Method for preparing alkoxyamines from nitroxides

Details Method for preparing alkoxyamines from nitroxides Method for preparing alkoxyamines from nitroxides

2001-02-23

2002-12-17

Raymond, Richard L. (Department: 1624)

Organic compounds -- part of the class 532-570 series

Organic compounds

Amino nitrogen containing

C546S184000, C546S192000, C558S087000, C558S175000, C564S300000

Reexamination Certificate

active

06495720

ABSTRACT:

This application is a 371 of pct/FR00/00750, filed Mar. 24, 2000.
The present invention relates to a process for preparing &agr;,&bgr;,&bgr;-trisubstituted hydroxylamines, referred to hereinbelow as alkoxyamines, obtained from nitroxides, which can be used in particular as radical-polymerization initiators. The use of alkoxyamines such as those derived from (2,2,6,6-tetramethylpiperidyl)-N-oxide (TEMPO) in the preparation of macromolecules has given rise to many publications.
Thus, Hawker C. J. et al. (Macromolecules 1996, 29, pages 5245-5254) showed that the use of TEMPO-based alkoxyamines such as (2′,2′,6′,6′-tetra-methyl-1′-piperidyloxy)methylbenzene as initiators for the radical-mediated polymerization of styrene made it possible to control the polymerization and to gain access to well-defined polymers with low polydispersity indices, and they found that the polymerization rates were substantially equivalent to the rates obtained when they used conventional initiators such as AIBN or benzoyl peroxide in the presence of TEMPO.
Alkoxyamines can be prepared according to methods known in the literature. The most common method involves the coupling of a carbon radical with a nitroxide radical.
If an alkoxyamine is denoted by:
Y
1
, Y
2
, Y
3
, Y
4
, Y
5
, Y
6
, Z being defined later, the carbon radical Z* can be generated by various methods described in the literature: decomposition of an azo compound, abstraction of a hydrogen atom from a suitable substrate, addition of a radical to an olefin. The radical Z* can also be generated from an organometallic compound such as an organomagnesium reagent Z-MgX as described by Hawker C. J. et al. in Macromolecules 1996, 29, 5245-5254 or from a halo derivative Z-X in the presence of an organometallic system such as CuX/bipyridine (X=Cl or Br) according to a reaction of ATRA (Atom Transfer Radical Addition) type as described by Dorota Greszta et al. in Macromolecules 1996, 29, 7661-7670.
One of the methods most commonly used for preparing alkoxyamines (I) is the method involving the ATRA reaction.
This method consists in transferring an atom or a group of atoms onto another molecule in the presence of a CuX/bipyridine organometallic system, in solvent medium, according to the scheme:
In the organometallic system, X preferably represents a bromine atom.
The procedure generally used consists in dissolving the organometallic system such as CuBr/bipyridine in an organic solvent, preferably an aromatic solvent such as benzene or toluene, and then in introducing the compound ZX and the nitroxide (II) into the solution.
This approach has the major drawback of requiring long reaction times, that are unacceptable for an industrial preparation of alkoxyamines, or of using a large excess of one of the reagents.
Furthermore, the organometallic system used involves expensive ligands (bipyridine or derivatives).
In addition, the removal of the residual metal from the products obtained is difficult, requiring expensive purification operations such as passing the products through a column of silica.
Thus, in international patent application WO 9B/40415, for example, Matyjaszewski K. et al. obtain 1-(2,2,6,6-tetramethylpiperidyloxy)-1-phenylethane in a yield of 69% after purification by column chromatography, by reactingTEMPO and (1-bromoethyl)benzene in a TEMPO/(1-bromoethyl)benzene molar ratio of 2 (i.e. a molar excess of TEMPO equal to 100%) for 2 hours at 90° C., in the presence of an organometallic system [4,4′-bis(5-nonyl)-2,2′-bipyridine/Cu(OTf)
2
/Cu
0
].
A process has now been found for preparing alkoxyamines of formula:
from nitroxides:
the said process consisting in reacting the said nitroxide (II) with a halocarbon compound ZX in which X represents a chlorine, bromine or iodine atom, in a water-immiscible organic solvent medium, in the presence of an organometallic system MA (L)n (III) in which:
