Benzene

“ Let us now take the case of the production of an aniline colour, and let us try to discover what aniline is, and how formed. I pointed to benzene or benzol in the table as a hydrocarbon, C6H6, which forms a principal colour-producing constituent of coal-tar. If you desire to produce chemical appetite in benzene, you must rob it of some of its hydrogen. ”

“ SOME DERIVATIVES OF BENZENE
Attention has been called to the complex nature of coal tar. Among the compounds present are the hydrocarbons, benzene, toluene, naphthalene, and anthracene. These compounds are not only useful in themselves but serve for the preparation of many other important compounds known under the general name of coal-tar products.
Nitrobenzene (oil of myrbane) (C6H5NO2) . When benzene is treated with nitric acid a reaction takes place which is expressed by the following equation:
C6H6 + HNO3 = C6H5NO2 + H2O.
The product C6H5NO2 is called nitrobenzene. ”

“ Substitution of the Benzene Ring.—As a general rule, homologues and mono-derivatives of benzene react more readily with substituting agents than the parent hydrocarbon; for example, phenol is converted into tribromphenol by the action of bromine water, and into the nitrophenols by dilute nitric acid; similar activity characterizes aniline. Not only does the substituent group modify the readiness with which the derivative is attacked, but also the nature of the product. ”

“ If each of the free units is satisfied by an atom of hydrogen, we obtain benzene, which, as Kekulé demonstrated, becomes the centre round which the great group of aromatic compounds might be said to revolve. Benzene was discovered by Faraday in 1825 among the volatile liquids condensed from the oil-gas made by the Portable Gas Company. It had already played a notable part in the development of chemical theory in connection with the124 discovery of isomerism. ”

“ Many of the popular synthetic remedies belong to the benzene series. Benzene is obtained from coal-tar, but, as shown by Berthelot, it is possible to prepare it by heating the gaseous hydrocarbon, acetylene, C2H2, in a closed vessel. By this means three molecules of acetylene are condensed into one, C6H6, which is benzene. Benzene acted upon by nitric acid yields nitrobenzene, and this by the action of nascent hydrogen is changed into aniline. ”

“ Both toluene and benzene are common solvents with multiple occupational uses; furthermore exposure to toluene and benzene (less commonly) can occur from environmental and other sources. This method measures the quantity of the two target metabolite analytes in urine. ”

“ H hydrocarbons.-Cyclo-hexane, or hexahydro benzene, CSHW, is obtained by the action of sodium on a boiling alcoholic solution of 1~6-dibromhexane, and by passing the vapour of benzene, mixed with hydrogen, over finely divided nickel. It is a liquid with an odour like that of benzene. It boils at 80-81° C. Nitric acid oxidizes it to adipic acid. ”

“ The constitution of the benzene ring, the isomerism of its derivatives, and their syntheses from aliphatic or open-chain compounds, are treated in the article Chemistry. A summary of its chemical transformations may be given here, and reference should be made to the articles on the separate compounds for further details.
Passed through a red-hot tube, benzene vapour yields hydrogen, diphenyl, diphenylbenzenes and acetylene; the formation of the last compound is an instance of a reversible reaction, since Berthelot found that acetylene passed through a red-hot tube gave some benzene. ”

“ Benzene is very stable to oxidants, in fact resistance to oxidation is a strong characteristic of the benzene ring. Manganese dioxide and sulphuric acid oxidize it to benzoic and o-phthalic acid; potassium chlorate and sulphuric acid breaks the ring; and ozone oxidizes it to the highly explosive white solid named ozo-benzene, C6H6O6. Hydriodic acid reduces it to hexamethylene (cyclo-hexane or hexa-hydro-benzene) ”

“ Santesson did not succeed in his experiments on animals in producing chronic poisoning by inhalation of benzine and of benzene fumes (which two completely different poisons he does not distinguish strictly from each other, as is the case, unfortunately, with many other writers) . My experimental researches upon the poisonous effect of pure benzene, pure toluene, cumene, thiophene, and the most important kinds of commercial benzol gave the following results:
For rabbits the limit of toxicity is a proportion of 0·015 to 0·016 per thousand pure benzene in the air, that is 0·015 to 0·016 c.c. ”

