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Originally appearing in Volume V22, Page 31 of the 1911 Encyclopedia Britannica.
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C2H 4Br2+2NaCH (CO2R)2->(CH2)2C (CO2R)2 +CH2 (CO2R)2 ; ethyl butane tetracarboxylate is also formed which may be converted into a tetramethylene carboxylic ester by the action of bromine on its disodium derivative (W. H. Perkin and Sinclair, ibid., 1829, 61, p. 36). The esters of the acids may also be obtained by condensing sodio-malonic ester with a-halogen derivatives of unsaturated acids: CH•CO2R CH8•CH: CBr•CO2R+NaCH(CO2R),_ CH3•CH~ \C(CO2R)2 ; by the action of diazomethane or diazoacetic ester on the esters of unsaturated acids, the pyrazoline carboxylic esters so formed losing nitrogen when heated and yielding acids of the cyclopropane series (E. Buchner, Ber., 189o, 23, p. 703; Ann., 1895, 284, p. 212; H. v. Pechmann, Ber., 1894, 27, p. 1890: CH2N2+ C!I. I H•CO2R N:N i H•CO2R H2C/CHCO2R CH•CO,R H2C—CH•CO2R \CHCO,R; and by the Grignard reaction (S. Malmgren, Ber., 1903, 36, pp. 668, 2622; N. Zelinsky, ibid., 1902, 35, p. 2687). Cyclo-propane Group. Trimethylene, C3H6, obtained by A. Freund (Monats., 1882, 3, p. 625) by heating trimethylene bromide with sodium, is a gas, which may be liquefied, the liquid boiling at -35° C. (749 mm.). It dissolves gradually in concentrated sulphuric acid, forming propyl sulphate. Hydriodic acid converts it into n-propyl iodide. It is decomposed by chlorine in the presence of sunlight, with explosive violence. It is stable to cold potassium permanganate. Cyclo-propane carboxylic acid, C3H6•CO2H, is prepared by heating the 1.1-dicarboxylic acid; and by the hydrolysis of its nitrile, formed by heating y-chlorbutyro-nitrile with potash (L. Henry and P. Dalle, Chem. Centralblatt, 1901, I, p. 1357; 1902, I, p. 913). It is a colour-less oil, moderately soluble in water. The 1.1 dicarboxylic acid is prepared from ethylene dibromide and sodio-malonic ester. The ring is split by sulphuric or hydrobromic acids. The cis 1.2-cyclo-propane dicarboxylic acid is formed by eliminating carbon dioxide from cyclo-propane tricarboxylic acid -1.2.3 (from af-dibrompropionic ester and sodio-malonic ester). The trans-acid is produced on heating pyrazolin-4.5-dicarboxylic ester, or by the action of alcoholic potash on a-bromglutaric ester. It does not yield an anhydride. Cyclo-butane Group. Cyclo-butane, C4H8, was obtained by R. Willstatter (Ber., 1907, 40, p. 3979) by the reduction of cyclobutene by the Sabatier and Senderens method. It is a colourless liquid which boils at 11-12° C,, and its vapour burns with a luminous flame. Reduction at 18o-2oo° C. by the above method gives n-butane. Cyclo-butene, C4H6, formed by distilling trimethyl-cyclo-butyl. ammonium hydroxide, boils at 1.5-2.0° C. (see N. Zelinsky, ibid., p. 4744; G. Schweter, ibid., p. 1604). When sodio-malonic ester is condensed with trimethylene bromide the chief product is ethyl pentane tetracarboxylate, tetramethylene I.I-dicarboxylic ester being also formed, and from this the free acid may be obtained on hydrolysis. It melts at 154-156° C., losing carbon dioxide and passing into cyclo-butane carboxylic acid, C4H7CO2H. This basic acid yields a monobrom derivative which, by the action of aqueous potash, gives the corresponding hydroxycyclo-butane carboxylic acid, C4H6(OH)•CO2H. Attempts to eliminate water from this acid and so produce an unsaturated acid were unsuccessful; on warming with sulphuric acid, carbon monoxide is eliminated and cyclo-butanone (keto-tetramethylene) is probably formed. The truxillic acids, C18H,604, which result by the hydrolytic splitting of truxilline, Ca8H46N2O8, are phenyl derivatives of cyclo-butane. Their constitution was determined by C. Liebermann (Bee., 1888, 