1024 ¹ 2002 WILEY-VCH Verlag GmbH&Co. KGaA, Weinheim 1439-4235/02/03/12 $ 20.00+.50/0 CHEMPHYSCHEM 2002, 3, 1024 ± 1030

Cubic Mesophase in an Unsymmetrical AlkylAmmonium Salt. Synthesis and Structural ModelCorinne Soulie¬ ,*[a] Pierre Bassoul,[b] and FranÁois Tournilhac[a]

N,N,N-butylethylpentylpropylammonium iodide 4 and relatedmolecules have been selectively synthesised from commerciallyavailable aldehydes, amines and alkyl iodides using a reductivealkylation procedure. The crystalline texture of 4 obtained oncooling is optically isotropic between crossed polarisers, indicatinga cubic structure. Differential scanning calorimetry (DSC,�10 Kmin�1) reveals a glass phase transition at �59 �C and amelting point at 192 �C. The melting entropy (23.9 Jmol�1 K�1)indicates a first-order transition between a highly disorderedmesophase and the isotropic liquid. Powder X-ray diffraction

patterns were indexed in the cubic system (a� 14.08ä; Pm3n spacegroup). In this cell, the molecular packing with Z� 6 corresponds toa rather low compactness of 65%. Iodine and tetraalkylammoniumions occupy positions with a 4m2 site symmetry. These highlysymmetrical states may be generated by stepwise rotation of theammonium cation. The same structural model for orientationallydisordered crystal (ODIC) phases can be applied to a series oftetraalkylammonium bromides and iodides.

KEYWORDS:

cubic mesophases ¥ mesomorphism ¥ X-ray diffraction

Ammonium cations with a chiral side chain are used in molecularrecognition[1] and in phase-transfer catalysis.[2] The maximumcoupling between electrostatic interaction and chirality may beexpected when nitrogen atom itself is chiral. This paper isconcerned with the synthesis and the structure of the iodine saltformed by a new quaternary ammonium molecule containingfour different alkyl side chains: pentyl, butyl, propyl and ethyl(5432I, compound 4 of Scheme 1).

C4H9NH2 + C4H9CHO C4H9NHC5H11.HClC4H9N=CHC4H9

N

C5H11

C3H7

C4H9 N+C5H11

C3H7C4H9

C2H5 I-

a)

c)

b)

d)

1 2

3 4

Scheme 1. Reagents and conditions: a) MeOH; b) 1) NaBH4, 2) NaOH, 3) HCl;c) 1) C2H5CHO, NaBH(OAc)3 , MeOH, 2) NaOH; d) C2H5I, toluene.

Tetraalkylammonium iodides with four identical side chainshave been shown to form different types of disorderedcrystalline mesophases.[3] Short-chain tetraalkylammonium salts(n� 4) show a well-defined transition from crystal to plasticcrystal or orientationally disordered crystals (ODIC). Long-chaincompounds (n�7) show conformational disorder and motionbefore melting. With intermediate chain lengths, both plasticand conformationally disordered crystal phases (condis crys-tals[4] ) have been reported. The crystalline structure of com-pound 4 was investigated by powder X-ray diffraction. Detailedstructural information, obtained from compactness, symmetryand structure factor analyses, allows us to discuss the relation-ships between the molecular characteristics and the orientationdisorder in the condensed phase.

Results

Synthesis

In principle, any alkylation procedure of a primary amine is ableto generate a quaternary ammonium cation with four differentradicals : The reaction of ethylamine with an equimolar mixtureof n-propyl-, n-butyl- and n-pentylhalide[5] will produce a mixtureof quaternary ammonium halides together with secondary andtertiary amines. The probability of obtaining the totally unsym-metrical N,N,N-butylethylpentylpropylammonium halide cannotbe higher than 6/27 (�0.22). Furthermore, as they only differ bythe length of their alkyl chains, the various salts will be extremelydifficult to separate.

Several methods have been proposed to avoid the over-alkylation of primary and secondary amines. A large excess ofstarting amine[6] and the use of protecting groups, such as tosyl,are suitable.[7]

We selected the reductive alkylation of amines[8] whichproduces rather pure adducts in a one-step procedure. Whenstarting from a very reactive amine, such as a primary aliphaticone, the introduction of the reductant prior to imine formation,as described in ref. [8] , always resulted in a large amount of

[a] Dr. C. Soulie¬, Dr. F. TournilhacMatie¡re Molle et ChimieEcole Supe¬rieure de Physique et de Chimie Industrielles10 rue Vauquelin 75231 Paris Cedex 05 (France)Fax (�33)40-79-51-17E-mail : Corinne.Soulie@espci.fr

[b] Dr. P. BassoulLaboratoire de Physique du SolideEcole Supe¬rieure de Physique et de Chimie Industrielles10 rue Vauquelin 75231 Paris Cedex 05 (France)

Supporting information for this article is available on the WWW under http://www.chemphyschem.org or from the author.

