5- -2-furfural

Furfural (2-furaldehyde), C4H30CH0, is a liquid aldehyde with a pungent almond-like odor. Colorless when freshly distilled, it darkens on contact with air. industrial furfural is light yellow to brown in color. 

Note Furfural is miscible with most common organic solvents except saturated aliphatic hydrocarbons. 

Furfural has a high order of thermal stability in the absence of oxygen. At temperatures as high as 230 C (446 F), exposure for many hours is required to produce detectable changes in the physical properties of furfural, with the exception of color (29). 

The production of aromatic chemicals from renewable materials is mainly concentrated on the exploitation of wood products together with recovery of furfural by converting pentosans. Pentosans are almost as widely distributed in nature as cellulose, although in lower quantities. Pentosan-rich materials are commonly used in the production of furfural, particularly waste from corncobs, grain chaff and cotton pod cases. 

Current world production of furfural is around 150,000 tpa the largest producer is Quaker Oats Chem. (USA). The main areas of application are the production of the solvents furfuryl alcohol and tetrahydrofurfuryl alcohol. Furfural itself is used as a solvent, especially for separating unsaturated and saturated compounds in petroleum refining. 

Furfuryl alcohol is the base material for ranitidine, one of the best selling drugs (see Chapter 14.1.1). 

Special resins are produced by condensing furfuryl alcohol and furfural with urea and formaldehyde (e.g. foundry resins). 

In a 12-1. round-bottom flask are placed 1500 g. of corn cobs (ground to about the size of corn kernels), 5 1. of 10 per cent sulfuric acid and 2 kg. of salt. The flask is shaken in order to secure a homogeneous mixture and is then connected with an upright tube water condenser and return tube as shown in Fig. 4 (p. 50). Heat is applied from a ring burner, the flame being adjusted so that the liquid distils at a rapid rate. 

The distillation process is continued until practically no more furfural can be seen collecting in the distilling flask used as a receiver. The above operation requires from five to ten hours. 

This distillate is now treated with enough sodium hydroxide so that the mixture is left just faintly acid and the furfural separated. It amounts to 180 to 220 g. The wet furfural is distilled under diminished pressure from a Claisen flask which is heated in an oil-bath. The temperature of the bath is never permitted to rise above 130°. At first, water together with some furfural distils, and this fraction is separated to be worked up with a later portion. Finally, pure furfural (b. p. 90° at 65 mm.) distils and this fraction, collected separately, is found to be practically colorless. Its boiling point at 745 mm. is IS9° The distillation of the crude material must not be carried out under ordinary pressure, or else the product turns dark rapidly 

Vacuum distillation of the product is essential. Moreover in this final distillation the precautions mentioned (the use of an oil-bath and an outside temperature of less than 130°) must be carefully observed. When the furfural is distilled under ordinary pressure or when it is distilled under diminished pressure with a free flame, a practically colorless product is at first obtained. After a few days and sometimes after a few hours this product will gradually darken until finally a black liquid results. This change, although most marked in the presence of light, takes 

Certain samples of ground cobs which had remained in the laboratory for a year did not give nearly such good yields of furfural as those which were fresher. 

Inconsistent results have been reported in a variety of genotoxic assays both in vivo and in 

lARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol 45, Occupational exposures in petroleum refining crude oil and major petroleum fuels, p 159. Lyon, International Agency for Research on Cancer, 1989 

Porter HO Aviators intoxicated by inhalation of JP-5 fuel vapors. Aviat Space Environ Med 61 654, 1990 

Carpenter CP et al Petroleum hydrocarbon toxicity studies XI. Animal and human response to vapors of deodorized kerosene. Toxicol Appl Pharmacol 36 443, 1976 

Morrison I, Sprague P Kerosene pneumonia Its incidence in Perth and case history of a recent fatality. Australas Radiol 20 118, 1976 

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To illustrate, predictions were first made for a ternary system of type II, using binary data only. Figure 14 compares calculated and experimental phase behavior for the system 2,2,4-trimethylpentane-furfural-cyclohexane. UNIQUAC parameters are given in Table 4. As expected for a type II system, agreement is good. 

Type C requires the most complex data analysis. To illustrate, we have reduced the data of Henty (1964) for the system furfural-benzene-cyclohexane-2,2,4-trimethylpentane. VLB data were used in conjunction with one ternary tie line for each ternary to determine optimum binary parameters for each of the two type-I ternaries cyclohexane-furfural-benzene and 2,2,4-... 

The optimum parameters for furfural-benzene are chosen in the region of the overlapping 39% confidence ellipses. The ternary tie-line data were then refit with the optimum furfural-benzene parameters final values of binary parameters were thus obtained for benzene-cyclohexane and for benzene-2,2,4-trimethyl-pentane. Table 4 gives all optimum binary parameters for this quarternary system. 

Figure 4-21. Parameters obtained for the furfural-benzene binary are different for the two ternary systems. An optimum set of these parameters is chosen from the overlapping confidence regions, capable of representing both ternaries equally well.

Figure 4-23. Calculated and experimental selectivities and distribution coefficients for the type-I ternaries in the 2,2,4-trimethyl pentane-cyclohexane-furfural-benzene system.

Calculated and Experimental Liquid-Liquid Equilibria for a Quarternary System at 25 C 2,2,4-trimethylpentane(1)-furfural(2)-cyclohexane(3)-benzene(4)... 

Molisch s test A general test for carbohydrates. The carbohydrate is dissolved in water, alcoholic 1-naphthol added, and concentrated sulphuric acid poured down the side of the tube. A deep violet ring is formed at the junction of the liquids. A modification, the rapid furfural test , is used to distinguish between glucose and fructose. A mixture of the sugar, 1-naphthol, and concentrated hydrochloric acid is boiled. With fructose and saccharides containing fructose a violet colour is produced immediately the solution boils. With glucose the appearance of the colour is slower. 

In the manufacture of base oils, one of the refining operations is to extract with the aid of an appropriate solvent (furfural most often) the most aromatic fractions and the polar components. When free of solvent, the extracted aromatic fraction can eventually be refined, particularly to remove color or to thicken it, or still further, to fractionate it. The term, aromatic extract is used in every case. 

Hydrorefining can substitute for extraction processes such as furfural where it integrates perfectly into the conventional process scheme. 

Molisch s Test. Dissolve about 01 g. of the carbohydrate in z ml. of water (for starch use 2 ml. of starch solution ), add 2-3 drops of a 1 % alcoholic solution of i-naphthol (ignoring traces of the latter precipitated by the water) and then carefully pour 2 ml. of cone. H2SO4 down the side of the test-tube so that it forms a heavy layer at the bottom. A deep violet coloration is produced where the liquids meet. This coloration is due apparently to the formation of an unstable condensation product of i-naphthol with furfural (an aldehyde produced by the dehydration of the carbohydrate). 

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