The Alkoxylation of Simple Furans and Related Reactions
Clauson-Kaas,Neils;Limborg,Franz;Fakstorp,Jorgen
Acta Chemica Scandinavia
Vol 2, 1948, pp.109-115
Abstract
By the addition of alkoxy groups to the a-carbons of furans, stable 2,5-dialkoxy-2,5-dihydrofurans are obtained. These addition products may be hydrolyzed under very mild conditions to the corresponding unsaturated 1,4-dicarbonyl compounds, which are often unstable and therefore difficult of accession. The procedure can be illustrated by the methoxylation of furan. In this article we report some experiments concerning the general applicability of the alkoxylation method. In conclusion, other methods for the preparation of dihydrofurans by oxidation of furans are discussed.
The Preparation of 2,5-Diacetoxy-2,5-Dihydrofuran, 2,5-Diacetoxytetrahydrofuran and Pyridazine
Clauson-Kaas,Niels;Si-Oh Li,Si-Oh;Elming,Neils
Acta Chemica Scandinavica
Vol. 4, 1950, pp.1233-1240
Abstract
It has previously been reported, that 2,5-diacetoxy-2,5-dihydrofuran may be obtained in a 70 per cent yield by oxidizing furan with bromine in acetic acid in the presence of potassium acetate. We have since observed that this method of preparation now and then fails totally because the diacetoxy-dihydrofuran, formed by the reaction, occassionally changes into a black insoluble mass. At the same time, acetic acid is formed. This conversion either takes place during the final distillation, or on standing after the distillation has been completed. Sometimes it takes several days before the distillate turns black, but usually the black mass is formed during the distillation or immediately after, with the evolution of heat and with almost explosive violence. If the preparation of larger batches is attempted, decomposition always occurs. It thus became clear that the directions given previously for the synthesis of diacetoxydihydrofuran were insufficient, and that much more minute information than is usually necessary in synthetic organic chemistry was required.
The Acyloxylation of Furan with Lead Tetracyloxylates; Cis-Trans Isomerism of 2,5-Diacyloxy-2,5-dihydrofurans and 2,5-Diacyloxytetrahydrofurans
Elming,Neils;Clauson-Kaas,Neils
Acta Chemica Scandinavia
Vol. 6, 1952 pp.535-544
Abstract
The formation of 2,5-diacetoxy-2,5-dihydrofuran form furan and lead tetraacetate has been previously reported (yield 45%). We have now worked out new directions for this synthesis, in order that larger amounts of diacetoxydihydrofuran can be easily prepared (yield 70 per cent).
Electrolytic Methoxylation of Furan
Clauson-Kaas,Neils;Limborg,Franz;Glens,Kirsten
Acta Chemica Scandinavia
Vol.6, 1952 pp.531-534
Abstract
When furan is treated with a methanolic solution of bromine or chlorine it adds two methoxy groups whereby 2,5-dimethoxy-2,5-dihydrofuran and two moles of hydrogen halide are formed. Since dimethoxydihydrofuran is sensitive to acids, the reaction is carried out in the presence of sodium carbonate or potassium acetate. We have found that dimethoxydihydrofuran prepared by this method is often contaminated wtih a small amount of some halogen-containing impurity, which may cause the formation of hydrogen halide and therefore greatly influence the stability of the acid sensitive dimethoxydihydrofuran.
Note on the Electrolytic Methoxylation of Furan
Clauson-Kaas,Neils;Tyle,Zdenek
Acta Chemika Scandinavia
VOl.6 1952 pp.962-963 (Short Communication)
Abstract
The electrolytic methoxylation of furan to 2,5-dimethoxy-2,5-dihydroxyfuran has been previously carried out by electrolyzing a methanolic solution of furan and ammonium bromide. It has now been found, that dimethoxydihydrofuran is also formed, when the ammonium bromide is replaced by ammonium nitrate, sodium nitrate, sodium formate, boron fluoride etherate or sulfuric acid. The yield of dimethoxy-dihydrofuran (38-56 per cent) is somewhat lower than when ammonium bromide is used (86 per cent). These experiments indicate, that not only halogens, but also other oxidizing agents can oxidize furan in methanolic solution to dimethoxydihydrofuran.