Cubic Mesophase in an Unsymmetrical Alkyl Ammonium Salt

CHEMPHYSCHEM 2002, 3, 1024 ±1030 1025

tertiary amine. The reductive alkylation of RNH2 was thereforeachieved in a one-pot, two-step procedure (imine formationfollowed by reduction) as shown in Scheme 1. This pathway canbe applied with different chain lengths. We use the followingnotation: Numbers represent the number of carbons in chainsand I or Br represent respectively the iodide or bromide anion.Thus, 4 is equivalently compound 5432I.[*]

Chemical Analysis

Infrared and 13C NMR spectra of compound 4 only show aconfused overlap of aliphatic CH2 and CH3 signals, in which thoseof the ethyl group can scarcely be distinguished. By comparisonwith the starting amine 3, 1H NMR spectroscopy reveals aquadruplet at 3.55 ppm indicating that the ethyl moiety hasbeen linked to the nitrogen centre. Furthermore, the signals ofthe methylene groups directly bonded to the nitrogen areshifted to lower fields by about 1 ppm, confirming the formationof the quaternary ammonium. More informative data come fromGC-MS. At an injection temperature of 250 �C, compound 4readily decomposes into the four possible amines and thecorresponding alkyl iodides (Scheme 2), as identified throughtheir mass spectra.

N

R3

R2R14

250°C+ R4I

3a-3d 5a-5d

Scheme 2. Pyrolytic decomposition of 4 (5432I) into amines 3a ±3d andiodoalkanes 5a ±5d occurring in the GC-MS experiment. R4� ethyl (Xa), propyl(Xb), butyl (X c) or pentyl (Xd).

A typical chromatogram is presented in Figure 1. At shortretention times (t� 1.6 min), alkyl iodides 5c ±5d were charac-terised through their [M]� , [M� I]� and [I]� fragments. At longerretention times, each of the four GC peaks corresponds to one ofthe possible amines 3a ±3d identified through the characteristicC��C� fragmentation[9] of the aliphatic chain (Table 1).

Figure 1. Gas chromatogram showing the decomposition products of 4 (5432I)into amines 3a ±d. Alkyl iodides 5c ±d are also detected.

Polymorphism

Microscopic investigations of 4 did not reveal any structuraltransformation from room temperature to its melting point at192 �C, at which the product slowly decomposes. Dendriticpolygonal textures obtained on cooling indicate a crystallinegrowth. Between crossed polarisers, the crystalline texture isoptically isotropic, which is a strong argument for a cubicstructure.[10] The DSC thermogram (heating 10 Kmin�1) reveals amelting entropy of 23.9 Jmol�1K�1.

According to literature data,[11] this value can be related to afirst-order transition between a disordered mesophase and theisotropic liquid. The arrangement of orientationally disorderedmolecules into a cubic lattice is the common feature of plasticcrystals.[12, 13] Below room temperature, the thermogram revealsa glass phase transition at �59 �C (50.7 JK�1mol�1), confirmingthat conformational disorder and motion coexist with periodicityin the crystalline mesophase.

A powder X-ray diffraction pattern recorded at room temper-ature is shown in Figure 2. The broad diffuse band observed inthe vicinity of 2�/q� 4.2 ä can be attributed to the correlationsbetween molten hydrocarbon chains, and a series of sharp peaksindicates a 3D periodic order.

Indexation of the sharp peaks was achieved in the primitivecubic system (a�14.08 ä). The hhl (l odd) and h00 (h odd) linesare absent and only the two space groups Pm3n and P43n arecompatible with these extinction rules. In a first attempt to forma model for the structure, the most symmetric group–thecentred Pm3n–was considered.

Discussion

Structural Model

In order to establish the crystallographic positions of the atomsin 4, it is first necessary to determine the number of moleculesper unit cell, Z, easily found from compactness evaluation. Let usdefine VK as the molecular volume of interpenetrating van derWaals spheres. Using typical bond lengths, bond angles andvan der Waals and ionic radii, we found for compound 4 volumesV��267 and V�� 44 ä3 for the cation and anion, and total VK�311 ä3.

