Use of nitromethane, nitroethane and 1-nitropropane for inhibiting the degradation of hydrochlorofluorocarbons utilized as foaming agents in the preparation of foamed polyurethanes and polyisocyanurates

Abstract: The invention relates to a method for inhibiting the degradation by dehydrohalogenation of hydrochlorofluorocarbons, such as for example the mixture of 123 and 123a, used as foaming agents during the formation reaction of foamed polyurethanes or polyisocyanurates starting from polyols and polyisocyanates. Prior to the reaction starting, a little amount of a stabilizing substance selected from the group consisting of nitromethane, nitroethane and 1-nitropropane is added to the reaction medium.

Description: It is known that the hydrochlorofluorocarbons, which are replacing the chlorofluorocarbons in their various applications, exhibit a lower chemical stability as compared with the latter, wherefore they are more subject to degradation in the presence of various substances and materials which they come in contact with during their various uses. This problem arises in particular when the hydrochlorofluorocarbons are utilized as foaming agents in the preparation of foamed polyurethanes or polyisocyanurates. As is known, these products can be prepared by reacting polyalcohols with polyisocyanates in the presence of aminic and organometallic catalysts and of a foaming agent consisting of a hydrochlorofluorocarbon having a boiling temperature not higher than about 70°C. When chlorofluorocarbons are utilized as foaming agents, a formulation based on polyol, catalysts and foaming agent is previously prepared. Such formulation is mixed with the polyisocyanate at the moment of carrying out the reaction. As it is usual to store the formulation even for several months, the chlorofluorocarbon tends to react with the organic compounds containing active hydrogen such as polyols and aminic catalysts. Furthermore, the metals coming from the containers exert a catalytic action on the reaction between chlorofluorocarbons and organic compounds containing active hydrogen atoms. Therefore the formulation is added with a little amount of a stabilizing agent capable of inhibiting the last-mentioned reaction. Thanks to the addition of such agent, the problems caused by the incompatibility between chlorofluorocarbons and polyols are solved also during the reaction between polyols and polyurethanes. According to British patent No. 1,009,041, the reaction between chlorofluorocarbons, in particular CFCl₃, and polyols is inhibited by adding particular ethylenically unsaturated compounds such as alpha-methylstyrene. According to British patent No. 1,018,809, the same reaction is inhibited by means of the same alpha-methylstyrene or other ehtylenically unsaturated compounds. The use of particular unsaturated hydrocarbons is described in British patent No. 1, 149, 458 and in U.S. patent No. 4,463,189. According to U.S. patent No. 3, 085, 116, the abovesaid reaction is inhibited by means of a mononitroalkane. Few are the documents which relate to the stabilizaction of hydrochlorofluorocarbons in the abovesaid formulations. Among these documents, Japanese patent application 1-211538 describes a method for stabilizing hydrochlorofluorocarbons such as HCFC 123 by using acrylic or methacrylic esters containing at least a hydroxylic, ethereal or epoxy group. Japanese patent application 1-211539 describes a method for stabilizing the same hydrochlorofluorocarbons by using one of the abovesaid esters and a hydrocarbon of formula: where R¹, R², R³ and R⁴ are hydrogen atoms or hydrocarbon groups containing 1 to 3 carbon atoms. Japanese patent application 1- 128 945 discloses the stabilization of hydrogen containing fluorocarbons, for example HCFC 123, toward polyols in the preparation of polyurethane foams by adding nitromethane or 1-nitropropane, nitroethane The Applicant has now found that for several hydrochlorofluorocarbons, such as for example HCFC 123, nitromethane, nitroethane or 1-nitropropane are not only useful