The Alkoxylation of Furans with a Negative alpha-Substituent; Preparation of 2,5-dimethoxy-2,5-dihydro-2-furoic Acid Methyl Ester and 2,5-Dimethoxytetrahydro-2-furoic Acid Methyl Ester
Clauson-Kaas,Neils;Franz Limborg,Franz
Acta Chemica Scandinavia
Vol. 6, 1952 pp.551-555
Abstract
The oxidation of furans to stable 2,5-disubstituted 2,5-dihydrofurans is a useful reaction since the dihydrofurans may serve as intermediates in the preparation of various types of compounds, which are otherwise difficult of accession. Several methods for the oxidation of furans to 2,5-dihydrofurans are known, Meinels method of methoxylation with halogens in methanol being by far the most convenient. This method is, however, not generally applicable as furans with negative a a-substituent can usually not be methoxylated in this way. Of 2-furoic acid, ethyl 2-furoate, ethyl 2-furylacrylate, furfural and 2-acetylfuran only furfural is methoxylated by bromine in methanol under the usual conditions. Besides furfural, the only other furan with a negative substituent which has been methoxylated, is methyl 2-furoate (Jones). Chlorine in boiling methanol was used for the methoxylation. But the yield of dimethoxydihydro-2-furoic acid methyl ester was only 12 per cent and the product, of which no analyses were reported, can not have been very pure since it boiled from 120' to 140' at 20mm.
Electrolytic Ethoxylation of Furan
Clauson-Kaas,Neils
Acta Chemica Scandinavia
Vol. 6, 1952 pp.569-571
Abstract
A new electrolytic method for the alkoxylation of furans with methanol, ethanol and the propanols has been described in a patent and detailed directions were then worked out for the methoxylation, on a laboratory scale, of a number of simple furans. It has now been found that electrolytic ethoxylation of furans may be carried out with the same set-up as was used for the methoxylations and in this communication the preparation of 2,5-diethoxy-2,5-dihydrofuran I by electrolysis is given as an example. Diethoxy-dihydrofuran has been prepared previously, but the electrolytic method is more convenient that the known methods of alkoxylation.
Preparation and Reactions of Dialkoxytetrahydrofurans
Falkstorp,Jorgen;Raleigh,Dolores;Schniepp,L
J. Am. Chem. Soc.
Vol.72(2) 1950 pp 869–874
DOI: 10.1021/ja01158a058
Abstract:http://pubs.acs.org/doi/abs/10.1021/ja01158a058
Abstract
The opening of the furan ring by means of hydrolytic agents has long has long attracted considerable interest. However, only in the case of methylfuran and dimethylfuran has hydrolytic cleavage led to the results of any practical importance. The investigations of Meinel and Clasuson-Kaas and co-workers resulting in methods for the preparation of stable dialkoxydihydrofurans which are cyclic acetyls of unsaturated 1,4-dicarbonyl compounds and easily convertible to these, represent important advances in this field.
Keywords:Dialkoxytetrahydrofuran;low-pressure hydrogenation;Dialkoxydihydrofuran;Raney nickel;transfer hydrogenation
Clauson-Kaas,Neils;Limborg,Franz;Fakstorp,Jorgen
Acta Chemica Scandinavia
Vol 2, 1948, pp.109-115
Abstract
By the addition of alkoxy groups to the a-carbons of furans, stable 2,5-dialkoxy-2,5-dihydrofurans are obtained. These addition products may be hydrolyzed under very mild conditions to the corresponding unsaturated 1,4-dicarbonyl compounds, which are often unstable and therefore difficult of accession. The procedure can be illustrated by the methoxylation of furan. In this article we report some experiments concerning the general applicability of the alkoxylation method. In conclusion, other methods for the preparation of dihydrofurans by oxidation of furans are discussed.
The Preparation of 2,5-Diacetoxy-2,5-Dihydrofuran, 2,5-Diacetoxytetrahydrofuran and Pyridazine
Clauson-Kaas,Niels;Si-Oh Li,Si-Oh;Elming,Neils
Acta Chemica Scandinavica
Vol. 4, 1950, pp.1233-1240
Abstract
It has previously been reported, that 2,5-diacetoxy-2,5-dihydrofuran may be obtained in a 70 per cent yield by oxidizing furan with bromine in acetic acid in the presence of potassium acetate. We have since observed that this method of preparation now and then fails totally because the diacetoxy-dihydrofuran, formed by the reaction, occassionally changes into a black insoluble mass. At the same time, acetic acid is formed. This conversion either takes place during the final distillation, or on standing after the distillation has been completed. Sometimes it takes several days before the distillate turns black, but usually the black mass is formed during the distillation or immediately after, with the evolution of heat and with almost explosive violence. If the preparation of larger batches is attempted, decomposition always occurs. It thus became clear that the directions given previously for the synthesis of diacetoxydihydrofuran were insufficient, and that much more minute information than is usually necessary in synthetic organic chemistry was required.
The Acyloxylation of Furan with Lead Tetracyloxylates; Cis-Trans Isomerism of 2,5-Diacyloxy-2,5-dihydrofurans and 2,5-Diacyloxytetrahydrofurans
Elming,Neils;Clauson-Kaas,Neils
Acta Chemica Scandinavia
Vol. 6, 1952 pp.535-544
Abstract
The formation of 2,5-diacetoxy-2,5-dihydrofuran form furan and lead tetraacetate has been previously reported (yield 45%). We have now worked out new directions for this synthesis, in order that larger amounts of diacetoxydihydrofuran can be easily prepared (yield 70 per cent).
