Fructose

Fructose (syn. fruit sugar, levulose), d-fructose, C₆H₁₂O₆, ketohexose. Of the two stereoisomers, only the levorotating form is found in nature, hence the name "levulose". The designation d-F. indicates that with respect to the position of H and OH at the lower asymmetric carbon atom, fructose belongs to the d-series, i.e., it has the configuration corresponding to d-glyceraldehyde. The open form of F. with a free carbonyl group is represented by the following formula: CH₂OH C=O | HOCH | HCOH | HCOH | CH₂OH d = (-)-fructose However, F., like other carbohydrates, has the structure of a cyclic hemiacetal. F. is included in di-, tri-, and polysaccharides (cane sugar, raffinose, inulin), phosphoric acid esters (hexosediphosphate) in the unstable furanoid form (fructofuranose) with a butylene oxide bridge (2,5), sometimes denoted as γ-F. When these compounds are cleaved, the liberated F. rapidly isomerizes to the more stable pyranose form with an amylene oxide bridge (2,6). F. exhibits weak mutarotation; specific rotation [α]D²⁰ = -(91.90 + 0.11p)°, where p represents the number of grams of F. in 100 g of solution. F. crystallizes with difficulty, in the form of needles and flakes. Crystals of composition C₆H₁₂O₆ + H₂O melt at 110°. F. is easily soluble in water, partially in alcohol, well in acetone, in a mixture of alcohol with ether. With phenylhydrazine, F. gives an osazone identical with the osazone of glucose and mannose; characteristic for F. is methylphenylosazone; F. gives a sparingly soluble compound with lime, C₆H₁₂O₆-Ca(OH)₂, is precipitated by lead acetate in the presence of ammonia. F. gives the Molisch, Tollen's, and Trommer reactions; the reducing capacity of F. with respect to copper oxide is somewhat less than that of glucose (ratio = 92.8:100). F. is very sensitive to alkalis and acids. When boiled with glucose even with dilute hydrochloric acid (7.5%), it is completely cleaved within 3 hours, while most of the glucose remains unchanged. In alkaline solutions, F. converts to glucose. F. ferments as easily as glucose. To distinguish F. from glucose, the formation of methylphenylosazone and the Selivanov reaction are used (see Urine). F. is very widespread in nature: it occurs together with glucose in free form in many fruits, in honey, is part of disaccharides (cane sugar, etc.), trisaccharides and polysaccharides (see Inulin); it is usually obtained by hydrolysis of inulin. Artificially, F. was first obtained by E. Fischer in racemic form and named α-acrose. Fructose has a very sweet taste, it is about 70% sweeter than cane sugar. When ingested with food, F. is absorbed in the intestine partly unchanged, partly after first converting to glucose. F. is a good glycogen-former; it is oxidized more easily than glucose, which is why it is given to diabetics. In the body, F. is found in blood serum; in some cases it was found in transudates; detected in the amniotic fluid of cows; on the content of F. in urine-see Urine, Levuloseuria. Fructose in the form of its phosphoric acid esters is apparently a normal intermediate product of fermentation and glycolysis.

M" Kalyagina. FLUORINE (from Greek phthoros - destruction, death), Fluorum (from Latin fluere - to flow), element of the halogen group, chemical symbol F; at. wt. 19.3; atomic number 9, stands in the 2nd row of group VII of the periodic system; gas of light yellow color, boiling point -187°, melting point -223°. In nature it is found in the form of the mineral fluorite (CaF₂), cryolite, AlF₃-3NaF, apatite, 3Ca₃(PO₄)₂-CaF₂; in small amounts it is a constant component of the bodies of animals and higher plants; in the animal organism it is found mainly in bones and teeth (up to 0.18% of their ash), in the skin (epidermis), hair, nails. The distribution of F. in the earth's crust (in the form of compounds) is 1/5 times greater than that of chlorine. -F. possesses very great chemical activity, easily enters into interaction with all elements except oxygen, chlorine, nitrogen and "noble" gases. With hydrogen it combines with explosion even in the dark and at low t°. It is easily soluble in water and, decomposing it, forms hydrofluoric acid (H₂F₂) and oxygen in the form of ozone; it displaces chlorine from NaCl and from CCl₄. F. and soluble salts of hydrofluoric acid even in very small concentrations stop glycolysis. Fluorite when heated with concentrated H₂SO₄ gives hydrofluoric acid; hydrofluoric acid is a colorless liquid, boiling at 19.6°, which corrodes glass but does not act on lead, gold, platinum, wax, paraffin, rubber. Aqueous solutions of hydrofluoric acid (hydrofluoric acid) are kept in paraffin or rubber vessels. The calcium salt of hydrofluoric acid is distinguished by its difficult solubility - CaF₂ (fluorite). Many compounds of F. are poisonous. The strongest effect is that of hydrofluoric acid, which causes very deep, difficult-to-heal burns. The introduction of H₂F₂ into the body leads to decalcification due to the transformation of compounds of Ca into insoluble CaF₂. The other phenomena are as with strong acids in general. When non-corrosive salts of F. are introduced into the digestive tract, diarrhea results, often bloody; the permeability of the intestinal walls is disturbed in places. Volatile compounds (H₂F₂, SiF₄) cause spasm of the larynx, rhinitis (from catarrhal to necrotic forms), bronchitis, pulmonary edema, disturbance of respiration, excited state, disturbance of the motor function of the eye muscles. Death - from cessation of respiration. Before death - convulsions, discharge of gases, urine, feces. Rapidly killing concentrations of F₂H₂ are 0.2-0.45 mg/l, lethal concentration - 0.03 mg/l, irritating - 0.01 mg/l. All compounds of F. in poisonous doses act paralytically on the vasomotor centers, lower body temperature, cause paralysis of respiration and collapse. The number of red blood cells is significantly so reduced when taken per os. From the side of the stomach and intestines - sharp pains, vomiting, often bloody, bloody diarrhea, acute gastroenteritis, cessation of respiration and cardiac activity; at autopsy - abundantly swollen mucous membranes with many hemorrhages, especially in the stomach and upper parts of the intestinal tract. In chronic poisoning - increased blood clotting, lesions of the bone marrow, increased excretion of Ca and Cl with urine and feces. Antidotes in acute (per os) poisoning: chalk, lime water, proteins (milk, egg white), symptomatic treatment; complete rest. In poisoning due to inhalation of F. or H₂F₂ - moist oxygen, rest; intravenous infusions of glucose, calcium chloride, bloodletting. Poisonings by F. are most often accidental or industrial. H₂F₂ is used in the "etching" of glass, in glass production, various salts of F. are used for impregnating railway ties, for preserving glues and other colloidal solutions, as well as in the fight against insects (addition of salts of F. to wallpaper glue, to paints for the walls of warehouses and storerooms). The medical use of F. and its compounds is very poorly developed: there were attempts to use solutions of H₂F₂ for cauterizations, for smearing malignant growths. Sodium fluoride, NaF, - a white powder soluble in 25 parts of water - was used in the treatment of tuberculosis, also in rheumatism and epilepsy (0.01 g per dose, up to 0.06 g per day); information about the results is very contradictory. Attempts were made to use 0.1% solutions of silver fluoride, AgF, sold under the name thiol, to destroy malignant neoplasms. Of the organic compounds of F., antitussin, Difluordiphenyl, FC₆H₄-C₆H₄F, is sometimes used in the form of a 5% ointment for smearing the chest and back in whooping cough (1-2 g of ointment per day); in 10% ointments or powders - in syphilitic ulcers. -F. in its pure form is not used in military-chemical affairs due to its high reactivity and action on membranes. But its compounds: fluorobenzyl (C₆H₅CH₂F), thionyl fluoride (SO₂F₂), arsenic fluoride (AsF₃), fluorophosgene (COF₂), fluorosulfonic acid [SO₂(OH)F] and others can be used to one degree or another as chemical warfare agents. The discovery of hydrofluoric acid and its salts in forensic chemical cases and in professional poisonings. Aqueous extract of the internal organs (with soluble fluorides in mind) is mixed with lime milk, evaporated and calcined. 1) Parts of the residue are poured in a platinum crucible with concentrated sulfuric acid. The crucible is quickly covered with a watch glass, the lower surface of which is covered with paraffin, the layer of which is partially removed by writing something with a sharp point. The crucible is left to stand for a day. Then the paraffin is removed and the resulting etched inscription is observed. 2) Part of the residue is mixed with sand, placed in a test tube; concentrated sulfuric acid is added. A glass rod with a drop of water is held in the opening of the test tube: the drop becomes cloudy due to the release of silicic acid from the resulting volatile silicon fluoride. For the detection of hydrofluoric acid in the air (e.g. in superphosphate production) air is drawn through rubber tubes into an absorber (see Poisons, isolation) with lime milk and the procedure is as described above. The quantitative determination of hydrofluoric acid in the air is based on the decrease in the color of the solution of iron thiocyanate (when compared with standard solutions of sodium fluoride) due to the formation of a complex of fluoride salt with iron salt: 6NaF+FeCl₃ -> Na₃FeF₆+3NaCl.