for the stabilization of hydrochlorofluoro carbons against polyol, but that during the formation reaction of foamed polyurethane several HCFC decompose, so giving rise to other degradation products, different from the ones which form during the storing of the HCFC-containing polyol. These degradation products, as well as the ones which form during said storing, are often toxic. while, for example, during the storing HCFC 123 (CF₃ - CHCl₂) tends to decompose to impurity HCFC 133a (CH₂Cl-CF₃), during the foamed polyurethane formation reaction it occurs a dehydrofluorination reaction, which leads to the formation of olefin CFC 1112a (CF₂=CCl₂). The degradation reactions, which occur during the formation of foamed polyurethane, are thought to depend on the concomitant action of Lewis bases,which are present in the reaction medium, and on the temperature. The Lewis bases which are present in the reaction medium are polyalcohols and aminic catalysts. As already mentioned, HCFC 123 leads to the formation of olefin CFC 1112a. Conversely, HCFC 123a (CHClF-CF₂Cl) leads to the formation of olefin CFC 1113 (CClF=CF₂). Both olefins are toxic. Since HCFC 123 - going to be put on the market - which is a foaming agent of particular interest for the preparation of the abovesaid foamed products, can contain a certain amount of HCFC 123a - depending on the preparation process - the use of the mixture of HCFC 123 and HCFC 123a can give rise to the simultaneous formation of the abovesaid olefinic impurities. Conversely, HCFC 141b (CH₃-CCl₂F) can lead to the formation of olefin HCFC 1131a (CH₂=CClF), which is toxic too. Apart from the generation of generally toxic impurities, the abovesaid degradation reactions cause other drawbacks, which are due to the introduction of HCl and/or HF into the reaction medium and into the foamed products. In the first place these acids are corrosive and can damage the metallic and non-metallic materials of the structures which they come in contact with. Furthermore, they tend to deactivate the basic catalysts, which play a leading role in controlling that the foam generation rate should be in accordance with the polymerization rate. In some cases, toxic olefins can form not by dehydrohalogenation of the HCFC used as foaming agents, but starting from other HCFC which have formed in consequence of other degradation reactions of the foaming HCFC. In particular, HCFC 123 can form radicals which, by coupling, can form HCFC 336 CF₃-CHCl-CHCl-CF₃, which is converted to toxic olefin HCFC 1326 CF₃-CH=CCl-CF₃ by dehydrochlorination. The last-cited type of degradation reaction gives rise, of course, to the same drawbacks as occur in the dehycrohalogenation reactions of the HCFC used as foaming agents. As already mentioned herein, the use of nitromethane, nitroethane or 1-nitropropane for inhibiting the abovesaid degradation reactions has not been proposed so far. Thus, it is an object of the present invention to inhibit such reactions by adding a little amount of a stabilizer to the reaction medium prior to the starting of the formation reaction of foamed polyurethane or polyisocyanurate, i.e. prior to the so-called "foaming". Another object is to inhibit the formation of toxic olefins during foaming. Still another object is to inhibit the formation of HCl and/or HF during foaming, thereby eliminating or reducing the drawbacks due to such formation. These and still other objects are achieved by the use of nitromethane, nitroethane or 1- nitropropane according to the present invention for inhibiting the degradation by dehydrohalogenation of hydrochlorofluorocarbons having two carbon atoms, on the first of which there is a chlorine or fluorine atom while on the second there is a hydrogen atom, the other atoms which are present on the two carbon atoms being indifferently H, Cl or F, with a total number of F atoms present in the molecule not higher than 4, and having a boiling temperature ranging from about -15°C to about 70°C, when said hydrochlorofluorocarbons are utilized as foaming