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 .