Electrolytic Methoxylation of Furan
Clauson-Kaas,Neils;Limborg,Franz;Glens,Kirsten
Acta Chemica Scandinavia
Vol.6, 1952 pp.531-534
Abstract
When furan is treated with a methanolic solution of bromine or chlorine it adds two methoxy groups whereby 2,5-dimethoxy-2,5-dihydrofuran and two moles of hydrogen halide are formed. Since dimethoxydihydrofuran is sensitive to acids, the reaction is carried out in the presence of sodium carbonate or potassium acetate. We have found that dimethoxydihydrofuran prepared by this method is often contaminated wtih a small amount of some halogen-containing impurity, which may cause the formation of hydrogen halide and therefore greatly influence the stability of the acid sensitive dimethoxydihydrofuran.
Note on the Electrolytic Methoxylation of Furan
Clauson-Kaas,Neils;Tyle,Zdenek
Acta Chemika Scandinavia
VOl.6 1952 pp.962-963 (Short Communication)
Abstract
The electrolytic methoxylation of furan to 2,5-dimethoxy-2,5-dihydroxyfuran has been previously carried out by electrolyzing a methanolic solution of furan and ammonium bromide. It has now been found, that dimethoxydihydrofuran is also formed, when the ammonium bromide is replaced by ammonium nitrate, sodium nitrate, sodium formate, boron fluoride etherate or sulfuric acid. The yield of dimethoxy-dihydrofuran (38-56 per cent) is somewhat lower than when ammonium bromide is used (86 per cent). These experiments indicate, that not only halogens, but also other oxidizing agents can oxidize furan in methanolic solution to dimethoxydihydrofuran.
The Alkoxylation of Furans with a Negative alpha-Substituent; Preparation of 2,5-dimethoxy-2,5-dihydro-2-furoic Acid Methyl Ester and 2,5-Dimethoxytetrahydro-2-furoic Acid Methyl Ester
Clauson-Kaas,Neils;Franz Limborg,Franz
Acta Chemica Scandinavia
Vol. 6, 1952 pp.551-555
Abstract
The oxidation of furans to stable 2,5-disubstituted 2,5-dihydrofurans is a useful reaction since the dihydrofurans may serve as intermediates in the preparation of various types of compounds, which are otherwise difficult of accession. Several methods for the oxidation of furans to 2,5-dihydrofurans are known, Meinels method of methoxylation with halogens in methanol being by far the most convenient. This method is, however, not generally applicable as furans with negative a a-substituent can usually not be methoxylated in this way. Of 2-furoic acid, ethyl 2-furoate, ethyl 2-furylacrylate, furfural and 2-acetylfuran only furfural is methoxylated by bromine in methanol under the usual conditions. Besides furfural, the only other furan with a negative substituent which has been methoxylated, is methyl 2-furoate (Jones). Chlorine in boiling methanol was used for the methoxylation. But the yield of dimethoxydihydro-2-furoic acid methyl ester was only 12 per cent and the product, of which no analyses were reported, can not have been very pure since it boiled from 120' to 140' at 20mm.
Electrolytic Ethoxylation of Furan
Clauson-Kaas,Neils
Acta Chemica Scandinavia
Vol. 6, 1952 pp.569-571
Abstract
A new electrolytic method for the alkoxylation of furans with methanol, ethanol and the propanols has been described in a patent and detailed directions were then worked out for the methoxylation, on a laboratory scale, of a number of simple furans. It has now been found that electrolytic ethoxylation of furans may be carried out with the same set-up as was used for the methoxylations and in this communication the preparation of 2,5-diethoxy-2,5-dihydrofuran I by electrolysis is given as an example. Diethoxy-dihydrofuran has been prepared previously, but the electrolytic method is more convenient that the known methods of alkoxylation.
Preparation and Reactions of Dialkoxytetrahydrofurans
Falkstorp,Jorgen;Raleigh,Dolores;Schniepp,L
J. Am. Chem. Soc.
Vol.72(2) 1950 pp 869–874
DOI: 10.1021/ja01158a058
Abstract:http://pubs.acs.org/doi/abs/10.1021/ja01158a058
Abstract
The opening of the furan ring by means of hydrolytic agents has long has long attracted considerable interest. However, only in the case of methylfuran and dimethylfuran has hydrolytic cleavage led to the results of any practical importance. The investigations of Meinel and Clasuson-Kaas and co-workers resulting in methods for the preparation of stable dialkoxydihydrofurans which are cyclic acetyls of unsaturated 1,4-dicarbonyl compounds and easily convertible to these, represent important advances in this field.
Keywords:Dialkoxytetrahydrofuran;low-pressure hydrogenation;Dialkoxydihydrofuran;Raney nickel;transfer hydrogenation
ClausonKaas.etal.Alkoxylation.of.Simple.Furans.pdf