agents during the formation reaction of foamed polyurethanes or polyisocyanurates starting from polyols and polyisocyanates and for inhibiting the dehydrohalogenation or hydrochlorofluorocarbons which form as degradation by-products of the abovesaid foaming agents during the aforesaid reaction. This use is characterized in that a little amount of a stabilizer selected from the group consisting of nitromethane, nitroethane and 1-nitropropane is added to the reaction medium prior to the reaction starting. The amount of added nitromethane generally ranges from 0.3 to 4% by weight calculated on the HCFC, the amount of added nitroethane generally ranges from 0.5 to 5% by weight and the amount of 1-nitropropane generally ranges from 0.5 to 5% by weig It is often preferred to use an mount of 0.5-1% by weight of nitromethane, 1-2% of nitroethane and 1-3% of 1-nitropropane. The preferred stabilizing agent is nitromethane. Among the hydrochlorofluorocarbons which are stabilized by the method according to the present invention there are to be cited,in particular, HCFC 123 (CF₃-CHCl₂), HCFC 141b (CH₃-CCL₂F), HCFC 123a (CHClF-CClF₂) and HCFC 141a (CHCl₂-CH₂F) arc the mixtures of 123 and 123a and of 141b and 141a. The hydrochlorofluorocarbons which form as degradation by-products, as explained hereinbefore, have generally 4 carbon atoms, wherein on one of two adjacent carbon atoms there is Cl or F atom and on the other carbon atom there is a H atom, while the other atoms which are present on the two adjacent carbon atoms are indifferently H, Cl or F atoms. In the cases in which the HCFC can react with the polyols and the amines contained in the polyol-based formulations - such cases being ascertainable by means of a storing test - it is convenient to mix the ingredients for the preparation of the foamed polymer (formulation based on polyol, polyisocyanate and HCFC) along with the stabilizer just before starting the foaming, or to mix the stabilizer-containing HCFC with the polyol-based formulation or with the polyisocyanate short before (i.e. within, for example, 24 hours) starting the foaming. The solution of the stabilizer in the HCFC can be stored for several months. However, nitromethane, nitroethane and 1-nitropropane efficaciously inhibit the degradation of many of the HCFC defined hereinbefore when the polyol-based formulations containing such HCFC are subjected to storing. That is the case of HCFC 123 and HCFC 141b. The amounts of stabilizers are the same as the ones utilized for the foaming. An effective stabilization of several HCFC, for exaple HCFC 123 and HCFC 141b, is also obtained with particular unsaturated substances, which will be described later on herein. Conversely, in the case of HCFC 123a, none of the abovesaid classes of products is capable of efficaciously inhibiting its degradation in olefin 1113 (CClF=CF₂) during the polyol storing. Instead of adding the hydrochlorofluorocarbons and nitromethane, nitroethane or 1-nitropropane before the foaming, it is therefore possible to add them, in various cases, to the polyol-based formulation prior to its storing. It is also possible, in various cases, to add the HCFC stabilized with particular ethylenically unsaturated additives to the polyol-based formulation prior to its storing and then to add nitromethane, nitroethane or 1-nitropropane before starting the foaming. The ethylenically unsaturated additives do not exert any stabilizing action during the foaming, as will be shown in comparative example No. 9. Among the ethylenically unsaturated additives suited to stabilize several of the above-defined HCFC, in particular HCFC 123 and HCFC 141b, during the polyol storing, a first class which is an object of the present invention, consists of straight or branched polyalkenes containing at least a pair of conjugated ethylenic double bonds, having 4 to 8 carbon atoms in the straight part of the chain and optionally containing one or more substituent groups -OCH₃. Other stabilizers, which are suitable for inhibiting the abovesaid reaction