Furfural derivatives, formation

Caramelization can occur under both acidic and basic conditions. Acids promote dehydration reactions resulting in the formation of furfural derivatives while alkalies favor isomerization and fragmentation reactions (6). 

The proof for the formula XII is as follows. The full methylation of difructose anhydride III yielded a hexamethyl derivative, non-crystalline but readily distillable at 161-165° in a vacuum of 0.42 mm. The hydrolysis of hexamethyl-difructose anhydride III in 0.8 N aqueous hydrochloric acid at 95° appeared to reach half completion in about ninety-one minutes it is evident that the substance is rather difficult to hydrolyze. There i.s some destruction of the hydrolytic products in the acid solution with the formation of furfural derivatives, and it was found best to stop the hydrolysis at the half stage and separate the trimethyl-D-fructose fraction from the unhydrolyzed material by distillation in vacuo, the hydrolyzed products being more volatile the still residue was again hydrolyzed to the half stage and the separation repeated. In this manner there was obtained a yield of about 58% redistilled trimethyl-D-fructose, the specific rotation of which in chloroform is in the range = + 25-30°. Although this value is near that of pure 3,4,6-trimethyl-D-fructose, which is - - 26.6°, the agreement proved to be fortuitous because the sirup was not solely 3,4,6-trimethyl-D-fructose. It contained 3,4,6-trimethyl-D-fructose (readily identified by oxidation to... 

Acids catalyze the reversible reaction that results in the formation and hydrolysis of glycosides. Also possible are acid-catalyzed epimerization and dehydration reactions that result in the formation of furfural derivatives and anhydro sugars. This article deals only with the reaction which predominates in dilute solutions of both glycoside and acid at temperatures of 1(X)° or below, that is, hydrolysis. 

A number of colorimetric procedures, relying on the formation of furfural derivatives of carbohydrates in concentrated sulphuric acid, employing... 

Fructose is dehydrated in acid medium for formation of furfural derivative, which complexs with cysteine hydrochloride to produce a chromophore at starting of green color that is... 

The classical methods for quantitative analysis of carbohydrates were based mainly on the formation of colored products on treatment of the analytes with strong mineral acids and condensation of the resulting 2-furaldehyde (furfural) derivatives with a suitable chromogenic reagent (usually a phenol or aromatic amine). Examples include the well-known procedmes involving the use of sulfuric acid with phenol, orcinol, cysteine, or anthrone. 

A number of well-known color reactions that are specific for carbohydrates depend on the formation of furfural derivatives by the action of strong acid. The furfural that is produced is condensed with a phenolic compound or an aryl amine. 

Esters of diphenylacetic acids with derivatives of ethanol-amine show mainly the antispasmodic component of the atropine complex of biologic activities. As such they find use in treatment of the resolution of various spastic conditions such as, for example, gastrointestinal spasms. The prototype in this series, adiphenine (47), is obtained by treatment of diphenyl acetyl chloride with diethylaminoethanol. A somewhat more complex basic side chain is accessible by an interesting rearrangement. Reductive amination of furfural (42) results in reduction of the heterocyclic ring as well and formation of the aminomethyltetrahydro-furan (43). Treatment of this ether with hydrogen bromide in acetic acid leads to the hydroxypiperidine (45), possibly by the intermediacy of a carbonium ion such as 44. Acylation of the alcohol with diphenylacetyl chloride gives piperidolate (46). ... 

Euran Furan resins are thermosetting polymers derived from furfuryl alcohol and Furfural. The cure must be carefully controlled to avoid the formation of blisters and delaminations. To obtain optimum strength and corrosion resistance, furan composites must undergo a postcure schedule at carefully selected temperatures depending upon the laminate thickness. Equipment made with furan resins exhibits excellent resistance to solvents and combinations of acids and solvents. These resins are not for use in strong oxidizing environments. 

