Gopalakrishnan, Janarthanan

Rao, M N Sudheendra

Srinivas, Janaswamy

Srinivasamurthy, G

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Indian Journal of ChemistryVol. 36B, January 1997, pp. 47-49X-ray structural characterization of dicyclohexylammonium chloride and itsconversion to bromo-, iodo- and hexafluorophosphate derivativesJanarthanan Gopalakrishnan", Janaswamy Srinivas'', G Srinivasarnurthy" & M N Sudheendra Rae"a Department of Chemistry, "Department of Physics,Indian Institute of TechnoJogy, Madras 600 036, IndiaReceived 13 May 1996; revised and accepted 22 August 1996Single crystal X-ray structural determination of dicyclohexylammonium chloride, prepared easily inquantitative yield by a modified procedure, reveals it to be strongly and intermolecularly hydrogenbonded. While its bromide derivative is readily obtained in nearly quantitative yield, the iodide andhexafluorophosphate salts are formed slowly ia moderate yields.Amine hydrochlorides, in general, are high melt-ing solids I and find use in synthesis? as source ofcorresponding amines especially if the amine con-sidered is either volatile or highly reactive. Relat-ively very less is reported on the structure andreactivity of these.' unlike amines. A detailedstructural information of amine hydrochlorideshave also been considered important for studieson hydrogen bonding. Very few single crystalX-ray structural data on them are available in li-terature=". It is likely that their high hygroscopicnature and consequent difficulty in handling havecontributed to this scenario.We report herein (i) a modified procedure suit-able for large scale synthesis of dicyclohexylam-monium chloride (DCAHCI) which is highlystable towards air and moisture, (ii) its single crys-tal X-ray structure, and (iii) its reaction with pota-ssium salts, K [X = Br, I, PF61.Experimental SectionReagents, Instrumentation and General Proce-dures. Dicyclohexylamine (E. Merck), KBr (S.D.),Kl (S.D.), KPF6 (Aldrich) and cone. HCI (Ran-baxy) were used as received. CH30H, CHCl3 andC6H6 were freshly distilled and dried according toliterature procedures 5•Spectral facilities used for characterization havebeen described earlier". Xvray powder pattern wasrecorded using Cu K, radiation with Ni filter andGe monochromator on SRD 3000P SEIFERTdiffractometer.Synthesis of DCA.HCt. Slow addition of cone.HCI (3.5 g, 96 mmoles) to a stirred solution of di-cyclohexylamine (17.4 g, 96 mmoles) in C6H6 (50mL) at 20°C resulted in the formation ofDCAHCI as a white precipitate which waswashed with C6H6 (15 mL) and dried (quantitativeyield). Its IH NMR spectrum in CP30D gavemultiplets centred at b 1.31 (10H), 1.90 (10H)and 3.20 (2H). The corresponding values for thefree amine appear at b 1.13 (10H), 1.72 (10H)and 2.50 (2H).Reactions of DCA.HCt with KX [X = Br, I,PF6]. An equimolar reflux reaction (16 hr) ofDCA.HCI (1.0 g in each case) with powdered KX[X = Br, I, PF61 in CH30H (30 mL) led to the is-olation of the byproduct KCl as the precipitate(identified by X-ray powder pattern). The solidresidue obtained after removing CH30H from thefiltrate was quickly washed with water (2 x 20mL) to obtain DCAHX as colourless to pale yel-low crystalline solid.DCA.HBr (84% yield): IR: 2960(s), 2860(s),2780(s), 2520(s), 2420(s), 2360(w), 2160(w),2060(w), 1930(w), 1460(vs), 1440(s), 1380(s),1310(s), 1270(w), 1050(vs), 1030(vs), 960(m),920(m), 900(s), 869(m), 550(w), 480(s) and440(m) cm - I.DCA.HI (50% yield): IR: 2960(s), 2850(s),2740(m), 2530(s), 2430(s), 2365(m), 2165(w),2060(w), 1960(w), 1460(vs), 1440(s), 1380(s),1320(s), 1050(vs), 1040(vs), 975(s), 960(m),925(m), 900(w), 860(m), 560(m), 480(s) and450(m) em - I.DCA.HPF6 (50% yield, m.p. 250-53°C, dec.): IR:2940(s), 2860(s), 2800(s), 2760(m), 2530(s),2430(s), 2360(w), 1460(vs), 1440(m), 