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Encyclopedia Britannica - Main :: PAI-PAS |
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PARAFFIN , in chemistry, the generic name given to the hydro-carbons of the general formula
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
heating
% 3.0 39.0 18.0 I0.0 30.0 of sodium, in absolute ether solution (A. Wurtz
(CnH2-F1)2 CO> (CnH2,,.{.1)2C C12i' (CH2,,.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
The principal members of the series are shown in the following table: Name. Formula
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 9899 Octane C,H,8 125126 Nonane C,H2o -51 15o Decane C,oH22 -31 1734 Undecane C11H24 -26.5 196 Dodecane C12H26 -12 214216 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
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
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
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