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Originally appearing in Volume V06, Page 55 of the 1911 Encyclopedia Britannica.
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OOH _CI3O I OH es-CI I CI 'CO2H ~lCH CO2H C' CI CO C OH CI 0 Cl2 CO2H Clio C~ C12 Cl2 c12 CCl2 CH3 (I) (a) (3) (4) (5) (6) Resorcin (1.3 or meta dioxybenzene) (1) is decomposed in a somewhat similar manner. Chlorination in glacial acetic acid solution yields pentachlor-m-diketo-R-hexene (2) and, at a later stage, heptachlor-m-diketo-R-hexene (3). These compounds are both decomposed by water, the former giving dichloraceto-trichlorcrotonic acid (4), which on boiling with water gives dichlormethylvinyl-a-diketone (5). The heptachlor compound when treated with chlorine water gives trichloraceto-pentachlorbutyric acid (6), which is hydrolysed by alkalis to chloroform and pentachlorglutaric acid (7), and is converted by boiling water into tetrachlor-diketo-R-pentene (8). This latter compound may be chlorinated to perchloracetoacrylic chloride (9), from which the corresponding acid (to) is obtained by treatment with water; alkalis hydrolyse the acid to chloroform and dichlormaleic acid (II). 4 Co-CC12~ CIOC•CCI:CCI•CO•CC13&— ( CO (8) 1 (9) Ccl=ccl~ HO2C•CCl:CC!.CO•CC13- ---•• H02C•CC1:CC1•CO2H+CHCI3 fro) (II) Hydroquinone (1.4 or para-dioxybenzene) (I) gives with chlorine, first, a tetrachlorquinone (2), and then hexachlor-p-diketo-R-hexene (3), which alcoholic potash converts into perchloracroylacrylic acid (4). This substance, and also the preceding compound, is converted by aqueous caustic soda into dichlormaleic acid, trichlorethylene, and hydrochloric acid (5) (Th. Zincke and O. Fuchs, Ann., 1892, 267, p. 1). OH O CI CI CI •--. ci Qjci ~Ct OH O O (I)- (a) (3) (4) (5) Phloroglucin (I.3.5-trioxybenzene) (1) behaves similarly to resorcin, hexachlor [1.3.5] triketo-R-hexylene (2) being first formed. This compound is converted by chlorine water into octachloracetylacetone (3) ; by methyl alcohol into the ester of dichlormalonic acid and tetrachloracetone (4) ; whilst ammonia gives dichloracetamide (5) (Th. Zincke and O. Kegel, Ber., 189o, 23, p. 1706). OH 0 (3) C13C•CO•CCIZCO•CCI3+CO2 ct2( `cl2~r (4) C12HC•CO•CHCl2+CH302C•CCVO4CH3 "''(5) Cl2HC•CONH2(I) (a) C(3) (4) (5) The reduction of o-oxybenzoic acids by sodium in amyl alcohol solution has been studied by A. Einhorn and J. S. Lumsden (Ann., 1895, 286, p. 257). It is probable that tetrahydro acids are first formed, which suffer rearrangement to orthoketone carboxylic acids. These substances absorb water and become pimelic acids. Thus salicylic acid yields n-pimelic acid, HOOC•(CH2),.COOH, while o-, m-, and p-cresotinic acids, CsH3(CH3)(OH)(000H), yield isomeric methylpimelic acids. Resorcin on reduction gives dihydroresorcin, which G. Merling (Ann., 1894, 278, p. 20) showed to be converted into n-glutaric acid, HOOC•(CH2)3•COOH, when oxidized with potassium permanganate; according to D. Vorlander (Ber., 1895, 28, p. 2348) it is converted into 7-acetobutyric acid, CH3CO•(CH2)3•000H, when heated with baryta to 150-16o°. Configuration of the Benzene Complex.—The development of the " structure theory " in about 186o. brought in its train an appreciation of the chemical structure of the derivatives of benzene. The pioneer in this field was August Kekule, who, in 1865 (Ann., 137, p. 129; see also his Lehrbuch der organischen Chemie), submitted his well-known formula for benzene, so founding the " benzene theory " and opening up a problem which, notwithstanding the immense amount of labour since bestowed upon it, still remains imperfectly solved. Arguing from the existence of only one mono-substitution derivative, and of three di-derivatives (statements of which the rigorous proof was then wanting), he was led to arrange the six carbon atoms in a ring, attaching a hydrogen atom to each carbon atom; being left with the fourth carbon valencies, he mutually saturated these in pairs, thus obtaining the symbol I (see below). The value of this ringed structure was readily perceived, but objections were raised with respect to Kekule's disposal of the fourth valencies. In 1866 Sir James Dewar proposed an unsymmetrical form (II); while in 1867, A. Claus (Theoretische Betrachtungen and deren A nwendung zur Systematik der organischen Chemie) proposed his diagonal formula (III), and two years later, A. Ladenburg (Ber., 2, p. 140) devised his prism formula (IV), the six carbon atoms being placed at the six corners of a right equilateral triangular prism, with its plane projections (V, VI). CH CH CH HC CH HC CH HC CH HC CH HC CH HC C~CH HC CH HC CH HCCH HC CH HC CH HC t^P,0` cH CH CH i Kekui 12 Dewar inClaus CH Ladenburg One of the earliest and strongest objections urged against Kekul6's formula was that it demanded two isomeric ortho-di-substitution derivatives; for if we number the carbon atoms in cyclical order from i to 6, then the derivatives 1.2 and 1.6 should Objections be different.' Ladenburg submitted that if the 1.2 and toKekule's i.6 compounds were identical, then we should expect the formula. two well-known crotonic acids, CH2.CH: CH•COOH and CH2: CH•CH2•000H, to be identical. This view was opposed by Victor Meyer and Kekule. The former pointed out that the supposed isomerism was not due to an arrangement of atoms, but to the disposition of a valency, and therefore it was doubtful whether such a subtle condition could exert any influence on the properties of the substance. Kekule answered Ladenburg by formulating a dynamic interpretation of valency. He assumed that if we have one atom It is now established that ortho compounds do exist in isomeric forms, instances being provided by chlor-, brom-, and amino-toluene, chlorphenol, and chloraniline; but arguments, e.g. E. Knoevenagel's theory of " motoisomerism," have been brought forward to cause these facts to support Kekule. H02C•CC1 : CH• CCl2 CO•CHCl2 1 (4) • CO2+ C1HC: CH• CO• CO• CHC12 OH COH (I) (s) 0 0 Cif .Cl2 y c llNzo clo Cl 2(a) Ci2(3) H02C• CClCHC1•CCIZ CO•CCI3 (6) 1 H02c.ccicHCI•CCIzCO2H+C HCI3 (7) COOH ,CO2H Cl2 CIC' cci2 cIC co, cl II ,+ cic 2 CCI CIC, CHCI CO COSH
End of Article: OOH

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