564 CHEMISTRY [ORGANIC. &c. ; the metameric alcohols do not undergo an analogous reaction. The homologues of phenol being di-derivatives of benzene are susceptible of the isomeric modifications already pointed out (p. 560). Thus there are known C 6 H 6 .CH 3 Methyl-benzene or Toluene. C 6 (HO)(CH 3 )HHHH 1 2 3166 Ortho-cresol. C 6 (HO)H(CH 3 )HHH C 6 (HO)HH(CH 3 )HH 123 456 1 2 3 i 56 Meta-cresol. Para-cresol. Isomerism analogous to that exhibited by the derivatives of benzene and its homologues likewise extends to all the derivatives of phenol and its homologues. The following is a brief list of the compounds of the present series : Alcohols. Benzyl alcohol, Xylyl alcohols, Phenyl-propyl alcohols C 6 H 5 .CH 2 HO C 7 H 7 .CH 2 HO C 8 H 8 .CH 2 HO Cuminyl alcohols Sycoceryl i alcohol C 8 H U .CH S HO C 17 H 27 .CH 2 HO Phenols. Phenol C >H 5 .HO 5 H 4 (CH 3 ).HO Xvlenols, Phlorol, &c., C 8 H 8 . HO Thymol, Carvacrol, C 10 H 13 .HO Cresols C The boiling-points of the alcohols are generally higher than those of the metameric phenols. Many of the compounds of the present series are trans parent oily liquids possessed of powerful odours ; others are white crystalline solids. Of the phenols the best known is phenol or carbolic acid, obtained from the acid portions of coal-tar. Series C,,H 2n _ 9 . HO comprises cinnam ic alcohol, C 9 H 9 . HO, and cholesterin, C 26 H 43 .HO . Series C n H 2n _ 13 .HO. Only one member is known, viz., naphthol, C 10 H 7 .HO. Series (C n H 2n )"(HO) 2 , Glycols. Of these dihydric alco hols the terms corresponding to the first six members of the olefine series are known, and are named ethene glycol, propene glycol, &c. The glycols are colourless, viscid liquids, miscible with water, They are generally prepared by acting on di-haloid olefine compounds with silver acetate : C n H 2n Br 2 + 2AgC 2 H 3 O 2 = C n H 2n (C 2 H 3 O 2 ) 2 + 2AgBr The resulting acetate is then heated with potas sium hydroxide : C B H 2B (C 2 H 3 O 2 ) 2 + 2KHO = C n H 2n (HO) 2 + 2KC 2 H 3 O 2 . The glycols are capable of existing in isomeric forms similar to those of analogous olefine corn- pounds (see p. 559), but these isomers are at present but imperfectly known. A series of compounds known as polyethenic glycols are formed from ethene glycol by con densation, with elimination of water. Their general for mula is {C a H 4 (HO) 2 } - (- 1)(OH 2 ), where the highest value of n is 6. Series C n H 3n _ 8 (HO) 2 , Dihydric Phenols. The following are known : Pyrocatechin (ortho-), Kesorcin (meta-), Hydroquinone 1 (para-) C 6 H 4 (HO) 2 Saligenin, Orcin, Guaiacol C 7 H 6 (HO) 2 Xylene glycol, Creasol, Veratrol C 8 H 8 (HO) 2 Hydrothymoquinone C 10 H J2 (HO) 2 Many of these compounds can be formed by suitable reactions from benzene hydrocarbons, phenols, &c.; others are found ready formed in lichens, or can be prepared from substances of vegetable origin. Series (C n H 2n _ 1 )" (HO) 3 comprises propenyl alcohol or glycerin, C 3 H 5 .(HO) 3 , and amyl-glycerin, C 5 H 9 .(HO) 3 . Glycerin can be formed synthetically, but is generally 1 The quinones are also closely related to ketones. obtained from glycerides, a group of ethereal salts com posed of glycerin and acids of the acetic and oleic series (see p. 572), which exist ready formed in most animal and vegetable oils and fats. Thus stearin (propenyl tristearatc), a constituent of many natural fats, when acted upon by super-heated steam, decomposes as shown in the equation C 3 H 5 (C 18 H 35 2 ) 3 + 30H 2 = C 3 H 5 (HO) 3 + 3H.C ]8 H 3 ,0 2 . Stearin. Glycerin. Steauc acid. Large quantities of glycerin are obtained by this means. Glycerin is a colourless, transparent, viscid liquid of a sweetish taste, readily soluble in water, and boiling (under 50 mm. pressure) at 210 C. Polyglycerins analogous to the polyethenic glycols are known. Series (C n H 2n _ 9 ) "(HO) 3 . Triliydric phenols comprising the isomerides pyroyallic acid (or pyrogallol] and pJdoro- Series (C n H 2n _ 2 ) Ir (HO) 4 . Erythrite, erythromannite or phycite, C 4 H 6 (HO) 4 , and propyl-phycite, C 3 H.,(HO) 4 . Series (C n H 2n _ 5 ) T (HO) r . Finite and quercite, C 6 H 7 (HO) 5 . Series (C n H 2n _ 4 ) T1 (HO) 6 . Mannite and dulcite, C 6 H 8 (HO) )3 , two natural sugars. Sugar, starch, gum, &c., are members of a group of compounds termed carbohydrates 2 , which are closely allied to the present series of alcohols. The names, classification, and relationship of these bodies are shown in the following table : CARBOHIDRATES. Saccharoses. Arnylosfs. Glucoses. Polyglucosic alcohols. Polyglucosic anhy C 6 H 12 6 . n(C e H 12 6 !-!n-l)(OH.,) drides. (n-2). n(C 8 H 10 O s ). Dextrose or grape- Saccharose or cane sugar. Starch. sugar. Lactose or milk-sugar. Inulin. Levulose. Galactose. Arabin or gum-arabic. Melitose. Dextrin. Cellulose or lignin. Sorbin. Melizitose. Glycogen. Eucalin. Trehalose or mvcose. Inosite. Arabinose. The glucoses exhibit the characters both of aldehydes and of alcohols; the saccharoses bear the same relationship to the glucoses that the polyethenic glycols bear to glycol; the amyloses are formed from the saccharoses by the elimina tion of one molecule of water. Many of the sugars are widely diffused throughout the vegetable kingdom the sugar in ordinary use being obtained from the sugar-cane and sugar-beet. Dextrose and levulose are found in honey, ripe fruits, &c., lactose in milk, inosite in flesh. Gum-arabic is the dried exudation of certain species of Acacia. All the amyloses, with the exception of glycogen, which is found in the liver of animals, are of vegetable origin. Cellulose or lignin is the chief constituent of the cells of plants; starch is found in the cells of most plants. Gun-cotton or pyroxylin is obtained from cotton-wool, which is almost pure cellulose, by the action of strong nitric acid; it has the composition of trinitro-cellulose, C 6 H 7 (N0 2 ) 3 5 . Many of the varieties of the sugars are physical isomerides differing from each other only in their rotatory action on polarized light. III. HALOID ETHERS. These compounds can be formed from saturated hydro carbons, ;and from hydrocarbons which behave as such by the direct action of the halogen : CH 2n+2 + C1 2 = C n H 2n+1 Cl + HC1 .
- So called because the hydrogen and oxygen are always present in