M represents a metal such as Cu, Ag or Au,
A represents a halogen atom, a carboxylate group or a triflate group,
L represents a ligand for the metal M,
n is 1, 2 or 3, according to the scheme:
 the said process being characterized in that it consists in carrying out the following steps:
a) a metal salt MA, the ligand L, the halocarbon compound ZX and the nitroxide (II) are mixed together with stirring, in an organic solvent, in a ZX
itroxide (II) molar ratio ranging from 1 to 1.4,
b) the reaction medium is kept stirring at a temperature of between 20° C. and 90° C. until the nitroxide (II) has completely disappeared,
c) the organic phase is recovered and washed with water, and then
d) the alkoxyamine (I) is isolated by evaporating the organic solvent under reduced pressure.
Preferably, M represents Cu, A represents a halogen such as Cl or Br, a carboxylate group such as acetate or a triflate group, and X represents a chlorine atom or a bromine atom.
According to the present invention, the ligand L for the metal M in the organometallic system (III) is chosen from the compounds represented by the general formula (IV):
in which R
1
, R
2
, R
3
and R
4
, which may be identical or different, represent a hydrogen atom, a linear or branched alkyl group containing a number of carbon atoms ranging from 1 to 10 and preferably ranging from 1 to 4, R
5
represents a hydrogen atom, a linear or branched alkyl group containing a number of carbon atoms ranging from 1 to 10 and preferably ranging from 1 to 4, a residue
in which R
6
and R
7
have the same meanings as R
5
, or alternatively at least two of the radicals R
1
, R
2
, R
3
, R
4
and R
5
may be linked together to form a ring; m, p and q, which may be identical or different, represent integers ranging from 1 to 4, preferably equal to 2, x ranging from 0 to 4.
By way of illustration of ligands L represented by formula (IV) mention will be made of:
tris [2-(dimethylamino)ethyl]amine:
 N,N,N′,N′,N″-pentamethyldiethylenetriamine (PMDETA):
 N,N,N′,N′-tetramethylethylenediamine:
(CH
3
)
2
—N—CH
2
CH
2
—N—CH
3
)
2
,
 1,1,4,7,10,10-hexamethyltriethylenetetramine (HMTETA):
 cyclic polyamines such as:
1,4,7-trimethyl-1,4,7-triazacyclononane,
1,5,9-trimethyl-1,5,9-triazacyclododecane,
1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane.
PMDETA will preferably be used.
The process according to the invention consists in mixing, with stirring, a metal salt MA, the ligand L, the compound ZX and the nitroxide (II) in an organic solvent which is preferably an aromatic hydrocarbon such as benzene, toluene or xylenes, or an alkylchloride such as CH
2
Cl
2
or alternatively an ether.
The oxidation state of the active species of the metal M is equal to 1 (M
I
)
According to the present invention, this active species can be added, without modification, to the reaction medium, preferably in the form of a metal halide M
I
A.
The preferred metal halide is CuBr.
The active species can also be generated in situ according to the redox reaction:
M
II
A+M
O
⇄2M
I
A
from a metal salt M
II
A in which the metal M is in oxidation state 2 (M
II
) and the same metal in oxidation state zero (M
O
).
According to this variant, the metal halide M
II
A which is preferred is CuBr
2
.
According to another variant, a metal salt MA in which the metal M is in oxidation state 1 (M
I
A) and the same metal M in oxidation-state zero (M
O
) may also be introduced into the reaction medium.
The ligand L is used in an L/M
I
molar ratio ranging from 1 to 5 and preferably ranging from 1 to 2.
The ZX
itroxide (II) molar ratio ranges from 1 to 1.4 and is preferably equal to 1.
The reaction mixture is then stirred at a temperature of between 20° C. and 90° C. and preferably in the region of room temperature.
The process is performed under an atmosphere of inert gas such as nitrogen or argon and preferably at atmospheric pressure.
The reaction times are very short. The end of the reaction can be monitored by the disappearance of the reagents, by chromatographic methods (GC, HPLC, TLC). Once the reaction is complete,.

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