Table 1. Characterisation of compound 4 through the GC-MS analysis of itsdecomposition into amines 3a ±3d. Data for the tertiary amine 3 is given forcomparison.

3d 3c 3b 3a 3

Retention time [min] 1.66 2.70 3.87 4.91 4.96GC ratio [%] 12 18 28 42 100Relative abundance (ratio)[M]� 7 (143) 9 (157) 13 (171) 16 (185) 16 (185)[M�CH3]� 1 (128) 2 (142) 3 (156) � 1 (170) � 1 (170)[M�C2H5]� 41 (114) 35 (128) � 1 (142) 62 (156) 63 (156)[M�C3H7]� 100 (100) � 1 (114) 78 (128) 79 (142) 80 (142)[M�C4H9]� �1 (86) 100 (100) 100 (114) 100 (128) 100 (128)

The m/z ratio of the fragments are indicated in parentheses.

[*] Beside this compound, other ammonium halides have been synthesisedwhich can be classified along their physical aspect either crystalline (7654I,6543I, 5432I) or viscous liquids ((12)864I, 8642I, 8641I, 7531I, 6543Br, 5432Br).All compounds show the same trends in their analytical data as for 4.

C. Soulie¬ et al.

1026 CHEMPHYSCHEM 2002, 3, 1024 ± 1030

The occupied volume per each cation and anion isa3/Z. The compactness of the packing � is thereforeequal to the ratio ��ZVK/a3, in which a3� 2791 ä3 is thevolume of the primitive unit cell. For Z� 4, 6 and 8 therespective � values are 0.45, 0.67 and 0.89. The value of0.45 is too small to be attributed to a molecular crystal,whereas 0.89 is also unrealistic since it exceeds thecompactness of close packed spheres (0.74). The inter-mediate value, 0.67, is in the typical range for disorderedsolids and also for smectic liquid crystals, and hence Z�6 is the only possible value.

Three types of atomic contributions to the reflectionintensities may be considered. In a first fitting step, thecontribution of light atoms (C, H, N) was disregarded;attention is focussed on the location of heavy atomsonly. In Pm3n the six iodine atoms have been locatedeither in 6c or in 6d Wyckoff positions; these two setshave the same symmetry and generate equivalentrepartitions of cations (Figure 3a).

In this approach, one tends to consider that iodineatoms occupy well-defined crystallographic positionswhereas alkylammonium cations, with alkyl side chainsin a liquidlike conformation, fill the rest of the cell. Thehistogram in Figure 3a shows the contribution of iodineatoms to the measured reflections intensities. Of coursethe fit is less than perfect; the damping of intensitieswith increasing h, k, l values is approximately followedbut the discrepancies at low q values are significant. Inparticular, this model is unable to predict the actualintensity of the (210) reflection. It should be noted thatthe intensity of this line is very sensitive to the relativeoccupation of 6c and 6d positions: In one limiting casethis reflection is extinguished when both 6c and 6dare occupied by atoms or molecules having the same

number of electrons; in the other limiting case thestructure factor F210 has extreme values, eitherpositive or negative, when only one set of thesepositions are occupied.

In the second fitting step, the ammonium cationsmay be considered as soft spheres located in 6dpositions. The cation is modelled with a Gaussiandistribution of electron density with a standarddeviation in radius r0 given by Equation (1).

�(r) � 1

r0exp

���

r2

r20

�(1)

The radius r0 is taken as an adjustable parameter,the fit is obtained when r0�5.1 ä. Experimentaland calculated intensities are shown in Figure 3b. Itis clear that this second model, with a singleadjustable parameter, is already acceptable forfitting the whole diffraction pattern. In particular,this model properly predicts the (210) intensity.Figure 2. Powder X-ray diffraction pattern (CuK� radiation), hhl (l odd) and h00 (h odd) lines are

absent.

Figure 3. The different models used. a) Heavy atoms (iodine) are localised in the 6dWyckoff positions of Pm3n. b) Ammonium cations (with a Gaussian electron densitydistribution) occupy the 6c positions. c) Part of the alkyl chain electron density is localisedin the 24k positions; thermal motion is introduced.

