Chemistry of Paraffin

PARAFFIN, CHEMISTRY OF. Paraffin is the generic name given to the saturated hydrocarbons of the general formula Many of these hydrocarbons exist as naturally occur ring products, the lower (gaseous) members of the series being met with as exhalations from decaying organic matter (marsh gas) or issuing from fissures in the earth, or in the gases from coal mines; the higher members occur in petroleum and ozokerite.

The principal members of the series are shown in the following table :— Sharples' Process.—The amorphous distillate is diluted with approximately an equal bulk of petrol or a fraction of petrol from which the more volatile part has been distilled off. The mixture is now very slowly cooled till it reaches a temperature of about 10° F throughout a period of 20-30 hours. It is then conveyed into the bowl of a centrifuge rotating at 30,00o revolu tions per minute when the slightly heavier wax is flung outward against the periphery whilst the slightly lighter solution occupies the middle of the bowl, by natural law. The centrifuge runs continuously and there are consequently ejected from spouts at the top, (a) amorphous wax that is melted by suitable heating means and (b) a petrol solution of de-waxed oil. These run away to separate tanks. The wax obtained after removing some of the solvent that is conveyed with it is in the micro-crystalline state and it is converted into macro-crystalline wax by a redistillation under cracking conditions, that is to say, by distilling at a relatively high temperature, thus permitting a re-adjustment of the molecules. The distillate from the amorphous wax contains oil and crystalline wax and may be put through the sheds along with the pressable wax distillate.

Uses of Paraffin.

Although paraffin wax may be regarded as a by-product of petroleum distillation, the world's supply is very considerable, amounting to approximately 200,000 tons a year. It finds its chief use in replacing and as a substitute for certain expensive natural waxes such as beeswax. It enters largely into the composition of floor polishes; it is used for filling leather and as an insulator in the electrical trades. A very large amount is also used for water-proofing paper and cardboard, and thus is an essential component of water-proof receptacles for packing; during the World War, for example, jam pots were made of stout paper rendered air-tight and water-proof by means of paraffin. In a similar way it may be applied for water-proofing The lowest members of the series are gases at ordinary temper ature; those of carbon content to C15 are colourless liquids, and the higher members from C16 onwards are crystalline solids. The highest members only volatilize without decomposition when distilled under diminished pressure. They are not soluble in water, although the lower and middle members of the series are readily soluble in alcohol and ether; the solubility, however, de creases with increase of molecular weight, so that the highest members of the series are almost insoluble in these solvents. The specific gravity increases with the molecular weight but always remains below that of water. The liquid paraffins have a char acteristic smell, more pronounced in the case of the branched chain members. The paraffin may be synthesized by reducing the alkyl halides (preferably the iodides) with nascent hydrogen, using either sodium amalgam, zinc and hydrochloric acid, con centrated hydriodic acid (Berthelot, Jour. prak. Chem. i868,

p. 103), aluminium amalgam (H. Wislicenus, ibid., 1896 [2], 54) or the zinc-copper couple (J. H. Gladstone and A. Tribe, Ber., 1873, 6, p. 202 seq.) as reducing agents.

They may also be derived from alkyl halides by heating to 120-140° C with aluminium chloride in the proportion of three molecules of alkyl halide to one molecule of aluminium chloride (B. Kohn, Ber., 1883, 16, p. 56o) ; by heating with zinc and water to 150-i60° C. (E. Frankland, Ann., 1849, 71, P. ; 74 p. 2RI-F 2Zn+ 2RH Zn(OH)2, by conver sion into zinc alkyls, which are then decomposed by water, by conversion into the Grignard reagent with metallic magnesium and decomposition of this either by water, dilute acids or preferably ammonium chloride (J. Houben, Ber., 1905 38, p. 3019), ; by the action of potassium hydride (H. Moissan, Comptes rendus, 1902, 134, P. 389) and by the action of sodium in absolute ether solution (A. Wurtz, Ann. chim. phys., [3], 44, P. 2RI+2Na=R.R+2NaI. They may also be obtained by the re duction of the higher fatty acids with hydriodic acid (F. Krafft, Ber., 1882, 15, pp. 1687-1711), by the reaction of unsaturated hydrocarbons with hydrogen in the presence of a "catalyst" such, for example, as reduced nickel, copper, iron or cobalt (P. Sabatier and J. B. Senderens, Ann. chim. phys., 1905 [8], 4, Pp. 433) ; by the elimination of carbon dioxide from the fatty acids on heating their salts with soda-lime or baryta, CRO-Na2CO3, or by heating their barium salts with sodium methylate in vacua (I. Mai, Ber., 1889, 22, p. 2133) ; by the electrolysis of the fatty acids (H. Kolbe, Ann., 1849, 69, P. and by the action of the zinc alkyls on the ketone chlorides, (CH3)2CCI2+Zn(C1/3)2=C5H12-1-ZnC12. The paraffins are char acterized by their great inertness towards most chemical reagents. Fuming sulphuric acid converts the middle and higher members of the series into sulphonic acids and dissolves the lower members (R. A. Worstall, Amer. Chem. Journ., 1898, 2o, p. Dilute nitric acid, when heated with the paraffins in a tube, converts them into secondary and tertiary nitro-derivatives (M. Konowalow, Ber., 1895, 28, p. 1852), whilst long boiling with strong nitric acid or nitro-sulphuric acid converts the middle and higher members of the series partly into primary mono- and di-nitro compounds and partly oxidizes them to carbonic, acetic, oxalic and succirric acids (Worstall, ibid., 20, p. 202; 21, p. 211). Fuming nitric acid only reacts slowly with the normal paraffins at ordinary temperature, but with those containing a tertiary carbon atom the reaction is very energetic, oxidation products (fatty acids and dibasic acids) and a small quantity of polynitro com pounds being obtained (W. Markownikow, Centralblatt, 2899, 1, p. 1064; Ber., 1899, 32, p. 1441). Chlorine and bromine react with the paraffins, readily substituting hydrogen. Isomeric hydro carbons in this series first appear with butane, the number in creasing rapidly as the complexity of the molecule increases. Isomerism in the paraffin series is due to the variety of linking between the carbon atoms.

occurs in the natural gas associated with petroleu

m to gether with propane and butane C4Hio; pentane and higher members up to decane are present in petrol, probably as isomers. Solid paraffin wax contains the higher members. (For methane see MARSH GAS.) (A. E. D.)