroangelensolide, is described (equation 84). 

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. 

Some of these processes can be controlled and used for the preparation of chemicals of industrial interest, such as 5-(hydroxymethyl-2-furaldehyde, HMF). HMF is the product of a triple dehydration of fructose, which is itself one of the first degradation products of sucrose. The preparation and the uses of HMF have been extensively studied and reviewed by Lichtenthaler.342 It can be obtained under various degradative conditions, including acid catalysis and catalysis by lanthanide ions.343 Processes for the production of HMF on the multi-ton scale have been developed as well as many uses, notably polycondensations.344,345 The polymerization of HMF has been shown to produce complex... 

The parent compound (15) and 2- and 3-methylfuro[2,3-c]pyridine derivatives have been synthesized from ethyl 3-hydroxyisonicotinate (90) as shown in Scheme 39 <86JHC549>. The parent compound (15) has been prepared using an alternative method starting with 3-furaldehyde... 

A simple procedure to prepare 5-aryl- and 5-pyridyl-2-furaldehydes from inexpensive, commercially available 2-furaldehyde diethyl acetal was reported. The reaction proceeded in a four-step, one-pot procedure and the yield of coupling step was usually between 58-91% <02OL375>. A facile route to 3,4-furandicarboxylic acids was developed. DDQ-oxidation of 2,5-dihydrofuran derivatives, which were produced from dimethyl maleic anhydride, furnished the desired esters of furan-3,4-dicarboxylic acid <02S1010>. The furan-fused tetracyclic core of halenaquinol and halenaquinone possessing antibiotic, cardiotonic, and protein tyrosine kinase inhibitory activities was synthesized. Intramolecular cycloaddition of an o-quinodimethane with furan gave the adduct as a single isomer via an enrfo-transition state, which was converted to trisubstituted furan by oxidation-elimination reactions <02T6097>. 

Incidental reactions that have been reported include the preparation of derivatives of 5-(hydroxymethyl)-2-furaldehyde by reaction of D-fructose in acetic or propionic acid in the presence of the respective anhydride.158 The condensation of D-glucose with phenol has been effected in acetic acid in the presence of dry hydrogen chloride, prior to resinification,157 and the reaction of sucrose with thionyl chloride in acetic acid-acetic anhydride produced partially acetylated chlorodeoxysucroses.158 Sucrose has been condensed with maleic anhydride in acetic anhydride mixed with acetic acid or formic acid, to give solid products having an undetermined structure.159... 

A number of tetrapyrrole-type macrocyclic systems have been prepared that contain both an even and an odd number of bridging atoms between the heterocyclic subunits. The first of these to be reported was the thiacycloheneicosin 4.175. This macrocycle was prepared in 1.3% yield via a Wittig reaction between 5,5 -thiodi-2-furaldehyde 4.173 and the phosphonium salt 4.174 (Scheme 4.5.1). While little in the way of information is available for this macrocycle, H NMR spectroscopic analyses led to the conclusion that, while formally a 22 n-electron system, compound 4.175 will not apparently sustain a diamagnetic ring current. Why this is so is not clear at present. 

The thioamide 159 has been prepared (22%) by treatment of the corresponding nitrile with H2S in DMF at 50-60 °C (83CCC3140). The thioaldehyde 160 is formed in 63% yield by treatment of the corresponding aldehyde with HMDST ((Me3Si)2S) (96S1185). 5-Amino-2-furaldehyde forms compound 161 upon treatment with 3-amino-2-oxazolidinone (62JMPC513, 68JOC2552). 

Syntheses of diketophosphonates by hydrolysis of a-hydroxy furylpliosphonate or by photooxidation of furylalkylphosphonates" have also been reported. Thus, diethyl l-(5-methyl-2-furyl)-l-hydroxymethylphosphonate, prepared from 5-methyl-2-furaldehyde and diethyl phosphite by a base-catalyzed reaction, is treated with 1.25 M HCl in acetone at 58°C to give diethyl ( )-... 

The preparation of 2-nitro alcohols was also achieved by reaction of equimolar amounts of nitroal-kanes and aldehydes in the presence of alumina-supported potassium fluoride without solvent (equation 12). A peculiar feature of diis method were reactions performed with aromatic aldehydes, such as benz-aldehyde and furaldehyde, which allowed preparation of the corresponding 2-nitro alcohols without dehydration of these into nitroalkenes, as observed when nitroaldol reactions were performed with organic bases in homogeneous medium or with alumina alone. 

Mucochloric acid can be prepared by the oxidative chlorination of fur-furaldehyde (furfural), or from furan carboxylic acid and butynediol. 

Stoll et al. (1967) prepared this ketone by condensation of 5-methyl-2-furaldehyde (1.66) with nitroethane followed by acid hydrolysis of the resulting oxime. 

Stoll et al. (1967) obtained it as described for the homolog 1.89 and by the oxidation of the keto alcohol prepared by a Grignard reaction on 2-furaldehyde. 

The aldehydes and ketones most commonly used are benzaldehyde, acetaldehyde, formaldehyde, and acetone. However, -butyraldehyde, n-propionaldehyde, salicylaldehyde, p-tolualdehyde, and 2-furaldehyde have also been employed. A number of unsaturated aldehydes, for example, 3,7-dimethyl-2,6-octadienal (citral) and cinnamaldehyde, have yielded cyclic acetals. Acetals have been prepared from 2-butanone, cyclohexanone, and glyoxal. ... 

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