348 



KNOWLEDGE. 



September, 1910. 



The last named author has criticised Schmidhn's 

 magnesium compounds. He states that both the 

 u and /3 modifications re-act w ith benzoyl chloride 

 and ethyl benzoate, forming benzpinacoline in an 

 80 % yield. Contrary to Schmidlin's statement. 

 Tschitschibabin finds the u-modification on treat- 

 ment with carbon dioxide in ethereal solution to 

 give triphenvlacetic acid in a 90 % yield : the action 

 of water on the re-action product leads td tlu- forma- 

 tion of triphenylmethane in good yield. The )iara- 

 benzoyltriphenylmethane obtained by Schmidlin was 

 formed most probably by the condensation of 

 triphen\hneth\l with benzaldehyde. 



Schmidlin has replied to the above criticism 

 as follows : — Triphenylmeth\l and .(-magnesium 

 triphenvlmethyl chloride result wlu'ii magnesium in 

 moderate excess re-acts gently with an ethereal 

 solution of triiihenylmethyl chloride in the presence 

 of a moderate amount of iodine. With a large 

 excess of iodine the quantit\ ot triphen\ Imethyl is 

 greath- diminished, and if the re-action proceeds 

 vigorouslw a partial con\ersion of the ((-magnesium 

 trii)henvlchlonnethane into the /^-isomeride occurs. 

 Tschitschibabin employed the latter conditions in 

 his exjieriments, leading him to doubt the existence 

 of two isomeric magnesium triphenylmethyl chlorides. 

 Schmidlin is of opinion that Tschitschiliabin's 

 solution could have contained little or none of the 

 (/-isomeride, that his explanation of the formation of 

 para-benzo\dtriphen\-lmethane is impossible, and 

 that its jiroduction from triphenylmethyl is negatived 

 b\- the three following experiments. An ethereal 

 solution of triphenvlmeth}-l, free from the magnesium 

 compound, does not re-act with benzaldehyde. 

 Solicl triphen\lmeth\l in benzene solution is equally 

 non-re-acti\'e. The re-action bet\\een magnesium 

 and triphen\-lmethvl chloride was so performed that 

 the ethereal solution contained the trijihenylmethyl 

 whilst the a-magnesium triphenylmethyl chloride was 

 present exclusiveh' in the precipitate : the solution did 

 not re-act with benzaldehyde, whereas the [)recipitate 

 yielded para-benzoyltriphenylmethane. The argument 

 that the so-called «- and /3-magnesiuni triphenyl- 

 methyl chlorides react in the same wa\ with benzoyl 

 chloride and ethyl benzoate is therefore counteretl by 

 the statement tfiat, under the conditions, the labile 

 a- form changes int(T the stable /:(-isomeride. 

 Tschitschibabin has made a further reply in which 

 he maintains that the reaction with benzaldehyde is 

 capable of explanation without the assumption of 

 two magnesium isomerides. He hasalread\- suggested 

 that this substance may re-act with benzaldehyde 

 normalK' x'ielding /3-benzpinacoline, and also 

 abnormalh' as follows, whereby [)ara-benzo_\ltri- 

 phenylmethane is produced. 



CiiHj.. CHO + (CnHj)3 C Mg Ci - 



- OH. CH. C,;H5Ci;H4 C (CcH.-.lMe Ci 



■^' 



CH. C,;H-. (OM.^Ci). CiHi. CH Cc,-,H.-,)-2. 



Illustiations of such abnormal condensation are 

 found in tin- re-action between formaldehyde and 

 magnesium l)enz\l chloride, whereb)' both beii/yl 



carbinol and o-tohl carbinol are formed, and also in 

 the re-action between benzaldeh\de and magnesium 

 benzyl chloride, which leads to the formation of 

 phen\-lbenz\-l carbinol, phen\-l-ortho-tolyl carbinol and 

 phen\l - para - tol\-lcarbinol. Tschitschibabin also 

 obtained both benzi)inacoline and para-benzoyl- 

 triphenylmethane from solutions of magnesium 

 triphenylmethyl chloride which, according to 

 Schmidlin, should contain onl\- the (8-modification 

 and also from solutions w liich should contain only the 

 ((-form. Hence he draws the conclusion that there 

 is no e\'idence for the existence of the isomeric 

 magnesium triphen\ Inutln I chlorides. 



To complicate the problem still further, 

 Schmidlin in I'JO.S made the remarkable discover}' 

 that there exists a colourless and a coloured 

 triphen\lmethvl. .V fresliK- prepared solution of 

 pure triphen\huLth\l in benzol remains colourless 

 for a few sec(_)nds aiul then gradually becomes 

 orange-yellow. The colour i if the solution disappears, 

 howexer. when the latt(_'r is shaken with air, 

 re-apjiearing again after a time and again disappear- 

 ing when agitated with air. until finall\- the solution 

 remains perfecth' colourless. The conclusion is 

 therefore drawn that the \'ellow solution of triphenyl- 

 methyl contains both a coloured and a colourless 

 form of triphenylniethxl. The two forms are conver- 

 tible one into the other and are present in solutions 

 and in the solid state in a definite condition of 

 equilibrium, ^\•hich depends both on the nature of the 

 soK'ent and on the teniiierature. 



The disappearance and re-appearance of the 

 colour of solutions of triphen\ Imethyl is due to the 

 fact that the coloured \-ariety oxidises far more 

 rapidh- than the colourless form. On shaking an 

 ethereal solution of triphenylmethyl with air. the 

 yellow form is oxidised, yielding the peroxide, which, 

 being insoluble in ether, may be filtered off: the 

 colourless filtrate quickly becomes yellow, and on 

 shaking yields a further (]uantit3- of peroxide. It 

 was found from the amount of peroxide formed, that 

 an ethereal solution of triphenylmethyl contains 

 roughly ten times as much of the colourless as of the 

 coloured form. The latter substance must conse- 

 quently have an exceedingly intense colour. 



The }ellow form also absorbs iodine far more 

 rapidly than the colourless. When a quantit}' of 

 iodine, slightly more than sufficient to combine with 

 the triphen\lmethyl present in the yellow form, is 

 added to a solution of triphenylmethyl in chloroform, 

 a reddish-brown solution is obtained. The colour of 

 the solution slowh' changes, and when a sufficient 

 quantity of the ^-ellow variety has been formed, the 

 solution has the pure yellow C(_il(.iur of the triphen.yl- 

 methyl iodide. 



The state of eijuilil^riuiu. 



Triplienvlineth\-| (cofoiirless) Z^^ Triplicnvlnietlivl (cotourc(3). 



is displaced towards the left liy a lowering of 

 temperature. A solution of triphenylmethyl in 

 chloroform, wlu(h is or.uige-\ ellow at Ij C, 