of several HCFC with the polyols during the formulation storing, are arylalkenes usually containing from 2 to 9 aliphatic carbon atoms and from 1 to 3 aromatic groups; said arylalkenes have at least an ethylenic double bond conjugated with one of the aromatic nuclei and optionally contain one or more -OCH₃ substituent groups on the aliphatic carbon atoms and/or in the aromatic groups; the aromatic groups are generally selected from the class consisting of phenyl, diphenyl, p-oxyphenyl phenyl and naphthyl. Examples of suitable polyalkenes are: allocymene CH₃-CH =C(CH₃)-CH=CH-CH=C(CH₃)₂ 2,5-dimethyl-hexadiene 2,4, 1-methoxy-1,3-butadiene, butadiene and isoprene. Examples of suitable arylalkenes are: the dimer of alpna-methylstyrene (a mixture of isomers 2,4-diphenyl-4-methyl-1-pentene and 2,4-diphenyl-4-methyl-2-pentene, the former being decidedly prevailing), anethol, m-diisopropenylbenzene, 1,3,5-triisopropenylbenzene. The polyalkene Or arylalkene amount, expressed with respect to the hydrochlorofluorocarbon, generally ranges from 0.1 to 2.5% by weight and, preferably, from 0.5 to 1.5%. The following examples are given for illustrative purposes and cannot be considered as a limitation of the scope of the present invention. EXAMPLES 1-3 The polyol-based formulation was VORANOL XZ 00 88 011 produced by Dow Chemical, having a hydroxyl number of 400 and a water content equal to 2.4 parts for 100 parts of polyol. The HCFC was a mixture containing 88% by weight of 123 and 12% of 123a. The stabilizer and its amount are indicated in Table 1. The polyisocyanate was TEDIMONT 31 produced by Enichem, having a number of isocyanate groups equal to 31% by weight and a mean functionality equal to 2.7. The foaming was effected in a cylindrical card board vessel having a diameter of 15 cm and a height of 30 cm. 50 g of polyol formulation were mixed with 18 g of HCFC 123+ 123a until obtainment of a homogeneous solution. 80 g of polyisocyanate were then added in a few seconds and the mixture was poured into the vessel. During the forming of the foam, a maximum temperature ranging from 140 to 150°C, depending on the tests, was reached. On conclusion of the foaming, the whole was allowed to stand for 24 hours. The foamy mass was then destroyed in a previously degassed vessel and the evolved gases were analyzed by means of gas chromatography. The CFC 1113/HCFC 123+123a ratio and the CFC 1112a/HCFC 123+123a ratio were determined; they are reported in Table 1. Test No. Stabilizer % by wg. on HCFC 123+123a CFC 1113 ppm on HCFC 123+123a CFC 1112a ppm on HCFC 123+123a 1 0 6300 514 2 CH₃NO₂ 0.5 73 27 3 CH₃NO₂ 1 21 15 3 bis C₂H₅NO₂ 1 2050 161 EXAMPLES 4-6 In these examples, the HCFC was composed of a mixture of 95.5% by weight of 123 and 4.5% of 123a. It was operated in like manner as in examples 1-3. The obtained results are reported in Table 2. Test NO. Stabilizer % by wg. on HCFC 123+123a CFC 1113 ppm on HCFC 123+123a CFC 1112a ppm on HCFC 123+123a 4 0 3,257 800 5 CH₃NO₂ 0.6 36 19 6 CH₃NO₂ 1 25 21 EXAMPLES 7-9 In these examples, the HCFC was 123 free from 123a. It was operated in like manner as in examples 1- 3. Test No. 9 was carried out, as a comparative example, with an olefinic stabilizer i.e. alpha-methylstyrene. The obtained results are reported in Table 3. Test No. Stabilizer % by wg. on HCFC 123 CFC 1113 ppm on HCFC 123 CFC 1112a ppm on HCFC 123 7 0 0 1,065 8 CH₃NO₂ 1 0 22 9 α-methylstyrene 1 0 1,010 EXAMPLES 10-12 The polyol-based formulation contained polyols-polyethers with a hydroxyl number ranging from 400 to 500 and had a water content equal to 2.5 parts for 100 parts of polyols-polyethers. The HCFC was a mixture containing 95.5% by weight of 123 and 4.5%, of 123a. The polyisocyanate was the same as in examples 1-3. It was operated in like manner as in examples 1 to 3, introducing 50 g of polyol-based formulation, 16.5 g of HCFC 123-123a and 73.5 g of polyisocyanate. The obtained results are reported in Table 4. Test No. Stabilizer % by weight on HCFC 123+123a CFC 1113 ppm on HCFC 123+123a CFC 1112a