‘United States Patent [19] [111 3,907,780 Hughes [45] Sept. 23, 1975

[54] PREPARATION OF 3,502,722 3/1970 Newmann..... 260/453 X CARBODIIMIDE_CONTAINING 3,761,502 9/1973 Man et al ...... 260/453 ISOCYANATES [75] lnventor: Jeffrey Hughes, Manchester, Primary Exami'f‘er_Lewls Gotts England Asszstant Exammer-Dolph H. Torrence Attorney, Agent, or Firm—Cushman, Darby & [73] Assignee: Imperial Chemical Industries Cushman Limited, London, England [ 22 1 F1‘e d: Jan .2, 1974 [57] ABSTRACT [21] Appl. No.: 429,807 A process for converting at least a proportion of the - _ _ 0 _ _ isocyanate groups in an organic isocyanate into carbo [30] Forelgn Apphcat‘on Prlonty Data diimide groups by heating the organic isocyanate with Jan. 15, 1973 United Kingdom ...... 2035/73 an organic phosphorus containing catalyst for the car bodiimide-forming reaction and an active hydrogen [52] U-S- Cl ------260/239 A; 260/25 AT; containing compound as co-catalyst. Further reaction 260/77-5AT; 260/453 AR; 260/453 P of the carbodiimide groups with isocyanate groups re [5l] Int. Cl.2 ...... C07C 119/055; C0713 229/00 sults in the formation of uretonimines. The products [581 Field of Search ----- .- 260/453 P, 453 AR, 239 A of the process are useful in the manufacture of poly urethanes. [56] References Cited UNITED STATES PATENTS 10 Claims, N0 Drawings 3,056,835 10/1962 Monagle et al...... 260/551 3,907,780 1 2 PREPARATION OF CARBODIIMIDE-CONTAINING tion between carbodiimide groups and isocyanate ISOCYANATES groups takes place with formation of uretonimine groups. In order to permit this reaction to proceed to This invention relates to isocyanates and the manu near completion it is normally necessary to allow the facture of carbodiimides therefrom. reaction mixture to stand for a time after heating to It is known to convert isocyanates to carbodiimides form carbodiimide, for the uretonimine forming reac by heating and in particular it is known to carry out the tion to take place. Conversion to uretonimine may not reaction in the presence of phosphorus containing cata normally go‘to absolute completion and there some lysts such as organic and . times remains in the composition a small amount of We have now found that the efficiency of such cata carbodiimide which is not converted to uretonimine lysts may be improved by the incorporation of active despite the presence of excess isocyanate. This may be hydrogen containing compounds as co-catalyst. in the form of carbodiimide dimer. Thus according to the present invention there is pro Thus the present process may be used for the intro vided a process for converting at least a proportion of duction of a number of carbodiimide groups into a the isocyanate groups in an organic isocyanate into car polyisocyanate composition and the product allowed'to bodiimide groups by heating the organic isocyanate stand to convert at least a proportion of such groups to with an organic phosphorus containing catalyst for the uretonimine groups by further reaction. The ?nal prod carbodiimide-forming reaction and an active hydrogen ucts containing a proportion of uretonimine groups are containing compound as co-catalyst. useful as polyisocyanate compositions for the manufac Any organic isocyanate may be used in the present 20 ture of polyurethane foams having a valuable range of process which is particularly applicable to organic iso properties, by processes as described in our cope‘nding‘ cyanates containing two or more isocyanate groups, i.e. British Application No. 27442/71, wherein the prepa polyisocyanates. As examples of organic isocyanates ration and use of uretonimine group-containing tolyl which may be used there may be mentioned tolylene ene diisocyanate compositions is described. ' diisocyanates including the well-known commercially 25 In carrying out the process of the present invention available mixtures of the 2,4- and 2,6»isomers thereof, the amount of phosphorus containing catalyst used is a diphenylmethane diisocyanates and the polyisocyanate catalytic quantity and although this may vary widely we compositions, often described as crude diphenylmeth~ prefer to use from 0.1 % to 10% by weight of the isocy ane diisocyanates obtained by phosgenating a crude anate. mixture of polyamines produced by condensation of In respect of the co-catalyst, it will be realized that aniline and formaldehyde in the presence of acid cata use of an excess of active hydrogen~containing com lysts, and comprising diphenylmethane diisocyanate in pound will only result in loss of isocyanate groups‘and admixture with higher methylene bridged polyphenyl we therefore prefer to use from 0.05% to 5% especially polyisocyanates of higher isocyanate functionality. 0.05% to 1% of co-catalyst‘by weight of the isocyanate. Mixtures of polyisocyanates for example tolylene diiso 35 Although formation of carbodiimide groups may take cyanate and diphenylmethane diisocyanate may also be place with certain of the phosphorus containing cata used. The invention is not con?ned to pure distilled iso lysts at room temperature it is preferred that the mix cyanates but may also be used with crude non-distilled ture of isocyanate and catalyst be heated'atja tempera isocyanates such as crude products of the phosgenation ‘ ture of from 40°C to 220°C preferably 120°C to'200°C of tolylene diamines or residues obtained therefrom 40 in order that the reaction proceeds a reasonable rate. after distillation or some or all of the diisocyanate. The degree of heating or the length of reaction time re Refined, i.e. distilled or crystallized diphenylmethane quired will depend on the degree of conversion to car diisocyanates are solids and the invention is particu bodiimide which is required. The reaction conditions larly applicable to such isocyanates, as conversion of a will vary with different catalysts but can easily be deter proportion of the isocyanate groups in such isocyanates 45 mined experimentally. to carbodiimides gives liqui?ed compositions