CHEMISTRY 727 connected with any other carbon atom not contiguous to energy of the system becomes reduced in the formation of it in the ring, although each is supposed in a measure to the substitution derivative, it is rather to be expected that exercise an influence over each and all the other carbon if acted on in the same way, i.e., if the nature of the atoms. This conception is represented by the following process be the same, substitution derivatives would be less symbol:— amenable than the parent compounds. The fact that this is not always so may, therefore, be regarded as punct!oa proof that the radicle introduced into a hydro- of radicle carbon in some cases itself plays an important ,n substipart in conditioning change, and is itself attrac- tutiontive. This view derives much support from the study of the behaviour of phenol and aniline, both of which are extraordinarily sensitive in comparison with benzene— the mere addition of bromine in excess to an aqueous Notwithstanding its vagueness, the centric symbol appears solution of either giving rise immediately to a precipitate to be better adapted than any of those hitherto proposed of the tribromo-derivative, although benzene itself is but as a means of formulating the behaviour of benzene. slowly and imperfectly converted into monobromo-benzene Whatever its structure, the benzene complex has alto- when placed in contact with an excess of the halogen. In gether peculiar properties. The hydrocarbon itself, under like manner the nitration of phenol is readily effected by Properties certain conditions, combines readily enough with means of dilute nitric acid, being without difficulty exof the chlorine and bromine, forming a hexachloride and tended to the formation of the tri-nitro compound, while benzene hexabromide; but none of its homologues and to nitrate benzene it is necessary to use a fairly concencomp ex. scarceiy any of its derivatives furnish similar comtrated acid, and nitration is with difficulty extended pounds. Under all “ ordinary ” conditions benzene and its beyond the formation of the di-derivative. Again, phenol homologues yield substitution derivatives. When subjected is rapidly sulphonated by ordinary concentrated sulphuric to the action of either chlorine or bromine, benzene responds acid, which acts but very slowly on benzene. In the case somewhat sluggishly, but much depends on the catalyst of the carbinols—the alcohols derived from the open used in determining the interchange ; comparatively little chain hydrocarbons—the action of acids is to form an heat is developed. The homologous hydrocarbons, as a ethereal salt; ordinary alcohol, for example, yields ethylic rule, are far more easily acted on by halogens. The hydrogen sulphate. Being alcohols the phenols should benzene hydrocarbons are also readily converted into nitro- behave similarly, and there is reason to suppose that they derivatives by nitric acid, and into sulphonic acids by do. The explanation of their apparently different behaviour sulphuric acid, the action of both agents taking place more is to be found in the fact that in the case of the sulphates readily in the case of the higher than of the lower terms derived from the carbinols there is no tendency for the of the series. There is every reason, however, to suppose S03 group to separate from the oxygen atom of the carthat substitution is not directly effected. In the case of binol, and eventually to enter into combination with the mono-derivatives, probably the centric mechanism breaks hydrocarbon radicle; in the case of the sulphate derived down initially, and a compound is formed by the union of from the phenol, however, such a change readily occurs, the agent with contiguous carbon atoms of the hydro- it being necessary, for example, to heat the salt carbon; this change is immediately followed by one in KS03.0C6H5 only moderately to convert it into the the reverse direction in which one of the radicles thus sulphonate H0.C6H4.S03K. On this account the formaintroduced into the molecule becomes separated together tion of the sulphate from the phenol is easily overlooked. with an atom of hydrogen. For example :— But it is necessary to go further in order to explain the behaviour of benzenoid derivatives generally, and to conA sider the cases in which the formation of intermediate A + HB compounds such as the sulphate cannot take place. The behaviour of the mixed ethers formed from phenols by introducing alkylic radicles in place of the hydroxylic hydrogen is specially suggestive. These compounds re+ HA semble phenol in being more amenable to treatment than The action may take place in one or the other direction, is benzene, but they are very distinctly less active than or in both, according to circumstances. Thus, on nitrate phenol. The difference is most striking, however, when ing benzene by nitric acid (H0.N02) alone, both nitro- corresponding derivatives are contrasted. Phenol is conbenzene and phenol are produced, the latter, of course, verted by sulphuric acid into phenolparasulphonic acid, undergoing further nitration, as it is readily acted on ; H0.C H .S0 H. If bromine be added to an aqueous 6 4 3 but if the nitration be effected in presence of sulphuric solution of this compound, diorthobromophenolparasulacid, the separation of water from the compound first phonic acid is produced almost immediately; if an excess formed by the union of the benzene with the nitric acid of bromine be used, the sulphonic group is also displaced is promoted owing to the affinity of this agent for water, by bromine, tribromophenol being formed, but this action and consequently nitro-benzene is practically the sole does not set in until the whole of the phenolsulphonic product. acid has been dibrominated. The corresponding sulphonate The mono-derivatives of benzene are all convertible into derived from methylphenyl ether, CH .O.C H , formed by 3 6 5 higher derivatives, and in some cases are far more readily introducing methyl in place of the hydrogen in the OH acted on than is the original hydrocarbon; but the ben- group in the phenolparasulphonic acid, behaves in a rezene hydrocarbons are not peculiar in this respect, as it is markably different manner towards bromine, yielding no well known that even in the paraffin series the higher trace of dibromo-acid, but only the monobrominated acid. terms are much more readily acted on than are the lower But only a part of the compound is thus acted upon ; from ones, and that the alcohols, for example, are readily the remainder the bromine simply displaces the sulphonic attacked under conditions under which the hydrocarbons group. Acid radicles have a still more marked effect, from which they are derived are unaffected. As it is to bromine being without action on benzoylated phenolparabe supposed that in most, if not in all cases, the available sulphonic acid (C H .CO).O.C H (SO H) under conditions 6 5 6 4 s
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