1390(s),1315(m), 1060(m), "1040(m), 970(w), 850(br, s),48 INDIAN J. CHEM. SEC B, JANUARY 1997560(vs), 470(m) and 440(w) cm-I; 31p NMR(CH30H soln, () in ppm): -145.9 (septet).X-ray analyses. Needle shaped crystals of[(C6Hll)2NH2]+Cl- were grown from a methanolsolution. The crystal data and experimental condi-tions are summarized in Table 1. The crystal wasglued at its sharpest point on to a glass fiber.Thecell constants were obtained from preliminaryphotographic examination and the extinctions ob-served are (oko), k= 2n + 1, (hol), /= 2n + 1,identified the space group at P2/C. All the datawere collected on an Enraf-Nonius CAD-4 dif-fractometer using MoKa radiation (A = 0.71069A) at room temperature. The cell constants andorientation matrix were determined by Least-squares refinement for 25 reflections in the range9 ~ 8 ~ 14. Totally, 2612 reflections were mea-sured using the w- 28 scan technique. The datawere collected for background, Lorentz and po-larization effects. 1908 reflections were observedwith 1~ 30(1) and 1713 unique reflections wereused for structure refinement. Absorption correc-tions were made using an in-built software of thediffractometer.The structure was solved by direct methods us-ing the programme package SHELXS-867. All thehydrogen atoms could be located from the differ-ence electron density maps during the refinement.All the non-hydrogen atoms were refined withanisotropic thermal parameters using the pro-Table I-Crystallographic parameters for' [(CI6HllhNHzJ+CIEmpirical formula C12Hz4CINFormula weight 217.77Crystal system MonoclinicSpace group P2/CUnit cell constantsa,Ab,Ac,Aa,degf3,degr,degVolume.t A}'ZDensity (calcd), mgm - JAbsorption coefficient, mm - IF(OOO)Crystal dimensions, mm"8" range scanned, deg.Index ranges5.3988(1\)11.7333 (11)20.0734 (2)9095.45 (3)901265.82 (3)41.1430.2694800.1 xO.12xO.322-250:-; h:-;6.\- 2:-; ks; 13,-23s I :-;2386.4,99.8minimax abs. corr, %gramme SHELXL-938. The quantity minimizedwas ~w(~ ~ ~ )2, where, w = 1/[2(~) = 0.040p2 + 0.2850 P], P= [~+ 2 ~]/3. The maximumand minimum electron densities in the final differ-ence map are 0.143 and - 0.149 respectively.The final residual factors are R1 = 0.0283 andwR2 = 0.0737. All the atomic scattering factorswere those incorporated in SHELXL-93.Results and DiscussionDicyclohexylamine reacts exothermically at am-bient conditions to produce dicyclohexylammoni-urn chlo ride in quantitative yield. It is thermallyquite stable (does not melt even up to 250°C) andis not attacked by air or moisture. High basic na-ture [PKa= 11.25; pKa of (C2H5hN = 10.729] of di-cylcohexylamine and steric protection of thechloide ion provided by the bulky dicyclohexy-lammonium ion could possibly be the reason forthis unusual stability observed unlike amine hy-drochlorides in general":The amino proton as well as the acidic protonare not detected in the IH NMR spectra (400MHz) of the amine and the salt recorded in deu-terated methanol. However, the methyne protonof the cyclohexyl group is substantially deshieldedby 0.7 () in the salt, as expected.Reactions of DCA.Hel. Amine hydrochlorideshave been used as a source of amines for conden-sation reactions 10. As the present X-ray structurerevealed highly stable nature of dicyclohexylam-monium ion, only chloride ion exchange reactionswere considered in this study. It was found thatDCA.HCl could be converted smoothly to thebromide, iodide and hexafluorophosphate salts byreflux reaction in methanol. The reactions are fa-voured by the formation of stable KCl lattice ineach case. KI and KPF6 are found to be compa-ratively less reactive. All these derivatives are airand thermally stable crystalline solids and are sol-uble in chloroform under hot conditions.The IH NMR spectral features were found tobe very similar for bromo, iodo and