21, p. 2342; 1889, 22, p. 124 seq.). They are polymers of cinnamic acid, into which they readily pass on distillation. The a-acid on oxidation yields benzoic acid, whilst the fl-acid yields benzil in addition. The a-acid is diphenyl-2.4-cyclo-butane dicarboxylic acid -1.3; and the l3-acid diphenyl-3.4-cyclo-butane dicarboxylic acid -1.2. By alkalis they are transformed into stereo-isomers, the a-acid giving y-truxillic acid, and the (3-acid S-truxillic acid. The a-acid was synthesized by C. N. Riiber (Ber., 1902, 35, p. 2411; 1904, 37, p. 2274), by oxidizing diphenyl-2.4-cyclo-butane-bismethylene malonic acid (fron cinnamic aldehyde and malonic acid in the presence of quinoline) with potassium permanganate. Cyclo-pentane Group. Derivatives may be prepared in many cases by the breaking down of the benzene ring when it contains an accumulation of negative atoms (T. Zincke, Ber., 1886-1894; A. Hantzsch, Ber., 1887, 2o, p. 2780; 1889, 22, p. 1238), this type of reaction being generally brought about by the action of chlorine on phenols in the presence of alkalis (see CHEMISTRY: Organic). A somewhat related example is seen in the case of croconic acid, which is formed by the action of alkaline oxidizing agents on heixa-oxybenzene: HO•C•C(OH) : C(OH) HO•C•CO•CO HO•C•CO II HO•C•C(OH) ; C(OH) HO.C•CO•CO HO•C•CO'CO Hexa-oxybenzene. Rhodizonic acid. Croconic acid. Cyclo-pentane, C5H1o, is obtained from cyclo-pentanone by reducing it to the corresponding secondary alcohol, converting this into the iodo-compound, which is finally reduced to the hydrocarbon (J. Wislicenus, Ann., 1893, 275, p. 327). It is a colourless liquid which boils at 50-51 ° C. Methyl-cyclo-pentane, C6HOCH3, first obtained by F. Wreden (Ann., 1877, 187, p. 163) by the action of hydriodic acid and red phosphorus on benzene, and considered to be hexahydrobenzene, is obtained synthetically by the action of sodium on 1.5 dibromhexane; and by the action of magnesium on acetylbutyl iodide (N. Zelinsky, Ber., 1902, 35, p. 2684). It is a liquid boiling at 72° C. Nitric acid (sp. gr. 1.42) oxidizes it to succinic and acetic acids. Cyclo-pentene, C5H8, a liquid obtained by the action of alcoholic potash on iodo-cyclo-pentane, boils at 45° C. Cyclopentadiene, C5H6, is found in the first runnings from crude benzene distillations. It is a liquid which boils at 410 C. It rapidly polymerizes to di-cyclo ,pentadiene. The .CH2. group is very reactive and behaves in a similar manner to the grouping .CO•CH2.CO• in open chain compounds, e.g. with aldehydes and ketones it gives the fulvenes, substances characterized by their intense orange-red colour HC: CH (J. Thiele, Ber., 1900, 33, p. 669). Phenylfulven, '>C:CHPh, HC: CH/ obtained from benzaldehyde and cyclo-pentadiene, forms dark red plates. Diphenylfulven, from benzophenone and cyclo-pentadiene, crystallizes in deep red prisms. Dimethylfulven is an orange-coloured oil which oxidizes rapidly on exposure. Concentrated sulphuric acid converts it into a deep red tar. Cyclo-pentanone, C6H80, first prepared pure by the distillation of calcium adipate (J. Wislicenus, Ann., 1893, 275, p. 312), is also obtained by the action of sodium on the esters of pimelic acid; by the distillation of ,calcium succinate; and by hydrolysis of the cyclopentanone carboxylic acid, obtained by condensing adipic and oxalic esters in the presence of sodium ethylate. Reduction gives cyclo-pentanol, C6H9OH. Croconic acid (dioxy–cyclo-pentene-trione), C6H206, is formed when triquinoyl is boiled with water, or by the oxidation of hexa-oxybenzene or dioxydiquinoyl in alkaline solution (T. Zincke, Ber., 1887, 20, p. 1267). It has the character of a quinone. On oxidation it yields cyclo-pentane-pentanone (leuconic acid). Derivatives of the cyclo-pentane group are met with in the breaking-down products