THE TRIPHEXYLMETHYL PROBLEM. 



By HERBERT H. HODGSON. M.A. (Camb.), B.Sc. (Lond.), Ph.D. (Heidelberg). 



Part IV. 

 THE HEX.\PHEXYLETHAXE PROBLEM. 



The question as to the constitution of triphenvl- 

 methyl is inevitably bound up with that concerning 

 the existence of hexaphenylethane. Since the 

 so-called hexaphen\lethane of Ullman and Borsum 

 was proved by Tschitschibabin to be none other 

 than benzhvdryltetraphenylmethane (CgHg), CH. 

 CgH^. ClCgHg)^, the formula of hexaphenylethane 

 has again entered the list of unsolved problems. 



Tschitschibabin and Hantzsch have expressed the 

 opinion that in triphenylmethvl we have the long- 

 sought-for hexaphenylethane. The latter chemist 

 compares hexaphenvlethane with hexanitroethane, 

 which it is impossible to prepare by the action of 

 trinitroiodomethane on silver nitroform owing to 

 its instability, since instant decomposition ensues. 

 Hantzsch is of opinion that in hexaphenvlethane 

 the two ethane carbon atoms must be so feeblv 

 adhered to each other that hexaphenvlethane 

 behaves as free triphenvlmeth\l. 



In opposition to this view of Tschitschibabin and 

 Hantzsch, Gomberg and Cone have put forward 

 their opinion that the real hexaphenylethane has 

 not been prepared, owing to suitable experimental 

 methods not having been evolved to deal with such 

 a peculiar case of instability as one would expect. 

 This view was fortified by the fact that Gomberg 

 and Cone had succeeded in the preparation of the 

 uns\mmetrical tetraphenylethane, and also penta- 

 phenvlethane, which bodies have a fairlv stable 

 behaviour. 



Tschitschibabin showed that pentaphenylethane 

 appeared to decompose at its melting point, and 

 when heated with hydrochloric acid in benzol 

 solution at 150'^ was transformed into tetra- 

 phenylethane, triphenjlmethane and triphenyl- 

 chlormethane. Cone and Robinson have also 

 obtained triphenvlchlormethane b}- heating penta- 

 phenylethane with phosphorous pentachloride. 



It should not appear hopeless to consider that in 

 pentaphenylethane, taking into account its reduced 

 stability, we have a stepping stone towards the pre- 

 paration of hexaphenvlethane, since the leap from 

 pentaphenylethane, a comparatively stable body, to 

 the extraordinarily unstable triphenylmethvl, appears 

 somewhat great. 



Experiments, starting out from ethane derivatives 

 in order to build up hexaphenylethane, must now 

 decide whether triphenvlmethvl and hexaphenvl- 

 ethane are one and the same body, or whether the 

 hexaphenvlethane formula corresponds to another, 

 as yet unknown, stable. hydrocarbon. 



Gomberg tried to prepare pentaphenjdethanol by 

 acting on a tetraphenyl derivative of ethane, viz. : 



on ,8 benzpinacoline with phenylmagnesium bromide, 

 but without success. In like manner to the re-action 

 bv which Ullmann and Munzhaber had prepared 

 .\minotetraphenylmethane, Schmidlin wished to con- 

 dense benzpinacone and aniline to diaminohexa-- 

 phenylethane, but without result. 



(CflHo 



(CbH^)-.. c o h 



+ 



H.Ci Hi. NH^ 



H.Ci Hj. NHi 



(C6H5)-..C. CcH,NH3 



I 

 tC,;H.5)-2.C. CeHjNH.. 



Even so unsuccessful was the attempt to pre- 

 pare pentaphenvlethanol bv the action of benzo- 

 phenone on the normal ,8-magnesium compound of 

 triphenylchlormethane. 



tCsHs). CO -I- (CeHs):! C.Mg Ci = (CcHilo.cto MgCi). C (c,;H5)3. 



In the above experiment a ver\- small quantity of 

 a bodv was obtained which, although not the 

 expected pentaphenylethanol, obstinately held mag- 

 nesium. This body did not appear to have been 

 formed b\- the interaction of benzophenone, but bv 

 the action of unchanged triphenylchlormethane on 

 the tS-magnesium compound. 



Full of promise appeared a method by which 

 triphenvlchlormethane should be allowed to reaction 

 with its ,8-magnesium derivative at a ver\' high 

 temperature (250° C), and under prolonged heating. 

 Schmidlin obtained by this method a ver\- small 

 quantity of a body melting at 270" C, but containing 

 magnesium as impurity. The analysis of this 

 substance, taking into account the ash, gave as its 

 formula that of hexaphenylethane. The magnesium, 

 which at first was regarded as an impurity, appeared, 

 however, to be ver\- firmly united. After shaking 

 for manv davs with concentrated hydrochloric acid 

 the magnesium was removed, but the resulting ash- 

 free substance had then completely lost its ability to 

 crystallise : in fact the molecule appeared to have 

 been disrupted. The high melting point compound, 

 therefore, appeared to be a magnesium compound 

 whose composition corresponded approximately to 

 the formula : — [(CgHj)^ Cj.j Mg. On removal of the 

 magnesium, however, no triphenylmethane was 

 obtained, but an uncrvstallisable product, and from 

 this it appears almost certain that the magnesium is 

 not united with the triphenylmethyl residue, but has 

 entered the benzene nucleus. 



A strenuous controversy has been waged for many 

 vears between Gomberg and Schmidlin on the one 

 hand, who have held the opinion that triphen}!- 

 methvl and hexaphenylethane were separate and 

 distinct substances, and on the other hand Tschits- 

 chibabin, who believes the two to be identical. 



347 



