Process for the electrochemical production of a...

Details Process for the electrochemical production of a... Process for the electrochemical production of a...

1999-08-27

2002-08-20

Weisberger, Rich (Department: 1774)

Adhesive bonding and miscellaneous chemical manufacture

Surface bonding means and/or assembly means therefor

C534S885000, C534S553000, C534S559000, C427S402000, C427S419100

Reexamination Certificate

active

06435240

ABSTRACT:

The present invention relates to a novel process for preparing, by electrochemical reduction, a carbon-containing material whose surface is modified with organic groups, in particular functionalized organic groups, this process comprising placing the carbon-containing material in contact with organic diazonium salt in solvent, optionally in the presence of an electrolyte, and negative polarization of the carbon-containing material relative to an anode which is also in contact with a solution of the said organic diazonium salt or in contact with an electrolytic solution separated by a suitable separator for the solution of the said salt.
The invention also relates to the modified carbon-containing materials obtained by the said process and to the use of these carbon-containing materials, in particular for the preparation of composite materials or for carrying out chemical or biological reactions, or for the complexation of metals.
European patent EP-B-569,503 has already described a process for preparing a carbon-containing material whose surface is modified with aromatic groups, in particular functionalized aromatic groups, by electrochemical reduction.
This process is characterized in that it consists in binding an aromatic group to the surface of this material by electrochemical reduction of a diazonium salt comprising this aromatic group, by placing the carbon-containing material in contact with a solution of the diazonium salt in an aprotic solvent and negatively polarizing the carbon-containing material relative to an anode which is also in contact with the diazonium salt solution.
This document furthermore indicates that, in order for the electrochemical reduction of the diazonium salt to lead to binding of the aromatic group of this salt to the surface of the carbon-containing material, it is necessary to carry out the reduction in an aprotic medium which contains neither any nucleophilic compounds nor any ethylenic compounds nor any species capable of reacting with the neutral radical faster than this radical binds to the carbon-containing surface, and to perform the process at a potential which is more negative than the reduction potential of the diazonium salt.
It has now been found, unexpectedly, that the use of this process in protic solvent in acidic medium leads to the binding of an organic group to the surface of the carbon-containing material.
The process according to the invention is thus characterized in that the electrochemical reduction is carried out on an organic diazonium salt in protic solvent in acidic medium.
The electrochemical reduction can be represented schematically according to the following reaction:
RN
2
+
+&thgr;
•
→RN
2
•
→R
•
+N
2
R being an organic residue.
The residue R binds to a carbon atom at the surface of the carbon-containing material. The covalent bond formed is of the type: carbon of the carbon-containing material-carbon of the organic residue.
According to the process of the invention, the cathode potential is set at a value such that the neutral radical R
•
is not reduced and does not give a carbanion. The potential should thus be adjusted to a value which is not too negative, in order to stabilize the neutral radical R
•
.
It will be noted that the term “residue” denotes the organic part of the diazonium.
It is understood that the invention covers all diazonium salts whose residues R in radical form will be stable enough to bind to a carbon of the carbon-containing material.
The term “group R” will denote the residue R bound to the carbon-containing material, it being understood that the group R will have a broader meaning than the residue R due to the subsequent chemical conversions which it may undergo, as will be understood in the light of the description which follows.
The invention relates in particular to a process characterized in that the diazonium salt corresponds to the formula:
ArN
2
+
X
−
  (I)
in which:
Ar is an optionally substituted C
6
-C
14
aromatic residue or an optionally substituted heteroaromatic residue of 5 to 14 atoms, comprising one or more hetero atoms chosen from oxygen, nitrogen, sulphur and phosphorus,
X
−
is an anion chosen from halogens, sulphates, phosphates, perchlorates, tetrafluoroborates, carboxylates and hexafluorophosphates.
The term “aromatic residue” means any residue comprising one or more C
6
-C
14
fused or independent benzenic nuclei known per se. Non-limiting examples which may be mentioned are phenyl, naphthyl and anthryl nuclei, triple-fused nuclei, biphenyl nuclei, etc.
The term “heteroaromatic residue” means any aromatic heterocycle comprising one or more hetero atoms such as N, O, S or P, in particular comprising 5 to 14 atoms.
In fact, it is understood that the invention is not limited to specific compounds, but, on the contrary, extends to any diazonium salt which can be reduced to give a neutral radical Ar
•
.
Among the aromatic residues which may be mentioned, by way of example, are aromatic residues whose substituents are chosen from the group consisting of:
linear or branched aliphatic radicals optionally comprising one or more double bond(s), optionally substituted with carboxyl, NO
2
, disubstituted protected amino, monosubstituted protected amino, cyano, diazonium, alkoxy, alkoxycarbonyl, alkylcarbonyloxy or optionally fluorinated vinyl radicals or halogen atoms,
aryl radicals optionally substituted with carboxyl, NO
2
, disubstituted protected amino, monosubstituted protected amino, cyano, diazonium, alkoxy, alkoxycarbonyl, alkylcarbonyloxy or optionally fluorinated vinyl radicals or halogen atoms,
carboxyl, NO
2
, disubstituted protected amino, monosubstituted protected amino, cyano, diazonium, alkoxy, alkoxycarbonyl, alkylcarbonyloxy or optionally fluorinated vinyl radicals or halogen atoms.
As regards the optionally fluorinated vinyl radicals, these should be compatible with the envisaged reaction of the diazonium.
The term “functionalized” means in particular that the aromatic or heteroaromatic or aliphatic radicals, when the aromatic or heteroaromatic radicals are substituted with an aliphatic radical, comprise one or more substituent(s) capable of reacting with a substrate or one or more substituent(s) capable of being converted into substituents capable of reacting with a substrate.
These substituents can thus be very varied depending on the applications for which the carbon-containing materials are intended.
Among the substituents capable of reacting directly with a resin, in particular an organic resin, mention may be made, for example, of —(CH
2
)
n
—COOH, —(CH
2
)
n
—CH
2
—OH and (CH
2
)
n
—NH
2
groups, n being an integer between 0 and 10, and —CH═CH
2
and —CF═CF
2
groups.
Among the precursor substituents which, after conversion, are capable of reacting with a resin, in particular an organic resin, mention may be made, for example, of NO
2
, N
2
+
, (CH
2
)
n
—CN, (CH
2
)
n
—CHO and (CH
2
)
n
—COOPr groups, Pr being a protecting group, and (CH
2
)
n
—NHP′r, (CH
2
)
n
—N(P′r)
2
and (CH
2
)
n
—N═P″r groups, P′r and P″r being protecting groups and n being an integer between 0 and 10.
Among the substituents capable of reacting directly with a biological molecule, mention may be made of —(CH
2
)
n
—COOH and —(CH
2
)
n
—NH
2
groups, n being an integer between 0 and 10.
Among the precursor substituents which, after conversion, are capable of reacting with a biological molecule, mention may be made of NO
2
, NO
2
, N
2
+
, (CH
2
)
n
—CN, (CH
2
)
n
—CHO and (CH
2
)
n
—COPr groups, Pr being a protecting group and n being an integer between 0 and 10.
Among the substituents capable of reacting directly with functional organic molecules, mention may be made of NO
2
, (CH
2
)
n
—CONH
2
, (CH
2
)
n
—CN, (CH
2
)
n
—CHO, (CH
2
)
n
—COOH, (CH
2
)
n
—CH
2
OH and (CH
2
)
n
—NH
2
groups, n being an integer between 0 and 10, and SO
2
H, SO
3
H, SO
2
R and SO
3
R groups, R being an aliphatic or aromatic carbon-containing chain of 1 to 2

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