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Part I, The Hofmann Rearrang-ement
. -
F i r s t -order rate constants and act ivat i o n parameters were determined for the rearr w~qement of eleven N-halogenoamides
.
The structures of tbe x<-halcqenanrn%d.es (RCO.hWX) d i f f e r e d in t h e leaving group (X
=
chlorine or bromine) and t h e m i m a t b ~ ~ W o u F(R e t h y l , isopropyl, t-but y l , d i p h e n y l m e t h y l , benayl, phenyl or
p - t o l y l ) . N - R r o m o a m i d e s and t h e corresponding N-chloreamfdes reanranged at s i m i l a r rates. %%en the leaving group was changed from brotcfde to chloride the activation energy was reduced by about
one k c a l . mole-' and the activation entropy was reduced by about three cnl. d e g ~ ' mole-'. IXlferences in the reactivity of halides as leaving groups from cnrbon and nitrogen are d i s c u s s e d . Changes
In the structure of a l k y l migrating gxoups resulted i n s m a l l
Lrrcgulfix changes in the a c t i v a t i o r ~ parameters. The kinetic data were c o n s i s t e n t w i t h a stepwise rearrangement mechanism in which halide departed from n i t r m n in t1w rate-determining s t e p to give
a short -lived nitrone intermediate which subsequently reaxranged to an isocyanate.
Qthez aspects of t h e Hof mmn rearrangement were imrest igated.
In t h e I.lofmnn reactson o f amides and h-ypohromits, N-brmination o f the anids was found to he much faster than t h e rearrangement of the intermediate N-bronoanlde conjugate base. In contrast, when amfdea and h _ v p o c h l o r i t e reacted in a l k a l i n e s o l u t i o n PT-chlozrination was not f a s t by comparison wfth t h e r e a r r a n g e m e n t of the
intermediate N-chloroamide conjuqate base.
Oxygen, i o d i d e , am1 hjrl~olhxomite did not i n h f S i t the Nof mann rearrangom@nt. R a a r r a ~ c m n t of N-brmoacetamiCk
,
N-brmopropionamide
,
N-br moisob!lt yramide and 3-brornopivalarnk'b in t h e presence of oxmen gave traces of n i t r i t e as a by-product.N i t r i t e nay r o s u l t from tias capture of an intemecliate nitrene by o x y w n .
I o n b a t i o n constants of s i x N-brornaamides nrwl one N-chloro-
amide were me~sursd. Of the W-halogenoemide8 which =re
investigated, t h e m o s t acidic was N-chlaroporfluoacobutf~r~mide (pK 2.45) and t h e least acidic was M-brmopropionamide (pK 7.95).
There aze no fanisat ion constants of N-ha1 ogenoatn i d e s recorded in t h e chemical literature.
Part 11, The Rearzangemnt of P-Ex otuo&halog~n&amider:
-
andN - B r o m ~ r h a l c n o a m 1 A e s .
Rev3 nus i n v e s t i g a t o r s of t h e reaxrangorent conelided that the conjugate base of the N-halogenoclmide reaxranged
intramolectslarly
-
via a c y c l i c four-membered transition s t a t e to g i v e an a l k y l h a l i d e and cyamte ion. T h i s mechanism isi n c o m p t 5 b l e w i t h evidence presented in t h i s t h e s i s . T h
rearraqementn of N-bramoper f luorobutyranf de and N - b o m s - g - c h l o r o - isobutyramide i n alkal%nc? solution \ e r e not first-order reactions.
T n neutral aqueous s o l u t fan, the N-halogehaamidc conjugate bases d i d not rmxiarzge. H o w e v e r , i n t h e presence of nn exccbss of hydr a i d e i o n , t h e N - h a l o g enoranj.de rearranged r e a d i l y . The
rearrangement was c a t a t ~ r 8 ~ d b y h!Croxide ion and ammonia and i n h i b i t e d by many reagents 5.ncluding oxygen, h y p o b r m i t e
,
%&ids, cwpric i~yc?raxibe, s i l v e r m U e , aud amides of c a r b o x y l f c ands u l p h o n i c acids, Possible rearrangement mechanisms are c?iacussed.
The effects of amall proportions of t h e inhibtltors showed that the rearrangement was a c h a i n reaction. Two probable eteps i n t h e claafin r e a c t i o n are the additton o f hydroxide i o n t o the
N-haPogenoamiAe conjugate baso to yiver a dianionfc intermediate and h e t e r o l y s i s of the nftrogon-bromine bond in this intermediate to give a nitrene.
Part 1x1, The Reaction of M a i nte.
In alkaline solution, mmc?elamide and h y p o h a l i t e yield benealdehyde, clmnolte and h a l i d e . Several mechanisms i h i c h were p o s t u l a t e d by previous f n v e s t i g a t o r s are excluded by evidence presented in t h i s t h e s i s
.
Zvbdence far an N-chloromandelamide intermediate in t b react ion of manclelamf de and hypochlorite w a s obtained. C h l o r i n a t 3. on of man8elamido in n e u t r a l or acidic~ a l u t i o n gave ~ ~ c h l o r o m a n d e l a m i d e and N ,N-Cfchloronan%elmfde.
In alkml im s o l u t i o n , the id-chlorotnancklamidea decomposecll t o give benaaldehyds and c y a n a t e . Th5s reaction was t ~ c h faster than the reaction of mandelamide find hypochlorite t o give t h e same products.
The react ions of hypobr o m i t c and h y p o i o d i t e w i t il macndelambde were also invasatigated. Nelthex oxygen nor an excess of hypobwoa;%ts inhibited t h e r e a c t i o n of a~anclolamide and hygobronrfte t o give
bcnzaldehyde and c - m a t e . ~ y p o i o d i t e (prepared from t h e reaction
of h y p c h l o r i t e and i o d i d e ) and i ~ ~ n c l e l a n i d e also gave bcnzalcfehyde and cyanate In high y i e l d . T11e mchanisrn most c o n s f s t e n t w i t h the evi<?encc Qnvolvea the rearranqcment of an intermediate
N-ha1mcno-o~-hflroxyamide con jugate base t o an e-hyCxoxyalkv'L isocyanate w h i c h subsequently decomposes to bonzaldehyde and cyanate. Mechanisms involving d %anionic intermediates were
disproved. Stofehiometric similar S t i e s in t h e rearrangements of M-hromo- a-halogenoamides and 3-halweno-*ti ydxoxyamides were shown to be f o r t u i t o u s and not the result of similarities in the
xoxrrangement mchaniams.
P a z t N , -@p;lrat i o n of t'imides, N-Bramoamides, and ~-Chloroami&s.
-
Preprorationzs of amides ane ~4-1mlogenonmi&s used fn thZs thesls axe described. Some of t h e N - h a l q e n o ~ m i d e s have not been reported pxavf ous ly, ffi?tltods fox prepaxing M-hrmo-
prhalofrenoamides ~ h i c h are described in the chemical l i t e r ~ t u x a involve t h e bromfnation of the s i l v e r salt of t h e pahalopenoamides in trifluoroacetic acid solution. A much simplex method fat
preparing N-hal~enoperhal04enoamides 5s descrfbed in t h i s t h e s i s .
