DE1618140C3 - Stabilization of 2-chlorobutadiene- (1,3) - Google Patents

Description

R ₂ -CNCR ₄

R ₅ OR ,,

(I)

in which Ri to Re are alkyl groups with 1 to 15 Carbon atoms are or Rs and R6 together can form the pyrrolidine or piperidine ring, adds.

2. Stabilization according to claim 1, characterized in that 2,2,6,6-tetramethylpiperidine-1-oxyl or 2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl is added.

3. Stabilization according to claim 1, characterized in that the total number of carbon atoms of the added nitroxide is 8 or 9.

30th

Under controlled conditions, 2-chlorobutadiene (l, 3) can form valuable, rubber-like polymers are polymerized, but the monomer also has a strong tendency to polymerize during the Manufacture, extraction and storage. Various have been used to stabilize the polymerizable monomers Proposed method, e.g. B. the addition of p-benzoquinone, hydroquinone or nitric oxide.

It has now been found that it is possible 2-chlorobutadiene- (1,3) to be much more effective against one Stabilize polymerization than is possible according to the prior art. The inventive, stabilized 2-chlorobutadiene- (1,3) shows less tendency to form colored products than that with Nitric oxide, a commonly used inhibitor, stabilized 2-chlorobutadiene- (1,3).

The invention relates to a method for stabilizing 2-chlorobutadiene (l, 3) against polymerization, which is characterized in that this 10 to 1000 parts of a nitroxide of the general Formula (I)

R ₂ -CNCR ₄ R ₅ OR ₆

(D

55

in which Ri to R6 are alkyl groups with 1 to 15 Carbon atoms are or Rs and R6 together Can form pyrrolidine or piperidine ring, adds.

The inventive method is particularly advantageous because it is much less by the Presence of molecular oxygen is influenced as stabilization with nitric oxide. The presence catalyzes even very small amounts of oxygen in a 2-chlorobutadiene (l, 3) stabilized with nitrogen oxide the formation of undesirable adducts of 2-chlorobutadiene (l, 3) with nitric oxide and nitrogen dioxide, which is common are colored. The nitroxides of the formula (I) can contain significantly higher oxygen concentrations than nitric oxide tolerate, without the formation of undesirable products and without a destruction of the ability to Stabilize monomers against polymerization. The stabilization according to the invention offers the great Advantage that a very small amount of oxygen penetration, e.g. B. as air, in 2-chlorobutadiene (l, 3) -containing Vessels, which is difficult to avoid in practice, is less damaging than nitric oxide Stabilizer would be. By using the method according to the invention, it is possible that method for Removal of oxygen from 2-chlorobutadiene (l, 3) and 2-chlorobutadiene (l, 3) -containing vessels, the are necessary when using nitrogen oxide, can be omitted. These procedures exist z. B. in purging the 2-chlorobutadiene (l, 3) with an inert gas, such as nitrogen, to remove dissolved oxygen, and are an additional complication when using nitric oxide. Although drastic removal and oxygen exclusion for best results using the Nitroxides of formula (I) may be useful, since the presence of oxygen causes a certain reduction the stabilizing effectiveness of nitroxides against 2-chlorobutadiene (l, 3) can bring with it the ability to omit the oxygen removal is a significant advantage of the invention The tolerable molar oxygen concentration can be equal to the molar nitroxide concentration being.

Another advantage of the method according to the invention is the possibility of a particularly effective one Suppression of the formation of a so-called "popcorn" polymer. This "popcorn" polymer is a very high molecular weight polymer which is insoluble in most solvents. His presence is highly undesirable as it blocks the reaction vessels and stills and out of each The vessel in which it forms is extremely difficult to remove.