ppm on HCFC 123+123a 10 0 77 0 11 CH₃NO₂ 0.3 29 0 12 CH₃NO₂ 1 24 0 12 bis C₂H₅NO₂ 1.5 39 0 12 ter C₃H₇NO₂ 2.5 32 0 EXAMPLES 13-14 It was operated in like manner as in examples 10-12, but instead of effecting the foaming in a not externally heated vessel, it was effected in the same vessel used in examples 1-3, placed in an oven thermoregulated at 140°C. On conclusion of the reaction, after about 30 minutes, the foamy material was taken out from the oven and was allowed to stand for 24 hours. The obtained results are reported in Table 5. Test No. Stabilizer % by wg. on HCFC 123+123a CFC 1113 ppm on HCFC 123+123a CFC 1112a ppm on HCFC 123+123a 13 0 778 123 14 CH₃NO₂ 1 35 24 EXAMPLES 15-26 These examples refer to an accelerated storing test of a polyether-polyol-based formulation for the preparation of polyurethanes, containing HCFC 123, in the presence or absence of various stabilizers. The formulation used in an amount of 25 g, was the composition BVH-D040116 produced by Bayer, containing a polyether-polyol with a hydroxyl number of 490 and a little amount of water and of an organometallic catalyst. The stabilizer was used in an amount of 0.4% by weight referred to HCFC 123. The test was conducted at 50°C for 21 days. The amounts of the various agents are indicated in Table 6. The stabilization effectiveness was evaluated by measuring, on conclusion of the test, the number of ppm of toxic impurity HCFC 133a with respect to HCFC 123 by means of gas chromatography. Tests 15-18, conducted under identical conditions, show the efficacy of two stabilizers conforming to the invention (tests 16 and 17) and the negligible stabilizing effect of an ethylenically unsaturated substance not conforming to the present invention (test 18). in tests 19-21 an aminic catalyst (triethylamine) was present, which ennanced the tendency to degradation. In tests 22-24 a previously degreased sheet-iron was present, which exhibited a surface of 0.22 cm² per cm³ of mixture. In tests 25-26 the triethylamine and the sheet-iron were contemporaneously present. The test without stabilizer was not carried out, but it is evident that it would have given worse results than the ones of test 22. EXAMPLES 27-29 In tests 27-29 the influence of increasing nitroethane amounts is illustrated. The formulation (25 g) was the same as in examples 15-26. The amounts of the various agents and the obtained results are reported in Table 7. The HCFC 133a amounts were determined by gas chromatography. No test without stabilizer was carried out, but it is evident that it would have given worse results than the ones of test 22 of Table 6. EXAMPLES 30-33 These tests were conducted at high temperature (120°C) for a time of 24 hours. Instead of using a formulation based on polyols for polyurethanes, the diglyme CH₃- (OCH₂-CH₂)₂ - OCH₃ was used as an organic substance containing reactive hydrogen atoms. The HCFC 133a amount, determined on conclusion of the tests by means of NMR, is indicated in ppm referred to HCFC 123. The complete data of the tests are reported in Table 8 along with the results. In tests 30-31, iron filings was added; in tests 32-33, a catalyst for the formation reaction of polyurethanes (consisting of dibutyltin dilaurate) was added. EXAMPLES 34-42 It was operated in like manner as in examples 15-26, utilizing the Bayer composition BVH-D040116, but using HCFC 141b instead of HCFC 123, in an amount of 34.56 parts by weight for 100 parts of polyol. Furthermore, the tests were conducted for longer stretches of time of 31, 53 and 85 days, respectively. The utilized stabilizers were nitromethane and nitroethane. The stabilizer amounts and the obtained results are reported in Table 9. From an examination of the Table it can be noticed that the two stabilizers inhibit the degradation of HCFC 141b to HCFC 151a, which is toxic. TEST NO. AGEING TIME (days) STABILIZER % by weight on HCFC 141 b HCFC 151a: ppm by weight on HCFC 141b 34 31 0 145 35 31 CH₃NO₂ O.409 13 36 31 C₂H₅NO₂O.409 20 37 53 0 169 38 53 CH₃NO₂ O.319 23 39 53 C₂H₅NO₂ O.409 32 40 85 0 207 41 85 CH₃NO₂ O,319 46 42 85 C₂H₅NO₂ O,409 64 EXAMPLES 43-46 It was operated in like manner as in examples 15-26, utilizing the Bayer composition BVH-D040116, using 35 parts by weight of HCFC 123 for 100 parts of polyol. The utilized stabilizers, their amounts, the duration of the test and the obtained results are reported in Table 10. TEST NO. DURATION OF AGEING (days) STABILIZER % by weight on HCFC 123 HCFC 133a: ppm by weight on HCFC 123 43 40 0 1790 44 40 CH₃NO₂ 1.05 50 45 40 C₂H₅NO₂ 1.28 60 46 40 C₃H₇NO₂ 1.46 90