Cubic Mesophase in an Unsymmetrical Alkyl Ammonium Salt

CHEMPHYSCHEM 2002, 3, 1024 ±1030 1027

In Pm3n, the 6d positions have 4m2 site symmetry, whichcorresponds to a tetrahedron with isoceles faces. The unsym-metrical ammonium cation, with a certain degree of disorder,may be accommodated in this symmetry; it is necessary that thefour alkyl chains rapidly exchange their positions. With thispicture in mind, we constructed a third model, in which 24 alkylchains of average formula C3.5H8 were symmetrically distributedaround 6d centres but with a preferred location in 24k positions.

In the third step, a portion � of the alkyl atomic density is stilldistributed in the ™ammonium sphere∫ and the remainder (1��)centred around 24k sites. In addition, the disorder of positionexisting in this phase has been modelled by classical Debye ±Waller damping. This third model is therefore characterised byfive fitting parameters, the radius r0 already mentioned, thecoordinates y and z in 24k, the portion of delocalised electrondensity � and the RMS amplitude of thermal oscillations �. Thisleads to the final expression, Equation (2), where I(�q) is thediffracted intensity in the Debye ± Scherrer geometry, m(�q) themultiplicity of the qh,k,l line and f(q) the diffusion factors of the C,H, N and I atoms; m, n and p describe the 6c, 6d and 24kpositions, respectively.

I(�q) � m(�q)1 � cos22�

sin2� cos�� F(�q) � 2 exp(�q2�2)

(2)

F(�q) ��6

m�1

f I(q)exp(� i�(�q ¥�rm))��6

n�1

{f N(q)� [14 f C(q)�32 f H(q)]�}

¥ exp(� i�(�q ¥�rn)) exp(� i�q2r20�

��24

p�1

[14 f C(q)�32 f H(q)]1� �

4exp[� i�(�q ¥�rp)]

The best fit was obtained with r0�4.39 ä, �� 0.62 ä, ��0.78,y� 0.12 and z� 0.24, and the results are presented in Figure 3c.Further refinements are certainly possible, however, due to thedisorder of this phase, the number of observable signals isintrinsically limited and, moreover, absorption and possibletextures of the sample also limit the reliability of measuredintensities.

The site symmetry found for the tetraalkylammonium ions is42m, reduced to 4 if the subgroup P43n is considered. In anycases, the nitrogen atom is surrounded by a distorted tetrahe-dron of iodine ions (Figure 4). The four alkyl side chains pointing

Figure 4. Structural model for 4, space group Pm3n. The 24k Wyckoff positionsgive the orientation of the alkyl chains pointing towards the centre and thecorners of the cubic cell.

toward the 24k sites have their axes normal to the faces of thetetrahedron. These structural features are characteristic of thetetraalkylammonium salts, see below. The inscribed sphere incontact with iodine ions has a diameter of 5.6 ä. This emptyspace does not allow an overall rotation of the tetraalkyl cation;an evaluation of the circumscribed sphere around the cation,even with alkyl chains in a flex state,[14, 15] gives a diameter of 11 ±12 ä. Nevertheless, there is no steric constraint which prevents arotation around the axis of one given alkyl chain; if this occursthe position of the three other chains will be exchanged and thesite symmetries fulfilled.

Structure of Tetraalkylammonium Salts

Symmetrical tetraalkylammonium bromides and iodides havebeen the subject of extensive investigations. A comparison maybe made between interion angles and distances found in theprevious model with those of closely related materials. Theplastically crystalline state occurs in the case for several studiedcompounds, but most of the structural data available concernthe lower temperature crystalline phases. Depending on thechoice of anion and length of alkyl chains, tetraalkylammoniumhalides display a wide variety of crystalline arrangements. Notless than seven different space groups are necessary to describethe crystal structures of nine derivatives (Table 2). Despite thisapparent disparity, one can find remarkably constant structuralfeatures throughout this series of compounds. The first neigh-bour shell of anions around the tetraalkylammonium cation hasbeen measured using Moldraw program.[16]