In the basic formula (I), the alkyl groups Ri to R6 can be identical or different and contain 1 to 15 carbon atoms or Rs and Rö can together form the pyrrolidine or piperidine ring. The use of nitroxides of the basic formula (I) in which Ri to Re is methyl, propyl Äthyloder stand or the two radicals R and R6 may form the Pyrridin- or piperidine ring together is particularly preferred. Suitable compounds of the basic formula (I) in which the radicals Rs and Re form one of the rings mentioned are pyrrolidine-1-oxyls and piperidine-1-oxyls, in particular 2,2,6,6-tetramethylpiperidine-1-oxyls, for example 2,2,6,6-tetramethylpiperidine-loxyl and 2,2,6,6-tetramethyl-4-hydroxypiperidine-loxyl.

Where the remaining valencies of compounds of the general formula (I) are replaced by alkyl groups Rs, R6 are saturated, also contain the groups Rs and R6 1 to 15 carbon atoms. Suitable groups Rs and Re are e.g. B. methyl, ethyl and propyl groups. One suitable compound of formula (I) is e.g. B. Di-tert-butyl nitroxide.

Preference is given to nitroxides of the formula (I) having 8 or 9 carbon atoms in the molecule, since they are used in the Suppression of the formation of the undesirable "popcorn" polymer επί are most effective.

It was found that with the preparations according to the invention a measurable increase in the time for which the monomer can be heated before the start of the polymerization is possible.

The amount of nitroxide which is necessary for a satisfactory increase in stability is expedient between 10 to 1000 parts per million, e.g. B. 10 to 100 Parts per million, however, concentrations outside these limits can be used.

example 1

There was prepared a 2-chlorobutadiene (l, 3) solution, tert di-1,2 ■ 10- ² mol / l of the initiator azo-bis (isobutyronitrile) and 1,2 ■ 10 ~ ³ mol / l. -butylnitroxide.

The solution was sealed in a strain gauge under vacuum, and that with heating to 50 ° C resulting reduction in volume was gemes

Comparative example 1

In a non-inventive comparative experiment, a 2-chlorobutadiene (l, 3) made Iösung and heated under the above-mentioned in Example 1 Bedinungen, except that in place of the Nitroxyds 1.2 x IO ³ mol / l "A'-diphenyl- ^ -picrylhydrazil a known free radical scavenger was present.

In both examples there was an induction period during which the 2-chlorobutadiene {13) was the slow formation of dimers, to which the polymerization of the monomer at a rate of 7 x 10 ^-2 moles / 1 / sec joined. The duration of the induction time with di-tert.-butylnitroxide was 260 minutes, while the time achieved with α, oc'-diphenyl-j? -Picrylhydrazil was only 140 minutes.

Example 2

There was prepared a 2-chlorobutadiene (l, 3) solution, tert di-1,2 ■ 10- ² mol / l of the initiator azo-bis (isobutyronitrile) and 4.7 x 10 ~ ⁴ mol / l. -butylnitroxide. The solution was sealed under vacuum in a strain gauge and heated to 50 ⁰ C.

Comparative example 2

According to Example 2, a 2-chlorobutadiene (1.3) solution was prepared and heated under the same conditions, but in place of the Nitroxyds 4.7 ■ IO ⁴ mol / l of the known stabilizer p-benzoquinone.

The benzoquinone gave an induction time of less than 5 minutes, while the induction time with di-tert-butyl nitroxide was 100 minutes. The rate of conversion of the monomer into polymer after the induction time was in each case 7 · 10 -2 mol / 1 / sec; ^ [ _{it was} the same rate found in the absence of any added inhibitor.