By careful choice of both the reaction conditions and the phenolic compound used, it may be possible to produce a colour that is characteristic of a particular carbohydrate or related group, so giving some degree of specificity to the method. Thus, Seliwanoff s test uses hydrochloric acid and either resorcinol or 3-indolylacetic acid to measure fructose with minimal interference from glucose. The colour produced by pentoses with orcinol (Bial s reagent) or p-bromoaniline is sufficiently different from that produced by hexoses to permit their quantitation in the presence of hexoses. However, none of the methods based on the formation of furfural or its derivatives can be considered to be entirely specific. 

Orcinol—sulphuric acid 200 mg orcinol in 100 ml 10% sulphuric acid Spray Formation of furfural and derivatives with heat and acid which condense with a phenol... 

Wenkert and Khatuya (51) examined the competition between direct insertion of a carbene into furan (via cyclopropanation) and ylide formation with reactive side-chain functionality such as esters, aldehydes, and acetals. They demonstrated the ease of formation of aldehyde derived carbonyl ylides (Scheme 4.30) as opposed to reaction with the electron-rich olefin of the furan. Treatment of 3-furfural (136) with ethyl diazoacetate (EDA) and rhodium acetate led to formation of ylide 137, followed by trapping with a second molecule of furfural to give the acetal 138 as an equal mixture of isomers at the acetal hydrogen position. 

Furfural identified in beef diffusate appears to be a prominent meat flavor intermediate. It is a dehydration product of pentoses similar to formation of hydroxy methyl furfural from hex-oses. These compounds are formed by dehydration of 1,2-enediols derived from deamination of Amadori compounds (51). 

Finally, the formation of derivatives of pyridine from 5-hydroxymethylfurfural and related compounds on treatment with ammonia 0 may be considered in this section on the furan ring. 5-Hydroxymethyl-furfural itself gives 2-hydroxymethyl-5-hydroxypyridine (XLIV) with ammonia, which is presumably formed by opening of the ring in the intermediate aldehyde-ammonia compound followed by closure to give the 6-membered ring. 

Methyl formate, ethyl formate, carboxylic acids and derivatives, acetic acid CH3COOCH, acetic anhydride CH3COOCOCH3, formic acid HCOOH, oxalic acid HOOCCOOH, phthalic anhydride C3H4O3 Acetaldehyde CH3CHO, acrolein H2C=CHCHO, formaldehyde HCHO, furfural C5H4O2... 

The synthesis of 4-substituted products from 2-acylfurans and 2-acylselenophenes is difficult. Their predominant formation was observed on bromination of aluminum chloride complexes of furfural and to a lesser extent of 2-acetylfuran (731ZV2733). Bromination of complexes of selenophene-2-carbaldehyde and 2-acetylselenophene with AICI3 leads mainly to 4-substituted derivative (exceeded 70%) (95JHC53). In all cases a significant amount of 4,5-dibromo-substituted products was obtained (Scheme 21). Competing reactions show that the complex of selenophene-2-carbaldehyde with aluminum chloride is brominated more rapidly than its thiophene analogue (95JHC53). 

Heating the wood also results in the formation of carbohydrate (cellulose and hemicellulose) breakdown products, e.g., the furanic derivatives furfural, 5-methyl-furfural, furfuryl alcohol, etc. (Chatonnet 1998). 

Dehydration Reactions. Detailed analysis of the pyrolysis tar as discussed previously (Figure 12 and Scheme 3) shows the presence of levoglucosan, its furanose isomer (1,6-anhydro-p-D-glucofuranose) and their transglycosylation products as the main components. In addition to these compounds, the pyrolyzate contains minor amounts of a variety of products formed from dehydration of the glucose units. The dehydration products detected include 3-deoxy-o-erythrohexo-sulose, 5-hydroxymethyl-2-furaldehyde, 2-furaldehyde (furfural), other furan derivatives, levoglucosenone (l,6-anhydro-3,4-dideoxy-P-D-glycerohex-3-enopyranos-2-ulose), l,5-anhydro-4-deoxy-D-hex-l-ene-3-ulose, and other pyran derivatives. The dehydration products are important as intermediate compounds in char formation. 

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