of the Organic phosphorus-containing catalysts which may said isocyanates. be used in the process of the invention include organic Although the process of the present invention may be phosphates or , phosphoramides, phos used for conversion of isocyanates to carbodiimides it phonamides and triarylamidophosphates. has been found particularly useful for the conversion of Representative examples of catalysts include triethyl a proportion only of the isocyanate groups into carbo , tributyl phosphate, trimethyl phosphate, tri diimide groups and in this aspect is particularly useful phenyl phosphate, triallyl phosphate, bis(,B-chloroe for producing isocyanates containing a proportion of thyl)vinyl , hexamethyl , uretonimine groups, say from 3% to 10% by weight, as N,N,N',N'-tetradodecyl dodecylphosphonamide and described in respect of tolylene diisocyanates in our co 55 triphenyl amido phosphate. pending British Application No. 27442/71. The trialkyl phosphate and phosphoramide type cata Uretonimine groups are produced by reacting an iso lysts are preferred as they enable a better control of the cyanate group with a carbodiimide group and may be reaction. The trialkyl phosphate type catalysts are rela easily introduced into an isocyanate composition by 60 tively inactive on standing at room temperature for converting some of the isocyanate groups to carbodiim long periods of time. The phosphoramide type catalysts ide groups by a reaction in which two isocyanate may be rendered inactive by complex formation with groups react to form a carbodiimide group for example an equivalent amount of chloroform or similar coupling by the process of the present invention and then allow agent. Although more vigorous catalysts are known and .ing the carbodiimide groups to react with a further por may be used e.g. phospholene oxides, phosphetane ox tion of the isocyanate to form uretonimine groups. ides, these tend to produce polymeric carbodiimides Once carbodiimide groups have been introduced into and are very active at room temperatures'and hence re for example, a tolylene diisocyanate composition, reac quire removal if a stable product is to be obtained. 3,907,780 3 4 Although a solvent may be used, this is not normally ditions and the similar‘degree of conversion obtained found to be necessary if the isocyanate is liquid. using a co-catalyst and a shorter heating cycle. Any active hydrogen-containing compound may be Examples 1, 3, 5 and 7 are for purposes of compari used as co-catalyst the only criterion being that the son. compound should contain at least one hydrogen atom 5 EXAMPLES 8 - 1'0 : capable of taking part in the Zerewitinoff reaction. We have found that water is a preferred co-catalyst 4,4’-diisocyanatodiphenylmethane (containing and is operative even in small amounts of the order of traces of the 2,4’-isomer) was heated at 175°C for 4 hours under an atmosphere of ‘nitrogen with the cata 0.05 % to 1 %. Water introduced into the reaction mix~ lysts shown in Table 2. After cooling rapidly to below ture may react to form ureas and biurets and such com pounds which themselves contain active hydrogen 60°C, the isocyanate content was determined by react ing a weighed amount of the sample with a standard so atoms act as co-catalysts. ' Other active hydrogen containing compounds which lution of di-n-butylamine, then back-titrating with acid may be used include aromatic or aliphatic amines such to determine the excess amine. as aniline and diethylamine, phenols, alcohols, carbox The additional activity of the co-catalyst system is ylic acids, mercaptans, acetoacetonates, malononi clearly shown by the increased conversion to carbodi triles, B-diketones or other groups having active hydro imide groups as measured by the fall in isocyanate gen atoms by virtue of being adjacent to electron with group content. drawing groups. Infra red spectroscopy showed the presence of sub Carbodiimides made by the process of the present in 20 stantial quantities of carbodiimide and uretonimine vention may be used in the manufacture of polymers groups in the product from Example 10. and ‘partial carbodiimide conversion products may be Table 2 further converted to uretonimine containing isocyanate compositions useful in the manufacture of polyure Example Catalyst used —-NCO group thanes. 25 No. content '7: w/w The invention is illustrated but not limited by the fol 8 0.1% water 33.4 lowing-examples in which all parts are by weight except 9 l7: 32.18 where otherwise stated. 10 l‘7( Hexamethylphosphoramide + 30.6 0.1‘7z water EXAMPLES l-7 30 Note: Diisocyunutodiphenylmethane has an —NCO group content of 33.67: w/w Tolylene diisocyanate (80:20 mixture of the 2,4- and 2,6-isomers) was heated under an atmosphere of nitro We claim: genwith the catalyst hexamethylene phosphoramide 1. A process for converting isocyanate groups in an and the respective cocatalysts as indicated in the fol organic isocyanate selected from the group consisting lowingtable. After completion of the heating period 35 of tolylene diisocyanates, diphenylmethane diisocya the reaction mixture was cooled to below 60°C and the nates and polyisocyanate compositions comprising di catalyst deactivated by the addition of an equivalent phenylmethane diisocyanate in admixture with higher 7 amount of chloroform. ' methylene bridged polyphenyl polyisocyanates of The reaction mixture was then allowed to stand to higher isocyanate functionality, into carbodiimide permit '~ conversion of the carbodiimide groups to 40 groups by heating the organic isocyanate with an or uretonimine groups by reaction with further isocyanate ganic phosphorus containing catalyst for the carbodii groups, the degree of conversion to carbodiimide mide-forming reaction, selected from the group con groups was then measured by measuring the uretoni sisting of organic phosphates or phosphonates, phos mine content by infra-red spectrometry. phoramides, phosphonamides and triarylamidophos Table 1