Example 3

A small germ of a 2-chlorobutadiene (1.3) "popcorn" polymer was found in four test tubes each Put a glass wool plug near the top of the tube. 2-chlorobutadiene (1,3) monomer was vacuum distilled into each tube and at the bottom of the tube, below the "popcorn" polymer used condensed. Then the tubes were filled with nitrogen at atmospheric pressure, closed with a stopper and stored in the dark at room temperature. In addition to the 2-chlorobutadiene (l, 3) three tubes contained a stabilizer as follows:

Tube A contained phenothiazine at a concentration of 0.1 percent by weight based on the Monomers;

Tube B contained 2,2,6,6-tetramethyl-4-hydroxypiperidin-1-oxyl at a concentration of 0.1 percent by weight of the monomer; Tube C contained di-tert-butyl nitroxide in one concentration from 0.1 percent by weight of the monomer;

Tube D did not contain any additive. After 6 days the contents of the tubes were examined and found the following:

Tube A contained a very small amount of a mobile liquid, with the remainder Monomers at the top of the pipe in "popcorn" polymer was transformed; Tube B contained one third of the original monomer as a mobile liquid; the The rest was present as "popcorn" polymer;

Tube C contained all of the original monomer as a mobile liquid; the germ the "popcorn" polymer had not grown;

Tube D contained half of the original monomer in the bottom in the form of a clear Rubber, the rest was present at the head of the pipe as "popcorn" polymer.

Tube C was re-examined after 205 days. There was almost no growth in the "popcorn" - Germ visible, and the lower part of the tube contained the original volume of a mobile liquid, which was a mixture of the monomers and dimers.

This example shows the superior stabilizing effect of the nitroxides according to the invention in comparison with phenothiazine. It is noted that the "popcorn" polymerization in the vapor space above the liquid 2-chlorobutadiene (l ^ monomers and not in the liquid itself had occurred and that inhibition, e.g. B. with phenothiazine, the liquid Can at least partially stabilize monomers, while preventing "popcorn" polymerization can be quite ineffective.

Example 4

A small nucleus of a 2-chlorobutadiene (1.3) "popcorn" polymer was found in two tubes each placed in a glass wool stopper near the top of the tube. There was monomer in each tube 2-chlorobutadiene (l, 3) is distilled in under vacuum and at the bottom of the tube, below the point of the "Popcorn" germs condensed The tubes were sealed under vacuum and kept in the dark Stored at room temperature The tube A contained 2,2,6,6-tetramethylpiperidine-1-oxyl in one concentration from 0.01 percent by weight of the monomer; Tube B did not contain any additive.

After 115 hours it was found that the "Popcom" seed in tube B had grown ten times its original size, while the Liquid at the bottom of the tube had become viscous. In tube A, there was no change in the size of the

"Popcorn" germs visible; the monomer on the tube sheet was colorless and mobile.

This test shows the effectiveness of the nitroxide according to the invention in avoiding polymerization in the liquid phase and a growth of the »Popcorne polymer from the monomer in the Vapor phase; furthermore, no colored adducts were formed from the nitroxide and 2-chlorobutadiene (1,3) been.

Example 5

5 ecm of freshly distilled 2-chlorobutadiene (l, 3) each were put with a pipette into tubes A and B, which had a volume of 10 ecm, so that in their Sealing 5 ecm of air at atmospheric pressure above the monomer were included. pipe A contained di-tert-butyl nitroxide at a concentration of 0.02 percent by weight of the monomer. Pipe B did not contain any addition. After 160 hours, only tube B remained on the bottom due to polymerization a very small amount of a liquid, viscous residue. The rest of the original liquid charge had formed a "popcorn" polymer in the vapor space at the top of the pipe. The liquid in tube A, on the other hand, was still mobile, and there was none in the vapor space in the upper part of the tube Growth of a "popcorn" polymer takes place.

The nitroxide could clearly be the 2-chlorobutadiene- (l, 3) stabilize against polymerization, even in the presence of some oxygen.

The nitro oxides to be used according to the invention are in part from the publications in J. of Am. Soc, 1961, Vol. 83, p. 4671 and Nature, 1962, Vol. 196, p. 472 known and can be produced by the processes described there.

Claims (1)

Patent claims: 1. Stabilization of 2-chlorobutadiene (l, 3), characterized in that the 2-chlorobutadiene (l, 3) 10 to 1000 parts of a nitroxide of the general formula (I) R,