Stabilized N-alkenyllactam

Details Stabilized N-alkenyllactam Stabilized N-alkenyllactam

2001-05-09

2003-06-24

Kifle, Bruck (Department: 1624)

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

Organic compounds

Unsubstituted hydrocarbyl chain between the ring and the -c-...

Reexamination Certificate

active

06583281

ABSTRACT:

The present invention relates to N-alkenyllactams having at least a 6-membered lactam ring, stabilized by phenothiazine and/or derivatives thereof.
N-Alkenyllactams are used inter alia for the preparation of homopolymers and copolymers for a very wide variety of applications, for example as pigment dispersants, as washing aids, as adjuvants in cosmetic and medicinal products and as auxiliary substances in textile processing and adhesives technology, and for radiation-curing surface coatings.
During processing, storage or transportation, for example, unstabilized N-alkenyllactams tend to undergo an undesirable and uncontrollable polymerization, constituting a high safety risk. To prevent this, stabilizers are generally added to N-alkenyllactams. The most widespread practice is to add N,N′-bis(1-methylpropyl)-1,4-phenylenediamine, which is marketed by BASF AG under the trade name Kerobit® BPD. In Ullmann's Encyclopedia of Industrial Chemistry, 6th edition, 1999 Electronic Release, Chapter “2-PYRROLIDONES-N-Vinyl-2-pyrrolidone”, N,N′-bis(1-methylpropyl)-1,4-phenylenediamine, for example, is mentioned as a typical stabilizer for N-vinyl-2-pyrrolidone.
Belgian patent BE 600 351 discloses the stabilization of N-vinylpyrrolidone against spontaneous polymerization during storage and distillation by the addition of an aromatic compound containing at least one secondary nitrogen atom bonded to an aromatic radical and one sulfur atom bonded to a carbon atom. One of the suitable compounds mentioned is phenothiazine, which suppresses the polymerization in concentrations down to 0.1% (1000 ppm), even at elevated temperatures.
Phenothiazine and derivatives thereof are also known as constituents of polymerization stabilizers for vinyl compounds having a vinyl group bonded to a carbon atom. JP 08081397-A describes the stabilization of acrylic acid by the presence of (i) phenothiazine and (ii) at least one halide salt. Patent application GB-A 2 285 983 describes the stabilization of acrylic acid by the presence of (i) phenothiazine, (ii) a copper dithiocarbamate compound and (iii) at least one metal or one metal compound containing Cr, Mg, Ti or Co. SU 734 216 and SU 737 406 disclose phenothiazine mixed with a quinone derivative as a polymerization inhibitor for styrene or methyl methacrylate.
JO 1268-675-A describes the stabilization of vinylpyridines, for example 4-vinylpyridine, by the presence of phenothiazine and derivatives thereof.
Another problem associated with N-alkenyllactams, apart from their tendency to undergo undesirable and uncontrollable polymerization, is their tendency to discolor, especially at temperatures above room temperature. Thus, for example, initially colorless N-vinylcaprolactam, which is stabilized with the stabilizer N,N′-bis(1-methylpropyl)-1,4-phenylenediamine conventionally used in industry, assumes a yellowish to brownish coloration even when stored for only a few hours at a temperature above room temperature, the intensity of said coloration increasing significantly with increasing storage temperature.
In many cases, when processed further, N-alkenyllactams are preferably used as the pure substances in liquid form, so all N-alkenyllactams which have a melting point above room temperature generally either have to be stored and transported at a temperature above the melting point or have to be melted by a heat treatment prior to processing. Either way, the abovementioned problem of discoloration has a particularly adverse effect, especially when dealing with N-alkenyllactams which have a melting point above room temperature, i.e. those having at least a 6-membered lactam ring. Examples which may be mentioned of N-alkenyllactams important in industry are N-vinylpiperidone, melting between about 42 and 48° C., and N-vinylcaprolactam, melting between about 34 and 35° C. (cf. Beilstein's Handbook of Organic Chemistry, 3rd and 4th supplements, volume 21, part 4, Springer Verlag Berlin, Heidelberg, N.Y. 1978, pages 3174 and 3207).