“ The fumes exhausted should be carefully condensed by cooling or absorbed by a spray of water or oil.
In view of the poisonous nature of benzene, the apparatus, stills, receivers, tanks, tank waggons, &c., should only be entered for the purpose of cleaning or repairing after preliminary thorough removal of all residue of benzene, complete isolation from all similar apparatus near, and thorough ventilation. [286] Workers entering the stills, &c., should always be equipped with breathing apparatus (smoke helmets) and with a supply of oxygen. ”

“ Thus detonating gas when exploded under pressure gives a brilliant light.
[45] If hydrogen gas be passed through a volatile liquid hydrocarbon—for instance, through benzene (the benzene may be poured directly into the vessel in which hydrogen is generated) —then its vapour burns with the hydrogen and gives a very bright flame, because the resultant particles of carbon (soot) become incandescent. Benzene, or platinum gauze, introduced into a hydrogen flame may be employed for illuminating purposes. ”

“ Now benzene also contains 92.3 per cent. of carbon and 7.7 per cent. by weight of hydrogen in its composition, but its molecule contains 6 atoms of each element. When the chemical formula representing a compound body indicates a substance which is, or can be obtained as, a gas or vapour, it convoys another idea over and above those mentioned on a previous page. The formula "C_2H_2," for example, means 1 molecule, or 26 parts by weight of acetylene, just as "H_2" means 1 molecule, or 2 parts by weight of hydrogen ”

“ Similarly, the replacement of hydrogen by a water-residue, hydroxyl, gives rise to a phenol. The group of carbon, oxygen, and hydrogen atoms which confers the property of acidity upon an organic compound is a half-molecule of oxalic acid—it is known as the carboxyl group. Thus benzoic acid is the carboxyl-derivative of benzene, and the phthalic acid with which we are now concerned is a dicarboxyl-derivative of benzene. It is related to benzoic acid in the same way that diamidobenzene is related to aniline. ”

“ It is insoluble in benzene, chloroform, acetone, ether and ligroin; soluble in glacial acetic acid, from which it separates on cooling in colorless, crystalline condition; insoluble in the cold in water, alcohol and ammonia, but by boiling with these reagents, or by long standing in the cold, it is dissolved with decomposition. It was dissolved in hot water and the solution, which was acid in reaction, was neutralized with potassium carbonate. ”

“ The sub-divisions of (2) the organic substances are into (a) the unsaturated carbon compounds—benzene, petroleum, methyl-, ethyl-, amyl-, and allyl-alcohol, oxalic acid, formal- and acetaldehyde, acrolein, acetone, methyl-bromide and iodide, nitro-glycerin, dimethyl-sulphate and amyl acetate, and (b) the aromatic series benzene, nitro-, chloro-nitro-, dinitro-, chloro-dinitro-benzene, phenol, picric acid, phenyl-hydrazine, aniline, and certain aniline colours, para-nitraniline, pyridine, naphthalene, nitro-naphthalene, naphthlyamine, naphthol, benzidine, acridine, turpentine, and nicotine. ”

“ The hydrocarbons mostly belong to the benzene series CnH2n–6, the naphthalene series CnH2n–12, and the anthracene and phenanthrene series CnH2n–18. Small quantities of “fatty” (“aliphatic”) hydrocarbons are never absent, even in pure tars, and are found in considerable quantities when shales and similar matters have been mixed with the coal in the gas-retorts. They belong mostly to the paraffins CnH2n+2, and the olefines CnH2n. The “asphalt” or soluble part of the pitch is also a mixture of hydrocarbons, of the formula CnH2n ”

“ What products come off depends not only upon the composition of the particular variety of coal used, but upon the heat, pressure and rapidity of distillation. The way you run it depends upon what you are most anxious to have. If you want illuminating gas you will leave in it the benzene. If you are after the greatest yield of tar products, you impoverish the gas by taking out the benzene and get a blue instead of a bright yellow flame. If all you are after is cheap coke, you do not bother about the by-products, but let them escape and burn as they please. ”

