KNOW Li:nGi: 



hodics. Acetylene and ethylene are coniliined to 

 form divinyl by heating them together in a tube 

 raised to a dull red heat; and tlie resulting divinyl 

 is converted into the methyl derivative (isoprcne) 

 by the action of methyl chloride, thus: — 



rH-=CH + CHi^-CHj ^ CH, = CH.CH^CHi, 

 Acetylene. laliylene. Dhiiiyl. 



His apparatus is shown and described in Figure H9. 

 Mr. Hcinemann, whose patents we have alreadv 

 referred to, finds that the yield of isoprene may 

 also be very considerably improved by passing the 

 turjientine vapour over finely-divided copper or 

 silver, or, better, by using tubes made of either of 

 these metals. The temiierature must be ke|)t low. 



Figure 89. Dr. O. Silbcrrad's Isoprene Apparatus. 



The .ipp.ir.mi5 consists of a licalin;; coil a, inside a hciling cliamber /', licalcil by tlie prod ucls of combustion from a number of iras Imrncrsr, electric pryromelers, .i, .i, lienij; 

 provided to determine llie lemper.lllirc. From the heating coil, a pipe .• leads to a water-cooling coil / situated in a water chamber jr. The hydpicarhons coiidenscil in the 

 coil / p.xss into a vessel h, and the uncondeiised vapours pass through a pipe k, provided with a inercury-gau-^e /, into another condensing chamber /«, from which further 

 hydrocarbons arc collected in the vessel «. The vacuum is produced by means of the vacuum and com|>ressing pump o, and the vapours pa.ssing the pump p.a.vs through a 

 cooling coil /, immersed in brine contained in the chamber l. Isoprene is condensed in the coil /, and is collected in the chamber r. From the chamlier r, the uncoiidelised 

 vapour passes by the pipe s to the chamber /, immersed in the brine contained in the vessel u. A blow-ofT valve v is provided from the top of this last condensing chamber. 



CH.. = ClI. C II 

 + CH, CI 



CH, 



Methyl chloride. 



Mcthvi diyiml or Isopreiu 

 + HCl 



The methods of producing isoprene from coniinon 

 substances of a more complex nature, whilst not 

 exactly syntheses of this substance, arc, however, of 

 more importance commercially. 



It was some time ago that Sir William Tiiden 

 discovered that isoprene could be obtainet-i In- 

 passing turpentine through an iron tube heated to 

 a dull red heat : hut the yield was very small, being 

 only about six per cent. Dr. Silberrad" finds 

 that the yield is very greatly increased if the 

 turpentine is heated under such conditions that the 

 vapour is produced in a highly rarefied condition. 



about 450''C. in the case of silver, or JO°C. higher 

 ill the case of copper, otherwise the isoprene is 

 converted largely into dipentene.^ 



The latter chemist has also patented a very 

 interesting method of con\-erting carbohydrates, 

 such as cane sugar, starch or cellulose (sawdust) 

 into isoprene*, as follows: — The carbohydrate is 

 first converted into laevulinic acid by boiling with 

 dilute hydrochloric acid. To this substance are 

 added one and a half parts of phosi)horus trisulphide, 

 and the mixture heated in a retort to 130"-150"C. 

 A violent reaction takes place, and thiotoleiie 

 (CH., — C4 Hg — S) is produced, thus, — 



,CH,-CH, PS,, CH-CH 



CH„-CO CO.OH ^ CH.t-C ill 



Laevulinic acid ^S 



Ihiotolene 



English Patent, 1910, No. 4.(K)1. (). Silberi;id. I'h.I).. I in/iiovciiu-iits in the M.inii/dctiirc of l^opniic. Our thanks 

 are dne to Dr. Silberrad for a photograph and particulars of his apparatus not given in the Kiiglish Patent Specilication. 

 I English Patent, 1910, No. 14,040. A. Heineniann, Improvements relating to flic Production of Isoprene. 

 I ICiiglisli P.itcnt, 1908, No. 13,252. .\. Heineniann, . I Process for Coni'crtinii Ciirboliydrittcs into Hydrocarbons. 