hexafluoro-phosphate derivatives.X-ray structure of DCA.HCI. The ORTEP plot!',packing diagram and important bond length, bondangle data for DCA.HCl are given in Figures 1, 2and Table II respectively. The main feature of thestructure is the significant intermolecular and un-symmetrical type of hydrogen bonding. Identicaland noticeably shorter than usual N-H distancesof the dicyclohexylammonium ion supports itshigh pK" value. The hydrogen b!:md distanceN-H ....Cl was observed to be 3.151 A which is ty-pical of those observed for amine hydrochlo-GOPALAKRISHNAN et al.: X-RAY STRUCTURAL CHARACTERIZATION OF DCA.HCI 49I~ellCIFig. I-ORTEP plot (50U;\, probability ellipsoids) and atomicnumbering scheme for l(C,HII),NH,j'CIFig. 2-Molecular packing of l(C,H" hNH,j' CI in the unitcell.rides!'. This distance is shorter by 0.151 Pi. whencompared to their Van der Waals' contact. Thebonds N-H ....C1 expected to he linear, is found tohe bent by 5° which may he due to the effect ofcyclohexyl groups that conform to chair confor-mation. The chloride ion bridging the two dicyc-lohexylammonium units is found to be equidistantfrom both the groups and makes an angle of120S which is a suhstantial deviation from theexpected near tetrahedral angle. This seems tohighlight the predominance of the steric bulk ofdicyc1ohexylammonium units over the lone paireffects of chloride ion. This has been further ex-emplified by enlarged angle at nitrogen defined bythe two cyclohexyl groups [< C1 NC7: 118S].Table II-Selected bond lengths (A) and bond angles (deg.)for [(ChH IIhNH2j I CIC(J)-N(J) 1.502(2) N(J)-H(2)C (7)-N (I) 1.505 (2) H (2)-CIN(I)-H(I) 0.891 (2) H(I)-CIH(I)-N(I)-H(2) 108.8(9) C(I)-N(I)-C(7)H(I)-N(I)-C(I) 107.2(8) N(I)-H(2)-CIH (I)-N (I )-C (7) 106.8 (9) N (I)-H (I)-CIH (2)-N (I )-C (I) 107.4 (9) H (I )-Cl-H (2)H (2)-N (I )-C (7) 107.9 (9)0.880 (2)2.27 (2)2.29 (2)118.5 (I)173.3 (15)174.8 (15)120.5 (9)ConclusionsHigh yield synthesis, air and moisture stahilityand different reaction possibilities of dicyclohexy-lammonium chloride offer it to be syntheticallyuseful as revealed by the derivatives with dcsir-ahle properties prepared in this study.AcknowledgementJG and JS thank lIT, Madras for financial sup-'0 port. RSIC and MSRC, lIT, Madras arc also ac-knowledged for spectral and XRD data.ReferencesI Morrison R T & Boyd R N. (),gtlllic Chemistry. 5th Edn(Prentice Hall of India, New Delhi). 1989.935.2 Greenwood N N & Earnshaw A. Chemistry of the ele-ments, 1st Edn (Pergamon Press. Great Britain), 1984.23H.3 Saul Patai, The Chemistry of the amino group, 2nd Edn(Interscience Publishers. New York). 1972.4 (a) Lindgren J & Olovsson I, Acta Crystallogr, Sect H24,1968,554.4 (b) Kertes A S, Gutmann H & Mayer I, J Appl Cryst, 4,1971. 93.5 Perrin D D, Armarego W L F & Perrin [) R, Purificationof laboratory chemicals, 2nd Edn (Pergamon PressvGreatBritain), 1980.6 Mohan T. Senthivel P & Sudheendra Rao M N. Indian JChern, 34A, 1995,961.7 Sheldrick G M, Acta Crystallogr, Sect M6, 1990,467.8 Sheldrick G M, Programme for the refinement of crystalstructure. Univ of Gottingen. Germany. 1993.9 Dean J A, Handbook of Organic Chemistry, 1st Edn(McGraw-Hili, New York), 1987.10 Chapman A C, Holmes W S, Paddock N L & Searle H T,J Chern Sac, 1961, 1825.II Johnson C K, ORTEP II, Report ORBNL-5138, OakRidge National Laboratory, Tannessee, USA, 1976.12 Lindgren J & Olovsson I, Acta Crystallogr. Sect H24.1968,549.

X-ray structural characterization of dicyclohexylammonium chloride and its conversion to bromo-, iodo- and hexafluorophosphate derivatives

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X-ray structural characterization of dicyclohexylammonium chloride and its conversion to bromo-, iodo- and hexafluorophosphate derivatives

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