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POLYMETHYLENES

Online Encyclopedia
Originally appearing in Volume V22, Page 30 of the 1911 Encyclopedia Britannica.
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POLYMETHYLENES, in chemistry, cyclic compounds, the simplest members of which are saturated hydrocarbons of general formula C„H2,,, where n may be 1 to 9, and known as tri-, tetra-, penta-, hexa-, and hepta-methylene, &c., or cyclopropane, -butane, -pentane, -hexane, -heptane, &c.: CH2(CIHI, CH2C.H2 CH2\CIH2•CH2, CH2\CH2•CH2TCH2,&c. Cyclo-propane, -butane, -pentane, -hexane. The unsaturated members of the series are named on theCH2.CH/ NCH2—•—C (6) I (5) (6) II. (5) As to the stability of these compounds, most trimethylene derivatives are comparatively unstable, the ring being broken fairly readily; the tetramethylene derivatives are rather more stable and the penta- and hexa-methylene compounds are very stable, showing little tendency to form open chain compounds under ordinary conditions (see CHEMISTRY: Organic). Isomerism.—No isomerism can occur in the monosubstitution derivatives but ordinary position isomerism exists in the di-and poly-substitution compounds. Stereo-isomerism may occur: the simplest examples are the dibasic acids, where a cis-(maleinoid) form and a trans- (fumaroid) form have been observed. These isomers may frequently be distinguished by the facts that the cis-acids yield anhydrides more readily than the trans-acids, and are generally converted into the trans-acids on heating with hydrochloric acid. 0. Aschan (Ber., 1902, 35, p. 3389) depicts these cases by representing the plane of the carbon atoms of the ring as a straight line and denoting the substituted hydrogen atoms by the letters X, Y, Z. Thus for dicarboxylic acids (CO2H=X) the possibilities are represented by X X (cis), X x (trans), x X (I). The trans compound is perfectly asymmetric and so its mirror image (I) should exist, and, as all the trans compounds synthetically prepared are optically inactive, they are presumably racemic compounds (see O. Aschan, Chemie der alicyklischen Verbindungen, p. 346 seq.). General Methods of Formation. Hydrocarbons nay be obtained from the dihalogen paraffins by the action of sodium or zinc dust, provided that the halogen atoms are not attached to the same or to adjacent carbon atoms (A. Freund, Monats., 1882, 3, p. 625; W. H. Perkin, jun., Journ. Chem. Soc., 1888, 53, p. 213): CH2•CH2 Br+zNa=zNaBr+ CH2•CH2; by the action of hydriodic acid and phosphorus or of phosphonium iodide on benzene hydrocarbons (F. Wreden, Ann., 1877, 187, p. 153; A. v. Baeyer, ibid., 1870, 1S5, p. 266), benzene giving methylpentamethylene; by passing the vapour of benzene hydrocarbons over finely divided nickel at 18o-25o° C. (P. Sabatier and J. B. Senderens, Comptes rendus, 1901, 132, p. 210 seq.); and from hydrazines of the type C„H2„_1•NH•NH2 by oxidation with alkaline potassium ferricyanide (N. Kijner, Journ. prak. Chem., 1901, 64, p. 113). Unsaturated hydro-carbons of the series may be prepared from the corresponding alcohols by the elimination of a molecule of water, using either the xanthogenic ester method of L. Tschugaeff (Ber. 1899, 32, p• 3332): C„H2,,_,ONa-)G,H2„_10-CS•SNa(R) -G,H2,,_2+COS+R•SH; or simply by dehydrating with anhydrous oxalic acid (N. Zelinsky, Ber., 1901, 34, p• 3249); and by eliminating the halogen acid from mono- or di-halogen polymethylene compounds by heating them with quinoline. Alcohols are obtained from the corresponding halogen compounds by the action of moist silver oxide, or by warming them with silver acetate and acetic acid; by the reduction of ketones with metallic sodium; by passing the vapours of monohydric phenols and hydrogen over finely divided nickel (P. Sabatier and J. B. Senderens, loc. cit.); by the reduction of cyclic esters with Geneva system in which the termination -ane is replaced by-ene, -diene, -triene, according to the number of double linkages in the compound, the position of such double linkages being shown by a numeral immediately following the suffix -ene; for example I. is methyl-cyclo-hexadiene—r. 3. An alternative method employs A. v. Baeyer's symbol 0.. Thus 0 2.4 indicates the presence of two double bonds in the molecule situated immediately after the carbon atoms 2 and 4; for example II. is A 2.4 dihydrophthalic acid. (2) (3) (2) (3) (I)CH3.C~ CH•CH \ CH(4)(t)H02C•CH/C(COzH):CH\CH(4) sodium and alcohol (L. Bouveault and G. Blanc, Corn pies rendus, 1903, 136, p. 1676; 137, p. 6o); and by the addition of the elements of water to the unsaturated cyclic hydrocarbons on boiling with dilute acids. Aldehydes and Ketones.—The aldehydes are prepared in the usual manner from primary alcohols and acids. The ketones are obtained by the dry distillation of the calcium salts of di-basic saturated aliphatic acids (J. Wislicenus, Ann., 1893, 275, p. 309): [CH2•CH2•CO2]2Ca--4CH2•CH2]2CO; by the action of sodium on the esters of acids of the adipic and pimelic acid series (W. Dieckmann, Ber., 1894, 27, pp. 103, 2475) CH2•CH2•CH2•CO2R CH2.CH2•CH . CH2•CH,•CO2R ~CH2•CH2C•02 by the action of sodium ethylate on 3-ketonic acids (D. Vor- lander, Bet., 1895, z8, p. 2348) CCH2•CH2\CO2H-> CH CH2•CH2 CH,( \CO; \CO•CH3 CO•CH2 from sodio-malonic ester and ai3-unsaturated ketones or ketonic esters: (R02C)2CH2+Ph•CH:CH•CO•CH3->PhCHCO/ CHCO2R; \CH2•CO by the condensation of two molecules of aceto-acetic ester with aldehydes followed by saponification (E. Knoevenagel, Ann., 1894, 28,, p. 25; 1896, 288, p. 321; Ber., 1904, 37, p. 4461): 2CH3•CO•CH2•CO2R+OHC.R'-->CH3•C/CH2•CHR'\CH2; "CH.—CO from I.5-diketones which contain a methyl group next the keto-group (W. Kerp, Ann., 1896, 290, p. 123): CH2•C(CH3) 3CH3•CO•CH3->(CHa)2C< %CH;
End of Article: POLYMETHYLENES
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