Byron 1. Hawbecker Ohio Northern University Ada, Ohio 45810
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The Rearrangement of Diazotized 4-Bromobenzophenone Hydrazone
T h e study of moIccuInr rmrrnngrments is n p:rrt of rvcry hwinninp course in orppnic rhmmistr?.. Usr~:~lly tlir rtuclrnt \vill 11:wethe opportunity to exprriment with onr or more such re:~rtinnsin thc lnbon~tnry, but oftrn t l ~ crxprrimrnt is performnl in :I rnutine f:~.;hion in whirh t11r stuclcnt is only v:rgurly nwnrc of t h r mrrhnnistir : ~ r d strrcnrhm1ir:tl f:wtors of thc prncrss. T h r Hrckrnnnn rr:~rtiouof kctonr oxirnes is prnh:lhly the most frrr111c1111yIIPMI prnerss for n Inhor:~tory rurrrisc illustr:~tinp n rcxmrnnprmn~t. Thin choicc is rrrt:~inlyjustili:hlr in view of the rxtensive intcrrst in thc. rc-:~rtiol~ silirr I1nkrnnnn originally r e o r t it I I ( I . Sillre thr~ttimr mnny rhemists hnvr rontributrrl to the ul~clrrst:~nclingof this now f:~rnnwprncrss. : u ~ itl II:IS hrrn rrvirwnl most rrcently hy I)on:~runi:~and IIrldt ( 2 ) . 111 h c t , thc wholc n ~ : ~ t tof r r t h r v:~rinusrr:~rnmgrmcntsinvolving c l n t m n drfirirnt nitrngrn is t h r suhjrrt of :I r n c n t comprrl~rnsivr rrvirw (d. i n the n~crhnni.stic drtnils of the Rnkmnnn rr:letion wrrr r ~ : m i n n I .it c v t v ~ t ~ ~ abccnme llv clear that 1111. rc.:~rtio~~ i.i :I strrn)s~~rcifir one in which t h r m u o
Aowrver, rrnrtions of this type with rnnny ketone osirnrs oftrn fxil to pirr n purr prndurt h n a u s r cquilihnition hrtwrrn osimr isnmrrs orrurs at :I rnte thnt is ron~l)nnihlrto tlir ntte of rr:~rr:~nprrnentunilrr usud ronditiot~s( n p ('2)). N--011 HO-S
by Fishel nnd Hnwbnkrr (6). Thry h:we p r r l ~ : ~ m l s c v r n ~ monosuhstitutrd l brnrophenonr hyilmzorrc~send h:wr, in eneh c : ~ brcn , :tblr to s r p n n ~ t r:1nc1 identify the gmmrtric isnmrr.;. This is ilIwtr:~tnlin np. (4) by the rrwtion of Chrnmobr~~zopl~c~rlo~~e.
Fishel nncl Hnwbnkcr were nhlc to clrmonstn~trthnt the reaction of 11given, purc hyclrnrone in the cliszotiaing mnlium occurs more r:~piclly t11r1r1intrrronvc-rsion hrt\vccn isomers nncl results in the fornx~tionof only n single nmicle (or n n i l i d ~since i~rnn~ntic krtonex were usc~l)prndnct. For I\ g i r r a I ~ y d c ~ z o n'the e nniliclc prc~lucrrlis the iwrner of the r~niliclc. rrsulting from rmrr:~ngemmt of the othrr hydr:~rnnc~ isnn~rr. Equ:~tions (.-I) nnd (6) clrrnonstrntr thcsc rcsults r ~ n dc l ~ ~ n i n tire t h r fnrt thnt it is nl\v:~yst h r prnuli nnli to tlir SIT? of thc hyclrnrone thnt miprntm during rc:~rr:mgrmrnt. In fnct, k'ishrl nncl IIn\vbnkrr h a r e sho\vn thnt the structure of the rr:lrnlnprnmcnt pmcluct mny he tnkrn RS wlid cviclencc for the pmmrtric ronlignr:~tionof the hytlrnsone rcnctant. N-NH:
0
I'P:IM~, C:wtrr, and G r w r (4, 5 ) have pointer1 out, tlw I~ycln~snnrs of errtnin krtonrs will h r h w c unclrr suitnhlc~ronclitions in :I mnnnrr similnr to the l%wkrnnnnrrwn~nprmrntof oximm (rqn. (3)). t11:tt