First of all, the distance value between nitrogen and itshalogen neighbors extend from 4.37 to 5.29 ä, whatever thelength of the alkyl chains. Similarly, crystalline phases in Table 2have a compactness value between 0.71 and 0.79. This valuedecreases to 0.64 and 0.67 in the cubic phase of tetrabutylam-monium iodide (4444I) and in 4 (5432I), respectively. The spatialdistribution of halogen anions around a given nitrogen atomalso displays a quite regular behaviour: In 1111Br, 3333Br, 1111Iand 2222I the shape of the anionic shell is a tetrahedron withisoceles triangular faces. In these compounds the nitrogen sitesymmetry is described by the point symmetry group 4m2 or itssubgroup 4, but in all cases the symmetry of the anionic shell is4m2. Thus, the picture is very similar to the one encountered in5432I with approximately the same interionic distances. Theother compounds of the series crystallise in the trigonal andmonoclinic systems, both incompatible with the inverse fourfoldrotation. In 3333I the tetrahedral shape is strongly distorted butstill present, with four iodine atoms almost equidistant to thenitrogen atom (N± I distances of 4.85, 4.96, 5.29 ä). Thetetrahedral shape is strongly flattened in butyl derivatives forwhich the structure becomes a layered one and the halogenshell is approximately a square. Finally, in tetraethyl ammoniumbromide the anionic shell is clearly not tetrahedral but prismatic,with N±Br distances between 4.62 and 5.26 ä.

The possibility for the ammonium cation to rotate around oneof its alkyl chains may be inferred from the geometry of thesurrounding anionic shell. In the case of compounds with 4 or42m site symmetry, the tetrahedral shell has isoceles triangular

C. Soulie¬ et al.

1028 CHEMPHYSCHEM 2002, 3, 1024 ± 1030

faces. The space available for an alkyl chain to rotate around itsaxis is given by the difference RC�RA� (Figure 5, Table 3) whereRC is the radius of the circle circumscribed to the triangular faceand RA� the ionic radius of the anion A.

In the case of methyl-substituted compounds, n(C) is 4, thecation is enclosed inside the tetrahedral shell and faces are too

Figure 5. a) Tetrahedral shell of 2222I from ref. [25] ; b) geometry of a triangularface of the tetrahedral shell, RC, Rch , R I� .

small to permit alkyl chain to pass. For compounds with n(C) of12 or 14, RC�RA� values found are greater than the cross-sectionradius of the rotating chain taken from the hexagonal rotatorphases of paraffins. Nevertheless, long alkyl chains could have

Table 2. Comparison of interatomic distances and angles of compound 4 with the literature data of symmetrical tetraalkylammonium halides in their crystal form.

comp. n(C)[a] Interatomic distances [ä] Space group N sitesymmetry

Shell Compact-ness �

Ref.N ± (I,Br) I ± I or Br ± Br

Me4NBr (1111Br) 4 4.37 7.70 P4/nmm 4m2 0.73 [17]6.84 (129)

Et4NBr[e] (2222Br) 8 4.62[b] 5.08[b] R3c 2 0.79 [18]5.26[c] 6.97[c] (167)

Pr4NBr (3333Br) 12 4.94 7.99 I4 4 0.71 [19]8.24 (82)

Bu4NBr (4444Br) 16 4.90[b] 6.97[b] C2/c 1 0.72 [20]4.99[c] 7.09[c] (15)

Me4NI (1111I) 4 4.56 7.96 P4/nmm 4m2 0.73 [21]7.19 (129)

Et4NI (2222I) 8 4.76 7.16 I4 4 0.76 [22]8.86 (82)

Pr4NI[f] (3333I) 12 4.65[b] 7.21[b] P212121 1 0.72 [23]5.29[c] 9.30[c] (19)

Bu4NI (4444I) 16 5.09[b] 6.87[b] C2 1 0.72 [20]5.18[c] 7.62[c] (5)

Bu4NI (4444I) 16 [d] Primitive cubic[d] 0.64 [20]

Comp. 4 (5432I) 14 4.98 8.62 Pm3n 4m2 0.67 This work7.04 (223)

[a] Total number of carbon atoms. [b] Minimum value. [c] Maximum value in the first neighbour shell. [d] No data available. [e] T� 163 K. [f] T� 173 K.

Table 3. Rotation space for alkyl chains

Compound n(C)[a] RC[b]� RA�

[c] [ä] Rch(cryst)[d] [ä] Rch(rot)

[d] [ä]

1111Br 4 2.183333Br 12 2.701111I 4 2.11 2.25 2.372222I 8 2.355432I (4) 14 2.78

[a] Total number of carbon atoms. [b] Radius of circumscribed circle (seeFigure 5). [c] Ionic radii are 2.20 (A� I�) and 1.96 ä (A�Br�). [d] Halfdistance between paraffinic chains in crystalline polyethylene.[24] [d] Cross-section radius perpendicular to the paraffinic chain in hexagonal rotatorphases.[25]

