Page:Encyclopædia Britannica, Ninth Edition, v. 5.djvu/577

Rh HALOID ETHERS.] CHEMISTRY 565 The substitution can in many cases be continued atom by atom, till tlie whole of the hydrogen is replaced ; thus: Methane ............... CH 4 Ethane ............... C 2 H 6 Benzene ............... C B H S Tctrachlonnethane CC1 Hexachlorethane C 2 C1 8 Hexachlorbenzene C S C1 S The reactions are often accelerated and in some cases remarkably modified by light or heat. The presence of iodine, antimony, itc., frequently assists the action of chlo rine. Chlorine is more energetic than bromine, and the action of iodine less energetic than that of bromine, iodine, in fact, does not act directly on the paraffins. By the direct action of halogens on paraffins a mixture containing more than one derivative is generally obtained. Thus, when chlorine and methane are mixed and exposed to diffused light (explosion takes place in direct sunlight), the whole series of derivatives CH 3 C1, CH 2 C1 2 , CHC1 3 , and CC1 4 are formed. Unsaturated hydrocarbons first of all combine directly with a certain number of halogen atoms. In some cases the number of halogen atoms thus taken up restores the compound to the type of a saturated body: C 2 H 4 + Cl., = C.,H 4 C1 2 = ethene dichloride = dichlorethane. Ethene. In other cases the restoration is not to the type of a saturated hydrocarbon : 2 = C 10 HCl 4 ,tetrachlorinated naphthalene, corresponding [to type C n H. n _g. The mono-haloid derivatives of paraffins and some other hydrocarbons are conveniently prepared by the action of haloid acids on the corresponding alcohols : CH 3 .HO + HC1 = CH 3 C1 + OH 2 Methyl Methyl alcohol. chloride. C 7 H..HO + HC1 = C 7 H 7 .C1 + OH,, 1 Naphtha- lene. Benzyl alcohol. Benzyl chloride C a H 8 (HO) 8 +llHI = Polyhydric alcohols may by these reactions have their hydroxyl only partially replaced by halogens : thus, by the action of hydrochloric acid on glycerin there are produced C S H 5 C1(HO) 2 (chlorhydrin} and C 3 H 5 C1 2 (HO) (dichlor- liydrin}. The haloid phosphorus compounds act upon alcohols in a manner similar to that of the halogen acids : 3C H-.HO + PBr,= A U O Ethvl alcohol. XH 5 Br + PH 3 3 Ethy 5 ! bromide. bromide. C 2 H 4 (HO), + 2PC1 5 = CoH 4 Cl 2 + 2POC1 3 + 2HC1 Ethene glycol&quot; .-^ &quot;f &quot; dichloride. C 3 H 5 C1 2 (HO) + PC1 5 = C 3 H 5 C1 3 + POC1 3 + HC1. Trichlorhydrin DichlorhyJrin. -&quot;- rhydr or allyl trichloride. The haloid ethers are liable to the same isomeric modi fications as their parent hydrocarbons and derivatives. The conditions which determine the production of any particular modification cannot in all oases be laid down with precision. For instance, the di-haloid paraffin deri vatives obtained from the paraffins are in some cases iden tical and in other cases isomeric with the correspondin compounds produced by the direct union of halogens with olefines. Again, the higher members of the paraffin series when acted on by chlorine yield simultaneously two iso meric (primary and secondary) mono-chlorinated derivatives As a final example, when chlorine acts upon toluene in the cold chloro-toluenes (C 6 H 4 C1.CH 3, C 6 H 3 C1 2 .CH 3 , &c.) are 1 The metameric phenol, cresol (p. 564), does not undergo a similar reaction. C 2 H 5 .C 2 H 4 I Normal butyl iodide. (CH 3 )(C 2 H 5 )CHI Pseudobutyl iodide. ormed, but when the action takes place with boiling toluene orming benzyl compounds (C 6 H 5 .CH 2 C1, &amp;lt;fec.) Alcohols are reproduced from their haloid ethers by the action of KHO (see p. 563), or by first converting the haloid ther into an acetate of the radicle by treatment with silver acetate, and then acting on the acetate with KHO. Tho alcohols thus formed are similar in isomeric constitution to the haloid ethers from which they are obtained. For instance, (CH 3 ) 2 CH.I (pseudopropyl iodide) when made to undergo the reactions specified is converted into (CH 3 ) 2 CH.HO (pseudopropyl alcohol) (see also p. 563). Isomeric haloid ethers are thus named in accordance with the radicle composing the alcohols from which they are obtained, or to which they give rise on conversion into acetates and treatment with KHO; thus, we have the following mono- iodobutanes : (CH 3 ) 2 CH.CH 2 I Isobutyl iodide. C(CH 3 ) 3 I. Katabutyl iodide. The same relations exist between the haloid ethers and their isomerides as between the paraffins and their isome- rides. Thus, the boiling points and specific gravities of the normal ethers are higher, and their chemical stability is greater than that of tha isomerides. By the action of nascent hydrogen many haloid ethers are restored to the hydrocarbons from which they are derived by an inverse substitution. Thus tetrachlor- methane (CC1 4 ) when treated with sodium amalgam and waber is ultimately converted into methane (CH 4 ), mono- chlorbenzene (C 6 H 5 C1) into benzene, &c. The action of caustic alkalies upon mono-haloid ethers will be best illus trated by the following examples: f Illustrating formation of an C 7 H 7 .C1 + KHO = C 7 H-.HO + KC1 alcohol. (See also p. 563.) Benzyl Benzyl &amp;lt; The inetameric monochlo- chloride. akohol. rophenols do not undergo I. an analogous reaction. ( Illustrating reduction of a saturated compound to a lower isologtie, i.e., for mation of CnHy, from type C n H 5n+3 . A similar change is sometimes ef- [ fected by heat alone. ( Illustrating reduction of an unsaturated compound to C 2 H 3 C1 + KHO = C 8 H 8 + KC1 + OH, a lower isologue, i. e., re- Mono- h. duction of type C n H 2n to chlorethene. n TT V. ^n-Tljn a &amp;gt; The mono-haloid olefines (typified by monochlorethene in the last equation) are obtained by the action of a caustic alkali on di-haloid paraffins (see p. 558). These mono-haloid olefines, like their parent olefines, are dyad radicles com bining with Ha. 2 and H//a. Their compounds with haloid acids are under some conditions identical and under other conditions isomeric with the corresponding compounds pro duced by the direct combination of the define with two halogen atoms. Of the haloid ethers derived from paraffins the best known is trichloromethane or chloroform (CHC1 3 ), a colourless, transparent, sweet-tasting, and somewhat fra grant liquid boiling at 62, largely used as an anaesthetic. It can be prepared by the direct action of chlorine on methane, but it is usually obtained ~y -the action of bleaching-powder on common alcohol. The corresponding bromine and iodine compounds, CHBr 3 and CHI 3 (bromo- form and iodoform), and CH(NO 2 ) 3 (nitroform), are known. Cyano-derivatives of Hydrocarbons. The metamerism exhibited by these compounds has been already referred to (p. 555), and^since they resemble in many respects the haloid ethers, their modes of preparation may be now touched upon. Propene. (CH 3 ).,CHI + KHO = C 3 H 6 + KI + OH, &amp;lt; Pseudopropyl iodide.
 * he substitution takes place in the methyl radicle, thus