Respondent

Kusch Olha Vasylivna

Theme

Mechanisms of N-hydroxyphthalimide effect in radical chain processes of polymerization and oxidation

Annotation

The  thesis  is  devoted  to  the  study  of  mechanisms  of  N-hydroxyphthalimide

(NHPI)  action  in  a  radical  chain  processes  –  polymerization  and  oxidation.  It  was

shown  that  N-hydroxyphthalimide  works  as  initiator  in  aerobic  and  anaerobic

polymerizations of vinyl monomers and as catalyst in the processes of oxidation with

molecular oxygen of different classes of organic compounds with the saturated C-H

bonds.

It was studied the EPR and UV / vis-spectra phthalimide-N-oxyl radicals (PINO)

– the key reactivе entity in the radical processes involving NHPI, formed in situ by

oxidation of NHPI or hydrogen abstraction from the O-H bond of NHPI. The kinetics

of the spontaneous decay of PINO radicals in the different solvents has been studied.

It  was  established  that  N-hydroxyphthalimide  is  an  efficient  initiator  of  the

radical polymerization of vinyl monomers. The initiation step in the presence of NHPI

proceeds through formation of a complex between NHPI and the vinyl compound due

to hydrogen bonding. The decomposition of this complex leads to the PINO radical

capable of initiating a polymerization chain.

The  rate  constants  of  the  addition  of  the  PINO  radical  to  π-bonds  of  vinyl

compounds have been measured. Monomers with donor substituents react considerably

more rapidly with PINO than monomers with acceptor substituents. This fact indicates

the electrophilic character of the PINO radical in the addition reaction to the double

bond  of  vinyl  compounds.  In  going  from  styrene  to  acrylonitrile  the  value  of  kadd

decreases very sharply. The reactivity of monomers in the elementary step of addition

of  the  PINO  radical  decreases  in  the  order  СН2 =С(СН36Н5   >  СН2 =СНС6Н5  >

СН2 =С(СН3)СООСН3 > СН2 =СНСОNH2  > СН2 =СНСООСН3  > СН2 =СНСООН >

СН2 =СНCN.

Polymethyl methacrylate obtained in the presence of NHPI has a high content of

syndiotactic  sequences.  This  finding  suggests  that,  under  conditions  of  the  vinyl

monomers polymerization, NHPI may have a dual role in the reactions of initiation and

propagation for stereochemical control of the tacticity of polymer chain. The action of

NHPI  as  stereoregulator  is  attributed  to  the  capacity  of  this  compound  to  form  a

hydrogen bond with growing macroradicals.  The best regulation of the propagation

step is achieved using N-hydroxyphthalimides with substituents in the benzene ring

having hydroxyl groups.

The  oxidative  polymerization  of  vinyl  monomers  (α-methylstyrene,  styrene,

methyl methacrylate, acrylonitrile) in the presence of NHPI was studied. It is shown

that oxidation of vinyl compounds under mild conditions (1 atm, ˂ 100 ° C) to form

the corresponding  polyperoxides,  whose  structure was studied  by  1H NMR  and  IR

spectroscopy,  thermal  stability  –  by  method  of  thermogravimetry.  Аnalysis  of

reactivity of the monomers in the oxidative polymerization processes with respect to

radicals of various structures was conducted.

The acenaphthene oxidation with molecular oxygen in the presence of NHPI has

been  investigated.  It  is  shown  that  the  main  oxidation  product  is  acenaphthene

hydroperoxide. The rate constant of H-abstraction (k H ) from acenaphthene by PINO

has been determined. The kinetic isotope effect and the activation parameters have also

been measured. On the basis of the results of our studies a plausible mechanism for the

oxidation process of acenaphthene with dioxygen catalyzed by NHPI was proposed.

The  synergetic  effect  of  the  catalytic  system  cobalt  (II)  acetate  –

N-hydroxyphthalimide  (NHPI)  was  studied  during  the  oxidation  of  alkylbenzenes

(cumene,  ethylbenzene,  toluene,  p-xylene).  It  was  established  that

N-hydroxyphthalimide is included in the internal coordination sphere of the metal; the

reaction  of  NHPI  with  cobalt  ions  in  the  internal  sphere  leads  to  the  formation  of

phthalimide-N-oxyl radicals that than participate in the catalytic cycle of the oxidation

of organic substrates. The stability constants of complexes of Со(ІІ)-NHPI and Со(ІІ)-

RH were determined.

The kinetics of the reactions of hydrogen atom abstraction from the C–H bonds

of substrates of different structures by phthalimide-N-oxyl radicals is studied, the rate

constants  of  this  reaction  are  measured.  It  is  shown  that  in  addition  to  the

thermodynamic  factor  Coulomb  forces  and  donor–acceptor  interactions  affect  the

reaction  between  phthalimide-N-oxyl  radicals  and  substrate  molecules,  altering  the

shape of the transition state. This favors the tunneling of hydrogen atoms and leads to

a substantial reduction in the activation energy of the process. It is shown that the lack

of internal rotation reactionary alkyl group in molecules of acenaphthene, fluorene and

tetralin increases of reagents entropy. It causes their high reactivity in the reactions of

hydrogen abstraction.

The influence of salts of manganese (II) on the efficiency of the catalyst system

NHPI / Co(OAc)2  in the oxidation of p-xylene was studied. Ions Mn (II) show high

reactivity  with  respect  to  peroxy  radicals  and  determine  rate  and  selectivity  of  the

oxidation of p-xylene to terephthalic acid.

The  effect  of  N-hydroxyphthalimide  structure  on  the  efficiency  of  catalysis

system  NHPI  /  Cu(I)  in  the oxidation of cumene  was studied. It  is  shown  that the

introduction of four phenyl substituents in the benzene ring of NHPI leads to a sharp

increase of the rate of oxidation. It was also revealed a positive effect of bromide anion

and a non-polar solvent chlorobenzene in the cumene oxidation process.

It is shown that the cause of the high selectivity of oxidation processes involving

NHPI  is  a  sharp  increase  in  the  chain  length.  Phthalimide-N-radical  in  oxidative

processes working as an mediator and can efficiently transfer a hydrogen atom from

the substrate to the radical chain carrying.

Keywords: N-hydroxyphthalimide, initiation, catalysis, radical chain processes,

polymerization, vinyl monomers, oxidation, molecular oxygen, alkylarenes, kinetics

mechanism.

Defence Date

14.06.2017

Dissertation File

Autosummary File