of the terpenes (q.v.). Cam pholactone, C9H1402, is the lactone of trimethyl-2.2.3-cyclopentanol-5-carboxylic acid-3. For an isomer, isocampholactone (the lactone of trimethyl-2.2.3-cyclo-pentanol-3-carboxylic acid-,) see W. H. Perkin, jun., Proc. Chem. Soc., 1903, 19, p. 61. Lauronolic acid, C9H1402, is trimethyl-2.2.3-cyclo-pentene-4-acid-I. Isolauronolic acid, C9H14O2, is trimethyl-2.2.3-cyclo-pentene-3-acid-4. Campholic acid, C1oH18O2, is tetramethyl- acid-3. Camphononic acid, C9H1403, is trimethyl-2.2.3-cyclo-pentanone-i-carboxylic acid-3. Camphorphorone, C9H140, is methyl-2-isobuty-lene-5-cyclo-pentanone-1. Isothujone, C10H160, is dimethyl-i.2-isopropyl-3-cyclo-pentene-I-one-5. (F. W. Semmler, Ber., 1909, 33, Bou eault and G. Blanc (Comptes rendus, 1903, 136, p. 1460), prepared hydrocarbons of the cyclo-pentane series from cyclohexane compounds by the exhaustive methylation process of A. W. Hofmann (see PYRIDINE). For phenyl derivatives of the cyclopentane group see F. R. Japp, Jour. Chem. Soc., 1897, 71, pp. 139, 144; H. Stobbe, Ann., 1901, 314, p. III; 315, p. 219 seq.; 1903, 326, p. 347. Cyclo-hexane Group. Hydrocarbons.—Cyclo-hexane, or hexahydro benzene, C6H12r is obtained by the action of sodium on a boiling alcoholic solution of i•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 8o–81 ° C. Nitric acid oxidizes it to adipic acid. When heated with bromine in a sealed tube for some days at 150–200° C., it yields–tetrabrombenzene (N. Zelinsky, Ber., 1901, 34, p. 2803). It is stable towards halogens at ordinary temperature. Benzene hexachloride, C0H6C16r is formed by the action of chlorine on benzene in sunlight. By recrystallization from hot benzene, the a form is obtained in large prisms which melt at 157° C., and at their boiling-point. decompose into hydrochloric acid and trichlorbenzene. The l3 form results by chlorinating boiling benzene in sunlight, and may be separated from the a variety by distillation in a current of steam. It sublimes at about 31o° C Similar varieties of benzene hexabromide are known. IZexahydrocymene (methyl-I-isopropyl-4-cyclo-hexane), C10H26, is important since it is the parent substance of many terpenes (q.v.). It is obtained by the reduction of 1.4 dibrommenthane with sodium (J. de Montgolfier, Ann. chim. phys., 1880 [5], 19, p. 158), or of cyrnene, limonene, &c., by Sabatier and Senderens's method. It is a colourless liquid which boils at 18o° C. Cyclo-hexene (tetrahydrobenzene), C6H19r was obtained by A. v. Baeyer by removing the elements of hydriodic acid from iodocyclo-hexane on boiling it with quinoline. It is a liquid which boils at 82° C. Hypochlorous acid converts it into 2-chlor-cyclo-hexanol-I, whilst potassium permanganate oxidizes it to cyclo-hexandi-ol. Cyclo-hexadiene (dihydrobenzene), C6H8.—Two isomers are possible, namely cyclo-hexadiene-i•3 and cyclo-hexadiene-1.4. A. v. Baeyer obtained what was probably a mixture of the two by heating 1.4 dibrom-cyclo-hexane with quinoline. C. Harries (Ann., 1903, 328, p. 88) obtained them tolerably pure by the dry distillation of the phosphates of I.3-diamino and I.4-diamino-cyclo-hexane. The 1.3 compound boils at 81-82° C. and on oxidation yields succinic and oxalic acids. The I.4 compound also boils at 81-82° C. and on oxidation gives succinic and malonic acids. Alcohols.—Cyclo-hexanol, C6H11OH, is produced by the reduction of the corresponding ketone, or of the iodhydrin of quinite. Nitric acid oxidizes it to adipic acid, and chromic acid to cyclo-hexanone. Quinite (cyclo-hexanediol-1.4) is prepared by reducing the corresponding ketone with sodium amalgam, cis-, and trans-modifications being obtained which may be separated by their acetyl derivatives. Phloroglucite (cyclo-hexane-triol-i•3.5) is obtained by reducing an aqueous solution of phloroglucin with sodium (W. Wislicenus, Ber., 1894, 27, p. 357). Quercite (cyclo-hexane-pentol-I.2.3'4'5), isolated from acorns in 1849 by H. Braconnot (Ann. chim. phys. [3], 27,p. 392), crystallizes in colourless prisms which melt at 234° C. When heated in vacuo to 24o° C. it yields hydroquinone, quinone and pyrogallol. It is dextro-rotatory. A laevo-form occurs in the leaves of Gymnema sylvestre (F. B. Power, Journ. Chem. Soc., 1904, 85, p. 624). Inosite (cyclo-hexane-hexol), C6H6(OH)6.