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PARAFFIN

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Originally appearing in Volume V20, Page 756 of the 1911 Encyclopedia Britannica.
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PARAFFIN, in chemistry, the generic name given to the hydro-carbons of the general formula CnH2a+2. Many of these hydrocarbons exist as naturally occurring products, the lower (gaseous) members of the series being met with as exhalations from decaying organic matter, or issuing from fissures in the earth; and the higher members of the series occur in petroleum (chiefly American) and ozokerite. They may be synthetized by reducing the alkyl halides (preferably the iodides) with nascent hydrogen, using either sodium amalgam, zinc and hydrochloric acid, concentrated hydriodic acid (Berthelot, Jour. prak. Chem. 1868, 104, p. 103), aluminium amalgam (H. Wislicenus, ibid., 1896 (2), S4) 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 I20'140' with aluminium chloride in the proportion of three molecules of alkyl halide to one molecule of aluminium chloride (B. KOhnlein, Ber., 1883, 16, p. 56o) ; by heating with zinc and water to 150—16o° C. (E. Frank-land, Ann., 1849, 71, p. 203; 185o, 74, p. 41), 2 RI+2Zn+2H20= 2RH+ZnI2+Zn(OH)2; by conversion into zinc alkyls, which are then decomposed by water, ZnR2+2H2O=2 RH+Zn(OH)2; 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), RMgI+ H2O = RH + MgI (OH) ; by the action of potassium hydride (H. Moissan, Comptes rendus, 1902, 134, p. 389) ; and by the action % 3.0 39.0 18.0 I0.0 30.0 of sodium, in absolute ether solution (A. Wurtz, Ann. chim. phys., t855 (3), 44, P. 275), 2RI+2Na=R•R+2NaI. They may also be obtained by the reduction of the higher fatty acids with hydriodic acid (F. Krafft, Ber., 1882, 15, pp. 1687, 1711), CnH2,~O,+6HI= CnH2n.F2+2H2O+312; by the conversion of ketones into ketone chlorides by the action of phosphorus pentachloride, these being then reduced by hydriodic acid, (CnH2„-F1)2 CO—> (CnH2,,.{.1)2C C12—i' (C„H2,,.i.i)2CH2; by the reduction of unsaturated hydrocarbons with hydrogen in the presence of a " contact " substance, such, for example, as reduced nickel, copper, iron or cobalt (P. Sabatier and J. B. Senderens, Ann. chim. phys., 1905 [8], 4, pp. 319, 433) ; by the elimination of carbon dioxide from the fatty acids on heating their salts with soda-lime or baryta, CH3CO2Na+NaOH=CH4+Na2CO,, or by heating their barium salts with sodium methylate in vacuo (I. Mai, Ber., 1889, 22, p. 2133) ; by the electrolysis of the fatty acids (H. Kolbe, Ann., 1849, 69, p. 257), 2C2H402=C2H6+2CO2+H2O; and by the action of the zinc alkyls on the ketone chlorides, (CH3)2CC12+ Zn(CH2)2 = C5H12+ZnC12. The principal members of the series are shown in the following table: Name. Formula. Melting- Boiling- Melting- point. point. Methane CH4 -184° — 164° (76o mm.) Ethane C2116 -172.1 ° — 84.1 ° (749 ,, ) Propane C3H6 -45° -4~•5° Normal Butane C4Hio — +1 Isobutane „ — -17° Normal Pentane . C51112 — +36.3° Secondary Pentane — +30.4° Tertiary Pentane — +9° Hexane C6H14 — +69° Heptane C7H16 — 98—99° Octane C,H,8 — 125—126° Nonane C,H2o -51° 15o° Decane C,oH22 -31° 173—4° Undecane C11H24 -26.5° 196° Dodecane C12H26 -12° 214—216° Tridecane C12Hz6 -6.2° 234° Tetradecane C,4H30 +4° 252° Pentadecane C16H32 +lo° 270° Hexadecane C161133 +18° 287° Heptadecane C171136 +22° 170° (15 mm.) Octadecane C16H66 +28° 317° Nonadecane C19H40 +32° 330° Eicosane C20Ha2 +37° 205° (15 mm.) Heneicosane C211-13.1 +4o° 215° („ ) Docosane C22H+6 +44° 224° Tricosane C25H 48 +48° 234° („ ) Tetracosane C24H,o +51° 243° ( ) Hexacosane C26H94 +58° — Hentriacontane C,1H6e +68° 302° (15 mm.) Dotriacontane C22H66 +70.5° 331° („ ) Pentatriacontane Ca6H72 +75° 331° l ) Dimyricyl CeoHl22 +102° — lowest members of the series are gases at ordinary temperature; those of carbon content C6 to C15 are colourless liquids, and the higher members from C19 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, decreasing 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 paraffins are characterized 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, 20, p. 664). Dilute nitric acid, when heated with the paraffins in a tube, converts them into secondary and tertiary nitro-derivatives (M. Konowalow, Ber., 1895, z8, 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 succinic 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 reactionis very energetic, oxidation products (fatty acids and dibasic acids) and a small quantity of polynitro compounds are obtained (W. Markownikow, Cenlralblatt, 1899, I, p. 1064; Ber., 1899, 32, p. 1441). Chlorine reacts with the paraffins, readily substituting hydrogen. Isomeric hydrocarbons in this series first appear with butane, the number increasing rapidly as the complexity of the molecule increases. For a means of deter-mining the number of isomers see E. Cayley, Ber., 1875, 8, p.Io56; F. Hermann, Ber., 1898, 31, p. 91. For Methane see MARSH GAS. Ethane, C2H6, occurs in crude petroleum. It may be prepared by the general methods given above; by heating mercury ethyl with concentrated sulphuric acid (C. Schorlemmer, Ann., 1864, 132, p. 234) ; or by heating acetic anhydride with barium peroxide (P Schtitzenberger, Zeit. Chemie, 1865, p. 703), 2(CH2CO)2O+BaO2=C2H6+Ba(C2H,02)2+2CO2. It is a colourless gas which can be liquefied at 4° C. by a pressure of 46 atmospheres. By slow combustion it yields first water and acetaldehyde, which then oxidizes to oxides of carbon and water (W. A. Bone; see FLAME), whilst in ozonized air at too° it gives ethyl alcohol, together with acetaldehyde and traces of formaldehyde (Bone, Proc. Chem. Soc., 1904, 29, p. 127). Dimyricyl (hexacontane), C60H122, is prepared by fusing myric l iodide with sodium (C. Hell and C. Hagele, Ber., 1889, 22, p. 502). It is only very slightly soluble in alcohol and ether.
End of Article: PARAFFIN
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