“ Hitherto we have generally restricted ourselves to syntheses which result in the production of a true benzene ring; but there are many reactions by which reduced benzene rings are synthesized, and from the compounds so obtained true benzenoid compounds may be prepared. Of such syntheses we may notice: the condensation of sodium malonic ester to phloroglucin tricarboxylic ester, a substance which gives phloroglucin or trioxybenzene when fused with alkalis, and behaves both as a triketohexamethylene tricarboxylic ester and as a trioxybenzene tricarboxylic ester ”

“ During recent years an immense number of ringed or cyclic compounds have been discovered, which exhibit individual characters more closely resembling benzene, naphthalene, &c. than purely aliphatic substances, inasmuch as in general they contain double linkages, yet withstand oxidation, and behave as nuclei, forming derivatives in much the same way as benzene. ”

“ Several benzene extracts of samples of aluminum reduction plant emissions were combined to give a solution containing 1.35 mg of benzene-soluble material per sample; nine aliquots of this solution gave residue weights with a relative standard deviation of 0.02. Benzene extracts of six blank filters gave residue weights with a relative standard deviation of 0.23 [6] . ”

“ The ringed structure of benzene, C6H6, was first suggested in 1865 by August Kekulé, who represented the molecule by six CH groups placed at the six angles of a regular hexagon, the sides of which denoted the valencies saturated by adjacent carbon atoms, the fourth valencies of each carbon atom being represented as saturated along alternate sides. ”

“ Another hexa-substituted benzene compound capable of direct synthesis is mellitic acid or benzene carboxylic acid, C6 (COOH) 6. This substance, first obtained from the mineral honeystone, aluminium mellitate, by M.H. Klaproth in 1799, is obtained when pure carbon (graphite or charcoal) is oxidized by alkaline permanganate, or when carbon forms the positive pole in an electrolytic cell (Ber., 1883, 16, p. 1209) . The composition of this substance was determined by A. von Baeyer in 1870, who obtained benzene on distilling the calcium salt with lime. ”

“ Based on the spiking data, if the total particulate loading was greater than or equal to 0.10 mg per filter, the measurement determination will be within 25% of the true value95% of the time if the true bias is less than 10.0%. The bias for the benzene-soluble fraction was negative (see the data above) , and since the bias for the benzenesoluble fraction varied little, the bias was pooled over the spiking range of 1.85 to 0.20 mg per filter. It was determined that the 25% accuracy criterion was met if the benzene-soluble fraction was greater than or equal to 0.20 mg per filter. ”

“ Properties of the hydrocarbons. The lower members of the first two series of hydrocarbons mentioned are all gases; the succeeding members are liquids. In some series, as the methane series, the higher members are solids. The preparation and properties of methane and acetylene have been discussed in a previous chapter. Ethylene is present in small quantities in coal gas and may be [Pg 401] obtained in the laboratory by treating alcohol (C2H6O) with sulphuric acid:
C2H6O = C2H4 + H2O.
Benzene, the first member of the benzene series, is a liquid boiling at 80°. ”

“ In other respects this preparation should correspond to the pharmacopeial tests for liquid petrolatum and have a specific gravity of about 0.860 to 0.875 at 15 C. Like the heavy variety of liquid petrolatum, it is insoluble in water and alcohol, but soluble in boiling absolute alcohol and rapidly soluble in ether, chloroform, carbon disulphid, petroleum benzin, benzene and fixed and volatile oils. It serves as a solvent for volatile oils and related substances like camphor, menthol and thymol. ”

“ It will be advantageous if the spectra of ammonia, benzene, aniline and dimethyl aniline be compared, when the remarkable coincidences will at once become apparent, as also the different weighting of the molecule. The spectrum of nitrobenzene is also worth comparing with benzene and nitric acid. In our own minds there lingers no doubt as to the easy detection of any radical which we have examined, . ”

“ Use forceps to fold and transfer the filter to a 10-mL volumetric flask. Add 10.0 mL 99:1 benzene:methanol. Stopper and shake the flask vigorously for 1 min. Allow the flask to stand at least 2 h. Transfer the solution in the impinger to a separatory funnel. Wash the impinger with two 15-mL portions of 0.1 M NaOH, and add the washings to the separatory funnel. Add 0.05 M H2SO 4 until the pH is less than 7. Extract the Kepone with two 5-mL portions of benzene. Shake vigorously for 2 min and allow 5 min for the phases to separate. Combine the benzene layers in a 10-mL volumetric flask. ”