—The inactive form occurs in the muscles of the heart and in other parts of the human body. The d-form is found as a methyl ether in pinite (from the juice of Pinus lambertina, and of caoutchouc from Mateza roritina of Madagascar), from which it may be obtained by heating with hydriodic acid. The 1-form is also found as a methyl ether in quebrachite. By mixing the d- and 1- forms, a racemic variety melting at 253° C. Is obtained. A dimethyl ether of inactive inosite is dambonite which occurs in caoutchouc from Gabon. Ketones.—Cyclo-hexanone, C6H16O, is obtained by the distillation of calcium pimelate, and by the electrolytic reduction of phenol, using an alternating current. It is a colourless liquid, possessing a peppermint odour and boiling at 155° C. Nitric acid oxidizes it to adipic acid. It condenses under the influence of sulphuric acid to form dodecahydrotriphenylene, C18H24, and a mixture of ketones (C. Mannul, Ber., 1907, 40, p. 153). Methyl-I-cyclo-hexanone-3, CH6.C6H90, is prepared by the hydrolysis of pulegone. It is an optically active liquid which boils at 168–169° C. Homologues of menthone may be obtained from the ketone by successive treatment with sodium amide and alkyl halides (A. Haller, Comptes rendus, 1905, 140, p. 127). On oxidation with nitric acid (sp. gr. 1.4) at 6o-7o° C., a mixture of —and- -methyl adipic acids is obtained (W. Markownikoff, Ann., 1905, 336, p. 299). It can be transformed into the isomeric methyl-I-cyclo-hexanone-2 (O. Wallach, Ann., 1904, 329, p. 368). For methyl-I-cyclo-hexanone-4, obtained by distilling y-methyl pimelate with lime, see O. Wallach, Ber., 1906, 39, P. 1492. Cyclo-hexane-dione-1.3 (dihydroresorcin), C6H802, was obtained by G. Merling (Ann., 1894, 278, p. 28) by reducing resorcin in hot alcoholic solution with sodium amalgam. Cyclo-hexane-dione-i•4 is obtained by the hydrolysis of succino-succinic ester. On reduction it yields quinite. It combines with benzaldehyde, in the presence of hydrochloric acid, to form 2-benzyl-hydroquinone. Cyclohexane-trione-1.3.5 (phloroglucin) is obtained by the fusion of many resins and of resorcin with caustic alkali. It may be prepared synthetically by fusing its dicarboxylic ester (from malonic ester and sodio malonic ester at 145° C.) with potash (C. W. Moore, Journ. Chem. Soc., 1904, 85, p. 165). It crystallizes in prisms, which melt at 218° C. With ferric chloride it gives a dark violet coloration. It exhibits tautomerization, since in many of its reactions it shows the properties of a hydroxylic substance. Rhodizonic acid (dioxydiquinoyl), C6H206, is probably the enolic form of an oxypentaketo-cyclo-hexane. It is formed by the reduction of triquinoyl by aqueous sulphurous acid, or in the form of its potassium salt by washing potassium hexa-oxybenzene with alcohol (R. Nietzki, Ber., 1885, 18, pp. 513, 1838). Triquinoyl (hexaketo-cyclo-hexane) C6O6.8H2O, is formed on oxidizing rhodizonic acid or hexa-oxybenzene. Stannous chloride reduces it to hexa-oxybenzene, and when boiled with water it yields croconic acid (dioxy-cyclo-pentene-trione). Cyclo-hexenones.—Two types of ketones are to be noted in this group, namely the a)3 and fry ketones, depending upon the position of the double linkage in the molecule, thus:
End of Article: C2H
C2H 6

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