Summary Adsorbed on kaolinite, aromatic amines are readily condensed with formaldehyde to give the corresponding diaminodiphenylmethanes. The methodology is novel in its simplicity, selectivity and ecofriendly nature. Introduction Diaminodiphenylmethanes find use in a variety of applications including curing agents and chain extenders in polymers.1 The conventional preparation is cumbersome involving specific use of mineral acids and alkalis at various stages.Polymerization is unavoidable resulting in poor selectivity. 2 Heterogeneous catalysis on clays under solvent conditions with ultrasound irradiation and also in dry media under microwave conditions have been extensively studied compared to catalysis over clays in aqueous media.3–14 Here we report the synthesis of 4,4A-diaminodiphenylmethanes employing natural kaolinite as catalyst in aqueous media for the first time.It is known that kaolinites intercalate with molecules as polar as water, formamide, N,N-dimethylformamide, dimethyl sulfoxide and dimethylselenoxide within their layers.15 Nevertheless, the catalytic activity of kaolinitic clays have been seldom exploited contrary to their smectite counterparts.Commercial catalysts like K10, KSF, Filtrol, etc. are derived from the latter variety. Results and discussion The experimental procedure involves the following steps: (a) mixing of catalyst and water; (b) addition of amine to the agitated slurry, and (c) dropwise addition of formaldehyde to the catalyst–water–amine mixture and continuing stirring for the completion of the reaction.Work-up involves simple filtration followed by dissolution of the product in hot alcohol from which it is recrystallised. The method employed is simple, efficient, reproducible and avoids the use of hydrocarbons, acid, alkali etc. unlike the conventional procedure.2 It is noteworthy that no conversion takes place when the reaction is performed on commercial silica or alumina (chromatographic grade).Moreover, the catalyst employed is regenerable by washing with hot acetone. The catalytic performance studied up to 5 cycles of the same reaction is found to be steady. Results are presented in Table 1. The condensation of aniline with formaldehyde is typical for the general procedure. In a typical experiment, the catalyst (1 g) was stirred with 200 ml of water.Aniline (9.3 g, 0.1 mol) was added to this solution under stirring. To this formaldehyde solution (37%, 4.5 ml, An easy synthesis of 4,4A-diaminodiphenylmethanes on natural kaolinites Damodaran Bahulayan, Rugmini Sukumar, Kuzhunellil Raghavanpillai Sabu and Malathy Lalithambika* Regional Research Laboratory [CSIR], Thiruvananthapuram - 695 019, India.E-mail:lali@csrrltrd.ren.nic.in Received 29th July 1999 0.05 mol) was added slowly and stirring was continued. The precipitated 4,4A-diaminodiphenylmethane was extracted into hot alcohol from which it is recrystallised: mp 98 °C [lit, mp 96–98 °C].2 Conclusion To summarise, we have developed an efficient method of synthesis of 4,4A-diaminodiphenylmethane catalyzed by an ecofriendly catalyst, kaolinitic clay, which is abundantly available.The conversion is significantly high with product selectivity in the range 68–98%. Besides, the operational ease makes the process attractive and cost effective. Acknowledgements We thank Dr Vijay Nair, Director, RRL, Trivandrum, for his wholehearted cooperation during the progress of this work. Fellowships to D. B. and K.R. S. by the CSIR, Government of India is also acknowledged. Green Chemistry August 1999 191 C G The polymer industry requires large quantities of 4,4A- diaminodiphenylmethanes. These compounds find use in various applications as polymer additives. Current synthetic methods involve the condensation of anilines with formaldehyde