Cubic Mesophase in an Unsymmetrical Alkyl Ammonium Salt

CHEMPHYSCHEM 2002, 3, 1024 ±1030 1029

conformations corresponding to a greater cross-section thanthat of extended chains. The existence of molecular rotation maybe assessed from thermodynamic data. A primitive cubic phaseis observed for some tetraalkylammonium salts before melting.Compounds gathered in Table 3 present the characteristicfeatures of structural dynamic disorder. A weak melting entropyis measured and, in the case no ordered phase occurs at lowtemperature, a glass phase transition is detected. Unfortunately,the parameter of the cubic phase is available for symmetric 4444Ionly. Nevertheless, the structural model built for compound 4(5432I) seems to be suitable for this series of ODIC phases. Whenmolecules are substituted with alkyl chains of different lengths,the cubic phase is observed from the melting point down to alow temperature glass phase transition.

Conclusion

Tetraalkylammonium cations with four different alkyl chains areeasily synthesised from commercially available amines, alde-hydes and alkyl iodides using a reductive alkylation procedure.The iodine salt is the versatile intermediate towards hydroxides,perchlorates, hexafluorophosphates, nitrates and others.[27]

Anion exchange may also enable the separation of R and Senantiomers,[28] however polarimetry in the visible range isprobably inadequate to assess the resolution: According to themodels developed for tetraalkylmethane homologues,[29] themolecular rotation of N,N,N-butylethylpentylpropylammoniumis estimated at the level of 10�5 �. We have begun spectroscopicstudies to characterise the chirality of the ammonium cation indiastereomeric salts formed with optically pure anions.

As an effect of side-chain dispersity, N,N,N-butylethylpentyl-propylammonium is an orientationally disordered crystal atroom temperature whereas symmetrical homologues exhibitthis state of matter solely at elevated temperatures. Thecomparison of crystal data of symmetrical and unsymmetricalcompounds has been attempted: At first sight there is noisostructural relation throughout the series, however, a carefulanalysis of interionic arrangements demonstrate that thetetrahedrally coordinated nitrogen atom of 4 is also found inthe majority of crystallized tetraalkylammonium bromides andiodides.

When the distribution of these tetrahedral shells follows thePm3n space group, substituted ammonium cations can rotatearound the axes of their alkyl chains.

Experimental Section

Characterisation : Infrared spectra have been recorded from neatliquid samples or from KBr pellets (Perkin ± Elmer 1600 spectrom-eter). 1H (300 MHz) and 13C (75 MHz) NMR analyses were carried out(Brucker AM300, CDCl3 solutions). Mass spectra were recorded with aGC-MS setup (Hewlett-Packard 5971 detector). DSC experimentswere recorded at �10 Kmin�1 (TA Instruments 2920). X-ray diffrac-tion powder patterns of 4 were recorded from powder samples in0.5 mm Lindemann glass tubes using the monochromatic CuK�

radiation (1.5405 ä). The diffracted intensities were measured inthe meridian plane using a curved position-sensitive detector (Inel

CPS 120) with a resolution of 0.14� FWHM. Powder diffractiondiagrams were indexed using the U-FIT software.[26] The accuracy ofthe fit was better than 0.1� in 2� for all observed reflexions withoutintroduction of any correction factor.

Synthesis : Pentanal (4.25 mL, 40 mmol) was added dropwise to asolution of butylamine (2.10 mL, 40 mmol) in methanol (20 mL)which led to N-butylpentylimine 1. This product was then reducedwith sodium borohydride (2.4 g, 64 mmol) to give N-butyl-pentyl-amine, isolated in its hydrochloride form 2 (68%). To a solution of 2(1 g, 5.6 mmol) and propanal (0.4 mL, 5.6 mmol) in the presence oftriethylamine (1.5 mL, 11.2 mmol), a portion of sodium triacetoxy-borohydride (1.4 g, 6.7 mmol) was added. After 15 min, threeportions of propanal (each 0.08 mL, 0.2 equiv) and of NaBH(OAc)3(each 0.356 g, 0.3 equiv) were added over a total period of 1 h. N,N-butylpentylpropylamine 3 was obtained in 70% yield. The free base(0.7g, 3.8 mmol) was then quaternised using iodoethane (1.15 mL,3.8 mmol) in toluene (10 mL) at 70 �C in a PTFE-coated high-pressurebomb. N,N,N-butylethylpentylpropylammonium iodide 4 was iso-lated as a white crystalline powder with a 50% yield afterrecrystallisation in ethyl acetate. Full chemical characterisation datais given in the Supporting Information.

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Received: May 13, 2002 [F420]Revised: August 13, 2002