It is therefore an object of the present invention to provide stabilized N-alkenyllactams having at least a 6-membered lactam ring which no longer exhibit the abovementioned disadvantages, which have a long shelf life and which exhibit only a very low tendency to discolor, even on melting or on prolonged storage at elevated temperatures. It is a further object of the present invention to find a process for the stabilization of N-alkenyllactams having at least a 6-membered lactam ring, which process yields stabilized N-alkenyllactams with the abovementioned properties. It is a further object of the present invention to find compounds capable of being used for the stabilization of N-alkenyllactams having at least a 6-membered lactam ring, the stabilized N-alkenyllactams having the abovementioned properties.
We have found that this object is achieved by the provision of an N-alkenyllactam having at least a 6-membered lactam ring, stabilized by phenothiazine and/or derivatives thereof.
The stabilizer to be used according to the invention can be either unsubstituted as the parent substance, or monosubstituted to octasubstituted as a phenothiazine derivative. It is characterized by general formula (I):
in which the radicals R
1
to R
8
independently of one another are a hydrogen atom, a carbon-containing organic radical, an amino group, a halogen, a nitro group or a cyano group.
A carbon-containing organic radical is to be understood as meaning an unsubstituted or substituted aliphatic, aromatic or araliphatic radical having from 1 to 10 carbon atoms. This radical can contain one or more heteroatoms such as oxygen, nitrogen or sulfur, for example —O—, —S—, —NR—, —CO— and/or —N═ in aliphatic or aromatic systems, and/or can be substituted by one or more functional groups containing e.g. oxygen, nitrogen, sulfur and/or halogen, for example by fluorine, chlorine, bromine, iodine and/or a cyano group. If the carbon-containing organic radical contains one or more heteroatoms, said radical can also be bonded via a heteroatom. Thus ether, thioether and secondary and tertiary amino groups, for example, are also included. Preferred examples of the carbon-containing organic radical which may be mentioned are C
1
to C
10
alkyl, especially C
1
to C
6
alkyl, C
6
to C
10
aryl, especially phenyl, C
7
to C
10
aralkyl, especially phenylmethyl, and C
7
to C
10
alkaryl, especially 2-methylphenyl, 3-methylphenyl and 4-methylphenyl.
Preferred compounds of formula (I) are those in which the radicals R
1
to R
8
independently of one another are a hydrogen atom or a C
1
to C
4
alkyl, for example methyl, ethyl, propyl, 1-methylethyl, butyl, 1-methylpropyl, 2-methylpropyl and 1,1-dimethylethyl.
Particularly preferred compounds of formula (I) are those in which at least seven of the radicals R
1
to R
8
are a hydrogen atom and at most one radical is a C
1
to C
4
alkyl. Examples of particularly preferred compounds are phenothiazine, 1-methylphenothiazine, 2-methylphenothiazine, 3-methylphenothiazine and 4-methylphenothiazine. Unsubstituted phenothiazine is very particularly preferred.
The stabilizer to be employed according to the invention can be used without the addition of other stabilizers, in a mixture with one or more phenothiazine derivatives or in a mixture with other stabilizers, for example N,N′-bis(1-methylpropyl)-1,4-phenylenediamine. Use without the addition of other stabilizers is preferred.
The N-alkenyllactam stabilized according to the invention is stabilized by a total amount preferably of 1 to 1000 ppm by weight, particularly preferably of 1 to 100 ppm by weight and very particularly preferably of 5 to 50 ppm by weight of phenothiazine and/or derivatives thereof, based on the total amount of N-alkenyllactam. The expression “total amount” is always to be understood as meaning the sum of the amount of N-alkenyllactam and the amount of phenothiazine and derivatives thereof used.
In addition to phenothiazine and/or derivatives thereof, the N-alkenyllactam stabilized according to the invention can also c

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