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Despite the v a s t amount of research reported on t h e acid-catalysed hydrolysis of amides, the mechanism of reaction has remained a source of controversy, The various l i t e r a t u r e r e s u l t s h w e been summarised i n the introduction,
Two s e r i e s of amides have been studied i n this investigation, one a s e r i e s of N-substituted,&hlorobenzmides, the other a s e r i e s of
substituted acetanilides, Their basicity (or s c i d d i s s o c i a t i o n ) constants have been waluated i n sulphuric acid, and the r a t e s of hydrolysis measured over a wide range of acid concentrations, Within each s e r i e s , v a r i a t i o n of the substituent causes the r a t e constant t o vary i n a way which i s
typical of a bimolecular reaction involving rate-determining nucleophilic attack of water on the protonated intermediate, By drawhg a comparison between
the two s e r i e s of amides, (i,e, t h e difference i n b a s i c i t i e s and r a t e s of hydrolysis) it becomes apparent t h a t the 0-protonated amide, which i s thermodynamically favaured, i s not the k i n e t i c a l l y zctive species, A new r a t e equation is proposed, the equation being based on a mechanism i n vhich water attacks the carbonyl carbon i n the rate-determining step, The equation confidently predicts the experimental rate-profiles f o r the
acid-hydrolysis of simple amides, It has been applied, i n two forms, t o the experimental r a t e data; the f i r s t form allows f o r the involvement of three water molecules i n the slow step of hydrolysis, and the second form allows f o r the involvement of only t e a vater molecules, The r a t e equation, i n these two forms, has also been applied t o ~.uch of the hydrolysis data reported i n the l i t e r a t w e and again i t h s s prcvcd t o be very s u c c e s s h l ,
I n contrast t o the amides, ureas have not Seen subjected t o extensive research, I n t h i s investigation, t h e basicity constants of a s e r i e s of
substituted phenylureas have been measured, ( i f not already available) and the hydrolysis reactions carried out over a wide range of sulphuric acid concentrations, as well as i n water, The M e t h y l and k h l o r o - phenylureas have also been hydrolysed i n a range of hydrochloric and
perchloric acid solutions; the effects of added salt were studied and the solvent isotope e f f e c t s on the r a t e were evaluated, A l l these r e s u l t s , together w i t h information obtained from application of the Hanunett equation t o the r a t e data, were i n agreement with a mechanism involving a
pre-equilibrium protonation t o form t h e minor, N-protonated conjugate acid, This is followed by a slow transfer of the proton attached t o the a l t e r n a t e nitrogen atom t o form the appropriately substituted phenylisocyanate, and rapid reaction of t h i s intermediate t o form products,
The substituent e f f e c t s on the n,m,r, spectra of the substituted acetanilides and phenylureas have also been reported,