Claims: Use of nitromethane, nitroethane or 1-nitropropane as a stabilizer for inhibiting the degradation of hydrochlorofluorocarbons by dehydrohalogenation during the formation of foamed polyurethanes or polyisocyanurates obtained from polyols and polyisocyanates, when said hydrochlorofluorocarbons are used as foaming agents during said formation, said hydrochlorofluorocarbons having two carbon atoms, on the first of which there is a chlorine or fluorine atom and on the second there is a hydrogen atom, while the other atoms present on the two carbon atoms are indifferently H, Cl or F, the total number of F atoms present in the molecule being not higher than 4, and having a boiling temperature ranging from -15°C to 70°C, A use of claim 1, wherein the added nitromethane amount ranges from 0.3 to 4 % by weight calculated on the hydrochlorofluorocarbon. A use of claim 1, wherein the added amount of nitroethane or 1-nitropropane ranges from 0.5 to 5 % by weight referred to the hydrochlorofluorocarbon. A use of claim 1, wherein the added nitromethane amount ranges from 0.5 to 1 % by weight calculated on the hydrochlorofluorocarbon. A use of claim 1, wherein nitroethane is added in an amount of 1 to 2 % or 1-nitropropane is added in an amount of 1 to 3 % by weight referred to the hydrochlorofluorocarbon. A use of one or more of the preceding claims, wherein the hydrochlorofluorocarbon is selected from the group consisting of HCFC 123, 141b, 123a, 141a and mixtures of 123 and 123a and of 141b and 141a. A use of one or more of the preceding claims, wherein the hydrochlorofluorocarbon and the stabilizing agent are mixed with the polyol-based formulation and the polyisocyanate before starting the foaming. A use of one or more of claims 1 to 6, wherein the hydrochlorofluorocarbon containing the stabiling agent is mixed with the polyol-based formulation or with the polyisocyanate before starting the foaming. A use of one or more of claims 1 to 6, wherein the hydrochlorofluorocarbon and the nitromethane, nitroethane or 1-nitropropane are added to the polyol-containing formulation prior to the storing thereof. A use of one or more of claims 1 to 6, wherein 1°) to the polyol-containing formulation there are added, prior to the storing thereof, the nydrochlorofluorocarbon and a stabilizer capable of inhibiting the reaction between the hydrochlorofluorocarbon and the formulation components during the abovesaid storing, said stabilizer being selected from one of the following classes: a) straight or branched polyalkenes containing at least a couple of conjugated ethylenic double bonds, having, in the straight part of the chain, 4 to 8 carbon atoms and optionally containing one or more -OCH₃ substituent groups, b) arylalkenes containing 2 to 9 aliphatic carbon atoms and 1 to 3 aromatic groups and having at least an ethylenic double bond conjugated with one of the aromatic nuclei and optionally containing one or more -OCH₃ substituent groups on the aliphatic carbon atoms and/or in the aromatic groups. 2°) before starting the reaction of formation of the foamed polyurethane or Polyisocyanurate, the stabilizing substance according to claim 1 is added to the reaction medium.

Inventors: BASILE GIAMPIERO, GIROLOMONI SAURO, MUSSO EZIO, TONELLI CLAUDIO, BASILE, GIAMPIERO, GIROLOMONI, SAURO, MUSSO, EZIO, TONELLI, CLAUDIO
Applicants: AUSIMONT SPA, AUSIMONT S.P.A.
Application year: 1992
Main classification: C08J9
IPC codes: C07C17, C08G101, C08G18, C08K5, C07C19, C08L75, C08J3, C08J9