The:\' 1impo-nl thnt the hydmrone renrrnngemcnt prnlmhly (wntrs r i a n mcrhnnistic path simil:rr to t h e : ~ r r p t c ol r I R r c k n ~ : nrnrticn. ~ A romplrte i - r I : ~ i i s t i cstudy of t h r rr:wrnngrment of h r ~ ~ s o l ~ h w hyclr:~zonrs ~nnr h w bcrn rnnclc very rrcrntly
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218 / JwrnoI of Chemiml Education
This rrnction oflcrs n pnrticulnr n k m t n g e ovrr the Rcrkmnnn rr:~rnuIgcrnrnt IIS an unclrrpc~clunte Inbort~torycxerrisr in t11:rt it is nlwnys possihlr, with cnrrful work, to obtrrin n high yield of :I pure nnilidc prnch~ct
derivnl from ench of two hydrnzonc isomers. This drmonstmtrs not only the prncticnl synthetic nsprcts but also the strrcospffificity of the reaction. Once the stuclrnt hnq obt~iinnlthe iwmcric nnili~lcs,he can iclcntify them ensily hy compnrisnn to authentic nnilidcs prrpnrnl by n strnight-fonwrd method (erln. (7)) (7).
Fishel n r ~ dHnwbrckcr (6)hnve pointed out thnt the rcnrrnngrmrnt pmbnbly tlors not involve a frrc "imrnonium ion" ( I = + ) since this should lend to rnisnl pmclurts. They hnvr postulnted thnt nitrogen lox* fmm the elinzotiznl hyclrnzone nnd the migrntion of t h r a n l i n n l gmup nrr sin~ultnnmuslending to only one pmcluct. The, n~ignrtion of t h r o n l i gmup vin n rner11:miatic pmrw* surh ns presrutnl below is the most, rrnsonnhlr explnnntion of thrir kinetic dntn, the uctivntion pnrnmrte.rs clrrivnl fmm thnt dntn, nnd the results of their nmr s t u d i n of the rrnction iotrrmediates. T h e pmbnhlc rnwhnnism for the rrnrrnn~rmentitsrlf is illt~r;lr:~t~ul by nlns. (8) nncl (9). + N-N-N
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stirring
t n I . Then add*l.Ri g d SnKO, with pw~lc nlways maintaining the temprature betrwn II a n d T,'C
reactive intermediate
T h e nctunl dinzotizntion pmccw is pmbnbly quite romplirntnl and uuclrr the wunl mnction conclitions occurs ;it n fnstcr r:ttr thnn the renrrnngement itsrlf (6). Some insight iuto t h r complicntions of dinzot izntion pmctwcs in genernl cnn b r founcl in nn excellent review by Ilidd (8). This rxpcriment mny be n d n p t d for use with 4-chlom or 4-methyl substitumts, nlthough it is somewhat more diflirult to obt:lin the crystnllinr form of the 4-methylI)rnzophctio~~r hyclr~uone. ~\ppmprinte physicnl clntn is givcu in Tnblcs 1 and 2.
Toble 1. Properties of Selected 4-Substituted Benzophenom Hydrazones 4I*\," iumerd--nnli iromerrnp 'C '; yield mp Substitucnt % yiekl - oil Br 8.5 l o o - ~ ( ~ ~ lo 211 oil CI XO llI~~-lO: :Jtl oil CiO i!CXl -ClIr -~ .The ayn and onli designalio~~s refer t o the nmfigurstion of the amino gmup rclat.ive to the a~rlaliltctedphew1 group. ~
Table 2.
Properties of Selected SubstiMed Benzanilides
Vohme 47, Number 3, March 1970 / 219
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