Example Catalyst System Reaction NCO Uretonimine Carbodiimide Biuret No. Conditions Value Groups (%) Groups (‘71) Groups (‘7() (‘76)

l i 1 ‘7r hexamethyl . 4 hrs. at 175°C 40.4 3.0 phosphoramide 2 l ‘71 hexamethyl 2 hrs at l75°C 39.6 2.7 phosphoramide + 0.l ‘7: Water 3 0.l r/1 Water 4 hrs. at 175°C 46.5 0.6 4 l ‘7: hexamethyl 4 hrs. at l75°C 34.8 5.6 1.0 phosphoramide + 0.5 ‘72 tolylene , diisocyanate urea 5 j000042‘7r tolylene 4 hrs. at 175°C 43.2 0.7 diisocyanate urea 6 l ‘7: hexamethyl 3 hrs. at 175°C 22.1 8.4 6.4 phosphoramide + l ‘7: aniline 7 1 ‘7r aniline 3 hrs. at l75°C 43.6 0.25 L2

The activity of the co-catalyst systems is illustrated phates, and an active hydrogen containing compound by the uncreased conversion to carbodiimide groups 65 as co-catalyst, selected from the group consisting of when using a co-catalyst under the same reaction con water and aniline. ‘~ . ~ 3,907,780 5 6 2. A process as claimed in claim 1 wherein the or amount of co-catalyst used is from 0.05% to 5% by ganic isocyanate is a tolylene diisocyanate. weight of the isocyanate. 3. A process as claimed in claim 1 wherein the or 7. A process as claimed in claim 6 wherein the ganic isocyanate is a re?ned diphenylmethane diisocya amount of co~catalyst is from 0.05% to 1% by weight nater of the isocyanate. 4. A process as claimed in claim 1 wherein the carbo‘ 8. A process as claimed in claim 1 wherein heating is diimide groups are allowed to react further to convert carried out at a temperature of from 40°C to 220°C. at least a proportion of such groups to urctonimine 9. A process as claimed in claim 1 wherein the cata» groups and the ?nal product contains from 3% to 10% lyst is a phosphoramide. by weight of uretonimine groups. 10. A process as claimed in claim 9 wherein the phos 5. A process as claimed in claim 1 wherein the phoramide catalyst is rendered inactive after the con amount of phosphorus containing catalyst is from 0.1% version, by complex formation with an equivalent to 10% by weight of the isocyanate. amount of chloroform. 6. A process as claimed in claim 1 wherein the * * * * =l< 15

20

25

30

35

40

45

55

60

65