under acidic conditions. As is common for such reactions, a substantial amount of waste acid needs to be neutralised, generating substantial aqueous salt waste which is likely to be contaminated with residual anilines and/or formaldehyde, both compounds of considerable toxicity.While a completely green solution to this problem might involve the replacement of this chemistry with an inherently less toxic combination of reagents, the replacement of the current homogeneous catalysts with a heterogeneous catalyst might ease the problems of a waste aqueous phase.Such a catalyst switch might improve the situation by allowing the easy separation of catalyst from product, without the need for neutralisation. Thus, the aqueous waste stream can be avoided, and the catalyst can be recovered. This article demonstrates a feasible process for this chemistry, using a readily available and reusable clay catalyst.Yields of a range of diamines are excellent, and the method avoids the use of problematic solvents. DJM Green ContextNotes and references The catalyst used is natural kaolinitic clay. SiO2 = 47.05%, Al2O3 = 36.98%, Fe2O3 = 0.34%, TiO2 = 0.34%, Na2O = 0.12%, K2O = 0.08%, Loss on ignition = 14.34%, BET surface area = 13.0 m2 g21, Hammett acidity function, Ho = 23.0 (0.03 mmol g21).The 4,4 A-diaminodiphenylmethanes obtained were characterized on the basis of 1H NMR (300 MHz), HPLC, GC-MS and elemental analysis. Selected data for 4,4A-diaminodiphenymethane: Anal. Calc. for C13H14N2+C 78.78, H 7.07, N 14.14%. Found: C 78.64, H 7.11, N 14.08%. 1H NMR (CDCl3, 300 MHz): d 3.4 (s, 2H, –CH2–), 3.7 (s, 4H, 2NH2), 6.4–6.8 (m, 8H, Ar).HPLC: CLC-NH2 (M) column, 1 ml min–1 CH3CN, Rt 3.07 min. GCMS +OV-101, m/z 298 (M·+). 1 Reaction Polymers, ed. W. F. Gum, W. Riese and H. Ulrich, Hanser, New York, Oxford University Press, 1992. 2 J. T. Scanlan, J. Am. Chem. Soc., 1935, 57, 890. 3 B. K. G. Theng, The Chemistry of Clay-Organic Reactions, Adam Hilger, London, 1974, p. 261. 4 W. G. Duben, J. M. Cogan and V. Behar, Tetrahedron Lett., 1990, 31, 3241. 5 D. Villemin, M. Hammadi and B. Martin, Synth. Commun., 1996, 26, 2895. 6 M. Hammadi and D. Villemin, Synth Commun., 1996, 26, 2901. 7 S. Chalais, P. Laszlo and S. Mathey, Tetrahedron Lett., 1986, 27, 2627. 8 P. G. Gassman and D. A. Singleton, J. Am. Chem. Soc., 1984, 106, 7993. 9 R.S. Verma and R. Dahia, Tetrahedron Lett., 1997, 38, 2043. 192 Green Chemistry August 1999 Table 1 Condensation of aromatic amines with formaldehyde, formation of 4,4A-diaminodiphenylmethanes Entry Amine Product Reaction time/min Isolated yield (%) 1 60 96 2 60 99 3 60 68 4 60 98 5 30 100 6 60 79 7 60 97 8 60 78 9 60 71 aAmine+formaldehyde = 2+1, ambient temperature.10 R. S.Verma, Green Chemistry, 1999, 1, 43. 11 K. R. Sabu, R. Sukumar and M. Lalithambika, Bull. Chem. Soc. Jpn., 1993, 66, 3535. 12 M. Lalithambika, Rugmini Sukumar, D. Bahulayan and K. R. Sabu, Bull. Catal. Soc. India , 1999, 9, 156. 13 A. Cornelis and P. Laszlo, Synthesis, 1985, 909. 14 D. Ponde, H. B. Borate, A. Sudalai, T. Ravindranathan and V. H. Deshpande, Tetrahedron Lett., 1996, 37, 4605. 15 C. Collet, A. Delville and P. Laszlo, Angew. Chem., Ind. Ed. Engl., 1990, 29, 535. Paper 9/06165G Green Chemistry August 1999 19310 R. S. Verma, Green Chemistry, 1999, 1, 43. 11 K. R. Sabu, R. Sukumar and M. Lalithambika, Bull. Chem. Soc. Jpn., 1993, 66, 3535. 12 M. Lalithambika, Rugmini Sukumar, D. Bahulayan and K. R. Sabu, Bull. Catal. Soc. India , 1999, 9, 156. 13 A. Cornelis and P. Laszlo, Synthesis, 1985, 909. 14 D. Ponde, H. B. Borate, A. Sudalai, T. Ravindranathan and V. H. Deshpande, Tetrahedron Lett., 1996, 37, 4605. 15 C. Collet, A. Delville and P. Laszlo, Angew. Chem., Ind. Ed. Engl., 1990, 29, 535. Paper 9/06165G Green Chemistry August 1999 193